heat resistant

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HEAT AND CORROSION RESISTANT CASTINGS:

THEIR ENGINEERING PROPERTIESAND APPLICATIONS

Publication N o 266

Ni Dl Distributed by theNickel Development Institute,courtesy of Inco Limited


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Part I. Heat-Resistant Alloy Castings ........................................................... 4-26

Introduction ....................................................................................................... 4Typical Casting Compositions of Heat-Resistant Alloy Castings, Table I ...... 4

Effect of Constituents ........................................................................................ 5

Groups of Heat-Resistant Alloy Castings ...................................................... 6-8Chromium-Iron Alloys (HA, HC, HD)Chromium-Nickel-Iron Alloys (HE, HF, HH, HI, HK, IN-519, HL)

Nickel-Chromium-Iron Alloys (HN, HP, HT, HU, HW, HX)Chromium-Nickel Alloys (50Cr-50Ni, IN-657)

Selecting the Proper Alloy ................................................................................. 8

Heat-Resistant Alloy Casting Design ................................................................ 9

High-Temperature Mechanical Properties ................................................... 9-15

High-Temperature Corrosion Resistance .................................................. 14,16

Room Temperature Properties ....................................................................... 16

Industrial Applications of Heat-Resistant Alloy CastingsAeronautical ................................................................................................. 17Cement ........................................................................................................ 17Glass & Enameling ................................................................................. 17-18Heat Treating .......................................................................................... 18-21Petroleum, Petrochemical Refining &Chemical ...................................... 22-24Power Plants ............................................................................................... 25Steel Mill Equipment .................................................................................... 26Smelting & Refining Equipment ................................................................... 26

Contents Pages


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Part II. Corrosion-Resistant Alloy Castings .......................................................... 27-47

Introduction ............................................................................................................... 27Typical Casting Compositions of Corrosion-Resistant Alloy Castings, Table V .... 27

Room Temperature Properties ................................................................................. 28

Effect of Constituents ........................................................................................... 29-30

Corrosive Attack ................................................................................................... 30-31

Groups of Corrosion-Resistant Alloy Castings ..................................................... 31-33Martensitic Alloys (CA-15, CA-40, CA-6NM, CA-6N)Ferritic and Duplex Alloys (CB-30, CC-50, CD-4MCu)Austenitic Alloys (CE-30, CF types, CG-8M, CH-20, CK-20, CN-7M, CN-7MS,IN-862)Precipitation Hardenable Alloys (CB-7Cu-1, CB-7Cu-2)Nickel-Base Alloys (CZ-100, M-35, CY-40, Alloy 625, CW-12M, N-12M, Ni-Si)

Corrosion Data ..................................................................................................... 34-37

Industrial Applications of Corrosion-Resistant Alloy Castings .............................. 38-48Aeronautical .......................................................................................................... 38Architectural .......................................................................................................... 38Chemical & Petroleum ....................................................................................... 39-40Process Industries Equipment ........................................................................... 41-44Hydraulics .............................................................................................................. 45Marine ................................................................................................................... 44Power–Nuclear & Conventional ........................................................................ 45-48

Part Ill. Fabrication Data for Heat & Corrosion-Resistant Alloy Castings .... 49-52

Machining ............................................................................................................. 49-51Welding ................................................................................................................. 51-52


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The heat-resistant casting alloys are those composi-tions that contain at least 12% chromium which arecapable of performing satisfactorily when used at tem-peratures above 1200 ºF. As a group, heat-resistant

compositions are higher in alloy content than thecorrosion-resistant types. The heat-resistant alloys arecomposed principally of nickel, chromium and iron to-gether with small percentages of other elements. Nickeland chromium contribute to the superior heat resistanceof these materials. Castings made of these alloys mustmeet two basic requirements:

1. Good surface film stability (oxidation and corro-sion resistance) in various atmospheres and at thetemperature to which they are subjected.

2.Sufficient mechanical strength and ductility to meethigh temperature service conditions.

The heat-resistant alloys are listed in Table I along withtheir chemical compositions and designations.Commercial cast heat-resistant alloys can be identifiedby designations of the Alloy Casting Institute, now adivision of the Steel Founders' Society of America, andthe American Society for Testing and Materials.* Someof these materials are also listed in the Aerospace Mate-

*See ASTM Specification A 297

rial Specifications (AMS) of the Society of AutomotiveEngineers, United States Government Military Specifi-cations (MIL), the Society of Automotive EngineersSpecifications and the Unified Numbering System

(UNS) developed by the Society of Automotive Engi-neers and the American Society for Testing and Mate-rials. Standard ACI designations are listed in Table I.

The Alloy Casting Institute designations use "H" toindicate alloys generally used in applications where themetal temperature exceeds 1200 ºF. The second letterindicates the nominal nickel content, increasing from Ato X.

The chemical compositions of the heat-resistant cast-ing alloys are not the same as those of the wroughtalloys. Therefore, Table I lists only the nearest wroughtalloy AISI type number. Alloy Casting Institute designa-

tions or their equivalents should always be used whenidentifying castings.

The SAE specification designations use the nearestwrought composition (AISI type number) and prefix itwith the number 70 ºFor heat-resistant castings: for ex-ample, 70310 is equivalent to HK. In the Unified Num-bering System, the Jxxxx number series is assigned tocast steels.

TABLE I

Compositions of Heat-Resistant Alloy Castings

CHEMICAL COMPOSITION, %AlloyCastingInstitute

Designation

AlloyType

ASTMSpecification

NearestAISIType

UNSNo. Ni Cr C Mn

maxSi

maxMomax

Other

HA 8-10Cr A217 – – – 8-10 0.20 max 0.35-0.65 1.00 0.90-1.20 Fe balHC 28Cr A297 446 J92605 4 max 26-30 0.50 max 1.00 2.00 0.5 Fe balHD 28Cr-6Ni A297 327 J93005 4-7 26-30 0.50 max 1.50 2.00 0.5 Fe balHE 28Cr-9Ni A297 312 J93403 8-11 26-30 0.20-0.50 2.00 2.00 0.5 Fe balHF 19Cr-9Ni A297 302B J92603 9-12 19-23 0.20-0.40 2.00 2.00 0.5 Fe balHH 25Cr-12Ni A297, A447 309 J93503 11-14 24-28 0.20-0.50 2.00 2.00 0.5 Fe balHI 28Cr-15Ni A297 – J94003 14-18 26-30 0.20-0.50 2.00 2.00 0.5 Fe balHK 25Cr-20Ni A297, A351

A567310 J94224 18-22 24-28 0.20-0.60 2.00 2.00 0.5 Fe bal

IN-519 1 24Cr-24Ni – – – 23-25 23-25 0.25-0.35 1.00 1.00 – Cb 1.4-1.8; Fe bal

HL 30Cr-20Ni A297 – J94604 18-22 28-32 0.20-0.60 2.00 2.00 0.5 Fe balHN 25Ni-20Cr A297 – J94213 23-27 19-23 0.20-0.50 2.00 2.00 0.5 Fe balHP 35Ni-26Cr A297 – J95705 33-37 24-28 0.35-0.75 2.00 2.00 0.5 Fe bal

HP-50WZ 35Ni-26Cr – – – 33-37 24-28 0.45-0.55 2.00 2.50 – W 4-6; Zr 0.1-1.0; Fe balHT 35Ni-17Cr A297, A351 330 J94605 33-37 15-19 0.35-0.75 2.00 2.50 0.5 Fe balHU 39Ni-18Cr A297 – J95405 37-41 17-21 0.35-0.75 2.00 2.50 0.5 Fe balHW 60Ni-12Cr A297 – – 58-62 10-14 0.35-0.75 2.00 2.50 0.5 Fe balHX 66Ni-17Cr A297 – – 64-68 15-19 0.35-0.75 2.00 2.50 0.5 Fe bal

ChromiumNickel 50Cr-5ONi A560 – – bal 48-52 0.10 max 0.30 1.00 – Fe 1.0 maxIN-657 1 50Cr-48Ni – – – bal 48-52 0.10 max 0.30 0.50 – Cb 1.4-1.7; N 0.16 max;

Fe 1.0 max1INCO Designation

Part IHeat-Resistant Alloy Castings


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EFFECT OF CONSTITUENTS

Nickel

Nickel is present in cast heat-resistant alloys inamounts up to 70%. Its principal function is to strengthenand toughen the matrix. Microstructurally, nickelpromotes the formation of austenite which is strongerand more stable at elevated temperatures than ferrite.Nickel contributes to resistance to oxidation, car-burization, nitriding and thermal fatigue.

Chromium

The chromium content in heat-resistant alloys variesfrom approximately 10 to 30%. Chromium imparts resis-tance to oxidation (scaling) at elevated temperatures,and to sulfur-containing atmospheres. Also, chromiumcarbides precipitate in the matrix and contribute to high-temperature creep and rupture strength. In some alloys,chromium increases resistance to carburization. It alsoimproves the resistance of the alloys to the action of

many other corrosive agents at normal and elevatedtemperatures. It promotes the formation of ferrite in themicrostructure.

Other Elements

Nickel and chromium have the greatest effect on theproperties of heat-resistant castings but the minor alloy-ing elements also influence the properties.

Carbon content ranges from 0.20 to 0.75%. It pro-motes dispersion-strengthening through the formation ofcarbide in the structure. Increasing the carbon contentimproves the high-temperature strength and creepresistance of the heat-resistant alloys at the expense oflower ductility.

Silicon has a beneficial effect on the high-temperature corrosion resistance and on resistance tocarburization. In amounts greater than 2%, it lowers thehigh-temperature creep and rupture properties and, ingeneral, the silicon content is limited to 1.5% in castingsintended for service above 1500 ºF. Silicon promotes theformation of ferrite.

Manganese, although important in melting opera-tions, has little or no effect on the mechanical propertiesor corrosion resistance when present in moderateamounts.

Molybdenum improves the high-temperature creepand rupture strength by promoting stabilization of car-bides. In some instances, it also increases high-temperature corrosion resistance. It slightly increasesresistance to carburization.

Work to improve the creep and stress rupture proper-ties of the heat resisting chromium-nickel-iron alloysthrough the addition of small amounts of tungsten, zirco-nium, titanium, columbium, nitrogen, or combinations ofthem, has been pursued for several years under SteelFounders' Society of America sponsorship and by

others in the United States, Japan and Britain. Alterationof the carbide morphology from lamellar to discreteparticles seems to be the important factor; HP-50WZ(Table I) and IN-657 (Tables I through IV) are examplesof commercial alloys with improved property levels.

INFLUENCE OF MICROSTRUCTUREThe iron-chromium-nickel heat-resistant alloys de-

signed for service up to 1200 ºF often have mixedferriteaustenite matrices. However, alloys intended forservice above 1200 ºF are austenitic. The compositionsof these alloys are generally adjusted to prevent the for-mation of ferrite which has a detrimental effect on high-temperature creep-rupture strength. Long-time expo-sure at high temperatures, e.g., 1500 ºF, can result intransformation of ferrite to the sigma phase with signifi-cant loss of toughness at room temperature. Thus, inthese alloys, the high-temperature strength is basedprimarily on the solid solution strengthening of the aus-tenite by the addition of nickel, chromium and certainminor elements.

Carbides also contribute to strengthening these al-loys. As noted previously, these alloys have carboncontents ranging from 0.20 to 0.75%. In the as-castcondition, the microstructures consist of carbides dis-persed in an austenite matrix which also contains dis-solved carbon. By interfering with dislocation move-ment, these precipitated carbides assist in strengthen-ing the alloy. During long service at elevated tempera-tures in the range 1000 to 1800 ºF, additional chromiumcarbides precipitate in finely divided form and also as-sist in strengthening the alloys. At temperatures some-what above 1800 ºF, the primary carbides have a ten-dency to coalesce and the secondary carbides to redis-solve in the matrix. Nickel and chromium retard thistendency.

GROUPS OF HEAT-RESISTANTALLOY CASTINGS

The heat-resistant alloys can be classified accordingto composition and metallurgical structure into three

broad groups:1. Chromium-iron alloys: HA, HC, HD.2. Chromium-nickel-iron alloys: HE, HF, HH, HI, HK,

IN-519, HL.3. Nickel-chromium-iron alloys: HN, HP, HT, HU, HW,

HX.In addition, chromium-nickel heat-resistant alloys in-

clude 50Cr-50Ni and IN-657.A general discussion of each group is followed by a

discussion of each alloy.


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CHROMIUM-IRON ALLOYS

This group consists of alloys in which chromium pre-dominates with up to 30% chromium and up to 7% nickel.These alloys are ferritic and have relatively low hotstrength. They are seldom used in critical loadbearingparts at temperatures above 1400 ºF, but have found usein applications involving uniform heating and certainatmospheric conditions, such as high-sulfur atmospheres.The alloys in this group include the HA, HC and HD types.

HA (9Cr)Type HA is a chromium-molybdenum-iron alloy that is

resistant to oxidation up to about 1200 ºF. The molyb-denum content contributes desirable strength propertiesto the alloy at these moderate temperatures. Typicaluses are furnace rollers, Lehr rolls, refiner fittings andtrunnions.

HC (28Cr-4Ni max)The HC type is limited to applications where strength

is not a consideration or for moderate load-bearingservice around 1200 ºF. It provides excellent resistanceto oxidation and flue gases containing sulfur at tempera-tures as high as 2000 ºF. It is also used where high nickelcontent tends to crack hydrocarbons through catalyticaction. Due to the low nickel content, the ductility andimpact toughness are very low at room temperaturesand the creep strength is very low at elevated tempera-tures. Typical uses are boiler baffles, furnace gratebars, kiln parts, recuperators, salt pots and tuyeres.

HD (28Cr-6Ni)

The HD type has the best hot strength, weldabilityand high-temperature corrosion resistance of thechromium-iron group. HD can be used for load-bearingapplications up to 1200 ºF, and where only light loadsare involved up to 1900 ºF. It is suitable for use in high-sulfur atmospheres. Long exposures to temperatures inthe range 1300 to 1500 ºF may in some cases result inconsiderable hardening, accompanied by a severe lossof room temperature ductility through the formation ofthe sigma phase. Typical applications are roaster fur-nace rabble arms and blades, salt pots and cement kilnends.

CHROMIUM-NICKEL-IRON ALLOYSThese alloys are characterized by good high-

temperature strength, hot and cold ductility, and resis-tance to oxidizing and reducing conditions. They areuseful for atmospheres high in sulfur, particularly underreducing conditions. These alloys contain 8 to 22%nickel and 18 to 32% chromium, and may have either apartial or a completely austenitic microstructure. Theyinclude types HE to HL.

HE (28Cr-9Ni)Thi s t e has excel lent h i h -t em era tu re cor rosion

resistance and is frequently recommended for service insigh-sulfur atmospheres where alloys containing highernickel cannot be used. Because of its high alloy content,it is suitable for use up to 2000 ºF. The alloy has moder-ately high hot strength and excellent ductility. It is widelyused for parts such as conveyors in furnaces, recupera-tors, coke oven exhaust castings, roasting furnace cen-ter shafts and tube support castings. Prolonged expo-sure at temperatures around 1500 ºF may promote for-

mation of the sigma phase with consequent low ductilityat room temperature.

HF (19Cr-9Ni)This type is comparable to the popular wrought

corrosion-resisting 18-8 compositions and is suitable foruse up to around 1600 ºF. It approaches the HH gradein many properties and combines moderately high hotstrength and ductility. Its microstructure is essentiallyaustenitic. Typical uses include burnishing and coatingrolls, furnace dampers, annealing furnace parts, etc.

HH (25Cr-12Ni)This type is one of the most popular of the heat-

resistant alloys and accounts for about one-fifth of allheat-resistant casting production. This alloy containsthe minimum quantities of chromium and nickel to sup-ply a useful combination of strength and corrosion resis-tance for elevated temperature service above 1600 ºF.The chromium range is high enough to assure goodscaling resistance up to 2000 ºF in air or normalproducts of combustion. Sufficient nickel is present,aided by carbon, nitrogen and manganese, to maintainaustenite as the major phase; however, themicrostructure is sensitive to composition balance. Forhigh ductility at 1800 ºF, a two-phase structure ofaustenite and ferrite is appropriate but such a structurehas lower creep strength If high creep strength isneeded and lower ductility can be tolerated, acomposition balanced to be completely austenitic isdesirable.

Alloy HH is covered by ASTM specification A 447which recognizes two types. Type I is partially ferriticand Type II predominately austenitic. Type I has a max-imum magnetic permeability of 1.70 and Type II of 1.05.

Because of its high creep strength and relatively lowductility, Type II is useful in parts subject to high constant

load conditions in the range from 1200 to1800 ºF Some typical uses are for furnace shafts, beams,rails and rollers, tube supports and cement and lime kilnends. Type I alloy is used where hot ductility is moreimportant than hot strength, and is preferred for welding.

Both types of HH alloy have good resistance to sur-face corrosion under the various conditions encoun-tered in industry, but are seldom used for carburizingapplications because of embrittlement caused by ab-sorption of carbon. Experience has indicated that HHalloys can withstand repeated temperature changes ordifferentials reasonably well; however, they are not gen-erally recommended for severe cyclic service such a


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HI (28Cr-15Ni)This alloy is resistant to oxidation up to 2150 ºF. Its

composition is such that it is more likely to be completelyaustenitic than the lower alloys of this group, hence ithas more uniform high-temperature properties. Thistype is used for billet skids, conveyor rollers, furnacerails, lead pots, retorts for magnesium production,hearth plates and tube spacers.

HK (25Cr-20Ni)The HK alloy provides one of the most economical

combinations of strength and surface stability at tem-peratures up to and above 1900 ºF and accounts foralmost half of the heat-resistant alloy tonnage.

It can be used in structural applications up to 2100 ºFbut is not recommended where severe thermal shock is afactor. It is used for parts where high creep and rupturestrengths are needed such as steam methane reformertubing, ethylene pyrolysis tubing, gas turbines, furnacedoor arches and chain, brazing fixtures, cement kilnnose segments, rabble arms and blades, radiant tubes,

retorts and stack dampers.

IN-519 (24Cr-24Ni-1.5Cb)This alloy is a modification of HK alloy in which the

25-20 base has been altered, the carbon content hasbeen reduced and columbium (niobium) has beenadded. As a result, the high-temperature stress-rupturestrength has been improved. It is used for centrifu-gally-cast catalyst tubes in steam-hydrocarbon re-former furnaces.

HL (30Cr-20Ni)

This alloy has excellent resistance to oxidation attemperatures over 2000 ºF, and is resistant to corrosionin flue gases containing a moderate amount of sulfur upto 1800 ºF. It is used where higher strength is requiredthan obtainable with lower nickel content alloys. Leadingapplications are for radiant tubes, furnace skids andstack dampers where excessive scaling must beavoided, such as in enameling furnace carriers andfixtures.

NICKEL-CHROMlUM-IRON ALLOYSThe nickel-chromium-iron alloys are fully austenitic

and contain 25 to 70% nickel and 10 to 26% chromium.

They can be used satisfactorily up to 2100 ºF becauseno brittle phase forms in these alloys. They have goodweldability and are readily machinable if proper toolsand coolants are used. The specific types of alloys inthis group are HN, HP, HT, HU, HW and HX.

These austenitic heat-resistant alloys have good hotstrength and good resistance to carburization and thermalfatigue. They are used widely for load-bearing appli-cations and for castings subject to cyclic heating andlarge temperature differentials. They will withstand re-ducing and oxidizing atmospheres satisfactorily but high-sulfur atmospheres should be avoided.

HN (25Cr-20Ni)This alloy has properties somewhat similar to the

more widely used HT alloy but has better ductility. It isused for highly stressed components in the18 00 -2000 ºF range. It has also given satisfactory ser-vice in several specialized applications, notably brazingfixtures at temperatures up to 2100 ºF. Among its appli-cations are chain, furnace beams and parts, pier caps,brazing fixtures, radiant tubes, tube supports and torch

nozzles.

HP (35Ni-26Cr)This alloy is related to the HN and HT types but

contains more nickel than the HN alloy and more chro-mium than the HT alloy. This composition makes the HPalloy resistant to both oxidizing and carburizing atmo-spheres at high temperatures and provides high stress-rupture properties in the range 1800-2000 ºF. It is usedfor ethlene pyrolysis tubing, steam methane reformertubing, heat treating fixtures and radiant tubes. Severalproprietary modifications containing columbium and/or

tungsten are also being used.

HT (35Ni-17Cr)About one-seventh of the total production of heat-

resistant castings is HT alloy because of its value inresisting thermal shock, its resistance to oxidation andcarburization at high temperatures, and its goodstrength at heat treating furnace temperatures. Exceptin high-sulfur gases, it performs satisfactorily up to2100 ºF in oxidizing atmospheres and up to 2000 ºF inreducing atmospheres. It is used for load-bearing mem-bers in many furnace applications, retorts, radiant tubes,cyanide and salt pots, hearth plates and trays quenchedwith the work.

HU (39Ni-18Cr)This type has an exceptionally high combination of

creep strength and ductility up to 2000 ºF and is usedwhere high hot strength is required. It is suited for severeservice conditions involving high stress and rapid thermalcycling. HU alloy has good resistance to corrosion byeither oxidizing or reducing hot gases containingmoderate amounts of sulfur. Typical uses are heat treat-ing salt pots, quenching trays, fixtures and gas dissocia-tion equipment.

HW (60Ni-12Cr)The HW alloy performs satisfactorily up to 2050 ºF in

strongly oxidizing atmospheres and up to 1900 ºF inoxidizing or reducing products of combustion, providedthat sulfur is low or not present in the gas. The adherentnature of its oxide scale makes HW alloy suitable forenameling furnace service where even small flecks ofdislodged scale could ruin the work in process. High-temperature strength, resistance to thermal fatigue andresistance to carburization, are obtainable with this alloyand its high electrical resistivity suits it for electrical


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heating elements. Other applications are cyanide pots,gas retorts, hardening fixtures (quenched with the work),hearth plates, lead pots, muffles and other parts incyaniding and carburizing operations.

HX (66Ni-17Cr)The high-alloy content of this grade confers high re-

sistance to hot gas corrosion even in the presence of

some sulfur and permits it to be used for severe serviceapplications where corrosion must be minimized at tem-peratures up to 2100 ºF. It is used to great advantagewhere maximum and widely fluctuating temperatures areencountered because of its ability to withstand cyclingwithout cracking or severe warping. Thus, a leadingapplication is for quenching fixtures. It is also useful incarburizing and cyaniding equipment. Typical applica-tions in which it gives excellent service include nitriding,carburizing and hardening fixtures (quenched with thework), heat-treating boxes, retorts and burner parts.

CHROMIUM NICKEL ALLOYSChromium-Nickel Alloy (50Cr-50-Ni)

This alloy was developed to improve the resistance ofheat-resistant alloys to fuel oil ash. It is widely usedworldwide (and in fact is specified almost exclusively inEurope) for resistance to oil ash corrosion in powerplants, petroleum refinery heaters and marine boilers attemperatures up to about 1650 ºF. Its applications in-

clude such parts as sidewall and roof hanger supports in-furnace radiant sections, tube sheets, re-radiation conetips in vertical furnaces and for burner parts.

IN-657 (50Cr-48Ni-1.5Cb)This more recent development is a columbium(niobium) modification of the 50Cr-50Ni alloy also withhigh resistance to fuel oil ash corrosion but with creepand stress-rupture properties superior to those of the50Cr-50Ni alloy. IN-657 is used in petroleum refineryheaters, marine and land-based boilers in such applica-tions as convection section tube sheets; it is producedby several U.S. and European foundries under license

from Inco.*

properties that must be matched with them. Some of these properties are listed below and are discussed later under "Alloy Casting Design."

Operating Conditions Related Property

1. Anticipated service and maximumtemperature of operation

Short-time tensile propertiesCreep strengthStress-rupture propertiesHot ductility

2. Type and size of maximum load Short-time tensile properties

Creep strengthStress-rupture propertiesHot ductility

3. Temperature cyclinga. Range of temperature cyclingb. Frequency of temperature cyclingc. Rate of temperature change

Thermal fatigue properties

4. Type of atmosphere or other corrosiveconditions

Oxidation resistanceCarburization resistanceSulfidation resistanceSurface stability

5. Size and shape of part Temperature gradients

6. Further processing, such as welding

and machining

Fabrication data

7. Abrasive or wear conditions –8. Cost –9. Ease of replacement –

The governing economic consideration in the selec-tion of heat-resistant alloy castings is the cost per hourat operating temperatures. Equipment downtime canresult in a loss of production that is far more expensivethan the cost of the alloy involved. Ease of replacement

must also be considered in the selection of the alloy.With rare exceptions, the use of heat-resistant alloys is

justified at all temperatures above 1200 ºF.In selecting heat-resistant alloys for castings, the sig-

nificant properties that must be considered are shown inTables II, III and IV.

*Trademark of the Inco family of companies.

SELECTING THE PROPER ALLOYThe selection of the proper cast alloy for a given

high-temperature application requires knowledge ofvarious factors and the related mechanical and physical


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HEAT-RESISTANT ALLOY CASTING DESIGNThe properties listed in Table II and Figures 1 through

4, inclusive, are the basis for the design of heat-resistantalloy castings. This selection is concerned with the ap-

plication of these properties in casting design togetherwith other design considerations that are not amenableto tabulation.

TABLE IIRoom Temperature Mechanical Properties of Heat-Resistant Alloy Castings

1Annealed2Normalized at 1825 ºF and tempered at 1250 ºF.30.2% Proof Stress4Minimum

HIGH-TEMPERATURE MECHANICALPROPERTIES son of alloys, and Table III shows the data on this basis.

This is sometimes expressed as 1 % creep in 10,000 hr.It should be kept in mind that when creep is expressedin the latter terms it does not mean that this rate of creepcan be expected to continue in every instance for 10,000hours without failure.

Figure 1 and Table III compare the creep strengthsof representative heat-resistant alloy castings.

Creep values that are obtained under constant loadand constant temperature conditions are applicable todesign, however, safety factors should always be incor-porated. The safety factor will depend on the degree towhich the application is critical.

Stress-Rupture PropertiesStress-rupture properties determined under constant

load at constant temperature are useful in approximatingthe life of the alloy (time to fracture) under the specificconditions and also for comparing alloys which aresubject to loading that might produce failure in arelatively short time.

In common with all metals, the load-carrying ability ofheat-resistant casting alloys decreases as the tempera-ture increases. However, the fall-off in strength is lesspronounced than it is with less highly alloyed materials.

At elevated temperatures, metals under stress aresubject to slow plastic deformation as well as to elasticdeformation. Therefore, time becomes a critical factorand conventional tensile tests do not furnish values thatare useful in design. The data required are those indica-ting the load which will produce no more than an allow-able percentage of elongation at a specified tempera-ture in a given period of time. Thus, the factors of timeand deformation as well as stress and temperature areinvolved in high-temperature strength properties.

Creep StrengthThe slow plastic deformation that occurs under load

at elevated temperatures is known as creep. In thedesign of furnace parts, experience indicates that acreep rate of 0.0001% per hr is satisfactory for compari-

PROPERTY HA HC HD HE HFType I

HHType II

HH HI HKIN-519 HL HN HP HT HU HW HX

50Cr-50Ni

IN657

Tensile Strength, ksiAs-Cast 95 1 70 85 95 92 85 80 80 75 75 82 68 71 70 70 68 65 80 4 87Aged 107 2 115 – 90 100 86 92 90 85 – – – – 75 73 84 73 – –

Yield Strength(0.2% offset), ksiAs-Cast 65 1 65 48 45 45 50 40 45 50 35 3 52 38 40 40 40 36 36 50 4 54 3 Aged 81 2 80 – 55 50 55 45 65 50 – – – – 45 43 52 44 – –

Elongation in 2 in., %As-Cast 23 1 2 16 20 38 25 15 12 17 25 19 13 11.5 10 9 4 9 15 28Aged 21 2 18 – 10 25 11 8 6 10 – – – – 5 5 4 9 – –

Brinell HardnessAs-Cast 180 1 190 190 200 165 185 180 180 170 – 192 160 – 180 170 185 176 – –Aged 220 2 - – 270 190 200 200 200 190 – – – – 200 190 205 185 – –

Aging Treatment - 24 hoursat

1400 ºFFurnaceCooled

– 24 hoursat


24 hoursat


24 hoursat


24 hoursat


24 hoursat


24 hoursat


– – – – 24 hoursat

1400 ºFAir

Cooled

48 hoursat

1800 ºFAir

Cooled

48 hoursat


48 hoursat

1800 ºFAir

Cooled

– –

Modulus of Elasticityin Tension, ksi x 10 3

29 29 27 25 28 27 27 27 27 23 27 27 27 27 27 25 25 – 30


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TABLE III

Elevated Temperature Properties of Heat-Resistant Alloy Castings

11470 ºF 41290 ºF21650 ºF 52010 ºF31830 ºF 61110 ºF

Stress-rupture properties are a valuable adjunct to

creep-strength values in the selection of heat-resistantcasting alloys and in the establishment of allowabledesign stresses. Figures 2, 3, and 4 compare the stress-rupture properties of representative casting alloys forvarious time periods. Frequently, designers of furnacesand furnace tubing use the 100,000-hour stress-ruptureproperties with some factor of safety. A comparison ofFigures 1 and 2 shows that, in general, stress-rupturetests rank the alloys in much the same order as thecreep tests.

DuctilityAn accurate comparison of hot ductility of heat-

resistant casting alloys is difficult since there is no gen-

erally accepted reference test. Total elongation valueson both creep and stress-rupture tests are often usedas criteria. Also, the elongation in short-time high-temperature tensile tests is commonly used in specifica-tions as an indication of high-temperature ductility. Inmany applications where castings are handled at normaltemperatures, room temperature ductility is a con-sideration. Heat treating to remove sigma phase byheating castings to 1800 ºF and cooling to below 1200 ºFimproves ductility.

PROPERTY HA HC HD HE HFType l

HHType II

H H H I H K I N- 51 9 H L H N HP HT H U H W H X 5 0C r- 50 Ni I N- 65 7Short-TimeTensileStrength, ksi, at

1000 ºF 67 – – – – – – – – – – – – – – – – 44 6 86 6 1200 ºF – – – – 60 – 60.5 – – – – – – 42.4 – – 45 40 4 79 4 1400 ºF – – 36 – 38 33 37.4 38 37.5 39 1 50 – 43 35 40 32 – 36 1 68 1 1600 ºF – – 23 – 21 18.5 21.5 26 23.3 23 2 30.4 20.2 26 18.8 19.6 19 20.5 18 2 36 2 1800 ºF – – 15 – – 9 10.9 – 12.4 15 3 18.7 11.9 14.5 11 10 10 10.7 – –2000 ºF – – – – – – 5.5 – 5.6 – 6.2 7.5 6 – – – – –

Short-Time YieldStrength (0.2%Offset), ksi, at

1000 ºF 42 – – – – – – – – – – – – – – – – – 36 6

1200 ºF – – – – 31.5 – 32.2 – – – – – – 28 – – 20 – 46 4

1400 ºF – – – – 25 17 19.8 – 24.4 20 1 – – 29 26 – 23 – – 29 1

1600 ºF – – – – 15.5 13.5 16 – 14.7 13 2 – 14.5 17.5 15 – 15 17.5 – 15 2

1800 ºF – – – – – 6.3 7.3 – 8.7 9 3 – 9.6 11.0 8 6.2 8 6.9 – –2000 ºF – – – – – – – – 5.0 – – 4.9 6.2 – – – – – –

Elongation in2 in., %, at

1000 ºF – – – – – – – – – – – – – – – – – 12 6 16 6

1200 ºF – – – – 10 – 14 – – – – – – 5 – – 8 4 4 15 4

1400 ºF – – 14 – 16 18 16 6 12 32 1 – – 15 10 – – – 3 1 15 1

1600 ºF – – 18 – 16 30 18 12 16 432

– 37 27 26 20 – 48 52

192

1800 ºF – – 40 – – 45 31 – 42 37 3 – 51 46 28 28 40 40 – –2000 ºF – – – – – – – – 55 – – 55 69 – – – – – –

Creep Stress0.0001%/hr, ksi, at

1000 ºF 16 – – – – – – – – – – – – – – – – – –1200 ºF 3.1 – – – 18 – 18 – – – – – – – – – – – 18 4 1400 ºF – 1.3 3.5 4 6.8 3 6.3 6.6 10.2 8.6 1 7.0 – – 8 8.5 6 6.4 – 6.51600 ºF – 0.75 1.9 2.4 3.9 1.7 3.9 3.6 6.0 4.5 2 4.3 6.3 5.8 4.5 5.0 3 3.2 – 2.51800 ºF – 0.36 0.9 1.4 – 1.1 2.1 1.9 2.5 1.8 3 2.2 2.4 2.8 2 2.2 1.4 1.6 – 0.52000 ºF – – 0.2 0.4 – 0 .3 0.8 0.8 0.65 – – 1.0 1.0 0.5 0.6 – 0.6 – –2150 ºF – – – – – – – 0.15 – – – – – 0.15 – – – – –

Stress to Rupturein 100 hr, ksi, at

1000 ºF 37 – – – – – – – – – – – – – – – – – –1200 ºF – – – – 33 – 35 – – – – – – – – – – – 30 4

1400 ºF – 3.3 10 11 13.5 14 14 13 15.5 14 1 15.0 – – 16 15 10 13 – 14.51600 ºF – 1.7 5 5.3 7.2 6.4 6.8 7.5 9.2 9 2 9.2 11 10 8.9 8 6 6.7 – 7.21800 ºF – 0.85 2.5 2.5 – 3.1 3.2 4.1 4.7 5

3

5.2 5.6 5.9 4.4 4.5 3.6 3.5 – 3.82000 ºF – – – – – 1.5 1.4 1.9 2.2 – – 2.9 2.8 2.1 – – 1.7 – 1.6


11/5211

Figure 1– Creep Strength of Heat-Resistant Alloy Castings (HT curve is included in bothgraphs for ease of comparison).


12/5212

Figure 2 –1,000-Hour Stress-Rupture Properties of Heat-Resistant Alloy Castings (HT curve isincluded in both graphs for ease of comparison).


13/5213

Figure 4–100,000-Hour Stress-Rupture Properties of Several Heat-Resistant Alloy Castings.


14/5214

Short-Time Tensile PropertiesShort-time hot-tensile tests in which the test speci-

men is held at the test temperature for one hour andthen pulled at temperature, cannot be relied upon toindicate how heat-resistant alloys will behave in service.The values obtained are as much as five or six timesthe limiting creep stress values, and, therefore, greatlyover-evaluate load-carrying ability over long periods oftime. Nevertheless, short-time tensile tests can be help-ful in evaluating resistance to momentary overloads andare included in some specifications. The short-timemechanical properties for the standard heat-resistantalloys are given in Table Ill.

Thermal FatigueIn many high-temperature applications, intermittent

or widely fluctuating temperatures (cyclic heating) areencountered, and therefore the ability of the variousheat-resistant casting alloys to withstand such thermalfatigue service must be considered.

Thermal fatigue failure involves cracking caused byheating and cooling cycles. Crazing and checking of

heat-treating fixtures are typical examples. Such fail-ures are the result of many reversals of thermal stressesin the part as contrasted to common mechanical fatiguefailures, which are caused by externally applied loads.

Very little experimental thermal fatigue information isavailable on which comparison of the various alloys canbe based, and no standard test as yet has beenadopted. Field experience indicates that, usually, resis-tance to thermal fatigue is improved with increasingnickel content. Columbium-modified ACI alloys havebeen employed successfully where a high degree ofthermal fatigue resistance is desired such as in reformeroutlet headers.

Temperature GradientsNon-uniform heating or cooling causes temperature

gradients and the attendant unequal dimensionalchanges result in stresses within the casting, Thesestresses may be accompanied, particularly at high tem-peratures, by some degree of plastic deformation. Themagnitude of the stress and/or the amount of the plasticdeformation will depend on the temperature differentialwithin the casting.

Heat-resistant alloys inherently have high coefficientsof thermal expansion and low heat conductivity, bothproperties tending to produce temperature and stressdifferences between various regions of a casting. Theunequal stresses set up within the casting tend to distortor fracture it; thus, maximum articulation should be de-signed into elevated temperature parts by making themof a number of small components that are free to expandand contract. All sharp corners and abrupt changes insection are to be avoided.

Proper design, taking all thermal conditions into con-sideration, is as important as alloy composition in deter-

mining the life of castings in service. For this reason, theheat-resistant casting user should consult with the pro-ducers in the early stages of design in order to obtain thebenefit of their experience with similar applications.

DESIGN DATAThe curves shown in Figure 5 are constructed to

indicate the values of allowable stress that result fromapplications of code criteria to the short-time tensile,creep, and stress-rupture properties of the heat-resistant alloys, HF, HH-II, HK and HN. The ASMEBoiler Code allowable stresses for wrought composi-tions are included in two of the graphs to offer a compari-son.

HIGH-TEMPERATURE CORROSIONRESISTANCE

High-temperature equipment is exposed to many dif-ferent atmospheres and corrosive conditions and animportant requirement of heat-resistant alloys is surfacefilm stability. No single alloy will show satisfactory resis-tance to all of the high-temperature environments.

High-temperature corrosive conditions may involvesimple oxidizing or reducing atmospheres or they may becomplicated by sulfur compounds in the products ofcombustion. Oxidizing flue gases are slightly more cor-rosive than air if the sulfur concentration is low. Corro-sive attack by reducing flue gases is similar to that of anoxidizing gas if the sulfur content is not greater than 100ppm. At higher sulfur concentrations, attack by reducinggas is much more severe. The high nickel alloys, typesHN to HW, give good service under oxidizing and reduc-ing conditions if the sulfur content of the gas is low.

Types HH and HL, for example, should be consideredfor service in sulfur-bearing atmospheres.Cyclic heating under reducing conditions increases

metal loss in alloys containing from 10 to 50% nickel.Under oxidizing conditions, cyclic heating has little ef-fect in alloys containing more than 20% nickel.

Different corrosive conditions are encountered withequipment in contact with fused salts or molten metals.Types HT to HX should be considered for service underthese conditions. Still other conditions are met in thechemical, petroleum, and petrochemical industrieswhere new processes with new corrosive conditions areconstantly under development.

In the heat-treating industry, only the high nickel-chromium alloys give satisfactory service under nitridingconditions. Another important process in the heat-treating industry is carburization, which is considered insome detail below.

Carburization ResistanceWhen heat-resistant castings are used as muffles,

holding fixtures or baskets for work being carburized,


15/5215

Figure 5–Design Data for Four Heat-Resistant Steels.


16/5216

the castings also pick up carbon. The same effect oc-curs in any high-temperature carbon-bearing atmo-sphere under reducing conditions. Some alloys absorbfrom 0.30 to 2% carbon within a period of severalmonths when used in a carburizing application. A largeincrease in carbon pickup leads to volume changeswhich can cause warpage and distortion. The additionalcarbon also leads to difficulties if repair welding of thecasting is necessary. Increasing the nickel content re-duces the effect of increased carbon content on themechanical properties of heat-resistant alloys. Hence,the nickel-chromium-iron grades HP to HX are preferredbecause they withstand thermal fatigue and shock load-ing at higher carbon levels than alloys with less nickel.

Resistance to carbon penetration increases as thenickel content increases and to some extent as thechromium content increases. Therefore the high nickeltypes HP to HX are all good in this respect with the HWand HX types, being highest in nickel content, rating asexcellent.

The high chromium types are generally not suitablefor service under carburizing conditions unless otherrequirements dictate their selection. In such cases, sili-

con content should be kept on the high side. Carburiza-tion resistance of types HH and HK is improved withsilicon content above 1.6%.

ROOM TEMPERATURE PROPERTIESThe room temperature properties of the various

alloys shown in Table II have little relationship to high-temperature behavior. These properties are useful onlyfor acceptance purposes and for instances where thenature of the service requires good strength at roomtemperature.

Acceptance tests of a particular composition at roomtemperature are used only with the supposition that thealloy will behave at elevated temperatures in the sameway that the same composition has behaved previouslyin the same application.

The room temperature properties after aging aregiven as an indication of the structural stability of thealloy after high-temperature exposure.

The physical properties of the heat-resistant alloys

are given in Table IV.

TABLE IVPhysical Properties of Heat-Resistant Alloy Castings

Property HA HC HD HE HFType l

HH

TypeII

HH HI HKIN-519 HL HN HP HT HU HW HX

50Cr-50Ni

I6

Density, lb/cu in. 0.279 0.272 0.274 0.277 0.280 0.279 0.279 0.279 0.280 0.286 0.279 0.283 0.284 0.286 0.290 0.294 0.294 0.291 a 0.2 Mean Coefficient of

Linear Thermal Expansion,in./in./° F x 10 -6

70 - 212 ºF 6.1 - - - - - - - - 7.2 1 - - - 7.9 - 7.0 - - 5.970 - 1000 ºF 7.1 6.3 7.7 9.6 9.9 9.5 9.5 9.9 9.4 9.1 2 9.2 9.3 9.2 8.8 8.8 7.9 7.8 7.470- 1200 ºF 7.5 6.4 8.0 9.9 10.1 9.7 9.7 10.0 9.6 - 9.4 9.5 9.5 9.1 9.0 8.2 8.1 -70 - 1400 ºF - 6.6 8.3 0.2 10.3 9.9 9.9 10.1 9.8 9.3 3 9.6 9.7 9.8 9.3 9.2 8.5 8.5 8.3

70 - 1600 ºF - 7.0 8.6 0.5 10.5 10.2 10.2 10.3 10.0 9.44

9.7 9.9 10.0 9.6 9.4 8.7 8.8 8.370 - 1800 ºF - 7.4 8.9 0.8 10.6 10.5 10.5 10.5 10.2 9.5 5 9.9 10.1 10.3 9.8 9.6 9.0 9.2 8.270 - 2000 ºF - 7.7 9.2 1.1 10.7 10.7 10.7 10.8 10.4 - 10.1 10.2 10.6 10.0 9.7 9.3 9.5 -

1200 - 1600 ºF - 8.7 10.3 2.2 11.5 11.4 11.4 11.0 - - 10.5 - 11.4 10.8 10.5 10.0 10.7 -1200 - 1800 ºF - 9.3 10.6 2.5 - 11.7 11.7 12.0 11.4 - 10.7 11.0 11.9 11.0 10.6 10.3 11.3 -

Specific Heat,Btu/Ib/° F at 70 ºF 0.11 0.12 0.12 0.14 0.12 0.12 0.12 0.12 0.13 0.11 0.12 0.11 0.11 0.11 0.11 0.11 0.11 - 0.11Specific ElectricalResistance,microhm-cm at 70 ºF 70 77 81 85 80 75-85 75-85 85 90 97 8 94 99.1 102 100 105 112 116 - 98Thermal Conductivity,Btu/hr/sq f t/ft/°F

At 212 ºF 15.0 12.6 12.6 8.5 8.3 8.2 8.2 8.2 7.9 8.2 8.2 7.5 7.5 7.0 7.0 7.2 7.2 - 8.2At 1000 ºF 15.7 17.9 17.9 12.4 12.3 12.0 12.0 12.0 11.8 12.9 6 12.2 11.0 11.0 10.8 10.8 11.1 11.1 13.4At 1400 ºF - - - 14.6 14.6 14.1 14.1 14.1 14.2 - 14.7 13.2 13.2 12.9 12.9 13.3 13.3 -At 1500 ºF - 20.3 20.3 - - - - - - 14.8 7 - - - - - - - 15At 2000 ºF - 24.2 24.2 18.2 - 17.5 17.5 17.5 18.6 - 19.3 17.0 17.0 16.3 16.3 17.0 17.0 -

Melt ing Point (approx) , ºF 2750 2725 2700 2650 2550 2500 2500 2550 2550 2490 2600 2500 2450 2450 2450 2350 2350 - 2400Magnetic Permeability Ferro-

Magnetic

Ferro-

Magnetic

Ferro-

Magnetic

1.3-2.5 1.00 1.0-1.9 1.0-1.051.0-1.7 1.02 - 1.01 1.10 1.02-1.25 1.10-2.00 1.10-

2.00

16.0 2.0 - -

168- 212 ºF 61110 ºF268- 930 ºF 71470 ºF368-1470 ºF 8 75 ºF468-1650 ºF aCalculated568-1830 ºF


17/5217

AERONAUTICALThe high temperatures encountered in aircraft power plants

and afterburners have been controlled by the use of heat-resistant alloy castings.

Typical Applications

Jet engine rotorsJet engine rings

Afterburner partsGun blast tubes

CEMENTIn kiln processes, heat, corrosion and abrasion are con-

stantly attacking operating equipment. High-alloy castingsresist high temperatures, corrosive gases and abrasives and

reduce breakage, shut-down time and rapid wear.

Typical ApplicationsBurner nozzlesConveyorsCooler liftersDampersKiln chains

Kiln end ringsKiln feed chutesKiln shell segmentsSlurry feed pipes

CONTINUOUS CAST CHAINAlloy: HH (25Cr-12Ni)Weight: 50 IbUse: Cement Kiln

GLASS AND ENAMELINGIn the glass, pottery and enameling industries, handling

equipment must have sufficient strength at elevated tempera-tures to resist bending and warpage. The alloys used mustresist scaling or flaking to prevent contamination of the prod-uct. Some heat-resistant cast alloys have both these charac-teristics and they are used extensively.

LEHR ROLLSAlloy: HF (19Cr-9Ni)Weight: 1040 IbSize: 8 in. O.D., 6 in. I.D., 168 in. longUse: Supports glass without bending at operating temperature of

1500 ºF.

Industrial Applicationsof Heat-Resistant Alloy Castings


TraysMolds

FixturesHangersBurning tools

Brick supportsSuspension bars

Hearth platesKilns and furnacesLehr rolls


18/5218

Glass and Enameling (Cont'd.)

ENAMELING FURNACE FLOOR IRONSAlloy: HT (35Ni-15Cr)Weight: 575 Ib (large casting)Use: Operates at 1800 ºF

HEAT TREATING

The advantages of high-alloy castings have been frequentlydemonstrated in heat-treating equipment. High temperatures,heavy loads, thermal shock and the continuous operation ofheat-treating furnaces require the use of heat-resistant alloy

castings for long uninterrupted service and low maintenanceand operating costs. The uses of high-alloy castings in heat-treating operations are extensive.

SHAFT FIXTURE ON TRAYAlloy: HU (39Ni-15Cr)Weight: 87 IbUse: Carburizing furnace

MUFFLER ASSEMBLIESAlloy: HT (35Ni-15Cr)Size: Each casting 24 in. long, wall thickness ¼ in.Use: Handle hot gases (1750-1800 ºF) of glassmaking furnace.


TraysBoxes and basketsRetortsFixturesConveyor belts and chainsFurnace hearthsFurnace hearth supportsRoller railsGrates

Roller conveyorsScrew conveyorsSkid railsHot fansMolten metal potsFurnace mufflesRadiant tubesDampersHeat exchangers


19/5219

Heat Treating (Cont'd.)

GEAR FIXTURE ON TRAYAlloy: HU (39Ni-18Cr)Weight: 75 IbUse: Carburizing furnace

TRAY WITH CRISS-CROSS FIXTUREAlloy: HU (39Ni-18Cr)Weight: 56 IbUse: Carburizing furnace

RIVETLESS CHAINAlloy: HW (60Ni-12Cr)Weight: 5 lb eachSize: 5 in. x 6 in. x 1¾in.Use: Convey parts through hardening

furnace operating at 1650 ºF.

TRAYAlloy: HU (39Ni-18Cr)Weight: 40 lbUse: Roller rail furnace

ARTICULATED TRAY WITH TUBULAR FIXTUREAlloy: HX (66Ni-17Cr)Weight: 178 lbUse: Solution treat aircraft parts (water quenched).


20/5220

SIDE HEARTH LINK BELTAlloy: HH (25Cr-12Ni)

Weight: According to sizeSize: 3 in., 4 in., or 6 in. pitchUse: Convey parts through continuous furnacesoperating at 1600 to 1800 ºF

TUBULAR BASE WITH GRIDSAlloy: HT (35Ni-17Cr)Weight: 1170 lbUse: Pit furnace base support

GRID WITH LIFTING LOOPSAlloy: HU (39Ni-18Cr)Weight: 265 lbUse: Pit furnace top support

TUBULAR GRID ROLLER TRAYAlloy: HT (35Ni-17Cr)Weight: 164 lbUse: Malleablizing furnace


21/5221

PIT FIXTURE WITH SPACER GRIDS

Alloy: HT (35Ni-17Cr)Weight: 1173 IbUse: Carburizing furnace

PIT FIXTURE CAGEAlloy: HX (66Ni-17Cr)Weight: 930 IbUse: Solution treat space parts.

TRAY WITH TWO CRISS-CROSS FIXTURESAlloy: HU (39Ni-18Cr)Weight: 115 IbUse: Carburizing furnace

PIT FURNACE RINGAlloy: HX (66Ni-17Cr)Weight: 849 IbUse: Solution treat space parts (water quenched).


22/5222

PETROLEUM, PETROCHEMICAL REFINING AND CHEMICALThe heat-resistant grades of high-alloy castings are used

extensively in the petroleum refining industry. High-pressureand high-temperature refining units depend on high-alloy sup-ports, tubes, headers and other castings which can withstandexcessive heat and corrosion. Metal parts used in refineriesand rectifying plants are subject to extreme temperatures,heavy loadings, and corrosive liquids and gases. Among heat-resistant alloy casting grades are those that assure protectionfrom deterioration caused by heating and cooling cycling andresist corrosive media at temperatures up to 2000 ºF. HK-40and IN-519 are used extensively for catalyst tubes in steam-hydrocarbon reforming furnaces. The chromium-nickel alloys,50Cr-50Ni and IN-657, show excellent resistance to fuel oilash attack and are used extensively in Europe to resist thismaterial.

High-alloy castings serve many applications in the chemicalequipment field where heat-resistant castings are permitting

high output operation under severe corrosive and temperatureconditions.

Typical ApplicationsBeams and channelsPumpsValvesPistonsRetortsRoof tube hangersDampers

Tube sheetsTubesTube supports and wall tiesHeater tubesFittingsBurners and nozzles

FLANGES AND REDUCERSAlloy: HF with 5-15% ferrite (19Cr-9Ni)Weight: 1500 lb (flanges)Use: High temperature piping in

petrochemical plant.

U-BEND RETURNAlloy: HK-40 (25Cr-20Ni)Weight: 45 IbSize: 4 in. O.D. x 10 in. center to centerUse: Ethylene converter furnace

CAST WELDING WYEAlloy: HP (35Ni-26Cr)Weight: 74 lbSize: 14 in. long, 10 in. center to centerUse: Pyrolysis furnace


23/5223

VERTICAL TUBULAR BEAMWITH LOOSE ACCESSORIESAlloy: HK (25Cr-20Ni)Weight: 153 IbUse: Petrochemical tube support

FURNACE TUBE ASSEMBLIESAlloy: HP (35Ni-26Cr)Weight: 500 lb per assemblySize: 3.75 in. O.D. x 3.12 in. I.D. x 20 ºFtlong Use: Coil, radiant section, pyrolysisfurnace

TUBE SUPPORTAlloy: HH (25Cr-12Ni)Weight: 15 IbUse: Petrochemical industry

WELD ELBOWWITH TRUNNION PADAlloy: HK-40 modified with Cb (25Cr-20Ni-Cb)Weight: 23 IbSize: 4 in. O.D. x 3 in. IDUse: Ethylene converter furnace


24/5224

TUBE SUPPORTSAlloy: HH (25Cr-12Ni)Weight: 6 IbUse: Petrochemical industry

SIDE SUPPORTS AND TUBE SHEETSAlloy: HK (25Cr-20Ni)Weight: Sheets, 170 lb; supports, 407 lb

HORIZONTAL TUBULAR BEAM WITH ACCESSORIESAlloy: HK (25Cr-20Ni)Weight: 253 IbUse: Petrochemical tube support

HORIZONTAL TUBULAR BEAM WITH ACCESSORIESAlloy: HK (25Cr-20Ni)Weight: 299 IbUse: Petrochemical tube support


25/5225

REDUCING ELBOWAlloy: HK-40 (25Cr-20Ni)Weight: 10 IbSize: I.D. reduction 4½ in. to 1½ in.Use: Reformer tube assemblies

CENTRIFUGALLY-CASTFURNACE TUBEAlloy: HK-40 (25Cr-20Ni)Weight: 245 IbSize: 4 in. O.D. x 3 in. I.D. x 156 in. longUse: Furnace tube section

BURNER DIFFUSERAlloy: HX (66Ni-17Cr)Weight: 27 IbUse: Petrochemical industry


Tube supportsHanger boltsBrick and tile supportsDampers

NozzlesBeamsBurner diffusersValve bodies

POWER PLANTS

Because of the higher operating temperatures being usedin superheater and boiler units, extensive use is beingmade of heat-resistant cast alloys. The proper use ofhigh-alloy castings avoids costly shutdowns and reducesmaintenance requirements

BURNER NOZZLESAlloy: HE (29Cr-9Ni)Weight: 10 to 15 lb eachUse: Burners operating at temperatures up to 1800 ºF


26/5226

STEEL MILL EQUIPMENTThe advantages of heat-resistant alloy castings have been

demonstrated by the steel industry in many high-temperatureapplications. These alloys are capable of operation at highspeeds, temperatures and loads and provide reliable opera-tion for long periods, thus reducing equipment upkeep andoperating costs.

FURNACE DRUMAlloy: HK-40 (25Cr-20Ni)Weight: 10,000 IbSize: 60 in. major O.D.Use: Turn-down roll in steel mill furnace for normalizing sheet.

GUIDESAlloy: HH (25Cr-20Ni)Weight: 2 and 14 IbUse: Steel rod mill guides

REFRACTORY-LINED BLOWPIPESAlloy: HP (35Ni-26Cr)Weight: 600 Ib (pipe)Size: 10 in. O.D. barrel with 14 in. O.D. bell endsUse: Steel mill blast furnace

SMELTING AND REFINING EQUIPMENTMany years ago, this industry recognized the savings that

were possible if high-alloy castings were properly utilized. Inthe sintering and smelting of ores, high temperatures, acidgases and abrasion contribute to the destruction of furnace,hearth, kiln and sintering machine parts. Heat-resistant alloycastings reduce operating and maintenance costs by provid-ing durability and heat resistance.


Rabble arms Feed spoutsPlows Hearth platesRabbles Lute ringsAir arms GrateChains Seal plates

Dampers Furnace tubes

COOLER GRATESAlloy: HH (25Cr-12Ni)Weight: 20 to 40 Ib

Use: Iron ore pelletizing and cement kiln

GRATE BARSAlloy: HH (25Cr-12Ni)Weight: 12 Ib

Use: Iron ore sintering and pelletizing furnace


BafflesFurnace beams and railsConveyor partsFurnace doors and framesDampers

RetortsRadiant tubesRecuperatorsSkid railsMuffles


27/5227

The corrosion-resistant casting alloys are those com-positions capable of performing satisfactorily in a largevariety of corrosive environments. They are composedprincipally of nickel, chromium and iron; sometimes alsocontaining other elements. Castings made of these al-loys offer two basic advantages:

1. Facility of the production of complex shapes atlow cost.

2. Ease of securing rigidity and high strength-to-weight ratios.

Some typical alloy compositions are given in Table V,the room temperature mechanical properties in Table

VI, the physical properties in Table VII and the heattreating temperatures in Table VIII.

Commercial cast corrosion-resistant alloy can beidentified by the designations of the Alloy Casting Insti-tute, now a division of the Steel Founders' Society ofAmerica, and the American Society for Testing andMaterials.* Some of these materials are also listed in theAerospace Material Specifications (AMS) of the Societyof Automotive Engineers, the United States Govern-ment Specifications (MIL and QQ), the Society of Auto-motive Engineers Specifications and the Unified Num-bering System (UNS) developed by the Society of Auto-motive Engineers and the American Society for Testingand Materials.

TABLE VCompositions of Corrosion-Resistant Alloy Castings

CHEMICAL COMPOSITION, %Alloy Casting

InstituteDesignation

AlloyType

ASTM(or other)

Specification

AISI(or other)Wrought

ComparativeUNSNo.

Ni Cr Mo Cu CMax

MnMax

SiMax

Other

CA-15 12Cr A296, A487 410 J91150 1.0 11.5-14.0 0.5 – 0.15 1.00 1.50 Fe balCA-40 12Cr A296 420 J91153 1.0 11.5-14.0 0.5 – 0.20-0.40 1.00 1.50 Fe balCA-6NM 12Cr-4Ni A296,A487 – J91540 3.5-4.5 11.5-14.0 0.40-1.0 – 0.06 1.00 1.00 Fe balCA-6N 1 12Cr-7Ni A296 – – 6.0-8.0 10.5-12.5 – – 0.06 0.50 1.00 Fe balCB-30 20Cr A296 442 J91803 2.0 18-22 – – 0.30 1.00 1.50 Fe balCB-7Cu-1 17Cr-4Ni A747 17-4PH 2 – 3.6-4.6 15.5-17.7 – 2.5-3.2 0.07 0.70 1.00 Cb 0.20-0.35; N 0.05

max; Fe balCB-7Cu-2 15Cr-5Ni A747 15-5PH 2 – 4.5-5.5 14.0-15.5 – 2.5-3.2 0.07 0.70 1.00 Cb 0.20-0.35: N 0.05

max; Fe balCC-50 28Cr A296 446 J92615 4.0 26-30 – – 0.50 1.00 1.50 Fe balCD-4MCu 26Cr-5Ni A296 – – 4.75-6.0 25-26.5 1.75-2.25 2.75-3.25 0.04 1.00 1.00 Fe balCE-30 29Cr-9Ni A296 312 J93423 8-11 26-30 – – 0.30 1.50 2.00 Fe balCF-3 19Cr-10Ni A296, A351 304L J92500 8-12 17-21 – – 0.03 1.50 2.00 Fe balCF-8 19Cr-9Ni A296, A351

MIL-S-867 304 J92600 8-11 18-21 – – 0.08 1.50 2.00 Fe balCF-20 19Cr-9Ni A296 302 J92602 8-11 18-21 – – 0.20 1.50 2.00 Fe balCF-3M 19Cr-10Ni A296, A351 316L J92800 9-13 17-21 2.0-3.0 – 0.03 1.50 1.50 Fe balCF-8M 19Cr-10Ni A296, A351 316 J92900 9-12 18-21 2.0-3.0 – 0.08 1.50 1.50 Fe balCF-8C 19Cr-10Ni A296, A351 347 J92710 9-12 18-21 – – 0.08 1.50 2.00 Cb 8XC min, 1.0 max or Cb-Ta 9XC min,

1.1 max; Fe balCF-16F 19Cr-10Ni A296 303 J92701 9-12 18-21 1.50 – 0.16 1.50 2.00 Se 0.20-0.35; Fe balCG-8M 19Cr-10Ni A296

MIL-S-867 317 J93000 9-13 18-21 3.0-4.0 – 0.08 1.50 1.50 Fe balCH-20 25Cr-12Ni A296, A351 309 J93402 12-15 22-26 – – 0.20 1.50 2.00 Fe balCK-20 25Cr-20Ni A296, A351

AMS 5365 310 J94202 19-22 23-27 – – 0.20 1.50 2.00 Fe balCN-7M 20Cr-29Ni A296, A351 – J95150 27.5-30.5 19-22 2.0-3.0 3.0-4.0 0.07 1.50 1.50 Fe balIN-862 3 – – – – 23-25 20-22 4.5-5.5 – 0.07 1.50 1.00 Fe balCW-12M 1 – A296, A494 – – bal 15.5-20.0 16.0-20.0 – 0.12 1.00 1.50 W 5.25 max; V 0.40max; Fe 7.50 maxCY-40 1 Ni-Cr-Fe A296, A494 INCONEL 4

alloy 600 – bal 14.0-17.0 – – 0.40 1.50 3.00 Fe 11.0 maxAlloy 625 3 – – – – bal 20-23 8.0-10.0 – 0.06 1.00 0.75 Cb 3.15-4.50;

Fe 5.0 maxCZ-100 1 Ni A296, A494 Nickel 200 – bal – – 1.25 1.0 1.50 2.00 Fe 3.0 maxM-35 1 Ni-Cu A296, A494 MONEL 4

QQ-N-288 alloy 400 – bal – – 26.0-33.0 0.35 1.50 2.00 Fe 3.50 maxN-12M 1 Ni-Mo A296, A494 – – bal 1.00 26.0-33.0 – 0.12 1.00 1.00 V 0.60 max; Fe 6.0 max

– Ni-Si – – – bal 1.00 – 2.4 – 0.50-1.25 8.5-10.0 W 1 max1ASTM designation 3INCO designation2Trademark of Armco Steel Corporation 4Trademark of the INCO family of companies

Note: ASTM A.296 will be replaced by two new standards, A 743 and A 744 in the 1978 Annual Book of ASTM Standards. A 743 will cover the martensitic and ferritic types and A 744 theaustenitic types. A 296 will appear in the 1978 Book of Standards but will be dropped in the 1979 Book.

*See ASTM Specification A 296

Part llCorrosion-Resistant Alloy Castings


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TABLE VIRoom Temperature Mechanical Properties of Corrosion-Resistant Alloy Castings

PROPERTY CA-15 CA-40CA-6NM

CA-6N CB-30

CB-7Cu-1

CB-7Cu-2 CC-50

CD-4MCu CE-30 CF-3 CF-8 CF-20 CF-3M CF-8M F-8C

CF-16F CG-8M CH-20 CK-20CN-7M

IN-862

CW-12M CY-40

Alloy625

CZ-100 M-35 N-

200 1 220 1 120 5 140 6 95 7 170 12a 170 12a 70 8a 108 9 95 10 77 11 77 11 77 11 80 11 80 11 77 11 77 11 82 11 88 11 76 11 69 11 60 72 6 65-90 10 70 6 50-65 10 65-85 10 135 2 150 2 150 12b 150 12b 95 8b 97 11

TensileStrength,ksi 115 3 140 3 145 12c 145 12c

100 4 110 4 135 12d 135 12d 125 12e 125 12e

Yield 150 1 165 1 100 5 135 6 60 7 145 12a 145 12a 65 8a 82 9 45 10 36 11 37 11 36 11 38 11 42 11 38 11 40 11 44 11 50 11 38 11 32 11 25 46 6 32-50 10,13 40 6 15-30 10,13 30-40 10,13

Strength 115 2 125 2 140 12b 140 12b 60 8b 63 11 (0.2% offset) 100 3 113 3 115 12c 115 12C ksi 75 4 67 4 110 12d 110 12d

97 12e 97 12e

Elongation 7 1 1 1 24 5 15 6 15 7 5 12a 5 12a 2 8a 25 9 15 10 60 11 55 11 50 11 55 11 50 11 39 11 52 11 45 11 38 11 37 11 48 11 40 4 6 20-10 10 20 6 30-15 10 50-25 10 in 2 in., % 17 2 10 2 9 12b 9 12b 15 8b 18 11

22 3 14 3 9 12c 9 12c 30 4 18 4 9 12d 9 12d

10 12e 10 12e

Brinell 390 1 470 1 69 5 – 195 7 375 12a 375 12a 212 8a 253 9 190 10 140 11 140 11 163 11 150 11 156–170 11 149 11 150 11 176 11 190 11 144 11 130 11 130 – 150–200 10 – 90– 130 10 125–17010

Hardness 260 2 310 2 311 12b 311 12b 193 8b 190 11 225 3 267 3 277 12c 277 12c 185 4 212 4 269 12d 269 12d

269 12e 269 12e Modulus ofElasticity,ksi x 10 3

29 29 29 29.5 29 28.5 – 29 29 25 28 28 28 28 28 28 28 28 28 29 24 – – 23 – 21.5 23 –

1 Air cooled from 1800 ºF. Tempered at 600 ºF.2

Air cooled from 1800 ºF. Tempered at 1100 ºF.3 Air cooled from 1800 ºF. Tempered at 1200 ºF.4 Air cooled from 1800 ºF. Tempered at 1400 ºF.5 Air cooled from above 1750 ºF. T empered at 1100-1150 ºF.6 Minimum7 Annealed at 1450 ºF. F.C. to 1000 ºF, then air cooled.8 a Under 1% Ni

b Over 2% Ni with 0.15 Nitrogen, minimum

9Solution annealed at 2050 ºF. Water quenched from 1900 ºF.10As cast11Water quenched from 2000-2050 ºF.12a PH heat treatment H900, minimum values.

b PH heat treatment H1025, minimum values.c PH heat treatment H1075, minimum values.d PH heat treatment H1100, minimum values.e PH heat treatment H1150, minimum values.

13 0.5% extension

TABLE VIIPhysical Properties of Corrosion-Resistant Alloy Castings

PROPERTY CA-15 CA-40CA-6NM CA-6N CB-30

CB-7Cu-1

CB-7Cu-2 CC-50

CD-4MCu CE-30 CF-3 CF-8

CF-20

CF-3M

CF-8M

CF-8C

CF-16F

CG-8M

CH-20

CK-20

CN-7M

IN-862

CW-12M CY-40

Alloy-625

CZ-100 M-35

Density, Ib/cu in. 0.275 0.275 0.278 0.280 0.272 0.280 0.269 a 0.272 0.280 0.277 0.280 0.2800.280 0.280 0.2800.280 0.280 0.280 0.279 0.280 0.289 0.292 a 0.336 a 0.300 0.305 0.3010.3120.33Specific Heat,

Btu db/°F at 70ºF

0 .11 0.11 0.11 - 0.11 0 .11 - 0.12 0 .11 0 .14 0.12 0.12 0.12 0 .12 0.12 0 .12 0.12 0 .12 0.12 0 .12 0 .11 - - 0.11 0 .10 0 .13 0 .13 -

Mean Coefficientof Linear ThermalExpansion,in./in ./°F x 10 6

70 - 212 ºF 5.5 5.5 6.0 5.7 6.0 - 5.9 6.3 - 9.0 9.0 9.6 8.9 8.9 9.3 9.0 8.9 8.6 8.3 8.6 - - - 7.1 - - -70 - 1000 ºF 6.4 6.4 7.0 6.2 1 6.5 6.4 6.9 9.6 10.0 10.0 10.4 9.7 9.7 10.3 9.9 9.7 9.5 9.4 9.7 - 7.8 -70 - 1200 ºF - - - - - 7.0 9.9 - 10.2 - - - - - - - - - - 8.2 -70 - 1300 ºF 6.7 6.7 - 6.7 - - - - - - - - - - - - - - - -70 - 1400 ºF - - - - - - 10.2 - - - - - - - - - - 8.9 8.5 8.970 - 1600 ºF - - - - - - 10.5 - - - - - - - - - - - - 8.8 -

SpecificElectricalResistancemicrohmcm at 70 ºF 78 76 78 - 76 77 - 77 75 85 76.2 76.2 77.9 82 82 71 72 82 84 90 89.6 - - 116 129 21 53 -ThermalConductivity,Btu/hr/sqft/f t/°F

at 212 ºF 14.5 14.5 14.5 - 12.8 9.9 - 12.6 8.8 8.5 9.2 9.2 9.2 9.4 9.4 9.3 9.4 9.4 8.2 7.9 12.1 - - 8.7 6.3 34 15.5 -

a t 1000 ºF 16.7 16.7 16.7 14 .5 17.9 13.4 12.4 12 .1 12.1 12 .1 12.3 12 .3 12.8 12 .3 12.3 12.0 11 .8 - 10.0Melting Point _ _(approx), ºF 2750 2725 2750 - 2725 2750 - 2725 2700 2650 2650 2600 2575 2600 2550 2600 2550 2550 2600 2600 2650 - - 2600 2460 2600 2400 -MagneticPermeability

Ferro-Magnetic

Ferro-Magnetic

Ferro-Magnetic –

FerroMagnetic

Ferro-Magnetic

- Ferro-Magnetic

Ferro-Magnetic

over1.5

1.20-3.00

1.00-1.30 1.01

1.50-3.00

1.50-250

1.20-1.80

1.00-2.00

1.50-3.00 1.71 1.02

1.01-1.10 1.00

170-600 ºF2Data from wrought equivalenta Calculated


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The Alloy Casting Institute and ASTM designationsuse "C" to indicate alloys used primarily for theircorrosion-resistant properties. The second letter indi-cates the nominal nickel content, increasing from A to Z.

The S.A.E. specifications use the nearest wroughtcomposition (AISI type number) and prefix it with thenumber 60 ºFor corrosion-resistant castings; for exam-ple, 60304 is equivalent to CF-8. In the Unified Num-

bering System, Jxxxx number series has been assignedto cast steels.

The chemical compositions of the corrosion-resistantcasting alloys are not the same as those of the wroughtalloys. Therefore, Table V lists only the nearest AISI orother wrought comparative. Alloy Casting Institute des-ignations or their equivalent should always be used toidentify castings.

1Reheat to 1500 ºF, air cool2Aging Temperature3Precipitation hardened

Temperature Condition900 ºF H 900925 ºF H 925

1025 ºF H10251075 ºF H10751100 ºF H11001150 ºF H1150

*Held 3 hours, slowly cooled to 1400-1750 ºF, cooled in water, oil or air.

EFFECT OF CONSTITUENTS

Chromium

A chromium content of at least 11.5% is required toprovide surface passivity under oxidizing conditions andto form an inert adherent surface film rich in chromiumoxide which is highly resistant to attack. A higher chro-mium content broadens the range of oxidizing condi-tions under which passivity is maintained. The chro-mium content of corrosion-resistant castings rangesfrom 12 to 28% in the ACI alloys.

NickelThe addition of nickel supplements the passivatingeffect of chromium under oxidizing conditions and alsoincreases the resistance of the alloys to attack underreducing conditions. Nickel in sufficient concentrationresults in a desirable austenitic structure and preservesthis structure through the many heat treatments towhich castings may be subjected during production andsubsequent fabrication. In the higher nickel alloys,nickel provides increased resistance to most reducing

TABLE VIIIHeat Treatment of Corrosion-Resistant Alloy Castings

Alloy CastingInstitute Designation Anneal at Harden at Temper at Quench

CA-15 1450-1650 ºF 1800-1850 ºF 600 ºF, max or 1100-1500 ºF -CA-40 1450-1650 ºF 1800-1850 ºF 600 ºF, max or 1100-1500 ºF -CA-6NM 1450-1500 ºF 1900-1950 ºF 600 ºF, max or 1100-1500 ºF -CA-6N 1900 ºF 1 - 800 ºF 2 air coolCB-30 1450 ºF, min - - air coolCB-7Cu-1 1925 ºF - 900-1150 ºF 3 air coolCB-7Cu-2 1925 ºF - 900-1150 ºF 3 air coolCC-50 1450 ºF, min - - air or furnace coolCD-4MCu 2050 ºF, min 4 - - -CE-30 2000-2050 ºF - - water, oil or airCF-3 1900-2050 ºF - - water, oil or airCF-8 1900-2050 ºF - - water, oil or airCF-20 2000-2100 ºF - - water, oil or airCF-3M 1900-2050 ºF - - water, oil or airCF-8M 1950-2100 ºF - - water, oil or airCF-8C 1950-2050 ºF - - water, oil or airCF-16F 1950-2050 ºF - - water, oil or airCG-8M 1900-2050 ºF - - water, oil or airCH-20 2000-2100 ºF - - water, oil or airCK-20 2000-2150 ºF - - water, oil or airCN-7M 2050 ºF, min - - water, oil or airIN-862 2150 ºF - - waterCW-12M 2200-2250 ºF - - waterCY-40 - - - -Alloy 625 2150 ºF - - waterCz-100 - - - -M-35 - - - -N-12M 2100-2150 ºF - - water


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environments. It also provides improved resistance tothose chemical compounds to which nickel is particu-larly resistant. These are typified by strong alkalies andhalogen compounds. In corrosion-resistant castings,the nickel content ranges from 1 to 96%.

MolybdenumMolybdenum has specific beneficial effects in improv-

ing resistance to sulfuric, phosphoric and hydrochloricacids. It also reduces the tendencies toward pitting insea water and other chloride solutions. In the ACI alloys,the molybdenum content ranges from none to 30%.

Other ElementsAlthough chromium, nickel and molybdenum have

the greatest influence on the properties of corrosion-resistant castings, other alloying elements also havetheir effects.

Carbon can have a detrimental effect on corrosionresistance by combining with chromium to form a car-bide. This undesirable effect can be eliminated by:

(a) Holding the carbon content below 0.03%.(b) Introducing columbium or titanium to form car-

bides of these elements instead of the harmfulchromium carbide.

(c) Heating the alloy to a temperature sufficientlyhigh to dissolve the carbon and cooling rapidlyenough to hold the carbon in solution.

Columbium is added as a stabilizer to prevent precipi-tation of chromium carbides.

Copper acts in the same manner as molybdenum toimprove resistance to sulfuric and phosphoric acids.

Selenium in small quantities improves machinabilitybut it reduces corrosion resistance somewhat.

Silicon also contributes to resistance to reducingacids such as sulfuric, but impairs resistance to nitricacid. The silicon content of cast corrosion-resistant alloysis higher than that of the wrought alloys because thiselement contributes the fluidity required to obtainsatisfactory casting characteristics. However, silicon is apromoter of ferrite formation and, as a consequence,tends to cause the formation of small amounts of ferrite inthe austenitic matrix. As one result, silicon increases theresistance of cast corrosion-resistant alloys to chlorideion stress-corrosion cracking.

CORROSIVE ATTACKCorrosion is a complex phenomenon in which numer-

ous variables influence not only the severity but also thetype of attack. Therefore, it is not possible to makespecific recommendations for alloy selection in a gen-eral publication. Certain limitations on the use ofcorrosion-resistant alloy castings and suggestions forcounteracting them are discussed below. Table IX isincluded to serve as a guide in selecting candidatealloys for an environment. Where corrosion data on cast

alloys were sparse, data on the wrought counterpartwere included on the assumption that corrosion rates forboth cast and wrought alloys would be similar.

Pitting CorrosionStainless steels are subject to localized loss of pas-

sivity and subsequent pitting by the action of chlorideions which penetrate the passive surface films. Theincidence of such pitting is determined by the competi-tion between the chloride ions which destroy passivityand dissolved oxygen or other oxidizing substanceswhich passivate the surface. It is affected also by thecomposition of the alloy and the exposure conditions.Favorable factors are the presence of molybdenum anda high nickel content represented, for example, by the51% Ni-17% Mo-16.5% Cr compositions which is usu-ally resistant to pitting by chloride solutions even underadverse conditions. Favorable environmental factors area plentiful supply of oxygen or other oxidizing agent or,conversely, no oxygen at all, a high alkalinity and lowtemperature, a medium to high flow rate and freedomfrom deposits. The most unfavorable condition is repre-sented by exposure beneath deposits to a stagnantsolution containing some dissolved oxygen. Turbulenceassociated with high velocity flow is generally beneficial.

SensitizationWhen an austenitic stainless steel containing more

than 0.03% carbon, which is not stabilized by the pres-ence of columbium or titanium, is heated in the 900-1400 ºF range, chromium carbide will precipitate at thegrain boundaries. The localized depletion of chromiummay make the alloy susceptible to intergranular attack inenvironments in which it ordinarily shows goodresistance. Sensitization can usually be avoided by

keeping the carbon content at 0.03% or less, by addingsmall quantities of columbium or titanium, or by heatingto 2000 ºF for one hour per inch of thickness followed byquenching in water.

Magnetic PropertiesThe Alloy Casting Institute grades containing up to

4% nickel are all magnetic, as is the CE-30 grade. AIlother grades fall within the austenitic alloy class, be-cause of their compositions, and are substantially non-magnetic. A small amount of magnetic ferrite is desir-able to facilitate weld repair although this ferrite may not

be detected by a magnet. Occasionally, when the chro-mium is on the high side of the specification and thenickel is on the low side, an unbalanced condition willdevelop in austenitic alloys that results in the formationof a two-phase alloy composed of austenite and ferriteThe presence of ferrite in the structure will cause thealloy to be slightly magnetic. This two-phase structurewill have corrosion resistance in practically all environ-ments equivalent to that of the single-phase austeniticstructure. An exception is in ammonium carbamate so-lutions such as are encountered in urea production.


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Stress-Corrosion CrackingUnder the combined effects of tensile stress and cor-

rosion by specific environments (most commonly con-centrated chlorides), certain stainless steel composi-tions are subject to stress-corrosion cracking. Nickelhas the greatest effect on resistance to this form ofattack. Resistance to such cracking is improved by in-creasing the nickel content above the 8% level of thecommon CF-8 grade.

Although cast austenitic stainless steels are oftenconsidered to be similar to their wrought counterparts,there is a difference. There is usually a small amount of

ferrite present in austenitic stainless steel castings, incontrast with the single-phase austenitic structure of thewrought alloys. The presence of ferrite in the castings isdesirable to facilitate weld repair but also increasesresistance to stress-corrosion cracking. There havebeen only a few stress-corrosion cracking failures withcast stainless steels in comparison with the approxi-mately equivalent wrought compositions. The principalreasons for this resistance are apparently (a) lowerstresses, (b) silicon added for fluidity is also beneficialfrom the standpoint of stress-corrosion cracking and (c)sand castings are usually tumbled or sandblasted toremove molding sand and scale which probably tends toput the surface in compression.

GROUPS OF CORROSION-RESISTANT ALLOY CASTINGS

The iron-base corrosion resistant alloys can be clas-sifed according to composition and metallurgical struc-ture into four broad groups:

1. Martensitic Alloys: CA-15, CA-40, CA-6NM,CA-6N

2. Ferritic and Duplex Alloys: CB-30, CC-50,CD-4MCu

3. Austenitic Alloys: CE-30, CF types, CG-8M,CH-20, CK-20, CN-7M, CN-7MS, IN-862

4. Precipitation Hardenable Alloys: CB-7Cu-1,Cb-7Cu-2

In addition, nickel-base corrosion-resistant alloys in-clude nickel, high nickel-copper alloys, high nickel-chromium alloys and other proprietary alloys.

MARTENSITIC ALLOYS

CA-15 (12Cr-1Ni)

This alloy contains the minimum content required toattain surface passivity under oxidizing conditions. Ithas good resistance to many mildly corrosive environ-ments that are oxidizing in character. It also has goodresistance to velocity effects in solutions for which it issuitable. The alloy is used widely for seats and discs invalves in steam service and for parts of turbines ex-posed to high velocity steam

CA-40 (12Cr-1Ni)This is the cutlery type of stainless steel which, by

virtue of its higher carbon content, can be hardened to agreater depth than type CA-15. It has good corrosionresistance to many environments, is tough and hasgood resistance to abrasion. It is used for chipperblades, cutter blades, cylinder liners, grinding plugs,shredder sleeves and steam turbine parts.

CA-6NM (12Cr-4Ni)This is an iron-chromium-nickel-molybdenum alloy

that is hardenable by heat treatment. In general corro-sion resistance, it is similar to CA-15 and has beenwidely substituted for CA-15 because of easier process-ing through the foundry cleaning room. Among uses arecompressor wheels, diaphragms, hydraulic turbine

parts, impulse wheels and pumps and valves for boilerfeedwater service.

CA-6N (12Cr-7Ni)This is a higher nickel content modification of CA-15

which has an excellent combination of strength, tough-ness and weldability. It has moderately good corrosionresistance.

FERRITIC AND DUPLEX ALLOYS

CB-30 (20Cr-2Ni)Because of its higher chromium content, this alloy has

better resistance to corrosion in many oxidizing environ-ments than the CA alloys. The addition of 2% nickelenhances corrosion resistance and increases tough-ness. It also has good abrasion resistance. Uses in-clude pump parts, turbine parts and valve trim.

CC-50 (28Cr-4Ni)Alloys containing about 28% chromium and up to 4%

nickel are resistant to a number of highly oxidizing me-dia such as hot nitric acid. They are also used in han-dling corrosives such as acid mine waters which areoxidizing and may be mildly abrasive. Among applica-tions are cylinder liners, digester parts, pump casingsand impellers.

CD-4MCu (26Cr-5Ni-3Cu-2Mo)As cast, this alloy has a duplex ferrite and austenite

structure. Because of its low carbon content, there areonly small amounts of chromium carbides distributedthroughout the matrix, but for maximum corrosion resis-

tance, these carbides must be dissolved by suitable heattreatment. Although the alloy can be precipitationhardened, the ACI recommends that this alloy be usedonly in the solution annealed condition. It is highly resis-tant to attack by some concentrations of sulfuric andhydrochloric acids and is exceptionally resistant tostress-corrosion cracking in chloride-containing solu-tions or vapors. It has also shown outstanding resis-tance to such mixtures as nitric-adipic acid slurries andwet process phosphoric acid slurries. Uses includecompressor cylinders, pump impellers, digester valvesand feed screws.


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AUSTENITIC ALLOYSCE-30 (29Cr-9Ni)

This alloy also is resistant to a number of highlyoxidizing corrosives and is particularly used for pumps,valves and fittings handling sulfite liquors in the paperindustry and some acid slurries in the metallurgical in-dustries. Because of its high chromium content, thealloy can be made with a higher carbon content than theCF type alloy without suffering the injurious effects ofcarbide precipitation. For the same reason, it may beused in place of the CF alloys where they must bewelded without subsequent heat treatment. While oftenused in the as-cast condition, ductility and corrosionresistance of the CE alloy may be improved somewhatby quenching from about 2000 ºF. Uses include digesternecks and fittings, circulating systems, fractionatingtowers, pump bodies and casings.

CF Alloys (19Cr-9Ni)The austenitic alloys containing about 19% chro-

mium, 9% nickel and less than 0.20% carbon constituteby far the most widely used group of corrosion-resistantstainless alloys. These alloys are used for handling awide variety of corrosive solutions in the chemical, tex-tile, petroleum, pharmaceutical, food and numerousother process industries. In the chemical industry, theyare particularly useful in handling oxidizing solutionssuch as nitric acid and peroxides and mixtures of acidssuch as sulfuric and phosphoric with oxidizing saltssuch as ferric, cupric, mercuric and chromic salts.These stainless alloys are resistant to most organicacids and compounds as encountered in the food, dairyand pharmaceutical industries. They also are resistantto most waters including mine, river, boiler and tapwaters. They are resistant to sea water under the highvelocity conditions associated with pumping but are

subject to severe pitting attack in stagnant or slow mov-ing sea water.

The limitation of the CF alloys is that most halogenacids and halogen acid salts tend to destroy their sur-face passivity. Thus, they are subject to considerableattack in such media as hydrochloric acid, acid chloridesalts, wet chlorinated hydrocarbons, wet chlorine andstrong hypochlorites.

For best resistance to corrosion, this alloy is producedin the low carbon CF-3 and CF-8 grades and should besolution annealed to prevent intergranular attack inseverely corrosive media. Heat treated CF-3 castings canbe field welded or hot formed without subsequent re-solution annealing, a major advantage in many appli-cations.

Columbium (niobium) or columbium plus tantalumare sometimes added to produce carbide-stabilized CF-8C alloy which, after heat treating, can be field welded orused at elevated temperatures without the precipitation ofchromium carbides and resultant susceptibility tointergranular attack of chromium depleted regions.

The addition of molybdenum as in grades CF-3M andCF-8M considerably increases the resistance of theCF-alloys to such corrosive media as sulfuric, sulfurous

and phosphoric acids and to certain hot organic acidssuch as formic, acetic and lactic acids. Molybdenumalso improves resistance to pitting in chloride salt solu-tions and sea water.

Grade CF-16F is similar to grades CF-8 and CF-20to which small amounts of selenium have been added toimprove the machinability. The corrosion resistance ofthis alloy is somewhat inferior to that of the CF-20 alloybut is adequate for many purposes.

Controlled Ferrite TypesThe strength of the CF alloys cannot be improved by

heat treatment but these alloys can be strengthened byincreasing the ferrite phase at the expense of the aus-tenite phase in these duplex microstructures. This facthas led to the introduction of controlled ferrite types,designated with an "A" suffix in some CF alloys, i.e.,CF-3A and CF-8A, for applications where higherstrength is desired than is obtainable in the CF-3 andCF-8 types. Minimum tensile strengths for these con-trolled ferrite types are 7 to 10 ksi higher than for theregular types. The increased ferrite content generally

improves the resistance of the alloy to stress-corrosioncracking in addition to increasing the strength. Becauseof the thermal instability of the higher ferrite microstruc-ture, however, the controlled ferrite types are not con-sidered suitable for service at temperatures above650 ºF (CF-3A) or 800 ºF (CF-8A).

CG-8M (19Cr-8Ni)The high molybdenum content of this alloy (3-4%)

gives it improved resistance to hot sulfurous and or-ganic acids and to dilute sulfuric acid. It also has greatresistance to pitting. Uses include dyeing equipment,flow meter components, pump parts and propellers.

CH-20 (25Cr-12Ni)With a carbon content of less than 0.20%, this alloy is

similar in corrosion resistance to the CE-30 composi-tion. It is used for specialized applications in the chemi-cal and paper industries. Uses include digester fittings,roasting equipment, valves and pump parts.

CK-20 (25Cr-20Ni)This alloy is somewhat similar to the CE and CH types

but has higher nickel content. It is sometimes made with acolumbium, or columbium plus tantalum addition, tominimize the effect of carbide precipitation. It is used inthe pulp and paper industry to handle sulfite solutions.Uses include digesters, filter press plates and frames,mixing kettles and return bends.

CN-7M (29Ni-20Cr)This designation covers a group of complex nickel

chromium-copper-molybdenum alloys containing morenickel than chromium. The increased nickel contenttogether with the addition of copper and molybdenumgive the alloy especially good resistance to sulfuric acidand to many reducing chemicals. It has good resistance


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34/5234

TABLE IX Corrosion Data

Corrosive Medium CA-15 CA-40 CB-30 CC-50 CD-4MCu CE-30CF-3CF-8

CF-20

CF-3MCF-8M CF-8C CF-16F

Acetic Acid5% 4 4 3 3 1 2 2 1 2 210% 4 4 4 4 1 2 2 1 2 215% 4 4 4 4 1 2 2 1 2 220% 5 5 4 4 1 2 2 1 2 330% 5 5 5 5 1 2 2 1 2 340% 5 5 5 5 1 2 2 1 2 350% 5 5 5 5 1 3 3 1 3 360% 5 5 5 5 2 3 3 2 3 380% 5 5 5 5 2 3 3 2 3 399.9% 5 5 5 5 2 3 3 2 3 3

Acetic Anhydride90% 5 5 5 5 2 3 3 2 3 3

Acetic Acid Vapors30% 5 5 5 5 2 3 3 2 3 3100 % 5 5 5 5 3 4 4 3 4 4

Aluminum Acetate 4 4 4 4 1 2 2 1 2 2Aluminum Chloride 5 5 5 5 4 5 5 5 5 5Aluminum Hydroxide 4* 4* 4* 4* 3 4* 4* 3 4* 4*Aluminum Sulfate

5% 4 4 4 4 1 2 2 1 2 210% 5 5 5 5 1 3 3 1 3 3Saturated 5 5 5 5 1 5 5 1 5 5

Alum (Aluminum Potassium Sulfate)10% 5 5 5 5 1 3 3 1 3 3Saturated 5 5 5 5 2 4 4 2 4 4

Ammonium Bicarbonate 3 3 2 2 1 1 1 1 1 2Ammonium Carbonate 3 3 2 2 1 1 1 1 1 2Ammonium Chloride

1% 2* 2* 2* 2* 1* 1* 1* 1 1* 1*10% 3* 3* 3* 3* 2* 2* 2* 2* 2* 2*20% 5 5 5 5 2* 4* 4* 3* 4* 4*50% 5 5 5 5 3* 4* 4* 3* 4* 4*

Ammonium Nitrate 2 2 2 2 1 1 1 1 1 1Ammonium Sulfate

1% 3 3 3 3 1 1 1 1 1 15% 3 3 3 3 1 2 2 1 2 210% 4 4 4 4 1 2 2 1 2 2Saturated 5 5 5 5 2 3 3 2 3 3

Bromine Liquid (Dry) 5 5 5 5 4 5 5 4 5 5Bromine Liquid (H 2O Saturated) 5 5 5 5 5 5 5 5 5 5

Bromine Water (Dilute) 5 5 5 5 4 5 5 4 5 5Calcium Chloride 5 5 5 5 4 5 5 5 5 5Calcium Hypochlorite 5 5 5 5 5 5 5 5 5 5Chlorine Gas (Moist) 5 5 5 5 5 5 5 5 5 5Copper Sulfate 4 4 3 3 1 2 2 1 2 2Ethylene Glycol 3 3 3 3 1 2 2 1 2 2Fatty Acids 300 ºF 300 ºF 300 ºF 300 ºF 600 ºF 400 ºF 400 ºF 600 ºF 400 ºF 400 ºFFerric Chloride 5 5 5 5 5 5 5 5 5 5Ferric Sulfate 4 4 4 4 2 3 3 2 3 3Ferrous Sulfate 4 4 4 4 1 2 2 1 2 2

LEGEND1. Good resistance to boiling. 4. Good resistance to 70 ºF.2. Good resistance to 160 ºF. 5. Not recommended.3. Good resistance to 120 ºF. *Subject to pitting. **Dilute concentrations.


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TABLE IX Corrosion Data

Corrosive Medium CA-15 CA-40 CB-30 CC-50 CD-4MCu CE-30CF-3CF-8

CF-20

CF-3MCF-8M CF-8C CF-16F

Fluosilicic Acid 5 5 5 5 4 5 5 4 5 5Formic Acid

5% 4 4 4 4 2 2 2

heat resistant

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