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HOT WORK TOOL STEEL

RAVNEX DC

The nameyou cantrust

C O N T E N T S GENERAL CHARACTERISTICS 02Chemical composition

Application

Microstructure in delivered condition

Toughness

Qualitative comparison

PHYSICAL PROPERTIES 05

MECHANICAL PROPERTIES 06Impact toughness at elevated temperatures

CONTINIOUS COOLING CURVES-CCT 07

HEAT TREATMENT 08Annealing

Stress relieving

Hardening

Tempering

Dimensional changes during hardening

and tempering

SURFACE TREATMENT 10Nitriding and nitrocarburising

WELDING AND EDM 11Welding

Electrical discharge machining

RECOMMENDATIONS FOR MACHINING 12

CASE STUDY 13

RAVNEX DC

CHEMICAL COMPOSITION (%)

GENERAL CHARACTERISTICS

M E T A L R A V N E • T h e n a m e y o u c a n t r u s t

Chemical element content is in wt.%

02

RAVNEX DC is a supreme hot-work tool steel

produced in METAL RAVNE, known for:

• High impact toughness

• High hot tensile properties and high working hardness

• High thermal conductivity

• Good polishability

• Nitrability

• High cleanliness

• Longer tool life

• Excellent homogeneity

• Weldability

METAL AISI W .Nr . C Si Mn Cr Mo V

RAVNEX DC H11 mod ~1.2343 0.36 0.20 0.30 5.00 1.35 0.45

APPLICATION

RAVNEX DC is primarily designed for die casting of light metals and alloys. It is often used for highly stressedhot-work structural parts where superior toughness is required (up to average Charpy V-notch value of 29.8 Jouleat 44-46 HRC according to NADCA#207).

RAVNEX DC is also recommended for die forging and extrusion. Because of its good polishability,the grade can be used for plastic molding applications and processing of glass.

RAVNEX DC is supplied in annealed condition, max. 209 HBW (705 N/mm2).

T h e n a m e y o u c a n t r u s t • M E T A L R A V N E

> TAB 2: ACCEPTABILITY CRITERIA OF ANNEALED MICROSTRUCTURE ACCORDING TO NADCA #207-2003

MICROSTRUCTURE IN DELIVERED CONDITION

RAVNEX DC is inspected in soft annealed condition according to SEP 1614 (Stahl-Eisen-PrüfblattSEP 1614 - September 1996), and according to NADCA#207 standard.

Cleanliness according to DIN 50602 is K1≤10.

> TAB 1: MICROHOMOGENEITY

50xIncreasing Degree of Segregation

Increasing Reduction R

atio

500x

Premium quality Standard quality Not acceptable

All microstructures etched with 5% NitalAcceptable Unacceptable

SA SB SC SD SE

03

RAVNEX DCannealed

Accepted rating charts of annealed RAVNEX DC.


QUALITATIVE COMPARISON

RAVNEX DC is a premium tool steel of highest toughness produced in Metal Ravne.Chart shows its toughness at high temperature compared to 1.2343 and conventional W.Nr1.2344 hot-work tool steel.

TOUGHNESS

Un-notched specimens (7 x 10 x 55 mm3) are used to test impact toughness in transverse direction,SEP 1314 (Stahl-Eisen-Prüfblatt SEP 1314- April 1990). Specimens are quenched and tempered to 45 +/- 2 HRC,and test is performed at 20 °C.

Average impact toughness of forged quality is higher than 299 Joule for average forging size of 900 x 400 mm.

DGM (Deutsche Gesellschaft fürMaterialkunde) recommendsimpact toughness of minimum250 Joules for hot-work tool steelin various hot-work applications.

STRENGTH means ultimatetensile strength derived from anengineering stress-strain curve.

TOUGHNESS is estimated byreduction in cross-section areaof tensile test probe at rupture.

RS GRADE STRENGTH TOUGHNESS

400

300

200

100

0

Impa

ct t

oug

hnes

s (J

oul

e)

44-46 HRC

DGMW.Nr. 1.2343

RAVNEX DC

04

W.Nr.1.2343

W.Nr.1.2344

RAVNEX DC


PHYSICAL PROPERTIES

D E N S I T Y ( g / c m 3 )

PHYSICAL PROPERTIES (TEMPERATURE DEPENDENTS)

* CTE is the mean coefficient of thermal expansion with reference temperature of 20 °C.

T H E R M A L C O N D U C T I V I T Y ( W / ( m . K ) )

E L E C T R I C R E S I S T I V I T Y ( O h m . m m 2 / m )

S P E C I F I C H E A T C A P A C I T Y ( J / ( g . K ) )

M O D U L U S O F E L A S T I C I T Y ( 1 0 3 x N / m m 2 )

C O E F F I C I E N T O F L I N E A R T H E R M A L E X P A N S I O N ( 1 0 - 6 ° C - 1 , 2 0 ° C ) *

7.85 (20 °C) 7.80 (450 °C) 7.69 (500 °C) 7.67 (550 °C) 7.65 (600 °C)

28.40 (100 °C) 30.1 (450 °C) 30 (500 °C) 29.90 (550 °C) 29.70 (600 °C)

0.50 (20 °C) 0.68 (450 °C) 0.86 (500 °C) 0.90 (550 °C) 0.96 (600 °C)

0.46 (20 °C) 0.51 (450 °C) 0.55 (500 °C) 0.57 (550 °C) 0.59 (600 °C)

12.40 (200 °C) 12.80 (300 °C) 13.20 (400 °C) 13.60 (500°C) 14.20 (600 °C)

05

215 (20 °C) 185 (450 °C) 176 (500 °C) 171 (550 °C) 165 (600 °C)

Impa

ct t

oug

hnes

s K

V (

Joul

e)

90

80

70

60

50

40

0

Testing temperature (° C)


MECHANICAL PROPERTIES

IMPACT TOUGHNESS AT ELEVATED TEMPERATURES

Figure shows impact toughness as function of temperature.Samples are taken from the core of a forged block in short transverse direction.They are quenched and tempered (Q+T; 1000 °C / oil / 2x tempering) to 45 +/- 1 HRC.Measurement: EN ISO 148: 2010

200 250 300 350 400 450 500 550 600

06

15010050

CONTINIOUS COOLING CURVES-CCT

Legend:A - AusteniteK - CarbideP - PerliteM - MartensiteB - Bainite

Austenitising temperature: 990 °C; soak time: 15 min

1200

1100

1000

900

800

700

600

500

400

300

200

100

0

Te

mp

era

ture

(°C

)

A + K

M + K

Ms

1 10

100

1 000 10 000 100 000

Seconds

TIME 101 1000

Minutes

100

B + K

Ac3 = 880 °C

P + K

QUENCH RATE SHOULD BE SUFFICIENT TO FORM PREDOMINANTLY MARTENSITIC STRUCTUREWITHOUT SIGNIFICANT AMOUNT OF BAINITE. SIGNIFICANT AMOUNT OF BAINITE FAVOURSTHERMAL FATIGUE AS A LESS STABLE PHASE CONSTITUENT WITH LOWER STRENGTH.

TIP 1

07


576 517 461

Ac1 = 805 °C

2,9 °C/s 0,2 °C/s 0,043 °C/s

Hardness HV0.3

1 10Hours

2 20

A N N E A L I N G

HEAT TREATMENT

FOR APPLICATIONS EXPOSED TO EXTREME THERMAL LOADING A PROPER HEAT TREATMENTIS ESSENTIAL. TO PREVENT EXCESSIVE GRAIN GROWTH DURING AUSTENITIZATION IT ISPREFERABLE TO LEAVE SOME OF THE CARBIDES NOT DISSOLVED.

TIP 2

Recommendations or NADCA#207.

HEATING

50 °C/h

Protect against oxidation, scaling anddecarburisation.

ANNEALING TEMPERATURE

800 - 850 °C

Min. 4 hours.

COOLING

20 °C/h

Slow in furnace. From 600 °C aircooling is possible.

S T R E S S R E L I E V I N G

HEATING

100 °C/h

STRESS RELIEVING

600 °C - 650 °C or 50 °C under thelast tempering temperature.

Min. 3 hours.

COOLING

20 °C/h

Slow and uniformly in the furnace toprevent formation of additionalresidual stresses. From approximately200 °C air cooling is possible.

Protect against oxidationand decarburisation.

H A R D E N I N G Hardness after hardening is 50-54 HRC (1680 - 1916 N/mm2).

HEATING AUSTENITISING COOLING

980 - 1000 °C See CCT diagram25 - 650 °C, 150 - 220 °C/h650 - 850 °C, ≤150 °C/h,850 - 1000 °C, ≤150 °C/h

Fast cooling is recommended inpressurized N2. For large dimensionhot-work tooling see NADCA#207 orGM DC-9999-1Rev.18 specification.

Hold in furnace atT = 650 °C / 850 °Cuntil TSURFACE-TCORE ≤≤110 °C / 60 °C

TSURFACE is measured at 15mmunderneath surface, maximum soaktime is 30 min.

08



INCREASED TOUGHNESS OF THIS SPECIAL GRADE OFFERS ONE TO SELECT HIGHER WORKINGHARDNESS. HIGHER THERMAL CONDUCTIVITY AND HIGH TEMPERATURE STRENGTH COMPAREDTO H11 GRADE ALSO CONTRIBUTE TO ITS IMPROVED RESISTANCE TO THERMAL FATIGUE.

TIP 3

DIMENSIONAL CHANGES DURING HARDENING AND TEMPERING

It is recommended to leave machining allowance before hardening of minimum 0.2 % of dimension,equal in all three directions.

TEMPERING

Tempering must start immediately after completion of quenching (when part reaches 90-70 °C).Three tempering treatments are recommended. First tempering destabilizes retained austenite.Second tempering tempers newly formed microstructure constituents.

HEATING TEMPERING TEMPERATURE COOLING

1st: 520 - 530 °C2nd: choose working hardness (see tempering diagram).3rd: 50 °C bellow 2nd tempering.

Cool in air or in the furnace toroom temperature betweentempering cycles.

150 °C/h - 250 °C/h

1 hour per 25mm wall thicknessbased on the furnace temperature.Minimum 2 hours.


Ha

rdn

ess

(H

RC

)

60

55

50

45

40

200 300 400 500 600 700

Tempering temperature (°C)

Ha

rdn

ess

(H

RC

)

60

55

50

45

40

500 600 700


09

550 650

25 mm/oil25 mm/oil


NITRIDING AND NITROCARBURISING

Nitriding treatment is commonly recommended to enhance surface properties of RAVNEX DC.

Nitriding treatment for hot-work applications is performed by producing diffusion zone only ( nitriding phase) of a depthdetermined by particular application requirements, and completely inhibit surface compound layer ( and nitriding phases).

Nitriding treatment for plastic-molding or cold-work applications with wear resistance requirements is performed byproducing surface compound layer of composition and thickness determined by particular application requirements.

For applications with requirement for additional surface protection, improvement of sliding properties, or improvementof corrosion resistance, it is recommended that oxidation treatment (Fe3O4) follows the nitriding.

For details on surface preparation and setup of nitriding treatment parameters to obtain required surface propertiesplease consult our approved nitriding specialist.

SURFACE TREATMENT

Te

mp

era

ture

(°C

)

0

Nitriding potential

0.1 1 10

800

700

600

500

400

300

10

Lehrer diagram presented in figure shows the effect of two parameters:(1) nitriding potential (a function of partial pressure of ammonia and hydrogen), and (2) temperature, on composition ofnitriding phases formed on material surface. Figure shows recommended selection of the two governing parameters forappropriate execution of nitriding for two extreme application regimes, hot work on one hand, and cold-work on the other.

Nitriding of hot-work applications (limited or no compound layer)

Nitriding of cold-work applications (well developed compound layer)

Nitriding for intermediate surface properties

WELDING

RAVNEX DC is a readily weldable alloy by TIG or MMA welding processes in hardened or soft-annealed condition. Fillermetal should be of the same or similar chemical composition.

Heat treatment after welding is recommended. Annealing should be performed after welding of soft annealed parts, whereastempering at temperature of about 50 °C below tempering temperature should be performed after welding of hardenedand tempered parts. Laser welding is recommended for repair of smaller cracks and edges.

WELDING AND EDM

ELECTRICAL DISCHARGE MACHINING

Electrical discharge machining (EDM) leaves a brittle surface layer due to melting and resolidification of surface material.

It is recommended to: (1) remove the resolidified layer by polishing, grinding or other mechanical methods,and (2) temper the work-piece at temperature of about 50 °C below the tempering temperature.Execution of tempering of re-hardened and jet untempered layer underneath the surface is critical.

PREHEATING TEMPERATURE

320 - 350 °C

MAXIMUM INTERPASS TEMPERATURE

470 °C

POST WELD COOLING

Approximately 30 °C / h to notless than 70 °C, then tempering.

WELDING METHOD

TIG, MMA

FILLER MATERIAL

H11

HARDNESS AFTER WELDING

~ 50 HRC

11



The information below is provided solely as a general machining guideline. It refers to material soft annealed condition.

RECOMENDATIONS FOR MACHINING

D R I L L I N G

INSERT DRILL DIAMETER (mm) CUTTING SPEED (m/min) FEED (mm/rev)

F A C E M I L L I N G

INSERT CUTTING SPEED (m/min) FEED (mm/tooth) DEPTH OF CUT (mm)

T U R N I N G

* c. = coated carbide

INSERT CUTTING SPEED (m/min) FEED (mm/rev) DEPTH OF CUT (mm)

12

P20-P30 c.* (rough turning) 180 - 220 0.20 - 0.40 2.00 - 4.00

P10 c.* (fine turning) 230 - 270 0.05 - 0.20 0.50 - 2.00

HSS (fine turning) 25 - 30 -0.30 -2.00

HSS 5 - 20 15 - 20 0.05 - 0.30

Coated HSS 5 - 20 35 - 40 0.05 - 0.30

P20-P40 c.* (rough milling) 150 - 220 0.20 - 0.40 2.00 - 4.00

P10 c.* (fine milling) 230 - 260 0.10 - 0.20 -2.00

CASE STUDY

HEAT TREATMENT OF RAVNEX DC

Control of quenching is critical to assure dimension stability, optimum microstructure and mechanical properties of anywork-piece.

Finite element modelling of heat treatment reveals that both hardening temperature and soaking time, as well as quenchingrate strongly depend on work piece size and geometry.

Figure 1 shows temperature distribution intwo workpieces of different thickness ata given time (t), (see Figure 2) duringquenching. One can observe a hot core and ahigh temperature gradient in a thick workpiece,while a thin workpiece has at same coolingtime almost uniform temperature distribution.

13

> FIG 1



Tem

pera

ture

(°C

)

0

Time (min)

10 20 30 40 50 60

> FIG 2

t

1100

T

900

800

700

600

500

400

300

200

100

0

A1

Figure 2 reveals temperature transient at quenching for both workpieces at two characteristic points:(1) a point 15mm underneath the surface, and (2) the core.

Figure 3 shows temperature difference between the two characteristic points for both workpieces for the samequenching transient. An extreme temperature gradient occurs in the thick workpiece, with high risk of causingdistortion or gross cracking. Application of isothermal quenching process (see NADCA#207) is recommendedto reduce the potential detrimental effects of extreme temperature difference. A short isothermal hold reducessignificantly the temperature gradient in the thick workpiece. (See surface temperature transifnt curveC1

ISO-Q in Figure 2 and Figure 3.)

A2 B1 B2 C1ISO-Q

0

Time (min)

10 20 30 40 50 60

> FIG 3800

700

600

500

400

300

200

100

0

A2 - A1

T (°

C)

B2 - B1 B2 - C1

14

ISO-Q

Figure 4 shows average cooling speed between 800 and 500 °C at the core of a generalized geometry workpiece. Both geometry and size of theworkpiece is defined by its volume (V) to surface (S) ratio. Medium quenching power in a vacuum-type furnace is applied to determine the workpiececooling speed (6 bar N2 overpressure with medium to high gas circulation). The plot is particularly useful for determining optimum quenchingspeed in workpieces where temperature at core is not possible to directly monitor by thermocouple.SURFACE - temperature at a point 15 mm underneath the center of largest workpiece surface.CORNER* - temperature at a point 15 mm underneath the most exposed part of workpiece.

* data presented are computed for a point 15mm underneath an angle of a cube.

SHARP EDGES ON THE TOOL IN HEAT TREATMENT SHOULD BE AVOIDED TO PREVENT GROSS CRACKINGOR MICRO QUENCHING CRACKS WHICH CAN LEAD TO FORMATION OF LEADING CRACKS.TIP 4

To achieve optimum material properties, heat treatment parameters should be adjusted to specific workpiece size andgeometry. Critical quench rate is needed to avoid both pearlite formation and carbide precipitation.

In order to run quenching of a particular dimension and geometry workpiece at optimum velocity it is critical to continuouslymonitor temperature of both the surface and the core throughout the cycle.

> FIG 4

Co

olin

g ve

loci

ty (

°C/m

in)

20

V/A (mm)

30

300

250

200

150

100

50

0

CORE SURFACE CORNER

40 50 60 70 80 90 100 110 120

15



16

Notes

Publisher: Ravne Steel Center • Text: Metal Ravne • Production: RD BORGIS • AD/D: XLMS • Photos: archive Metal Ravne • Print: ALE d.o.o. • June 2014

METAL RAVNE, d.o.o.Koroπka cesta 14, 2390 Ravne na Koroπkem, Slovenia

Telephone: +386 2 870 7000, Telefax: +386 2 870 7006E-mail: [email protected]

www.metalravne.com

RAVNEX HD is produced by:

RAVNEX HD is distributed by:

HOT WORK TOOL STEEL

RAVNEX HD

The nameyou cantrust

RAVNEX HDC O N T E N T S GENERAL CHARACTERISTICS 02

Chemical composition

Application

Microstructure in delivered condition

Toughness

Qualitative comparison

PHYSICAL PROPERTIES 05

CONTINIOUS COOLING CURVES-CCT 06

HEAT TREATMENT 07Annealing

Stress relieving

Hardening

Tempering

Dimensional changes during hardening

and tempering

HARDNESS 09

MECHANICAL PROPERTIES 09Impact toughness at elevated temperatures

SURFACE TREATMENT 10Nitriding and nitrocarburising

WELDING AND EDM 11Welding

Electrical discharge machining

RECOMMENDATIONS FOR MACHINING 12

CASE STUDY 13Heat treatment of RAVNEX HD RS 450

CHEMICAL COMPOSITION (%)

Controlled chemical composition with minimal content of detrimental elements compared to standard steel grades.

GENERAL CHARACTERISTICS


RAVNEX HD is a supreme hot-work tool steelproduced in METAL RAVNE, known for:

• Excellent impact toughness

• High hot tensile properties and high working hardness

• Excellent thermal conductivity

• Good polishability

• Excellent hardenability

• Nitrability

• High cleanliness

• Longer tool life

• Excellent homogeneity

• Weldability

APPLICATION

RAVNEX HD is primarily designed for die casting of light metals and alloys. Due to its excellent hardenabilityit is especially recommended for high-dimension tooling. It is often used for highly stressed hot-work structural partswhere superior toughness is required.

RAVNEX HD is also recommended for die forging and extrusion. Because of its good polishability, the gradecan be used for plastic molding applications and processing of glass.

RAVNEX HD is supplied in annealed condition, max. 235 HBW (791 N/mm2).

Chemical element content is in wt.%

METAL AISI W .Nr . C Si Mn Cr Mo V Ni

RAVNEX HD - - 0.37 0.25 0.43 4.90 1.60 0.59 1.60

02


> TAB 2: ACCEPTABILITY CRITERIA OF ANNEALED MICROSTRUCTURE ACCORDING TO NADCA #207-2003

MICROSTRUCTURE IN DELIVERED CONDITION

RAVNEX HD is inspected in soft annealed condition according to SEP 1614 (Stahl-Eisen-Prüfblatt SEP 1614 - September1996), and according to NADCA#207 standard.

Cleanliness according to DIN 50602 is K1≤10.

> TAB 1: MICROHOMOGENEITY

Accepted rating charts of annealed RAVNEX HD.

50xIncreasing Degree of Segregation

Incr

easi

ng R

educ

tio

n R

atio

500x

Premium quality Standard quality Not acceptable

All microstructures etched with 5% NitalAcceptable Unacceptable

SA SB SC SD SE

03

RAVNEX HDannealed


QUALITATIVE COMPARISON

RAVNEX HD is a premium tool steel of highest toughness produced in Metal Ravne. Chart shows its impact toughnesscompared to W.Nr1.2343, conventional W.Nr1.2344 hot-work tool steel and to RAVNEX DC.

TOUGHNESS

Un-notched specimens (7 x 10 x 55 mm) are used to test impact toughness in transverse direction, SEP 1314(Stahl-Eisen-Prüfblatt SEP 1314- April 1990). Specimens are quenched and tempered to 45 +/- 2 HRC, and testis performed at 20°C.

Average impact toughness of forged quality is higher than 299 Joule for average forging size of 900 x 400 mm.

DGM (Deutsche Gesellschaft fürMaterialkunde) recommendsimpact toughness of minimum250 Joules for hot-work tool steelin various hot-work applications.

STRENGTH means ultimatetensile strength derived from anengineering stress-strain curve.

RS GRADE STRENGTH TOUGHNESS

400

300

200

100

0

Impa

ct t

oug

hnes

s (J

oul

e)

44-46 HRC

DGMW.Nr. 1.2343

RAVNEX HD

W.Nr.1.2343

W.Nr.1.2344

RAVNEX DC

RAVNEX HD

04


PHYSICAL PROPERTIES

D E N S I T Y ( g / c m 3 )

PHYSICAL PROPERTIES (TEMPERATURE DEPENDENTS)

* CTE is the mean coefficient of thermal expansion with reference temperature of 20 °C.

T H E R M A L C O N D U C T I V I T Y ( W / ( m . K ) )

E L E C T R I C R E S I S T I V I T Y ( O h m . m m 2 / m )

S P E C I F I C H E A T C A P A C I T Y ( J / ( g . K ) )

M O D U L U S O F E L A S T I C I T Y ( 1 0 3 x N / m m 2 )

C O E F F I C I E N T O F L I N E A R T H E R M A L E X P A N S I O N ( 1 0 - 6 ° C - 1 , 2 0 ° C ) *

7.83 (20 °C) 7.70 (450 °C) 7.68 (500 °C) 7.66 (550 °C) 7.65 (600 °C)

32.80 (100 °C) 34.30 (450 °C) 34.10 (500 °C) 33.90 (550 °C) 33.50 (600 °C)

0.50 (100 °C) 0.58 (450 °C) 0.63 (500 °C) 0.68 (550 °C) 0.73 (600 °C)

0.44 (20 °C) 0.64 (450 °C) 0.68 (500 °C) 0.72 (550 °C) 0.83 (600 °C)

210 (20 °C)

11.60 (200 °C) 11.80 (300 °C) 12.02 (400 °C) 12.04 (500 °C) 12.01 (600 °C)

05


CONTINIOUS COOLING CUR VES-CCT

Legend:A - AusteniteK - CarbideP - PerliteM - MartensiteB - Bainite

Austenitising temperature: 1030 °C; soak time: 15 min

1200

1100

1000

900

800

700

600

500

400

300

200

100

0

Te

mp

era

ture

(°C

)

A + K

M + K

Ms

1 10

100

1 000 10 000 100 000Seconds

TIME 101 1000Minutes

100

B + K

1 000 000

Ac3 880 °C

Hardness HV10 161453479633655685

P + K

QUENCH RATE SHOULD BE SUFFICIENT TO FORM PREDOMINANTLY MARTENSITIC STRUCTUREWITHOUT SIGNIFICANT AMOUNT OF BAINITE. SIGNIFICANT AMOUNT OF BAINITE FAVOURSTHERMAL FATIGUE AS A LESS STABLE PHASE CONSTITUENT WITH LOWER STRENGTH.

TIP 1

06

Ac1 790 °C

A N N E A L I N G


HEAT TREATMENT

FOR APPLICATIONS EXPOSED TO EXTREME THERMAL LOADING A PROPER HEAT TREATMENTIS ESSENTIAL. TO PREVENT EXCESSIVE GRAIN GROWTH DURING AUSTENITIZATION IT ISPREFERABLE TO LEAVE SOME OF THE CARBIDES NOT DISSOLVED.

TIP 2

Recommendations or NADCA#207.

HEATING

50 °C/h

Protect against oxidation, scaling anddecarburisation.

ANNEALING TEMPERATURE

800 - 850 °C

Min. 4 hours.

COOLING

20 °C/h

Slow in furnace. From 600 °C aircooling is possible.

S T R E S S R E L I E V I N G

HEATING

100 °C/h

STRESS RELIEVING

650 °C or 50 °C under the lasttempering temperature.

Min. 3 hours.

COOLING

20 °C/h

Slow and uniformly in the furnace toprevent formation of additionalresidual stresses. From approximately200 °C air cooling is possible.


H A R D E N I N G Hardness after hardening is 56-58 HRC (2030 - 2180 N/mm2).

HEATING AUSTENITISING COOLING

1030 - 1050 °C See CCT diagram25 - 650 °C, 150 - 220 °C/h650 - 850 °C, ≤150 °C/h,850 - 1030 °C, ≤150 °C/h

Fast cooling is recommended inpressurized N2. For large dimensionhot-work tooling see NADCA#207 orGM DC-9999-1Rev.18 specification.

Hold in furnace atT = 650 °C / 850 °Cuntil TSURFACE-TCORE ≤≤110 °C / 60 °C

TSURFACE is measured at 15mmunderneath surface, maximum soaktime is 30 min.

07


INCREASED TOUGHNESS OF THIS SPECIAL GRADE OFFERS ONE TO SELECT HIGHER WORKINGHARDNESS. HIGHER THERMAL CONDUCTIVITY AND HIGH TEMPERATURE STRENGTH COMPAREDTO H11 GRADE ALSO CONTRIBUTE TO ITS IMPROVED RESISTANCE TO THERMAL FATIGUE.

TIP 3

DIMENSIONAL CHANGES DURING HARDENING AND TEMPERING

It is recommended to leave machining allowance before hardening of minimum 0.2 % of dimension,equal in all three directions.

TEMPERING

Tempering must start immediately after completion of quenching (when part reaches 90-70 °C). Three tempering treatmentsare recommended. First tempering destabilizes retained austenite. Second tempering tempers newly formed microstructureconstituents.

HEATING TEMPERING TEMPERATURE COOLING

1st: 540 - 550 °C2nd: choose working hardness (see tempering diagram).3rd: 50 °C bellow 2nd tempering.

Cool in air or in the furnace toroom temperature betweentempering cycles.

150 °C/h - 250 °C/h

1 hour per 25mm wall thicknessbased on the furnace temperature.Minimum 2 hours.


Ha

rdn

ess

(H

RC

)

60

55

50

45

40

100 200 300 400 500 600 700


T austenization = 1030 °C

T austenization = 1050 °C

Ha

rdn

ess

(H

RC

)

60

55

50

45

40

550 600 650


08

25 mm/oil25 mm/oil

Ha

rdn

ess

(H

RC

)

60

55

50

45

40

35

480



HARDNESS

500 520 540 560 580 600 620 640 660

1050 / 1x 2h

1050 / 2x 2h

09

MECHANICAL PROPERTIESIMPACT TOUGHNESS AT ELEVATED TEMPERATURES

TEMPERING DIAGRAM RAVNEX HD

Impa

ct t

oug

hnes

s K

V (

Joul

e)

90

80

70

60

50

40

30

0


100 200 300 400 500

Figure shows impact toughness as function of temperature.Samples are taken from the core of a forged block in short transverse direction.They are quenched and tempered (Q+T; 1030 °C / oil / 2x tempering) to 45 +/- 1 HRC.Measurement: EN ISO 148: 2010

25 mm/oil


NITRIDING AND NITROCARBURISING

Nitriding treatment is commonly recommended to enhance surface properties of RAVNEX HD.

Nitriding treatment for hot-work applications is performed by producing diffusion zone only ( nitriding phase)of a depth determined by particular application requirements, and completely inhibit surface compound layer( and nitriding phases).

Nitriding treatment for plastic-molding or cold-work applications with wear resistance requirements is performed byproducing surface compound layer of composition and thickness determined by articular application requirements.

For applications with requirement for additional surface protection, improvement of sliding properties, or improvementof corrosion resistance, it is recommended that oxidation treatment (Fe3O4) follows the nitriding.

For details on surface preparation and setup of nitriding treatment parameters to obtain required surface propertiesplease consult our approved nitriding specialist.

SURFACE TREATMENT

Lehrer diagram presented in figure shows the effect of two parameters:(1) nitriding potential (a function of partial pressure of ammonia and hydrogen), and (2) temperature, on composition ofnitriding phases formed on material surface. Figure shows recommended selection of the two governing parameters forappropriate execution of nitriding for two extreme application regimes, hot ork on one hand, and cold-work on the other.

Nitriding of hot-work applications (limited or no compound layer)

Nitriding of cold-work applications (well developed compound layer)

Nitriding for intermediate surface properties

Te

mp

era

ture

(°C

)

0

Nitriding potential

0.1 1 10

800

700

600

500

400

300

10

WELDING

RAVNEX HD is a readily weldable alloy by TIG or MMA welding processes in hardened or soft-annealed condition.Filler metal should be of the same or similar chemical composition.

Heat treatment after welding is recommended. Annealing should be performed after welding of soft annealed parts, whereastempering at temperature of about 50 °C below tempering temperature should be performed after welding of hardenedand tempered parts. Laser welding is recommended for repair of smaller cracks and edges.

WELDING AND EDM

ELECTRICAL DISCHARGE MACHINING

Electrical discharge machining (EDM) leaves a brittle surface layer due to melting and resolidification of surface material.

It is recommended to: (1) remove the resolidified layer by polishing, grinding or other mechanical methods,and (2) temper the work-piece at temperature of about 50 °C below the tempering temperature.Execution of tempering of re-hardened and jet untempered layer underneath the surface is critical.

PREHEATING TEMPERATURE

320 °C

MAXIMUM INTERPASS TEMPERATURE

470 °C

POST WELD COOLING

Approximately 30 °C / h to notless than 70 °C, then tempering.

WELDING METHOD

TIG, MMA

FILLER MATERIAL

H11, exceptional H13

HARDNESS AFTER WELDING

~ 50 HRC

11



The information below is provided solely as a general machining guideline. It refers to material in soft annealed condition.

RECOMENDATIONS FOR MACHINING

D R I L L I N G

INSER DRILL DIAMETER (mm) CUTTING SPEED (m/min) FEED (mm/rev)

K15 - K20 5 - 20 70 0.05 - 0.15

F A C E M I L L I N G

INSERT CUTTING SPEED (m/min) FEED (mm/tooth) DEPTH OF CUT (mm)

P30-P40 c.* (rough milling) 60 - 100 0.20 -2.00

P10-P20 c.* (fine milling) 75 - 130 0.20 -2.00

T U R N I N G

* c. = coated carbide

INSERT CUTTING SPEED (m/min) FEED (mm/rev) DEPTH OF CUT (mm)

P30-P40 c.* (rough turning) 65 - 100 -1.00 -4.00

P10 c.* (fine turning) 140 - 200 -0.30 -2.00

12

CASE STUDY

HEAT TREATMENT OF RAVNEX HD

Control of quenching is critical to assure dimension stability, optimum microstructure and mechanical properties of anywork-piece.

Finite element modelling of heat treatment reveals that both hardening temperature and soaking time, as well as quenchingrate strongly depend on work piece size and geometry.

Figure 1 shows temperature distribution intwo workpieces of different thickness at agiven time (t), (see Figure 2) during quenching.One can observe a hot core and a hightemperature gradient in a thick workpiece,while a thin workpiece has at same coolingtime almost uniform temperature distribution.

13

> FIG 1



Tem

pera

ture

(°C

)

0

Time (min)

10 20 30 40 50 60

> FIG 2

t

1100

T

900

800

700

600

500

400

300

200

100

0

A1

Figure 2 reveals temperature transient at quenching for both workpieces at two characteristicpoints: (1) a point 15mm underneath the surface, and (2) the core.

Figure 3 shows temperature difference between the two characteristic points for both workpieces for the samequenching transient. An extreme temperature gradient occurs in the thick workpiece, with high risk of causingdistortion or gross cracking. Application of isothermal quenching process (see NADCA#207) is recommendedto reduce the potential detrimental effects of extreme temperature difference. A short isothermal hold reducessignificantly the temperature gradient in the thick workpiece.(See surface temperature transifnt curve C1 ISOQ in Figure 2 and Figure 3.)

A2 B1 B2 C1ISOQ

0

Time (min)

10 20 30 40 50 60

> FIG 3800

700

600

500

400

300

200

100

0

A2 - A1

T (°

C)

B2 - B1 B2 - C1

14

Figure 4 shows average cooling speed between 800 and 500°C at the core of a generalized geometry workpiece. Both geometry and size of theworkpiece is defined by its volume (V) to surface (S) ratio. Medium quenching power in a vacuum-type furnace is applied to determine the workpiececooling speed (6 bar N2 overpressure with medium to high gas circulation). The plot is particularly useful for determining optimum quenchingspeed in workpieces where temperature at core is not possible to directly monitor by thermocouple.SURFACE - temperature at a point 15 mm underneath the center of largest workpiece surface.CORNER* - temperature at a point 15 mm underneath the most exposed part of workpiece.

* data presented are computed for a point 15mm underneath an angle of a cube.

SHARP EDGES ON THE TOOL IN HEAT TREATMENT SHOULD BE AVOIDED TO PREVENT GROSS CRACKINGOR MICRO QUENCHING CRACKS WHICH CAN LEAD TO FORMATION OF LEADING CRACKS.TIP 4

To achieve optimum material properties, heat treatment parameters should be adjusted to specific workpiece size andgeometry. Critical quench rate is needed to avoid both pearlite formation and carbide precipitation.

In order to run quenching of a particular dimension and geometry workpiece at optimum velocity it is critical to continuouslymonitor temperature of both the surface and the core throughout the cycle.

> FIG 4

Co

olin

g ve

loci

ty (

°C/m

in)

20

V/A (mm)

30

300

250

200

150

100

50

0

CORE SURFACE CORNER

40 50 60 70 80 90 100 110 120

15



16

Notes

Publisher: Ravne Steel Center • Text: Metal Ravne • Production: RD BORGIS • AD/D: XLMS • Photos: archive Metal Ravne • Print: ALE d.o.o. • June 2014

METAL RAVNE, d.o.o.Koroπka cesta 14, 2390 Ravne na Koroπkem, Slovenia

Telephone: +386 2 870 7000, Telefax: +386 2 870 7006E-mail: [email protected]

www.metalravne.com

RAVNEX HD is produced by:

RAVNEX HD is distributed by:

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