17-4ph stainless steels

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j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j m a t p r o t e c

Influence of hardness on the wear resistance of 17-4 PH

stainless steel evaluated by the pin-on-disc testing

J.D. Bressana,, D.P. Daros a, A. Sokolowski b, R.A. Mesquita c, C.A. Barbosa d

a Departamento de Engenharia Mec anica, CCT, UDESC Joinville, Campus Universit ario, 89223-100 UDESC Joinville, SC, Brazilb Engenheiro Qumico, Pesquisador Senior da Villares Metals S.A., Sumar e, SP, Brazilc Engenheiro de Materiais, Pesquisador Senior da Villares Metals S.A., Sumar e, SP, Brazild Engenheiro Metalurgista, Gerente de Tecnologia da Villares Metals S.A., Sumare, SP, Brazil

a r t i c l e i n f o

Article history:

Received 9 July 2007

Received in revised form

22 September 2007

Accepted 20 November 2007

Keywords:

Wear test

Wear resistance

PH stainless steel

Heat treatment

a b s t r a c t

Present work aimed at investigating the wear resistance of AISI 630 (UNS S17400) or 17-4

PH stainless steel hardened by precipitation hardening or aging at various hardness levels.

The PHs steels are an interesting family of steels for applying in highly stressed parts for its

corrosion resistance and relative high hardness, attaining up to 49 HRC by low-temperature

aging heat treatment, low distortion and excellent weldability. The wear tests by sliding

and/or abrasion were performed in a pin-on-disc tribometer whose pins had three different

hardness levels (43, 37 and 33 HRC) obtained by varying the precipitation hardening treat-

ment. The counterface discs were machined from the same steel composition and aged to

the hardness of 43 HRC. The steels wear resistances were evaluated, using sliding velocity

of 0.6 m/s, normal load of 30 N, total sliding distance of 2400m and controlled room tem-

perature and humidity of 27 C and 60%, respectively. From the analysis of plotted graphs of

cumulative lost volume versus sliding distance, it was observed the different wear rates as

function of the heat treatment and hardness. Due to the pins different hardness, the wear

resistance varied substantially. The wear mechanisms were also investigated through scan-

ning electron microscopy observations of the worn surfaces of the pins. It can be asserted

that the decrease in the pin hardness yields to lower pin wear resistance. The disc wear

was more severe as the difference in hardness between pin and disc increased. It was pre-

sented a list of mean wear resistance, establishing the best heat treatment that minimize

the wear in this material for sliding wear applications. For the investigated range of heat

treatment and hardness, the 17-4 PH steel pins with hardness of 43 HRC showed the best

wear resistance of 1941 and the pin with 33 HRC the worst wear resistance of 1581.

2007 Elsevier B.V. All rights reserved.

1. Introduction

Brazil is one of the largest soya bean producers in the world.

One of the main down-stream industries is the soya oil

production. In this industry, the chain conveyors take an

Corresponding author. Tel.: +55 47 4009 7958; fax: +55 47 4009 7940.E-mail addresses: [email protected] (J.D. Bressan), [email protected](D.P. Daros),

[email protected](A. Sokolowski), [email protected](R.A. Mesquita),[email protected] (C.A. Barbosa).

important role in the transportation of products during pro-

cessing. A critical component is the conveyor chain composed

by different sliding parts. The main wear mechanism present

in these chains is the relative wear due to metalmetal sliding

(Magee, 1992). Fig. 1 shows one example of a worn component

0924-0136/$ see front matter 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.jmatprotec.2007.11.251
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]://localhost/var/www/apps/conversion/tmp/scratch_5/dx.doi.org/10.1016/j.jmatprotec.2007.11.251http://localhost/var/www/apps/conversion/tmp/scratch_5/dx.doi.org/10.1016/j.jmatprotec.2007.11.251mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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354 j o u r n a l o f m a t e r i a l s p r o c e s s i n g t e c h n o l o g y 2 0 5 ( 2 0 0 8 ) 353359

Fig. 1 Worn pin utilized in the conveyor chain of a soya

processing plant. The pin was fabricated with 17-4 PH steel

heat treated to 33 HRC by aging H 1100.

in such chains. The main steel selection criteria for parts sub-

mitted to wear is usually based on the surface hardness of the

component. Besides this criterion, the corrosion resistance is

also very important steel selection factor due to the acidity,

temperatures and humidity present in the soya processing

conveyor chains. The combination of high hardness levels

and toughness, as well as good corrosion resistance, can

be fulfilled by the precipitation hardening stainless steels,

named commonly by PH steels.

Nowadays, the PH steels are an interesting family of steels

to apply in many components due to its heat treatment char-

acteristics and combination of good corrosion resistance, high

strength, low distortion, excellent weldability and relativehigh hardness up to 49 HRC. These steels are classified in

functionof the chemical composition and the different phases

present in the microstructure. The 17-4 PH steel (AISI Type 630

or UNSS17400) is a low-carbon martensitic stainless steel con-

taining nickel and copper, hardenable by precipitation. It can

be fabricated in various shapes of worked products as bars,

wires, sheets, forged parts, cast products, powder metallurgy

andpowderinjection molding products. In steel plants, itspro-

duction starts generally by melting in an electric arc furnaces

or open air induction furnaces or even vacuum induction fur-

naces.In addition, forcritical applications, as in theaerospace

industry, it is commonly submitted to refining by vacuum

arc remelting process, VAR or electroslag remelting, ESR. The17-4 PH steel is a versatile steel that shows good combina-

tion of high strength, toughness, resistance to corrosion, wear

and weldability. Its corrosion resistance in various environ-

ments is comparable to the 304 austenitic stainless steel and

its resistance to oxidation is superior to the 410 martensitic

stainless steel. Its metallurgy allows to be machined in the so-

called solution treated condition(solution heattreatment with

fast cooling) when has relative low hardness. After machining

operations, it can be hardened for a wide range of mechan-

ical properties and hardness by the precipitation aging heat

treatment in the temperatures between 480 and 620 C. The

increase in hardness and strength is due to the precipitation

hardening that occurs over the martensite structure previ-

ously formed during the solution treatment. Its application

hardness is commonly in the range of 3445 HRC. During

age hardening occurs a finely dispersed submicroscopic pre-

cipitation of intermetallic phase, rich in copper, inside the

martensitic matrix with low-carbon content and stable at

room temperature.

Besides the mechanical components for movement trans-

mission, the typical applications of this steel also includesstructural parts of airplanes, various aerospace components,

vapor turbine blades, hydraulic valve parts, surgical instru-

ments, high-precision rollers that can operate up to 300 C,

high-pressure pump body, pump and boat shafts.

Mechanical strength is commonly defined by the yield

stress or the ultimate tensile strength. On the other hand,

wear is defined as the surface progressive loss of mass of a

solidin relativemotion, leading to surface damage or rupture.

Wear can be mild or severe, depending on the contact con-

ditions between the surfaces: pressure, contact temperature,

coefficient of friction and materials hardness. The contact

conditions or contact severity can defined by an equation that

relates these variables.The wear resistance of materials is usually obtained by

performing wear tests in a laboratory equipment named tri-

bometer. A standard laboratory test that simulates the severe

conditions of mechanical components is the pin-on-disc test-

ing, according to the ASTM G99-95 standard (ASTM, 1995). In

this equipment, the test is carried out at selected constant

parameters as the total sliding distance, the normal load on

the pin, the sliding velocity and controlled conditions of tem-

perature and relative humidity (Bressan and Hesse, 2001).

The aim of present work is to investigate the wear resis-

tance of 17-4 PH steel specimens obtained from rolled bars

produced by conventional melting process and with three dif-

ferent heat treatments, consequently, various hardness, usingthe pin-on-disc testing in accordance with the ASTM G99-95

standard. Both counterface or discs and pins were fabricated

from the same 17-4 PH steel composition.

2. Laboratory wear testing

Wear resistance is a relevant issue in the material selection

for mould and dies, thus, consequently, laboratory wear tests

were developed aimed at measuring wear resistance under

controlled conditions similar to working situations. Through

testing, wear resistance and mechanisms can be investigated

and to classify the materials for these applications.The correlation among the laboratory simulation tests and

its application in the design of moulds, dies and mechani-

cal components is of great importance for practical tribology.

However, the diversityof variables that influences wear makes

this correlation sometimes rather difficult. Wear resistance

and friction coefficient are not characteristic material proper-

ties, but depend on both the material properties and surface

geometric features as well as on the wear process parameters

as load, temperature, sliding velocity and environment.

The experimental results of wear carried out in laboratory

are commonly analyzed by the Archads (Hutchings, 1995) or

Rabinowiczs equation (Rabinowicz, 1965) that assess thewear

rate and the wear coefficient, relating the cumulative lost vol-


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ume per sliding unit with the wear resistance through the

linear equation (Hutchings, 1995):

Q (mm3/m) =V

S= K

FN

H(1)

where Q is the parameter that measures the wear ratio or

wear rate (cumulative lost volume Vor lost mass per sliding

unit S), FN is the applied normal load, H is the softer material

hardness and K is the wear coefficient: is non-dimensional

and less than 1. In general, the wear resistance is defined as

1/K. Therefore, the wear coefficient is given by

K =QH

FN= KSH (2)

where KS is the specific wear coefficient (KS = Q/FN) which unit

is mm3/m N. Notice that both coefficients refer to the softer

material. In the present wear testing of pin-on-disc the softer

material is the pin. The cumulative lost volume is obtained by

V= m

(m = mass; = density) (3)

The wear coefficient K is of fundamental importance and

provides a valuable parameter of comparison for the severity

of the wear process in various tribologic systems. Thus, the

Archad wear equation provides parameters that describes the

severity of wear through the coefficient K, but its value cannot

be used to confirmthe existenceor not of a determined mech-

anism of material removal. It is necessary to use the optical

microscope or the scanning electron microscope to identify

the main acting wear mechanisms.

3. Experimental procedure and materials

The experimental wear resistance results for the 17-4 PH steel

were obtained by carrying out the wear testing in the pin-on-

disc equipment for a selected constant total sliding distance,

constant normal load on the pin and a sliding velocity also

constant (Bressan and Hesse, 2001; Williams, 1997). Table 1

shows the used parameters during the testing operation. For

each pin hardnesslevel, three tests were performed, totalizing

ninepins of 17-4 PH steel at three different hardness levels.

3.1. Preparation of specimens

Pins: in thefabrication of pins,roundbarsof 17-4 PHsteel(V630Villares Trademark) was utilized. The pins were machined

by the conventional methods, i.e., turning and grinding to

obtain the desired pin shape with a rounded tip with radius

approximately 10 mm as seen in Fig. 2. After the solution heat

Table 1 Parameters utilized for performing the weartests

Sliding velocity (m/s) 0.6

Load 30 N (kgf) 2.953

Total sliding distance (m) 2400

Track radius (mm) 14.3

Fig. 2 Disc or counterface and pin of 17-4 PH steel utilized

in the pin-on-disc testing.

Table 2 Experimental tensile mechanical properties ofthe 17-4 PH steel pins

Tensile properties Set 1 Set 2 Set 3

0.2 % yield strength (MPa) 1237 1096 921

Rupture strength (MPa) 1332 1140 1017

Elongation (%) 14.2 15.0 18.0

Hardness (HRC) 43 37 33

treatment, the pins were machined and submitted to the pre-

cipitation hardening treatment, according to the utilization

goal as chains parts, to increase its hardness and strength.

Table 2 shows the mechanical properties, for each pin type,

obtained experimentally after the correspondent heat treat-

ment. Table 3 presents the heat treatment conditions of thepins and their respective hardness. The toughness, evalu-

ated by the energy of Charpy V impact testing specimens of

pins material heat treated to the different hardness levels,

are shown in Fig. 3 as a function of hardness. From Table 2

and Fig. 3, it is demonstrated an inverse relationship between

toughness andhardness in therange of the investigated hard-

ness which were obtained by varying the aging temperature

and time.

Discs: the counter face or disc, Fig. 2, was obtained by cut-

ting a slice from a 17-4 PH steel bar in the solution heat

treated condition (Table 4). All discs were machined to 50 mm

Table 3 Heat treatment conditions for the pins and theobtained hardness

Heat Treatment Pins 1A,1B, 1C

Pins 2A,2B, 2C

Pins 3A,3B, 3C

Quenching

Heating (1 h) 1040 C 1040 C 1040 C

Cooling in water 25 C 25 C 25 C

Aging

Heating 480 C, 1 h 550 C, 4 h 600 C, 4 h

Cooling in air 25 C 25 C 25 C

Hardness HRC 43 37 33


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Fig. 3 Evolution of the 17-4 PH toughness vs. hardness at

room temperature (25 C) evaluated by the Charpy-V impact

testing specimens after precipitation hardening at different

aging temperatures.

Table 4 Heat treatment conditions for the discs and theobtained hardness

Heat treatment Discs

Quenching

Solution (1 h) 1040 C

Cooling in water 25 C

Precipitation

Heating 480 C

Cooling in air 25 C

Hardness HRC 43

in diameterand 3 mm thickness. Following, thehardening pre-

cipitation heat treatment was performed and afterwards, the

discs were grinded and polished. The mean final hardness of

all discs was 43 HRC, see Table 4.

3.2. Microstructure of 17-4 PH steel

In Fig. 4, the microstructure of the serie 2 pins in the

transversal sections can be observed. The microstructure is

constituted of aged martensite. The chemical attack used was

Vilella reagent by immersion. The chemical composition of

pins and discs are shown in Table 5.

3.3. Procedure for pin-on-disc testing

The specimens were submitted to a rigorous preparation pro-

cedure to eliminate any trace of dust, dirt or oxidation. Next,

Fig. 4 Typical microstructure of the 17-4 PH steel pins, set

2, after aging at hardness of 37 HRC. Transversal section

after etching with Vilella.

the pin and the disc were weighed in an analytical balance

with resolution 0.1 mg to determine its initial mass before

testing.

Following, the sliding track radius, the rotation velocity of

disc and the revolutions counter were set to the operation

conditions. The revolution counter was programmed to stop

at each 200m of sliding distance for the total of 2400m, in

orderto allow intermediate measurements of pinand disc lost

mass. These measurements were always preceded by a com-

plete cleaning of specimens by rubbing a dry cloth and, next,

using a fluxof compressed air. Before weighing, the specimens

were dried out in a furnace at 80 C for 10min toavoid any sol-

vent or humidity in the specimen so to evaluate the real masslost from the pin and disc. The pin and disc were fixed in the

same position and orientation by an initial sign. The pin-on-

disc apparatus was equipped with a large glass campanula

thatcovered the specimens. Temperature and humidityinside

the campanula were kept at approximately 25 C and 5560%

of relative humidity. One value of normal load on pin was

selected for each test: 30 N. The17-4 PH steel discs were tested

in both faces, using three pins per each hardness level.

4. Results and discussions

In Fig. 5, the experimental results for the discs in the pin-on-

disc tests are presented. Although all the discs have the same

hardness value of 43 HRC, the disc wear rate varied substan-

tially due to the pin different hardness.

The discs from set 1, 1A-1, 1A-2 and 1B-1, were tested

against pins of hardness 43 HRC, the discs from set 2, 2A-1,

Table 5 Chemical composition of the 17-4 PH steel pins and discs and the range specified in the standard ASTM (% inmass)

C Si Mn Cr Ni Cu Nb P S Mo

ASTM A564 Max. 0.07 Max. 1.0 Max. 1.0 15.017.0 3.05.0 3.05.0 0.150.45 Max. 0.040 Max.0.030

Sample analysis 0.035 0.42 0.65 15.2 4.32 3.37 0.23 0.025 0.002 0.21


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Fig. 5 Pin-on-disc experimental results. Evolution of the

discs cumulative lost volume versus sliding distance. Discs

hardened to 43 HRC. Normal load of 30 N.

Fig. 6 Evolution of pin cumulative lost volume versus

sliding distance for the pin-on-disc tests. Pin hardness is

indicated. Discs hardness are 43 HRC. Normal load of 30 N.

Fig. 7 Evolution of pin cumulative lost volume versus

sliding distance for the pin-on-disc tests. Pin hardness is

indicated. Discs hardness are 43 HRC. Normal load of 30 N.Table6Averagewearparametersof

the17-4PHsteelpins

Pinsetand

number

AveragewearrateQ=V

/S

(mm

3/m)(10

3)

MeanvaluesQ=V/S

(mm

3/m)(103)

Wearcoefficient

(K)(10

4)

Meanvalues(K)

(104)

Wearresistance

(1/K)

Mean

values(1/K)

Hardness

Rockwell

HRC

Vickers

HV

1A

3.64

3.64

5

.15

5.1

1941

.7

1941.7

43

425

1B

3.64

5

.15

1941

.7

43

425

1C

3.64

5

.15

1941

.7

43

425

2A

3.75

4.86

4

.56

5.94

2193

.0

1736.5

37

365

2B

5.40

6

.63

1508

.3

37

365

2C

5.45

6

.63

1508

.3

37

365

3A

5.91

5.75

6

.50

6.32

1538

.4

1581.1

33

330

3B

5.45

6

.00

1666

.7

33

330

3C

5.91

6

.50

1538

.4

33

330


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2A-2 and 2B-1, were tested against pins of hardness 37 HRC

and the discs from set 3, 3A-1, 3A-2 and 3B-1, were tested

against pins of hardness 33 HRC. In general, the disc wear rate

Q(=V/S) is constant andlinear, butincreased with thedecrease

in the pin hardness, i.e., the wear was more severe as the dif-

ference in hardness between pin and disc increased. The disc

maximum average wear rate was 4.54 103 mm3/m and the

minimum was 2.95103 mm3/m which yields the wear coef-

Fig. 8 SEM micrographs of the worn surface morphology at the pin tip before and after sliding 50, 100 and 2400 m.

Magnifications 50 and 500.

ficients K =0.643 103 and 0.418103, respectively, using

Eq. (1). Therefore, in the case of the harder material, the

disc, the hardness H in the wear Eq. (1) should be possi-

bly substituted by an equivalent hardness He defined as:

1/He = 1/Hdisc + 1/Hpin. Certainly, the adhesive mechanism in

the pin and the micro-delamination mechanisms in the disc

were more stressed for pin and disc from the same material

and pin with lower hardness as will be observed latter.


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Onthe other hand, in Fig. 6, the pinwear ratescan be inves-

tigated. The figure shows, the higher the hardness the lower

the wear rate, i.e., the curve of lost volume versus sliding dis-

tance is situatedmore lower, in accordance withthe prediction

of Eq. (1). The range of variations of pins wear rates is higher

than for the discs.

In Table 6, the summary of pins wear parameters under

load of 30N, such as the average wear rate Q, the wear coef-ficient K and the wear resistance are presented. The average

wear rate of the pins with the lowest hardness of 33 HRC was

5.75 103 mm3/m and for the highest hardness of 43 HRC

was 3.64 103 mm3/m. In Fig. 7, the relationship between

the wear rate among the pins with hardness 43, 37 and 33

HRC is shown. It is clear that the precipitation hardening

heat treatment that yielded the pin hardness of 43 HRC is

the most wear resistant steel, attaining the wear resistance

value of 1941, instead of the pin material with the minimum

hardness of 33 HRC which has only a wear resistance value

of 1581.

In Fig. 8, the photographs obtained by SEM from the worn

area of the pin tip, set 3, are presented. The photographswere taken before the wear test and after 50, 100 and 2400 m,

in order to identify the acting wear mechanisms. It is noted

the mechanisms of micro-grooving, adhesion and micro-

delamination (Zum Gahr, 1998). In the micro-delamination

mechanism, small flakes of material are pulled out from the

surface during the pin sliding on the disc.

5. Conclusions

From the pin-on-disc experimental results shown in the plots

of cumulative lost volume versus sliding distance of 17-

4 PH steel discs and pins and from the scanning electronmicroscope observations of the worn surface, the following

conclusions can be drawn:

In general, the trend of the wear rate curve for discs ver-

sus the sliding distance is constant and linear after the initial

stage. That is, the instantaneous wear ratio (tangent to the

curve) is approximately constant. The discs plotted curves

shows two distinctstages or regimes:initialstage1 upto 200m

or initial run in phase with accelerated wear and the second

stage of constant wear rate up to the test end.

However, the disc wear rate increased with the decrease

of the pin hardness. In this case, for the harder material, the

disc, the Archad Eq. (1) for wear rate has to be reformulated,

possibly substituting the hardness H by an equivalent hard-ness He (1/He = 1/Hdisc + 1/Hpin), i.e., Q= KFN/He, the disc wear

rate increases with the increase in the hardness difference

between pin and disc.

The trend of the pin wear rate curves with the sliding dis-

tance is approximately constant and linear. However, in the

final stage, some pins presented the tendency to decrease the

wear rate. This is due the decrease in the real contact pres-

sure with the increase of the pin contact area and/or increase

in the hardness of the disc track.The observed wear mechanisms in the SEM are micro-

grooving or micro-cutting, adhesion and micro-delamination

or micro-flaking.

The average wear rate of pins under load of 30N and

hardness of 33 HRC was 5.75 103 mm3/m, the pins with

hardness 37 HRC was 4.86 103 mm3/m and for hardness of

43 HRC was 3.64 103 mm3/m. This yields a wear coefficient

K =0.632103, 0.594 103 and 0.515103, respectively.

The correspondingwear resistance is: 1581, 1736 and 1941.

Thus, for the investigated range of heat treatment, the 17-4

PH steel pin with hardness of 43 HRC has presented the best

wear resistance of 1941 and the pin with 33 HRC the worst

wear resistance of 1581.

Acknowledgements

The authors would like to gratefully acknowledge the financial

support received from The Brazilian Research Council-CNPq

as a research and scientific initiation scholarships, as well

as the University of Santa Catarina State-UDESC and Villares

Metals for supplying the material of the discs and pins.

r e f e r e n c e s

ASTM, 1995. Designation: G99-95; Standard Test Method for WearTesting with a Pin-on-Disk Apparatus, pp. 336390.

Bressan, J.D., Hesse, R., 2001. Construction and validation tests ofa pin-on-disc equipment. In: XVI Congresso Brasileiro deEngenharia Mecanica, ABCM (Ed.), COBEM, Uberlandia/MG,dezembro.

Hutchings, I.M., 1995. Tribology: Friction and Wear of EngineeringMaterials, Arnold.

Magee, J.H., 1992. Wear of Stainless steels, ASM Handbook, vol.18, pp. 710724.

Rabinowicz, E., 1965. Friction and Wear of Materials. Wiley, NewYork.

Williams, J.A., 1997. The laboratory simulation of abrasive wear.Tribotest J. 3, 267306.

Zum Gahr, K.H., 1998. Wear by hard particles. Tribol. Int. 31 (10),587596.

17-4ph stainless steels

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