Content uploaded by Celso Antonio Barbosa
Author content
All content in this area was uploaded by Celso Antonio Barbosa on Apr 14, 2019
Content may be subject to copyright.
journal of materials processing technology 20 5 (2008) 353–359
journal homepage: www.elsevier.com/locate/jmatprotec
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. Darosa, A. Sokolowskib, R.A. Mesquitac, C.A. Barbosa d
aDepartamento de Engenharia Mec ˆ
anica, CCT, UDESC Joinville, Campus Universit´
ario, 89223-100 UDESC Joinville, SC, Brazil
bEngenheiro Qu´
ımico, Pesquisador Senior da Villares Metals S.A., Sumar´
e, SP, Brazil
cEngenheiro de Materiais, Pesquisador Senior da Villares Metals S.A., Sumar´
e, SP, Brazil
dEngenheiro Metalurgista, Gerente de Tecnologia da Villares Metals S.A., Sumar´
e, SP, Brazil
article info
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
abstract
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 2400 m 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: dem2jdb@joinville.udesc.br (J.D. Bressan), deividdaros@yahoo.com.br (D.P. Daros),
alexandre.sokolowski@villaresmetals.com.br (A. Sokolowski), rafael.mesquita@villaresmetals.com.br (R.A. Mesquita),
celso.barbosa@villaresmetals.com.br (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 metal–metal 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
354 journal of materials processing technology 20 5 (2008) 353–359
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 relative
high hardness up to 49 HRC. These steels are classified in
function of the chemical composition and the different phases
present in the microstructure. The 17-4 PH steel (AISI Type 630
or UNS S17400) 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
and powder injection molding products. In steel plants, its pro-
duction starts generally by melting in an electric arc furnaces
or open air induction furnaces or even vacuum induction fur-
naces. In addition, for critical applications, as in the aerospace
industry, it is commonly submitted to refining by vacuum
arc remelting process, VAR or electroslag remelting, ESR. The
17-4 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 heat treatment 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 34–45 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 includes
structural 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
solid in relative motion, 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, using
the 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 diversity of 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 Archad’s (Hutchings, 1995)or
Rabinowicz’s equation (Rabinowicz, 1965) that assess the wear
rate and the wear coefficient, relating the cumulative lost vol-
journal of materials processing technology 20 5 (2008) 353–359 355
ume per sliding unit with the wear resistance through the
linear equation (Hutchings, 1995):
Q(mm3/m) =
V
S
=KFN
H(1)
where Qis the parameter that measures the wear ratio or
“wear rate” (cumulative lost volume Vor lost mass per sliding
unit S), FNis the applied normal load, His the softer material
hardness and Kis 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 KSis 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 Kis 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 confirm the existence or 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 hardness level, three tests were performed, totalizing
ninepins of 17-4 PH steel at three different hardness levels.
3.1. Preparation of specimens
Pins: in the fabrication of pins, round bars of 17-4 PH steel (V630
Villares 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 10mm as seen in Fig. 2. After the solution heat
Table1–Parameters utilized for performing the wear
tests
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 of
the 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 the
pins 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 and hardness in the range 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 the
obtained 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 ◦C25
◦C25
◦C
Aging
Heating 480 ◦C, 1 h 550 ◦C, 4 h 600 ◦C, 4 h
Cooling in air 25 ◦C25
◦C25
◦C
Hardness HRC 43 37 33
356 journal of materials processing technology 20 5 (2008) 353–359
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 the
obtained 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 diameter and 3 mm thickness. Following, the hardening 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 200 m of sliding distance for the total of 2400 m, in
order to allow intermediate measurements of pin and disc lost
mass. These measurements were always preceded by a com-
plete cleaning of specimens by rubbing a dry cloth and, next,
using a flux of compressed air. Before weighing, the specimens
were dried out in a furnace at 80 ◦C for 10min to avoid any sol-
vent or humidity in the specimen so to evaluate the real mass
lost 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
that covered the specimens. Temperature and humidity inside
the campanula were kept at approximately 25◦C and 55–60%
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 (% in
mass)
CSiMnCrNiCuNb P SMo
ASTM A564 Max. 0.07 Max. 1.0 Max. 1.0 15.0–17.0 3.0–5.0 3.0–5.0 0.15–0.45 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
journal of materials processing technology 20 5 (2008) 353–359 357
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 30N.
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 30N.
Table6–Averagewearparameters of the 17-4 PH steel pins
Pin set and
number
Average wear rate Q=V/S
(mm3/m) (×10−3)
Mean values Q=V/S
(mm3/m) (×10−3)
Wear coefficient
(K)(×10−4)
Mean values (K)
(×10−4)
Wear resistance
(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
358 journal of materials processing technology 20 5 (2008) 353–359
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 and linear, but increased with the decrease
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 ×10−3mm3/m and the
minimum was 2.95 ×10−3mm3/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 ×10−3and 0.418 ×10−3, respectively, using
Eq. (1). Therefore, in the case of the harder material, the
disc, the hardness Hin the wear Eq. (1) should be possi-
bly substituted by an equivalent hardness Hedefined 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.
journal of materials processing technology 20 5 (2008) 353–359 359
On the other hand, in Fig. 6, the pin wear rates can 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 situated more lower, in accordance with the 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 30 N, such as the average wear rate Q, the wear coef-
ficient Kand the wear resistance are presented. The average
wear rate of the pins with the lowest hardness of 33 HRC was
5.75 ×10−3mm3/m and for the highest hardness of 43 HRC
was 3.64 ×10−3mm3/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 photographs
were taken before the wear test and after 50, 100 and 2400m,
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 electron
microscope 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 distinct stages or regimes: initial stage 1 up to 200 m
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 Hby 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 30 N and
hardness of 33 HRC was 5.75×10−3mm3/m, the pins with
hardness 37 HRC was 4.86×10−3mm3/m and for hardness of
43 HRC was 3.64 ×10−3mm3/m. This yields a wear coefficient
K= 0.632 ×10−3, 0.594 ×10−3and 0.515 ×10−3, respectively.
The corresponding wear 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.
references
ASTM, 1995. Designation: G99-95; Standard Test Method for Wear
Testing with a Pin-on-Disk Apparatus, pp. 336–390.
Bressan, J.D., Hesse, R., 2001. Construction and validation tests of
a pin-on-disc equipment. In: XVI Congresso Brasileiro de
Engenharia Mec ˆ
anica, ABCM (Ed.), COBEM, Uberlˆ
andia/MG,
dezembro.
Hutchings, I.M., 1995. Tribology: Friction and Wear of Engineering
Materials, Arnold.
Magee, J.H., 1992. Wear of Stainless steels, ASM Handbook, vol.
18, pp. 710–724.
Rabinowicz, E., 1965. Friction and Wear of Materials. Wiley, New
York.
Williams, J.A., 1997. The laboratory simulation of abrasive wear.
Tribotest J. 3, 267–306.
Zum Gahr, K.H., 1998. Wear by hard particles. Tribol. Int. 31 (10),
587–596.
