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Wear 263 (2007) 674–678

The formation of martensite during wear ofAISI 304 stainless steel

Morteza Zandrahimi, M. Reza bateni ∗, A. Poladi, Jerzy A. SzpunarShahid Bahonar University of Kerman, Material Science and Engineering Group,

Jomhourieslami boulevard, Kerman, Iran

Received 13 September 2006; received in revised form 22 January 2007; accepted 22 January 2007Available online 23 May 2007

bstract

Austenitic stainless steels are alloys with high corrosion resistance combined with high mechanical properties. However, the tribological propertyf the material is not sufficient and it suffers from wear and friction. In this paper, attempts have been made to evaluate the wear behavior of austenitictainless steel, during sliding contacts. A pin-on-disk tribometer was employed to perform wear tests and in addition to wear, structural changesf AISI 304 stainless steel were investigated under wear condition. Scanning electron microscope (SEM) and X-ray diffraction analysis were

mployed to study the structural changes during wear process. Study of worn surfaces indicated that depending on wear condition and appliedoad, different features of wear were involved, and during wear austenite transformed to martensite. The intensity of martensite peaks in X-rayattern depends on the magnitude of the applied load.

2007 Published by Elsevier B.V.

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eywords: Austenitic stainless steel; Wear; Martensite; Phase transformation

. Introduction

Wear of materials used in mining, metals and materials pro-essing, directly or indirectly, impact the nation financially inerms of material loss and associated equipment downtime forepair and replacement of worn components [1,2,3]. The inter-ction among abrasion, rubbing, and impact could significantlyncrease total material losses and the reduction of wear signifi-antly reduces the total material loss [4].

Austenitic stainless steels are widely used materials becausef their excellent corrosion resistance in various aggressive envi-onments. However, they exhibit a relatively low hardness andoor tribological properties. Among austenitic stainless steels,ISI 304 stainless steels have shown the lowest wear resistanceoth in dry sliding and under lubricated conditions and severedhesive and abrasive wear have been observed, associated with

ignificant mass losses [5]. The inherent poor tribolgical behav-or of austenitic stainless steels has been a barrier to their widerpplication under wear conditions. Therefore, researchers have

∗ Corresponding author. Tel.: +98 341 2114053; fax: +98 341 2111856.E-mail address: reza bateni@hotmail.com (M.R. bateni).

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043-1648/$ – see front matter © 2007 Published by Elsevier B.V.oi:10.1016/j.wear.2007.01.107

ong dreamed of developing new technologies to enhance theear resistance of stainless steels without losing their attractive

stainless” characteristics [6].The austenitic stainless steels have an austenitic structure in

nnealed condition, but partially transform to martensite dur-ng deformation. The low stacking fault energy, in AISI 304ustenitic stainless steel, makes it amenable to these transforma-ion mechanisms by giving rise to planar faults and dislocationile-ups [7]. The martensite is stronger and harder than theustenitic structure, causing a composite strengthening and thushigh strain hardening effect. The strain hardening effect causesigher strengths after cold working, which contributes to the highuctility in annealed condition [8].

In this work, attempts have been made to investigate the effectf wear on the microstructural changes of AISI 304 stainlessteel. In addition the wear mechanisms will be discussed.

. Materials and experimental techniques

.1. Materials

AISI 304 stainless steel samples were used as the substrate.he chemical composition is shown in Table 1. Stainless steel

M. Zandrahimi et al. / Wear 263 (2007) 674–678 675

Table 1Chemical compositions of samples used in wear tests

Grade C (wt.%) Mn (wt.%) Si (wt.%) P (wt.%) S (wt.%) Cr (wt.%) Ni (wt.%) Fe (wt.%)

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less steel before wear test, and after wear test at 200 and 300 Nloads, respectively. The presence of austenite peaks observedin the X-ray diffraction pattern of as-received sample (Fig. 4).After wear test, martensite observed on the worn area (Fig. 5).

Fig. 1. The worn area and the presence of martensite and austenite (200×).

304 0.08 2.0 1.0 0.032100 1.05 0.4 0.25 0.02

amples were annealed at 850–900 ◦C for an hour before wearest, in order to relieve internal stresses. Optical microscopyvaluations did not show the formation of carbide phase aftertress relieving step.

.2. Wear testing

A pin-on-disk wear-testing machine was employed to evalu-te wear resistance of austenitic stainless steel samples. Wearests were conducted at room temperature, a humidity of5–35%, and a velocity of 0.01 m/s. AISI 52100 steel pins60HRC hardness) were employed as the counterface. AISI 304tainless steel discs were 50 mm in diameter and 5 mm in thick-ess and the pins were 5 mm in diameter and 50 mm in length.ear tests were carried out under different loads of 100, 200,

nd 300 N. For this purpose, a new sample was examined at eachoad. After each 100 m, the sample were taken out of the wear

achine and weight change was measured. After the test, theounterface and the worn sample were carefully weighed.

.3. Evaluation techniques

X-ray diffraction (XRD), optical microscopy, microhard-ess, and scanning electro microscope (SEM) were used forhase identification of the deformed layers. XRD patternsere recorded using Cu K� radiation at a step scan mode of.1◦ min−1. The metallographic sections of the samples weretudied by optical microscope, and scanning electron micro-cope (SEM). In order to distinguish martensite from austenite,he worn samples were etched. The etching solution was com-osed of 15 ml HCl and 5 ml HNO3 and the polished samplesere immersed into the etchant solution for 1 min. A Ziessicrohardness tester was employed for determination of hard-

ess profile using a load of 50 g. The profiles were obtained onetallographic sections from the worn area towards unworn sur-

ace. At each depth three readings were obtained and the averagealue reported as the Vickers microhardness.

. Results and discussion

Fig. 1 shows the microstructure of worn region after wear testt 200 N load and after 1000 m. The presence of martensite andustenite were observed in the wear track (Fig. 1). An averagerain size of about 20 microns was observed at this area. Twiningffect was also obvious in the microstructure. The presence ofartensite was investigated under higher magnifications through

EM. Fig. 2 shows the existence of martensite lathe in the wornrea, which is surrounded by un transformed austenite grains.ig. 3 shows the variation of weight loss versus sliding dis-

ance under different loads. The weight loss values versus sliding F

0.04 19 9 Remainder0.025 1.45 Nil Remainder

istances show linear behavior at different load. By increasinghe applied load from 100 to 300 N, the weight loss increasedpproximately in the order of 2.

Figs. 4–6 show X-ray diffraction patterns of AISI 304 stain-

ig. 2. SEM micrograph of the worn area and the presence of martensite lathe.

676 M. Zandrahimi et al. / Wear 263 (2007) 674–678

Fig. 3. Variation of weight loss vs. sliding distance under different loads.

Fig. 4. X-ray pattern of AISI 304 stainless steel before wear test.

Fig. 5. X-ray pattern of AISI 304 stainless steel after wear test at 200 N load.

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Fig. 6. prime: X-ray pattern of AISI 304 stain

ig. 7. The variation of microhardness vs. distance away from worn surface.

RD patterns of the worn surfaces under different loads showedhat by increasing the applied load the intensity of martensiten the worn surface increased (Figs. 5 and 6). The higher thentensity of XRD peaks for martensite, the higher the amount of

artensite in the microstructure.Fig. 7 shows the variation of microhardness versus distance

way from the worn surface. The worn area revealed higherardness than unworn area. The higher hardness is due to thelastic deformation, which took place during the wear test. Dur-ng plastic deformation, austenite could transform to martensitehase at lower temperatures. By increasing the applied loadrom 100 to 300 N the hardness of deformed area increased.he increase in hardness could be due to the higher amount ofartensite at higher loads and higher plastic deformation. The

ariation of microhardness versus distance away from worn sur-ace showed that the thickness of plastically deformed area didot relate to the amount of applied load. However, by increasinghe applied load from 100 to 300 N, the thickness of the deformedayer should have increased. The variation of weight loss versuspplied load (Fig. 3) showed that the amount of weight loss at00 N was almost twice of that at 100 N load. The higher the

eight loss, the higher the possibility of detaching deformed

ayer during wear test. The microhardness value for marten-ite and austenite are 572 and 220 HV, respectively [9,10]. The

less steel after wear test at 300 N load.

M. Zandrahimi et al. / Wear

Fig. 8. SEM micrograph of worn surface of AISI 304 stainless steel, after weartest at 300 N load and after 1000 m. (a) The presence of ploughing on the wornsurface. (b) SEM micrograph of an isolated wear particle. (c) The presence ofdelamination on the worn surface.

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263 (2007) 674–678 677

ower microhardness value could be due to heat generation andccumulation during wear test. High temperature values coulde obtained at the asperity spot-to-spot contacts that are mainlyesponsible for the tribochemical reactions and various phaseransformations [11]. Austenitic stainless steels have shown theowest thermal conductivity among carbon steels and other stain-ess steels. Therefore, by increasing the applied load, more heatas generated at contact areas. Increasing the temperature at the

ontact area and low thermal conductivity of austenitic stainlessteels, caused heat accumulation at the contact area. The accu-ulation of heat and subsequent stress relief process decreased

he microhardness of austenite and martensite phases.Fig. 8a shows the SEM micrograph of AISI 304 stainless

teel at 300 N load and after 1000 m. Abrasive ploughing effectsbserved on the worn surface, which could cause by hard abrad-ng particles or the higher hardness of counterface than theubstrate. The presence of hard abrading particles is due to

ig. 9. SEM micrograph from the cross-section of worn sample (a) The presencef crack under the worn surface. (b) The presence of voids under the worn surface.

678 M. Zandrahimi et al. / Wear

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ig. 10. SEM micrograph of pin surface after wear test at 200 N load and after000 m.

he transformation of austenite and the formation of martensiteebris during wear test. Fig. 8b shows an isolated wear parti-le, which indicated the existence of abrasive wear. On the otherand, worn surface of sample also indicated plate-like debrishat pulled out from the surface (Fig. 8c). The observation oflate-like debris indicates that delamination happened duringear process. SEM micrograph from the cross-section of worn

ample, showed the presence of voids and crack under the wornurface, which under repeated load would delaminate and pullut from the surface (Fig. 9a and b). The formation of cracknd voids could be due to plastic deformation processes, suchs fatigue. The cross-section of the worn surface showed thatnder 100 N load and after 1000 m, the thickness of deformedayer reached to 40–50 �m.

Fig. 10 shows SEM micrograph of pin surface after wear testt 200 N load and after 1000 m. The worn surface of pin indicatedlate-like debris that was pulled out from the surface, as a resultf delamination. The presence of deformation and microscopicoids are obvious on the pin surface. As the wear test continued,icron-size voids joined together to form plate-like debris. The

resence of such voids and delaminated debris on the pin surfacemphasized that delamination is the dominant wear mechanismn pin samples.

. Conclusions

. During wear test of AISI 304 stainless steel, due to colddeformation, austenite phase partially transformed to marten-

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site. The intensity of martensite and austenite peaks in XRDpattern after wear test depends on the amount of appliedload. The higher the applied load, the higher the intensityof martensite peaks.

. In AISI 304 stainless steel samples, abrasive and delami-nation wear were predominant wear mechanism, where theabrasion wear could be due to the higher hardness of coun-terface surface than the substrate.

. In AISI 52100 pins delamination is the predominant wearmechanism. The formation and connection of voids, underrepeated plastic deformation, could cause pulling out anddelamination of detached layers.

. Increasing of temperature at the contact area and low thermalconductivity of 304 stainless steels are responsible for heataccumulation and consequently stress relief, which couldlower the microhardness values.

cknowledgements

The authors gratefully acknowledge the contribution of Met-llurgical Group, at Shahidbahonar University of Kerman, andhe Mining & Metallurgical Department of McGill University.

eferences

[1] M. Reza Bateni, J.A. Szpunar, X. Wang, D.Y. Li, Wear and corrosion wearof medium carbon steel and 304 stainless steel, Wear 260 (1–2) (2006)116–122.

[2] W.J. Schumacher, Corrosive wear principles, Mater. Performance 23 (7)(1993) 50–150.

[3] W.J. Schumacher, Corrosive wear synergy of alloy and stainless steel,wear of materials, Vancouver, 1985, ASME, New York, 1985, pp. 558–566.

[4] S.W. Watson, F.J. Friedersdorf, B.W. Madsen, S.D. Cramer, Methodsof measuring wear-corrosion synergism, Wear 181–183 (1995) 476–484.

[5] C. Brin, J.-P. Riviere, J.-P. Eymery, J.-P. Villain, Structural characterizationof wear debris produced during friction between two austenitic stainlesssteel antagonists, Tribol. Lett. 11 (2) (2001) 127–132.

[6] T. Bell, Surface engineering of austenitic stainless steel, Surf. Eng. 18 (6)(2002) 415–422.

[7] Amar K. De, David C. Murdock, Martin C. Mataya, John G. Speer, DavidK. Matlock, Quantitative measurement of deformation-induced martensitein 304 stainless steel by X-ray diffraction, Scripta Materialia 50 (12) (2004)1445–1449.

[8] V.F. Zackay, E.R. Parker, D. Fahr, R.A. Busch, The enhancement ofductility in high-strength steels, ASM Trans. Quart. 60 (2) (1967) 252–259.

[9] X. Zhao, T.F. Jing, Y.W. Gao, G.Y. Qiao, J.F. Zhou, W. Wang, Anneal-ing behavior of nano-layered steel produced by heavy cold-rolling of lathmartensite, Mater. Sci. Eng. A 397 (1–2) (2005) 117–121.

10] F.M. El-Hossarya, N.Z. Negma, S.M. Khalila, A.M. Abed Elrahmana, D.N.McIlroy, RF plasma carbonitriding of AISI 304 austenitic stainless steel,

Surf. Coat. Technol. 141 (2–3) (2001) 194–201.

11] M. Kalin, Influence of flash temperatures on the tribological behavior inlow-speed sliding: a review, Materials Science & Engineering, A: StructuralMaterials: Properties, Microstructure and Processing A374 (1–2) (2004)390–397.