Dry sliding friction and wear behaviour of hardened AISI D2 tool steel with different hardness levels

Dry sliding friction and wear behaviour of hardened AISI D2 tool steel with different hardness levels

Tribology International 66 (2013) 165–173 Contents lists available at SciVerse ScienceDirect Tribology International journal homepage: www.elsevier...

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Tribology International 66 (2013) 165–173

Contents lists available at SciVerse ScienceDirect

Tribology International journal homepage: www.elsevier.com/locate/triboint

Dry sliding friction and wear behaviour of hardened AISI D2 tool steel with different hardness levels Linhu Tang a,n,1, Chengxiu Gao a, Jianlong Huang b, Hongyan Zhang a, Wenchun Chang a a b

Department of Mechanical Engineering, Lanzhou Institute of Technology, Lanzhou, PR China College of Mechano-Electronic, Lanzhou University of Technology, Lanzhou, PR China

art ic l e i nf o

a b s t r a c t

Article history: Received 6 January 2013 Received in revised form 6 April 2013 Accepted 7 May 2013 Available online 22 May 2013

The influence of the sliding speed and hardness on the friction and wear performance, and their related mechanisms of hardened tool steel AISI D2 with different hardness levels were investigated. Friction and wear tests of the estimated specimens with different hardness levels versus Si3N4 balls were carried out under dry sliding friction condition in ball-on-disc tester. The results showed that the influence of the hardness on the friction coefficient at the sliding speeds of 0.05 and 0.5 m/s is more prominent than that at 0.10 m/s, while the wear rate shows great sensitivity to the sliding speed and hardness. & 2013 Elsevier Ltd. All rights reserved.

Keywords: Sliding speed Hardness Friction coefficient Wear rate

1. Introduction In manufacturing of components, a large number of tool steels are applied in milling, drilling, sawing and the measuring tool as well as mold. In their work, they have to undergo great tension-compression stress and friction-wear, which exert great influence on their service life. Therefore, the properties of high hardness, strength and wear resistance are required for tool steel in the manufacturing industry. In recent years, a considerable number of papers about the wear performance of the tool steel AISI D2 have been investigated by many scholars. Bourithis et al. [1] have investigated the wear properties of two commercial tool steels (AISI D2 and O1) with the same hardness of 60 HRC by using pin-on-disk tester. They have obtained the results that the tool steel microstructures play the most important role in determining the wear properties. The sliding wear resistances of ZrN and (Zr, 12 wt%Hf) N coating deposited on a hardened tool steel AISI D2 were studied by Atar et al. [2]. After the tool steel AISI D2 were subjected to the different heat treatments, the relationship between the hardened-and-tempered condition of the tool steel and its abrasive wear resistance were tested and studied by Gorscak et al. [3]. Besides Omer and Muammer [4], who have studied and compared the wear performances of seven different, uncoated die materials (AISI D2, Vanadis 4, Vancron 40, K340 ISODUR, Caldie, Carmo, 0050A) by using a newly developed wear testing device, Sen et al. [5] have investigated the tribological

behavior of Alumina and AISI 52100 steel in a ball-on- disc tester. In these tests, the molybdenum boride coated tool steel AISI D2 was used as the mating sliding surface. The results showed that the friction coefficient decreases with the increase of sliding speed, while the wear rate drops. Some researchers [6–9] have also investigated the wear behavior and resistance of the tool steel AISI D2 by deep cryogenic and sub-zero treatment under the condition of different sliding speeds and normal loads. They considered that the wear behavior can be clearly correlated with the reduction in the retained austensite content and the increase in the amount of secondary carbide particles of the microstructure. Up to now, very few studies have only been reported on the influences of the hardness and sliding speed on the wear performance and mechanism of the hardened tool steel AISI D2. In this paper, the influences of different hardened levels (5171, 5571, 5871, 6271, and 6571 HRC) of the tool steel AISI D2 and sliding speeds (0.05, 0.10, and 0.50 m/s) at the normal load of 5 N on the friction coefficient, wear rate, and related mechanisms were investigated. Friction-wear tests were conducted on a ball-on-disc tester at room temperature under dry sliding friction condition.

2. Experimental procedures 2.1. Material

n

Corresponding author. Tel: +86 18919080745. E-mail addresses: [email protected], [email protected] (L. Tang). 1 Present address: 1 Gongjiaping East Road, Lanzhou, Gansu Province 730050, PR China. 0301-679X/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.triboint.2013.05.006

The material chosen in this investigation was a commercial tool steel AISI D2 (Cr12MoV, China) bar. Its chemical composition is presented in Table 1.

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Table 1 Chemical composition of the tool steel AISI D2 (wt%). C

Cr

Mo

Mn

Si

P

S

V

1.55

11.25

0.45

0. 35

0.35

0.025

0.025

0.20

2.2. Heat treatment Earlier results showed that the tool steel AISI D2 could get fineneedle martensite, high-diffusion, and uniform distribution finegrain carbide by using the quenching temperatures of 1000– 1040 1C[10]. According to the methods of heat treatment in the literature [11], the specimens were inserted into an electrical resistance furnace at 1000–1040 1C, then quenched in oil, and finally tempered at various low temperatures. 2.3. Hardness measurement Fig. 1. Finished specimens.

The hardness values of the differently treated specimens were estimated by Rockwell hardness tester. At least three readings have been taken to estimate the average hardness value of hardness of every specimen. The obtained hardened specimens were in different hardness levels of 5171, 5571, 5871, 6271, and 6571 HRC. 2.4. Microstructure of the hardened tool steel AISI D2 with different hardness levels After mounting, grinding, polishing, and etching (etchant used: 4% Nitric acid alcohol solution for 40 s), microstructure examination of the hardened specimens were carried out utilizing a scanning electron microscope (SEM). The polishing has been carried using a semi-automatic grinding and polishing machine from Buehler. The processes are as follows: Fig. 2. THT friction-wear testing machine.

1. Grinding: using Ultra prep (9 μm) Metal-bonded disc at a normal load of 20 N and rotate speed of 120 rev/min (Rotating direction is the same.) for 5 min. 2. Polishing: using surface of preparation with the TriDent polishing cloth (3 μm) and MetaDi polishing liquid at a normal load of 25 N and rotate speed of 120 rev/min (Rotating direction is the same.) for 10 min. Fig. 1 is the finished specimens.

2.5. Dry sliding wear tests 2.5.1. Testing systems Dry sliding wear testing systems are made up of THT frictionwear tester and 2206 surface roughometer. THT friction-wear tester made in CSM in Switzerland shown in Fig. 2 was utilized to measure the friction coefficient and wear rate of the hardened specimens and a 2206 surface roughometer was utilized to measure the cross-section profile of the worn surface. 2.5.2. Experimental details The experimental details are described in Table 2. Schematic diagram of the ball-on-disc wear test rig is shown in Fig. 3. Dry sliding friction and wear tests were conducted on a ball-on-disc tester at a room temperature of about 22 1C, and relative humidity of about 40%. The hardened tool steel AISI D2 (5171, 5571, 5871, 6271, and 6571 HRC) discs of 28 mm diameter, 8 mm length, and a surface roughness of 0.336 μm Ra were tested against the N3Si4 balls with a diameter of 3.0 mm. The friction and wear tests were carried out at a normal load of 5 N and different sliding speeds of 0.05, 0.1, and 0.5 m/s. The wear volumes were obtained from track cross-section

Table 2 Experimental details. Condition Method of of experiment contact Ball-ondisc Mating material

Scheme of Si3N4 the wear ball test

Temperature

Sliding Relative Normal distance humidity load (N) (m)

Room temperature 40% 5 100 (22 1C) Hardness of estimated Sliding speeds (m/s) specimens ( 7 1 HRC) 51 55 58 62 65

0.05 0.05 0.05 0.05 0.05

0.10 0.10 0.10 0.10 0.10

Fig. 3. Schematic diagram of the wear test rig.

0.50 0.50 0.50 0.50 0.50

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measurements after running a sliding distance of 100 m. Furthermore, the wear rates were calculated from Eqs. (1) and (2). The averaged values of the friction coefficient within steady-state were given.

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track cross-section in mm2 determined by its profile and G is perimeter of the wear track in mm (in cases of 0.05, 0.10, and 0.50 m/s, the perimeters of the worn surfaces are 12.56, 25.12, and 37.68 mm, respectively).

2.6. Dealing with the results 2.7. Analysis of wear mechanisms As shown in Fig. 3, the N3Si4 ball at accurately controlled normal load is contacted vertically on the mating surface of the estimated specimens. The ball is connected with the elastic lever by using a clamp. In the friction and wear tests, friction coefficient values were given automatically by a conduction system after the friction forces were transformed into the friction coefficient by the deformation of the elastic lever. The wear rates W are calculated from equations W ¼ V=LD

ð1Þ

V ¼ AG ð2Þ where V is the volume of the specimen wear track in mm3, L is the normal load in N, D is the total sliding distance in m, A is the wear

The worn surface and wear debris of estimated specimens were examined in a SEM. Furthermore, elemental mapping of the worn surface was conducted in a SEM equipped with Energy dispersive X-ray spectroscopy (EDS) detector.

3. Results and discussion 3.1. Microstructure of the estimated specimens Fig. 4a–e presents the SEM micrographs of the microstructure of the hardened tool steel AISI D2 with different hardness levels of

Fig. 4. Microstructure of the estimated specimens. (a) 51±1 HRC, (b) 55±1 HRC, (c) 58±1 HRC, (d) 62±1 HRC and (e) 65±1 HRC.

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517 1, 5571, 6271, 58 71, and 65 71 HRC, respectively. It can be seen from this figure, the lower the hardness the more is the retained austenite and the microstructures are mainly comprised

of the tempered martensite+carbide+retained austenite when the hardness reaches the value as high as 6271 HRC. 3.2. Dry sliding friction performance 3.2.1. Influence of the sliding speed Fig. 5 shows the variation of the friction coefficient with sliding distance in the case of a 62 71 HRC hardness. As can be seen explicitly in Fig. 5, the sliding speed is of great importance on the sliding distance of reaching steady-state. At beginning of dry sliding, the friction coefficient sharply increases with the extension of the sliding distance, and it fluctuates at a certain range after attaining steady-state. In general, various interface temperatures, surface films with different properties, and friction performances at different contact states appear in the worn surface. As shown in Fig. 5a, b and c, the slower the sliding speed the more rapid is the rise in the friction coefficient. In addition, their fluctuant amplitudes grow larger and larger gradually with increments of the sliding speed, which indicates that the sliding speed exerts great influence on the amplitudes of the friction coefficient values. Fig. 6 describes the variation of the friction coefficient with the hardness and sliding speed at a load of 5 N. It can be seen from this figure that there are different changing laws for the friction coefficient of the specimens with different hardness levels. The two specimens with 51 and 58 71 HRC hardness have the lower friction coefficient, whereas the higher friction coefficient is obtained in the cases of 55, 62, and 65 71HRC at a sliding speed of 0.05 m/s. It is also obvious that the influence of the hardness on the friction coefficient of the specimens at a sliding speed of 0.10 m/s is less than that at 0.05 and 0.50 m/s. In the cases of 51 and 587 1 HRC hardness, the friction coefficient gradually increases with increments of the sliding speed; while it gradually decreases in the cases of 55, 62 and 657 1 HRC hardness. Therefore, it is evident that the sliding speed and hardness only exert slight influence on the friction coefficient. The literature [12] showed that the friction coefficient evidently increases with the increase of the sliding speed as the Si4N3 ball is tested against the stainless steel, which is not in agreement with the results obtained in this paper. 3.2.2. Influence of the quenching hardness Fig. 7 presents the variation of the friction coefficient of five hardened specimens with the sliding distance at a sliding speed of 0.05 m/s. As shown in Fig. 7, the higher the hardness the longer is the sliding distance of reaching steady-state. The possible reasons inducing this phenomenon are as follows: firstly, the hardened specimens with lower hardness levels comprise of more retained austenite content (Fig. 4a–c) than those with higher hardness, which can produce lubricious metal film on the worn surface, and result in the decrease of the friction coefficient; while those specimens with higher hardness levels comprise of less retained austenite and more martensite content (Fig. 4d and e) which is difficult to produce lubricious metal film, and the harder martensite leads to the larger vibration, compare

Fig. 5. Variation of the friction coefficient with sliding distance (6271 HRC). (a) Gyration radius of 2 mm, sliding speed of 0.05 m/s, (b) Gyration radius of 4 mm, sliding speed of 0.10 m/s, and (c) Gyration radius of 6 mm, sliding speed of 0.50 m/s.

Fig. 6. v−μ property of different hardness specimens (Normal load:5 N).

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with those softer austenite. Secondly, although the microstructure in the hardened specimen with 65 71 HRC hardness is similar to that of a 62 71 HRC hardness, its friction coefficient is smaller than that of 62 71 HRC hardness. It is obvious that there are additional reasons for resulting in the different phenomenon. Fig. 8a–c shows the SEM micrographs of the fracture specimens with different hardness levels of 55 71, 62 71, and 65 71 HRC, respectively. As can be seen from this figure, the amount of the brittle and hard carbide particles in a specimen of 62 71 HRC is more than those of 65 71 HRC, which results in the decrease of the friction coefficient of a specimen with 65 71 HRC.

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It can be seen from Fig. 9 that, apart from a specimen with 587 1HRC, the wear rates of the hardened specimens increase with increments of the sliding speed. For the hardened specimens with the hardness of 51, 55, and 62 71 HRC, the wear rates increase non-linearly with increments of the sliding speed. While in the case of the specimen with 657 1HRC, the wear rates increase almost linearly with increments of the sliding speed, which is similar to the results obtained in the literature [12]. The wear rates of the hardened specimens can be divided into the following different grades shown in Table 3, according to the physical interpretation in the literature [13].

3.3. Wear rates 3.3.1. Influence of the sliding speed Fig. 9 presents the variation of the wear rates with the hardness and sliding speed.

3.3.2. Influence of the quenching hardness It can be seen from Fig. 9 that the wear rates decrease with increments of the hardness at the sliding speeds of 0.05, 0.10 and 0.50 m/s, which is similar to Archard's wear equation. However, it

Fig. 7. Variation of the friction coefficient with the hardness (Gyration radius of 6 mm,sliding speed of 0.05 m/s). (a) 517 1 HRC, (b) 557 1 HRC, (c) 587 1 HRC, (d) 627 1 HRC, (e) 657 1HRC.

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It can be observed from Fig.10 that the same trend of the wear rates of the hardened specimens is mirrored with their tensile strength examined in a electronic multipurpose tensile-compress testing machine (Type:WDW-E200D) controlled by a computer at a room temperature of about 22 1C. Consequently, it is likely that brittleness of the specimen with 65 HRC results in strength loss,

Wear rate(10 -6mm3/N·m)

should be noted that the wear rate of a hardened specimen with 657 1 HRC is the highest at the sliding speeds of 0.10 and 0.5 m/s.

30 25 20 15 10 5 0

51±1HRC 58±1HRC 65±1HRC

0.05

55±1HRC 62±1HRC

0.10 Sliding speed v (m/s)

0.50

Fig. 9. v−w property of various hardness specimens (normal load: 5 N).

Table 3 Wear resistance of the hardened tool steel AISI D2. Hardness ( 7 1 HRC)

Sliding speed (m/s)

Grade of wear

51

0.05 0.10 0.50 0.05 0.10 0.50 0.05 0.10 0.50 0.05 0.10 0.50 0.05 0.10 0.50

Low wear Moderate wear Moderate wear Low wear Low wear Moderate wear Low wear Low wear Moderate wear Low wear Low wear Moderate wear Low wear Moderate wear Moderate wear

55

58

62

65

Tensile strength (MPa)

2000 1900 1800 1700 1600 1500

51

55

58

62

65

Specimen hardness (±1HRC) Fig. 8. SEM micrographs of the fracture specimen at different hardness levels. (a) 55 71 HRC, (b) 627 1 HRC, (c) 65 71 HRC.

Fig.10. The effect of specimen hardness on tensile strength. (a) Fractured tensile specimen in the case of 557 1 HRC, and (b) graph of tensile strength.

L. Tang et al. / Tribology International 66 (2013) 165–173

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Fig. 11. SEM micrographs in the worn surfaces of the specimens with 51, 55, 58, 62 65 7 1 HRC at a fixed sliding speed of 0.10 m/s. (a) 517 1HRC, (b) 557 1HRC, (c) 58 7 1HRC, and (d) 62 71HRC.

hence its wear resistance drops at elevated specimen hardness level. For these specimens with lower hardness (e.g. 51 71 and 55 71 HRC), one possible explanation of the observed phenomenon is that they show more plastic. Therefore, the wear resistant is comprehensive embodiment of strength (hardness) and plasticity of materials. 3.4. Dry sliding wear mechanism Fig. 11 illustrates the SEM micrographs in the worn surfaces of the hardened specimens with 51 71, 557 1, 58 71, 62 71, and 65 71 HRC at a fixed sliding speed of 0.10 m/s. It can be observed from Fig. 11a that the grooves are deeper, wider and have more density per unit area in the worn surface of the specimen with 517 1 HRC compared with 58 71 HRC; moreover, the local adhesive scars do occur in the worn surface as shown in Fig. 11a marked with ellipse. These result in more material removal of the

specimen with 51 71 HRC than that of 58 71 HRC, as shown in Fig. 9. In the worn surface of the specimen with 58 HRC (Fig. 11c), other than abrasion marks occurring by micro-plowing with relatively narrow scars in the direction of sliding and some wear debris adhering to the worn surfaces, nothing else can be detected by SEM at a magnification of  1000. As can be seen from Fig. 11 b and d, the varisized flakes are visible in the worn surface. The mechanisms resulting in these flakes are different due to the hardness levels of the specimens. For the hardened specimen with a hardness of 55 71 HRC, there are not only varisized flakes of broken adhesion joint, plastic flow and cracking, but also abrasive dusts resulted from the breakage of the bonds between the estimated specimen and mating ball, as shown in Fig.11b. Besides, there are two other aspects that induce these flakes. On one hand, the dry sliding between the estimated specimen and mating ball results in heat generation, hence instantaneous high-temperature happens [14],

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Element content (wt

Fig. 12. Analysis of the elements in the mating Si3N4 ball. (a) SEM micrograph in the worn surfaces of the mating ball, and (b) EDS analysis in the contact zone of the mating ball.

)

Fig. 14. Analysis of the elements in case of the specimen with 55 7 1HRC at a fixed sliding speed of 0.05 m/s. (a) Zone of the element analysis, and (b) EDS analysis in the contact zone of the mating ball.

35 30 25 20 15 10 5 0

51

55

58

62

65

Hardness of specimens H (±1 HRC) Fig. 15. Variation of elements in the worn surface of specimens with different hardness levels at a sliding speed of 0.05 m/s.

Fig. 13. SEM micrograph of the worn surfaces in the mating ball.

as leads to the softening effect between the friction and wear pairs. On the other hand, the number of abrasive dusts adhered to the worn surface snowballed. Then, these particles with considerable sizes are compressed by the contact load and sheared. Furthermore, the small flakes are conglutinated in the worn surface. Although the normal load is only 5 N, the contact stress between the ball and disc is fairly high. Therefore, the fatigue

cracks do occur because of highly concentrated stress imposed by the mating sliding Si3N4 ball. Cracks may initiate in the highly hardened layer, particularly in the subsurface region. As a result, a small flake around the crack is removed through delamination in the form of metallic flakes when cracks grow and get interconnected, this is a combination of adhesive wear and fatigue wear, as shown in Fig. 11b. While flakes in the specimen with 627 1 HRC is not detached from the worn surface before crack get interconnected as marked with ellipse in Fig.11d, thereby reducing the material removal. As also can be observed in Fig. 11d, a more slight plastic deformation exists in the worn surface for a specimen with 6271 HRC. According to above discussion, the main wear mechanism in the cases of 55 and 627 1 HRC hardness is adhesive wear. Further increase in the hardness shows in addition to cracks more deteriorated surface shown in Fig. 11e, which is

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characterized by brittle fracture of the specimen with 65 HRC. Again this may confirm that it become harder and more brittle, which in turn leads to cracks and delamination wear as marked with ellipse in Fig. 11e. These result in its higher wear rates and lower wear resistance. The element content in the worn surface of the mating Si3N4 ball was analyzed by EDS as the sliding distance reaches 100 m at a sliding speed of 0.05 m/s. It can be observed from Fig. 12, there are a mass of C and a small quantity of additional elements transferred from the estimated specimen in the contact zone, which indicates that the transfer of the elements between both of them happened in these tests. Furthermore, it is known that sliding between the specimen and the mating ball results in heat generation in the tests and believed that C element appears in the carborundum and oxidated carbide forms. Fig.13 describes the partial enlarged SEM micrograph of the worn surface in the contact zone of the mating ball. Similarly, the elements are also transferred from the mating ball to the friction-wear disc. Fig.14 presents the SEM micrograph and elements analysis in the worn surfaces of the specimen with 55 71 HRC at a 0.05 m/s sliding speed. The elements transferred from the mating ball are also visible in the worn surface (Fig. 14b). According to above discussion, it is believed that it is the adhesive wear that induces the elements transfer when the Si4N3 ball is mated against the hardened tool steel, which is in agreement with the literature [15]. Fig. 15 describes the variation of the oxygen and nitrogen elements in the worn surface of the specimens with the hardness at a 0.05 m/s sliding speed. As can be seen from this figure, the hardness has great influence on the transfer of the elements in the tests. And the oxygen and nitrogen elements in the worn surface of the estimated specimens increase gradually with increments of the hardness. The reason can be attributed to the rise in high temperature, as induces some certain chemical reactions between the friction-wear specimens and consequently leads to a series of wear effects. 4. Conclusions In this paper, dry sliding friction and wear performance and mechanism of the hardened tool steel AISI D2 with different hardness levels were investigated. The conclusions can be drawn from the above analysis: 1. The sliding speed exerts more influence on the fluctuant amplitude of the friction coefficient within steady-state period compare with the hardness. And the higher the hardness and sliding speed the longer is the sliding distance of reaching steady-state. 2. The specimen with 587 1 HRC hardness have the lower friction coefficient, whereas the higher friction coefficient is obtained in the cases of 51, 55, 62, and 65 71HRC at a sliding speed of 0.05 m/s. The influence of the hardness on the friction coefficient of the hardened specimens at a 0.10 m/s sliding speed is less than that at 0.05 and 0.50 m/s. 3. The wear rates for the hardened specimens with 55, 58 and 627 1 HRC are in the order of 10−6 mm3/N m (low wear) at the

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sliding speeds of 0.05 and 0.01 m/s, while they are in the order of 10−5 mm3/N m (moderate wear) at a sliding speed of 0.5 m/s. In the cases of 51 and 657 1 HRC hardness, the wear rate values are in the order of 10−6 mm3/N m (low wear) at a 0.05 m/s sliding speed, while they are in the order of 10−5 mm3/N m (moderate wear) at the sliding speeds of 0.10 and 0.5 m/s. 4. The flakes can be attributed to three main mechanisms, namely, the fatigue cracks induced by the contact stress, the softening effect due to high temperature and snowballing effect. 5. Different wear mechanisms are observed. The main wear mechanism is adhesive wear for the specimens with 55 and 6271 HRC, abrasive wear for 51 and 58 71 HRC. Besides, delamination wear for the specimen with 6571 HRC due to its brittleness is the dominated wear mechanism.

Acknowledgments This investigation was supported by the Youth Science and Technology Innovation Foundation of Lanzhou Institute of Technology. The authors wish to thank Prof. J. Huang and the anonymous reviewers for their careful review and insightful comments that helped us improve this paper. References [1] Bourithis L, Papadimitriou GD, Sideris J. Comparison of wear properties of tool steels AISI D2 and O1 with the same hardness. Tribology International 2006;39:479–89. [2] Atar E, Sabri Kayali E, Cimenoglu H. Sliding wear behavior of ZrN and (Zr, 12 wt % Hf)N coatings. Tribology International 2006;39:297–302. [3] Gorscak D, Filetin T, Grilec K. Analysis of abrasive wear resisitance of the D2 tool steel in relation to heat treatment. Materials Technology 2008;42:131–2. [4] Omer NC, Muammer K. Experimental investigations on wear resistance characteristics of alternative die materials for stamping of advanced highstrength steels (AHSS). International Journal of Machine Tools and Manufacture 2009;49:897–905. [5] Sen U, Unal H, Mimaroglu A, Yilmaz S, Sen S. Wear behavior of alumina and AISI 52100 steel against molybdeniym boreide coated AISI D2 steel. Tehnologia Inovativa 2007;59:105–8. [6] Das D, Ray KK, Dutta AK. Influence of temperature of sub-zero treatments on the wear behavior of die steel. Wear 2009;267:1361–70. [7] Das D, Dutta AK, Ray KK. Correlation of microstructure with wear behavior of deep cryogenically treated AISI D2 steel. Wear 2009;267:1371–80. [8] Das D, Dutta AK, Ray KK. Sub-zero treatments of AISI D2 steel: Part I. Microstructure and hardness. Materials Science and Engineering A 2010;527:2182–93. [9] Das D, Dutta AK, Ray KK. Sub-zero treatments of AISI D2 steel: Part II. Wear behavior. Materials Science and Engineering A 2010;52:2194–206. [10] Zhou AQ, Deng FY. Experimental study on the heat treatment process for Cr12MoV steel. Die and Mold Industry 2001;000:55–7. [11] Wang LJ, Miao B, Meng XX. Analysis on the hardness and metallographic structure of Cr12MoV steel under different heat treatment. Die and Mold Industry 2005;000:2–56. [12] Zhang YZ. Dry tribology of materials. 1st ed. Baijing: Science Press; 2007. [13] Dellacorte C. Tribological composition optimization of chromium-carbidebased solid Lubricant coatings for foll gas bearings at temperatures to 650 1C. Surface and Coatings Technology 1988;36:87–97. [14] Gomes JR, Miranda AS, Viera JM, Silva RF. Sliding speed–temperature wear transition maps for Si3N4/iron alloy couples. Wear 2001;250:293–8. [15] Zhao X, Liu J, Zhu B. Wear behavior of Si3N4 ceramic cutting tool material against stainless steel in dry and water-lubricated conditions. Ceramics International 1999;25:309–15.