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Dry sliding wear behavior of low carbon dual phase powder metallurgy steels
Materials & Design Materials and Design 28 (2007) 1685–1688 www.elsevier.com/locate/matdes
Short communication
Dry sliding wear behavior of low carbon dual phase powder metallurgy steels S. Tekeli b
a,*
¨ zyu¨rek , A. Gu¨ral a, D. O
b
a Materials Division, Technical Education Faculty, Gazi University, 06500 Besevler-Ankara, Turkey Casting Division, Karabu¨k Technical Education Faculty, Zonguldak Karaelmas University, 078100 Karabu¨k, Turkey
Received 14 September 2005; accepted 16 March 2006 Available online 5 May 2006
Abstract Dry sliding wear behavior of Fe + 0.3% graphite powder metallurgy processed (PM) steels was investigated at constant sliding speed, load and distance. For this purpose, atomized iron powder was mixed with 0.3% graphite powder and sintered at 1200 C for 30 min under Argon gas atmosphere. The sintered PM specimens were intercritically annealed at different temperatures (728 and 760 C) and then water-quenched. After sintering, a typical ferrite + pearlite microstructure was obtained. In the microstructure of the intercritically annealed PM specimens, a ferrite + martensite microstructure was produced. After wear tests, it was seen that the wear rate of the intercritically annealed specimens was very low in comparison to as-sintered specimen. The specimen intercritically annealed at 728 C showed the lowest wear rate, despite its lower martensite volume fraction. 2006 Elsevier Ltd. All rights reserved.
1. Introduction Wear is one of the important mechanical properties expected from steels in actual service condition for some of the aerospace and automobile parts. Most of these parts are made by powder metallurgy (PM) technique and are required to exhibit good wear resistance [1]. In a dry sliding wear process, there are several mechanisms contributing to wear behavior of PM steels, such as, melt wear, oxidation-dominated wear and mechanical wear process depending on wear condition, metallurgical structure, composition and porosity of PM steels [2]. Sudhakar et al. [1] investigated the wear behavior of high density Fe–2%Ni based PM alloys and concluded that the wear rate decreased with an increase in hardness level. Anto´n et al. [3] studied the dry sliding wear behavior of the sintered PM steel containing high Mn–Ni contents as a function of density, porosity content and hardness and found
*
Corresponding author. Tel.: +90 312 4399760; fax: +90 312 2120059. E-mail address: [email protected] (S. Tekeli).
0261-3069/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2006.03.013
that the deformation of austenitic areas could provoke a diminishing of wear strength in material with high nickel content. Also lower friction coefficient was obtained in material with martensite structure. Khorsand et al. [4] observed the effect of manufacturing conditions on fatigue and wear properties of Fe–1.75Ni–1.5Cu–0.5Mo–0.6C sintered steel. Their results showed that the wear and fatigue resistance were increased by decreasing porosity level and by heat treatment. Simchi and Danninger [5] studied the dry sliding wear behavior of sintered ferrous materials in order to evaluate the influence of surface porosity on the wear characteristics. Wang and Danninger [2] investigated the wear behavior of Mo alloyed sintered steels and showed that the wear rate increased under quenching and tempering conditions in comparison to as-sintering condition. They indicated that the martensitic phase is not beneficial for the wear resistance of the Mo steels, despite its higher hardness [2]. Dual phase steel structure is obtained by heating low alloy hypoeutectoid steels between the Ac1–Ac3 temperatures, forming ferrite + austenite phases with subsequent rapid cooling in order to transform the austenite to
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S. Tekeli et al. / Materials and Design 28 (2007) 1685–1688
martensite. By controlling shape, size, amount and dispersion of martensite in ferrite matrix, desired strength–ductility relationship and toughness are obtained [6–9]. Materials, which have ductile and hard phases are widely used as wear resistance materials [7]. In a steel with constant carbon content, the hardness of martensite islands increases as the martensite volume fraction decreases and this improves the wear strength of dual phase steels [7,8]. In this study, dry sliding wear behavior of PM processed plain carbon dual phase steels having different martensite volume fractions was investigated and the results were compared with as sintered specimen. 2. Experimental procedure In this study, atomized iron (Ancorsteel 1000, Hoeganaes, USA) (<0.01 C, <0.01 Si, 0.2 Mn, 0.07 Cr, 0.1 Cu, 0.08 Ni, 0.018 S, 0.009 P, 0.14 O, 0.002 N, in wt%) and natural graphite (Alfa Aesar, Germany) powders were used. In order to apply intercritical annealing heat treatments, specimens were prepared by mixing 0.3% graphite with iron powder. The mixed powders were cold pressed at 700 MPa with a single action die and sintered at 1200 C for 30 min under pure (99.999%) Ar gas atmosphere. The sintered specimens were intercritically annealed at different temperatures (728 and 760 C), and then water quenched. These specimens were coded as HT728 and HT760. Schematic illustrations of the heat treatments are shown in Fig. 1. For the microstructural investigations, the specimens were ground, polished and etched with the 2% Nital solution. Scanning electron microscopy (SEM) (JEOL 6060) was used to characterize the microstructure of the specimens. Mean linear intercept method was used for the calculation of martensite volume fraction. The density of specimens was measured from volume and weight after sintering and heat treatments. Macrohardness values of each specimen were measured by Vickers tester (Instron Wolpert) using 30 kg load. Microhardness values of phases in the microstructure were determined by Vickers tester (Instron Wolpert) using 1 kg load. All hardness measurements were made at least at 10 different areas of each specimen and average values were taken. A pin-on-disc sliding wear machine with a continuously rotating alloy steel plate of hardness 55 HRC was used for wear tests under dry conditions. The wear tests were carried out at a constant load of 25 N and a sliding speed of 2.08 m s 1. Total sliding distance was selected as 3000 m. After wear tests, the specimens were cleaned carefully and weighed in. The wear rate was calculated by dividing the volume of the worn out material by the sliding distance. The worn surfaces of the specimens were also examined using SEM.
3. Results and discussion 3.1. Microstructure and hardness SEM microstructure of the specimen sintered at 1200 C for 30 min is shown in Fig. 2. A typical ferrite + pearlite microstructure was obtained in the sintered specimen. The density of the sintered specimen was 7.47 g cm 3. It is known that the sintered density of PM specimens changes depending on pressing load, particle size, added alloying elements and sintering temperature and time. Macrohardness value of the specimen after sintering was 98 HV30. Generally the macrohardness values of the sintered PM specimens are low [3,10]. For this reason, it is necessary to apply heat treatments especially to low alloy PM steels after sintering. Dual phase microstructures of HT728 and HT760 specimens which were intercritically annealed at temperatures of 728 and 760 C, respectively, are shown in Fig. 3. In these specimens, martensite islands formed at ferrite grain boundaries and martensite (austenite) volume fraction (MVF) increased with increasing intercritical annealing temperatures. MVF in HT728 and HT760 specimens was obtained as 13% and 25%, respectively. After intercritical annealing heat treatments, the density of HT728 and HT760 specimens were similar to as-sintered specimen (Table 1). In the HT728 and HT760 specimens, macrohardness values remained almost the same despite to increasing MVF (Table 1). In PM steels, porosity and microstructure are the most important factors determining macrohardness values. Macrohardness of PM steels can also be effected by proportion of hard phases (such as bainite, martensite, etc.) or soft phases (such as ferrite). In the intercritically specimens, average microhardnees values of the martensite islands decreased with increasing intercritical annealing temperature (MVF after quenching). 3.2. Wear rates The wear rates of the sintered and intercritically annealed specimens are given in Table 1. The wear rate of the sintered 800 700
1
400
500 400
C. mi n -1
in C.m
600
600
5˚
800
Temperature, (˚C)
5 ˚C .min 1
1000 4˚
Temperature, (˚C)
760 ˚C 728 ˚C
1200 ˚C
1200
300 200
200
100 0
(a)
100
200
300 400 Time, (min)
500
600 (b)
Water-quencing
20 40 60 80 100 120 140 160 Time, (min)
Fig. 1. Schematic illustrations of the heat treatments applied to the PM specimens (a) sintering and (b) intercritical annealing.
S. Tekeli et al. / Materials and Design 28 (2007) 1685–1688
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Table 1 Density, hardness and wear properties of the specimens
Fig. 2. SEM microstructure of the sintered specimen (F: Ferrite, P: Pearlite).
specimen was found to be very high. The reason for this is that the macrohardness of the sintered specimen was low, in spite of this specimen having similar density with the intercritically annealed specimens. Also the as-sintered specimen lacked in hard phases like martensite, (martensite phase is present in HT728 and HT760 specimens) which shows resistance to wear. In order to improve the wear strength of PM steels, heat treatments are needed. For this reason, the most common heat treatment applied to PM steels is quenching + tempering. However, some time, the production of fully martensitic structure in the microstructure of PM steel does not increase the wear rate as expected. Martensite phase in a microstructure is easily cracked under loads and thus the weight loss from the surface is increased [2]. Therefore, in this study, intercritical annealing heat treatment is applied as an alternative heat treatment to improve wear strength of PM steels (see Fig. 4). It was seen that, the wear rate of the HT728 specimen was lower than that of the HT760 specimen although MVF of the HT760 specimen was higher than that of the
Specimen
Density (g cm 3)
Macrohardness (HV30)
Microhardness of martensite (HV1)
Wear rate (·10 13 m3/m)
As-sintered HT728 HT760
7.47 7.46 7.47
98 178 183
– 858 516
104 5.9 29.1
HT728 specimen. In the HT728 specimen, the martensites islands had high hardness. Thus, the wear resistance of this specimen was high. It is known [7] that the carbon content in austenite phase decreases with a change in the austenization temperature from intercritical temperature Ac1 to Ac3. During this process, martensite volume fraction increases while its hardness decreases, which results in a decrease in wear resistance of dual phase steels. Also, wear resistance of dual phase steels affect their ductility. If dual phase steels have high ductility, they have high wear resistance as well [7,8]. Generally, dual phase steels having lower MVF have high ductility [6,8]. Therefore, as the HT728 had lower MVF, it can be expected to have higher ductility and thus high wear resistance. The morphology of worn surfaces is shown in Fig. 3. Flake like wear debris were seen in the worn subsurface of the sintered specimen (Fig. 3(a)). This was due to higher wear rate of the sintered specimen. The worn surfaces of the HT728 and HT760 specimens are given in Fig. 3(b) and (c). The deformed layers along the sliding direction can be easily seen in these specimens. A few craters resulting from debris during sliding were also observed on the worn surfaces of these specimens. While the wear mechanism of the HT728 specimen was predominantly adhesive, the HT760 specimen was worn by a mixture of adhesive and dominantly abrasive wear mechanisms. The wear rate increases with abrasive wear [2]. The wear rate of the HT760 specimen was higher than that of the HT728 specimen at constant load and sliding speed (Table 1). If the wear sliding speed had been lower
Fig. 3. SEM microstructures of (a) HT728 and (b) HT760 specimens (F: Ferrite, M: Martensite).
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Fig. 4. Worn surfaces of (a) as-sintered, (b) HT728, and (c) HT760 specimens.
or higher than the ones used in this study, other wears mechanisms such as oxidation or melting could have occurred. Tyagi et al. [11] stated that dual phase steel consisting of hard martensite islands embedded in a relatively soft and ductile ferrite matrix is a typical two phase material where the oxidation products of both the phases are the same. 4. Conclusion The wear behavior of dual phase PM steel was investigated. The sintered specimen showed very high wear rate which was caused by severe plastic deformation of surface resulted by low hardness. Dual phase PM steels having lower MVF showed high wear resistance. Macrohardness values were remained almost the same despite to increasing MVF, but microhardness of martensite decreased with increasing MVF. Acknowledgments This work is supported by DPT (The State Planning Organization of Turkey) under project number 2002K120250 and by the Scientific Research Project Program of Gazi University under project number 07/2005-24.
References [1] Sudhakar KV, Sampathkumaran P, Dwarakadasa ES. Dry sliding wear in high density Fe–2%Ni based P/M alloys. Wear 2000;242:207–12. [2] Wang J, Danninger H. Dry sliding wear behavior of molybdenum alloyed sintered steels. Wear 1998;222:49–56. [3] Anto´n N, Delgado JL, Velasco F, Torralba JM. Influence of alloying element additions on tribological behaviour of sintered steels with high content in manganese–nickel. J Mater Process Technol 2003;143–144:475–80. [4] Khorsand H, Habibi SM, Yoozbashizade H, Janghorban K, Reihani SMS, Rahmani Seraji H, et al. The role of heat treatment on wear behavior of powder metallurgy low alloy steels. Materials and Design 2002;23:667–70. [5] Simchi A, Danninger H. Effects of porosity on delamination wear behaviour of sintered plain iron. Powder Met 2004;47(1):73–80. [6] Davies RG. Deformation behavior of a vanadium-strengthened dual phase steel. Metall Trans A 1978;9:41–52. [7] Aksoy M, Karamısß MB, Evin E. An evaluation of the wear behaviour of a dual-phase low carbon steel. Wear 1996;193:248–52. [8] Bayram A, Ug˘uz A. Effect of microstructure on the wear behaviour of a dual phase steel. Mat.-wiss U Werkstoffech 2001;32:249–52. [9] Tekeli S, Gu¨ral A. Microstructural characterization and impact toughness of intercritically annealed PM steels. Mater Sci Eng A 2005;406:172–9. [10] Selecka´ M, Sˇalak A, Danninger H. The effect of boron liquid phase sintering on properties of Ni-, Mo- and Cr-alloyed structural steels. J Mater Process Tech 2003;141(3):379–84. [11] Tyagi R, Nath SK, Ray S. Modelling of dry sliding oxidationmodified wear in two phase materials. Wear 2003;255:327–32.
Short communication
Dry sliding wear behavior of low carbon dual phase powder metallurgy steels S. Tekeli b
a,*
¨ zyu¨rek , A. Gu¨ral a, D. O
b
a Materials Division, Technical Education Faculty, Gazi University, 06500 Besevler-Ankara, Turkey Casting Division, Karabu¨k Technical Education Faculty, Zonguldak Karaelmas University, 078100 Karabu¨k, Turkey
Received 14 September 2005; accepted 16 March 2006 Available online 5 May 2006
Abstract Dry sliding wear behavior of Fe + 0.3% graphite powder metallurgy processed (PM) steels was investigated at constant sliding speed, load and distance. For this purpose, atomized iron powder was mixed with 0.3% graphite powder and sintered at 1200 C for 30 min under Argon gas atmosphere. The sintered PM specimens were intercritically annealed at different temperatures (728 and 760 C) and then water-quenched. After sintering, a typical ferrite + pearlite microstructure was obtained. In the microstructure of the intercritically annealed PM specimens, a ferrite + martensite microstructure was produced. After wear tests, it was seen that the wear rate of the intercritically annealed specimens was very low in comparison to as-sintered specimen. The specimen intercritically annealed at 728 C showed the lowest wear rate, despite its lower martensite volume fraction. 2006 Elsevier Ltd. All rights reserved.
1. Introduction Wear is one of the important mechanical properties expected from steels in actual service condition for some of the aerospace and automobile parts. Most of these parts are made by powder metallurgy (PM) technique and are required to exhibit good wear resistance [1]. In a dry sliding wear process, there are several mechanisms contributing to wear behavior of PM steels, such as, melt wear, oxidation-dominated wear and mechanical wear process depending on wear condition, metallurgical structure, composition and porosity of PM steels [2]. Sudhakar et al. [1] investigated the wear behavior of high density Fe–2%Ni based PM alloys and concluded that the wear rate decreased with an increase in hardness level. Anto´n et al. [3] studied the dry sliding wear behavior of the sintered PM steel containing high Mn–Ni contents as a function of density, porosity content and hardness and found
*
Corresponding author. Tel.: +90 312 4399760; fax: +90 312 2120059. E-mail address: [email protected] (S. Tekeli).
0261-3069/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2006.03.013
that the deformation of austenitic areas could provoke a diminishing of wear strength in material with high nickel content. Also lower friction coefficient was obtained in material with martensite structure. Khorsand et al. [4] observed the effect of manufacturing conditions on fatigue and wear properties of Fe–1.75Ni–1.5Cu–0.5Mo–0.6C sintered steel. Their results showed that the wear and fatigue resistance were increased by decreasing porosity level and by heat treatment. Simchi and Danninger [5] studied the dry sliding wear behavior of sintered ferrous materials in order to evaluate the influence of surface porosity on the wear characteristics. Wang and Danninger [2] investigated the wear behavior of Mo alloyed sintered steels and showed that the wear rate increased under quenching and tempering conditions in comparison to as-sintering condition. They indicated that the martensitic phase is not beneficial for the wear resistance of the Mo steels, despite its higher hardness [2]. Dual phase steel structure is obtained by heating low alloy hypoeutectoid steels between the Ac1–Ac3 temperatures, forming ferrite + austenite phases with subsequent rapid cooling in order to transform the austenite to
1686
S. Tekeli et al. / Materials and Design 28 (2007) 1685–1688
martensite. By controlling shape, size, amount and dispersion of martensite in ferrite matrix, desired strength–ductility relationship and toughness are obtained [6–9]. Materials, which have ductile and hard phases are widely used as wear resistance materials [7]. In a steel with constant carbon content, the hardness of martensite islands increases as the martensite volume fraction decreases and this improves the wear strength of dual phase steels [7,8]. In this study, dry sliding wear behavior of PM processed plain carbon dual phase steels having different martensite volume fractions was investigated and the results were compared with as sintered specimen. 2. Experimental procedure In this study, atomized iron (Ancorsteel 1000, Hoeganaes, USA) (<0.01 C, <0.01 Si, 0.2 Mn, 0.07 Cr, 0.1 Cu, 0.08 Ni, 0.018 S, 0.009 P, 0.14 O, 0.002 N, in wt%) and natural graphite (Alfa Aesar, Germany) powders were used. In order to apply intercritical annealing heat treatments, specimens were prepared by mixing 0.3% graphite with iron powder. The mixed powders were cold pressed at 700 MPa with a single action die and sintered at 1200 C for 30 min under pure (99.999%) Ar gas atmosphere. The sintered specimens were intercritically annealed at different temperatures (728 and 760 C), and then water quenched. These specimens were coded as HT728 and HT760. Schematic illustrations of the heat treatments are shown in Fig. 1. For the microstructural investigations, the specimens were ground, polished and etched with the 2% Nital solution. Scanning electron microscopy (SEM) (JEOL 6060) was used to characterize the microstructure of the specimens. Mean linear intercept method was used for the calculation of martensite volume fraction. The density of specimens was measured from volume and weight after sintering and heat treatments. Macrohardness values of each specimen were measured by Vickers tester (Instron Wolpert) using 30 kg load. Microhardness values of phases in the microstructure were determined by Vickers tester (Instron Wolpert) using 1 kg load. All hardness measurements were made at least at 10 different areas of each specimen and average values were taken. A pin-on-disc sliding wear machine with a continuously rotating alloy steel plate of hardness 55 HRC was used for wear tests under dry conditions. The wear tests were carried out at a constant load of 25 N and a sliding speed of 2.08 m s 1. Total sliding distance was selected as 3000 m. After wear tests, the specimens were cleaned carefully and weighed in. The wear rate was calculated by dividing the volume of the worn out material by the sliding distance. The worn surfaces of the specimens were also examined using SEM.
3. Results and discussion 3.1. Microstructure and hardness SEM microstructure of the specimen sintered at 1200 C for 30 min is shown in Fig. 2. A typical ferrite + pearlite microstructure was obtained in the sintered specimen. The density of the sintered specimen was 7.47 g cm 3. It is known that the sintered density of PM specimens changes depending on pressing load, particle size, added alloying elements and sintering temperature and time. Macrohardness value of the specimen after sintering was 98 HV30. Generally the macrohardness values of the sintered PM specimens are low [3,10]. For this reason, it is necessary to apply heat treatments especially to low alloy PM steels after sintering. Dual phase microstructures of HT728 and HT760 specimens which were intercritically annealed at temperatures of 728 and 760 C, respectively, are shown in Fig. 3. In these specimens, martensite islands formed at ferrite grain boundaries and martensite (austenite) volume fraction (MVF) increased with increasing intercritical annealing temperatures. MVF in HT728 and HT760 specimens was obtained as 13% and 25%, respectively. After intercritical annealing heat treatments, the density of HT728 and HT760 specimens were similar to as-sintered specimen (Table 1). In the HT728 and HT760 specimens, macrohardness values remained almost the same despite to increasing MVF (Table 1). In PM steels, porosity and microstructure are the most important factors determining macrohardness values. Macrohardness of PM steels can also be effected by proportion of hard phases (such as bainite, martensite, etc.) or soft phases (such as ferrite). In the intercritically specimens, average microhardnees values of the martensite islands decreased with increasing intercritical annealing temperature (MVF after quenching). 3.2. Wear rates The wear rates of the sintered and intercritically annealed specimens are given in Table 1. The wear rate of the sintered 800 700
1
400
500 400
C. mi n -1
in C.m
600
600
5˚
800
Temperature, (˚C)
5 ˚C .min 1
1000 4˚
Temperature, (˚C)
760 ˚C 728 ˚C
1200 ˚C
1200
300 200
200
100 0
(a)
100
200
300 400 Time, (min)
500
600 (b)
Water-quencing
20 40 60 80 100 120 140 160 Time, (min)
Fig. 1. Schematic illustrations of the heat treatments applied to the PM specimens (a) sintering and (b) intercritical annealing.
S. Tekeli et al. / Materials and Design 28 (2007) 1685–1688
1687
Table 1 Density, hardness and wear properties of the specimens
Fig. 2. SEM microstructure of the sintered specimen (F: Ferrite, P: Pearlite).
specimen was found to be very high. The reason for this is that the macrohardness of the sintered specimen was low, in spite of this specimen having similar density with the intercritically annealed specimens. Also the as-sintered specimen lacked in hard phases like martensite, (martensite phase is present in HT728 and HT760 specimens) which shows resistance to wear. In order to improve the wear strength of PM steels, heat treatments are needed. For this reason, the most common heat treatment applied to PM steels is quenching + tempering. However, some time, the production of fully martensitic structure in the microstructure of PM steel does not increase the wear rate as expected. Martensite phase in a microstructure is easily cracked under loads and thus the weight loss from the surface is increased [2]. Therefore, in this study, intercritical annealing heat treatment is applied as an alternative heat treatment to improve wear strength of PM steels (see Fig. 4). It was seen that, the wear rate of the HT728 specimen was lower than that of the HT760 specimen although MVF of the HT760 specimen was higher than that of the
Specimen
Density (g cm 3)
Macrohardness (HV30)
Microhardness of martensite (HV1)
Wear rate (·10 13 m3/m)
As-sintered HT728 HT760
7.47 7.46 7.47
98 178 183
– 858 516
104 5.9 29.1
HT728 specimen. In the HT728 specimen, the martensites islands had high hardness. Thus, the wear resistance of this specimen was high. It is known [7] that the carbon content in austenite phase decreases with a change in the austenization temperature from intercritical temperature Ac1 to Ac3. During this process, martensite volume fraction increases while its hardness decreases, which results in a decrease in wear resistance of dual phase steels. Also, wear resistance of dual phase steels affect their ductility. If dual phase steels have high ductility, they have high wear resistance as well [7,8]. Generally, dual phase steels having lower MVF have high ductility [6,8]. Therefore, as the HT728 had lower MVF, it can be expected to have higher ductility and thus high wear resistance. The morphology of worn surfaces is shown in Fig. 3. Flake like wear debris were seen in the worn subsurface of the sintered specimen (Fig. 3(a)). This was due to higher wear rate of the sintered specimen. The worn surfaces of the HT728 and HT760 specimens are given in Fig. 3(b) and (c). The deformed layers along the sliding direction can be easily seen in these specimens. A few craters resulting from debris during sliding were also observed on the worn surfaces of these specimens. While the wear mechanism of the HT728 specimen was predominantly adhesive, the HT760 specimen was worn by a mixture of adhesive and dominantly abrasive wear mechanisms. The wear rate increases with abrasive wear [2]. The wear rate of the HT760 specimen was higher than that of the HT728 specimen at constant load and sliding speed (Table 1). If the wear sliding speed had been lower
Fig. 3. SEM microstructures of (a) HT728 and (b) HT760 specimens (F: Ferrite, M: Martensite).
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S. Tekeli et al. / Materials and Design 28 (2007) 1685–1688
Fig. 4. Worn surfaces of (a) as-sintered, (b) HT728, and (c) HT760 specimens.
or higher than the ones used in this study, other wears mechanisms such as oxidation or melting could have occurred. Tyagi et al. [11] stated that dual phase steel consisting of hard martensite islands embedded in a relatively soft and ductile ferrite matrix is a typical two phase material where the oxidation products of both the phases are the same. 4. Conclusion The wear behavior of dual phase PM steel was investigated. The sintered specimen showed very high wear rate which was caused by severe plastic deformation of surface resulted by low hardness. Dual phase PM steels having lower MVF showed high wear resistance. Macrohardness values were remained almost the same despite to increasing MVF, but microhardness of martensite decreased with increasing MVF. Acknowledgments This work is supported by DPT (The State Planning Organization of Turkey) under project number 2002K120250 and by the Scientific Research Project Program of Gazi University under project number 07/2005-24.
References [1] Sudhakar KV, Sampathkumaran P, Dwarakadasa ES. Dry sliding wear in high density Fe–2%Ni based P/M alloys. Wear 2000;242:207–12. [2] Wang J, Danninger H. Dry sliding wear behavior of molybdenum alloyed sintered steels. Wear 1998;222:49–56. [3] Anto´n N, Delgado JL, Velasco F, Torralba JM. Influence of alloying element additions on tribological behaviour of sintered steels with high content in manganese–nickel. J Mater Process Technol 2003;143–144:475–80. [4] Khorsand H, Habibi SM, Yoozbashizade H, Janghorban K, Reihani SMS, Rahmani Seraji H, et al. The role of heat treatment on wear behavior of powder metallurgy low alloy steels. Materials and Design 2002;23:667–70. [5] Simchi A, Danninger H. Effects of porosity on delamination wear behaviour of sintered plain iron. Powder Met 2004;47(1):73–80. [6] Davies RG. Deformation behavior of a vanadium-strengthened dual phase steel. Metall Trans A 1978;9:41–52. [7] Aksoy M, Karamısß MB, Evin E. An evaluation of the wear behaviour of a dual-phase low carbon steel. Wear 1996;193:248–52. [8] Bayram A, Ug˘uz A. Effect of microstructure on the wear behaviour of a dual phase steel. Mat.-wiss U Werkstoffech 2001;32:249–52. [9] Tekeli S, Gu¨ral A. Microstructural characterization and impact toughness of intercritically annealed PM steels. Mater Sci Eng A 2005;406:172–9. [10] Selecka´ M, Sˇalak A, Danninger H. The effect of boron liquid phase sintering on properties of Ni-, Mo- and Cr-alloyed structural steels. J Mater Process Tech 2003;141(3):379–84. [11] Tyagi R, Nath SK, Ray S. Modelling of dry sliding oxidationmodified wear in two phase materials. Wear 2003;255:327–32.