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Mechanical Engineering Department, Al-Huson University Collage, Al-Balqa Applied University, Jordan
Received: November 07, 2011 / Accepted: December 01, 2011 / Published: April 25, 2012.
Abstract: The aim of this work is to give a scientific basis for the requirements specified for the structures of the iron-based materials(cemented and nitro-cemented steels, Surfaced coats, etc.), providing high wear resistance of these materials in Conditions of abrasive wear. The article represents results of the theoretical analysis of strength and wear resistance of the composite materials comprising hard particles inside a metal matrix, as well as experimental results of cementation of steels alloyed with carbide-forming
Key words: Cementite, abrasive wear, hypoeutectoid, heterophase.
1. Introduction??
The abrasive wear is the process of splitting off of metal particles from the wearing surface by means of abrasive grains. These grains, under the regular loading, penetrate into the metal surface and cut off the micros Warf from the surface when it is moving. Abrasive grains for metallic materials are particles with hardness higher than that of metal due to natural particles of mineral origin like quartz, granite, alumina, etc. Their distinctive characteristic is high hardness and high mechanical endurance. The most wide-spread natural abrasive is quartz sand with hardness equal to 10,000 MPa and its compression endurance is 280 MPa. This paper present analysis of abrasion resistance of metallic materials with cementite contained structures.
2. Result and Discussion
Splitting off of wear debris from the metal surface in the abrasive wear is caused by either single or multiple influences of abrasive grains on the metal volume unit. In the first case and in the friction zone the process of microcutting is realized. The second case takes a place
equations. In this sphere along with power factors there are also structure characteristics and fatigue properties of a wearing material which play the most important role in wear resistance rate determination.
There are a lot of works on wear which touch upon, such as Refs. [1, 2]. It is generally accepted that materials with multiphase (hetero phase) structure enriched with solid and refractory phases such as carbides, nitrides, borides, etc. which have the highest wear resistance.
Differences in wear resistance of such materials are determined by the type of inclusions, their quantity, size and form. Besides hetero phase structures wear resistance are influenced by the type of matrix metal and its properties, mainly by toughness and fatigue strength.
The analysis from Ref. [3] which give the results of built-up ferro-chromium alloys auxiliary properties test allow to get the idea of how metallic materials structures influence their wear resistance and impact toughness.
The microstructures of some alloys set according to the carbon proportion increase and their properties are given in (Table 1.) This table has been developed on the basis of Ref. [3].
The chemical composition of the materials(building-ups) given in Table 1 differs only in the carbon content; however, the structure and the properties of these materials are different. The hypoeutectoid alloys (No. 1 and No. 2 in Table 1) have low hardness and relatively low wear resistance but their impact toughness is very high, especially for an alloy No. 1 with the ferrito-pearlite structure.
The hypoeutectoid alloys (No. 3 and No. 5 in Table 1) with a solid carbide grid structure have higher hardness and wear resistance in comparison with the first alloys but their impact toughness is extremely low. Obviously their brittleness is caused by the fact that a destructive crack does not meet any tough areas resistance while passing through the carbide grid. The alloy No. 4 stays apart form the other considered materials as it has the highest hardness and wear resistance and at the same time its impact toughness rate is quite satisfactory. The mentioned alloy No. 4 possesses such a favourable combination of properties due to its specific structure.
As it can be seen on the microphoto given in Table 1 the structure of the alloy No. 4 consists of large carbide inclusions separated from each other by means of thin viscous solid solution areas which raise the impact toughness of the material.
Thus we can conclude that to get the highest possible wear resistance and high impact toughness the heterophase material structure should correspond to the so-called Charpy rule which is the solid phase particles should be separated from each other by plastic ductile matrix areas.
The solid phase content in the wearing material structure produces a decisive effect on the abrasion resistance. In kolmkov and Pereverzev[4] it is shown how cementite particles in the 30%Cr-3%C-2%V steel diffuse layer structure influence its abrasion resistance, as shown in Fig. 1.
As shown in (Fig. 1) and under the influence of quartz sand the wear resistance of the cementite-contained material with small solid phase particles proportion (approximately up to 50%) in the structure is quite low (? = 1.5-3), it is practically in direct ratio to this phase content (area I is shown in Fig. 1). At a higher cementite proportion (more than 80%) in the wearing layer structure its wear resistance is intensively increasing (? = 40-100 and more) (area II is shown in Fig. 1).
When the proportion of solid inclusions in the material structure is low, the material abrasion mechanism corresponds to microcutting shows a wear particles split off the metal surface at one pass of an abrasive grain (a sand particle). At the high (large) solid phase proportion in the material structure multiple passes of abrasive grains are required to split off the same amount of wear particles from the wearing surface that is multiple elastic and plastic deformation of the material before its destruction.
The microstructure of the nitro-cementite layer of 30%Cr-3%C-2%V steel corresponding to the wear resistance ? = 50 (according to the scheme shown(in Fig. 1) is demonstrated in (Fig. 2).
The carbide (cementite) proportion on the surface is 80%; the relative wear resistance at quartz abrasion is? = 50 (the sample model is steel) (×500).
Thus to get high steel wear resistance under the influence of abrasive particles it is necessary to get the maximum quantity of carbides or other solid phases in the diffuse layers at the steel hardening (cementation). On the other hand carbides are known for their high brittleness and dynamic loading can cause their fracture and can decrease the hardening effect. To provide the high impact toughness rate of heterophase materials it is necessary to form some specific structure type that will be capable to resist abrasion as well as impacts at wear when hardening.
To determine the role of the carbide phase in the alloy abrasion resistance increase we have studied the plastic matrix deformation and carbide particles destruction connected with it, separation of the matrix and the carbide particles (interphase boarder pore formation) that is simple acts which compose abrasive wear.
In Ref. [5] the influence of spheroidized steel(1.05-1.47% of carbon) cementite particles and discovered that at its deformation there can be fractures on the boarder surface between a carbide particle and the matrix as well as carbide particles cracking. The pore formation on the separation boarders starts a big-sized particles and the same time there starts big-sized particles cracking. If for example the average size of all the carbide particles in the steel is 1.3 nm
of the steel under the chemical and heat treatment there will form the excess solid phase particles then on the surface of this steel there will be structure strain stresses and that has a great practical importance. While Ref. [8] showed that rapid cooling from 700 °C will cause a new Micro structure with a tensile tension due to difference in expansion coefficient for the Carbide and the Ferrite matrix.
Pereverzev and Bartenev [9] experimentally proved that as a result of the Cr-V-C steel cementation under the temperature of 920 °C there appeared a great quantity of excess cemetite and the strain residual stresses were formed; these stresses are 2 times higher than the same stresses in the non-cemented samples(Fig. 4).
Thus the experimental data proves that a low possibility of carbide particles separation as well as their splitting off under the influence of abrasive grains at wear exists.
When the solid phase particles proportion in the structure reaches the value when the tough destruction turns into brittle destruction (for cementite-typed particles this proportion is approximately 75%-80%)
p. 95.
[4] V.I. Kolmykov, V.М. Pereverzev, Wear process analysis of carbide hardened drills, Efficiency and Quality Increase of Kursk Magnetic Anomaly Subsurface Use, Voronezh: VSU, 1980, pp. 94-98.
[5] I. Gurland, Observation on the fracture of cementite particles in a spheroidised 1.05% c steel deformed at room temperature, Abta. Met. 20 (5) (1972) 735-741.
[6] L. Anand, I. Garland, Effect of internal boundaries on the yield strengths of spheroid zed steel, Met. Trans. 7 (2)(1976) 191-197.
[7] G. Gourland, Destruction of composites with disperse particles in metal matrix, Destruction and Fatigue, 1978, pp. 58-105.
[8] H. Stuart, N. Ridley, Thermal expansion of some carbides and tessellated stresses in steels, Iron and Steel Inst. 208(12) (1970) 1089-1092.
[9] V.B. Pereverzev, V.B. Bartenev, Influence of cementation technique on hardening stress distribution in steels, Surface Impregnation of Steels and Alloys, Minsk: BPI, 1977, pp. 66-68.
[10] V.I. Gumanov, L.А. Koiukhova, G.S. Kreimer, Effective surface energy and toughness of short alloys, Physics of Metals and Metal Science 38 (4) (1974) 843-849.
[11] J. Suchánek, V. Kuklík, Influence of heat and thermochemical treatment on abrasion resistance of structural and tool steels, Wear 267 (11) (2009) 2100-2108.
Received: November 07, 2011 / Accepted: December 01, 2011 / Published: April 25, 2012.
Abstract: The aim of this work is to give a scientific basis for the requirements specified for the structures of the iron-based materials(cemented and nitro-cemented steels, Surfaced coats, etc.), providing high wear resistance of these materials in Conditions of abrasive wear. The article represents results of the theoretical analysis of strength and wear resistance of the composite materials comprising hard particles inside a metal matrix, as well as experimental results of cementation of steels alloyed with carbide-forming
Key words: Cementite, abrasive wear, hypoeutectoid, heterophase.
1. Introduction??
The abrasive wear is the process of splitting off of metal particles from the wearing surface by means of abrasive grains. These grains, under the regular loading, penetrate into the metal surface and cut off the micros Warf from the surface when it is moving. Abrasive grains for metallic materials are particles with hardness higher than that of metal due to natural particles of mineral origin like quartz, granite, alumina, etc. Their distinctive characteristic is high hardness and high mechanical endurance. The most wide-spread natural abrasive is quartz sand with hardness equal to 10,000 MPa and its compression endurance is 280 MPa. This paper present analysis of abrasion resistance of metallic materials with cementite contained structures.
2. Result and Discussion
Splitting off of wear debris from the metal surface in the abrasive wear is caused by either single or multiple influences of abrasive grains on the metal volume unit. In the first case and in the friction zone the process of microcutting is realized. The second case takes a place
equations. In this sphere along with power factors there are also structure characteristics and fatigue properties of a wearing material which play the most important role in wear resistance rate determination.
There are a lot of works on wear which touch upon, such as Refs. [1, 2]. It is generally accepted that materials with multiphase (hetero phase) structure enriched with solid and refractory phases such as carbides, nitrides, borides, etc. which have the highest wear resistance.
Differences in wear resistance of such materials are determined by the type of inclusions, their quantity, size and form. Besides hetero phase structures wear resistance are influenced by the type of matrix metal and its properties, mainly by toughness and fatigue strength.
The analysis from Ref. [3] which give the results of built-up ferro-chromium alloys auxiliary properties test allow to get the idea of how metallic materials structures influence their wear resistance and impact toughness.
The microstructures of some alloys set according to the carbon proportion increase and their properties are given in (Table 1.) This table has been developed on the basis of Ref. [3].
The chemical composition of the materials(building-ups) given in Table 1 differs only in the carbon content; however, the structure and the properties of these materials are different. The hypoeutectoid alloys (No. 1 and No. 2 in Table 1) have low hardness and relatively low wear resistance but their impact toughness is very high, especially for an alloy No. 1 with the ferrito-pearlite structure.
The hypoeutectoid alloys (No. 3 and No. 5 in Table 1) with a solid carbide grid structure have higher hardness and wear resistance in comparison with the first alloys but their impact toughness is extremely low. Obviously their brittleness is caused by the fact that a destructive crack does not meet any tough areas resistance while passing through the carbide grid. The alloy No. 4 stays apart form the other considered materials as it has the highest hardness and wear resistance and at the same time its impact toughness rate is quite satisfactory. The mentioned alloy No. 4 possesses such a favourable combination of properties due to its specific structure.
As it can be seen on the microphoto given in Table 1 the structure of the alloy No. 4 consists of large carbide inclusions separated from each other by means of thin viscous solid solution areas which raise the impact toughness of the material.
Thus we can conclude that to get the highest possible wear resistance and high impact toughness the heterophase material structure should correspond to the so-called Charpy rule which is the solid phase particles should be separated from each other by plastic ductile matrix areas.
The solid phase content in the wearing material structure produces a decisive effect on the abrasion resistance. In kolmkov and Pereverzev[4] it is shown how cementite particles in the 30%Cr-3%C-2%V steel diffuse layer structure influence its abrasion resistance, as shown in Fig. 1.
As shown in (Fig. 1) and under the influence of quartz sand the wear resistance of the cementite-contained material with small solid phase particles proportion (approximately up to 50%) in the structure is quite low (? = 1.5-3), it is practically in direct ratio to this phase content (area I is shown in Fig. 1). At a higher cementite proportion (more than 80%) in the wearing layer structure its wear resistance is intensively increasing (? = 40-100 and more) (area II is shown in Fig. 1).
When the proportion of solid inclusions in the material structure is low, the material abrasion mechanism corresponds to microcutting shows a wear particles split off the metal surface at one pass of an abrasive grain (a sand particle). At the high (large) solid phase proportion in the material structure multiple passes of abrasive grains are required to split off the same amount of wear particles from the wearing surface that is multiple elastic and plastic deformation of the material before its destruction.
The microstructure of the nitro-cementite layer of 30%Cr-3%C-2%V steel corresponding to the wear resistance ? = 50 (according to the scheme shown(in Fig. 1) is demonstrated in (Fig. 2).
The carbide (cementite) proportion on the surface is 80%; the relative wear resistance at quartz abrasion is? = 50 (the sample model is steel) (×500).
Thus to get high steel wear resistance under the influence of abrasive particles it is necessary to get the maximum quantity of carbides or other solid phases in the diffuse layers at the steel hardening (cementation). On the other hand carbides are known for their high brittleness and dynamic loading can cause their fracture and can decrease the hardening effect. To provide the high impact toughness rate of heterophase materials it is necessary to form some specific structure type that will be capable to resist abrasion as well as impacts at wear when hardening.
To determine the role of the carbide phase in the alloy abrasion resistance increase we have studied the plastic matrix deformation and carbide particles destruction connected with it, separation of the matrix and the carbide particles (interphase boarder pore formation) that is simple acts which compose abrasive wear.
In Ref. [5] the influence of spheroidized steel(1.05-1.47% of carbon) cementite particles and discovered that at its deformation there can be fractures on the boarder surface between a carbide particle and the matrix as well as carbide particles cracking. The pore formation on the separation boarders starts a big-sized particles and the same time there starts big-sized particles cracking. If for example the average size of all the carbide particles in the steel is 1.3 nm
of the steel under the chemical and heat treatment there will form the excess solid phase particles then on the surface of this steel there will be structure strain stresses and that has a great practical importance. While Ref. [8] showed that rapid cooling from 700 °C will cause a new Micro structure with a tensile tension due to difference in expansion coefficient for the Carbide and the Ferrite matrix.
Pereverzev and Bartenev [9] experimentally proved that as a result of the Cr-V-C steel cementation under the temperature of 920 °C there appeared a great quantity of excess cemetite and the strain residual stresses were formed; these stresses are 2 times higher than the same stresses in the non-cemented samples(Fig. 4).
Thus the experimental data proves that a low possibility of carbide particles separation as well as their splitting off under the influence of abrasive grains at wear exists.
When the solid phase particles proportion in the structure reaches the value when the tough destruction turns into brittle destruction (for cementite-typed particles this proportion is approximately 75%-80%)
p. 95.
[4] V.I. Kolmykov, V.М. Pereverzev, Wear process analysis of carbide hardened drills, Efficiency and Quality Increase of Kursk Magnetic Anomaly Subsurface Use, Voronezh: VSU, 1980, pp. 94-98.
[5] I. Gurland, Observation on the fracture of cementite particles in a spheroidised 1.05% c steel deformed at room temperature, Abta. Met. 20 (5) (1972) 735-741.
[6] L. Anand, I. Garland, Effect of internal boundaries on the yield strengths of spheroid zed steel, Met. Trans. 7 (2)(1976) 191-197.
[7] G. Gourland, Destruction of composites with disperse particles in metal matrix, Destruction and Fatigue, 1978, pp. 58-105.
[8] H. Stuart, N. Ridley, Thermal expansion of some carbides and tessellated stresses in steels, Iron and Steel Inst. 208(12) (1970) 1089-1092.
[9] V.B. Pereverzev, V.B. Bartenev, Influence of cementation technique on hardening stress distribution in steels, Surface Impregnation of Steels and Alloys, Minsk: BPI, 1977, pp. 66-68.
[10] V.I. Gumanov, L.А. Koiukhova, G.S. Kreimer, Effective surface energy and toughness of short alloys, Physics of Metals and Metal Science 38 (4) (1974) 843-849.
[11] J. Suchánek, V. Kuklík, Influence of heat and thermochemical treatment on abrasion resistance of structural and tool steels, Wear 267 (11) (2009) 2100-2108.