Effect of alloying and heat treatment on the structure and tribological properties of nitrogen-bearing stainless austenitic steels under abrasive and adhesive wear

The effect of nitrogen, silicon, and aging modes on the structure, resistance to abrasive and adhesive wear, friction factor, and mechanical properties of nitrogen-bearing (0.27–0.83% N) chromium-manganese austenitic steels is studied. It is shown that it is possible to ensure a favorable combination of mechanical and tribological properties in such steels by choosing the appropriate chemical composition and aging mode. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 9–18, May, 2007.     

Structural transformations,strengthening, and wear resistance of titanium nickelide upon abrasive and adhesive wear

Wear resistance and structural transformations upon abrasive and adhesive wear of titanium nickelide Ti49.4Ni50.6 in microcrystalline (MC) and submicrocrystalline (SMC) states have been investigated. It has been shown that the abrasive wear resistance of this alloy exceeds that of the steel 12Kh18N9 by a factor of about 2, that of the steel 110G13 (Hadfield steel), by a factor of 1.3, and is close to that of the steel 95Kh18. Upon adhesive wear in a testing-temperature range from −50 to +300°C, the Ti49.4Ni50.6 alloy, as compared to the steel 12Kh18N9, is characterized by the wear rate that is tens of times smaller and by a reduced (1.5–2.0 times) friction coefficient. The enhanced wear resistance of the Ti49.4Ni50.6 alloy is due to the development of intense strain hardening in it and to a high fracture toughness, which is a consequence of effective relaxation of high contact stresses arising in the surface layer of the alloy. The SMC state produced in the alloy with the help of equal-channel angular pressing (ECAP) has no effect on the abrasive wear resistance of the alloy. The favorable effect of ECAP on the wear resistance of the Ti49.4Ni50.6 alloy takes place under conditions of its adhesive wear at temperatures from −25 to +70°C. The electron-microscopic investigation showed that under conditions of wear at negative and room temperatures in the surface layer (1–5 μm thick) of titanium nickelide there arises a mixed structure consisting of an amorphous phase and nanocrystals of supposedly austenite and martensite. Upon friction at 200–300°C, a nanocrystalline structure of the B2 phase arises near the alloy surface, which, as is the case with the amorphous-nanocrystalline structure, is characterized by significant effective strength and wear resistance.     

Effect of the carbide phase on the tribological properties of high-manganese antiferromagnetic austenitic steels alloyed with vanadium and molybdenum

Effect of special carbides (VC, M ₆C, Mo₂C) on the wear resistance and friction coefficient of austenitic stable (M _s below −196°C) antiferromagnetic (T _N = 40–60°C) steels 80G20F2, 80G20M2, and 80G20F2M2 has been studied. The structure and the effective strength (microhardness H _surf, shear resistance τ) of the surface layer of these steels have been studied using optical and electron microscopy. It has been shown that the presence of coarse particles of primary special carbides in the steels 80G20F2, 80G20M2, and 80G20F2M2 quenched from 1150°C decreases the effective strength and the resistance to adhesive and abrasive wear of these materials. This is caused by the negative effect of carbide particles on the toughness of steels and by a decrease in the carbon content in austenite due to a partial binding of carbon into the above-mentioned carbides. The aging of quenched steels under conditions providing the maximum hardness (650°C for 10 h) exerts a substantial positive effect on the parameters of the effective strength (H _surf, τ) of the surface layer and, correspondingly, on the resistance of steels to various types of wear (abrasive, adhesive, and caused by the boundary friction). The maximum positive effect of aging on the wear resistance is observed upon adhesive wear of the steels under consideration. Upon friction with enhanced sliding velocities (to 4 m/s) under conditions of intense (to 500–600°C) friction-induced heating, the 80G20F2, 80G20M2, and, especially, 80G20F2M2 steels subjected to quenching and aging substantially exceed the 110G13 (Hadfield) steel in their tribological properties. This is due to the presence in these steels of a favorable combination of high effective strength and friction heat resistance of the surface layer, which result from the presence of a large amount of special carbides in these steels and from a high degree of alloying of the matrix of these steels by vanadium and molybdenum. In the process of friction, there are formed nanocrystalline austenitic structures possessing high effective strength and wear resistance on the wear surface of these steels.     

Effect of the rigidity of the stress state on the wear resistance of materials in hydraulic and impact abrasion wear

In the process of use many parts are subjected to the impact action of abrasive particles contained in a flow (jet) of gas or liquid and ones present on the contacting surfaces in the form of an abrasive layer. Despite the large number of publications devoted to problems of wear of parts, no universal criterion has been developed for evaluating the wear resistance of materials operating under various wear conditions. The present work concerns hydraulic and impact abrasion of various steels and alloys of nonferrous metals. In establishing the dependence of the wear resistance of the studied materials on their properties the authors take into account for the first time the rigidity of the stress state of the worn surface, which allows them to explain the special features of the behavior of the materials when subjected to various kinds of abrasion wear. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 22–30, April, 1997.     

Fundamental principles for choosing steels on the basis of results of wear tests

The development of scientific foundations for the creation of new high-strength steels with high wear resistance and their application is a very important problem of modern engineering. The difficulties of its solution are connected with the absence of methodological foundations for a reliable estimation of the wear resistance. The fundamental scientific principles for control over this characteristic with allowance for the structural changes and the corresponding changes in the mechanical properties of steels have not been developed. The place of this characteristic and its relationship with the structure in the theory of fracture of materials under various loads has not been determined yet. At the same time, the wear resistance is a parameter that can characterize the operational reliability of steels under various conditions. However, the methods for determining the wear resistance should be substantiated experimentally and theoretically. The aim of the present work consisted in choosing steels for parts operating under the conditions of composite loads and abrasive wear. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 28–30, February, 1998.     

Effect of laser treatment on the wear resistance of steels

It is known that laser hardening increases the wear resistance of friction parts quite substantially. At the same time, many problems connected with the effect of the treatment process and the special features of laser hardening on the characteristics of wear resistance require detailed consideration. The present paper is devoted to the development of recommendations on choosing the optimum location and proportion of the areas of the hardened and unhardened regions of the surface of structural steels after their treatment with radiation of a continuous CO₂ laser. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 10–12, October, 1998.     

Effect of ion nitriding on the abrasive wear resistance of ultrahigh-strength steels with different silicon contents

This article studies the effect of silicon (Si) on ultrahigh-strength AISI 4340 steels in connection with the thermal treatment, as well as the influence of this element on nitriding and, consequently, abrasive wear. Four alloys with different Si contents were nitrided at 350 °C (4 and 8 h) and 500 and 550 °C (2 and 4 h) in a gas mixture of 80 vol.% H₂ and 20 vol.% N₂. The nitrided layers were characterized by microhardness and pin-on-disk tests, optical microscopy, scanning electron microscopy with energy-dispersive x-ray spectrometry, and x-ray diffraction (XRD). The increase in Si enhanced the tempering resistance of the steels and also improved considerably the hardness of the nitrided layers. The increase in Si produced thinner compound layers with better hardness quality and high abrasive wear resistance. XRD analysis detected a mixture of nitrides in the layers γ′-Fe₄N, ε-Fe_2–3N, CrN, MoN, and Si₃N₄ with their proportions varying with the nitriding conditions.     

Isothermal decomposition of supercooled austenite in chromium-nickel steel-copper pseudoalloys

The industries of developed countries widely use alloy steel-copper pseudoalloys. In copper-infiltrated steels the strength, ductility, and wear resistance increase due to the creation of a structure with a greater proportion of metastable austenite. Such a structure can be obtained by a substantiated choice of the composition, concentration inhomogeneity, and appropriate heat-treatment regime of the material. The present paper is devoted to the decomposition of supercooled austenite in chromium-nickel steel-copper pseudoalloys with an optimum distribution of the alloying additives. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 11–14, January, 2000.     

Slurry Erosion Studies on Surface Modified 13Cr-4Ni Steels: Effect of Angle of Impingement and Particle Size

Hydroturbine steels, such as 13Cr-4Ni martensitic steels, are generally subjected to heavy-erosive wear and loss of efficiency due to solid particulate entrainment in the water. Surface-modified steels have proven to give better performance in terms of erosive wear resistance. In the present study, an attempt is made to investigate the effect of angle of impingement and particle size on slurry-jet erosion behavior of pulsed plasma nitrided and laser hardened 13Cr-4Ni steels. Laser hardening process has shown good performance at all angles of impingement due to martensitic transformation of retained austenite. Plastic deformation mode of material removal was also an evident feature of all laser-hardened surface damage locations. However, pulsed-plasma nitrided steels have exhibited chip formation and micro-cutting mode of erosive wear. Erosion with 150-300 μm size was twice compared to 150 μm size slurry particulates.     

Decomposition of supercooled austenite of powder phosphorus steels

The structure of powder phosphorus steels is investigated. New models of isothermal decomposition of super-cooled austenite are suggested which make it possible to predict the kinetics of the γ→α transformation in the pearlite and bainite temperature ranges. It is shown that mechanical alloying has a favorable effect on the formation of structure in steels. Grain disintegration accelerates the decomposition of austenite mainly due to the growth of the specific surface. At the same time, the contribution of 0.65–1.1% phosphorus additives to the process is low. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 3–7, May, 1999.     

Dependence of the recrystallization of austenite in boron steel 20G2R on the processes of temperature and strain treatment

Sparingly alloyed boron steels like 20G2R, 35G1R, 30KhR, 30G1R that contain a low amount of boron (0.001–0.005%), titanium (0.02–0.05%), and aluminum (0.02–0.05%) can be promising substitutes for steels 38KhA, 38KhGNM, and 40Kh used traditionally for the production of high-strength industrial holders and fasteners. The operational characteristics of boron-bearing steels are in many cases no worse or even better than the properties of steels alloyed by more expensive elements. The present paper describes the processes of austenite recrystallization in boron steel 20G2R under high-temperature straining with controlled cooling and in controlled rolling. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 12–13, February, 1998.     

New concept of the mechanism of intergranular corrosion of stainless steels

The electronic structure of chromium-nickel austenite stainless steels of type X20H20 and X10H20, in particular, added with 4 to 6% Si, is studied using nuclear γ-resonant (M?ssbauer) spectroscopy. The structure varies significantly depending on the chromium and silicon content. Low-chromium steels are used for the modeling of chromium-depleted boundary zones that neighbor chromium-rich excess phases. Eventually, a mechanism of the intergranular corrosion of stainless steels that takes into account the changes in the electronic structure of the chromium-depleted boundary zones is first suggested. These changes in the chemisorption interaction of the iron carcass ions with corrosive components of the medium, cannot but affect the zones’ stability. It is this interaction that synergistically intensifius the intergranular corrosion of austenite stainless steels containing combinations of silicon dopant and carbon impurity, or the phosphorus and carbon impurities. Original Russian Text ? O.V. Kasparova, Yu.V. Baldokhin, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 3, pp. 256–261.     

Raising the heat and wear resistances of hardened carbon steels by friction strengthening treatment

The effect of friction treatment by a hard-alloy indenter on the microhardness and resistance to the heat-induced softening upon tempering of hardened medium-and high-carbon steels at 100–600°C is studied. The x-ray and electron microscopy methods are used to determine the causes of the increase in the heat resistance of the friction-strained steel surfaces. A comparative analysis of the effect of the hardening treatment by a hard-alloy indenter and by abrasive particles on the friction-induced heat resistance is performed for the case of high-speed friction treatment of a high-carbon laser-hardened steel. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 57–62, March, 2007.     

Phase composition and hardening of steels of the Fe-Cr-Ni-Co-Mo system with martensite-austenite structure

The phase composition and mechanical properties of maraging steels of the Fe-Cr-Ni-Co-Mo system are studied as a function of the alloying and of the temperatures of quenching and aging. The intermetallic phases strengthening martensite in different aging stages are determined. The degree of the hardening and the variation of the impact toughness at cryogenic temperatures are compared for steels with different structures (martensite and martensite-austenite) in the stages of maximum hardening and overaging. The effect of retained and reverted austenite on the resistance to crack propagation under impact loading is determined for steels with martensite of a different nature and amount of hardening phases. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 32–37, April, 2007.     

碳含量对铌微合金化高碳钢制金属针布耐磨性的影响

通过微合金原理,设计了3种含0.8%~1.0%碳及0.03%~0.04%铌的高碳钢。结果表明,碳含量增加可完全消除网状渗碳体,并使更多的碳在热处理加热时固溶于奥氏体中,从而获得更高的淬火硬度。对比不同碳含量钢的淬火显微组织,当碳含量为0.90%时,马氏体基体可以在获得最高硬度的同时保持超细晶粒。由此制造的梳理针布的平均齿尖硬度可以达到841 HV0.2, 晶粒度可以达到13.5级。通过快速磨损试验以及客户现场试验,针布的耐磨性相对于高端针布钢材80WV提高约30%。     

Isothermal decomposition of austenite in concentration-inhomogeneous nickel steels

Current research in the field of powder structural steels is connected with the development of manufacturing methods and obtaining structures that provide mechanical properties comparable to or exceeding the conventional level under minimum heat treatment. The main alloying element in powder steels is nickel. It is chosen due to a number of special features of it, including its availability, a low affinity for oxygen, simultaneous elevation of virtually all mechanical properties when used as an additive to a steel, and deceleration of the γ→α transformation in the pearlitic and bainitic regions of the decomposition diagrams of supercooled austenite. The present work is aimed at studying the isothermal decomposition of austenite in concentration-inhomogeneous nickel powder steels. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 20–24, May, 1998.     

Effect of the structure of babbit B83 on the intensity of wear of tribocouplings

The effects of thermal deformation treatment and of modification of the friction surface by composite coatings on the wear resistance of B83 babbit antifriction alloy used in highly loaded friction couplings is studied. It is shown that the creation of a fine-grained structure uniformly saturated with fine dispersed inclusions decreases considerably the wear intensity. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 44–46, February, 2006.     

Influence of Ni Content on Dry Sliding Wear Behavior of Sintered and Carburized Steels

The dry sliding wear behavior of two sintered and carburized steels with different Ni amounts has been investigated. The microstructure of the two steels comprises martensite, bainite, and the Ni-rich austenite. Under the sliding conditions investigated, wear is either oxidative or adhesive. In both cases, the lower amount of the soft Ni-rich austenite results in a better wear resistance. A design procedure for parts subject to dry sliding wear applications is proposed, based on the maximum acceptable wear depth, in order to evaluate the practical significance of the differences between the two materials.     

High-strength crack-resistant concentration-inhomogeneous powder nickel steels

Conclusion The transformation of metastable austenite into strain martensite in concentration-inhomogeneous powder nickel steels under a load promotes an increase in their strength and crack resistance. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 28–32, November, 1999.     

Effect of the severe plastic deformation and aging temperature on the strengthening,structure, and wear resistance of a beryllium bronze

The effect of the aging temperature, severe plastic deformation by equal-channel angular (ECA) pressing at 400°C, and subsequent aging on the rate of wear, friction coefficient, and microhardness of a commercial beryllium bronze Br.B2 quenched from 800°C has been investigated. The bronze structure before and after tribological tests has been studied with the help of metallographic and electron-microscopic methods of analysis. It has been shown that tempering (aging) of the bronze at 250–400°C for 3 h leading to a sharp growth of the hardness substantially increases the wear rate of the bronze in pair with the steel 45 under the conditions of both dry and boundary sliding friction. The cause of this is a decrease in the toughness of the surface layer of the bronze due to the precipitation of particles of the strengthening γ′ phase (CuBe) from the α solid solution. Severe plastic deformation (ECA pressing) markedly enhances the wear resistance of the bronze subjected to subsequent aging at 250–400°C. This is because ECA pressing favors the formation of an extremely dispersed nanocrystalline structure with α-phase crystals 40–50 nm in size at the wear surface of the bronze; whereas in the friction zone of the quenched bronze or the quenched and aged bronze, there arises a significantly less dispersed structure with matrix crystals to 300 nm in size. It has been assumed that under conditions of the rotational mechanism of plastic deformation operating upon sliding friction in the near-surface layer of the bronze, the increase in dispersity of its structure attained by using ECA pressing enhances the toughness and, correspondingly, wear resistance of the aged bronze.