Special features of strain aging of sheet automobile IFBH steel

Strain aging of commercial sheet automobile IF steels is investigated. The aging process is studied by measuring the dynamic modulus of elasticity, the amplitude-independent dislocation internal friction, the mechanical properties, and the microhardness. Analysis of the results obtained reveals the complex mechanism of strain aging of the steels. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 38–45, January, 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.     

Ductile-brittle transition in steels at near-solidus temperatures

A complex study of the nature of the little-investigated phenomenon of high-temperature brittleness of steels, i.e., the ductile-brittle transition observed in the temperature range t = (0.92–0.98)t _melt, is described. Regular features in the behavior of mechanical properties of low-alloy steels in this temperature range are considered. The effects of the chemical composition (carbon, impurities), preliminary plastic deformation, high-temperature annealing, and test medium on the mechanical properties are studied. Special features of the fracture mechanism at the studied temperatures are described. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 9–20, April, 2006.     

Carbide transformations in Cr−Mo steels in the process of long-term aging and operation

Chromium-molybdenum steels are widely used in machine-building as a material for pipes for different purposes. They operate at elevated temperatures for long durations and undergo structural changes that can worsen their mechanical properties. For this reason, it is interesting to study their structural changes as a function of the temperature and time of aging or operation in order to determine the regular features of the redistribution of the alloying elements in the process of phase transformations. The given work is devoted to carbide transformations in steels with different contents of chromium and molybdenum in the process of aging after heat treatment and in the process of long-term operation in industrial installations. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 9–13, September, 1997.     

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.     

Effects of Rare Earth Metals addition and aging treatment on the corrosion resistance and mechanical properties of super duplex stainless steels

Effects of rare earth metals addition and aging treatment on corrosion resistance and mechanical properties of super duplex stainless steels were investigated using optical/SEM/TEM metallographic examination, an X-ray diffraction test, a potentiodynamic anodic polarization test and a tensile test. The performance of the experimental alloy with 0.32% REM addition was compared with commercial super duplex stainless steel such as SAF 2507 when they were exposed to solution annealing heat treatment and aging treatment. The corrosion resistance in Cl⁻ environments and mechanical properties of the experimental alloy were found superior to those of the commercial duplex stainless steel. The REM with larger atomic radii than those of Cr, Mo and W may fill vacancies inside the matrix and around the grain boundaries, retarding formation of harmful intermetallic σ and η phases. In addition, fine REM oxides/oxy-sulfides (1–3 μm) seemed to enhance the retardation effects. With REM additions, strength and ductility increased due to the phase and grain refinement caused by fine REM oxides and oxy-sulfides.     

Role of mesostructure in thermomechanical treatment of metallic materials

The problem of formation of mesostructure appearing in various steels and alloys due to various modes of thermomechanical treatment (TMT) is discussed. The role of plastic strain in the formation of mesostructure and the relation between the changes in the crystal structure due to TMT and the mechanical properties of the steels are considered. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 30–34, January, 2007.     

Influence of Al-Ti-B addition on the microstructure and mechanical properties of A356 alloys

The mechanical properties (σb,σ0.2,and δ) and fracture behavior of tensile specimens of the refined A356 alloys were investigated as a function of the addition level of Al-Ti-B master alloy under both as-cast and T6 heat-treated conditions. The results show that as the addition level of Al-5Ti-1B master alloy increases from 0.1 wt.% to 5.0 wt.%,the mechanical properties of refined A356 alloys improve steadily and then decrease slightly under both as-cast and T6 heat-treated conditions. Also,they display exc...     

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 thermohydrogen treatment on mechanical and process properties of low-carbon steel

The effect of etching followed by dehydrogenation treatment on mechanical and process properties of thin hot-rolled normalized sheets from steel 10 and of cold-rolled sheets from steel 08kp is studied. Results of operating tests of the steels for bending strength and of mechanical tensile tests are described. Load-extension curves are plotted for the sheets in the state as delivered and after thermohydrogen treatment. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 25–27, June, 2007.     

Structure and properties of stainless steels subjected to severe plastic deformation

The physical, mechanical, and corrosion properties of stainless steels with microcrystalline and submicrocrystalline structures obtained with the use of different techniques of thermal deformation treatment are considered. A comparative study of formation of a dispersed structure in austenitic and ferritic steels is performed. The effect of the type of structure on mechanical properties is discussed. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 27–32, February, 2006.     

A study of thermal aging of steels for nuclear power plant reactor vessels aimed at prolonging the service life of the equipment to 60 years

The effect of thermal aging in the range of 250–400°C on the critical brittle point of pearlitic steels for nuclear power plant reactor vessels is studied. The structural mechanisms of the embrittlement of the steels are investigated by determining the activation energy. Methods are suggested for predicting the shift of the critical brittle point due to thermal aging of vessel steels for determining the design service life of nuclear power plants of a new generation. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 23–27, July, 2006.     

Structure and properties of low-carbon martensitic steels

Sudies begun in the 1960s under the guidance of R. I. éntin at the Institute of Metal Physics of the Bardin Central Research Institute of Ferrous Metals have shown that high stability of low-carbon austenite in both the “normal”² and bainite regions can be provided at a specific proportion of carbon and the alloying elements. The starting temperature of martensite transformationM ₅ remains at 300–400°C. This makes it possible to obtain in steels the structure of lath martensite in large cross sections by air cooling. These low-carbon martensite steels (LCMS) possess a favorable combination of mechanical properties and a number of technological advantages even in the quenched state, which widens their range of application in industry. In recent years several new groups of LCMS have been created. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 46–48, August, 1999.     

Effect of combined treatment on the stability of austenite and the mechanical properties of chromium-manganese steels

The phase composition, the stablity of austenite with respect to the γ→α′ transformation under a load, and the mechanical properties in torsion of Cr−Mn steels 17Kh13G7S, 20Kh14G7, and 40Kh14G7 with metastable austenite after straining and heat treatment by various regimes are investigated. Methods for a combined treatment of Cr−Mn steels are suggested in order to provide a high level of their strength and ductility properties. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 18–21, January, 1997.     

Structural inheritance and special features of fracture of high-speed steels

Interest in the problem of improving the mechanical properties of high-speed steels has increased due to newly opened opportunities to manufacture inexpensive cast tools by utilizing waste of grinding production. Modification is a simple and effective means of improving the properties of cast alloys of various classes. The present paper is devoted to the effect of structural inheritance on the properties of high-speed steels. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 9–11, February, 1997.     

Microstructure and mechanical properties of welded joints of NPP pipelines after long-term operation

The microstructure and mechanical properties of welded joints of cuts from Du 300 and Du 500 pipelines of the Leningradskaya and Novovoronezhskaya nuclear power plants are studied after 70 and 100 thousand hours of operation. The effects of thermal aging simulating operational impact on the microstructure and properties of welded joints of the cuts and of a model coil are determined. It is shown that long-term operation can be accompanied by embrittlement and decrease in the crack resistance of the metal of welds in Du 300 and Du 500 pipelines produced from steels 08Kh18N10T and 08Kh18N12T. The discovered changes in the microstructure can lead to deterioration of the mechanical properties of the metal of welded joints in operation of Du 300 and Du 500 pipelines. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 36–42, July, 2006.     

Effect of the aging regime on the hardness and amount of γ-phase in high-temperature nickel alloys KhN56VMTYu and KhN77TYuR

It is known that the properties of high-temperature nickel alloys depend considerably on the amount of γ'-phase, which is determined, first of all, by the aging, regime. In order to evaluate the properties of these alloys it is expedient to establish the relation between the parameters of the aging regime and the amount of γ'-phase or, which is even more important, between the aging parameters and the mechanical properties. The present paper concerns high-temperature nickel alloys KhN56VMTYu and KhN77TYuR, which are used to establish the relations between the amount of γ'-phase, the hardness, and its increment due to aging and the aging temperature. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 27–30, November, 1997.     

Special features of the formation of microstructure of heat-treated low-alloy steel

The strength and the operational properties of low-alloy thick-sheet steels is increased by heat treatment in the line of the mill with the use of the rolling or furnace heat. The present work concerns the special features of structure formation and the mechanical properties of rolled stock from sheet structural steel 09G2S with a strength level C345 (σ_y=325-345 MPa) in a hot-rolled and a normalized state after accelerated cooling from the normalizing furnace and after rolling behind the finishing stand. As a result of the rapid cooling in the line of the mill the sheet acquires properties corresponding to steels with a C390–C440 strength level (σ_y=390-440 MPa). Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 9–11, August, 1998.     

Mechanical properties of injection molded Fe-6% Ni-0.4% C steels with varying Mo contents of 0.5 to 2%

In our previous studies, sintered and heat-treated alloy steels (Fe−6Ni−0.5Mo−0.4C (mass%)) produced by a MIM process showed excellent mechanical properties of 2000 MPa tensile strength and 5% elongation. This was attributed to the solid solution strengthening and the mezzo-heterogenous microstruture, which consisted of martensite or retained austenite (Ni and Mo rich phases) surrounded by a network of tempered martensite. This study has been performed to clarify the effect of Mo on the mezzo-heterogeneous microstructure and the mechanical properties of MIM processed and sintered alloy steels (Fe−6Ni−0.4C) with varying Mo content (0.5–2 mass%). The tensile properties of the heat-treated steels with added 2 mass% Mo were lower than those of the steels with added 0.5 mass% Mo. The reduction in the tensile properties, particularly the appearance of large pores formed at the original location of Mo power through the transient liquid phase formation and the low hardness of the matrix, was due to the low sintered density. By using mechanically milled fine Ni and Mo powders, the heat-treated steel (Fe−6Ni−2Mo−0.4C) showed excellent properties, including tensile strength of 1800 MPa and ductility of 2.2% elongation. This article is based on a presentation made in the symposium “The 3rd KIM-JIM Joint Symposium on Advanced Powder Materials”, held at Korea University, Seoul, Korea, October 26–27, 2001 under auspices of The Korean Institute of Metals and Materials and The Japan Institute of Metals.     

Deformation-plastic behavior of highly irradiated stainless steels 12Kh18N10T and 08Kh16N11M3 at cryogenic and elevated temperatures

In the temperature range from −115 to +120°C, mechanical tests of samples of austenitic stainless steels 12Kh18N10T and 08Kh16N11M3—materials for the casings of spent fuel assemblies of a reactor BN-350 irradiated by neutrons to damaging doses of 11–55 dpa—have been carried out. In the range of cryogenic temperatures, in these highly irradiated steels there was discovered and investigated a new phenomenon—a “wave of plastic deformation,” which consists in the initiation, development, and propagation of a deformation band over the length of the sample, which leads to a possibility of reaching total relative deformation of 20% and greater, instead of 3–5% usually observed at given damaging doses. The role of a martensitic γ → α′ transformation in the formation of the “wave” and in the improvement in the mechanical properties of the metastable steel irradiated by neutrons is discussed.