Metal Science and Heat Treatment最新文献

Current problems of metallurgical and mechanical engineering enterprises that use heat treatment in their production are considered. An example of vacuum carburizing is used to consider the options for solving the problems using information systems. An example of successful operation of information systems in furnace units is presented.

The effect of plastic deformation of steel C70D and different modes of spheroidizing annealing after drawing on the mechanical properties and microstructure is studied. The suitability of the wire for certification to meet the special requirements of the user is assessed. After experimental fivefold drawing of the wire with diameter 3.7 mm and processing of the data of the mechanical tests, a reliable linear regression equation is obtained for determining the change in the tensile strength (σ_r) of the wire as a function of the total reduction, which makes it possible to estimate the hardening factor of the wire material. To reduce the strength of the cold-drawn wire to the demanded values of σ_r ≤ 650 MPa, the spheroidizing annealing mode is selected to be 710°C for 6 h, which provides the required grade of granular pearlite in the steel structure according to TU 14-178-110–89.

The effect of the final rolling temperature during the thermomechanical treatment process on the microstructure and mechanical properties of high-strength Ti – Zr composite microalloyed steel plate was studied using TEM, SEM, EBSD, optical microscopy and tensile tests. It has been shown that the final microstructure of Ti – Zr composite microalloyed steel with isothermal exposure at 600°C consists of polygonal ferrite and acicular ferrite when the final rolling temperature is in the range of 1000 – 850°C. Adecrease in the final rolling temperature promotes the formation of acicular ferrite in the steel structure, the average ferrite grain size is refined, and the uniformity of the structure increases. As a result, the yield strength and tensile strength of the steel increase with a slight change in elongation. It has been established that with a decrease in the final rolling temperature, the recrystallization of deformed austenite is inhibited, resulting in an increase in dislocation density, promoting strain-induced precipitation in the austenite of (Ti, Zr)C, and reducing the number of fine TiC precipitates in the ferrite. The quantitative analysis of strengthening mechanisms shows that the changes in final rolling temperature mainly affect the contribution of fine grain strengthening, dislocation strengthening, and precipitation strengthening to strength.

The microstructure, mechanical properties and corrosion resistance of promising medical Zn – 1% Mg – 0.1% Dy and Zn – 1% Mg – 0.1% Mn alloys after high-pressure torsion (HPT) are studied. It is shown that the HPT results in formation of an ultrafine-grained structure of α-Zn with grain size 450 – 700 nm in both alloys. The grain-boundary magnesium phase is refined to a nanosize and Mn- and Dy-enriched particles are precipitated. This refinement of the structure leads to a simultaneous increase in the strength and ductility of both alloys without changing their corrosion resistance. At the same time, the corrosion rate of the alloys both before and after the HPT does not exceed 0.35 mm/year.

The effect of combined processing by rotary swaging at room temperature followed by equal-channel angular pressing at 150°C and subsequent aging on the structure, phase transformations and strength characteristics of Al – Mg₂Si alloys with Sc and with joint additions of (Sc + Zr) and (Sc + Hf) is studied. The results obtained are used to recommend the aging modes for alloys in the initial state and after the combined processing to ensure an increase in their strength and ductility. The best set of mechanical characteristics is obtained for the Al – Mg₂Si – (Sc + Hf) composition.

The microstructure of coatings obtained by cold spraying of stainless and copper wires onto steel St3 (A284Gr.D) and aluminum alloy D16AT (2024), respectively, is studied. A newly developed facility is used for depositing the coatings, which differs from the existing counterparts in the method of creation of additional layer and in the weight and size characteristics. The thickness of the sprayed layer is 0.2 – 0.3 mm. The structure of the coating is nonuniform due to the difference in the spraying rates of the finely dispersed components blown from the welding arc.

The effect of isothermal annealing on the microstructure and mechanical properties of hypereutectoid steel U10A(W110, AISI/ASTM) for subsequent cold plastic deformation by rolling is studied. To increase the ductility of the steel, an isothermal annealing mode is suggested, which ensures satisfactory deformability during cold rolling. After such annealing and subsequent rolling with a relative reduction of 67%, the steel has the tensile strength values no lower than 1270 MPa as required for high-strength cold-rolled strips according to GOST 21996–76 and a hardness no lower than 375 HV without the risk of damage to the rolling rolls.

The influence of various heat treatment modes on the structure, mechanical and thermal properties of 51CrV4 steel was studied. The steel was quenched in two different cooling environments and then tempered at different temperatures. After all heat treatment modes, the structure of the steel was analyzed using the SEM-EDS method and the hardness of the steel was measured, and its thermal properties were determined using the xenon flash method. Based on the results of experiments, it is recommended to use quenching in an oil bath at room temperature, followed by low or medium tempering. This heat treatment regime provides an increase in thermal diffusivity and thermal conductivity coefficient with a slight decrease in the hardness of 51CrV4 steel.

The phase composition and mechanical properties of corrosion-resistant steels with 15 wt.% Cr for the production of pipes used for utilization of carbon dioxide by injecting it into absorption wells are studied. The Thermo-Calc software is used to simulate the phase composition of the steels at different temperatures with allowance for variations of the alloying elements. The dilatometric method is used to find the critical points of the steels during heating and cooling. The mechanical properties of the steels after quenching and tempering are determined. The possibility of formation of an advanced combination of properties (strength, ductility, viscosity and cold resistance) is demonstrated.

The mechanical properties and deformation characteristics of steel 08Mn2Nb manifesting different magnitudes of the effect of strain aging after the heat treatments with heating at 250°C (τ = 30 min) and air cooling and heating at 680°C (τ = 30 min) and water cooling are studied. It is shown that despite the significantly different strength and ductility properties of the steel after the two treatment modes, it is deformed in the yield plateau according to the same Luders mechanism. The mechanism involves emergence and growth of nucleating centers and nuclei of localized strain bands, their intersection at the center of the sample and formation of initiating centers. Tracing of the parameters that determine the initiating stress of the sources emitting dislocations of planar series, which form the growing nucleus of the band, has made it possible to explain the influence of various factors on the top and bottom yield points in the region of the yield drop. The conditions of implementation of the band deformation mechanism and its combination with distributed deformation, in which dislocations propagate simultaneously in different slip systems, are analyzed.