International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

The article presents a comparison of different computational approaches used to study the surface treatment of a NiCrMoV steel with 0.55% Carbon content by a plasma jet. Metallographic observations show formation of martensite layer due to high cooling rate by heat transfer into the bulk steel. Heat affected zone (HAZ) was 1 mm deep and 10-12 mm wide. The treated surface maximum hardness was measured at 763 HV0.1 whereas untreated steel was at 210 HV 0.1. The computation indicates a hardening sink near the surface that went undetected in the experimental observations. The ability of the different computational approaches to explore the process related phenomena and to give reliable results is put into discussion.

Phase transformations in metals have a major influence on the material behaviour in several common engineering applications. Steels exhibiting enhanced response to transformation-induced plasticity (e. g. high strength TRIP-steels for automotive production) are examples of the important role martensite formation can play. An externally stressed specimen in the process of a phase transformation may show a significant nonlinear behaviour, which is known as transformation plasticity. Even under an externally applied load stress with the corresponding equivalent stress being small in relation to the “normal” yield stress of the material, plastic deformation occurs.
An aim of a research was to determine relaxation and transformation plasticity properties of alloyed tool steel while is tempered at elevated temperatures and for different tempering duration.

This study aims to optimize the heat treatment of tool steel 75Cr1 which is used for heavy loaded elements in transmissions. A salt bath was used to quench and temper the steel at different temperatures. Mechanical tests and microstructural characterization were done to define the heat treatment parameters corresponding to the optimal performance of the elements. Optical microscopy, electron back scatter diffraction and x-ray diffraction were used to characterize the microstructure, while tensile tests and toughness tests were employed to determine the mechanical properties after different heat treatments. It was found that the yield strength decreases with increasing annealing temperature and that the toughness decreases with increasing annealing time and temperature. The changes of the mechanical properties are discussed in relation with the thermal treatment and the corresponding microstructures.

The present study aims to determine the optimum temperature regime for oxy-nitrocarburizing of AISI D2 steel in order to ensure high mechanical properties of both diffusion and compound zones. The examined samples are quenched and high temperature tempered in advance, thus having a hardness equivalent up to HRc 54-55 before saturation. The vacuum oxy-nitrocarburizing is held at temperatures of 500 ºС, 550 ºС and 590 ºС for 4 hours in a cycling gas flow rate. The proportion of NH₃ and CO₂ gases used is 90:10 volume fractions. The results of the examination are based on the analysis of X-ray diffraction patterns, cross-section microstructures and measurements of micro-hardness values on the surface and in depth of the diffusion zone. The core hardness of the substrate is also measured after the vacuum process for the purpose of establishing a possible hardness decrease after the oxy-nitrocarburizing process. Conclusions have been drawn in relation to the practice.

The results of studies of the influence of the type of machining and tool material to the structural state of the surface layer and the fatigue strength of ХВСГsteel during machining are shown. Processing with the composite-10 tool in a surface layer for α – and γ – phases is accompanied only by compressing residual pressure while abrasive processing promotes occurrence of stretching pressure of an I-type. Increasing of cutting speed of the composite-10 tool from 50 to 200 m/min does not lead to significant changes in fatigue strength.