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

A technique for determining the generalized degree of covalence of the interatomic Fe – C bond is proposed by the addition rule taking into account the fractions of Fe2C, Fe4C and Fe6C clusters and cementite in steel. The correlation dependence of the generalized degree of covalence of the interatomic Fe – C bond with the hardness of microstructures observed in eutectoid carbon steel, as well as the hardness of ferrite and cementite, is revealed. A functional relationship between the generalized degree of covalence of the Fe-C interatomic bond and the martensite hardness at different mass content of carbon is established, which ensures the correspondence of the
calculated and experimental data.

This study explores the metal of a coating deposited by a high-chromium flux-cored wire alloyed with a BN-TiB2-ZrB2 complex. We investigated the changes in the durometric properties and fine structure of the coating after tempering and subsequent quenching. It is shown that the hardening of the metal of such a coating after quenching consists in the formation of a complex composite structure with an iron-chromium martensitic matrix, a large amount of eutectic and particles of hardening complexes, which leads to an increase in hardness and wear resistance. It has been established that phase transformations in the metal of such a coating are caused by the formation of an eutectic component based on chromium and iron borides, a framework structure and a large number of dispersed titanium nitride particles up to 2.5 μm in size.

The research paper presents the improvement on the mechanical and service properties of the austenitic stainless 0.07% C-17% Cr-9% Ni-0.7%-Ti steel in the fully austenitic state obtained by equal-channel angular pressing (ECAP) at the temperatures of 200 °C and 400 °C. Subgrain oriented structure in the Cr-Ni-Ti steel after ECAP significantly enhances the strength characteristics of steel at satisfactory plasticity. The fatigue limit of steel after ECAP at T = 200 ° C is higher than that after ECAP at T = 400 ° C, increasing in comparison with the initial state by 2.2 and 1.7 times, respectively. It was revealed that severe plastic deformation by ECAP increases the friction coefficient of the material by the 1.1 and 1.7 times at T = 200 ° C and 400 ° C, respectively. Despite this, the wear rate after ECAP at T = 200 ° C and 400 ° C decreases by 7 and 40 times, respectively, compared to initial state.

In the present work, in order to evaluate the metastable structural state of high-strength steel immediately after the phase transformation as well as during the following tempering, the SEM-based EBSD is employed. The lattice orientation gradient in the alfa-phase of steel is mapped by a standard GAM function (“grain average misorientation”) that makes it possible to identify various types of martensite and bainite distinguishable in the dislocation density and phase stresses. The GAM sensitivity to the crystal curvature not only allows one to tell between different types of alfa-phase in the non-equilibrium quenched state but also reveals their change during tempering.

Basic idea in this metallographic investigation is checking the effect of induction (surface) quenching of produced part, two-side lever made of 42CrMo4 steel. This part is build in railway wagon. According its production assignation it has to be surface hardened just in some positions. Formerly surface hardness of this part was realized by chemical-heat treatment i.e. case hardening of 16MnCr5 steel. But because of specific form of the part and increased britlness which appear in the thinnest parts of lever (between the rounded opening and the surface) and idea was obtained to change the case hardening with induction quenching. Efficiency of performed induction quenching i.e. hardness values and depth of quenched layer was controlled by optical microscopy and hardness measurement.

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.