Mathematical modelling of joint reliability indicators taking into account complex formation of surface quality metrics and physical and mechanical properties of functional surface materials

The article deals with the problems of engineering support of the main indicators of reliability (durability) for the shape elements of molds. The influence of geometric, physico-mechanical, and physico-chemical parameters of surface quality on the formation of the required service characteristics of mating parts that ensure the established operating time of the product for failure is studied. The results of the influence of ion-plasma treatment on the structure and phase composition are presented: 1.2344 and 1.2379 tool steels (DIN). It is evaluated that the glow discharge treatment leads to the erosion of the fingerprints, appearing in the process of nitriding of this type of steel and it also causes thickening of defects in the matrix phase α-Fe together with fine grading CrN, as well as the dispersion of carbide inclusions and their uniform distribution in the surface layer to a depth of up to 80 microns, resulting in the increase of the microhardness of the surface by 15 - 18 %.

Modification of steel surface layer by electroslag surfacing using compounds with high melting point

The authors have studied the effect of alloying on the structure, microhardness and abrasive wear resistance of electroslag surfacing layers on low-alloy structural steel 09G2S. For modification, mixtures of Si3 N4 + FeSi2 + Si powders obtained in the Department of Structural Macrokinetics of the Tomsk Scientific Centre SB RAS by the method of SHS synthesis, as well as powder compositions based on TiC, were used. A molten electrode was made of low-alloy steel St3, on which modifying compositions Si3 N4 + FeSi2 + Si were poured out, in the first case, and modifying compositions Si3 N4 + FeSi2 + Si, located below, in the second case. Metallography and X-ray microanalysis methods were used to determine the structure and to analyze the composition of the deposited layers, heat-affected zone (HAZ) and the base metal, on the basis of which assumptions were made about the nature of the formation of coating properties – hardness and wear resistance. It is shown that the main influence on the wear resistance is exerted by structure of the surfacing metal. There is a positive effect of modifying coatings by alloying materials with the alloys Si3 N4 + FeSi2 + Si + St3 and TiC + St3. In the molten layer, many new crystallization centers are released in the form of dispersed TiC particles. Dispersed TiC particles with a high melting point (3180 °C) are the first to fall out of the melt and not only serve as multiple crystallization centers, but also prevent the growth of austenitic grains, which ensures the formation of dispersed structure. The coatings contain TiC carbide particles, as well as inclusions of other phases. At the same time, an increase in hardness of the deposited layer containing titanium carbide inclusions is observed in direction of the boundary with the base. Wear resistance of the layer increases when a TiC-based coating is formed. The obtained data can be used to create deposited layers on the metal surface with high resistance against abrasive wear.

Modelling of operational, physical and mechanical properties of tool steels for cold deformation dies

Correlations between the parameters of the structure of the hardened layer and the operational properties of cold deformation dies made of case-hardened steels are considered. Correlation coefficients are calculated and a correlation graph is built. A stable (95 %) correlation is shown between wear resistance, the amount and size of carbide inclusions, the effective thickness and hardness of the case-hardened layer. Keywords: correlation graph, carbonization, diffusion layer, carbides, wear resistance, hardness, strength, impact toughness. [email protected]

Influence of the Composition of Boriding Mixture on the Saturation of the Surface of Various Steels with Boron during High-Speed HFC-Boriding

The use of borate fluxes is an important component of the part hardening process by HFC-heating. The article discusses the possibility of using various coatings to saturate the surface of steel parts, as well as the features of using various boriding agents. Microstructures of the obtained boride coatings at various fractions of the boriding agent have been considered, and the areas of carbide inclusions and average thickness of the resulting coatings have been analyzed. The expediency of P-0.66 fused flux using and changes in the resulting coatings due to the changes in the mass fraction of this flux in various boriding mixtures have been investigated. Based on the obtained data on the microstructures of boride coatings, conclusions were made concerning the most appropriate compositions of boriding mixtures and the mass fraction of fused flux in their composition.

Mechanism of failure of working faces of big bearings in the process of operation

The article presents the results of analyzing the mechanism of failure of working faces of big roller bearings made of 0,2C2Cr4Ni (E3316 AISI) structural steel. The microstructure was investigated with the help of a METAM LV-31 metallographic microscope. The surface of the bearing rings and rollers was tested for various kinds of defects using a TESCAN Vega SB scanning microscope. The PMT-3 micro-hardness tester was used to measure micro-hardness. Studies show that the microstructure of steel is a fine-needled tempered martensite with chromium carbide inclusions observed near the surface. The depth of the cementation zone was determined on the basis of the measurement results. The value of the depth exceeds the standard established by the manufacturer. The destruction of the bearing roller assembly is characterized by spalling, stratification and cratering. The destruction of the bearing ring is characterized by scouring and indentation caused by metal particles caught up in the ring-roller contact in the process of operation. These defects result in the formation of micro-cracks and, as a result, further spalling and peeling. It is possible to prevent the defects by reducing the depth of the carbonization zone, as well as reducing the surface maximum hardness by changing the mode of final heat treatment.

13C-depleted moissanites in subduction-related rocks: tracers of slab fluids in the Earth’s mantle and a new diamond exploration tool

A magnesian low-Ti shoshonite dike intruding Archean Norwegian Terrane includes numerous grains of black, blue and gray moissanite (SiC). Moissanite contains inclusions of native Si, Fe and Al, Fe-Cr carbides, Fe-Cr-Mn alloys and diamond. The range of observed δ13C values (-24.8 to -29.6‰) is similar to ophiolite-hosted SiC, lower mantle diamonds and slab-derived biogenic carbon. Norwegian moissanites may have been formed during interaction of Earth’s mantle with carbonaceous slab fluids under extremely reducing conditions as suggested by native metal and carbide inclusions. 13C-depleted moissanite can be used as a new exploration tool for sub-lithospheric diamonds in Archean to Phanerozoic accreted terranes and mobile belts.

The Influence of Heat Treatment on the Size of the Carbide Inclusions and Hardness of Multilayer Composite Material ZD-0803

Technological methods are used to ensure high homogeneity of structure and composition of metals, and thereby to improve operational characteristics and technological properties of tool materials (steels, carbide steels, hard alloys, etc.). At the same time, one of the promising field for improving the technological and operational properties of these materials is the formation of their structural and chemical heterogeneity. The alternation of a large number of layers of steels with different constituents makes it possible to obtain a set of properties that are unattainable for homogeneous steel. The use of modern diffusion bonding technologies has made it recently possible to create a number of new composite materials based on steels with various constituents, and their properties can be used in the manufacture of cutting tools. The purpose of the real work is the study of influence of heat treatment modes on the structure and operational properties of multilayered compositions ZD-0803, produced by LLC "AiR Company". During the study, the structure of the composite material, its hardness and microhardness after annealing and hardening the metal were analyzed. The obtained data show that the studied material has a pronounced layered structure with a sharp transition from one layer to the next one. The technology used in the production of composites provides the practical absence of a transition zone and the absence of such frequent defects of diffusion bonding, as stratifications, pores, oxide inclusions, etc. The study proves that during heat treatment process, the size of the carbides inclusions decreases but their number increases. The work shows that these structural transformations lead to increasing of surface hardness and microhardness of the studied material layers.