Моделирование Процесса Свс-Прессования Крупногабаритных Кольцевых Изделий

Based on the analysis of the literature and production data, it is shown that the wear resistance of steel grinding balls, which are the main grinding medium for crushing various types of raw materials in the drum type mills, is determined not only by hardness of the surface layer, but also by the quality of their macro- and microstructure. At the same time, there is a complex nature of dependences of the balls impact resistance on the above mentioned parameters with their simultaneous impact, which determines the relevance of research in this direction. Series of experimental studies was carried out in order to obtain scientifically based dependencies of impact resistance of grinding balls on the quality of their macro- and microstructure. The grinding balls with a diameter of40 mm,50 mmand60 mmproduced by OJSC “EVRAZ ZSMK” (Novokuznetsk) and by JSC “Industrial Solutions” (Nizhny Tagil) were used. The research was carried out by metallographic, durometric and fractographic methods of analysis; tests of grinding balls on the impact resistance were performed on the impact drop machine. According to the results of metallographic studies it was determined that the volume-hardened balls are characterized by a three zone structure. The surface hardened layer with a depth from 1.9 to7.4 mmis martensite. The transition zone with thickness from 1.0 to1.7 mmhas a structure martensite + troostite. The central zone occupies the entire remaining volume of the ball and has several varieties of microstructure: ferrite + perlite, martensite + troostite + ferrite, martensite + troostite. On the basis of generalization of the obtained experimental data, it was established that at surface hardness of balls within 42 – 52 HRC the quality of macrostructure (presence of ﬂakes) is the parameter determining impact resistance. For balls with high surface hardness (57 – 61 HRC) the most significant impact on impact resistance is provided by non-uniform microstructure of metal, which causes a significant diﬀerence in hardness across the balls crosssection.

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Influence of Macro- And Microstructure of Steel Grinding Balls on Their Impact Resistance

Yur’ev

Golovatenko

Осколкова

et al. 2019

Izv. vysš. učebn. zaved., Čern. metall.

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Influence of deformation parameters on quality of billets and grinding balls during their production from rejects of rail steels

Yur’ev

Симачев

Dumova

2022

Izv. vysš. učebn. zaved., Čern. metall.

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The conducted studies have determined the regularities of influence of rolling parameters of billets and grinding balls in their production from the rejects of K76F rail steel on probability of defects formation during deformation. Modeling of the rolling process of high-grade billets from the rejects of continuously cast ingots of rail steel of the specified grade in DEFORM-2D software package allowed us to establish a significant effect of such parameters as: partial coefficients of drawing along the transfer bar, frequency of rolling edges, and rolling temperature, on the probability of defect formation, characterized by the maximum value of the Cockcroft-Latham criterion in cross section of the rolls. It is shown that an increase in the coefficients of drawing (compression) along the transfer bar, due to intensification of the rolling mode and an increase in frequency of edging, reduces the likelihood of defects forming during rolling by reducing the temperature inhomogeneity along the rolls section. The established effect of temperature increase on reducing the probability of defects formation is due to an increase in plasticity of the considered rail steel. Based on the data obtained, general recommendations are formulated on the directions of improving the rolling modes of billets from the rejects of rail steels and restrictions on their application in practice. Based on the results of modeling the rolling of grinding balls from the rejects of rail steel on a helical rolling mill, a significant effect of an increase in the deformation temperature on reduction of cracking in the balls axial zone, due to an increase in the steel ductility, was established. Therefore, a new mode of rolling grinding balls from the rejects of K76F rail steel was developed, which provides an increase in impact resistance of grinding balls while maintaining high surface hardness. Effectiveness of this mode is confirmed by the results of its pilot testing in conditions of the ball rolling mill at JSC “Guryevskii Metallurgical Plant”.

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Occurrence of characteristic defects of grinding balls from rejects of continuously cast billets of rail steel

Yur’ev

Morozov

Протопопов

et al. 2023

Izv. vysš. učebn. zaved., Čern. metall.

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On the basis of metallographic studies, the authors determined the characteristic defects of grinding balls rolled from the rejects of continuously cast billets of K76F rail steel. Relationship of the presence of internal defects of the balls with their impact resistance was established. Defects in the form of internal cracks with accumulations of non-metallic inclusions in the area of their localization and flocks have the greatest impact on the reduction of balls impact resistance. Such defects are the cause of balls destruction during impact resistance tests in 62 and 17 % of cases, respectively. The effect of internal cracks without significant accumulations of non-metallic inclusions and quenching microcracks located along the boundaries of the phase interface was estimated at 12 and 9 %. The regularities and mechanism of influence of the rejects chemical composition of K76F rail steel billets on the probability of destruction of the balls produced from them during impact resistance tests were established. An increase in sulfur content in the billets of the studied rail steel reduces impact resistance of the balls produced from them, as it contributes to formation of non-plastic sulfides that concentrate in the area of internal cracks. An increase in hydrogen content in rail steel naturally contributes to an increase in probability of formation of the flocks, which significantly reduce the balls stability to shock loads. An increase in carbon content in the initial billets affects the increase in probability of destruction of K76F steel balls during copra tests. It is explained by formation of cementite-type carbides when carbon content corresponding to the eutectoid steel is reached. In general, the relative degree of influence of the K76F rail steel chemical composition on impact resistance of grinding balls is 48 %.

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Моделирование Процесса Свс-Прессования Крупногабаритных Кольцевых Изделий

Cited by 6 publications

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Influence of Macro- And Microstructure of Steel Grinding Balls on Their Impact Resistance

Influence of Macro- And Microstructure of Steel Grinding Balls on Their Impact Resistance

Influence of deformation parameters on quality of billets and grinding balls during their production from rejects of rail steels

Occurrence of characteristic defects of grinding balls from rejects of continuously cast billets of rail steel

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