| China is a large producer of wear-resistant materials,of which considerable economic losses are caused by the wear and tear in the industrial areas every year.The market demands,size and consumption of grinding ball continue to increase year by year with the development of Chinese semi-self-grinding technology,and the domestic market situation puts forward higher standards on grinding ball production in order to meet the grinding demand of domestic semi-self-grinding.At present mines need to develop the large-size balls with high hardness,high toughness,wear resistance applying to large-scale semi-self-grinding machine.The paper aims at the contradiction of can not give consideration between hardness and toughness of wear-resistant materials.Research object is bainite/martensite multi-phase large diameter wear-resistant steel ball with a size ofΦ150mm.Alloy composition would be optimized further on the basis of alloy composition,combining with pre-experimental defects in the material.The grinding ball blanks were cast with different height-diameter ratio according to the optimized composition,and research the forging process of large diameter ball,working out the forging process parameters of large diameter grinding ball.The results showed that:the steel with the composition of C～0.6-Si～1.6-Mn～2.0-Cr～0.8(wt%)is suitable for the preparation of large diameter ball with forging;The forging billet sizeΦ108×216mm and forging high diameter ratio(H/D)2.0 after the heat treatment have the best mechanical properties.The complete annealing was carried out before blank forging,and one forging forming was completed with the method of air hammer hammer forging.With the development of height-diameter ratio of cylinder,the deformation and toughness are increased but grain size is decreased.The large diameter ball with a size of Φ150mm owing good quality can be obtained when the heating power of the ball blank is 700kw,the average heating rate is 5.5～7.5 ℃/s,the average heating time is 2’50"～3’30",the forging temperature is 950℃～1050℃.In order to improve consideration between hardness and toughness and the comprehensive mechanical properties,the heat treatment process was studied with different alternating water cooling and air cooling time and different holding time The microstructure content ratio of bainite/martensite multi-phase with different positions inside the grinding ball was marked and calculated combining the color metallographic analysis.The effects of different phase contents on the comprehensive performance of large diameter grinding balls and the effect of different height-diameter ratio blanks on the performance of grinding balls under different grading quenching process were obtained.The time of graded quenching alternating water cooling-air cooling and the time of the large-diameter grinding ball in the heat preservation stage were optimized during the heat treatment,and heat treatment parameters of large diameter grinding balls were worked out and the organization of large diameter grinding balls was controlled in the preparation process.The bainitic transformation dynamic equation of large diameter was obtained,which was provided the theoretical basis for the production process of large diameter ball.The content ratio of bainite/martensite was calculated combining color metallographic analysis technique.The influence of tissue and mechanical properties was found by the analysis of microstructure and mechanical properties of the grinding balls.The heat treatment process of Φ150mm large diameter ball with the composition of C～0.6-Si～1.6-Mn～2.0-Cr～0.8(wt%)was defined:the ball was heated to the austenitizing temperature of 900 ℃ and hold in the heating furnace for 2.5h.Then graded quench treatment was carried out with the water cooling 15s-air cooling 15s,alternating cycle 3 times,in the salt bath at 330℃ for 5 5min～60min after air-cooled to room temperature.The hardness of HRC is 52,the impact toughness value is αk>20,and the lower bainite content is between 20%and 30%.the martensite content is between 50%and 70%.the austenite content is between 5%and 20%.The phase transformation dynamic equation of large diameter ball lower bainite with different position was fitted according to the lower bainite phase transformation at different isothermal time points. |
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