| The consumption of the large diameter grinding balls is increasing as the popularity of large semi autogenous grinding in mines enterprises which lead to the traditional wear-resistant grinding ball unable to meet the needs of the new period of grinding. Therefore, it is a big problem that need to be solved urgently in the mine enterprises to develop a new grinding ball which with the properties of high strength, toughness,wear resistance and large diameter.Bainite/martensite dual phase structure is an ideal wear-resistant materials because of its good comprehensive mechanical properties, good strength and toughness.This research is based on our former study achievements in the field of bainite/martensite dual phase steel ner (alloy components s C-0.5～Si～2.0～Mn～3.0(wt%)) and combined it with the research of large diameter grinding balls.The alloy also been designed optimally by supplement micro amount of alloying elements Cr and B.We developed a low cost material for the large diameter grinding ball of which the composition is C-0.5-Si～1.8-Mn-2.5-Cr～0.5-B～0.005 (wt%) finally.In this study, we designed different components of Si-Mn low carbon steels which treated with several heat treatments,such as water quenched+isothermal salt bath and air cooling+isothermal salt bath. We used the color metallographic analysis technical and quantitative metallographic analysis technical to distinguish and calculate relative contents of lower bainite, martensite and residual austenite in the bainite/martensite duplex-phase structure which treated with different the resulting heat treatment process.In the combine performance test, we analysed regular patterns of the impacts of different contents of lower bainite dual phase on the properties of duplex phase steel.We also explored the association of the proportion of bainite, martensite and retained austenite and material properties which provides a theoretical basis for structure controls in the high-performance bainite/martensite dual phase steel.The results show that, the components of the steel which is suitable for the manufacture of large diameter ball is C-0.5～Si-1.8-Mn-2.5～Cr-0.5～B-0.005 (wt%); Adopting color metallography technique we can distinguish lower bainite, martensite and retained austenite in composite steel effectively, and we can calculate the proportion of each composite organization phase when combine it with quantitative metallographic analysis; we got lower bainite content (14.9-56.26%) of different bainite/martensite duplex-phase structure of which the material properties was greatly improved than the cast, the impact toughness was increased by 92-183%, hardness was increased by 31 to 55% and wear properties was increased by 1.4-2.3 times by water quenched+isothermal salt bath and air cooling+isothermal salt bath; the content of bainite and residual austenite that in the bainite/martensite duplex-phase structure were increased and the amount of martensite was reduced by reducing the amout of C, Si, and Mn. Bainitic/martensitic composite body tissues, lower bainite content of 30 to 40% martensite content of 50 to 60%, residual austenite content is 5 to 14%, the hardness≥55HRC more complex phase steel, toughness≥ 15J/cm2, a good hard match toughness; bainite/martensite steel, lower bainite content increases, the yield strength of steel increased from 1480MPa to 1532MPa, and then gradually decreased to about 1100MPa, the moment bainite content of about 29%, the yield strength of steel is the highest, reaching 1532MPa; lower bainite content increases, the wear resistance of steel to reduce, and then leveled off, and finally continue to reduce, in Belleville body content in the range of 25 to 45%, the wear resistance of composite steel decreased from 7.5 to 6.2 g-1, did not change significantly, basically stable, visible, the design of the organization, can be in a wide The range of variation in the content of the lower bainite, help to reduce the difficulty of the production control of the microstructure. |
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