Research On Microstructure And Properties Of Impact Hardened Layer Of CADI Grinding Ball In Semi-autogenous Mill

Carbidic austempered ductile iron(CADI)grinding ball has strong ability of work hardening.When it was working in the semi-autogenous mill,CADI grinding ball knocked against ores,liner,or the other ball,then the hardened layer of CADI grinding ball would be obtained.At present,the research mainly focuses on the CADI grinding performance after heat treatment,and the hardened layer of CADI grinding ball has not been systematically studied.Unfortunately the microstructure and performance of the hardened layer surface has a very significant influence on their life.In this paper,frist of all,the effect of impact wear on the microstructure and properties on the CADI sample surface was studied.And then,the effect of quenching temperature on the microstructure and residual stress of CADI grinding ball was researched.At last,the microstructure,stress state and performance of the hardened layer of CADI grinding ball were explored.It will provide a reference and theoretical basis for further optimization of CADI performance and expanding application scope.The results show that:(1)With the manganese content increased from 2.0wt.% to 3.0wt.%,resistance to plastic deformation and work hardening capacity of CADI samples gradually increased,at the same time,wear resistance of CADI samples gradually increased.However,the tangential residual stress increased on the hardened layer surface of the CADI grinding ball,and the peeling was more severe.(2)The quenching temperature in the range of 200℃~260℃,the tangential transformation stress on the CADI grinding ball surface was tensile stress,and linear gradually reduced.After the heat treatment,if the amount of high-carbon austenite in the CADI grinding ball is increased by 1.0wt.%,the tangential phase transformation stress on the surface is reduced by 4.68 MPa.(3)In the falling test,the mechanical stress caused by the collision of the grinding balls is about-502.4MPa on the hardened layer surface,and it accounts for 65% of the total residual stress to 77%,the phase transformation stress by mechanical induction is 20%~32%.The rest is the residual stress produced by the heat treatment.With unit transformation of the high-carbon austenite by mechanical induction,the tangential phase transformation stress on the hardened layer surface increased-10.9MPa.(4)The high-carbon austenite in the hardened layer of CADI grinding ball was investigated,the transformation on the hardened layer surface was the largest,about 17 wt.%.With the increase of the hardened layer depth,the transformation of high-carbon austenite decreases gradually,and the transformation at 15 mm is reached to a minimum,then the transformation increased.But the transformation would decreased after 28 mm.The transformation reduced to 2wt.% to 4wt.% at the depth of 30 mm to 32 mm,finally remain stable.(5)It was found that the hardness on the hardened layer surface of the CADI grinding ball was more than 55 HRC,ΔH ≥ 8HRC.As the depth of the hardened layer increases,the hardness gradually decreases,and the depth of the hardened layer is about 20mm~25mm.In the falling test,the hardness(ΔH)of the hardened layer was the most affected by the mechanical residual stress,followed by the transformation of high-carbon austenite in the hardened layer.(6)In the acidic medium,the corrosion resistance of the CADI grinding ball hardened layer is higher than that before the impact,and the corrosion resistance of the CADI grinding ball is higher than that of the forged steel ball.In the neutral and alkaline medium,the corrosion resistance of the hardened layer and the forged steel ball is basically flat.