The Effect Of Natural Aging On The Microstructure And Hardness Of High Chromium Cast Iron

High chromium cast iron is known as the best wear-resistant material in the contemporary era.The microstructure after heat treatment is high-strength,high-hardness martensite,M₇C₃ eutectic carbide and secondary carbide.The high hardness M₇C₃ eutectic carbides are rod-shaped,broken network-shaped distribution.This kind of microstructure makes high chromium cast iron with high hardness and high wear resistance.It is widely used in mining,metallurgy,building materials,electric power and chemical industries.The matrix structure of as-cast high chromium cast iron is austenite,with low hardness and poor wear resistance.It needs proper heat treatment to improve its performance.High chromium cast iron can obtain better performance after destabilizing treatment.This article mainly discusses the effect of destabilizing treatment temperature on the structure,hardness and impact properties of high chromium cast iron.The matrix structure of high chromium cast iron is martensite after destabilizing treatment,which provides a basis for natural aging.Therefore,this paper further studies the effect of natural aging on the structure and hardness of high chromium cast iron,and uses the first performance principle to calculate the stability and theoretical hardness of Fe_2-xCr_xC(x=1?2)alloy carbides.Research indicates:(1)In the range of 900?-1050?,the hardness of high chromium cast iron first increases and then decreases with the quenching temperature.The hardness is the largest at 950?,which is63.6 HRC.The matrix structure is martensite+retained austenite.After quenching,the secondary carbides in high chromium cast iron are a mixture of M₂₃C₆ and M₃C,which are dispersed between the matrix and the eutectic carbides.The content of secondary carbides increases first and then decreases with the quenching temperature.The quenching temperature has little effect on the impact performance of high chromium cast iron.High chromium cast iron is a brittle material.The fracture mode is brittle fracture.At the fracture,there are microcracks in both the martensite matrix and the eutectic carbide M₇C₃.(2)Naturally age the high chromium cast iron samples cold-quenched to room temperature at900?-1000?for 1 hour.After natural aging treatment,finely dispersed?-(Fe,Cr)₂C carbides were precipitated from the martensite matrix,which increases the hardness of high chromium cast iron by 2?3 HRC and reduces the microhardness of the matrix.(3)The?-(Fe,Cr)₂C carbide formation energy is lower and more stable than that in?-Fe₂C carbide,which was proved by the first-principles calculation.The?-(Fe,Cr)₂C carbide has a higher theoretical hardness of 12.87 GPa.The precipitation of high-hardness carbides further increases the hardness of high-chromium cast iron.