Mechanism of Si on the Cementite Type Transformation in As-cast High Carbon Chromium Bearing Steel

Abstract

Four as-cast high carbon chromium bearing steels with different Si contents （0. 29%、0. 42%、0. 71% and 1. 50%）were prepared using a vacuum induction furnace， the carbides in the steel were extracted by nonaqueous solution electrolysis method. The two-dimensional and three-dimensional morphology of carbides in steel was observed through scanning electron microscopy. the types of carbides at different Si contents were investigated by X-ray diffractometer， the essential mechanism of influence of Si content on cementite type was determined by thermodynamics and first principles calculation. The research results indicate that there are two types of carbides in as-cast high carbon chromium bearing steel with different Si contents， namely layer cementite （Fe1-XMnX ）3C and grain boundary carbides M23C6. With the in crease of Si content （0. 29%-1. 50%）， the M23C6 grain boundary carbides change from a continuous coarse rod-shaped structure to a discontinuous fine point like structure， which indicate that the increase of Si content has an inhibitory effect on the precipitation of grain boundary carbides. In addition， the increase in Si content reduces the proportion of Mn in （Fe1-XMnX ）3C cementite， and the transformation trend of cementite type is from Fe1. 8Mn1. 2C to Fe3Mn0C. The possible rea son is that during the precipitation process of cementite formation， Si atoms are discharged into area around cementite to form a Si rich micro zone， which hinders the diffusion of Mn atoms from the matrix to the cementite， reduces the activity and diffusion migration ability of Mn in the matrix. Thus， the relative content of Mn in the cementite is reduced.

Keywords

• high carbon chromium bearing steel； cementite； si content； thermodynamic calculations； first principles