Effect of Steel Matrix with Different C Content on the Growth Mechanism, Microstructure and Properties of the Chromized Layer

Abstract

The C content of the steel matrix has significant influence on the growth mechanism, microstructure and properties of the chromized layer. However, the relevant research literature is scarce. In this paper, seven kinds of low carbon alloy steels with C content ranging from 0.08wt.% to 0.45wt.% were selected as matrix for chromizing experiments under the same parameters. The effects of matrix C content on the growth mechanism, growth rate, structure and properties of the chromized layer were discussed. The results show that the chromized layer is composed of outer porous (Cr, Fe)23C6 and (Cr, Fe)7C3 carbides layer and inner dense Fe-Cr phase layer for matrix with C content lower than or equal to 0.2wt%. While when the matrix C content is more than 0.2wt.%, the chromized layer becomes three-layer structure: the surface (Cr, Fe)23C6 phase layer, the middle (Cr, Fe)7C3 phase layer and the bottom Fe-Cr solid solution phase layer. The structure and thickness of Cr23C6 phase layer formed in the early stage of chromizing play a decisive role in the inward diffusion of surface adsorbed Cr atoms and the growth rate of the permeated layer. With the C content of the matrix increases from low(0.08wt.%C) to high(0.45wt.%C), the dense layer phases in chromized samples gradually changes from Fe-Cr alloy phase with BCC structure to (Cr, Fe)23C6 and (Cr, Fe)7C3 carbides. And the wear resistance of the chromized layer increase. However, when the matrix C content is above 0.4wt.%, the structure and phases of the chromized layer are almost not affected by the matrix C content, so are the thickness and wear resistance. The results are helpful to the selection of steel matrix composition for chromizing and the optimization of chromizing process.

Keywords: Pack chromizing, Growth mechanism, Wear resistance, Microhardness