Effects of Cu and Other Tramp Elements on Steel Properties. Effects of Cu on Diffusional Transformation Behavior and Microstructure in Fe-Mn-Si-C Steels.

Abstract

The amount of scrap has been increasing in recent years and the recycle of scrap has become a very important issue in point of preserving ecological environment. Actually the quality of scrap has been declining these days due to the increasing concentration of tramp elements, which mean the impurities such as Cu, Sn, As, Sb, Cr, Ni, etc., that are hard to be removed from the steel and accumulated in scrap during steel making process. Therefore it is necessary to make use of the scrap by taking into account the effect of tramp elements on the quality of steels. In this study, Cu was picked up as a target element and effects of Cu addition on the isothermal transformation behavior and the transformed structure have been investigated in Fe-1.48Mn-0.48Si-0.15C-(0, 1.51)Cu (wt%) steels. The main results are; (1) The transformation behavior is retarded by the addition of Cu in the temperature range of 873 to 973 K. (2) The isothermally transformed structure at 903 K is mainly acicular ferrite in 0 Cu steel, but is equiaxed ferrite with lots of subgrains in 1.5 Cu steel. (3) Both the nucleation rate and growth rate of ferrite are decreased by the addition of Cu and this is considered to be caused by the reduction in austenite grain boundary energy due to segregation of Cu and the solute drag effect by Cu.