Effect of nano-scale copper sulfide precipitation on mechanical properties and microstructure of rapidly solidified steel with tramp copper element

Abstract

Copper is one of the main residual elements in steel, especially in recycled scrap steel, whereas sulfur is one of the main impurities in steel. A large quantity of slag and CO2 is produced during the process of removing the sulfur from the steel. However, copper and sulfur may combine to form copper sulfide, especially during the rapid cooling process. In this paper samples containing and not containing fine copper sulfide are prepared by the rapid solidification process. The microstructure, sulfide precipitates, and the mechanical properties of the samples are investigated by optical microscopy. Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), and the tensile testing. A large difference in the yield strength between the samples containing and not containing copper sulfides is observed. Each contribution of solid solution strengthening, grain refining strengthening, and sulfide precipitates strengthening in the samples with and without copper sulfide has been discussed. Particular attention has been paid to effect of the nano-scale copper sulfides. that is. main factor contributing to the alloy strengthening. Contribution of reduction of the copper sulfide particle size has also been discussed by comparing the results of two rapid solidification processes with different cooling rates. © 2006 The Japan Institute of Metals.