Sulfide Precipitation in Titanium-Added Steel with Residual Level of Copper (1)-Precipitation in Austenite Region

The authors previously reported that even a trace level of copper (0.01% Cu) acts as a sulfide-former to form copper sulfide (Cu-S) in non-Ti-added steel in which Mn has been thought to be the only sulfide-former so far. A new concept of copper-related sulfide precipitation is now extended to Ti-added steel. In addition, the total sulfide precipitation in Ti-added steel is reconfigured with the new knowledge of Cu-S. The new concept is shown in three consecutive papers. This first paper focuses on the sulfide precipitation in austenite-heat-treated Ti-added steel. Through TEM observation and quantitative chemical analysis, it is reported that the sulfide precipitation in austenite-heat-treated Ti-added steel reflects not only the precipitation in the austenite region but also the inevitable precipitation behavior during the cooling process from austenite to ferrite region, especially trace-level-Cu-induced Cu-S precipitation in ferrite region during rapid cooling. The mechanism of the inevitable sulfide precipitation during the cooling process is mainly based upon TiS-decomposition-induced morphological change and the reprecipitation of sulfur which remains solute over precipitatable limit during the heat-treatment in austenite region, and is precisely discussed in relation with Cu-S precipitation. [doi:10.2320/matertrans.MRA2008298]