Precipitation behavior of Cu and MnS at high temperature in Fe-10mass%Cu alloys

Copper (Cu) in steels is usually considered as a harmful tramp element, because it causes surface cracking at high temperature. Cu also retards recrystallization in aluminum-killed steels. On the other hand, Cu is useful for increasing hardness of steels and improving r-value in IF steel sheets. In this study, Fe-10mass%Cu alloys were investigated to observe the precipitation behavior of Cu and MnS at high temperature using a confocal scanning laser microscope. After the in-situ observation the precipitates were analyzed by SEM and 200 kV FE-TEM. As a result, the three types of Cu precipitates were found. "A" type is the liquid Cu forming at the austenite grain boundaries. "B" type is the ε-Cu precipitate at the non-metallic inclusions inside the austenite grains. "C" type is the fine ε-Cu precipitate in the grains. It was found that Mn and S added to steels helped a lot of CuS precipitates to form with (Mn, Cu)S ("B" type) and increased the number of Cu precipitates ("B" and "C" type) inside the grains.