Abstract
This report is the second paper in three consecutive papers to know the whole sulfide precipitation in Ti-added steel by adding a new knowledge that even a trace level of copper (0.01%Cu) acts as a sulfide-former to form copper sulfide (Cu-S). The second paper focuses on the sulfide precipitation in ferrite region in Ti-added steel, especially in real-produced hot-rolled and annealed steel sheets.
Although it has been believed that the sulfide precipitation is completed only in austenite region except for a few limited papers, Ti4C2S2, MnS and Cu-S are really formed in ferrite region. When as-hot-rolled Ti-added steel is annealed, the sulfide precipitation transforms morphologically and compositionally. The phenomenon can be explained through the same mechanism in the first paper that TiS-decomposition-induced re-solute sulfur is re-precipitated. When annealed in ferrite region, already-precipitated TiS is changed into Ti4C2S2 and re-solute sulfur comes out along the estimated reaction “4TiS+2[C]→Ti4C2S2+2[S]”, and it is re-precipitated in ferrite region as other precipitates (Ti4C2S2, MnS and Cu-S). The precipitation of Cu-S is estimated to occur at the lowest temperature among re-precipitated sulfides, and therefore is affected by the precedent sulfide precipitation phenomena.
