Effects of alloying elements on solidification structures in Cr-Mn-Ni austenitic stainless steels

The effects of alloying elements on solidification structures in ingots were investigated in five types of Cr-Mn-Ni austenitic stainless steels: 14%Cr-1.2%Ni-10%Mn-0.13%N, 15%Cr-4%Ni-8%Mn-0.05%N, 15%Cr-4%Ni-8%Mn-0.12%N, 17%Cr-4.5%Ni-3.5%Mn-0.3%Mo-0.10%N and 17%Cr-4%Mn-6.5%Ni-0.05%N. Delta-ferrite contents in ingots were increased with the increase of Cr contents and were decreased with the increase of Ni and Cu contents, and the each tendency in these alloying elements was almost equal regardless of types of steel, moreover the effect of Mo was the same as Cr. On the top of that, the relationship between Mn and delta-ferrite contents could be approximated by quadratic function. And different Mn contents in each type of steel produced different minimum delta-ferrite contents. Therefore it was obtained that the role of Mn, austenite or ferrite former, was changed by the balance between other alloying elements. In some steels, martensite in solidification structures increased with the decrease in Ni, Cu and Mn contents. Finally, in Cr-Mn-Ni austenitic stainless steels, the predictable equation of delta-ferrite contents in ingots, Cr and Ni equivalents were obtained by regression analysis between compositions and delta-ferrite contents.