Influence of C, N and Nb Contents on Cold Formability in Solution Treatment and Tensile Property in Peak Aging of SUS630(17-4PH)

摘要

The influence of C, N and Nb contents on cold formability in solution treatment and tensile property in peak aging of SUS630(17-4PH) were studied considering grain size.1) The grain growth temperature Tg is indicated as follows, log((mass percent Nb)·((mass percent C)+(mass percent N)))=-17600 / Tg + 11.2.2) The contribution of C content on the increment of solution treated hardness is twice as much as that of N content. Grain size and Nb are less influential in solution treated hardness than C, N.3) The critical upsetting ratio increases with decreasing C content. On the contrary, the addition of N does not lower the critical upsetting ratio.4) Making C content down from 0.054 mass percent to 0.005mass percent, the flow stress of SUS630 decreases about 20 percent, and it is comparable with the flow stress of SUS XM7(18Cr-8Ni-3Cu) in the region over 0.6 in true strain.5) There is no influence of C, N contents on 0.2 percent proof stress and tensile strength in peak age. But decreasing C, N contents is detrimental to ductility because of grain coarsening.