LOW-ALLOY DUPLEX STAINLESS STEEL WHEREIN WELD HEAT-AFFECTED ZONES HAVE GOOD CORROSION RESISTANCE AND TOUGHNESS

摘要

The present invention provides a lean duplex stainless steel able to suppress the drop in corrosion resistance and toughness of a weld heat affected zone and is characterized by containing, by mass%, C: 0.06% or less, Si: 0.1 to 1.5%, Mn: 2.0 to 4.0%, P: 0.05% or less, S: 0.005% or less, Cr: 19.0 to 23.0%, Ni: 1.0 to 4.0%, Mo: 1.0% or less, Cu: 0.1 to 3.0%, V: 0.05 to 0.5%, Al: 0.003 to 0.050%, O: 0.007% or less, N : 0.10 to 0.25%, and Ti: 0.05% or less, having a balance of Fe and unavoidable impurities, having an Md30 value expressed by formula (1) of 80 or less, having an Ni-bal expressed by formula (2) of -8 to -4, having a relationship between the Ni-bal and the N content satisfying formula (3), having an austenite phase area percentage of 40 to 70%, and having a 2xNi+Cu of 3.5 or more: Md �¢ 30 = 551 - 462 × C + N - 9.2 × Si - 8.1 × Mn - 29 × Ni + Cu - 13.7 × Cr - 18.5 × Mo - 68 × Nb Ni - bal = Ni + 0.5 �¢ Mn + 0.5 �¢ Cu + 30 �¢ C + 30 �¢ N - 1.1 �¢ Cr + 1.5 �¢ Si + Mo + W + 8.2 N % ‰¤ 0.37 + 0.03 × Ni - bal