Ni-reduced austenite stainless steel
Provided is an Ni-reduced austenite stainless steel having excellent recyclability with no problem of producibility depression to be caused by the surface property thereof and having good workability, season cracking resistance, corrosion resistance and stress corrosion cracking resistance in point of the material characteristics thereof. The steel comprises C in an amount of more than 0.05% (by mass) and within a range of from 0.15 to 0.3% as (C+N), Si in an amount of at most 1%, Mn in an amount of from 0.5 to 2.5%, Ni in an amount of from 3 to 6%, Cr in an amount of from more than 16 to 25% and Cu in an amount of from 0.8 to 4%, and has Md30 of the following formula (1) of from −50 to 10 and SFE of the following formula (2) of at least 5: Md30=551−462(C+N)−9.2Si−8.1Mn−29(Ni+Cu)−13.7Cr (1), SFE=2.2Ni+6Cu−1.1Cr−13Si−1.2Mn+32 (2).
1 . An Ni-reduced austenite stainless steel having excellent workability, season cracking resistance, corrosion resistance, stress corrosion cracking resistance and surface property, which comprises, by mass %, C in an amount of more than 0.05% and within a range satisfying the following formula (3), Si in an amount of at most 1%, Mn in an amount of from 0.5 to 2.5%, Ni in an amount of from 3 to 6%, Cr in an amount of from more than 16 to 25%, Cu in an amount of from 0.8 to 4%, N in an amount within a range satisfying the following formula (3), and a balance of Fe and inevitable impurities, and which is so constituted that the austenite stability index defined by the following formula (1), Md30 is from −50 to 10 and the index value of stacking fault energy defined by the following formula (2), SFE is at least 5:
Md30=551−462(C+N)−9.2Si−8.1Mn−29(Ni+Cu)−13.7Cr (1),
SFE=2.2Ni+6Cu−1.1Cr−13Si−1.2Mn+32 (2),
0.15≦C+N≦0.3 (3).