Austenitic stainless steel excellent in fine blankability
An austenitic stainless steel comprising (C+½N) up to 0.060 mass %, Si up to 1.0 mass %, Mn up to 5 mass %, S up to 0.003 mass %, S/Mn ratio up to 0.003, 15–20 mass % Cr, 5–12 mass % Ni, Cu up to 5 mass %, 0–3.0 mass % Mo and the balance being Fe except inevitable impurities under the condition that a value Md 30 (representing a ratio of a strain-induced martensite) defined by the under-mentioned formula is controlled within a range of −60 to −10. Hardness increase of the steel sheet after being cold-rolled is preferably 20% or more as Vickers hardness. A metallurgical structure of the steel sheet is preferably adjusted to grain size number of #8 to #11 in a finish annealed state. The steel sheet is blanked with high dimensional accuracy, and a die life is also prolonged. Md 30 =551−462(C+N)−9.2Si−29(Ni+Cu)−8.1Mn−13.7Cr−18.5Mo.
1. An austenitic stainless steel, which has an excellent property in fine blankability, consisting essentially of 0.010–0.050 mass % C, 0.010–0.030 mass % N, (C+½N) up to 0.060 mass %, Si up to 1.0 mass %, Mn up to 5 mass %, S up to 0.003 mass %, S/Mn ratio up to 0.003, 15–20 mass % Cr, 5–12 mass % Ni, Cu up to 5 mass %, optionally Mo up to 3.0 mass % and the balance being Fe except inevitable impurities, under the condition that a value Md 30 representing a ratio of a strain-induced martensite phase defined by the under-mentioned formula is within a range of −60 to −15.2:
Md 30 =551−462(C+N)−9.2Si−29(Ni+Cu)−8.1Mn−13.7Cr−18.5Mo;
and wherein a blanked sheet of said austenitic stainless steel will have a shear plane ratio of 100%.
2. The austenitic stainless steel according to claim 1 , wherein the austenitic stainless steel achieves a 20–150% ratio increase of Vickers hardness by cold-rolling after annealing and pickling, the ratio calculated by
{(Vickers hardness of a cold-rolled steel sheet)−(Vickers hardness of an annealed steel sheet)}/(Vickers Hardness of an annealed steel sheet)×100(%).
3. The austenitic stainless steel according to claim 1 , wherein the austenitic stainless steel has a grain size number of #8 to #11.
4. The austenitic stainless steel according to claim 1 , wherein the C content is 0.010–0.030 mass %.