Stainless steel sheet and method for producing thereof

A method for producing a stainless steel thin sheet having high fracture resistance comprising the steps of:

• preparing a stainless steel strip consisting essentially of:
• 0.01 to 0.2 wt. % C, 0.1 to 2 wt. % Si, 0.1 to 2 wt. % Mn, 4 to 11 wt. % Ni, 13 to 20 wt. % Cr, 0.01 to 0.2 wt. % N, 0.0005 to 0.0025 wt. % soluble Al, 0.002 to 0.013 wt. % O, 0.08 to 0.9 wt. % Cu, 0.009 wt. % or less S, and the balance being Fe and inevitable impurities;
• said inevitable impurities existing as non-metallic inclusions having a composition situated in a region defined by nine points given below on terms of percentage by weight in a phase diagram of a 3-component system of "Al.sub.2 O.sub.3 --MnO--SiO.sub.2 ",
• Point 1 (Al.sub.2 O.sub.3 :21%, MnO:
• 12%, SiO.sub.2 :
• 67%),
• Point 2 (Al.sub.2 O.sub.3 :
• 19%, MnO:
• 21%, SiO.sub.2 :
• 60%),
• Point 3 (Al.sub.2 O.sub.3 :
• 15%, MnO:
• 30%, SiO.sub.2 :
• 55%),
• Point 4 (Al.sub.2 O.sub.3 :
• 5%, MnO:
• 46%, SiO.sub.2 :
• 49%),
• Point 5 (Al.sub.2 O.sub.3 :
• 5%, MnO:
• 68%, SiO.sub.2 :
• 27%),
• Point 6 (Al.sub.2 O.sub.3 :
• 20%, MnO:
• 61%, SiO.sub.2 :
• 19%),
• Point 7 (Al.sub.2 O.sub.3 :
• 27.5%, MnO:
• 50%, SiO.sub.2 :
• 22.5%),
• Point 8 (Al.sub.2 O.sub.3 :
• 30%, MnO:
• 38%, SiO.sub.2 :
• 32%),
• Point 9 (Al.sub.2 O.sub.3 :
• 33%, MnO:
• 27%, SiO.sub.2 :
• 40%);
• applying to the stainless steel strip a process of annealing --pickling--first cold rolling (CR.sub.1)--first intermediate annealing--second cold rolling (CR.sub.2)--second intermediate annealing--third cold rolling (CR.sub.3)--final annealing--fourth cold rolling (CR.sub.4)--low temperature heat treatment;
• reduction ratios of said first cold rolling, of said second cold rolling, and of said third cold rolling, each being 30% to 60%;
• a reduction ratio of said fourth cold rolling being 60 to 76%, and a reduction ratio per pass of the said fourth cold rolling being 3 to 15%;
• annealing temperatures in said first intermediate annealing, second intermediate annealing and final annealing, each being 950.degree. to 1150.degree. C.;
• said low temperature heat treatment being performed at a temperature of 300.degree. to 600.degree. C. for 0.1 sec to 300 sec.;
• and
• said final annealing and said low temperature heat treatment being performed in a non-oxidizing atmosphere containing H.sub.2 of 70 vol. % or more.