Austenitic stainless steel product and a method for manufacturing same

A method for the manufacturing of a very strong austenitic stainless steel product, selected from the group consisting of a plate, a steel strip, a steel bar and steel wire wherein the steel product is cold-rolled and heat-treated, comprising the following steps:

• a—cold-rolling the steel;
• b—providing a total reduction ratio of the cold-rolling to be at least 50%;
• c—changing at most 30% of the volume of the austenitic stainless steel into martensite during the cold-rolling;
• and
• d—heat-treating the cold-rolled steel product for recrystallizing its structure, in which case the annealing temperature is higher than 670° C. and lower than 950° C. and the annealing time is at most 10 minutes,
• wherein the tensile strength (Rm) of the steel product is greater than 600 MPa and less than 1000 MPa,
• wherein the chemical composition of the steel fulfills the following relationship:
• Ni equiv.=1×% Ni+30×% C+30×% N+0.5×% Mn≥9.0 and
• Cr equiv.=1×% Cr+1×% Mo+1.5×% Si+0.5×% Nb≥17.0,
• wherein the steel has C≤0.03 wt %, and
• wherein the average grain size of the recrystallized austenitic structure is at most 6 μm,
• wherein less than 25% of the structure is non-recrystallized austenite,
• wherein the yield strength (Rp0.2) is at least 350 MPa, and the uniform elongation (Ag) is at least 5%.