This invention to a process for producing a plate or forging (bar, stamp work or the like), of ferrite-austenite two-phase stainless steel, containing at most 0.03 % C, at most 2.0 % Si, at most 2.0 % Mn, 25 to 35 % Cr, 6 to 15 %
Ni,'at most 0.35 % N, remainder Fe and inevitable impurities with or without the addition of 0.001 to 0.030 % B with the following nickel balance value specified at -13 to -9: Ni balance value = Ni% + 0.5 Mn% + 30 x (C+N)%
-1.1 (Cr% + 1.5 Si%) + 8.2
The process of the invention is characterized in that the average crystal grain size is controlled to at most 0.015 mm by heating an ingot of the above-mentioned ferrite-austenite two-phase stainless steel at a temperature of at most 1,200°C and keeping the forging ratio by hot working at a value of at least 5.