Stainless steel resistant to delayed cracking and a method for its production

Abstract

The invention relates to a stainless steel exhibiting transformation-induced plasticity (TRIP) effect resistant to delayed cracking and to the method for producing the stainless steel. The resistance to delayed cracking in the stainless steel is achieved limiting the total hydrogen content of the stainless steel measured by inert gas fusion method below 4 weight ppm, preferably below 3 weight ppm by a heat treatment performed at the temperature range between 100° C. and 700° C. for 0.1-300 hours, preferably at 200-600° C. for 1-100 hours, and more preferably at 250-500° C. for 1-100 hours.

1 . Stainless steel exhibiting transformation-induced plasticity (TRIP) effect resistant to delayed cracking, characterized in that the resistance to delayed cracking for a flat stainless steel product is achieved limiting the total hydrogen content of the steel measured by inert gas fusion method below 4 weight ppm, by a heat treatment performed at the temperature range between 100° C. and 700° C. for 0.1-300 hours, preferably at 200-600° C. for 1-100 hours. 
     
     
         2 . Stainless steel exhibiting transformation-induced plasticity (TRIP) effect according to the  claim 1 , characterized in that the stainless steel is an austenitic stainless steel containing in weight % 0-0.15% C, 0-3% Si, 0-15% Mn, 10-30% Cr, 0-8% Ni, 0-3% Mo, 0-3% Cu, 0-0.5% N, 0-0.5% Nb, 0-0.5% Ti, 0-0.5% V, the balance of Fe and inevitable impurities including hydrogen. 
     
     
         3 . Stainless steel exhibiting transformation-induced plasticity (TRIP) effect according to the  claim 1 , characterized in that the stainless stainless steel is a duplex austenitic-ferritic stainless steel whose microstructure contains 10-95% ferrite phase and which contains in weight % 0-0.10% C, 0-2% Si, 0-10% Mn, 10-30% Cr, 0-8% Ni, 0-3% Mo, 0-3% Cu, 0-0.4% N, 0-0.5% Nb, 0-0.5% Ti, 0-0.5% V, the balance of Fe and inevitable impurities including hydrogen. 
     
     
         4 . Stainless steel exhibiting transformation-induced plasticity (TRIP) effect according to  claim 1 , characterized in that the stainless steel is in the form of a flat product such as a plate, a sheet, a strip, a coil. 
     
     
         5 . Stainless steel exhibiting transformation-induced plasticity (TRIP) effect according to  claim 1 , characterized in that for the stainless steel after deep drawing a drawing ratio up to 2.0 or even higher is achieved without occurrence of delayed cracking. 
     
     
         6 . Method for producing a stainless steel exhibiting transformation-induced plasticity (TRIP) effect and resistant to delayed cracking, characterized in that for the resistance to delayed cracking the steel is heat treated at the temperature range between 100C and 700° C. for 0.1-300 hours. 
     
     
         7 . Method according to the  claim 6 , characterized in that the steel is heat treated in a batch furnace, to reduce hydrogen content of the steel and improve the resistance to delayed cracking. 
     
     
         8 . Method according to the  claim 6 , characterized in that the steel is heat treated in a continuous annealing line to reduce hydrogen content and improve the resistance to delayed cracking. 
     
     
         9 . Method according to the  claim 6 , characterized in that the heat treatment is performed in atmosphere containing at least partly protective gas to enhance effusion of hydrogen from the steel. 
     
     
         10 . Method according to the  claim 6 , characterized in that the heat treatment is performed in vacuum to enhance effusion of hydrogen from the steel. 
     
     
         11 . Method according to the  claim 6 , characterized in that the heat treatment is performed in air atmosphere to enhance effusion of hydrogen from the steel. 
     
     
         12 . Method according to  claim 6 , characterized in that the steel is strengthened by cold-rolling before the heat treatment. 
     
     
         13 . Method according to  claim 6 , characterized in that the steel is strengthened by cold-rolling after the heat treatment.