Austenitic stainless steel

Abstract

Austenitic stainless steel utilizing the TRIP effect with a balanced pitting resistance equivalent for high corrosion resistance. The austenitic stainless steel contains 0-0.04 weight % C, 0.2-0.8 weight % Si, 0-2.0 weight % Mn, 16.0-19.0 weight % Cr, 4.0-6.5 weight % Ni, 1.0-4.0 weight % Mo, 0-4.0 weight % W, 0-2.0 weight % Cu, 0.20-0.30 weight % N, the rest being iron and inevitable impurities occurring in stainless steels, the proportion of the ferrite phase in the microstructure is 0-10.0 volume %, the rest being austenite, when quenched and heat treated at the temperature range of 900-1200° C., preferably 950-1150° C.

1 . An austenitic stainless steel utilizing the TRIP effect with a balanced pitting resistance equivalent for high corrosion resistance wherein the austenitic stainless steel contains 0-0.04 weight % C, 0.2-0.8 weight % Si, 0-2.0 weight % Mn, 16.0-19.0 weight % Cr, 4.0-6.5 weight % Ni, 1.0-4.0 weight % Mo, 0-4.0 weight % W, 0-2.0 weight % Cu, 0.20-0.30 weight % N, the rest being iron and inevitable impurities occurring in stainless steels, the proportion of the ferrite phase in the microstructure is 0-10.0 volume %, the rest being austenite, when quenched and heat treated at the temperature range of 900-1200° C., preferably 950-1150° C. 
     
     
         2 . The austenitic stainless steel according to  claim 1 , wherein the pitting resistance equivalent value (PRE) is in the range of 27-35. 
     
     
         3 . The austenitic stainless steel according to  claim 1 , wherein the calculated M d30  temperature is in the range of −70 to +60° C., preferably in the range of −30 to +60° C. 
     
     
         4 . The austenitic stainless steel according to preceding  claim 1 , wherein the calculated SFE is in the range of 10.0-16.0 mJ/m 2 . 
     
     
         5 . The austenitic stainless steel according to  claim 1 , wherein the critical pitting temperature CPT is 30-50° C. 
     
     
         6 . The austenitic stainless steel according to  claim 1 , wherein the chromium content is 16.5-18.7 weight %. 
     
     
         7 . The austenitic stainless steel according to  claim 1 , wherein the nickel content is 4.5-6.2 weight %. 
     
     
         8 . The austenitic stainless steel according to  claim 1 , wherein the manganese content is 0-1.5 weight %. 
     
     
         9 . The austenitic stainless steel according to  claim 1 , wherein the copper content is less than 0-1.5 weight %. 
     
     
         10 . The austenitic stainless steel according to  claim 1 , wherein the tungsten content is 1.0-3.8 weight %. 
     
     
         11 . The austenitic stainless steel according to  claim 1 , wherein the sum of the molybdenum (Mo) and tungsten (W) contents according to the formula (Mo+0.5 W) is in the range 0-4.0 weight %, preferably 2.2-4.0 weight %. 
     
     
         12 . The austenitic stainless steel according to  claim 1 , wherein nitrogen content is 0.21-0.29 weight %. 
     
     
         13 . The austenitic stainless steel according to  claim 1 , wherein the stainless steel further contains one or more added elements selected from the group consisting of 0.0001-0.04 weight % Al, preferably 0.0001-0.03 weight % Al, 0.0001-0.004 weight % B, 0.0001-0.004 weight % Ca, 0.0001-0.1 weight % Ce, 0.0001-0.1 weight % Co, 0.0001-0.1 weight % Nb, 0.0001-0.1 weight % Ti, 0.0001-0.2 weight % V. 
     
     
         14 . The austenitic stainless steel according to  claim 1 , wherein the stainless steel contains as inevitable impurities 0.0001-0.010 weight %, preferably 0.0001-0.005 weight % S, 0.0001-0.040 weight % P so that the sum (S+P) is 0.0001-0.04 weight %, and the total oxygen content is in the range 0-100 ppm. 
     
     
         15 . The austenitic stainless steel according to  claim 1 , wherein the chemical composition window, which lies within the frame of the area a′, b′, c′, d′, e′, f′ and g′ in  FIG.  1   , is defined with the following labelled positions of the coordination in weight %. 
       
         
           
                 
                 
                 
                 
                 
               
                     
                     
                 
                     
                   Si + Cr % 
                   Cu + Mo + 0.5 W % 
                   C + N % 
                   Mn + Ni % 
                 
                     
                     
                 
                     
                 
                 
                 
                 
                 
                 
               
                   a′ 
                   19.8 
                   1.0 
                   0.24 
                   8.5 
                 
                   b′ 
                   19.8 
                   4.4 
                   0.21 
                   4.0 
                 
                   c′ 
                   18.8 
                   5.6 
                   0.21 
                   4.0 
                 
                   d′ 
                   17.4 
                   6.0 
                   0.21 
                   5.5 
                 
                   e′ 
                   16.2 
                   6.0 
                   0.30 
                   4.0 
                 
                   f′ 
                   16.2 
                   2.1 
                   0.33 
                   6.2 
                 
                   g     
                   19.6 
                   1.0 
                   0.28 
                   6.2 
                 
                     
                 
             
                
                
                
               
               
                
               
            
             
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         16 . The austenitic stainless steel according to  claim 1 , wherein the chemical composition window, which lies within the frame of the area p′, q′ r′ and s′ in  FIG.  3   , is defined with the following labelled positions of the coordination in weight %. 
       
         
           
                 
                 
                 
                 
                 
               
                     
                     
                 
                     
                   Si + Cr % 
                   Cu + Mo + 0.5 W % 
                   C + N % 
                   Mn + Ni % 
                 
                     
                     
                 
                     
                 
                 
                 
                 
                 
                 
               
                   p′ 
                   17.6 
                   3.5 
                   0.34 
                   4.0 
                 
                   q′ 
                   16.2 
                   5.7 
                   0.34 
                   8.5 
                 
                   r′ 
                   19.0 
                   1.8 
                   0.20 
                   8.5 
                 
                   s′ 
                   19.0 
                   1.8 
                   0.20 
                   4.0 
                 
                     
                 
             
                
                
                
               
               
                
               
            
             
                
                
                
                
                
               
            
           
         
       
     
     
         17 . The austenitic stainless steel according to  claim 1 , wherein the steel is produced as ingots, slabs, blooms, billets, plates, sheets, strips, coils, bars, rods, wires, profiles and shapes, seamless and welded tubes and/or pipes, metallic powder, formed shapes and profiles.