Low ni content austenitic stainless steel with high strength / ductility properties

Abstract

Austenitic Stainless Steel alloy compositions are provided with reduced Ni content. These alloys, combined with a process that includes a martensite thermomechanical treatment with a thickness reduction preferably higher than 65%, provides a new generation of Advanced High Strength Steels with combination of tensile strength and total elongation in the range of 1000 MPa/35-55% to 1350 MPa/25-45% and good formability and weldability properties, which are useful in the manufacture of many products, particularly in the car industry.

1 .- 26 . (canceled) 
     
     
         27 . An alloy composition, comprising:
 Ni: between 2.00 and 3.60 wt %;   Mn: between 6.0 and 7.0 wt %;   Cr: between 15.0 and 16.5 wt %;   N: between 0.085 and 0.180 wt %;   Mo: between 0.00 and 0.50 wt %;   Nb: above 0.00 and not higher than 0.40 wt %;   Cu: between 0.00 and 1.00 wt %;   Si: between 0.40 and 1.00 wt %;   C: between 0.060 and 0.095 wt %;   S: between 0.00 and 0.007 wt %;   P: between 0.00 and 0.045 wt %;   Ti: above 0.00 and not higher than 0.45 wt %;   Fe: to balance the composition and incidental impurities;   characterized by an M d30  value, obtained according to the equation M d30 (° C.)=551-462(% C+% N)−9.2% Si−8.1% Mn−13.7% Cr−29(% Ni+% Cu)−18.5% Mo−68% Nb, of at least 55.   
     
     
         28 . The alloy composition according to  claim 27  wherein the amounts of the elements are independently selected from any of the alternatives a) to l):
 a) Ni: above 2.00 and below 3.60 wt %; 
 b) Mn: above 6.0 and below 7.0 wt %; 
 c) Cr: above 15.0 and below 16.5 wt %; 
 d) N: between 0.085 and 0.180 wt %; 
 e) Mo: above 0.00 and below 0.50 wt %; 
 f) Nb: above 0.00 and below 0.40 wt %; 
 g) Cu: above 0.00 and below 1.00 wt %; 
 h) Si: above 0.40 and below 1.00 wt %; 
 i) C: between 0.060 and 0.095 wt %; 
 j) S: below 0.007 wt %; 
 k) P: below 0.045 wt %; 
 l) Ti: above 0.00 and below 0.45 wt %. 
 
     
     
         29 . The alloy composition according to  claim 27 , comprising:
 Ni: above 2.00 and below 3.60 wt %;   Mn: above 6.0 and below 7.0 wt %;   Cr: above 15.0 and below 16.5 wt %;   N: between 0.085 and 0.180 wt %;   Mo: above 0.00 and below 0.50 wt %;   Nb: above 0.00 and below 0.40 wt %;   Cu: above 0.00 and below 1.00 wt %;   Si: above 0.40 and below 1.00 wt %;   C: between 0.060 and 0.095 wt %;   S: below 0.007 wt %;   P: below 0.045 wt %;   Ti: above 0.00 and below 0.45 wt %;   Fe: to balance the composition and incidental impurities.   
     
     
         30 . The alloy composition according to  claim 27 , wherein the M d30  value, obtained according to the equation M d30 (° C.)=551-462(% C+% N)−9.2% Si−8.1% Mn−13.7% Cr−29(% Ni+% Cu)−18.5% Mo−68% Nb, is at least 60. 
     
     
         31 . The alloy composition according to  claim 27  wherein the amounts of the elements are independently selected from any of the alternatives a) to i):
 a) Ni: above 2.00 and below 3.40 wt %; 
 b) Mn: above 6.2 and below 6.9 wt %; 
 c) Cr: above 15.2 and below 16.3 wt %; 
 d) N: between 0.100 and 0.180 wt %; 
 e) Nb: above 0.00 and below 0.40 wt %; 
 f) Cu: above 0.00 and below 0.70 wt %; 
 g) Si: above 0.50 and below 0.90 wt %; 
 h) C: between 0.065 and 0.095 wt %; 
 i) Ti: above 0.00 and below 0.40 wt %. 
 
     
     
         32 . The alloy composition according to  claim 27 , comprising:
 Ni: above 2.00 and below 3.40 wt;   Mn: above 6.2 and below 6.9 wt %;   Cr: above 15.2 and below 16.3 wt %;   N: between 0.100 and 0.180 wt %;   Mo: above 0.00 and below 0.50 wt %;   Nb: above 0.00 and below 0.40 wt %;   Cu: above 0.00 and below 0.70 wt %;   Si: above 0.50 and below 0.90 wt %;   C: between 0.065 and 0.095 wt %;   S: below 0.007 wt %;   P: below 0.045 wt %;   Ti: above 0.00 and below 0.40 wt %;   Fe: to balance the composition and incidental impurities.   
     
     
         33 . The alloy composition according to  claim 27  wherein the amounts of the elements are independently selected from any of the alternatives a) to i):
 a) Ni: above 2.00 and not higher than 3.20 wt %; 
 b) Mn: above 6.2 and below 6.8 wt %; 
 c) Cr: above 15.2 and below 16.2 wt %; 
 d) N: between 0.100 and 0.180 wt %; 
 e) Nb: above 0.00 and below 0.30 wt %; 
 f) Cu: above 0.00 and below 0.60 wt %; 
 g) Si: above 0.50 and below 0.80 wt %; 
 h) C: between 0.070 and 0.095 wt %; 
 i) Ti: above 0.00 and below 0.30 wt %. 
 
     
     
         34 . The alloy composition according to  claim 27 , comprising:
 Ni: above 2.00 and not higher than 3.20 wt;   Mn: above 6.2 and below 6.8 wt %;   Cr: above 15.2 and below 16.2 wt %;   N: between 0.100 and 0.180 wt %;   Mo: above 0.00 and below 0.50 wt %;   Nb: above 0.00 and below 0.30 wt %   Cu: above 0.00 and below 0.60 wt %;   Si: above 0.50 and below 0.80 wt %;   C: between 0.070 and 0.095 wt %;   S: below 0.007 wt %;   P: below 0.045 wt %;   Ti: above 0.00 and below 0.30 wt %;   Fe: to balance the composition and incidental impurities.   
     
     
         35 . The alloy composition according to  claim 27  wherein the amounts of the elements are independently selected from any of the alternatives a) to i):
 a) Ni: above 2.10 and not higher than 3.20 wt %; 
 b) Mn: above 6.2 and below 6.7 wt %; 
 c) Cr: above 15.2 and not higher than 15.9 wt %; 
 d) N: between 0.100 and 0.160 wt %; 
 e) Nb: above 0.00 and below 0.20 wt %; 
 f) Cu: above 0.40 and below 0.60 wt %; 
 g) Si: above 0.50 and below 0.75 wt %; 
 h) C: between 0.070 and below 0.095 wt %; 
 i) Ti: above 0.00 and below 0.10 wt %. 
 
     
     
         36 . The alloy composition according to  claim 27 , comprising:
 Ni: above 2.10 and not higher than 3.20 wt %;   Mn: above 6.2 and below 6.7 wt %;   Cr: above 15.2 and not higher than 15.9 wt %;   N: between 0.100 and 0.160 wt %;   Mo: above 0.00 and below 0.50 wt %;   Nb: above 0.00 and below 0.20 wt %   Cu: above 0.40 and below 0.60 wt %;   Si: above 0.50 and below 0.75 wt %;   C: between 0.070 and below 0.095 wt %;   S: below 0.007 wt %;   P: below 0.045 wt %;   Ti: above 0.00 and below 0.10 wt %;   Fe: to balance the composition and incidental impurities.   
     
     
         37 . The alloy composition according to  claim 27 , comprising:
 S: above 0.00 and below 0.007 wt %; and/or   P: above 0.00 below 0.045 wt %.   
     
     
         38 . A method for producing austenitic stainless steel, comprising the following steps:
 a) melting and casting an alloy composition as defined in  claim 27 ;   b) hot rolling the alloy from step a);   c) Solution annealing the alloy from step b); and   d) Subjecting the alloy from step c) to a martensite thermomechanical treatment comprising a cold rolling step and a final annealing step.   
     
     
         39 . The method according to  claim 38  wherein the hot rolling is carried out at a temperature between 1200° C. and 1300° C. 
     
     
         40 . The method according to  claim 38  wherein the solution annealing is carried out at a temperature from 1000° C. to 1200° C. 
     
     
         41 . The method according to  claim 38  wherein the martensite thermomechanical treatment of step d) comprises a cold rolling step to reduce the thickness by 50% or more. 
     
     
         42 . The method according to  claim 38 , comprising the following steps:
 a) Melting and casting an alloy composition as defined in  claim 27 ;   b) hot rolling the alloy from step a) at a temperature between 1200° C. and 1300° C.;   c) Solution annealing the alloy from step b) at a temperature of from 1000° C. to 1200° C.; and   d) Subjecting the alloy from step c) to
 a martensite thermomechanical treatment comprising a cold rolling step to reduce the thickness by 50% or more, and 
 a final annealing step at a temperature between 900° C. and 1200° C. for a time between 30 seconds and 300 seconds, depending on the thickness of the steel. 
   
     
     
         43 . The austenitic stainless steel of  claim 27 , with a tensile strength value in the range of 1000-1350 MPa, with a total elongation in the range of 35-55% for a tensile strength of 1000 MPa and a total elongation in the range of 25-45% for a tensile strength of 1350 MPa, as measured according to the standard UNE-EN ISO 6892-1:2017. 
     
     
         44 . The austenitic stainless steel of  claim 27 , wherein it is selected from flat, long or powder products. 
     
     
         45 . A product in automotive, transport, consumer goods and construction sectors, comprising the austenitic stainless steel of  claim 27 . 
     
     
         46 . The product of  claim 45 , wherein said automotive, transport, consumer goods and construction sectors are selected from a vehicle, household or building parts. 
     
     
         47 . The product of  claim 45 , wherein said automotive sector is a car.