Austenitic stainless steel and production method thereof

Abstract

Provided are an austenitic stainless steel that has high strength and favorable shape retention properties after a heat treatment, and a production method thereof. One aspect of the present invention is the austenitic stainless steel wherein a component composition satisfies C: less than or equal to 0.12% by mass; Si: greater than or equal to 0.1% by mass and less than or equal to 1.0% by mass; Mn: greater than or equal to 0.1% by mass and less than or equal to 3.0% by mass; P: less than or equal to 0.05% by mass; S: less than or equal to 0.01% by mass; Cr: greater than or equal to 13.0% by mass and less than or equal to 22.0% by mass; Ni: greater than or equal to 4.0% by mass and less than or equal to 12.0% by mass; Cu: greater than or equal to 0.01% by mass and less than or equal to 0.50% by mass; Mo: less than or equal to 5.0% by mass; Al: less than or equal to 0.03% by mass; Nb: greater than or equal to 0.05% by mass and less than or equal to 0.30% by mass; N: greater than or equal to 0.10% by mass and less than or equal to 0.50% by mass; and a balance consisting of Fe and inevitable impurities, and a crystal grain size number is greater than or equal to 7.0.

1 . An austenitic stainless steel, wherein
 a component composition satisfies
 C: less than or equal to 0.12% by mass; 
 Si: greater than or equal to 0.1% by mass and less than or equal to 1.0% by mass; 
 Mn: greater than or equal to 0.1% by mass and less than or equal to 2.7% by mass; 
 P: less than or equal to 0.05% by mass; 
 S: less than or equal to 0.01% by mass; 
 Cr: greater than or equal to 13.0% by mass and less than or equal to 22.0% by mass; 
 Ni: greater than or equal to 4.0% by mass and less than or equal to 12.0% by mass; 
 Cu: greater than or equal to 0.01% by mass and less than or equal to 0.50% by mass; 
 Mo: less than or equal to 5.0% by mass; 
 Al: less than or equal to 0.03% by mass; 
 Nb: greater than or equal to 0.05% by mass and less than or equal to 0.30% by mass; 
 N: greater than or equal to 0.10% by mass and less than or equal to 0.50% by mass; and 
 a balance consisting of Fe and inevitable impurities, and 
   a crystal grain size number is greater than or equal to 7.0.   
     
     
         2 . The austenitic stainless steel according to  claim 1 ,
 wherein the component composition satisfies inequality (1):
   200≤−2090[% C]+12.8[% Cr]+320[% N]+42.3[% Nb]≤300  (1)
 
   wherein, in the inequality (1), [% C], [% Cr], [% N], and [% Nb]represent a content (% by mass) of each component.   
     
     
         3 . The austenitic stainless steel according to  claim 1 , wherein a maximum crystal grain diameter is less than or equal to 60 μm. 
     
     
         4 . The austenitic stainless steel according to  claim 1 ,
 wherein the component composition satisfies inequality (2):
   0.20[% C]+[% N]0.40  (2)
 
   wherein, in the inequality (2), [% C] and [% N]represent a content in % by mass, of each component.   
     
     
         5 . The austenitic stainless steel according to  claim 1 , wherein a maximum surface roughness height Ry is less than or equal to 10 μm. 
     
     
         6 . The austenitic stainless steel according to  claim 1 , wherein the austenitic stainless steel is configured as a seamless steel tube. 
     
     
         7 . An automobile fuel injection tube constituted of the stainless steel according to  claim 1 . 
     
     
         8 . A method for producing the austenitic stainless steel according to  claim 1 , comprising:
 performing cold working on a steel material with a working rate per pass of greater than or equal to 20%; and   performing a heat treatment on the steel material before and after performing the cold working,   wherein a component composition of the steel material satisfies   C: less than or equal to 0.12% by mass:   Si: greater than or equal to 0.1% by mass and less than or equal to 1.0% by mass;   Mn: greater than or equal to 0.1% by mass and less than or equal to 2.7% by mass;   P: less than or equal to 0.05% by mass;   S: less than or equal to 0.01% by mass;   Cr: greater than or equal to 13.0% by mass and less than or equal to 22.0%   Ni: greater than or equal to 4.0% by mass and less than or equal to 12.0% by mass;   Cu: greater than or equal to 0.03% by mass and less than or equal to 0.50% by mass;   Mo: less than or equal to 5.0% by mass;   Al: less than or equal to 0.03% by mass;   Nb: greater than or equal to 0.05% by mass and less than or equal to 0.30% by mass;   N: greater than or equal to 0.10% by mass and less than or equal to 0.50% by mass; and   a balance consisting of Fe and inevitable impurities, and   wherein a heat treatment temperature T (° C.) in the heat treatment satisfies inequality (3):
   1,000≤T≤−2090[% C]+12.8[% Cr]+320[% N]+42.3[% Nb]+900  (3)
 
   wherein, in the inequality (3), [% C], [% Cr], [% N], and [% Nb]represent a content (% by mass) of each component in the steel material.   
     
     
         9 . A method of producing the austenitic stainless steel according to  claim 1 , comprising:
 performing cold working on a steel material with a working rate per pass of greater than or equal to 20%; and   performing a heat treatment on the steel material before and after performing the cold working;   wherein a component composition of the steel material satisfies   C: less than or equal to 0.12% by mass;   Si: greater than or equal to 0.1% by mass and less than or equal to 1.0% by mass;   Mn: greater than or equal to 0.1% by mass and less than or equal to 2.7% by mass;   P: less than or equal to 0.05% by mass;   S: less than or equal to 0.01% by mass;   Cr: greater than or equal to 13.0% by mass and less than or equal to 22.0% by mass;   Ni; greater than or equal to 4.0% by mass and less than or equal to 12.0% by mass;   Cu: greater than or equal to 0.01% by mass and less than or equal to 0.50% by mass;   Mo: less than or equal to 5.0% by mass;   Al: less than or equal to 0.03% by mass;   Nb: greater than or equal to 0.05% by mass and less than or equal to 0.30% by mass;   N: greater than or equal to 0.10% by mass and less than or equal to 0.50% by mass; and   a balance consisting of Fe and inevitable impurities, and   wherein a heat treatment temperature T (° C.) in the heat treatment is greater than or equal to 1,000° C. and less than or equal to 1,200° C.   
     
     
         10 . The method of method of producing the austenitic stainless steel according to  claim 8 , wherein a final heat treatment after performing the cold working comprises bright annealing. 
     
     
         11 . The method of method of producing the austenitic stainless steel according to  claim 9 , wherein a final heat treatment after performing the cold working comprises bright annealing.