Austenitic stainless steel and process for removing hydrogen therefrom

Abstract

By focusing on the non-diffusible hydrogen that causes hydrogen embrittlement of austenitic stainless steel, the present invention provides an austenitic stainless steel in which the non-diffusible hydrogen is removed by maintaining the austenitic stainless steel in a vacuum of 0.2 Pa or less and heating at a heating temperature of 200° C. to 500° C. for 460 hours or less to remove the hydrogen (H) contained therein to a level of 0.00007 mass % (0.7 mass ppm) or less.

1 . An austenitic stainless steel having an austenitic phase in which a crystalline structure is a face centered cubic lattice structure,
 wherein diffusible hydrogen and non-diffusible hydrogen, which are cause of hydrogen embrittlement in the austenitic stainless steel, are removed therefrom such that the hydrogen (H) contained in the austenitic stainless steel is removed to a level of 0.00007 mass % (0.7 mass ppm) or less.   
   
   
       2 . The austenitic stainless steel according to  claim 1 ,
 wherein the diffusible hydrogen and non-diffusible hydrogen are removed therefrom such that the hydrogen (H) is removed to a level of 0.00004 mass % (0.4 mass ppm) or less.   
   
   
       3 . The austenitic stainless steel according to  claim 2 ,
 wherein the diffusible hydrogen and non-diffusible hydrogen are removed therefrom such that the hydrogen (H) is removed to a level of 0.00001 mass % (0.1 mass ppm) or less.   
   
   
       4 . The austenitic stainless steel according to any one of  claims 1  to  3 ,
 wherein the austenitic stainless steel is heat-treated at a heating temperature of 200° C. or higher to remove the diffusible and non-diffusible hydrogen therefrom.   
   
   
       5 . The austenitic stainless steel according to  claim 4 ,
 wherein the heating temperature is a temperature from 200° C. to 500° C.   
   
   
       6 . A process for removing hydrogen from an austenitic stainless steel, in which the austenitic stainless steel having an austenitic phase in which a crystalline structure is a face centered cubic lattice structure is heat-treated in a heat treatment to remove the hydrogen present in the austenitic stainless steel,
 wherein the austenitic stainless steel is heated to a heating temperature of 200° C. or higher to remove the diffusible hydrogen and non-diffusible hydrogen in the austenitic stainless steel to a level of 0.00007 mass % (0.7 mass ppm) or less.   
   
   
       7 . The process for removing hydrogen from austenitic stainless steel according to  claim 6 ,
 wherein the heating temperature is a temperature from 200° C. to 500° C., and both the diffusible hydrogen and non-diffusible hydrogen, which are present in the austenitic stainless steel, diffuse via the stress-induced martensitic phase brought about by cyclic loading, concentrate in the cracks undergoing concentrated stress, and cause hydrogen embrittlement therein, are removed therefrom such that the hydrogen (H) contained therein is removed to a level of 0.00007 mass % (0.7 mass ppm) or less.   
   
   
       8 . The process for removing hydrogen from austenitic stainless steel according to  claim 6 ,
 wherein the austenitic stainless steel is maintained at a temperature from 200° C. to 500° C., which is a temperature lower than the sensitization temperature at which chromium (Cr) carbide in the austenitic stainless steel precipitates due to the heat, for 460 hours or less, and   both the diffusible hydrogen and non-diffusible hydrogen, which cause hydrogen embrittlement in the austenitic stainless steel, are removed therefrom such that the hydrogen (H) contained in the austenitic stainless steel is removed to a level of 0.00004 mass % (0.4 mass ppm) or less.   
   
   
       9 . The process for removing hydrogen from an austenitic stainless steel according to  claim 7  or  8 ,
 wherein the hydrogen (H) contained in the austenitic stainless steel is removed to a level of 0.00001 mass % (0.1 mass ppm) or less.   
   
   
       10 . The process for removing hydrogen from an austenitic stainless steel according to  claim 6 ,
 wherein the austenitic stainless steel is maintained at the heating temperature and in a temperature range below a melting point thereof for 30 seconds or more during the manufacturing process thereof to remove the diffusible hydrogen and non-diffusible hydrogen contained therein to a level of 0.00007 mass % (0.7 mass ppm) or less.   
   
   
       11 . The process for removing hydrogen from austenitic stainless steel according to  claim 10 ,
 wherein the heating temperature in the heat treatment to remove the hydrogen present therein is 700° C. or more and also in a temperature range below the melting point of the austenitic stainless steel.   
   
   
       12 . The process for removing hydrogen from austenitic stainless steel according to  claim 11 ,
 wherein the heating temperature in the heat treatment to remove the hydrogen present therein is 920° C. or higher, and the diffusible hydrogen and non-diffusible hydrogen therein are removed to a level of 0.00004 mass % (0.4 mass ppm) or less.