Austenitic stainless steel, and method for removing hydrogen therefrom

Abstract

The present invention focuses on diffusible hydrogen and non-diffusible hydrogen that cause hydrogen embrittlement in an austenitic stainless steel, and provides the austenitic stainless steel having diffusible hydrogen and non-diffusible hydrogen removed therefrom, and a method for removing hydrogen therefrom. In order to remove diffusible hydrogen and non-diffusible hydrogen, which cause hydrogen embrittlement in the austenitic stainless steel, an aging treatment is performed to the austenitic stainless steel at a temperature ranging from 200 to 1100° C. while being kept in an air atmosphere. As a result, the hydrogen (H) content in the austenitic steel is removed to 0.001 wt % (1 wt ppm) or less.

1 . An austenitic stainless steel having an austenitic phase where a crystalline structure is a face-centered cubic lattice structure,
 wherein the austenitic stainless steel is subjected to a thermal treatment in an air atmosphere, at a heating temperature ranging from 200° C. to 1100° C., to remove thereby diffusible hydrogen and non-diffusible hydrogen that cause hydrogen embrittlement in the austenitic stainless steel, and remove a content of hydrogen (H) in the austenitic stainless steel to 0.0001 wt % (1.0 wt ppm) or less.   
     
     
         2 . The austenitic stainless steel according to  claim 1 ,
 wherein the diffusible hydrogen and the non-diffusible hydrogen are removed so that the hydrogen (H) is 0.00002 wt % (0.2 wt ppm) or less.   
     
     
         3 . The austenitic stainless steel according to  claim 2 ,
 wherein the diffusible hydrogen and the non-diffusible hydrogen are removed so that the hydrogen (H) is 0.00007 wt % (0.7 wt ppm) or less.   
     
     
         4 . The austenitic stainless steel according to  claim 3 ,
 wherein the diffusible hydrogen and the non-diffusible hydrogen are removed so that the hydrogen (H) is 0.000007 wt % (0.07 wt ppm) or less.   
     
     
         5 . The austenitic stainless steel according to any one of  claims 1  to  4 ,
 wherein the austenitic stainless steel is heated at a heating temperature ranging from 200° C. to 1100° C. for 2 hours to 500 hours to remove the diffusible hydrogen and the non-diffusible hydrogen. 
 
     
     
         6 . A method for removing hydrogen from an austenitic stainless steel, which is a thermal treatment method in which the austenitic stainless steel, having an austenitic phase where a crystalline structure is a face-centered cubic lattice structure, is subjected to a thermal treatment to remove hydrogen present in the austenitic stainless steel, the method comprising
 heating the austenitic stainless steel in an air atmosphere, at a heating temperature ranging from 200° C. to 1100° C., to remove thereby diffusible hydrogen and non-diffusible hydrogen in the austenitic stainless steel, to a content of 0.0001 wt % (1.0 wt ppm) or less.   
     
     
         7 . The method for removing hydrogen from an austenitic stainless steel according to  claim 6 ,
 wherein there are removed the diffusible hydrogen and the non-diffusible hydrogen that are present in the austenitic stainless steel, diffuse via a mechanically-induced martensitic phase brought about by cyclic loading, accumulate in cracks that are under stress concentration, and cause hydrogen embrittlement in the austenitic stainless steel.   
     
     
         8 . The method for removing hydrogen from an austenitic stainless steel according to  claim 6 ,
 wherein the austenitic stainless steel is held, from 2 hours to 500 hours at a temperature lower than a sensitization temperature at which chromium (Cr) carbides in the austenitic stainless steel precipitate due to heating,   and there are removed the diffusible hydrogen and the non-diffusible hydrogen that cause hydrogen embrittlement in the austenitic stainless steel.   
     
     
         9 . The method for removing hydrogen from an austenitic stainless steel according to  claim 7  or  8 ,
 wherein the hydrogen (H) content in the austenitic stainless steel is 0.00007 wt % (0.7 wt ppm) or less. 
 
     
     
         10 . The method for removing hydrogen from an austenitic stainless steel according to  claim 9 ,
 wherein the hydrogen (H) content in the austenitic stainless steel is 0.00002 wt % (0.2 wt ppm) or less.   
     
     
         11 . The method for removing hydrogen from an austenitic stainless steel according to  claim 10 ,
 wherein the hydrogen (H) content in the austenitic stainless steel is 0.000007 wt % (0.07 wt ppm) or less.   
     
     
         12 . The method for removing hydrogen from an austenitic stainless steel according to  claim 6 ,
 wherein the diffusible hydrogen and the non-diffusible hydrogen diffuse via a mechanically-induced martensitic phase brought about by cyclic loading at low-frequency, accumulate in cracks that are under stress concentration, increase thereby the growth rate of fatigue cracks, and cause hydrogen embrittlement in the austenitic stainless steel.