Austenitic stainless steel, and hydrogenation method thereof

Abstract

Disclosed are an austenitic stainless steel, and a hydrogenation method thereof, in which occurrence of fatigue cracks and growth of fatigue cracks are suppressed by charging the austenitic stainless steel with hydrogen. In particular, focusing on the amount of diffusible hydrogen and non-diffusible hydrogen, which cause hydrogen embrittlement in austenitic stainless steel, the fatigue strength characteristics of austenitic stainless steel are improved by bringing the amount of diffusible hydrogen and non-diffusible hydrogen contained in the austenitic stainless steel to 0.0030 wt % (30 wt ppm) or higher. The austenitic stainless steel is subjected to a thermal treatment at a heating temperature of 200 to 500° C. for up to 460 hours in a hydrogen environment. The hydrogen (H) contained in the austenitic stainless steel is brought thereby to 0.0030 wt % (30 wt ppm) or higher.

1 . An austenitic stainless steel having an austenitic phase the crystalline structure of which is a face-centered cubic lattice structure,
 wherein the austenitic stainless steel undergoes a manufacturing process such that a region in which a concentration of hydrogen (H) comprising diffusible hydrogen and non-diffusible hydrogen contained in the austenitic stainless steel is locally 0.0030 wt % (30 wt ppm) or higher has a thickness of 100 μm or more from the surface of the austenitic stainless steel into the austenitic stainless steel, and wherein occurrence of fatigue cracks in the austenitic stainless steel is delayed, and/or growth of the fatigue cracks is slowed down.   
     
     
         2 . The austenitic stainless steel according to  claim 1 ,
 wherein the concentration of the hydrogen (H) in the entirety of the austenitic stainless steel has a value of 0.0030 wt % (30 wt ppm) or higher.   
     
     
         3 . The austenitic stainless steel according to  claim 1 ,
 wherein the concentration of the hydrogen (H) is 0.0050 wt % (50 wt ppm) or higher.   
     
     
         4 . The austenitic stainless steel according to  claim 2 ,
 wherein the concentration of the hydrogen (H) in the entirety of the austenitic stainless steel has a value of 0.0050 wt % (50 wt ppm) or higher.   
     
     
         5 . The austenitic stainless steel according to  claim 1 ,
 wherein the Vickers hardness (HV) of the austenitic stainless steel is 1.05 or higher, 1 being the Vickers hardness (HV) of an austenitic stainless steel in which the concentration of the hydrogen (H) in the entirety of the austenitic stainless steel is 0.0005 wt % (5 wt ppm) or less.   
     
     
         6 . The austenitic stainless steel according to  claim 1 ,
 wherein the hydrogen is stored in the austenitic stainless steel by subjecting the austenitic stainless steel to a thermal treatment at a heating temperature of 80° C. or higher in a hydrogen environment.   
     
     
         7 . The austenitic stainless steel according to  claim 6 ,
 wherein the heating temperature ranges from 200° C. to 500° C.   
     
     
         8 . An austenitic stainless steel hydrogenation method of adding hydrogen to an austenitic stainless steel, in order to increase the concentration of hydrogen in an austenitic stainless steel having an austenitic phase the crystalline structure of which is a face-centered cubic lattice structure, the method comprising the step of:
 heating the austenitic stainless steel at a heating temperature of 80° C. or higher in a hydrogen environment, to cause thereby a region in which a local concentration of the hydrogen contained in the austenitic stainless steel is 0.0030 wt % (30 wt ppm) or higher to be formed to a thickness of 100 μm or more from the surface of the austenitic stainless steel into the austenitic stainless steel.   
     
     
         9 . The austenitic stainless steel hydrogenation method according to  claim 8 ,
 wherein the hydrogen is stored in the austenitic stainless steel by keeping the austenitic stainless steel for up to 460 hours at a temperature ranging from 200° C. to 500° C., being a temperature lower than a sensitization temperature at which chromium (Cr) carbides in the austenitic stainless steel precipitate by heating.   
     
     
         10 . The austenitic stainless steel hydrogenation method according to  claim 8 ,
 wherein an overall concentration of the hydrogen (H) contained in the austenitic stainless steel is 0.0030 wt % (30 wt ppm) or higher.   
     
     
         11 . The austenitic stainless steel hydrogenation method according to  claim 8 ,
 wherein the local concentration of the hydrogen (H) contained in the austenitic stainless steel is 0.0050 wt % (50 wt ppm) or higher.   
     
     
         12 . The austenitic stainless steel hydrogenation method according to  claim 10 ,
 wherein the overall concentration of the hydrogen (H) contained in the austenitic stainless steel is 0.0050 wt % (50 wt ppm) or higher.