Non-magnetic austenitic stainless cast steel and manufacturing method of the same

Abstract

A non-magnetic austenitic stainless cast steel having high yield strength at room temperature without losing ductility at liquid nitrogen temperature, permitting easy casting without requiring the solution heat treatment, containing (by mass %) 0.08 percent or less carbon, 0.1 to 1.5 percent silicon, 0.1 to 1.5 percent manganese, 13 to 15 percent nickel, 18 to 19 percent chromium, 2 to 2.5 percent molybdenum, 0.005 to 0.1 percent aluminum, and 0.12 to 0.2 percent nitrogen, with the remainder of the steel being iron and incidental impurities, and having an elongation at liquid nitrogen temperature having 30 percent or more, 0.2% yield strength at room temperature having 240 MPa or more and relative magnetic permeability having 1.10 or less.

What we claim are:  
     
         1 . A non-magnetic austenitic stainless cast steel comprising (by mass %) 0.08 percent or less carbon, 0.1 to 1.5 percent silicon, 0.1 to 1.5 percent manganese, 13 to 15 percent nickel, 18 to 19 percent chromium, 2 to 2.5 percent molybdenum, 0.005 to 0.1 percent aluminum, and 0.12 to 0.2 percent nitrogen, the balance being iron and incidental impurities, and having an elongation at liquid nitrogen temperature having 30 percent or more, 0.2% yield strength at room temperature having 240 MPa or more.  
     
     
         2 . The non-magnetic austenitic stainless cast steel of  claim 1 , wherein the steel comprises a relative magnetic permeability having 1.10 or less.  
     
     
         3 . The non-magnetic austenitic stainless cast steel of  claim 1 , wherein the steel is obtained by being heated at temperature T(° C.) ranging from 300° C. to 550° C. and defined by the equations (1) and (2) described below for two hours or more and subsequently cooled to below 200° C. by air-cooling or slow-cooling: 
       T≦12500[N]−1200  Eq.1T≦−5000[N]+1300  Eq.2 
       wherein [N] indicates the nitrogen content (%).  
     
     
         4 . The non-magnetic austenitic stainless cast steel of  claim 1 , wherein the steel is a member used below liquid nitrogen temperature.  
     
     
         5 . The non-magnetic austenitic stainless cast steel of claims  1 , wherein the steel is a member for an electromagnet.  
     
     
         6 . A method of manufacturing a non-magnetic austenitic stainless cast steel, comprising: 
 preparing a cast steel comprising (by mass %) 0.08 percent or less carbon, 0.1 to 1.5 percent silicon, 0.1 to 1.5 percent manganese, 13 to 15 percent nickel, 18 to 19 percent chromium, 2 to 2.5 percent molybdenum, 0.005 to 0.1 percent aluminum, and 0.12 to 0.2 percent nitrogen, with the remainder of the steel being iron and incidental impurities;    heating the cast steel at temperature T(° C.) ranging from 300° C. to 550° C. and meeting equations (1) and (2) described below for two hours or more; and    cooling the cast steel to below 200° C. by air-cooling or slow-cooling:   T≦12500[N]−1200  Eq.1T≦−5000[N]+1300  Eq.2   wherein [N] indicates the nitrogen content (%).