Heat resistant steel for exhaust valve

Abstract

The present invention provides a heat resistant steel for an exhaust valve, containing: more than 0.50% by mass but less than 0.80% by mass of C, more than 0.30% by mass but less than 0.60% by mass of N, 17.0% by mass or more but less than 25.0% by mass of Cr, 4.0% by mass or more but less than 12.0% by mass of Ni, 7.0% by mass or more but less than 14.0% by mass of Mn, 2.0% by mass or more but less than 6.0% by mass of Mo, more than 0.5% by mass but less than 1.5% by mass of Si, and 0.025% by mass or more but less than 1.0% by mass of Nb, with the balance consisting of Fe and unavoidable impurities, in which a content of P contained in the unavoidable impurities is regulated to less than 0.03% by mass, a total content of C and N is from 0.85% by mass to 1.3% by mass, and a ratio of the content of Nb to the content of C is 0.05 or more but less than 1.8.

1 . A heat resistant steel for an exhaust valve, comprising:
 more than 0.50% by mass but less than 0.80% by mass of C,   more than 0.30% by mass but less than 0.60% by mass of N,   17.0% by mass or more but less than 25.0% by mass of Cr,   4.0% by mass or more but less than 12.0% by mass of Ni,   7.0% by mass or more but less than 14.0% by mass of Mn,   2.0% by mass or more but less than 6.0% by mass of Mo,   more than 0.5% by mass but less than 1.5% by mass of Si, and   0.025% by mass or more but less than 1.0% by mass of Nb,   with the balance consisting of Fe and unavoidable impurities,   wherein a content of P contained in the unavoidable impurities is regulated to less than 0.03% by mass,   wherein a total content of C and N is from 0.85% by mass to 1.3% by mass, and   wherein a ratio of the content of Nb to the content of C is 0.05 or more but less than 1.8.   
     
     
         2 . The heat resistant steel for an exhaust valve according to  claim 1 , which further comprises 0.001% by mass or more but less than 0.01% by mass of Mg and Ca in total. 
     
     
         3 . The heat resistant steel for an exhaust valve according to  claim 1 , which further comprises at least one selected from the group consisting of:
 0.001% by mass or more but less than 0.03% by mass of B, and   0.001% by mass or more but less than 0.1% by mass of Zr.   
     
     
         4 . The heat resistant steel for an exhaust valve according to  claim 2 , which further comprises at least one selected from the group consisting of:
 0.001% by mass or more but less than 0.03% by mass of B, and   0.001% by mass or more but less than 0.1% by mass of Zr.   
     
     
         5 . The heat resistant steel for an exhaust valve according to  claim 1 , which further comprises 0.01% by mass or more but less than 5.0% by mass of Co. 
     
     
         6 . The heat resistant steel for an exhaust valve according to  claim 2 , which further comprises 0.01% by mass or more but less than 5.0% by mass of Co. 
     
     
         7 . The heat resistant steel for an exhaust valve according to  claim 3 , which further comprises 0.01% by mass or more but less than 5.0% by mass of Co. 
     
     
         8 . The heat resistant steel for an exhaust valve according to  claim 4 , which further comprises 0.01% by mass or more but less than 5.0% by mass of Co.