FERRITIC Cr-STEEL FOR HEAT-RESISTANT PRECISION COMPONENT AND METHOD FOR PRODUCING SAME, AND HEAT-RESISTANT PRECISION COMPONENT AND METHOD FOR PRODUCING SAME

Abstract

A ferritic Cr-steel for a heat-resistant precision component contains Cr in an amount of from 13% by mass to 30% by mass, and has a thermal expansion coefficient of 15×10 −6 or less in a temperature range of from room temperature to 800° C., and a minimum creep rate of 1×10 −4 /h or less at 700° C. under stress of 100 MPa. The ferritic Cr-steel for a heat-resistant precision component is produced by hot working a ferritic Cr-steel in a temperature range of 850 to 1,200° C., forming the ferritic Cr-steel into a predetermined shape, subjecting the steel to an annealing treatment in a temperature range of 1,000 to 1,250° C., and cooling the steel to 400° C. or less at a cooling rate of 100° C./min or higher. The production of the ferritic Cr-steel realizes a heat-resistant precision component, such as the rotor, disc, and blade of a turbine, that can withstand use under high temperatures above 600° C.

1 - 10 . (canceled) 
     
     
         11 . A ferritic Cr-steel for a heat-resistant precision component,
 characterized in that the ferritic Cr-steel is of a chemical composition that includes, in % by mass,   Cr: 13 to 30%,   Ni: 1×10 −1  to 2.5%,   C: 1×10 −3  to 1×10 −1 %, and   N: 1×10 −3  to 1×10 −1 %, and   
       that the ferritic Cr-steel additionally includes one or more of the following additional components in % by mass,
 Mo: 5×10 −1  to 5%, 
 W: 5×10 −1  to 1×10%, 
 V: 5×10 −2  to 4×10 −1 %, 
 Nb: 1×10 −2  to 1×10 −1 %, 
 Co: 1×10 −1  to 1×10%, and 
 B: 2×10 −3  to 4×10 −3 %, and 
 wherein the ferritic Cr-steel allows for inclusion of unavoidable impurities, includes Fe as the remaining part, and forms a ferrite phase, and 
 wherein the ferritic Cr-steel has a thermal expansion coefficient of 15×10 −6 /° C. or less in a temperature range of from room temperature to 800° C., and a minimum creep rate of 1×10 −4 /h or less at 700° C. under stress of 100 MPa. 
 
     
     
         12 . The ferritic Cr-steel for a heat-resistant precision component according to  claim 11 , wherein Ni is added in an amount that satisfies the relationship Ni>10(C+N), where Ni, C, and N each represent the amount of each component added (in % by mass), when C is added in 1×10 −2 % by mass or more and/or Ni is added in 1×10 −2 % by mass or more. 
     
     
         13 . The ferritic Cr-steel for a heat-resistant precision component according to  claim 11 , wherein the ferrite phase is 70 volume % or more. 
     
     
         14 . The ferritic Cr-steel for a heat-resistant precision component according to  claim 11 , wherein at least one of carbide and nitride, and an intermetallic compound are precipitated in crystal grains. 
     
     
         15 . The ferritic Cr-steel for a heat-resistant precision component according to  claim 14 , wherein Mo and W are added in amounts that satisfy the relationship Mo+0.5W≧3.0% by mass, where Mo and W each represent the amount of each component added (in % by mass). 
     
     
         16 . A process for producing a ferritic Cr-steel for a heat-resistant precision component,
 the process comprising hot working the ferritic Cr-steel of the chemical composition of  claim 11  in a temperature range of 850 to 1,200° C., forming the ferritic Cr-steel into a predetermined shape, subjecting the steel to an annealing treatment in a temperature range of 1,000 to 1,250° C., and cooling the steel to 400° C. or less at a cooling rate of 100° C./min or higher.   
     
     
         17 . A heat-resistant precision component formed from the ferritic Cr-steel for a heat-resistant precision component of  claim 11 . 
     
     
         18 . The heat-resistant precision component according to  claim 17 , wherein the heat-resistant precision component is any one of a rotor, a disc, and a blade of a turbine. 
     
     
         19 . A process for producing a heat-resistant precision component,
 the process comprising hot working the ferritic Cr-steel of the chemical composition of  claim 11  in a temperature range of 850 to 1,200° C., forming the ferritic Cr-steel into a component shape, subjecting the steel to an annealing treatment in a temperature range of 1,000 to 1,250° C., and cooling the steel to 400° C. or less at a cooling rate of 100° C./min or higher.