Ferritic heat resistant steel

Abstract

Heat-resistant steel excellent in high-temperature long-term creep strength and creep-fatigue strength is provided. This heat-resistant steel comprises C: 0.01 to 0.13%, Si: 0.15 to 0.50%, Mn: 0.2 to 0.5%, P: not higher than 0.02%, S; not higher than 0.005%, Cr: exceeding 8.0% but lower than 12.0%, Mo: 0.1 to 1.5%, W: 1.0 to 3.0%, V: 0.1 to 0.5%, Nb: 0.02 to 0.10%, sol. Al: not higher than 0.015%, N: 0.005 to 0.070%, Nd: 0.005 to 0.050% and B: 0.002 to 0.015%, with the balance Fe and impurities; the content of Ni is lower than 0.3%, the content of Co is lower than 0.3% and the content of Cu is lower than 0.1% among the impurities; the steel contains Nd inclusions at a Nd inclusion density of not lower than 10000 inclusions/mm 3 . This steel may contain, in addition to the above-specified components, one or more elements of Ta, Hf, Ti, Ca and Mg.

1 . Ferritic heat-resistant steel which comprises C, 0.01 to 0.13%, Si: 0.15 to 0.50%, Mn: 0.2 to 0.5%, P: not higher than 0.02%, S; not higher than 0.005%, Cr: exceeding 8.0% but lower than 12.0%, Mo: 0.1 to 1.5%, W: 1.0 to 3.0%, V: 0.1 to 0.5%, Nb: 0.02 to 0.10%, sol. Al: not higher than 0.015%, N: 0.005 to 0.070%, Nd: 0.005 to 0.050% and B: 0.002 to 0.015%, with the balance Fe and impurities, wherein the content of Ni is lower than 0.3%, the content of Co is lower than 0.3% and the content of Cu is lower than 0.1% among the impurities, said steel containing Nd inclusions at a Nd inclusion density of not lower than 10000 inclusions/mm 3 .  
     
     
         2 . Ferritic heat-resistant steel according to  claim 1 , which is characterized in that it contains at least one of Ta: not higher than 0.04%, Hf: not higher than 0.04% and Ti: not higher than 0.04% in place of part of Fe.  
     
     
         3 . Ferritic heat-resistant steel according to  claim 1 , which is characterized in that it contains one or both of Ca: not higher than 0.005% and Mg: not higher than 0.005% in place of part of Fe.  
     
     
         4 . Ferritic heat-resistant steel according to  claim 1 , which is characterized in that it contains at least one of Ta: not higher than 0.04%, Hf: not higher than 0.04% and Ti: not higher than 0.04%, and it also contains one or both of Ca: not higher than 0.005% and Mg: not higher than 0.005%, in place of part of Fe.  
     
     
         5 . Ferritic heat-resistant steel according to  claim 1 , which is characterized in that the total content of rare earth elements, except for Nd, among the impurities is not higher than 0.04%.  
     
     
         6 . Ferritic heat-resistant steel according to  claim 1 , which is characterized in that it contains at least one of Ta: not higher than 0.04%, Hf: not higher than 0.04% and Ti: not higher than 0.04% in place of part of Fe, and also characterized in that the total content of rare earth elements, except for Nd, among the impurities is not higher than 0.04%.  
     
     
         7 . Ferritic heat-resistant steel according to  claim 1 , which is characterized in that it contains one or both of Ca: not higher than 0.005% and Mg: not higher than 0.005% in place of part of Fe, and furthermore characterized in that the total content of rare earth elements, except for Nd, among the impurities is not higher than 0.04%.  
     
     
         8 . Ferritic heat-resistant steel according to  claim 1 , which is characterized in that it contains at least one of Ta: not higher than 0.04%, Hf: not higher than 0.04% and Ti: not higher than 0.04%, and it also contains one or both of Ca: not higher than 0.005% and Mg: not higher than 0.005%, in place of part of Fe, and furthermore characterized in that the total content of rare earth elements, except for Nd, among the impurities is not higher than 0.04%.  
     
     
         9 . Ferritic heat-resistant steel according to  claim 1 , which is characterized in that the creep-fatigue life thereof under the CP type strain wave form at 600° C. under the conditions of a strain rate of 0.01%/sec on the tensile side, a strain rate of 0.8%/sec on the compressive side and a total strain range of 0.5% is not shorter than 5000 cycles.  
     
     
         10 . Ferritic heat-resistant steel according to  claim 2 , which is characterized in that the creep-fatigue life thereof under the CP type strain wave form at 600° C. under the conditions of a strain rate of 0.01%/sec on the tensile side, a strain rate of 0.8%/sec on the compressive side and a total strain range of 0.5% is not shorter than 5000 cycles.  
     
     
         11 . Ferritic heat-resistant steel according to  claim 3 , which is characterized in that the creep-fatigue life thereof under the CP type strain wave form at 600° C. under the conditions of a strain rate of 0.01%/sec on the tensile side, a strain rate of 0.8%/sec on the compressive side and a total strain range of 0.5% is not shorter than 5000 cycles.  
     
     
         12 . Ferritic heat-resistant steel according to  claim 4 , which is characterized in that the creep-fatigue life thereof under the CP type strain wave form at 600° C. under the conditions of a strain rate of 0.01%/sec on the tensile side, a strain rate of 0.8%/sec on the compressive side and a total strain range of 0.5% is not shorter than 5000 cycles.  
     
     
         13 . Ferritic heat-resistant steel according to  claim 5 , which is characterized in that the creep-fatigue life thereof under the CP type strain wave form at 600° C. under the conditions of a strain rate of 0.01%/sec on the tensile side, a strain rate of 0.8%/sec on the compressive side and a total strain range of 0.5% is not shorter than 5000 cycles.  
     
     
         14 . Ferritic heat-resistant steel according to  claim 6 , which is characterized in that the creep-fatigue life thereof under the CP type strain wave form at 600° C. under the conditions of a strain rate of 0.01%/sec on the tensile side, a strain rate of 0.8%/sec on the compressive side and a total strain range of 0.5% is not shorter than 5000 cycles.  
     
     
         15 . Ferritic heat-resistant steel according to  claim 7 , which is characterized in that the creep-fatigue life thereof under the CP type strain wave form at 600° C. under the conditions of a strain rate of 0.01%/sec on the tensile side, a strain rate of 0.8%/sec on the compressive side and a total strain range of 0.5% is not shorter than 5000 cycles.  
     
     
         16 . Ferritic heat-resistant steel according to  claim 8 , which is characterized in that the creep-fatigue life thereof under the CP type strain wave form at 600° C. under the conditions of a strain rate of 0.01%/sec on the tensile side, a strain rate of 0.8%/sec on the compressive side and a total strain range of 0.5% is not shorter than 5000 cycles.