Heat Resistant Ferritic Steel and Ferritic Heat Transfer Member

Abstract

This invention provides a ferritic heat transfer member and a heat resistant ferritic steel which are excellent in heat transfer characteristics and steam oxidation resistance properties. The heat resistant ferritic steel includes a base material, and an oxidized layer A on the surface of the base material. The base material has a chemical composition containing, in mass %: C: 0.01 to 0.3%, Si: 0.01 to 2.0%, Mn: 0.01 to 2.0%, Cr: 7.0 to 14.0%, N: 0.005 to 0.15%, and sol. Al: 0.001 to 0.3%, and one or more types of element selected from the specific oxidized layer forming elements of 0.5 to 7.0%, with the balance being Fe and impurities. An oxidized layer A includes a chemical composition containing, in mass %: Cr and Mn in a total amount of 20 to 45%, and one or more types of element selected from the specific oxidized layer forming elements of 0.5 to 10%.

1 . A heat resistant ferritic steel comprising:
 a base material, and   an oxidized layer A on a surface of the base material;   wherein:   the base material has a chemical composition consisting of, in mass %:   C: 0.01 to 0.3%,   Si: 0.01 to 2.0%,   Mn: 0.01 to 2.0%,   P: 0.10% or less,   S: 0.03% or less,   Cr: 7.0 to 14.0%,   N: 0.005 to 0.15%,   sol. Al: 0.001 to 0.3%,   one or more types of element selected from the group consisting of Mo: 0 to 5.0%, Ta: 0 to 5.0%, W: 0 to 5.0% and Re: 0 to 5.0%: 0.5 to 7.0% in total,   Cu: 0 to 5.0%,   Ni: 0 to 5.0%,   Co: 0 to 5.0%,   Ti: 0 to 1.0%,   V: 0 to 1.0%,   Nb: 0 to 1.0%,   Hf: 0 to 1.0%,   Ca: 0 to 0.1%,   Mg: 0 to 0.1%,   Zr: 0 to 0.1%,   B: 0 to 0.1%, and   rare earth metal: 0 to 0.1%,   with the balance being Fe and impurities; and   the oxidized layer A has a chemical composition containing, in mass %:   Cr and Mn: 20 to 45% in total, and   one or more types of element selected from the group consisting of Mo, Ta, W and Re: 0.5 to 10% in total.   
     
     
         2 . The heat resistant ferritic steel according to  claim 1 , wherein the chemical composition of the base material contains one or more types of element selected from the group consisting of:
 Cu: 0.005 to 5.0%,   Ni: 0.005 to 5.0%, and   Co: 0.005 to 5.0%.   
     
     
         3 . The heat resistant ferritic steel according to  claim 1 , wherein the chemical composition of the base material contains one or more types of element selected from the group consisting of:
 Ti: 0.01 to 1.0%,   V: 0.01 to 1.0%,   Nb: 0.01 to 1.0%, and   Hf: 0.01 to 1.0%.   
     
     
         4 . The heat resistant ferritic steel according to  claim 1 , wherein the chemical composition of the base material contains one or more types of element selected from the group consisting of:
 Ca: 0.0015 to 0.1%,   Mg: 0.0015 to 0.1%,   Zr: 0.0015 to 0.1%,   B: 0.0015 to 0.1%, and   rare earth metal: 0.0015 to 0.1%.   
     
     
         5 . A ferritic heat transfer member, comprising:
 a base material having a chemical composition according to  claim 1 , and   an oxide film on a surface of the base material;   wherein:   the oxide film comprises:   an oxidized layer B containing Fe 3 O 4  and Fe 2 O 3  in a total amount of 80% or more in vol %, and   an oxidized layer C that is disposed between the oxidized layer B and the base material; and   a chemical composition of the oxidized layer C contains, in mass %:   Cr and Mn: more than 5% to 30% in total, and   one or more types of element selected from the group consisting of Mo, Ta, W and Re: 1 to 15% in total.   
     
     
         6 . The ferritic heat transfer member according to  claim 5 , wherein a chemical composition of the oxidized layer B contains, in mass %:
 Cr and Mn: 5% or less in total.   
     
     
         7 . The ferritic heat transfer member according to  claim 5 , wherein the oxidized layer C contains, in vol %, 5% or less of Cr 2 O 3 . 
     
     
         8 . The heat resistant ferritic steel according to  claim 2 , wherein the chemical composition of the base material contains one or more types of element selected from the group consisting of:
 Ti: 0.01 to 1.0%,   V: 0.01 to 1.0%,   Nb: 0.01 to 1.0%, and   Hf: 0.01 to 1.0%.   
     
     
         9 . The heat resistant ferritic steel according to  claim 2 , wherein the chemical composition of the base material contains one or more types of element selected from the group consisting of:
 Ca: 0.0015 to 0.1%,   Mg: 0.0015 to 0.1%,   Zr: 0.0015 to 0.1%,   B: 0.0015 to 0.1%, and   rare earth metal: 0.0015 to 0.1%.   
     
     
         10 . The heat resistant ferritic steel according to  claim 3 , wherein the chemical composition of the base material contains one or more types of element selected from the group consisting of:
 Ca: 0.0015 to 0.1%,   Mg: 0.0015 to 0.1%,   Zr: 0.0015 to 0.1%,   B: 0.0015 to 0.1%, and   rare earth metal: 0.0015 to 0.1%.   
     
     
         11 . The heat resistant ferritic steel according to  claim 8 , wherein the chemical composition of the base material contains one or more types of element selected from the group consisting of:
 Ca: 0.0015 to 0.1%,   Mg: 0.0015 to 0.1%,   Zr: 0.0015 to 0.1%,   B: 0.0015 to 0.1%, and   rare earth metal: 0.0015 to 0.1%.   
     
     
         12 . The ferritic heat transfer member according to  claim 6 , wherein the oxidized layer C contains, in vol %, 5% or less of Cr 2 O 3 .