US-12624433-B2 - Ferritic stainless steel and method for manufacturing same

US12624433B2US 12624433 B2US12624433 B2US 12624433B2US-12624433-B2

Abstract

Realized is ferritic stainless steel which has excellent high-temperature strength and excellent red scale resistance. The ferritic stainless steel contains not more than 0.025% by mass of C, 0.05% by mass to 3.0% by mass of Si, 0.05% by mass to 2.0% by mass of Mn, not more than 0.04% by mass of P, not more than 0.03% by mass of S, not more than 0.5% by mass of Ni, 10.5% by mass to 25.0% by mass of Cr, not more than 0.025% by mass of N, 0.05% by mass to 1.0% by mass of Nb, not more than 3.0% by mass of Mo, not more than 1.8% by mass of Cu, not more than 0.2% by mass of Al, and not more than 0.5% by mass of Ti. The sum of the concentrations of Cr and Si, each of which is present as oxide or hydroxide, at a surface of the ferritic stainless steel and at depths to 6 nm from the surface is a given value or more.

Inventors

Yoshitomo Fujimura
Takahito Hamada
Taichiro MIZOGUCHI

Assignees

NIPPON STEEL STAINLESS STEEL CORPORATION

Dates

Publication Date: 20260512
Application Date: 20210304
Priority Date: 20200312

Claims (3)

1 . Ferritic stainless steel comprising: not more than 0.025% by mass of C, not less than 0.05% by mass and not more than 3.0% by mass of Si, not less than 0.05% by mass and not more than 2.0% by mass of Mn, not more than 0.04% by mass of P, not more than 0.03% by mass of S, not more than 0.5% by mass of Ni, not less than 10.5% by mass and not more than 25.0% by mass of Cr, not more than 0.025% by mass of N, not less than 0.39% by mass and not more than 1.0% by mass of Nb, not more than 3.0% by mass of Mo, not more than 0.13% by mass of Cu, not more than 0.2% by mass of Al, not more than 0.5% by mass of Ti, and iron and an inevitable impurity as a remainder, when spectra are measured by XPS analysis at a surface of said ferritic stainless steel and at depths of from 0.5 nm to 6 nm from the surface in increments of 0.5 nm, said ferritic stainless steel satisfying the following Expression (1): 240≤Cr(O)+Si(O)≤261 (1) where (i) Cr(O) represents a value obtained by calculating, for each measurement depth in terms of an atomic percent concentration with use of each of the spectra, a proportion of the total number of atoms of Cr which is present as oxide or hydroxide to the total number of atoms of Fe, Cr, Ti, Nb, Mo, and Si each of which is present as a simple substance, oxide, or hydroxide and integrating all calculated atomic percent concentrations, and (ii) Si(O) represents a value obtained by calculating, for each measurement depth in terms of an atomic percent concentration with use of each of the spectra, a proportion of the number of atoms of Si which is present as oxide to the total number of atoms of Fe, Cr, Ti, Nb, Mo, and Si each of which is present as a simple substance, oxide, or hydroxide and integrating all calculated atomic percent concentrations.
2 . The ferritic stainless steel as set forth in claim 1 , further comprising one or more of: not more than 2.5% by mass of W, not more than 0.01% by mass of B, not less than 0.0002% by mass and not more than 0.0030% by mass of Ca, not less than 0.001% by mass and not more than 0.5% by mass of Hf, not less than 0.01% by mass and not more than 0.40% by mass of Zr, not less than 0.005% by mass and not more than 0.50% by mass of Sb, not less than 0.01% by mass and not more than 0.30% by mass of Co, not less than 0.001% by mass and not more than 1.0% by mass of Ta, not less than 0.002% by mass and not more than 1.0% by mass of Sn, not less than 0.0002% by mass and not more than 0.30% by mass of Ga, not less than 0.001% by mass and not more than 0.20% by mass of a rare earth element, and not less than 0.0003% by mass and not more than 0.0030% by mass of Mg.
3 . The ferritic stainless steel as set forth in claim 2 , further comprising one or more of: not more than 0.1% by mass of La, and not more than 0.05% by mass of Ce.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a 35 U.S.C. § 371 national stage filing of International Application No. PCT/JP2021/008317, filed on Mar. 4, 2021, which claims priority to Japanese Patent Application No. 2020-043212, filed on Mar. 12, 2020. The entire contents of each of the aforementioned applications are incorporated herein by reference. TECHNICAL FIELD The present invention relates to ferritic stainless steel. More specifically, the present invention relates to ferritic stainless steel which has excellent red scale resistance and excellent high-temperature strength in a high-temperature water-vapor atmosphere, and also relates to a method for manufacturing the ferritic stainless steel. BACKGROUND ART In a case where stainless steel is used in applications such as an exhaust gas passage member, a stove burning appliance, a member for a fuel cell, or a plant-related material, the stainless steel is usually heated to a temperature as high as 300° C. to 900° C. In the above applications, since the stainless steel is used in an environment which contains water vapor, red scales (Fe-based oxide) may be generated. Therefore, in a high-temperature water-vapor atmosphere, ferritic stainless steel which has red scale resistance and high-temperature strength is desired. Conventionally, there have been known various methods for enhancing the red scale resistance and the high-temperature strength. Patent Literatures 1 and 2 disclose adding Si so as to promote diffusion of Cr, thereby increasing the amount of Cr-based oxide to be generated and strengthening an oxide film. In this manner, the inventions disclosed in Patent Literatures 1 and 2 have enhanced water vapor oxidation resistance and enhanced red scale resistance. CITATION LIST Patent Literature [Patent Literature 1] Japanese Patent Application Publication Tokukai No. 2003-160844 [Patent Literature 2] Japanese Patent Application Publication Tokukai No. 2003-160842 SUMMARY OF INVENTION Technical Problem A conventional technique as described above focuses on Cr and Si contained in steel, and is for optimizing the amount of Cr and Si contained in the steel. The inventors of the present invention focused on the point that the concentrations of oxide and hydroxide of Cr and oxide of Si in a passive film are important to enhance red scale resistance and high-temperature strength. However, in the conventional technique, no findings were obtained on the concentrations of Cr-based oxide and Si-based oxide in the passive film. An object of an aspect of the present invention is to realize ferritic stainless steel which has excellent high-temperature strength and excellent red scale resistance. Solution to Problem In order to attain the above object, ferritic stainless steel in accordance with an aspect of the present invention is ferritic stainless steel containing not more than 0.025% by mass of C, not less than 0.05% by mass and not more than 3.0% by mass of Si, not less than 0.05% by mass and not more than 2.0% by mass of Mn, not more than 0.04% by mass of P, not more than 0.03% by mass of S, not more than 0.5% by mass of Ni, not less than 10.5% by mass and not more than 25.0% by mass of Cr, not more than 0.025% by mass of N, not less than 0.05% by mass and not more than 1.0% by mass of Nb, not more than 3.0% by mass of Mo, not more than 1.8% by mass of Cu, not more than 0.2% by mass of Al, and not more than 0.5% by mass of Ti and containing iron and an inevitable impurity as a remainder, when spectra are measured, by XPS analysis, at a surface of the ferritic stainless steel and at depths of from 0.5 nm to 6 nm from the surface in increments of 0.5 nm, the ferritic stainless steel satisfying the following Expression (1): Cr(O)+Si(O)≥240 . . . (1) where (i) Cr(O) represents a value obtained by calculating, for each measurement depth in terms of an atomic percent concentration with use of each of the spectra, a proportion of the total number of atoms of Cr which is present as oxide or hydroxide to the total number of atoms of Fe, Cr, Ti, Nb, Mo, and Si each of which is present as a simple substance, oxide, or hydroxide and integrating all calculated atomic percent concentrations, and(ii) Si(O) represents a value obtained by calculating, for each measurement depth in terms of an atomic percent concentration with use of each of the spectra, a proportion of the number of atoms of Si which is present as oxide to the total number of atoms of Fe, Cr, Ti, Nb, Mo, and Si each of which is present as a simple substance, oxide, or hydroxide and integrating all calculated atomic percent concentrations. A method for manufacturing ferritic stainless steel in accordance with an aspect of the present invention is a method for manufacturing ferritic stainless steel which contains not more than 0.025% by mass of C, not less than 0.05% by mass and not more than 3.0% by mass of Si, not less than 0.05% by mass and not more than 2.0% by mass of Mn, not more th