Chromium Diffusion Coating on an ODS Ferritic-Martensitic Steel and Its Oxidation Behavior in Air and Steam Environments

Chaewon Kim,Changheui Jang,Ji-Hwan Cha,Sung Hwan Kim,Tae Kyu Kim

doi:10.3390/coatings10050492

Chaewon Kim, Changheui Jang + Show 3 more

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https://doi.org/10.3390/coatings10050492

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Abstract

A chromium diffusion coating was applied on an oxide dispersion strengthened ferritic-martensitic (ODS-FM) steel to improve oxidation resistance at high temperature. By carrying out physical vapor deposition followed by inter-diffusion heat treatment, a thin Cr-rich carbide layer was produced on the ODS-FM steel. Both the as-received and surface-modified specimens were oxidation-tested at 650 °C in air and steam environments for 500 h. The surface-modified specimens showed improved oxidation resistance in both environments. In an air environment, both conditions exhibited a thin and continuous chromia layer, but the formation of Cr2O3 and (Mn, Cr)3O4 nodules resulted in greater weight gain for the as-received specimen. In a steam environment, weight gain increased for both the as-received and surface-modified specimen. Especially, the as-received specimen showed much greater weight gain with the formation of a thick oxide layer consisted of outer Fe-rich oxide and inner (Fe, Cr, Mn) oxide layers. On the other hand, a thin and continuous chromia layer was formed for the surface-modified specimen, which resulted in much less weight gain in a steam environment.

Highlights

The operating temperature of power generation plants have been increasing to achieve better efficiency and meet the high demands of electricity [1,2]
Since this study focused only on the role of surface layer on high temperature oxidation, details on inter-diffusion zone (IDZ) were not dealt in this paper
To improve high temperature oxidation resistance, an oxide dispersion strengthened ferritic-martensitic (ODS-FM) steel was surface-modified by Cr diffusion coating method

Summary

Introduction

The operating temperature of power generation plants have been increasing to achieve better efficiency and meet the high demands of electricity [1,2]. For such high temperature applications, many heat-resistant alloys have been developed including ferritic-martensitic (FM) steels [3,4,5]. The FM steels show high strength, high creep resistance, and reasonable oxidation resistance to be used as structural materials in power plants. In ODS-FM steels, numerous nano-oxide particles are uniformly dispersed, which hinder the dislocation movement and maintain the high strength and creep resistance at higher temperature up to 700 ◦ C [6,7,8]. When water vapor is present in the environment, the breakaway oxidation was reported for FM steels [11]

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