Steam Oxidation of Austenitic Heat-Resistant Steels TP347H and TP347HFG at 650⁻800 °C.

Zhiyuan Liang,Qinxin Zhao

doi:10.3390/ma12040577

Abstract

Steam oxidation of austenitic heat-resistant steels TP347H and TP347HFG at 650–800 °C was investigated. Comprehensive micro-characterization technologies containing Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) were employed to observe and analyze the oxidation products. Results show that breakaway oxidation behaviors were observed on TP347H at 700 °C and 800 °C. The oxidation kinetics of TP347HFG at 650–800 °C followed a parabolic law. The oxide scales formed on TP347HFG were composed of MnCr2O4 and Cr2O3. A thin and protective Cr-rich oxide scale was replaced by Fe2O3 nodules due to the insufficient outward migration of metallic ions, including Cr and Mn at the subsurface of coarse-grain TP347H. Smaller grain of TP347HFG promoted the formation of the compact Cr-rich oxide scales. At higher temperatures, the incubation period for breakaway oxidation of the Cr-rich oxide scale was much shorter because of quick evaporation of the Cr2O3 oxide scale and the slower outward diffusion of metallic ions via the grain boundaries.

Highlights

Increasing the steam temperature of modern coal-fired power plants is the best approach to improve the efficiency of fossil fuel and reduce pollutants
Results show that breakaway oxidation behaviors were observed on TP347H at 700 ◦ C and 800 ◦ C
The aim of this paper is to investigate the steamoxidation behavior of austenitic heat-resistant steels TP347HFG and TP347H

Summary

Introduction

Increasing the steam temperature of modern coal-fired power plants is the best approach to improve the efficiency of fossil fuel and reduce pollutants. More and more ultra-supercritical (USC) and supercritical (SC) power plants have been built worldwide. As of almost 100 ultra-supercritical and supercritical power plants have been built in China. Proper materials for superheaters and reheaters, which are the hottest in the whole power plant, are still challenged, especially for the use of coarse-grain and fine-grain heat-resistant steel. One of the most important factors for material selection is the oxidation resistance at elevated temperatures in steam [1,2,3,4,5]. There are many papers describing the steam oxidation of heat-resistant steel used in USC power plants [6,7,8,9,10,11,12,13,14,15,16]. A stable chromia layer forms on the surface of Cr-containing steels and alloys at elevated temperatures to provide protection against severe environments [17,18,19,20]

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