Creep Rupture of the Simulated HAZ of T92 Steel Compared to that of a T91 Steel.

Yu-Quan Peng,Sheng-Long Jeng,Leu-Wen Tsay,Tai-Cheng Chen,Tien-Jung Chung,Rong-Tan Huang

doi:10.3390/ma10020139

Abstract

The increased thermal efficiency of fossil power plants calls for the development of advanced creep-resistant alloy steels like T92. In this study, microstructures found in the heat-affected zone (HAZ) of a T92 steel weld were simulated to evaluate their creep-rupture-life at elevated temperatures. An infrared heating system was used to heat the samples to 860 °C (around AC1), 900 °C (slightly below AC3), and 940 °C (moderately above AC3) for one minute, before cooling to room temperature. The simulated specimens were then subjected to a conventional post-weld heat treatment (PWHT) at 750 °C for two hours, where both the 900 °C and 940 °C simulated specimens had fine grain sizes. In the as-treated condition, the 900 °C simulated specimen consisted of fine lath martensite, ferrite subgrains, and undissolved carbides, while residual carbides and fresh martensite were found in the 940 °C simulated specimen. The results of short-term creep tests indicated that the creep resistance of the 900 °C and 940 °C simulated specimens was poorer than that of the 860 °C simulated specimens and the base metal. Moreover, simulated T92 steel samples had higher creep strength than the T91 counterpart specimens.

Highlights

The increased application of ultra-supercritical (USC) power plants to reduce CO2 emissions and save fossil fuels has driven the development of advanced creep-resistant alloy steels
This study experimentally investigated the effects of simulated microstructures similar to those found in the heat-affected zone (HAZ) of a T92 steel weld on their creep rupture at elevated temperatures
The major findings of this study can be summarized as follows: The AC1 and AC3 temperatures of the T92 steel determined by a dilatometer at a heating rate of 0.5 ◦ C were respectively 869 ◦ C and 921 ◦ C

Summary

Introduction

The increased application of ultra-supercritical (USC) power plants to reduce CO2 emissions and save fossil fuels has driven the development of advanced creep-resistant alloy steels. Tempered 9-12 Cr steels are favored for high temperature applications such as boiler and turbine components in fossil fuel power plants, due to their excellent combination of mechanical and oxidation-resistant properties at high temperature. The addition of B into 9Cr ferritic steel delays the softening or coarsening of the M23 C6 carbides [2,3] and suppresses grain refinement in the heat-affected zones (HAZ) of the weld [4]. With the addition of tungsten into the 9Cr-Mo steel, the stabilized M2 X carbonitrides (M = Cr, Fe; X = C, N), uniform distribution of fine.

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