Improvement in Weldment of Dissimilar 9% CR Heat-Resistant Steels by Post-Weld Heat Treatment

Jiankun Xiong,Guijun Mao,Ting Li,Lin Yang,Jian Xu,Jianping Yang,Xinjian Yuan

doi:10.3390/met10101321

Jiankun Xiong, Guijun Mao + Show 5 more

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https://doi.org/10.3390/met10101321

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Abstract

The effect of the post-weld heat treatment on the microstructures and mechanical properties of the dissimilar joint of G115, a novel developed martensite heat resistant steel, and CB2 steel, currently used in an ultra-super-critical power unit, was investigated. The results indicate that the quenched martensite underwent decomposition and transformation, and the amount of dislocations were sharply decreased in the weld metal after post-weld heat treatment (PWHT). Many nano-scale M23C6 precipitates present in the weldment were distributed on the grain and grain boundary in a dispersed manner with PWHT. The average microhardness of the weldment decreased from about 400 HV to 265–290 HV after PWHT and only a slight decrease in the microhardness of CB2 steel was detected after PWHT at 760 °C. In contrast to the case of the as-received joint, the tensile strength of the joint was improved from 630 MPa to 694 MPa and the fracture location moved from the weld metal to the base metal after PWHT. The fracture surface consisted of a cleavage fracture mode without PWHT, whereas many dimples were observed on the fracture surface with PWHT.

Highlights

Heat resistant steels are widely used as structural materials for boilers, main steam pipes, and turbines of power plants [1,2]
The G115 steel plate with dimensions of 200 × 150 × 40 mm, which was produced by China BaoWu Steel Group Corporation Limited (Shanghai, China), was in the condition of quenching and high temperature tempering
The filler wire was made by Atlantic China Welding

Summary

Introduction

Heat resistant steels are widely used as structural materials for boilers, main steam pipes, and turbines of power plants [1,2]. The upper limit of the operating temperature of the commercial heat-resistant steel is about 600 ◦ C. The key factor restricting the construction of a 630 °C power station is the ability to produce heat-resistant steel in the higher temperature range of 630 ◦ C [5,6]. In this context, many attempts have been made to overcome this limitation. A martensitic heat-resistant steel with a 9Cr-3W-3Co composition system is pivotal to research and development

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Discussion

Conclusion