The Effect of Microstructure on Stress Corrosion CrackingGrowth Rates of LowAlloy High Strength Steel Welded Joint

Tongjiao Chu,Haichao Cui,Fenggui Lu,M Anis,B Munir

doi:10.1051/matecconf/201926903006

Abstract

The correlation of multi-microstructure and stress corrosion sensitivity based on the low alloy high strength steel welded joint was systematically studied in NaCl solution at the hightemperature. Through comparatively measuring the stress corrosion crack (SCC) rate in the different area of base metal (BM) and weld metal (WM) respectively, the SCC resistance in welded joint was evaluated and analysed. The SCC test indicated that the WM presented a lower crack growth rate (CGR) compared to the BM. The reason for that was mainly ascribed to the columnar of WM that impeded the crack growth in the vertical direction of stress. Meanwhile, the interwoven microstructure of nonparallel ferrite strips and fine acicular ferrite in the WM led to the zigzag propagated path and decreased the CGR.

Highlights

Stress corrosion cracking (SCC) of welded joint continues to be a crucial problem for the power industry [1, 2]
The welded joint was composed by base metal (BM) with temper bainites, heat-affected zone (HAZ) with large size of prior austenite grain (PAG), and weld metal (WM) with fine ferrites
The WM was divided into columnar grain zone and fine grain zone due to welding thermal cycles

Summary

Introduction

Stress corrosion cracking (SCC) of welded joint continues to be a crucial problem for the power industry [1, 2]. Complex microstructure in welded joint increases the difficulty to analysis stress corrosion behaviour. Kim et al [6] investigated the repairing-layer of nuclear power plant, and indicated that high stress in weld metal increases the sensitivity to SCC. The thermal cycles in multi-layers and multipasses could severely change the material properties [7, 8], such as microstructure, element segregation, precipitation of grain boundary carbides, affected the stress corrosion behaviour in the weld metal. The stress corrosion cracking tests on the welded joint of low alloy high strength steel were conducted in a chloride solution at high temperature with O2. Low alloy high strength steels as BMs are used to fabricate the welded joint investigated in this study. The narrow gap submerged arc welding (NGSAW) technique was selected to manufacture the welded joint through the multi-layers and multi-passes processes

SCC test

Microstructure characterization

Results and discussion

Conclusions