Abstract
The embrittlement of heat affected zones (HAZs) resulting from the welding of a P-doped 2.25Cr-1Mo steel was studied by the analysis of the fracture appearance transition temperatures (FATTs) of the HAZs simulated under a heat input of 45 kJ/cm with different peak temperatures. The FATTs of the HAZs both with and without tempering increased with the rise of the peak temperature. However, the FATTs were apparently lower for the tempered HAZs. For the as-welded (untempered) HAZs, the FATTs were mainly affected by residual stress, martensite/austenite (M/A) islands, and bainite morphology. The observed embrittlement is a hardening embrittlement. On the other hand, the FATTs of the tempered HAZs were mainly affected by phosphorus grain boundary segregation, thereby causing a non-hardening embrittlement. The results demonstrate that the hardening embrittlement of the as-welded HAZs was more severe than the non-hardening embrittlement of the tempered HAZs. Consequently, a post-weld heat treatment should be carried out if possible so as to eliminate the hardening embrittlement.
Highlights
2.25Cr-1Mo steel, with a high temperature creep resistance, is one of the most important Cr-Mo low alloy steels, and is widely used in the power industry, where high temperatures and pressures are involved [1]
The the as-welded heat affected zones (HAZs) consisted of allotriomorphic ferrite (AF), granular bainite (GB) and lath bainite microstructures of the as-welded HAZs consisted of allotriomorphic ferrite (AF), granular bainite (LB), while some of the bainite dissolved into the matrix after tempering
There bainite in the HAZs with lower peak temperatures (1000 ◦ C and 1100 ◦ C), whereas the lath bainite was was more granular bainite in the HAZs with lower peak temperatures (1000 °C and 1100 °C), preferentially formed in the as-welded HAZs with higher peak temperatures (1200 ◦ C and 1320 ◦ C)
Summary
2.25Cr-1Mo steel, with a high temperature creep resistance, is one of the most important Cr-Mo low alloy steels, and is widely used in the power industry, where high temperatures and pressures are involved [1]. Owing to the high capacity of power plants, the pressure vessel should be made of the steel with a thick wall. A high heat input welding needs to be employed to ensure high efficiency during the manufacturing of pressure vessels [2]. The embrittlement of the weld joint induced by high heat input welding is a serious problem [2,3]. The performance of the fusion zone may be improved by metallurgy during welding, but this is impossible for the heat-affected zone (HAZ) [4]. Close attention should be paid to the embrittlement of HAZs in 2.25Cr-1Mo steel
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