Abstract
The Gleeble 1500 test machine was used to simulate the single-pass welding thermal cycle of BWELDY960Q steel under different heat input conditions. In this paper, microstructure observation and mechanical properties of BWELDY960Q steel specimens in coarse grain heat affected zone (CGHAZ) under different heat input conditions were investigated. The results show that under different heat input conditions, the microstructure of CGHAZ is lath martensite, granular bainite, or M-A constituent. As heat input increases, the number and size of the M-A constituent increase accordingly, and the microstructure gradually changes from lath martensite to granular bainite. Meanwhile, compared with the previous samples, the CGHAZ austenite grain diameter increases, and the grain size scale decreases. Furthermore, the value of the CGHAZ impact absorbing energy increases at first but then decreases, while microhardness monotonously decreases. At –20 °C compared with the base metal, the impact absorbing the energy of CGHAZ is significantly reduced, and embrittlement occurs.

Key words
BWELDY960Q steel, heat inputs, coarse grain heat affected zone, microstructure, mechanical properties

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