Significant influence of heat input on microstructure evolution and mechanical properties of the simulated CGHAZ in a 1000 MPa grade ultra-high strength steel

ABSTRACT

The microstructure, impact properties, and crystallographic characteristics of the coarse-grained heat-affected zone (CGHAZ) in a new 1000 MPa grade ultra-high strength steel with varying heat inputs through were investigated by single-pass welding thermal simulations. As the heat input increased from 10 to 50 kJ/cm, the main microstructural constituents of the CGHAZ transitioned from lath martensite (LM) to lath bainite (LB) and subsequently to a combination of LB and granular bainite (GB). The CGHAZ exhibited a brittle fracture behaviour, and the impact energy initially increased and then declined with higher heat input. The lowest microhardness and the highest impact toughness were observed at a heat input of 20 kJ/cm. According to the results of EBSD, the proportions of high angle grain boundaries (HAGBs) and lower kernel average misorientation (KAM) values were the highest at a heat input of 20 kJ/cm. These factors collectively contributed to the enhancement of impact toughness.

KEYWORDS:

• Coarse-grained heat affected zone
• heat input
• ultra-high strength steels
• impact toughness

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was funded by the Research and Development Fund of Xi’an Thermal Power Research Institute Co., Ltd. [TQ-23-TYK13], the Opening Fund of Shaanxi Key Laboratory of Friction Welding Technology [20200101], and the Natural Science Basic Research Program of Shaanxi [2018JM5076].