Effect of Heat Input on Microstructure and Properties of SAW Joints of Q440qENH Weathering Steel

doi:10.3901/JME.2025.04.147

Abstract

Abstract: Q440qENH weathering steel is welded by submerged arc welding(SAW) under welding heat inputs i.e. 20 kJ/cm, 25 kJ/cm, 30 kJ/cm respectively, and effects of heat input on microstructure and properties of the weld joints are studied by means of optical microscopy, scanning electron microscopy and transmission electron microscopy. The results show that the microstructure of weld metal consists of proeutectoid ferrite, ferrite side-plate and acicular ferrite and M-A constituent, and the microstructure of the coarse grain zone consists of lath bainite, granular bainite and M-A constituent, the microstructure of fine-grained zone consists of fine bainite. With the increasing of heat input, the content of acicular ferrite in weld metal gradually decreases, the lath of ferrite gradually coarsens, the content and size of M-A constituent and the proportion of long strip M-A constituent gradually increase, resulting in the gradual decrease of impact toughness and hardness of weld metal; With the increasing of heat input, the microstructure of coarse grain zone gradually coarsen, the content and size of granular bainite and M-A constituent, the lath of bainite transforms from fine interlaced to coarse parallel, resulting in a gradual decrease in the impact toughness of the heat affected zone. The tensile test specimens of the welded joints are all fractured at the base metal, and the bending test specimens are all intact.

Key words: Q440qENH weathering steel, heat input, welded joints, microstructure, properties

CLC Number:

TG445

ZENG Daoping, ZHENG Shaoxian, AN Tongbang, ZUO Yue, MA Chengyong. Effect of Heat Input on Microstructure and Properties of SAW Joints of Q440qENH Weathering Steel[J]. Journal of Mechanical Engineering, 2025, 61(4): 147-155.

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