低合金钢制方管闪光对焊裂纹的原因分析

doi:10.13228/j.boyuan.issn1001-0777.20230048

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Abstract Aiming at the transverse welding crack problem of Q355B steel strip (thickness of 7.5 mm) during the preparation of square pipe by welding, the composition analysis, mechanical property inspection and metallographic structure inspection were conducted. The results showed that the structure of base metal steel strip was composed of ferrite + pearlite + very small amount of bainite, which could meet the standard requirements. The crack initiation position of the square tube was in the heat-affected zone of the weld. The metal grains were distorted at the end of crack, which belonged to the extension morphology after stress crack tearing. The microstructure was the Widmannstatten structure with extremely poor plastic toughness, and there were large-size cluster inclusions at the weld which severely cut the continuity of the matrix. After comprehensive analysis, it was believed that the high welding power and too fast cooling speed led to the formation of coarse Widmannstatten structure at the weld, which seriously reduced the ductility and toughness. Combined with the impurity discharge of inclusions such as Si and Mn oxides in the weld pool, the continuity of the weld was destroyed. Under the action of tensile stress in the subsequent correction process, the crack extension was formed, which was the main reason to cause transverse cracks after welding. Such kind of problems could be avoided by optimizing the flash butt welding process and reasonably controlling the austenite grain size in the weld.

Key words： Q355B steel strip pearlite welding crack Widmannstatten structure

Received: 30 May 2023

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	Articles by authors
	SUN Qian
	XU Ruiliang
	YIN Haiyuan
	LI Cheng
	ZHU Gaofeng
	LIU Shanshan

Cite this article:

SUN Qian,XU Ruiliang,YIN Haiyuan等. Cause analysis of crack in flash butt welding of low alloy steel square pipe[J]. PHYSICS EXAMINATION AND TESTING, 2024, 42(1): 37-43.

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http://www.chinamet.cn/Jweb_wlcs/EN/10.13228/j.boyuan.issn1001-0777.20230048 OR http://www.chinamet.cn/Jweb_wlcs/EN/Y2024/V42/I1/37

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