Effect of Heat Input and Niobium on the Microstructure and Toughness of Coarse Grain Heat-Affected Zone in HSLA Steels

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Abstract The influence of Nb on the coarse grain heat-affected zone (CGHAZ) microstructure, mechanical property and the transformation kinetics of HSLA steels under different heat inputs, has been investigated. When welded at higher heat inputs (100~60kJ cm-1), impact toughness values of the steel without Nb are much higher than the steel with Nb, and the lowest span is 153J at 60kJ cm-1. But only a little higher values are observed at lower heat inputs (40~30kJ cm-1), and the highest span is 68J at 30kJ cm-1. Dilatation studies indicate continuous cooling transformation start temperatures (Ts) of CGHAZ for the steel with Nb are approximately 15~30��C lower than the steel without Nb at all heat inputs. Under higher heat inputs Nb in solid solution suppress ferrite transformation and promote the formation of granular bainite which has detrimental effect on impact toughness. Under lower heat inputs higher Charpy impact energy values in the steel with Nb are associated with the formation of low carbon self-tempered martensite.

Received: 24 April 2008

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ZHANG Ying-qiao ZHANG Han-qian. Effect of Heat Input and Niobium on the Microstructure and Toughness of Coarse Grain Heat-Affected Zone in HSLA Steels[J]. Chinese Journal of Iron and Steel, 2009, 16(5): 73-73.

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http://gt.chinamet.cn/Jweb_gtyjxb_en/EN/ OR http://gt.chinamet.cn/Jweb_gtyjxb_en/EN/Y2009/V16/I5/73