Effect of Heat Input on Microstructure and Toughness of Coarse Grain Heat Affected Zone in Nb Microalloyed HSLA Steels

• Published in: Journal of iron and steel research, international Vol. 16; no. 5; pp. 73 - 80
• Main Authors: ZHANG, Ying-qiao, ZHANG, Han-qian, LI, Jin-fu, LIU, Wei-ming
• Format: Journal Article
• Language: English
• Published: Singapore Elsevier Ltd 01.09.2009; Springer Singapore
• Subjects: Applied and Technical Physics; coarse grain heat affected zone; Engineering; Heat affected zone; heat input; High strength low alloy steels; HSLA steel; impact toughness; Iron and steel industry; Machines; Manufacturing; Materials Engineering; Materials Science; Metallic Materials; Microstructure; Niobium; Physical Chemistry; Processes; Steel making; Steels; Transformations; 低合金高强度钢; 冲击韧性值; 微合金; 热量输入; 焊接热输入; 粗晶热影响区; 高强钢; coarse grain heat affected zone; heat input; impact toughness; Niobium; HSLA steel
• ISSN: 1006-706X; 2210-3988; 2210-3988
• DOI: 10.1016/S1006-706X(10)60014-3

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