SH-CCT Diagram， Microstructure and Properties of Coarse Grain Heat-Affected Zone in Q1100 Ultra-high Strength Steel

doi:10.12068/j.issn.1005-3026.2017.06.010

Abstract

Abstract:

It is generally believed that coarse grain heat-affected zone (CGHAZ) in welded region is the weakest part in the welding joint of low alloy ultra-high strength steel. The thermomechanical simulator was employed to simulate the welding thermal cycle processes of CGHAZ in Q1100 ultra-high strength steel. By using thermal expansion measurement combined with OM，SEM observations and hardness test， the critical phase transformation points at the equilibrium state and welding conditions were determined and SH-CCT diagram at different cooling rates was plotted. TEM observation and Lepera reagent were used to reveal the morphology of M-A constituent. The results showed that the austenitizing temperature of this steel in the welding condition was significantly higher than that in equilibrium state. The microstructure of CGHAZ mainly consisted of bainite， bainite and martensite， and martensite accompany with the increase of cooling rate. The hardness increased gradually with the increase of cooling rates， the maximum hardness was HV464. The M-A constituent occurred when the cooling rate was lower than 10℃/s， and the lower cooling rate， the more M-A constituent.

Key words: ultra-high strength steel, SH-CCT diagram, coarse grain heat-affected zone(CGHAZ), microstructure, M-A constituent

CLC Number:

TG40

WEN Chang-fei， DENG Xiang-tao， WANG Zhao-dong， WANG Guo-dong. SH-CCT Diagram， Microstructure and Properties of Coarse Grain Heat-Affected Zone in Q1100 Ultra-high Strength Steel[J]. Journal of Northeastern University Natural Science, 2017, 38(6): 809-813.

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