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Title:: Research Progress on Microstructure and Coalesced Bainite of Welded Deposited Metal to High Strength Steel with Tensile Strength above 690 MPa

Author(s):: LI Zhuoxin 1; SU Xiaohu1; LI Hong1; KIM Hee Jin2; (1. College of Materials Science and Engineering，Beijing University of Technology，Beijing 100124, China）
(2. Advanced Joining Research Team, Korea Institute of Industrial Technology, Cheonan-si 330-825, Korea)

Keywords:: high-strength steel; microstructure; coalesced bainite; welded deposited metal; strength-toughness

Abstract:: The development and application of high-strength steel whose tensile strength is above 690 MPa are limited to lacking of welded materials with matching strength-toughness. The welded deposited metal to high-strength steel whose tensile strength is below 690 MPa, mainly consists of acicular ferrite. The theory of strengthening-toughening for it is not suitable for welded deposited metal of new generation high-strength steel. Therefore, the key to solve the problem is to obtain the ideal microstructure of welded deposited metal. The effect of coalesced bainite and other various microstructures on strength-toughness of welded deposited metal to highstrength steel whose tensile strength is above 690 MPa, was reviewed. It is found that the interlace multiphase microstructure composed by different bainites and acicular ferrite can make welded deposited metal achieve good strength-toughness matching. However, due to its large grain size, coalesced bainite, as a kind of lower bainite, can significantly decrease the strength-toughness of welded deposited metal to high-strength steel. Moreover, the properties of welded deposited metal to highstrength steel can be improved by physical metallurgy.