Comparative Study Of Weld Properties Between TMCP Q370qE And Normalized Q370qE Steel

In order to study the difference of welding performance between TMCP Q370qE steel and normalized Q370qE steel comparativly,the micro structure and mechanical properties of Coarse Grain Heat Affected Zone(CGHAZ)of these two Q370qE steels were investigated with the simulated thermal cycle process conducted in a Gleeble-3500 system.The welding performance under the same welding condition were also compared according to weldability evaluation test and mechanical properties test.The micro structure and fracture morphology were observed by optical microscope,EBSD and scanning electron microscope,and the low temperature toughening mechanism of TMCP Q370qE welded joints was explored.The results show:In the range of 10～50kJ/cm,the CGHAZ of two Q370qE steels were composed of acicular ferrite,granular bainite and lath bainite.Compared with the normalized Q370qE steel,TMCP Q370qE has a lower hardness,smaller original austinite grain size,less M-A content,bigger number fraction of high misorientation angle,and then the impact energy at-40℃ is better.Compared with normalized Q370qE steel,due to a significant reduction of carbon content and carbon equivalent,the TMCP Q370qE steel plate has a lower tendency of weld hardening tendency and crack susceptibility.Preheating is not required when the thickness is less than 50mm.Toughness and brittle transition property of the joints under the welding condition of conventional submerged arc weld were excellent,and the Ductile-brittle transition temperature of the weld and heat affected zone were low,the structure was brittle fracture resistance.The joints also had low hardness and superior impact property.As the micro structures of TMCP Q370qE steel were significantly refined,the number of brittle phases was reduced in the weld zone,heat affected zone and base metal zone,the impact energy was improved and the impact toughness was better than that of normalized Q370qE steel.The results of this study provide theoretical basis for the application of Q370qE steel in practical production.