The comparative study of submerged arc welding(SAW)and laser hybrid welding(LHW)was carried out for a 690 MPa high strength steel with thickness of 20 mm.Microstructure and ductile–brittle transition temperature(DBTT...The comparative study of submerged arc welding(SAW)and laser hybrid welding(LHW)was carried out for a 690 MPa high strength steel with thickness of 20 mm.Microstructure and ductile–brittle transition temperature(DBTT)evolution in welded zone were elucidated from the aspect of crystallographic structure,particularly,digitization and visualization of 24 variants.The impact toughness of each micro zone in LHW joint is better than that of SAW,in which the DBTT of equivalent fusion line and heat-affected zone(HAZ)can reach−70 and−80℃,while that of SAW is only−50℃.LHW technology induces narrowing of the HAZ and refining of the microstructure obtained in weld metal and HAZ.Meanwhile,the austenite grain size and transformation driving force in the coarse grained heat-affected zone(CGHAZ)are reduced and increased,respectively.It makes variant selection mechanism occurring in CGHAZ of LHW dominate by close-packed plane grouping,which promotes lath bainite formation with high density of high angle grain boundary,especially block boundary dominated by V1/V2 pair.While for SAW,the lower transformation driving force inferred from the large amount of retained austenite in CGHAZ induces Bain grouping of variants,and thus triggers the brittle crack propagating straightly in granular bainite,resulting in lower impact toughness and higher DBTT.展开更多
A hot-rolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductile-brittle transition temperature （DBTT） lower than -70℃ has been developed in laboratory. The results show that ado...A hot-rolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductile-brittle transition temperature （DBTT） lower than -70℃ has been developed in laboratory. The results show that adopting finishing rolling temperature of around 800℃ is rational, and coiling temperature is between 400 and 500℃ The strength of developed 700 MPa hot-rolled high strength steel is derived from the cumulative contribution of fine grain size, dislocation hardening and precipitation hardening. The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength, and good elongation and toughness are predominantly due to fine grain ferrite.展开更多
基金financially supported by the National Natural Science Foundation of China(No.52001023)the Special Fund for Science and Technology Project of Guangdong Province(No.SDZX2020008)the Key Research and Development Program of Shandong Province,China(No.2019JZZY020238).
文摘The comparative study of submerged arc welding(SAW)and laser hybrid welding(LHW)was carried out for a 690 MPa high strength steel with thickness of 20 mm.Microstructure and ductile–brittle transition temperature(DBTT)evolution in welded zone were elucidated from the aspect of crystallographic structure,particularly,digitization and visualization of 24 variants.The impact toughness of each micro zone in LHW joint is better than that of SAW,in which the DBTT of equivalent fusion line and heat-affected zone(HAZ)can reach−70 and−80℃,while that of SAW is only−50℃.LHW technology induces narrowing of the HAZ and refining of the microstructure obtained in weld metal and HAZ.Meanwhile,the austenite grain size and transformation driving force in the coarse grained heat-affected zone(CGHAZ)are reduced and increased,respectively.It makes variant selection mechanism occurring in CGHAZ of LHW dominate by close-packed plane grouping,which promotes lath bainite formation with high density of high angle grain boundary,especially block boundary dominated by V1/V2 pair.While for SAW,the lower transformation driving force inferred from the large amount of retained austenite in CGHAZ induces Bain grouping of variants,and thus triggers the brittle crack propagating straightly in granular bainite,resulting in lower impact toughness and higher DBTT.
基金Item Sponsored by High Technology Development Program of China(2001AA332020)
文摘A hot-rolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductile-brittle transition temperature （DBTT） lower than -70℃ has been developed in laboratory. The results show that adopting finishing rolling temperature of around 800℃ is rational, and coiling temperature is between 400 and 500℃ The strength of developed 700 MPa hot-rolled high strength steel is derived from the cumulative contribution of fine grain size, dislocation hardening and precipitation hardening. The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength, and good elongation and toughness are predominantly due to fine grain ferrite.
