大热输入焊接用EH40船板钢焊接热影响区组织转变与力学性能

Microstructure transformation and mechanical properties of EH40 shipbuilding plate steel for high heat input welding application

河钢集团采用氧化物冶金技术开发出了大热输入焊接用EH40船板钢,利用DIL805L淬火相变膨胀仪结合焊接热模拟技术,研究了EH40船板钢焊接热影响区(HAZ)连续冷却转变行为和不同冷却速度下HAZ的组织转变。同时,采用Gleeble-3800热模拟试验机对EH40船板钢进行焊接热模拟试验,并对其焊接HAZ力学性能进行了测定。焊接HAZ连续转变曲线(SHCCT)表明,当冷却速率≤1℃/s时,主要发生铁素体/珠光体转变;随着冷却速率增大至2℃/s时,贝氏体开始析出;当冷却速率在2~3℃/s时,发生铁素体/珠光体和粒状贝氏体转变;当冷却速率在5~10℃/s时,发生铁素体/粒状贝氏体转变;而且随着冷却速率增大,粒状贝氏体所占比例逐渐升高;当冷却速率增大至15℃/s时,开始出现板条状贝氏体;当冷却速率在30~100℃/s时,开始出现马氏体,并且马氏体所占比例逐渐升高。另外,焊接热模拟和冲击试验结果表明,经过200 kJ/cm热输入焊接热模拟后,EH40船板钢HAZ在-40℃下的平均冲击吸收能量为205 J,远大于国标要求的41 J。采用扫描电镜及配套的能谱仪对EH40船板钢焊接HAZ析出粒子进行了分析,结果表明(Ti,Mn,Si,Mg)O x-MnS粒子可以作为形核质点促进焊接HAZ针状铁素体的形成,有效地提高了焊接HAZ的低温韧性。

HBIS group developed EH40 shipbuilding plate steel for high heat input welding application by oxide metallurgy technology.The continuous cooling transformation behavior and microstructure transformation under different cooling rates of welding heat affected zone(HAZ)in EH40 shipbuilding plate steel were studied by DIL805L quenching and phase transformation dilatometer in combination with thermal simulation technology.In addition,thermal simulation experiments were conducted on a Gleeble-3800 thermal simulation testing machine,and then the mechanical properties of HAZ were tested.Simulated HAZ continuous cooling transformation(SHCCT)curves showed that ferrite and pearlite formed when the cooling rate was less than 0.1℃/s.As the cooling rate increased to 0.2℃/s,bainite began to precipitate.When the cooling rate was 2~3℃/s,ferrite/pearlite and granular bainite transformation occurred.When the cooling rate was 5~10℃/s,ferrite/granular bainite transformation occurred.Moreover,with the increase of cooling rate,the proportion of granular bainite increased gradually.Lath bainite formed when the cooling rate increased to 15℃/s.When the cooling rate increased to 30~100℃/s,martensite began to generate and the proportion of martensite became increased.Furthermore,the results of welding thermal simulation and impact test showed that the average impact absorbed energy in HAZ of EH40 shipbuilding plate steel was 205 J at-40℃after a simulated welding thermal cycle of 200 kJ/cm heat input,which was much higher than the national standard value of 41 J.The scanning electron microscope and energy dispersive spectrometer were adopted to analyze particles precipitated in HAZ of EH40 shipbuilding plate steel,the results illustrated that(Ti,Mn,Si,Mg)O x-MnS particles were nucleation sites to promote the formation of acicular ferrite in HAZ,which could effectively improve the low temperature toughness of HAZ.