特厚EH47止裂钢板及焊接热影响区的组织性能

为开发大型集装箱船用特厚EH47止裂钢板,提出了一种低碳微合金MnCrNiCu钢,研究了其变形奥氏体连续冷却相变规律,使用控轧控冷工艺(TMCP)试制出最大厚度为85 mm特厚EH47级钢板,使用埋弧焊(SMA)和药芯焊丝气保焊(FCAW)技术对最厚钢板进行焊接试验,研究钢板和焊接接头的显微组织和性能.通过系列V缺口 ...

Microstructures and mechanical properties in ultra-thick EH47 steel plates and heat affected zones

A microalloyed low carbon MnCrNiCu steel has been proposed to develop EH47 steel plates via thermomechanical controlled processing(TMCP)route.The effect of hot deformation of austenite or cooling rate on phase transformation in the steel was investigated.Heavy steel plates with maximum thickness of 85 mm were rolled.Submerged arc welding(SMA)and flux-cored arc welding(FCAW)processes were employed in welding trials,respectively,to evaluate the weldability of the thickest plate.Microstructures in the plates and the coarse-grained heat affected zone(CGHAZ)were characterized.Ductile-to-brittle transition temperatures(DBTTs)in the plates were measured based on a series of instrumented Charpy V notch(CVN)impact tests,followed by the determination of the local cleavage fracture stresses(σf).Microhardness and CVN impact toughness in the heat affected zone(HAZ)produced by either SMA or FCAW were also tested.Full thickness crack tip open displacement(CTOD)in the mother plate or the weld joints was tested at -10℃leading to evaluation on the crack-initiation toughness(Kc)in the ultra-thick plate or the weld joints.A temperature dependency of crack-arrest toughness(Kca)in the ultra-thick plate was determined based on a series of large scale double tension(DT)tests across the entire thickness of the ultrathick plate.The results show that:a mixture of polygonal ferrite(PF)+acicular ferrite(AF)associated with dispersed martensite-austenite constituents was produced in the plates.An increase inσfleads to a decrease in DBTT.The critical events of cleavage fracture during the CVN testing and DT crack arrest testing are identical being grain-sized cracks.In comparison with the CGHAZ where quasi-polygonal(QPF)+AF are produced by SMA,cleavage crack can be initiated more easily in the CGHAZ by FCAW due to the formation of brittle GB.As a result,K_cassociated with the latter CGHAZ is lower than the former.K_caat -10℃is determined being 7 140 N/mm^(3/2 )indicating satisfactory crack arrestability in the mother plate.