Metallograph and high-temperature impact toughness of circumferential joint by SAW of BHW35 steel

BHW35 steel was welded by automatic submerged-arc welding(SAW) with H08Mn2MoA welding wires and flux HJ350.After stress relief annealing by the postweld heat-treatment system,impact tests on welded joint and base metal were carried out at 20,100,200 and 350℃,and the scanning electron microscopy(SEM) fractograph,metallograph,hardness and chemical compositions of welding seam were analyzed.The results indicate that the highest hardness of HAZ is 291.6 HV.The toughness increases greatly compared with that at room temperature.The temperature peak value of impact absorbing energy of welding seam occurs at weld of 100℃ and both HAZ and base metal of 200℃.The impact toughness in HAZ is better than that in welding seam.The impact absorbing energy of welded joint is over 47.33 J at room temperature and 134.67 J at 350℃,which meets the toughness demand for the welded joint and base metal.SEM fractograph indicates that all impact fractures of base metal exhibit ductile dimple,and the impact fractures in welded joint at room temperature exhibit quasi-cleavage and ductile dimple.With the temperature increasing,the fractures subjected high temperature impact all exhibit ductile dimple;the better toughness is,the more obvious tearing feature of ductile dimple is,and the larger the ductile dimple is,the more obvious non-uniform distribution is.