Effect Of Original Microstructure On Hot Affected Zone Of Dual Phase Weathering Steel Cu-P-Cr-Ni-Mo

In this paper, Cu-P-Cr-Ni-Mo weathering steel with different martensite volumefraction and martensite shape are prepared by heat treatment and hot rolling. The effects ofwelding heat input and original microstructure on microstructure and mechanicalproperties of coarse grain heat affected zone (CGHAZ) of Cu-P-Cr-Ni-Mo weatheringsteel were studied by welding thermal simulation techniques, metallographic microscopeand mechanical properties test. The embrittlement mechanism of CGHAZ of dual phasesteel were analyzed and discussed.The results indicated that the M-A contained multi-phases microstructure formed inall the CGHAZs of Cu-P-Cr-Ni-Mo weathering steel but with different morphologiesunder five welding heat input(10kJ/cm~30kJ/cm). With the increasing of welding heatinput, the amount of lath bainite gradually reduces, the granular bainite decreases afterincreasing, and the proeutectoid ferrite increases, the densely distributed granular M-A isgradually replaced by the more isolated massive M-A; Moreover, an increase in weldingheat input causes the hardness and the impact energy of simuated CGHAZ to decrease andthe fracture mode change from dimple plastic fracture to quasi-cleavage brittle rupture.The microstructure of CGHAZ is composed of staggered lath bainite and granular M-A atthe welding heat input of10kJ/cm, which show the best toughness, crack nucleationappeared in the interface of M-A and substrate and extend later in the form of microporousmerger. The microstructure of CGHAZ is composed of bulky polygon ferrite and blockM-A gathered in the grain boundary at the welding heat input of20kJ/cm, cracknucleation appeared between M-A and interface of substrate and unstable propagate in theform of cleavage way, which leads to the deterioration of the toughness.Proeutectoid ferrite and granular bainite formed in all the CGHAZs ofCu-P-Cr-Ni-Mo weathering steel with different martensite contents(2.8vol%~15vol%).With the increasing of martensite contents of dual phase steel, the amount of proeutectoidferrite decreases after increasing, the impact energy of base metal and CGHAZ increasesafter decreasing and the impact energy of CGHAZ is higher than base metal for thegranular bainite formed in it. Proeutectoid ferrite formed dificultly for the high carbon content in the ferrite of base metal and granular M-A is distributed, when the martensitecontent is2.8vol%, so the base metal and CGHAZ both show higher impact energy with165J.The amount of bainite of CGHAZ increased at an expense of proeutectoid ferritewhen the island martensite of dual phase steel is replaced by fibrous martensite; isolatedmassive M-A was gradually replaced by the densely distributed granular M-A with adeceasing of size and a inceasing of dispersion; the impact energy of base metal isdecreasing and the CGHAZ increasing, the toughness of CGHAZ is worse than basemetal.