Microstructure And Properties Of The Joint Welded With Two Dissimilar High Strength Ship Hull Steels

With modern marine technology development, better properties of HSLA steel weldingjoint is required. In order to research the application performance of the joint welded with10MnNiMo and12Ni2MnCrMo HSLA steels by certain welding process, the microstructure,mechanical property and corrosion resistance were studied and analyzed systematically bymeans of OM, SEM, EDS, XRF, XRD and electrochemical equipment in this dissertation. Thecomprehensive performance of the integral joint and the corrosion mechanism of differentzones in the joint were investigated in depth. The weak link of the welding joint wasdiscussed in this dissertation.The results indicated that the weld metal was composed of fine acicular ferrite, whichbrought about the best comprehensive machanical propertiy. The quench-hardenability of theweld heat-affected zone(HAZ) of12Ni2MnCrMo steel was relatively poor for high alloycontent. Because of the strengthening effect of the the second phase, the low temperaturetoughness of12Ni2MnCrMo’s HAZ was enhanced. The aging embrittlement zone of12Ni2MnCrMo steel was the weak zone in tensile property of the welding joint. Theimmersion test in artificial seawater indicated that weld metal had the lowest seawatercorrosion resistance in the integral joint, however, its corrosion rate would slow because ofgalvanic corrosion. The seawater corrosion resistance of12Ni2MnCrMo steel was better than10MnNiMo steel at the initial stage of corrosion, but with the extention of corrosion time, thecorrosion resistance of12Ni2MnCrMo became worse than10MnNiMo’s and theinhomogeneity of microstructure became the main factor influencing the seawater corrosionresistance of the HAZs in the later stage of corrosion. At the early stage of corrosion, thecorrosion rate of10MnNiMo steel was accelerated by galvanic corrosion, but due to theincrease in oxidation film’s thickness and alloy elements enrichment, the galvanic corrosionwas restrained in the later period of corrosion. The stress corrosion sensitivity test indicatedthat the welding joint was not sensitve to the stress corrosion cracking under the test condition.But HAZ of10MnNiMo steel and the base metal had worse stress corrosion resistanceproperties. The stress corrosion resistance property of weld metal was the best in the integraljoint.