Study On Corrosion Resistance And Microstructure Of Welding Joint Of Hull Steel

The hull steel survived a heavy corrosion in ocean,especially for the welded joints. The welded joints of A32 hull steel was studied in micro structure so that a theory can be an guidance for the real ship building.In order to research the application performance of the joint welded through certain welding process,the corrosion resistance was studied and analyzed systematically by means of OM,SEM,EDS,XRD and electrochemical equipment in this dissertation.The comprehensive performance of the integral joint and the corrosion mechanism of different zones in the joint were investigated in depth.The resistant of the stress and corrosion was tested by SSRT and a proper heat treatment temperature was received.The weak link of the welding joint was discussed in this dissertation.The results indicated that the weld metal was composed of fine acicu Iar ferrite.Which brought about the best comprehensive mechanical property.The immersion test in artificial seawater indicated that weld metal had the lowest seawater corrosion resistance in the integral joint.The seawater corrosion resistance of after600℃treatment steel was better than no treatment steel at the initial stage of corrosion,but with the extention of corrosion time.The corrosion resistance of treatment steel became worse,and the inhomogeneity of the micro structure became the main factor influencing the seawater corrosion resistance of the HAZ in the later stage of corrosion.At the early stage of corrosion.The corrosion rate of treatment steel was accelerated by galvanic corrosion,but due to the increase in oxidation film’s thickness and alloy elements enrichment,the galvanic corrosion was restrained in the later period of corrosion.The stress corrosion sensitivity test indicated that the welding joint was not sense to the stress corrosion cracking under the test condition.But the steel and the base metal had worse stress corrosion resistance properties.The stress corrosion resistance property of weld metal was the best in the integral joint.