| The development and application of high strength seawater corrosion resistant stainless steel is a major project of materials. In order to meet the working condition (non-periodical immersion in sea water) and mechanical property (yield strength above 850MPa) of spare parts, several alloys were used to experiment and analyze based on whichl7-4PH stainless steel was selected as the material of spare parts. Optimization of heat treatments was carried on the stainless steel and four treatments were finally determined. The metallurgical structure before and after tests was observed by OM and SEM with EDS.The mechanical property was investigated by tensile test, Charpy notch impact test, torsion test and bend test; the corrosion resistance was studied towards potential dynamic polarization and cyclic polarization curves. The influence of microstructure after heat treatments on mechanical and corrosion resistance properties was analyzed.The result showed that 17-4PH stainless steel with different heat treatments possesses yield strength above 1000MPa. The strength of stainless steel after same solution treatment declines and the plastic property increases when temperature of aging rises. 17-4PH stainless steel with intermediate-aging treatment had lowest strength but best plastic property with twice toughness value and 1.40 times fracture torsion angle. The full seawater corrosion resistance property of specimens was better than those with directly aging, however, pitting corrosion developed quickly after it occurred.Martensite, high density dislocation and strengthening effect of precipitates make high strength of the 17-4PH stainless steel. Presence of residual austenite is conducive to maintain excellent plastic property and the toughness. Inhomogeneity of microstructure leads to electrochemical corrosion. The addition of Nb decreases the Cr deplete district, enhancing the corrosion resistance property. Refine Martensite made better corrosion resistance.
|
PDF Full Text Request