With Oil and gas exploration on land and in shallow water close to the peak, deepwater exploration became a new hot spot. Offshore platform is the large welded steel structure for development of offshore oil and gas resources, with its increasingly large-scale, more and more problems arise: joints welded with dissimilar steel at key components show high stress concentration caused by severely inequality in composition, microstructure and properties,which severely restrict the long-term operation of offshore platforms.To research the joint welded with EH36 and ASTM A514 Gr.Q steels by certain welding process, the microstructure, mechanical property and corrosion resistance were studied systematically by means of tensile tester, impact tester, metallographic and stereo microscope,microhardness tester, SEM, and electrochemical equipment in this dissertation, focusing on exploring the effects of fusion ratio and postweld heat treatment times on joints, in order that better properties of the dissimilar steel welding joint is acquired.The main work is as follows: the preheat temperature, heat input, inter-bead temperature,fusion ratio and postweld heat treatment times were systematically analyzed. The experiments of SMAW welding under different processing parameters were carried out. Mechanical property tests such as microstructure analysis, tensile, impact, microhardness test were utilized to evaluate the mechanical behavior of welding joints, mainly exploring the effects of fusion ratio and postweld heat treatment times on joints. Corrosion potential in the integral joint and galvanic corrosion tendency in each region were analyzed, and combined with polarization curves and electrochemical impedance spectroscopy, its corrosion resistance property were comprehensively evaluated. The results indicate that, the higher fusion ratio,the higher tensile strength of welded joints. The higher fusion ratio reaches the best due to the homogeneity of the weld beam. Heat treatment process release the residual stress of welded joints to some extent, especially that of the heat-affected zone, which in direct contact with the base metal and equivalent to hardening process. Toughness is proportional to the ratio of dimples in the impact fracture, that of PWHT(3) joints decreased significantly, which was connected to coarse grain in HAZ. The immersion test in artificial seawater indicates that corrosion potential vary with the distance from weld center, and postweld heat treatment can not eliminate this difference. That of weld beam and HAZ is lower, thus form "small anode" to the base metal. Corrosion prevention in dissimilar weld joints must be done well, in case of local preferential corrosion in marine environment. |