Study on the Micro-structure and Micro-hardness of Thick Plate 16Mn Steel welding joints

The 16Mn steel has good mechanical properties and welding performance, so it is used widely in pressure vessels, petroleum storage tanks and pipelines of oil and gas. Submerged arc welding was employed to weld 16Mn, by OM, the microstructure in every region of welding joint was observed, by means of IT software, grain sizes of every region of welding joints were investigated. Then the micro-hardness of welding joints was measured through micro-hardness testing. The results show that 60mm thick 16Mn steel plates, by submerged arc welding(in DC) and under appropriate craft conditions, the welded joint appearance is good, microstructure is uniform, it is ferrite+pearlite, the micro-hardness obtains the max at the edge of welded joint and HAZ. In HAZ zones, grain size grows up. Thick welded steel plates of big line energy, high energy, low cooling rate and coarse grain of the welding heat affected zone (HAZ) may lead to welding joint ductility decrease, it is the weak link([1]) of the structural failure. Through research and analysis of 60mm thick plate 16Mn steel welding joint microstructure and mechanical properties, it is possible to provide the theory foundation for the actual welding process of 16Mn thick plate.