Analysising The Microstructure And Properties Of Dissimilar Weld Joints Between Q245R And SUS304Filled With Ni Wire

Dissimilar weldments have been widely used in shipbuilding and chemical industry because of reducing fabrication costs as well as the full advantage of each outstanding physical property, such as stainless steel with corrosion and oxidation resistance. Although the welding joints of austenite stainless steel (ASS) and low alloy steel (LAS) are often applied in the manufacture of pressure vessels. However, the joint of dissimilar metals is generally more challenging because of great difference in chemical compositions, the physical and chemical properties of the base metals to be jointed. For now, the LAS and ASS are jointed by using SMAW and TIG. But as the base metal has higher dilution rate to weld metal, the problem of solidification transition layer and carbon migration is easy to appear in the fusion zone close to LAS side, result in including the some pores and microcracks in the weld metal, the usability is severely degraded. For all this, submerged arc welding filled with Ni wire is adopted, aim at the welding process realization, the joint microstructure and the property guarantee. This paper has done some research on the following aspects:(1) The experimental system and temperature measuring platform about submerged arc welding filled with non-heated wire are set up. The experimental system is made up of ordinary submerged arc welding machine and wire feeder, that can realize the procedure process of submerged arc welding filled with non-heated wire. The temperature measuring platform is composed of small Pt-Rh B-type thermocouple and MCGS configurable software. The molten pool temperature field of the different speed of cold filling wire is measured, and achieving the thermal cycle curve. Exploring the correlation of cold wire filling process and weld appearance parameters.(2) The mechanical properties tests of welded joints include tensile test, bending test, Vickers hardness, Charpy’V notch impact test and microhardness measurement. The results show that the value of impact energy and tensile strength increase, the sudden change range of microhardness decreases with the filling speed of Ni wire increasing. The austenite phase increased and the brittle nitrides phase reduced with the filling speed of Ni wire increasing. This is a major reason for the improvement of ductility and crack resistance. Therefore, the plasticity of welded joint can be guaranteed by means of the filling process of Ni wire. (3) The microstructure characterizations of the dissimilar joints are analyzed using optical microscope (OM), scanning electron microscopy (SEM), Energy-dispersive spectroscopy (EDS), X ray diffractometer (XRD). The results show that through controlling the filling quantity of Ni wire, the peak temperature and holding time at elevated temperature can be controlled, the reasonable temperature distribution is provided to weld metal and heat-affected zone, thus the structure of weld metal and heat-affected zone can be controlled. Ni wire compensates adequate austenite forming element for the diluting effect of LAS on WM, thereby the transition width close to LAS side fusion zone is decreased gradually.In conclusion, adopting submerged arc welding filled with Ni wire to weld the LAS(Q245R) and ASS(SUS304), The satisfactory microstructure and mechanical properties can be achieved through adjusting the filling speed of Ni wire.