Microstructure And Properties Of Welded Joints Of Q460 Steel Used In Nuclear By Submerged Arc Welding

As the development of nuclear power industry, the demand of bearing capacity of nuclear reactor pressure vessel stent is higher and higher. And the application of Q460 steel in nuclear reactor pressure vessel stent conduces to increase the yied strength and bearing capacity of the stent. However, understanding of welding process of Q460 steel is lacked at present. So, it is necessary to research on welding processes of Q460 steel in nuclear.In this paper, 45 mm thick Q460 steel used in nuclear was welded by submerged arc with different heat input. Heat input was respectively 24kJ/cm, 40kJ/cm, 50kJ/cm. Effect of different heat input on the microstructure and mechanical properties of welded joints was researched by testing methods of Optical Microscopy(OM), Scanning Electron Microscopy(SEM), Energy Dispersive Spectrometer(EDS), Transmission Electron Microscopy(TEM),Electron Back-Scattered Diffraction(EBSD), tensile, bent, impact and so on. To simulate the irradiation on working conditions, welded joints was conducted by heat treatment of610? and insulation 29 h, heat input of which was respectively 24kJ/cm, 40kJ/cm, 50 k J/cm,so that effect of heat treatment on the microstructure and mechanical properties of welded joints can be studied.Under different heat input, weld was composed of acicular ferrite and a little proeutectoid ferrite. With the increase of heat input, the portion of proeutectoid ferrite,high-angle grain boundaries, the effective grain size less than 2?m and surface density of inclusions reduced. CGHAZ was composed of bainite and a little martensite. With the increase of heat input, there were more bainite and coarse grains in CGHAZ. The maximum hardness appeared in the fusion line near the heat-affected zone, and it decreased with the increase of heat input. Coarse organization of the weld and heat affected zone caused that low temperature impact toughness of heat input 50kJ/cm showed poor performance.After the heat treatment, Impact energy of welded joints with heat input 24kJ/cm met project targets(AKV(-40?)?34J). Organization of weld and heat affected zone significantly thicked. The weld was composed of proeutectoid ferrite and massive ferrite. However,acicular ferrite and M-A component has basically disappeared. High angle grain boundaries of the weld and effective grain size of less than 2?m have declined. CGHAZ were granular bainite and ferrite. And there were also massive ferrite of different sizes in the fine grain region and a portion of the transition region. And the highest hardness near the fusion line inHAZ also decreased significantly. Strength of welded joints and low temperature impact toughness of weld and heat affected zone came to decrease.Welded joints have a high strength and toughness under different heat input. But only welded joints of heat input 24kJ/cm exhibited good mechanical properties before and after heat treatment.