Surface Modification Process And Thermal Analysis Of The Low Carbon Steel Welding Deposition

In order to obtain a better service performance of the steel in aviation, aerospace, nuclear energy, petrochemical industry and. etc, surface cladding of other alloy layers on low carton steel substrate was conducted using a TIG deposition method. The SG-CuSi3copper welding wire, the ER49-1mild steel welding wire and the MGL-309L stainless steel welding wire were applied to clad the Q235A steel. The relationship between the forming parameters and the welding parameters of the every kind welding wire was studied; the associated molten pool shape regression equation was established based on the welding current, speed and wire feeding speed. The optimum forming parameters to the corresponding welding wire of cladding Q235A steel were identified.A model of heat source was established in the ANSYS based on the actual geometry dimensions of the deposition layer. In this model, the heat transfer process was simulated by a Gaussian distribution surface heat source with the birth and death elements technology. The results showed that with the increase of the welding heat input, the highest temperature of the deposition metal and the base metal rose, the temperature gradient and the cooling rate of the deposition metal decreased and the quantity of molten base metal rose. The simulation results was verified by comparison of the thermal cycle curves between experimental and calculated results, and the predicted results by the model introduced in this paper were in good agreement with the experimental ones.Microstructure characteristic of the cladding layer and the bonding interface of the welding joints were investigated by using an optical microscopy and a scanning electron microscopy (SEM) installed with an energy dispersive spectrometer (EDS). Results show:(i) with the increase of the welding heat input, Fe atoms near the Cu/Fe interface enter the copper molten pool due to the welding arc force. Subsequently, the formations of the spherical, dendritic, petaloid and platelike Fe-rich phases take place,(ii) a carburized and decarburized layer generate during the Q235A and stainless steel welding process at a high temperature owing to the carbon diffusion. Taking into the consideration of more Cr with carbophile in the stainless steel, C atoms in the Q235A steel diffuse into the stainless steel through the welding fusion line, which consequently a decarburized layer forms at the Q235steel side, a carburized layer forms at the stainless steel side and a carbide of white band forms because of the carbide gathering near the fusion line.(iii) the worm-like, skeleton-like, lath-shaped and globular ferrite coexists in the austenitic stainless steel in the stainless steel deposition layer.(iv) the microstructure of the copper deposition layer was mainly composed of dendrites with low heat input, and the pan-iron phase was discovered with high heat input.Results of the mechanical properties tests show that the uniformity of microstructure and the distribution of Fe element have great influence on the hardness; the average microhardness of the deposited layer increases with the enhancing of the welding heat input; Q235steel has good corrosion resistance after modified by cladding alloy layer on its surface.