| International Nickel Study Group?INSG? and Word Bureau of Metal Statistics?WBMS? reported that the proportion of producing capacity and consumption of global nickel reduces gradually, and the demand for nickel increases in countries around the world year by year. Nickel-base alloy, with excellent high temperature resistance and corrosion resistance, has been widely applied to aerospace, nuclear power and offshore oil industry. Inconel 625 alloy?Ni-Cr-Mo-Nb?, a kind of nickel base superalloy with excellent corrosion resistance, can be widely used in the manufacture of aircraft engine components, aerospace structural components and chemical equipment. Thus, it is one of the most widely used nickel-base alloy today.However, Inconel 625 alloy is easy to produce weld defects, such as needle hole, lack of penetration and hot cracking because of poor liquidity, and high susceptibility to cracking. At present, to match base metal of Inconel 625 alloy, ENiCrMo3T0-4 nickel-based flux-cored wire has been developed but expensive. There are not research papers on porosity and hot cracking sensitivity of weld metals, and its engineering application related. Therefore, the study on effects of flux-cored ingredients and welding parameters on porosity and hot cracking sensitivity of weld metals of ENiCrMo3T0-4 nickel-based flux-cored wires is of great importance.In this paper, the effects of flux-cored ingredients and welding parameters on porosity sensitivity of weld metals of ENiCrMo3T0-4 flux-cored wires were investigated by stereomicroscope and optimum design software. The results showed that porosity sensitivity was reduced with the ratio of SiO2/ZrO2, TiO2/ZrO2, and?TiO2+ZrO2+SiO2?/MnO decreasing in flux-cored ingredients. The flow rate of shielding gas had little influence on number of needle holes on weld surface, but wormholes were formed if flow rate was too low. The number of needle holes and porosity sensitivity of weld metal were the lowest when arc voltage was 25 V, welding current 160 A and wire stick-out 20 mm. The porosity sensitivity of weld metal can be reduced by enlarging solid-liquid phase temperature and hydrogen solubility in high temperature slag.The effects of flux-cored ingredients and welding parameters on hot cracking sensitivity of ENiCrMo3T0-4 flux-cored wires were studied by FISCO test apparatus. The results showed that hot cracking sensitivity was decreased with the ratio of?TiO2+ZrO2+SiO2?/MnO decreasing. When the ratio was 1.57, the crack rate was the highest?73.7%?. When it was 0.80, no cracking was formed. Under low welding current and arc voltage, the crack rate was the lowest. Under high welding current and low arc voltage or low welding current and high arc voltage, the crack rate was in the middle range. Under high welding current and arc voltage, the crack rate was the highest. The size of wire stick-out had little influence on the crack rate.On the basis, an ENiCrMo3T0-4 flux-cored wire FN 625 was developed, and meets the requirement of SFA-5.34/SFA-5.34 M standard. A synthetic comparision with flux-cored wires of FN 625, a#, and b#, and c# electrode was conducted. The results showed that ratio of CaO/?SiO2+TiO2? decreased in flux-cored ingredients, the lower the basicity of melting slag was, and the better the welding arc stability was. Compared with standard deviation and coefficient of variation of arc voltage and welding current, and coefficient of variation of burning time, standard deviation of short-circuiting and burning times and coefficient of variation of short-circuiting time can more accurately reflect arc stability. In the range of normal welding parameters, the arc stability became more stable with an increase of welding parameters. FN 625 wire had excellent welding performance, its mechanical properties were close to the others, and could meet the requirements of engineering application. |
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