| Hastelloy C-276 is the representative material of the Hastelloy. It is recognized as the all-purpose erosion-resisting Ni-Cr-Mo wrought alloy, and widely used in areas such as corrosion resistance and heat resistance of petrochemical industry, nuclear power, etc. To ensure that the quality of Hastelloy C-276 welded joint achieves the safety requirements of the equipment, the effect of welding parameters on microstructure and properties of welded joint are mainly studied in this paper. The physical simulating method is adopted to simulate the process of welding thermal cycle, and the effect of different heating temperature on microstructures, properties and corrosion resistance of welded joint are analyzed, in order to find out the weak area of welded joint, and find an effective method to improve the microstructure and properties of welded joint.The properties of welded joint of the Hastelloy C-276 board made by different welding processes are discussed. The result shows that welding heat input has an obvious influence on mechanical properties and microstructure. The value of welding current is from 85 ampere to 85 ampere. With the increase of welding heat input, the crystal size is increased and the trend of segregation of weld composition is enhanced. The integrated performance of welded joint is significantly decreased compared with parent metal. The tensile fractures all exist in heat affected zone, and heat affected zone is the performance weak area of welded joint.The effect of different heating peak temperature on microstructure and properties of Hastelloy C-276 under air cooling and spray cooling conditions is gained by air cooling or spray cooling the Hastelloy C-276, which is heated to different temperature, and then physical simulating the processes of thermal cycle of different areas in heat affected zone. The test result shows under the condition of air cooling, the changes of microstructure in low temperature range are little, and the microstrcture is austenite structure in high temperature range. The tensile strength and yield strength of Hastelloy C-276 are decreased with the increase of the physical simulating peak temperature, and reach a minimum value at 900?, which are 402.94 MPa and 775.82 MPa respectively. The Plasticity and hardness have no obvious change compared with the base metal, the tensile fractures are all ductile fractures. When physical simulating peak temperature is 1050 ?, the corrosion resistance reaches its worst; Under the spray cooling condition, the sizes of crystal grow serious with the increase of temperature. The tensile strength and yield strength of Hastelloy C-276 are all higher than those of air cooling, elongation and contraction of cross sectional area are higher than those of parent metal as a whole, but when physical simulating peak temperature reaches 900?, the plasticity performs worst. The hardness is increased compared with parent metal and reaches the maximum, which is 425 HV, at about 1050?. The dimples of tensile fracture are small and shallow, Hastelloy C-276 heated to the same physical simulating peak temperature under the spray cooling condition has a higher corrosion resistance than that of air cooling.To find out an efficient method to improve the microstructure and properties of welded joint, three different strengthening and toughening treatments, which are spray cooling, liquid nitrogen cryogenic treatment and surface spinning, are adopted to deal with the specimens after being heated to different peak temperature. Performance measuring, metallographic analysis, fracture morphology analysis and corrosion resistance analysis are conducted to study the effect of different strengthening and toughening treatment processes on properties of welded joint. The result shows the tensile strength of material is all increased after spray cooling or liquid nitrogen cryogenic treatment. When the heating temperature is 1050?, the plasticity of material after spray cooling is decreased largest. When the peak temperature is above 900?, the plasticity of material after liquid nitrogen cryogenic treatment is promoted obviously, while the plasticity of material has no promotion when the peak temperature is low; the tensile strength of material after surface spinning increases by 100-210 MPa, and the material still maintains good plasticity. The three kinds of process all contribute to the increase of corrosion resistance, and material dealt by the surface spinning gained the best effect of corrosion resistance. It can be obtained from the analysis of mechanical property and corrosion resistance that the surface spinning is the best method of these three strengthening and toughing treatment process.This paper provides reasonable welding parameters of Hastelloy C-276 applied in engineering practice application, indicates the weak area of welded joint, finds an efficient strengthening and toughing treatment process to improve the welded joint of Hastelloy C-276, and has realistic guiding significance for ensuring the safety of equipment. |
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