Study On Heat Treatment Of Zr-Nb Alloy And Fatigue Performance Of Fillet Weld Of FV520B

Zr alloys have been widely used in chemical and nuclear industries owing to the excellent corrosion resistance and mechanical properties. With the rapid development of nuclear power and chemical industry, the corrosion mechanism of Zr alloys has been paid more and more attention. The mechanical performance and corrosion resistance of Zr-Nb alloy (Zr705) after being treated in different ways is tested. It is found that the properties of Zr-Nb alloy are significantly affected by heat treatment. The most important parameter during the heat treatment is quenching temperature. The Zr-Nb alloy, quenched below the critical quenching temperature Tcq (a temperature or a range of temperature between 850℃-870℃), shows good corrosion resistance performance. However, alloy quenched above the Tcq, gets a high strength and a decrease on corrosion resistance. Zr705 quenched 870℃and tempered can get both high strength and good corrosion resistance. Through the study on the basis of the evidences gotten by means of metallographic, SEM, EPMA and TEM, the conclusion can be drawn as that the effect of heat treatment on the performances of Zr-Nb alloy is primarily because of the mechanism of the changing of the distribution of Nb, the quantity of (3-Zr, and the morphology of grains.FV520B stainless steel is a new type of martensitic stainless steel. Due to the excellent mechanical properties, high corrosion resistance and good welding performance, the steel is widely used in blade material of wind turbine industry. The fatigue performance of leaves is an important factor in the running of wind turbine. Therefore, the fatigue performance of fillet weld of FV520B stainless steel was tested. Under the applied nominal average stress of 481MPa, the nominal fatigue limit 56MPa with fatigue life 5×106 was obtained. The fractures, separated into two types, were observed by SEM. Combined SEM results with macro and micro metallographic of base metal and weld, it was found that the heat treatment after welding eliminated the adverse effects of the heat-affected zone; two types of fractures were caused by, respectively, differences between the microstructures of the welding and base metal as well as the inclusions existed between the weld heads. Furthermore, the fatigue mechanism was also researched here.