Study On The Heat Treatment, Microstructure And Properties Of M5 Zirconium Alloy

M5 zirconium alloy is mainly applied in the nuclear reactor core as the fuel cladding tubes and structure materials. Recently with the continuous development of reactor technology, fuel cladding tubes face with the harsh environment involving internal stress, neutron radiation and high temperature and high pressure,which puts forward higher requirements on the mechanical properties and corrosion resistant of M5 zirconium alloys. In order to extend the life of nuclear fuel cladding tubes, this paper proposes to improve microstructure and properties by heat treatment of M5 zirconium alloys on recrystallization annealing state. The aim is to promote the localization of nuclear fuel cladding tubes and provide some theoretical references.In this paper, by using orthogonal test method to research on the influences of heat treatment to microstructure and properties of M5 zirconium alloys cladding tubes. These experiments are designed to compareing the microstructure and mechanical properties of M5 zirconium alloy cladding tubes on various parameters of heat treatment. The optimum techniques is concluded. The main research results are as follows:Using optical metallographic microscope, transmission electron microscopy, scanning electron microscopy and other analysis methods to research on microstructure of recrystallization annealing state of M5 zirconium alloys. The results indicate that the recrystallization annealing microstructure is equiaxed grains. The grans size are small. The alloys get a complete recrystallization. Larger number of dislocation density and more dislocation tangle are found in the mareix. There are a lot of precipitation particles on the grain and grain boundary.The fracture analysis of the tensile specimens at room temperature of annealing state with M5 zirconium alloys show:the macroscopic fracture is gray fibrous. The micro fracture mechanism is microvoid coalescence fracture. The dimples are deep and large. The plastic of recrystallization annealing state is good, but low intensity.The microstructures are transform into martensiteα' byβphase quenching at different preservation time on heat treatment of M5 zirconium alloy. The grain diameter is smallest by 3 miutes preservation. The grain diameter become larger.with the extension of preservation time on heat treatment, The results of micro hardness test show that hardness value fluctuation is minimum by 3 miutes heat preservation. The organization is more uniform, the micro hardness values above the annealing microstructure.The orthogonal test results on the process ofβphase heat treatment of M5 zirconium alloys show:there was martensiteα' transformation in microstructure after quenching. After tempering, alloys retained martensitic morphology. The significant effect on the mechanical properties is quenching temperature, the effects of tempering time come second and the effects of tempering temperature wast'n obvious. With increasing quenching temperature, the tensile strength retained increases. Plasticity and fracture toughness become lower. With the tempering time prolonged, the strength index of the alloy decreases first and then increases, the maximum value appeared before turning. The plasticity index of elongation and the reduction of area continue to fall. After comprehensive analysis, the best heat treatment proeess of M5 zirconium alloys is quenching at 960℃for 3 min and empering at 530℃for 6h.