Effect of Phase Water Quenching on the Corrosion Resistance of Zirconium 4 Alloy in Nuclear Power Engineering ZHOU Bangxin LI Qiang Miao Zhi Institute of Materials Research, Shanghai University, 200072 Key Laboratory of Nuclear Fuel and Materials, China Nuclear Power Research and Design Institute, Chengdu, 610041, China Corrosion resistance. Phase water slats have very fine lath-like grains, no phase precipitates, high dislocation density in the grains, and residual B = 0.355. This type of structure has poor corrosion resistance and easily forms white and off-white. Oxide film. After annealing for 7001 hours, two kinds of microstructures can be obtained, such as the coarsening of the strip-like grains, the precipitation of the 26,2 phase on the grain boundary, the obvious improvement of the corrosion resistance, and the black bright oxide film. . The other kind is equiaxed large grain structure, which is the result of abnormal growth of crystal grains after recrystallization. The grain diameter reaches 0.20.5. The corrosion resistance of this kind of structure is poor, and it is corroded in 400 superheated steam. At the time, a clear swarthy etched spot forms.

In the manufacturing process of nuclear fuel elements, the zirconium 4 alloy cladding needs to be welded and sealed, and the vacuum electron beam welding method is one of them. This is a high-energy-density welding method with a small welding melting zone, a fast heating speed, and a fast cooling rate. Since the welding is performed in a high vacuum, after the alloy is melted, due to the different partial pressures of vapors of various alloying elements, the alloying elements may be depleted due to volatilization. The past work has proved (1) that zirconium alloys similar to zirconium 4 are vacuum electron beams. After welding, the loss of 56 alloy elements in the melt zone is as high as 30 50, which is detrimental to the corrosion resistance of the melt zone. However, as long as the welding parameters are properly controlled and the loss of alloying elements is minimized, the degree of corrosion resistance degradation caused by this welding method is still acceptable. On the other hand, from the phase cooling rate of about 5003 will also make the corrosion resistance worse 121. Therefore, it is necessary to study the microstructure after 0-phase rapid cooling, and its impact on the corrosion resistance in order to high-energy density welding The method may cause changes in the corrosion resistance of the zirconium alloy to be evaluated and guide the selection of welding parameters.

2 Experimental Methods Thirty-six zirconium 4-sheet samples of size 8, 30, thickness 0.6, and 1 were vacuum-enclosed in a cM2mrn quartz tube. In order to prevent the sample from being contaminated during the heat treatment process, the sample was prepared in the same manner as the sample to be etched prior to encapsulation, while the quartz tube was broken to rapidly cool the sample. The blue-gray oxide film produced by the water quenching of the sample surface was removed with sandpaper, 15 pieces of the sample were taken out by pickling and washing with water, dried and then heat-treated again in a vacuum for 7001 hours. Ten samples were taken from each of the two treated samples, pickled and washed with standard methods, and then autoclave corrosion tests were performed in 4000.33 superheated steam. Considering that the sample is sanded, the thickness of the removed surface during pickling is more than conventional.

The sample was thinned to approximately 0.08 by pickling. Afterwards, a 33-positive sample was cut, and a radiostat was prepared by double jet electrolytic polishing. The desired thin sample was observed. The electrolytic polishing solution was 20 glacial acid in glacial acetic acid. .

3 Experimental results and discussion 3.1 Microscopic slides. The quality of dislocations in the granules after quenching by 0 phase water quenching is very small, and the dislocation density in the granules is also high. 3 The increase in enamel surface and the increase in dislocation density can cause deterioration of the corrosion properties of thorium. The signs of phase precipitation indicate that the alloying elements are almost all in supersaturated solution. For comparison, the crucible is a microscopic woven fabric that has been heated in the air after being heated on the day phase. After that, the slats have large grains and there are 2 on the grain boundaries. The first phase precipitates. This kind of microstructure has excellent corrosion resistance to corrugation, but the poor resistance to uniform corrosion over a long period of time will lead to the first turning of corrosion. These are considered to be related to the degree of supersaturation of the zero-element alloy cords. The microstructure of the sample after water quenching is reheated at 700 ft. and the seven grains are coarsened by migration of grain boundaries. The first phase is precipitated on the grain boundary, and the other is grain boundary migration, and the large number of lath-like grains are engulfed to grow into equiaxed grains, and recrystallization takes place and causes grain growth. From the metallography photos with lower multiples. It can be more clearly seen that the characteristics of the 1 micro-organisms of the cricket team are 24 chan and 1 chan 15, and that in the alloy, when the air is cooled by the hue, there are 2+ rich in the grain boundaries of the slats, but in the There have been no similar reports in Zr4 alloys. In this experiment, it was observed that there was a residual 0 phase after the Z4 sample was p-phase water quenched, and 3 was the bright field dark field and the selected area diffraction diffraction defect of the residual phase. Due to the volume change during the phase change, the residual 0 phase is deformed and the dislocation density is increased, and the lattice constant of aZr is used to calibrate, and the lattice constant of 2 is obtained. 3.2 Corrosion performance, for comparison, the corrosion time is also Unzinced zirconium 4 samples were cast. After the same treatment, the block samples, their weight gain data are often dispersed, this large, and water quenching every B2 by Sugi Iwumi after reheating 7001 heating 讣 蛀 纽 纽 织 织 织 存在 存在 存在 存在 存在 存在In related, 30 samples were placed in a mesh quartz tube for heating and water quenching. From the change in weight gain, it can be seen that the corrosion gain of the samples after re-annealing after water quenching and water quenching is much higher than that of samples without quenching. However, 700 丈 annealing after water quenching can cause corrosion to start at the beginning of corrosion. The corrosion resistance of 16 days ago was improved, but the corrosion increase in the later period was increased, which was related to the generation of corrode corrosion. Two of the 4 samples were water-quenched and the weight gain data for each of the 700 specially heated samples were similar to those of the untreated water-treated zirconium 4, which may be the same as the samples quenched during water quenching. In the tube, the cooling rate is relatively high, and the weight gain data of these two samples are not included in the shadow of the curve.

An unevenly distributed white oxide film appeared on the surface of the water-quenched sample, and irregularly distributed verrucose erosion occurred in the 700 reheated sample. It is interesting to note that the distribution of the verrucous plaques is similar to that of the two sides of the sample, whereas the white tincture of the water quenched samples is not strictly distributed on both sides of the same sample. The worm-like eclipses occur only in areas where equiaxed flaws are formed after recrystallization. For example, these grains are large, about 0.20.5 in diameter, and some have already passed through the sample. At this time, verrucous corrosion will be generated on both sides of the intergranular grains, and the lath-like grain planes that are not recrystallized will still be young black oxide oysters. The water-quenched white oxide formed on the sample surface does not have a worm-like morphology. 菹 6 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在 在It is proved that the crevice corrosion formation mechanism proposed by the author of this paper is that in this phase, the hot water in the phase of boiling water, the phase of water in the unfired phase, and the hot water in the heavy melting point of 7,0 are in the heating range of 40010.3. In the case of quasi-etched 45-day samples, the oxidation rate was influenced by the crystal structure and positive; the b-supported surface; c water-quenched samples were etched 45 after 45 days; , Formed after the school. After 43 days of water-like corrosion, the anisotropic cross-section of the crucible was generated. The oxide film grew faster on certain orientations of the crystal face, resulting in a thicker oxide film. After zirconium oxidation to produce zirconia, the volume occurs and the expansion ratio is 1.56. It is believed that in the thicker oxidation, the metal body under the metal will be subjected to tensile stress. Due to the large grain size, the influence of this stress is also greater when the oxidation occurs. After the film is increased to a certain thickness, the formed stress is enough to deform the metal substrate under the carrier film, which accelerates the growth of the oxide film at the place and forms rust corrosion. In this experiment, it was observed that quasi-corrosion was formed during the corrosion in 4000 superheated vapor, apparently related to the abnormal growth of recrystallized grains. It is speculated from the formation mechanism of this corona corrosion that the size of the phase particles of the alloy composition and In the case that the distribution of the solid content of the alloy in the 121 matrix is ​​constant, full grain refinement will also be a way to increase the resistance to crater corrosion. From the discussion of the relationship between microstructure and corrosion resistance, when choosing the parameters for electron beam welding, it is important to control the cooling rate of the weld zone and the heat affected zone, and not to make the slat grains too small.

4 Conclusion Zirconium 4 after 0 phase water quenching, get very fine lath-like grains, high dislocation density in the grain, can not observe the first phase precipitation, but there are residual phases, the lattice constant 3 = O355nm.

After the 3 phase water quenching, the heat treatment is resumed for 7001 hours. The grain of the fine laths is coarsened by the grain boundary migration, and the 212th phase precipitates on the grain boundary. In the area where water quenching causes a large change in distortion, it can happen again. Crystallization, the formation of equiaxed grains with a diameter of 0.20.5 by abnormal grain growth.

When the corrosion test was performed in 400 superheated steam, the corrosion resistance of the 3-phase water quenched samples was extremely poor, and after the formation of non-uniformity, the coarse grained areas of the laths significantly improved the corrosion resistance, but the crystal grains were abnormally long. In large areas, their corrosion resistance is poor.

1 Zhou Bangxin, Zheng Sikui, Wang Shunxin. Effect of Vacuum Electron Beam Welding on Microstructure and Corrosion Property of Zirconium 2 Alloy Melt Zone . Nuclear Science and Engineering, 1988, 82130.

3 Zhou Bangxin, Zhao Wenjin, Miao Zhi et al. Improve the study of 24 corrosion resistance. Nuclear Science and Engineering, 1995, 153142.

Study on the microstructure of Zhoubangxin 75 series alloy. Biological and Environmental Materials, Melon 296 Material Workshop, Chemical Industry Press, 1997, 6 Zhou Bangxin. Zirconium alloy corrosion ask. Nuclear Science and Engineering, author brief introduction Chang Huajian, male, born in 1965, associate researcher. He graduated from Tsinghua University in 1986, majoring in reactor engineering. He is now engaged in reactor structural design and mechanics research.

Li Qiang, male, born in October 1967, assistant researcher. He graduated from Chengdu University of Science and Technology with a degree in polymer chemistry in 1990 and is currently engaged in material research.

Miao Zhi, male, born in 1956, senior engineer. In 1980, he graduated from Tsinghua University, majoring in nuclear materials. Now he is mainly engaged in nuclear material research.