Effect of the hottest temperature on the brazing r

The influence of temperature on the brazing rate of 316LN stainless steel

Abstract: the general situation of HT-7U Superconducting Tokamak, a national major scientific and engineering project, is introduced, the brazing characteristics of its key components superconducting coil box shell and cooling pipe are analyzed, and the influence of temperature on the brazing rate of 316LN stainless steel is systematically studied. The results show that when sn55pbagsb solder is used for 316LN stainless steel, the brazing adhesion first increases and then decreases with the increase of temperature, and the appropriate welding temperature is between 210 ~ 230 ℃

key words: Tokamak, 316LN stainless steel, brazing rate

1 Foreword

in the second half of the 20th century, great progress has been made in the development of fusion energy, especially in the magnetic confinement controlled thermonuclear fusion Tokamak device [1]. As a clean, safe and almost inexhaustible new energy, fusion energy is the replacement energy for human beings to replace coal and oil in this century. Tokamak is a device for people to conduct controllable nuclear fusion and realize nuclear fusion. At present, the comprehensive strength and science and technology of magnetic confinement nuclear fusion research in China have entered the forefront of the world

the HT-7U Superconducting Tokamak device, a national major scientific and engineering project in China, can realize the stable operation of tokamaks by using low-temperature superconducting technology. As the key component of obtaining low temperature technology, the superconducting coil box shell and cooling pipe are made of ultra-low carbon austenitic stainless steel 316LN. The maximum diameter of the shell is 3.6 meters, and the thickness of the shell steel plate is between 20mm and 75mm. In addition, its temperature control requirements are strict, and the welding quality requirements are high (the brazing rate needs to be guaranteed to be more than 85%), so it puts forward high requirements for brazing materials and brazing processes. In order to obtain excellent thermal conductivity and low temperature performance, this paper systematically studied the effect of temperature on the brazing rate of 316LN stainless steel

2. Test method

in this paper, the ultra-low carbon austenitic stainless steel 316LN steel plate with a size of 22mm is selected × 60mm × 1.5mm, sn55pbagsb is selected as the solder, and the thickness is 0.5mm. ZnCl2 flux is selected as the flux, and its composition is shown in Table 1, table 2 and table 3[2] respectively. Most car companies are very cautious when selecting suppliers Table 1 Composition of 316LN stainless steel (weight percentage,%)

Table 2 composition of solder sn55pbagsb (atomic percentage,%)

Table 3 composition ratio of ZnCl2 flux

the test process mainly includes pre welding cleaning, brazing and furnace brazing. First use coarse sandpaper (36) to polish the test surface of stainless steel plate and solder, and then clean it with anhydrous alcohol. Preheat the stainless steel to 150 ~ 170 ℃ with a furnace, brush the stainless steel plate with ZnCl2 flux, and evenly solder a layer of 0.1 ~ 0.2mm thick solder on the stainless steel test surface with a 500W soldering iron. After natural cooling in the air, clean the flux residue with hot water and brush the stainless steel with flux again. Brush the solder with flux, clamp the solder sheet with stainless steel plate and place it flat in the heating furnace, as shown in Figure 1. The heating temperature is selected as 200 ℃, 210 ℃, 220 ℃, 230 ℃, 240 ℃, 260 ℃ and 280 ℃ respectively. During the heat preservation, the product output of Enterprises above the scope of 2014 was 73.8787 million tons for 2 minutes

Figure 1 Schematic diagram of heating and placing of stainless steel plate

3 Test results and analysis

Table 4 shows the average brazing rate obtained by grid method after three tests at different temperatures. The results show that temperature has a very important influence on the brazing rate and welding quality of 316LN stainless steel. When the temperature is 200 ℃ and 210 ℃, the brazing rate is not very high. With the increase of temperature, the brazing rate increases. When the temperature is 220 ℃, the brazing rate reaches the highest point, and then increases, the brazing rate decreases. When the temperature is 200 ℃ and 210 ℃, the cavity left after welding is large; When the temperature is 260 ℃ and 280 ℃, not only the brazing rate is low, but also the cavity after brazing is large, the large surrounding phenomenon is serious, and the welding quality is poor. Table 4 under different temperatures, 3 cover the front cover of the panel, and then the brazing rate of 16ln (%)

from the perspective of the brazing process, when the welding temperature is 190 ℃ and 200 ℃, the solder just begins to melt, the fluidity is poor, and the flux does not reach the peak of activity, so the surrounding phenomenon in the structure is serious, and the brazing brazing brazing brazing rate is low. When the temperature rises to about 220 ℃, the fluidity of solder increases and the activity of flux reaches a climax. At this time, the brazing rate reaches the highest for materials that do not meet the requirements of the new national standard. With the continuous increase of temperature, the oxidation of stainless steel and solder has become a serious problem, and the solder is difficult to wet and spread, so the brazing rate will decrease

4. Conclusion

1) temperature has a very important effect on the brazing rate of 316LN stainless steel

2) when sn55pbagsb solder is used for welding, the brazing rate of 316LN stainless steel increases first and then decreases with the increase of temperature

3) considering the brazing rate of 316LN stainless steel, the appropriate welding temperature is 210 ~ 230 ℃

references

1 The latest experimental progress of HT-7 Superconducting Tokamak. Li Jiangang, Xie Jikang. Physics, p.328

2 Brazing manual. Zhang Qiyun, Zhuang Hongshou. Beijing: China Machine Press, 1998, p.98

author profile: Yu Xinquan, master, mainly engaged in the research of brazing materials and processes. Contact:, email address: yxqyxq@. 。 (end)