PRODUCT CATEGORIES

Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Vacuum Brazing Technology of Stainless Steel Surgical Instruments

A surgical instrument for holding suture needles and knotting, the working end of which is inlaid with cemented carbide by inlaying technology, so as to obtain better wear resistance and anti-skid performance and facilitate maintenance and replacement. In recent years, the vacuum brazing heat treatment composite process has been adopted for such products, that is, the original vacuum brazing and vacuum heat treatment processes are combined into one, and certain results have been achieved.

1 Process method and material composition

The original processing procedure of the product: machining → quenching → high-frequency welding of the working end → surface treatment → inspection. The disadvantage of this process is that the workpiece is quenched as a whole and then partially welded. The welding heat will change the local structure of the workpiece, which not only affects the mechanical properties and corrosion resistance of the product, but also affects the performance of the product. It is a manual operation, and the quality control is difficult; again, the welding and heat treatment are operated separately, with a long construction period and high energy consumption. The improved processing procedure is: machining→vacuum brazing/quenching→surface treatment→inspection. The main improvement lies in the use of the composite process of brazing and quenching, that is, welding and heat treatment are completed at the same time, which not only reduces energy consumption, improves work efficiency, and improves operating environment, but also overcomes the quality defects of the original process. The workpiece base material is 20Cr13 steel; the cemented carbide is K40, which is equivalent to YG11, and the size is 15 mm x 5 mm x 0.8 mm; the solder is nickel-based brazing material. The chemical composition and main technical characteristics of cemented carbide, stainless steel and solder are shown in Table 1, Table 2 and Table 3, respectively.

2 Process parameters

The welding and quenching equipment of the workpiece is a vacuum high pressure gas quenching furnace. The final hardness of the workpiece matrix is 44~45 HRC. Although brazing and heat treatment are processes of different nature, for martensitic stainless steels, the two processes have a lot in common. Whether the brazing and quenching composite process is feasible depends on whether the characteristics of both can be taken into account. This is the case under normal conditions, and it is no exception under vacuum conditions. Therefore, based on the vacuum quenching process of 20Cr13 steel, we formulate the composite process of brazing heat treatment of 20Cr13 steel and cemented carbide.

The basic parameters of vacuum quenching process include vacuum degree, heating speed, heating temperature, holding time and cooling method, etc.; while the parameters of vacuum brazing process usually also include vacuum degree, heating speed, brazing temperature, brazing time and cooling method, etc. . When formulating the process, the setting of the final heating temperature should not only consider the normal quenching temperature of stainless steel, but also ensure that the comprehensive performance of the cemented carbide is not affected. The quenching temperature of 20Cr13 steel is usually about 1000 ℃, so the nickel-based brazing alloy with a similar melting temperature is selected, and the working temperature is 25~60 ℃ higher than the melting point of the brazing alloy), so as to improve the fluidity and wettability of the brazing alloy. It is in the best state; heated under vacuum conditions, the vacuum degree in the furnace is 4~4×10-1 Pa at low temperature; when heated to above 800 ℃, an appropriate amount of nitrogen is filled into the furnace to prevent the Cr element of 20Cr13 steel from volatilizing ;The heating speed is based on the premise of ensuring that the precipitation gas in the furnace is fully extracted and the workpiece is heated evenly. The method is to slowly heat up and carry out two-stage preheating at 550 ℃ and 800 ℃; according to the effective thickness of the workpiece and the amount of the furnace at one time, determine the brazing Welding/quenching heating time; high pressure gas quenching is done in a furnace.

The key factors that affect the quality of vacuum brazing include the process parameters of vacuum brazing, the leakage rate of vacuum equipment, the cleanliness of workpieces and tooling, the gap between welds and the placement of workpieces. Satisfactory results can only be achieved by grasping these key factors.

3 Analysis and discussion

Vacuum brazing is an advanced process for joining parts without flux in a vacuum atmosphere. Compared with other welding methods, it has a series of advantages such as no oxidation, carbonization, decarburization and pollution, and higher cleanliness and strength of welded joints. Studies have also shown that vacuum heat treatment can significantly improve toughness and strength while maintaining the high hardness and wear resistance of cemented carbide. For martensitic stainless steel, the brazing heat treatment composite process can achieve the purpose of quenching at the same time as brazing, and has obvious advantages in quality, cost, efficiency, etc. It is a process method worthy of popularization and application.

4 Conclusion

1) The vacuum brazing heat treatment composite process can achieve a win-win situation of product quality and economic benefits, and is a process with high application value.

2) When adopting the stainless steel vacuum brazing heat treatment composite process, the characteristics of two different processes must be taken into account, and the determination of reasonable process parameters is the key to the success of the composite process.