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Vacuum Brazing of Cemented Carbide and Martensitic Stainless Steel
WC cemented carbide is widely used because of its high hardness, wear resistance, good red hardness, low coefficient of thermal expansion and good chemical stability. However, the plasticity and toughness of cemented carbide are poor and expensive. Generally, the size of cemented carbide parts is relatively small, and they must be fixed on a larger and thicker supporting material.
2Cr13 martensitic stainless steel has high hardness, wear resistance and fatigue resistance, as well as excellent heat resistance and medium corrosion resistance. Using martensitic stainless steel as the supporting material of cemented carbide tools can not only improve the wear resistance and corrosion resistance of the whole workpiece, thus improving its service life, but also significantly reduce the cost of the workpiece. Vacuum brazing has been more and more widely used because of its remarkable advantages. The integration of vacuum brazing and heat treatment in vacuum furnace saves the secondary austenite heating, which can reduce the cost to a certain extent.
Base metal 2Cr13 and YG8 are processed to size of 16.5mm × 16.5mm × 5mm。 The filler metal used is flake CuMnCo alloy. Its composition (mass fraction,%) is 86 ～ 88Cu, 9.5 ～ 10.5Mn, 2.5 ～ 3.5Co, and its melting temperature range is 991 ～ 1045 ℃.
Pre welding treatment: remove the oxide skin on the brazing surface and spreading surface of 2Cr13 and the surface of CuMnCo solder, and polish the brazing surface and spreading test surface of YG8, and ensure that the surfaces are smooth. Then soak it in acetone for about 10min, wipe the surface with absorbent cotton to remove oil stains and sundries, and blow it dry.
Select base metal 16.5mm × 16.5mm surface is the spreading test surface, 16.5mm × The 5mm surface is the brazing surface. The amount of filler metal shall be determined according to the specific brazing gap, and the size shall be close to the brazing seam as far as possible. Butt joint is adopted for the brazing joint, the hard alloy is placed on the 2Cr13 stainless steel, and the joint type assembly is shown in the figure.
Brazing and quenching are carried out in a double chamber vacuum furnace, which has a hot chamber and a cold chamber. The brazing process is carried out in a hot chamber, and the vacuum degree is maintained at 5 × ten ² Above Pa. The brazing temperature range is 1040~1100 ℃. The brazing clearance is 0.10 to 0.40mm. Heat to 850 ℃ at the rate of 11 ℃/min for 30min, then heat to brazing temperature at the rate of 10 ℃/min for 15min, and cool down in the furnace. The brazing experiment and spreading experiment are carried out according to this process. The quenching process is carried out in the cold chamber. After brazing, the sample can be directly put into the cold chamber for quenching treatment. The quenching temperature is 970 ℃, and the quenching medium is 40 ℃ vacuum oil.
Factors Affecting Brazing Quality
The change of the brazing gap significantly affects the bending strength of the joint. With the increase of the brazing gap, the bending strength of the joint first increases and then decreases. When the brazing gap is 0.20mm, the bending strength of the joint reaches the maximum. When the brazing gap is 0.05mm, the fracture position of the joint is near the brazing joint of the hard alloy.
With the increase of brazing gap, the ability of brazing joint to form metallurgical bond gradually weakens. The too wide brazing seam weakens the diffusion ability between atoms. It is difficult for elements to diffuse to the interface area between cemented carbide side and steel side for long range to form sufficient metallurgical bond, which leads to the poor mechanical properties of brazing joint. With small brazing gap, although it is easier for Fe in the base metal to react with Co in the filler metal to produce a large amount of solid solution structure, forming strong metallurgical bonding, excessive reaction products will also significantly reduce the plasticity of the brazing seam structure and can not effectively release the residual stress generated during the brazing cooling process. The proper brazing gap can effectively release the residual stress of the brazed joint and make the joint form sufficient metallurgical bonding. The practice shows that the joint performance is the best when the clearance is 0.2 mm, which is the best brazing clearance.
Effect of Quenching on Brazed Joints
When the brazing temperature is 1085 ℃ and the brazing gap is 0.2mm, the bending strength of the joints obtained by furnace cooling after brazing and quenching after brazing can be seen that the mechanical properties of the joints obtained by quenching after brazing are slightly less than those obtained by not quenching after brazing. The bending strength of the brazed joint quenched after brazing is lower than that of the joint not quenched, but still higher. Quenching optimizes the structure of the base metal steel. The vacuum brazing and heat treatment integration process is feasible.
Heat treatment equipment selection: process technology must be matched with excellent equipment to play a role, and the brazing furnace selected in vacuum brazing is crucial. The RHVB vacuum high temperature brazing furnace produced by SIMUWU is an excellent product for handling this kind of process. With its excellent temperature control accuracy and temperature uniformity, the brazing of workpieces can be carried out smoothly and evenly, so as to achieve a high-level brazing level, reduce scrap rate, increase production efficiency and reduce costs.
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