Defects of vacuum quenching in heat treatment

Vacuum quenching technology is gradually popularized, but at the same time, the existing problems are also pointed out.

The first is the evaporation of Cr, Mn and other alloy elements, as well as the surface heterogeneous structure from the heat-resistant fixture to the workpiece produced by CR vacuum evaporation. Countermeasures to be taken. It is to reduce the vacuum and introduce control gas into the furnace.

The second is the problem of insufficient cooling capacity. For SKH51 die, 5 ~ 6bar of pressurized nitrogen is used for cooling. For skd6l die casting die, 20bar of super pressurized nitrogen is used for cooling, which is close to the solution.

Third, the problem of quenching deformation. Vacuum quenching and small quenching deformation are its commercial characteristics, but we all know that this is a misunderstanding. Although the deformation is small, recently it is also tending to improve the furnace structure to reduce quenching deformation.

The fourth is the problem of oxidation coloring. Although the workpieces can be used in practice, they reduce the commodity value and increase the claims from mold users.

Nowadays, many heat treatment plants use vacuum quenching furnace to heat treat bearing rings, which will cause workpiece deformation. Heshenglong vacuum equipment makes a simple analysis on product deformation for you, hoping to help you.

First of all, it is the problem before using the vacuum quenching furnace for quenching treatment, which may be the problem of processing deformation before quenching. The forming of bearing rings mainly includes the following ways:

(1) After spheroidizing annealing, cold-rolled bearing steel pipes and hot-rolled bearing steel pipes are cold-rolled into cold-rolled steel pipes of corresponding specifications according to the specification requirements, and then turned into shape, or directly turned into shape. The residual stress of the two processing methods is relatively larger, which will increase the distortion in the subsequent heat treatment.

(2) Cold forging means that the steel is first spheroidized and annealed, then cold forged or milled, and finally turned. This way may also cause the deformation of the workpiece before heat treatment in the vacuum quenching furnace.

(3) Hot forging means that the steel is first spheroidized and annealed, then cooled before turning. The same may cause workpiece deformation before vacuum heat treatment.

(4) Hot rolled steel tube refers to the way of spheroidizing annealing and turning forming.

At present, most of the bearing rings with outer diameter ≤ 100mm are formed by cold rolling. This process is widely used because it can save energy and reduce cost effectively. However, the stress produced by this process is also relatively large, which brings certain difficulty to the final heat treatment. Therefore, the heat treatment process needs to be more accurate and operation needs to be more serious. At the same time, the equipment for heat treatment (vacuum quenching furnace can meet the requirements) is also required to be higher. Only in this way can we meet the technical requirements of the product.