Vacuum heat treatment defect

How to prevent quenching defect of vacuum heat treatment from material aspect

Quenching crack is a common quenching defect, which is caused by many reasons. As the defect of heat treatment starts from the product design, the work to prevent the crack should start from the product design. Simuwu vacuum heat treatment suggests that the materials should be selected correctly, the structure design should be carried out reasonably, the appropriate technical requirements of heat treatment should be put forward, the process route should be arranged properly, and the reasonable one should be selected Heating temperature, holding time, heating medium, cooling medium, cooling method and operation mode, etc.

1. Carbon is an important factor affecting the tendency of quenching crack. With the increase of carbon content, Ms point decreased and the tendency of quenching crack increased. Therefore, under the condition of satisfying the basic properties such as hardness and strength, the lower carbon content should be selected as far as possible to ensure that it is not easy to crack.

2. The influence of alloy elements on the tendency of quenching crack is mainly reflected in the hardenability, Ms point, grain growth tendency and decarburization. Alloy elements affect the tendency of quenching crack through their influence on hardenability. Generally speaking, with the increase of hardenability and hardenability, the quenching medium with weak cooling ability can be used to reduce the quenching deformation to prevent the deformation and crack of complex parts. Therefore, for the parts with complex shape, in order to avoid quenching cracks, it is a better plan to select the steel with good hardenability and use the quenching medium with weak cooling capacity.

Generally speaking, the lower MS is, the greater the tendency of quenching crack is. When MS is high, the martensite formed by transformation may be self tempered immediately, so as to eliminate some transformation stress and avoid quenching crack. Therefore, when the carbon content is determined, a small amount of alloy elements should be selected, or steel grades containing elements that have little influence on MS point should be selected.

3. When selecting steel, overheating sensitivity should be considered. The steel sensitive to overheating is easy to crack, so attention should be paid to the selection of materials.