Reasons for insufficient hardness during quenching of automotive stamping molds?

In production, sometimes the quenching hardness of metal stamping parts is insufficient, which is a common defect in the process of heat treatment and quenching. “Insufficient hardness” has two manifestations, one is the low hardness value of the whole workpiece, the other is It is manifested as insufficient local hardness or soft spots. When the hardness of the metal stamping die is insufficient, it is necessary to use the hardness test or metallographic analysis to analyze which “hardness is insufficient”, and then find out from the raw materials, heating process, cooling medium, cooling method and tempering temperature, etc. The reasons; the main reasons are as follows;

• 1. Improper selection of raw materials or wrong materials, the parts that should have been made of medium carbon steel or high carbon steel in the metal stamping die were chosen to be wrongly made of low carbon steel, or the parts that should have been made of alloy tool steel were Wrong use of ordinary high carbon steel will cause insufficient hardness or soft spots;
• 2. The uneven microstructure of the raw material causes insufficient local hardness or soft spots; the microstructure appears as follows; carbide segregation or aggregation, such as ferrite aggregation, graphite, severe Widmansite structure, etc., will cause insufficient hardness or soft spot;
• 3. The quenching heating temperature is low and the holding time is insufficient;
• 4. The quenching heating temperature is too high and the holding time is too long;
• 5. During quenching and heating, the surface of the workpiece is decarburized;
• 6. Improper selection of quenching medium;
• 7. The influence of quenching medium temperature;
• 8. The medium is too old during quenching;
• 9. Improper cooling time control, etc.

In a word, insufficient hardness often occurs during quenching of automobile stamping parts, and the operator should analyze it according to different situations and find out the reasons to overcome it;