Method of Preventing Defects in Cold Treatment of Die Steel
The essence of cold treatment is the continuation of quenching. The quenching stress at room temperature and the quenching stress at zero are superimposed, and when the stack response force exceeds the strength limit of the material, cold treatment cracks are formed.
Die steel is mostly medium and high carbon alloy steel. After quenching, some of the subcooled austenite has not been transformed into martensite, and it remains in the service state and becomes retained austenite, which affects the performance. If it is placed below zero to continue cooling, it can promote the martensite transformation of the retained austenite.
Any quote here
The specific prevention methods can be divided into two points:
(1) After quenching, place the mold in boiling water for 30-60 minutes before cold treatment, which can eliminate 15%-25% of the internal quenching stress and stabilize the retained austenite, and then perform conventional cold treatment at -60°C, or at -120°C Cryogenic treatment, the lower the temperature, the more the amount of retained austenite is transformed into martensite, but it is impossible to complete the transformation.
Experiments show that about 2%-5% of retained austenite is retained, and a small amount of retained austenite is retained as needed. The tensile can relax the stress and act as a buffer. Because the retained austenite is soft and tough, it can partially absorb the rapid expansion energy of mart sensitization and ease the transformation stress;
(2) After the cold treatment is completed, take out the mold and put it in hot water to heat up, which can eliminate 40%-60% of the cold treatment stress. After heating to room temperature, it should be tempered in time, and the cold treatment stress will be further eliminated to avoid the formation of cold treatment cracks, obtain stable tissue performance, and ensure the mold No distortion occurs during product storage and use.