1. Influence of heating rate
Generally speaking, during quenching heating, the faster the heating speed, the greater the thermal stress generated in the mold, which is likely to cause deformation and cracking of the mold. Especially for alloy steel and high-alloy steel, due to their poor thermal conductivity, special attention should be paid to preheating For some high-alloy molds with complex shapes, multiple preheating steps are required. However, in individual cases, rapid heating can sometimes reduce deformation. At this time, only the surface of the mold is heated, while the center remains "cold", so the tissue stress and thermal stress are reduced accordingly, and the core deformation resistance is greater , Thereby reducing the quenching deformation, according to some factory experience, used to solve the hole pitch deformation has a certain effect.
2. Influence of heating temperature
The quenching heating temperature affects the hardenability of the material, and at the same time affects the composition and grain size of austenite.
(1) From the perspective of hardenability, high heating temperature will increase thermal stress, but at the same time increase hardenability, so the structural stress also increases, and gradually dominates. For example: carbon tool steels T8, T10, T12, etc., when quenched at general quenching temperature, the inner diameter shows a tendency to shrink, but if the quenching temperature is increased to ≥850°C, the hardenability increases and the structural stress gradually accounts for Dominance, so the inner diameter may show a tendency to expand.
(2) From the perspective of austenite composition, the increase in quenching temperature increases the austenite carbon content, and the squareness of martensite after quenching (increased specific volume), which increases the volume after quenching.
(3) From the perspective of the influence on the Ms point, the higher the quenching temperature, the coarse austenite grains, which will increase the deformation and cracking tendency of the parts.
In summary, for all steel grades, especially some high-carbon medium and high alloy steels, the quenching temperature will obviously affect the quenching deformation of the mold. Therefore, the correct selection of the quenching heating temperature is very important.
Generally speaking, choosing too high a quenching heating temperature is not good for deformation. Under the premise of not affecting the performance, always use a lower heating temperature. However, for some steel grades with more retained austenite after quenching (such as Cr12MoV, etc.), the amount of retained austenite can also be adjusted by adjusting the heating temperature to adjust the deformation of the mold.