What are the heat treatment methods for pre-hardened plastic mold steel?

Manufacturing process line of pre-hardened plastic mold steel: For molds processed directly using purchased modules, because the steel has been pre-hardened in the supply state, the molds can be directly polished and assembled after processing and forming; or during processing and forming After adding a stress relief annealing, polishing, assembly. For those who want to forge into a blank and then process it, the process route is blanking → reforging → spheroidizing annealing → planing and milling → pre-hardening treatment (32-42HRC) → mechanical roughing → stress relief annealing → mechanical finishing →Polishing→Assembly. The pre-hardening treatment of the white steel knife is usually a high-temperature tempering (quenching and tempering treatment) after quenching. Solid hardenability is an important process index of pre-hardened steel.

The level of hardenability will directly affect the final mechanical properties of the mold. Must understand when quenching process. When determining the quenching temperature of the die steel, you can refer to the critical points of various steels.

The critical points of some pre-hardened steels are listed in Table 1-1.

The hardness of the pre-hardened steel after high temperature tempering (greater than 450℃), under the condition of a certain blank size, depends on the tempering stability of the steel, which is related to the alloying elements of the steel, and can pass the tempering test at different temperatures , Determine the relationship between the hardness of the steel and the tempering temperature curve as a reference. The cooling rate of the front steel after high temperature tempering should also be noted. For some pre-hardened steels, when they cool slowly from the high temperature tempering temperature, temper embrittlement will often occur. Tempered embrittlement steel will not only have lower impact toughness at room temperature than normal steel, but also greatly increase the brittle transition temperature of the steel.

After tempering the pre-hardened steel, the rapid cooling from the high temperature tempering temperature (oil cooling) can reduce or eliminate brittleness, but it is difficult to achieve for large modules. It has been known that adding certain Mo or W to steel can effectively suppress the temper brittleness, so it is necessary to pay attention to the selection of pre-hardened steel materials for large modules.