Heat Treatment Method For Mold Steel

In addition to the reasonable selection of materials and various forming processes, heat treatment is often necessary. Heat treatment of molds is one of the important processes in mechanical manufacturing. By changing the microstructure inside the workpiece or changing the chemical composition on the surface of the workpiece, Or improving the performance of the workpiece. Its characteristic is to improve the intrinsic quality of the workpiece, which is generally not visible to the naked eye. The microstructure of iron and steel is complex, but the heat treatment of injection mold steel is the main content in the heat treatment process. Of course, other metal materials can also be added to change their mechanical, physical, and chemical properties to give full play to their performance.

Regardless of injection mold, stamping mold, or die-casting mold, there are certain material processing methods to meet a certain manufacturing method. For example, where it is often subjected to friction, stretching, and impact, heat treatment is one of the ways to change the mechanical properties of the material. Although it is the same composition of steel, when the heat treatment methods are different, there are significant differences in the properties that appear. Heat treatment is a very complicated science, and there are many different metallurgical structures involved, which is difficult to explain in a few words. Looking at the heat treatment methods, only a few commonly used ones are outlined here.

1. Quenching

The steel is rapidly cooled to room temperature under high temperatures. This process is to make the structure in the steel material very hard and brittle.

2. Annealing

Heat to a proper temperature and keep it for a while, then slowly cool in a furnace or in a heat-insulating material. The correct annealing temperature should be obtained from the manufacturers of different steels. The main purpose of annealing is to soften the steel, remove residual stress and increase machinability.

3. Flame quenching

Use an oxyacetylene flame to rapidly heat the steel surface to the quenching temperature before the central part of the material reaches the quenching temperature, spray cold water to cool the surface to harden.

4. Normalizing

The steel is heated to about 100 ℃ above the hardening temperature and then placed in still air to cool naturally. After the normalization process, the structure of the steel becomes finer and the machinability is improved, which can make the structure of the steel product after forging or casting more stable, and it has the expected effect on the further heat treatment reaction.

5. Carburizing

Heat low carbon steel (0.1-0.3% C) to 850-930 ° C to make activated carbon atoms penetrate into the surface of the steel. After hardening and tempering, the surface layer is hard and the inner part is still attractive.

6. Tempering

Tempering is an operation that must be performed after quenching. The purpose of tempering is to remove the internal stress of the steel, prevent cracks that may occur after quenching, adjust some hardness and increase the tensile strength so that the steel will not crack when subjected to a slight impact. The tempering temperature is from about 100 ° C to below the hardening temperature, depending on the carbon content of the steel.

7. Nitriding

Heat the furnace filled with nitrogen to 500-550 ° C to decompose the nitrogen obtained from the decomposition of ammonia into the surface of the steel. After cooling, a layer of nitride is obtained on the steel. The nitrided layer has high hardness, high wear resistance, and corrosion resistance.