Discussion on Forging Process of Tool Steel
Forging is a kind of metal forming process which contains plastic deformation to achieve certain mechanical property through heating, hammering and other thermo-mechanical processes. Tool steel is a kind of alloy steel with high hardness and wear-resistance. It is mainly used to manufacturing the tools and fixtures for cutting metal. In order for the tool steel to achieve a higher degree of uniformity and strength, it is necessary to rely on forging process.
The forging process of tool steel includes open die forging and closed die forging. In open die forging, the block or billet of tool steel is heated in a furnace to a forging temperature. Then it is forged by pressing force between octahedral/sectional dies and hammers. Open die forging can obtain parts with approximate shape and size, but the precision is much lower than that of closed die forging. Closed die forging is to configure a certain shape of cavity before forging. After the tool steel is heated up to the forging temperature, it will be placed into pre-configured cavity, and then a hammer or a press will process the tool steel with different shapes and sizes depending on the configured cavity. Compared with open die forging, closed die forging could better suit the complex profile and precise dimension of the finished products.
At the same time, depending on the different shapes and sizes of the finished products, we can use different kinds of forging technology of tool steel, such as rolling, pulsing and isothermal forging. Rolling is applicable to the tool steel which needs to have a rod shape products or products with a large cross-sectional reduction. Pulsing forging involves impacting or pressing the hot tool steel with an external force in a periodic frequency and a certain amplitude. Isothermal forging is a kind of process that can obtain the installation of tool steel at a constant temperature. In the process of isothermal forging, the shape and size of the tool steel parts will be changed by squeezing them under certain conditions.
In addition, during the process of forging tool steel, it is important to consider the size of the forging force, the forging temperature and the corresponding cooling rate. Generally, the appropriate forging temperature is about 150～250℃ higher than the tool steels recrystallization temperature. As for the forging force, it should correspond with the properties of tool steel and the complexity of the parts. Different cooling rate should also be adopted for different shapes of products. For example, open die forging of a tool steel ingot requires a slower cooling rate and a lower forging pressure, while warm forging requires a higher forging pressure and a faster cooling rate.
In conclusion, the forging process of tool steel is quite complicated, and different kinds of forging process and control conditions should be carefully considered according to the shape, size and properties of the required parts. The choice of proper forging process and control conditions not only can ensure the dimensional accuracy of the parts, but also can improve the fatigue strength and wear resistance of the products.
