Material Selection and Manufacturing Process of Hot Forging Dies

Mold is an important process equipment to realize advanced manufacturing technology in the production process, and in recent years, it has been widely used in modern industrial production. From the perspective of use, the quality of the mold mainly depends on the material selection of the mold and the heat treatment process. According to the conditions of use, the mold is divided into cold forming mold, warm forging mold, hot forging mold, plastic forming mold and casting mold, etc. This article mainly involves the material selection and manufacturing process of hot forging mold.

1. Material selection rules and heat treatment technical requirements of hot forging dies：

Through the analysis of the general failure form of the hot forging die, it can be seen that the die should be considered in the process of material selection are thermal hardness, harden-ability, strength and toughness, thermal fatigue performance and so on. From the point of view of heat treatment, it is necessary to consider wear resistance, surface decarburization, hardness, etc.

Thermal rigidity, also known as red rigidity, refers to the mold in a high temperature environment to maintain the stability of the organization and performance, with the ability to resist softening. This ability mainly depends on the chemical composition of the material itself and the process of heat treatment. Generally speaking, steels with high melting points such as V, W, Co, Nb, Mo and easy to form multiple carbide elements are higher in heat hardness.

Strength and toughness are mainly considered according to the bearing capacity of the mold, the grain size of the steel, the form, distribution, size, quantity of carbide and the content of residual austenite will affect the strength and toughness of the mold. These factors mainly depend on the chemical composition of the steel, the state of the organization and the rational use of the heat treatment process.

Harden-ability refers to the hardness range that can be achieved after the quenching process of the material, which is directly related to the carbon content of the material. Of course, there are many factors affecting the life of hot forging dies, and materials should be reasonably selected according to the use conditions of hot forging dies.

2. Hot forging die processing technology：

First, blanking, forging and spheroidizing annealing treatment：The mold materials provided by the steel factory are mainly in the form of bars or forging billets, and the carbides in the internal organization are distributed in a network state along the grain boundaries. If the mold materials in this form are not further processed, cracks are easy to initiation and expansion along the grain boundaries during construction, reducing the bearing capacity of the mold and ultimately reducing the service life of the mold. Through forging and spheroidizing annealing treatment, small, uniform and dispersed carbide can be formed, the internal organizational conditions of the mold are improved, and the cracking phenomenon caused by local stress concentration in the heat treatment process is avoided, and the service life of the mold is improved.

Second, finishing treatment: Arrange cutting before heat treatment, the main purpose of which is to avoid the formation of tensile stress on the surface of the mold during machining and reduce the fatigue resistance of the mold. Electrical pulse processing is a material melting processing process. After electrical pulse processing, a melting layer and a heat-affected layer are easily formed on the surface of the mold, which has a certain impact on the hardness and wear resistance of the mold surface. In order to reduce the compressive stress formed on the surface of the mold after heat treatment, electrical pulse processing is generally no longer carried out after the heat treatment is completed, but by reducing the processing allowance. Or use the way of grinding and polishing after processing to reduce the impact on the surface processing layer to avoid cutting, especially the electrical pulse processing to the mold surface damage and affect the life of the mold.

Third, heating treatment: reasonable processing technology should be used to reduce the deformation of the mold in the heat treatment process, such as the use of multi-stage heating process, which can prevent the mold from heating cracking. At the same time, the heat treatment method should avoid the evaporation of alloying elements, and within the allowable range of material harden-ability, gas quenching technology and vacuum heat treatment should be used as far as possible to reduce heat treatment deformation and avoid the increase of processing allowance after the heat treatment link, resulting in high surface temperature and affecting the service life of the mold.

Next, shot blasting, grinding, polishing treatment: after quenching and tempering process, before surface heat treatment, shot peening should be carried out to form a compressive stress layer on the surface of the die, so as to change the surface tensile stress state of the die after quenching and tempering treatment; the mold polishing treatment can also eliminate the defects of the mold processing surface and improve the service life.

Then, Ion deep nitrogen: in order to further improve the fatigue resistance and wear resistance of the mold, it is best to use N2 and avoid NH3, because the H+ in NH3 has a hydrogen embrittlement effect on the mold. It should be noted that the deep nitrogen temperature should be lower than the tempering temperature after quenching, so as to avoid the reduction of the hardness of the mold matrix, resulting in the failure of the mold.

Lastly, cryogenic treatment: the principle of cryogenic treatment is to reduce the residual austenite and form compressive stress on the surface of the mold to improve the hardness and surface wear resistance of the mold. But you need to be safe. General specifications for cryogenic treatment: mold (room temperature state) - liquid nitrogen (-196) "C/2 hours - natural return to room temperature a 160-170C/4 hours empty cooling.

All in all, manufacturing a hot forging die is not an easy job，there are lots of details to pay attention to and plenty of rules to be noticed and followed, hoping the above information can help you to some extent. Welcome to leave your questions and thoughts below. ZZBETTER as a professional and proficient company，we also have produced many tungsten carbide hot forging dies and other WC products, so please contact us if you have any inquiry as well.