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Vacuum heat treatment process of cold work die steel

Cold work die steel generally belongs to high-carbon alloy steel, with a carbon mass fraction above 0.8%. Chromium is an important alloying element of this type of steel, and most of its structure belongs to hypereutectoid steel or ledeburite steel. Commonly used steels are high Carbon low alloy steel, high carbon high chromium steel, chromium molybdenum steel, etc. How to choose cold working mold materials reasonably and determine the vacuum heat treatment process route is directly related to product quality, economic benefits and service life of molds.

1 Failure mode analysis of cold work die steel

When cold work die steel is working, due to the relatively large deformation resistance of the processed material, the working part of the die bears a lot of pressure, bending force, impact force and friction force. Therefore, the normal reason for the scrapping of cold work dies is generally wear and tear, and there are also early failures due to fracture, collapse force and deformation tolerance.

(1) Friction failure. When the blank is plastically denatured in the mold cavity, it flows and slides along the surface of the cavity, causing severe friction between the surface of the cavity and the blank, which leads to the failure of the mold due to wear, so the wear resistance of the material is the most basic, One of the most important properties. For cold stamping and cold extrusion dies with strict requirements on the surface size and quality of the workpiece, on the premise of ensuring that the die material has sufficient bearing capacity so as not to break, improving the service life of the die depends on the wear resistance of the die surface.

(2) Fatigue failure. Most of the loads borne by cold working dies are periodically applied at a certain impact speed and certain energy. During use, the dies suddenly appear large cracks or breakage and fail, such as chipping of punching dies, punches of cold extrusion dies, etc. , Die fracture. Analyzing the microscopic morphology of fatigue failure shows that improving the stress state of the material surface is an effective way to improve fatigue resistance.

(3) Overload failure. Overload failure refers to the failure caused by the insufficient bearing capacity of the material itself to resist the working load. If the toughness of the material is not enough, it is easy to cause cracking failure and brittle fracture. This is a kind of fracture failure in an unstable state. Common punches and molds are broken and cracked. The reason is mostly due to the lack of sufficient strength and toughness of the mold material. related to the large workload.

To sum up, the working parts of the cold working mold are subjected to various mechanical forces such as tension and compression, bending, impact, fatigue, friction, etc., which will cause brittle fracture, collapse, wear, bite, bite, etc. of the mold parts. Failure due to softening and other phenomena. Therefore, the steel for cold work dies should have the following properties: ① high hardness, so that the cutting edge can be kept sharp during work; ② good wear resistance; ③ sufficient strength and toughness; ④ good processing technology and formability, relatively Good quenching safety, small deformation in vacuum heat treatment, not easy to be brittle on complex sections.

2 Vacuum Heat Treatment Process of Cr12MoV Cold Work Die Steel

According to the performance requirements of cold work die steel, the commonly used steels for cold work die mainly include T10A, 9siCr, 9Mn2v, CrWMn, etc. Use Cr12, Cr12MoV and other steels. The vacuum heat treatment process of Cr12MoV steel is briefly introduced below.

Cr12MoV steel is a high-carbon and high-chromium ledeburite steel. The main vacuum heat treatment process route is: vacuum annealing after forging, vacuum quenching and vacuum tempering. The overall vacuum heat treatment process route is shown in Figure 1.

(1) Vacuum annealing after forging of Cr12MoV steel. Figure 2 is the vacuum annealing process curve after forging; the annealing holding time is 1~2h after all the furnace materials are heated to the annealing temperature, and the isothermal holding time during cooling is 3~4h. When it is necessary to obtain a relatively low receding hardness, a high-temperature tempering can be added. After the forging is heated to 760-790 ° C, it is kept for a period of time, and then cooled to room temperature in air or furnace.

(2) Vacuum quenching. During vacuum quenching, Cr12MoV steel can formulate a specific vacuum quenching process route according to the required mechanical properties and dimensional deformation requirements. The relationship between the quenching temperature and the required hardness is shown in Figure 3.

(3) Vacuum tempering. According to the tempering specifications of Cr12MoV steel, tempering is mainly used to remove stress or remove stress, reduce hardness or remove stress and form secondary hardening. The tempering medium mainly includes oil or nitrate, and the heating temperature and specifications are based on the tempering purpose It varies from person to person, and finally formulate a reasonable vacuum tempering plan based on the different mechanical properties required.

In addition, surface treatment methods such as cold treatment or nitriding can also be used to treat the surface of Cr12Mov steel to further improve the surface properties of Cr12MoV steel.

3 Epilogue

In order to ensure the manufacturing quality of cold working dies and reduce the cost of production, the materials should have good forgeability, machinability, hardenability, hardenability and grindability. After selecting the appropriate mold material, according to the specific working conditions and performance requirements, the performance requirements of the cold working mold can be achieved through the vacuum heat treatment process. The vacuum heat treatment of cold work die steel should pay attention to the following points.

(1) Cold work die steel contains many alloy elements and varieties, the alloying is more complex, the shape of cold work die parts is complex, the processing cycle is long, the thermal conductivity of steel is poor, and the austenitization temperature is high, so heating and cooling During the process, attention should be paid to the generation of thermal stress and tissue stress, and methods such as preheating or stepwise heating and isothermal quenching, graded quenching, high-pressure gas quenching, and air-cooling quenching are often used.

(2) In order to effectively remove stress, reduce hardness or form secondary hardening, attention should be paid to the tempering treatment specifications of Cr 12Mo V steel.

(3) In order to further strengthen, surface strengthening treatment methods such as cold treatment or nitriding are often used.

Vacuum furnace selection: A process technology must be equipped with excellent equipment to play a role. The vacuum heat treatment furnace provided by SIMUWU is an excellent product for processing this type of process. It has the characteristics of good temperature uniformity and high temperature control accuracy. SIMUWU provides a professional team of engineers who can solve various problems encountered in the production process and is committed to giving customers the most convenient and efficient experience.