(1) Mould meets working conditions

1. When the abrasion-resistant blank is plastic degenerated in the die cavity, it flows and slides along the surface of the die cavity, causing severe friction between the surface of the die cavity and the blank, which leads to the failure of the die due to wear. So the wear resistance of materials is one of the basic and important properties of dies. Hardness is the main factor affecting wear resistance. Generally speaking, the harder the die parts are, the smaller the wear amount is and the better the wear resistance is. In addition, the wear resistance is also related to the type, quantity, morphology, size and distribution of carbides in the material.

2. The working conditions of the strong and tough dies are mostly bad, and some of them often bear large impact load, which leads to brittle fracture. In order to prevent the sudden brittle fracture of die parts, the die should have high strength and toughness. The toughness of the die mainly depends on the carbon content, grain size and structure of the material.

3. Fatigue fracture often results in fatigue fracture under long-term cyclic stress during the working process of the fatigue fracture performance die. Its forms include low energy multiple impact fatigue fracture, tensile fatigue fracture, contact fatigue fracture and bending fatigue fracture. The fatigue fracture performance of the die mainly depends on its strength, toughness, hardness and inclusion content in the material.

4. High temperature performance when the working temperature of the die is higher, the hardness and strength will decrease, leading to early wear or plastic deformation of the die and failure. Therefore, the die material should have high temper resistance stability to ensure that the die has high hardness and strength at working temperature.

5. Cold and thermal fatigue resistance Some dies are in the state of repeated heating and cooling in the working process, which causes surface cracking and spalling, increases friction, hinders plastic deformation and reduces dimensional accuracy, resulting in die failure. Thermal and cold fatigue is one of the main failure modes of hot working dies, and the die should have high cold and thermal fatigue resistance.

6. Corrosion resistance of some moulds such as plastic moulds when working, due to the presence of chlorine, fluorine and other elements in the plastics, after heating decomposition of hci, HF and other strong corrosive gases, erosion of the die cavity surface, increase its surface roughness, aggravate wear failure.

(2) Mould meets process performance requirements

Die manufacturing usually goes through forging, cutting, heat treatment and other processes. In order to ensure the manufacturing quality of the die and reduce the production cost, the material should have good malleability, cutting machinability, hardenability, hardenability and grindability, and should also have small oxidation, decarbonization sensitivity and quenching deformation cracking tendency.

1. Forgetability has low resistance to hot forging deformation, good plasticity, wide forging temperature range, low tendency of forging cracking, cold cracking and precipitation of network carbides.

2. The spheroidizing annealing temperature range of annealing process is wide, the annealing hardness is low and the fluctuation range is small, and the spheroidizing rate is high.

3. Machinability cutting parameters are large, tool wear is low and machined surface roughness is low.

4. Oxidation and decarbonization are sensitive to high temperature heating. They have good antioxidant capacity, slow decarbonization speed, insensitive to heating medium and little tendency to produce pitting.

5. After hardening, it has uniform and high surface hardness.

6. Deep hardening layer can be obtained after hardenability quenching, and hardening can be achieved by using mild quenching medium.

7. Quenching deformation cracking tendency The volume change of conventional quenching is small, the shape warpage and distortion are slight, and the abnormal deformation tendency is low. Conventional quenching has low cracking sensitivity and is insensitive to quenching temperature and workpiece shape.

Grindable grinding wheel has low relative wear, large non-burn limit grinding consumption, insensitive to grinding wheel quality and cooling conditions, and is not easy to occur grinding damage and grinding cracks.

(3) Mould meets economic requirements

In the selection of die materials, we must consider the principle of economy and reduce the manufacturing cost as much as possible. Therefore, on the premise of meeting the service performance, the first choice is low price, carbon steel can be used instead of alloy steel, domestic materials can be used instead of imported materials. In addition, the production and supply situation of the market should also be taken into account when selecting materials. The selected steel grades should be as few as possible, concentrated and easy to purchase.