The hardness of cold working die steel is the main technical index of die steel. The die must have enough hardness to keep its shape and size unchanged under high stress. The hardness of cold working die steel is generally kept around HRC60 at room temperature, and that of hot working die steel is generally kept within hrc40 ~ 55 according to its working conditions.

对于同一钢种，在一定的硬度值范围内，硬度与变形抗力成正比；但硬度相同、成分和组织不同的钢，其抗塑性变形能力可能存在明显差异。红色硬度高温下工作的热作模具需要保持其结构和性能稳定，以保持足够的硬度。这种性质称为红色硬度。

For the same steel, in a certain range of hardness value, the hardness is proportional to the deformation resistance; However, the plastic deformation resistance of steels with the same hardness, different composition and microstructure may be significantly different. The hot working die with red hardness working at high temperature needs to keep its structure and performance stable to keep enough hardness. This property is called red hardness.

冷作模具钢

Cold working die steel

碳素工具钢和低合金工具钢可在180~250℃的温度范围内保持这一性能，铬钼热作模具钢可在550~600℃的温度范围内保持这一性能。钢的红色硬度主要取决于其化学成分和热处理工艺。抗压屈服强度和抗压弯曲强度模具在使用过程中经常受到高强度压力和弯曲，因此要求模具材料要有一定的抗压强度和弯曲强度。

Carbon tool steel and low alloy tool steel can keep this property in the temperature range of 180 ~ 250 ℃, and Cr Mo hot working die steel can keep this property in the temperature range of 550 ~ 600 ℃. The red hardness of steel mainly depends on its chemical composition and heat treatment process. Compressive yield strength and compressive bending strength the die is often subjected to high strength pressure and bending in the process of use, so the die material is required to have a certain compressive strength and bending strength.

在很多情况下，压缩试验和弯曲试验的条件与模具的实际工作条件比较接近(例如，所测得的模具钢的压缩屈服强度与冲头工作时的抗变形能力很吻合)。弯曲试验的另一个优点是应变值大，可以灵敏地反映不同钢种之间以及不同热处理和显微组织条件下的变形抗力差异。在工作过程中，模具承受冲击载荷。为了减少断裂和崩边形式的损伤，要求模具钢具有一定的韧性。

In many cases, the compression test and bending test conditions are close to the actual working conditions of the die (for example, the measured compression yield strength of die steel is very consistent with the deformation resistance of the punch). Another advantage of bending test is that the strain value is large, which can sensitively reflect the deformation resistance difference between different steel grades and under different heat treatment and microstructure conditions. In the working process, the die bears the impact load. In order to reduce the damage of fracture and edge collapse, the die steel is required to have certain toughness.

模具钢的化学成分、晶粒尺寸、纯度、数量、形态、碳化物和夹杂物的大小和分布、热处理制度和金相组织对钢的韧性有很大影响。尤其是钢的纯净度和热加工变形对其横向韧性的影响更为明显。

The chemical composition, grain size, purity, quantity, morphology, size and distribution of carbides and inclusions, heat treatment system and microstructure of die steel have great influence on the toughness of the steel. In particular, the influence of steel purity and hot working deformation on its transverse toughness is more obvious.

钢的韧性、强度和耐磨性往往是矛盾的。因此，需要合理选择钢的化学成分，采用合理的精炼、热加工和热处理工艺，使模具材料的耐磨性、强度和韧性达到匹配。

Toughness, strength and wear resistance of steel are often contradictory. Therefore, it is necessary to select the chemical composition of the steel reasonably and adopt reasonable refining, hot working and heat treatment processes to match the wear resistance, strength and toughness of the die material.