The hot working die bears a great impact force when it works. The die cavity contacts with high temperature metal and is heated and cooled repeatedly, so its service condition is extremely bad. In order to meet the requirements of hot working die, hot working die steel should have the following basic characteristics:

热作模具钢厂一般说来，锤锻模用钢有两个问题比较突出一是工作时受冲击负荷作用.故对钢的力学性能要求较高，特别是对塑变抗力及韧性要求较高;二是锤锻模的截面尺寸较大(<400mm)故对钢的淬透性要求较高，以保证整个模具组织和性能均匀。不同类型的锤眼模应选用不同的材料。对中小型的锤锻模通常选用5CrMnMO钢。

Generally speaking, there are two problems in the steel used for hammer forging die in hot working die steel works. One is that it is subjected to impact load during working. Therefore, it requires higher mechanical properties of steel, especially higher plastic deformation resistance and toughness; Second, the cross-section size of hammer forging die is larger (< 400mm), so the hardenability of steel is required to be higher, so as to ensure the uniform structure and performance of the whole die. Different materials should be selected for different types of hammer eye dies. 5CrMnMo steel is usually used for medium and small hammer forging dies.

热挤压模的工作特点是加载速度较慢，因此，模腔受热温度较高，通常可达500一800℃。对这类钢的使用性能要求应以高的高温强度(即高的回火稳定性)和高的耐热疲劳性能为主。

The working characteristic of the hot extrusion die is that the loading speed is slow, so the heating temperature of the die cavity is high, usually up to 500-800 ℃. High high temperature strength (i.e. high tempering stability) and high thermal fatigue resistance are the main requirements for the service performance of this kind of steel.

(1)较高的高温强度和良好的韧性。热作模具，尤其是热锻模，工作时承受很大的冲击力，而且冲击频率很高，如果模具没有高的强度和良好的韧性，就容易开裂。

(1) High temperature strength and good toughness. Hot working dies, especially hot forging dies, bear a lot of impact force when working, and the impact frequency is very high. If the die does not have high strength and good toughness, it is easy to crack.

(2)良好的耐磨性能，由于热作模具丁作时除受到毛坯变形时产生摩擦磨损之外，还受到高温氧化腐蚀和氧化铁屑的研磨，所以需要热作模具钢有较高的硬度和抗黏附性。

(2) Good wear resistance, because the hot work die is not only subject to friction and wear when the blank is deformed, but also subject to high temperature oxidation corrosion and grinding of iron oxide chips, so the hot work die steel needs to have high hardness and anti adhesion.

(3)高的热稳定性。热稳定性是指钢材在高温下可长时间保持其常温力学性能的能力。热作模具工作时，接触的是炽热的金属，甚是液态金属，所以模具表面温度很高，一般为400～700℃。这就要求热作模具钢在高温下不发生热化，具有高的热稳定性，否则模具就会发生塑性变形，造成堆塌而失效。

(3) High thermal stability. Thermal stability refers to the ability of steel to maintain its mechanical properties at room temperature for a long time at high temperature. When the hot working die works, the contact is hot metal, even liquid metal, so the surface temperature of the die is very high, generally 400 ~ 700 ℃. This requires that the hot work die steel does not heat at high temperature and has high thermal stability, otherwise the die will have plastic deformation, resulting in collapse and failure.

(4)优良的耐热疲劳性，热作模具的工作特点是反复受热受冷，模具一时受热膨胀，一时又冷 却收缩，形成很大的热应力，而且这种热应力是方向相反，交替产生的。在反复热应力作用下，模具表面会形成网状裂纹(龟裂)，这种现象称为热疲劳，模具因热疲劳而过早地断裂，是热作模具失效的主要原因之一。所以热作模具钢必 须要有良好的热疲劳性。

(4) Excellent heat resistance and fatigue. The working characteristic of hot working die is that it is repeatedly heated and cooled. The die expands when heated and shrinks when cooled, forming great thermal stress. Moreover, this kind of thermal stress is produced alternately in the opposite direction. Under the action of repeated thermal stress, network cracks (cracks) will form on the surface of the die, which is called thermal fatigue. The premature fracture of the die due to thermal fatigue is one of the main reasons for the failure of the hot working die. So hot work die steel must have good thermal fatigue.

(5)高淬透性。热作模具一般尺寸比较大，热锻模尤其是这样，为了使整个模具截面的力学性能均匀，这就要求热作模具钢有高的淬透性能。

(5) High hardenability. Generally, the size of hot working die is large, especially for hot forging die. In order to make the mechanical properties of the whole die section uniform, it requires high hardenability of hot working die steel.

(6)良好的导热性。为了使模具不致积热过多，导致力学性能下降，要尽可能降低模面温度，减小模具内部的温差，这就要求热作模具钢要有良好的导热件能。

(6) Good thermal conductivity. In order to avoid excessive heat accumulation of the die, which leads to the decline of mechanical properties, it is necessary to reduce the temperature of the die surface and the temperature difference inside the die as much as possible, which requires that the hot work die steel should have good thermal conductivity.

(7)良好的成形加工工艺性能，以满足加工成形的需要。

(7) Good forming process performance to meet the needs of forming.