The working temperature of hot die is high (generally, the initial forging temperature is 1200 ℃ and the final forging temperature is 800 ℃), and the working condition is bad. When working, the strong pressure and impact load make the blank metal flow in the mold cavity, and there is severe friction between the blank metal and the cavity surface, which is easy to wear the cavity surface.

同时锻模要在不断反复冷却条件下工作，由于冷热交变的结果，型腔表面在交变应力作用下易产生疲劳裂纹。使用过程中，磨损、疲劳是热模具失效的主要形式。为此，我们对热模具进行热处理工艺研究，以提高其工作寿命。

At the same time, the forging die has to work under the condition of repeated cooling. Due to the alternating cold and hot stress, the fatigue crack is easy to appear on the surface of the die cavity under the action of alternating stress. During use, wear and fatigue are the main failure forms of hot die. Therefore, we study the heat treatment process of the hot die to improve its working life.

随着淬火温度的升高，淬火硬度也有所提高，低于1200℃淬火时，回火时2次硬化现象不明显。若高于此温度淬火，碳化物溶解较多，奥氏体合金度增加，从而强化了马氏体，回火时由马氏体中析出较多的弥散碳化物，2次硬化才显示出来。

With the increase of quenching temperature, the quenching hardness also increases. When the quenching temperature is lower than 1200 ℃, the secondary hardening phenomenon is not obvious during tempering. If the quenching temperature is higher than this temperature, more carbides are dissolved and the alloying degree of austenite increases, thus strengthening the martensite. During tempering, more dispersed carbides are precipitated from the martensite, and the secondary hardening is shown.

提高回火温度，以防止在模具使用过程中发生马氏体向屈氏体转变，以减小组织应力。由传统工艺1次回火，改为3次回火，以使淬火后，材料中低硬度的残余奥氏体较充分地转变为高硬度的2次马氏体，提高模具力学性能。改进后的热处理工艺为：

The tempering temperature should be raised to prevent the transformation from martensite to troostite and to reduce the structural stress. By changing the traditional process from one tempering to three tempering, the retained austenite with low hardness can be fully transformed into secondary martensite with high hardness after quenching, so as to improve the mechanical properties of the die. The improved heat treatment process is as follows

淬火：550℃装炉（箱式电阻炉加热，加热时模腔用“生铁屑+渗碳剂”保护，以防止模腔脱碳），保温40min；再升温1150℃，保温120min，然后出炉油冷室温。

Quenching: furnace charging at 550 ℃ (box resistance furnace heating, mold cavity is protected by "green iron filings + carburizing agent" during heating to prevent mold cavity decarburization), holding for 40 min; then heating to 1150 ℃, holding for 120 min, and then discharging oil cooling to room temperature.

回火：回火3次，每次加热温度为660℃，保温90min（采用井式回火炉加热）。

Tempering: tempering for 3 times, heating temperature for each time is 660 ℃, holding time is 90min (well type tempering furnace is used for heating).

用该热处理工艺处理的模具使用寿命可达4500次，降低了模具费用，提高了生产效率。

The service life of the die treated by the heat treatment process can reach 4500 times, which reduces the cost of the die and improves the production efficiency.