Significance of waste heat utilization
Forging industry is a large energy consumer, and forging heat treatment is a major energy consumption in forging production, accounting for about 30% - 35% of the total energy consumption of the whole forging production. Making full use of forging waste heat for heat treatment has obvious advantages in energy saving, consumption reduction and efficiency improvement. It not only saves energy, shortens process flow, but also protects environment.
Heat treatment of hot die forging waste heat
After forging, the heat of forging is directly used for heat treatment. There are three ways of heat treatment for waste heat.
1. After forging, the waste heat is homogenized. After the forging is formed, it is directly sent to the heat treatment furnace and is still carried out according to the conventional heat treatment process. The temperature of different parts of the forging is the same after uniform temperature, which can shorten the holding time. This method is called waste heat homogenization heat treatment. For the forgings with complex shape, especially with large cross-section change, the process can ensure the quality stability of forgings.
2. Direct waste heat treatment after forging. After forging, forging waste heat is directly used for heat treatment. Forging and heat treatment are closely combined, which saves a lot of energy consumption and waste caused by reheating of common heat treatment.
3. After forging, part of the waste heat is used for heat treatment. After the forging is formed, the forging is cooled to about 600 ~ 650 ℃, and then the forging is heated to the required temperature for heat treatment. The method of grain refinement from room temperature to 600 ℃ can save energy.
The key point is forging waste heat quenching
Forging waste heat quenching is a process to obtain martensite or bainite structure when the forging temperature is higher than a certain temperature between Ar3 and AR1 after forging.
After forging heat quenching and tempering, the forging can not only obtain better comprehensive mechanical properties, but also save energy, simplify process flow, shorten production cycle, reduce personnel and save investment cost of quenching furnace. The strength and hardness of forgings after quenching and tempering at high temperature are generally higher than those of ordinary quenching and tempering, while the plasticity and toughness are slightly lower than those of ordinary quenching and tempering (when the tempering temperature is the same). If the tempering temperature is 40-80 ℃ higher than that of ordinary quenching and tempering, the plasticity and toughness of the quenched steel are equal to or slightly higher than that of ordinary quenching and tempering. The strength and hardness of the forging after quenching by forging waste heat can be obviously improved on the premise of maintaining plasticity and toughness. In addition, the machinability of the material can be improved due to the coarser grain size compared with the ordinary quenching.
Control points of waste heat quenching process
1. Stable and controllable heating system. The temperature measurement system of medium frequency heating, medium frequency heating and blank temperature control is qualified.
2. It can be controlled effectively. The appropriate quenching temperature of forging waste heat should be determined according to the test. In practice, it can be achieved by controlling the forging heating temperature and residence time after forging. The retention time after forging is recommended to be less than 60s for carbon steel and 20-60s for alloy steel. Equipped with infrared thermometer and temperature sorting system, the forgings lower than quenching temperature are sorted out; when the forging heating temperature is stable and the forging process is stable, the process time measurement and alarm system can be configured to control the quenching temperature by controlling the process time.
3. Good quenching system. On the premise of ensuring the quenching effect, the quenchant with slow cooling capacity is selected to prevent serious quenching deformation and cracking. As the quenching temperature of forging waste heat is higher than that of ordinary quenching, the hardenability of forgings is good, so oil or PAG quenchant is generally used for carbon steel and alloy steel. The quenching tank should have enough volume and controllable cooling time. In addition, it should be equipped with quenching medium circulation, cooling system and heating device. The quenching medium temperature should be controlled automatically, and the ventilation device should be equipped. Strengthen the maintenance of quenching medium, regularly test the cooling performance of quenching medium, clean the oxide scale and other impurities in the liquid tank and circulation system, and keep the quenching medium clean.
4. Tempering after quenching and configuration position of tempering furnace. After quenching, there is a large stress in the forging, which leads to large deformation and even cracking in the process of placing. In order to prevent the parts from deformation and cracking after quenching, the forgings should be tempered in time after quenching. The shelf life of forgings after quenching is related to the forging material, shape and ambient temperature, which should be determined according to the test. In order to save energy, improve the utilization rate of tempering furnace and reduce the energy consumption of heat preservation, forgings quenched by waste heat are generally tempered in heat treatment workshop.
Application example: (quenching of mini car crankshaft by waste heat)
The material of a mini car crankshaft forging is 40crh (GB / t5216-2004). According to the technical requirements of heat treatment, after quenching and tempering, the microstructure of the forging is between 1 and 4, and the hardness is 241-285hbw. The common quenching and tempering process is that the forging is air cooled to room temperature after forming, then heated to 850 ℃, and then quenched in 10% PAG quenchant after holding for a certain time, then tempered, and quenched and tempered in continuous quenching and tempering line.
The process of forging waste heat quenching is quenching in quenching oil after forming and tempering in continuous tempering furnace after quenching. After inspection, it adopts forging waste heat quenching process, and various performance indexes meet the requirements of customers. By using waste heat quenching process, the quenching and heating process of ordinary quenching and tempering is omitted, and 259kwh / T of quenching heating power is saved. At the same time, the process is simplified and the production cycle is shortened.
UCON designated agent in China
BOVO Chemical Technology Co., Ltd. is the designated agent of Dow Chemical's UCON quenchant in China, distributing UCON A and UCON At the same time, our company has a number of experts in heat treatment industry, quenching medium application experts, as well as a complete quenching medium analysis and test center, which can provide you with a full range of high-quality services, if you need to contact us.