How to reduce the heating time of forging blank heat treatment?


Release time:

2022-06-14

The ratio of the time of the surface temperature of the forging after heating the furnace to temperature (referred to as uniform temperature) and the time of the center to temperature (insulation) to the total heating time varies with the heating temperature.

  The ratio of the time of the surface temperature of the forging after heating the furnace to temperature (referred to as uniform temperature) and the time of the center to temperature (insulation) to the total heating time varies with the heating temperature. The lower the heating temperature, the higher the ratio, and the higher the heating temperature, the larger the holding time. It can be seen that the key to shortening the heating time lies in the stage where the total heating time accounts for a large proportion. According to the principle of heat transfer, there are ways to shorten the heating time:
  1. Uniform heating
  When the workpiece is heated, if the temperature is uneven, the surface will be heated unevenly, resulting in eccentric heating center, which is equal to increasing the cross-sectional size, such as 1.4D ( Diameter) for correction, the heating time should be extended by 30~50%. Therefore, homogeneous heating is the first issue that should be considered in shortening the heating time. Here, the working environment of the heating furnace should be kept good, the temperature of the heating furnace should be sensitive, and the furnace gas circulation conditions should be considered in the furnace loading method of the workpiece. .
  2. Reasonably select the cross-section temperature difference
  . After the surface of the forging is heated to temperature, due to the limitation of heat conduction, the center temperature is consistent with the surface temperature, which takes a long time. Therefore, the heating time in the process should be determined according to the actual needs of the workpiece center, that is, a certain cross-sectional temperature difference is allowed. For example, forging heating, for ordinary structural steel, requires no deformation. Heating does not need to be heated close to the surface temperature; when the wrought center is defective, the center must be heated to a sufficiently high temperature. Analyzing the heating standards of foreign forgings, it can be seen that the cross-sectional temperature difference is within 10 °C when the high-temperature wide-top strong pressing process is adopted, while the allowable cross-sectional temperature difference of ordinary forgings is close to 100 °C, and the heating time is only 60% of the former. The same problems also exist in the heat treatment process, that is, solid solution of alloying elements, grain refinement, microstructure transformation and tempering parameters, etc., no matter what purpose, there is a suitable temperature range. Therefore, studying the suitable temperature range of different steel types and different process requirements, and determining the reasonable heating allowable section temperature difference can shorten the heating time better under the premise of ensuring quality.
  3. Properly increase the furnace temperature
  When the forging blank is heated, the surface temperature always lags behind the furnace temperature. After the temperature in the furnace rises to the required temperature, the surface of the forging can reach the highest temperature within a considerable period of time. The length of this period of time is closely related to the required heating temperature. As the heating temperature decreases, the surface heat transfer coefficient decreases, and the required time also increases. Therefore, before the surface temperature of the forging is reached, increasing the furnace temperature appropriately can greatly shorten the time for the surface of the forging to reach temperature. This method is especially suitable for workpieces with simple shapes. Through the calculation of the temperature field, the degree of furnace temperature and the holding time can be increased according to the size of the workpiece, the required heating temperature and heating speed.
  4. Strengthen convection
  At high temperature, the heat exchange on the surface is mainly convective heat transfer. When the temperature of the furnace gas is constant, the velocity of the furnace gas in contact with the surface of the furnace charge and the forging billet determines the surface heat transfer coefficient and affects the time for the surface to reach temperature. Existing coal gas and heavy oil heating furnaces mainly rely on the combustion air flow for forced convection, and under low-temperature heating at 200-400°C, the burner is turned off a small amount. The reduction of the air volume will inevitably greatly affect the heating efficiency in the low temperature area. Therefore, for the low-temperature heating furnace, if the structure of the furnace body is improved and the gas circulation is strengthened, the heating efficiency can be improved and the heating time can be shortened.