Waste heat normalization (annealing)
(1) It is necessary to grasp the temperature before the forging is put into the furnace. When the temperature of the part is high, the forging is required to be blown to cool, so that the temperature of the part is lowered to the required normalizing temperature, and the power demand of the heat dividing furnace is sufficient, and heating is performed before the start of manufacturing and when the temperature of a small amount of forging is low.
(2) Determine the reasonable holding time. If the holding time is too long, the crystal grains will be thick and the holding time will be too short, which will cause the structural transformation to be insufficient. The material, shape and size of the forging can be determined experimentally.
(1) Master temperature of forging after casting. The temperature after forming the forging must be above Ar3 (for the sub-eutectoid steel). When the temperature of the forged part is stable, the method of quenching and quenching can be accepted. When the temperature of the forged part is large or the section of the forging is changed greatly, the temperature history must be increased. Make the temperature of the parts uniform before quenching, otherwise the forgings or different cross-section temperatures will be greatly different after quenching, resulting in very structural (bainite or martensite).
(2) The quenching cooling rate is mastered. In the quenching process, the forgings are required to be rapidly cooled, and at the same time, the uniform forgings and the same batch of forgings are uniformly uniform (or similar) after cooling. At the same time, the demand for the quenching rate is mastered, and the too fast quenching rate will produce the Wei's structure in the forging structure. Generally, the quenching rate is controlled at 30 to 42 ° C / min.
(3) Temperature control after quenching. After quenching, the forging temperature must be in the pearlite transformation zone, and should not be lower than the bainite transformation starting temperature (Bs). Otherwise, the bainite (or granular bainite) structure will appear in the structure; if the temperature is too high after quenching, it will cause The amount of ferrite is increased first, and the spacing of the pearlite sheets after the structural transformation is large, resulting in low hardness of the parts. After the forging is quenched, the temperature is generally above 80 ° C to 100 ° C above the Bs temperature.
(4) Selection of isothermal temperature. The roughness of the isothermal temperature simply affects the hardness of the forged part after isothermal normalizing, the hardness is low when the isothermal temperature is high, and the hardness is high when the isothermal temperature is low. The isothermal temperature is generally 50 to 80 ° C above the Bs temperature of the forging material. The specific temperature needs to be determined experimentally according to the material and shape of the forging.
(5) The isothermal holding time is fixed. The pearlite transformation occurs in the isothermal history, so it is necessary to have sufficient holding time. If the isothermal time is too short, the supercooled austenite will not be transformed into pearlite, and it will be transformed into bainite or horse in the subsequent cooling process. The body, causing the isothermal division to have a divergent lattice and a high hardness. The isothermal time can be initially determined by the isothermal transformation curve of the material and adjusted according to the experimental conditions.