H13 Steel of Heat treatment process
The quenching and tempering process of H13 steel can be heated by salt bath furnace, protective atmosphere furnace, vacuum furnace and flowing particle furnace. The surface of the mold is smooth, the heat treatment is small, and the mold life is long. In particular, the external thermal corundum flow particle furnace protects and heats. This heating method absorbs the advantages of salt bath furnace and vacuum furnace heating, and is very suitable for heat treatment of hot work die steel.
In the heat treatment process of H13 steel, the first stage should be preheated from 800 °C to 850 °C, and then raised to the austenitizing temperature. The purpose of the stage preheating is to avoid too much heating caused by the stress caused by the temperature gradient formed in the cavity to cause distortion of the mold; it is also effective to promote austenite homogenization.
The austenitizing temperature of H13 steel ranges from 1000 ° C to 1060 ° C. In order to obtain high red hardness, the upper limit of austenitizing temperature can be used; in order to obtain good toughness and prevent cracking, the lower limit of austenitizing temperature can be used. The actual quenching temperature is selected to ensure that sufficient carbon and alloying elements are dissolved in the austenite to obtain high hardness and red hardness, and that the austenite grain size is smaller than ASTM9 to ensure sufficient toughness. The quenching temperature is higher than the annealing temperature, and measures should be taken to prevent oxidative decarburization.
H13 steel can be quenched by air quenching, gas quenching, 500 ° C ~ 550 ° C classification quenching and oil quenching. Taking H13 steel of 100mm bar as an example, when oil quenching, the cooling rate curve of the center of the bar does not meet the carbide precipitation line in the TTT curve, so the impact toughness of the steel is not affected, and the disadvantage is that the deformation is large; Quenching and quenching in a salt bath at 500 °C results in precipitation of carbides along the cross section. Therefore, the impact toughness of steel is affected. However, compared with oil quenching, fractional quenching can reduce the risk of cracking and deformation of the mold. In view of the fact that the hot working die is generally no longer processed after heat treatment and avoiding deformation cracking of the mold and oxidative decarburization during cooling, stepwise quenching is generally employed. In the case of step hardening, air cooling can be performed when the temperature in the mold table is the same. Oil quenching is only used when the mold dimensional change requirements are not too high or can be trimmed after tempering.
In addition to the use of salt baths and fluidized furnaces for quenching to reduce mold distortion, the use of certain cooling characteristics of the fluidized bed can also be very effective in reducing the deformation and cracking tendency of certain molds. For example, when Wallace Engineering of the United States quenched the H13 hot work die weighing 300kg, firstly, the mold up to 1024 °C was cooled in a fluid bed cooling furnace with a large cooling rate (48.6 °C/min) from 10 min to 538 °C. Then it was transferred to another fluid bed cooling furnace with a slower cooling rate (16.7 °C/min) to cool l0min to 371 °C, and finally air-cooled. This method successfully solved the warpage of H13 steel hot work die quenching. Qu and cracking problems.