High-speed steel contains high carbon and a large number of alloying elements, and the hardness after heat treatment is as high as 63~79HRC. These characteristics make high-speed steel often appear cracks, insufficient hardness, overheating or overburning, local erosion, and deformation during heat treatment. And other defects, especially the heat treatment of thick and complex parts. Process analysis pointed out that the problem of insufficient hardness is mainly caused by decarburization during heat treatment. Insufficient heat preservation time or too low temperature may also cause insufficient hardness. The problem of overheating, overburning or melting is due to the high quenching temperature or the high temperature holding time too long. The problem of cracks is due to overheating of quenching, too fast heating rate, too fast quenching cooling rate, untimely or insufficient tempering. High-speed steel parts with complex shapes, sudden changes in part cross-sections, and large thickness differences are more prone to cracking. Large-size, large-thickness, high-speed steel parts that require high hardness, the stress generated during the heat treatment process is large, the quenching cooling rate is difficult to increase, and the thickness difference of different parts of the part is large, not only easy to crack during heat treatment, but also thick parts often appear The hardness is not enough, and the thin part is locally overheated or eroded.

In response to the above-mentioned problems, AVIC Changhe Aircraft Co., Ltd. has improved the heat treatment of large parts of high-speed steel. The main points are as follows:

1. Forgings should be annealed in time if the forgings are damaged. In order to eliminate the internal stress generated by the blank during forging, refine the grains, and prepare the structure for quenching, high-speed steel must be annealed in time after forging. The annealed structure is sorbite and carbide.

Second, optimize the quenching process. In order to avoid the loss of carbon and alloying elements in high-speed steel, neutral salt bath protection and heat treatment should be adopted as much as possible in the heat treatment process, and the salt bath should be more strictly deoxidized. In order to eliminate the cutting stress and reduce the temperature difference between the inside and outside of the parts during the heat treatment heating process, on the basis of the 800-850℃ preheating, an additional 500-600℃ preheating is added, and each preheating must be fully heated. It is necessary to select the quenching heating temperature appropriately, not only to fully dissolve the carbides, but also to avoid the abnormal growth of crystal grains and the accumulation of residual carbides. For W18Cr4V steel, 1260~1280℃ can be used to make the austenite grain size 9-10. Similarly, the selection of the holding time, according to the size and shape of the part, heating medium and use requirements, not only must ensure the maximum dissolution of carbides, but also prevent any part of the parts from excessive growth and burning of crystal grains; especially thick Large parts, mainly to ensure the hardness and cutting performance of the blade. The thickness of the blade part should be used as the base to determine the holding time to eliminate defects such as coarse grains, brittleness, cracking or local erosion at the blade. For thick and large parts with complex shapes, it is difficult to ensure the hardness without cracking by quenching and cooling with oil quenching or air cooling, and it is necessary to use graded salt bath or multiple salt bath cooling. For W18Cr4V steel, on the basis of 600~650℃ isothermal treatment, 280~300℃ salt bath isothermal treatment can be added to ensure the transformation of surface martensite and the transformation of martensite and bainite in the core to reduce stress and prevent Oxidation.

Three, improve the tempering process. After quenching, the austenite content of high-speed steel will reach 30%, and it is difficult to eliminate it at one time during tempering. Therefore, it is tempered three times at 560℃, and each tempering is appropriately extended, and the parts are kept for one hour after the parts are heated through.

The test proved that after the optimization of the heat treatment process, a microstructure of fine tempered martensite + more granular carbides and a small amount of retained austenite is obtained, and the hardness is 63~66HRC. Its comprehensive mechanical properties are good and fully meet the requirements of use.