Process analysis of heat treatment using high frequency induction heating machine for W18 steel machine woodworking blades

The machine woodworking blade was originally an imported piece and may chip during use. Now it is a self-made part, using W18 steel. According to the failure mode of the blade, a reasonable heat treatment plan has been drawn up. The hardness requirement is 58-62HRC. After heat treatment with a high-frequency induction heating machine, the blade has sufficient strength, hardness and good toughness, which greatly improves the performance and life of the blade. Today, the editor will tell you about its heat treatment process.

From the heat treatment process of W18 steel machine woodworking blades, it can be concluded that the process has two significant characteristics. One is to reduce the quenching temperature and increase the tempering temperature. The second is to obtain a small amount of martensite in advance during cooling, and then perform bainite isothermal quenching.

①Reduce the quenching heating temperature. The purpose of lowering the quenching heating temperature is to inhibit the dissolution of carbides, reduce the content of carbon and alloy elements in austenite, and create conditions for obtaining lath martensite during quenching. The annealed state of W18 steel contains three types of carbides: M6C, MC and M23C6. The dissolution temperatures of various types of carbides are different. M23C6 is completely dissolved into austenite at about 1100°C, effectively improving the hardenability and oxidation resistance of steel. M6C and MC are more stable than M23C6 and only dissolve in a small amount at 1170-1180°C. Therefore, the content of carbon and alloy elements in austenite is lower than normal quenching heating. After quenching, lath martensite with good strength and toughness is obtained. At the same time, the dispersed distribution of undissolved carbides hinders the growth of austenite grains and achieves a good grain refinement strengthening effect.

② Bainite isothermal quenching. During the quenching and cooling process of high-speed steel, grading at 580-620°C is an effective method to reduce thermal stress and reduce deformation. After classification, it is cooled in a nitrate salt bath at about 180°C lower than the Ms point. When the blade is close to or equal to the temperature of the nitrate salt, a small amount of austenite has transformed into martensite, and then immediately transfers to 260 to 280°C. ℃ nitrate salt isothermal 35-40min.

During the isothermal process, austenite undergoes lower bainite transformation, and the small amount of martensite preformed before isothermal strongly promotes the bainite transformation at higher temperatures. Therefore, the time to complete the tissue transformation is greatly shortened, and isothermal 35-40 minutes is sufficient. Moreover, isothermally reduces the thermal stress generated during cooling and the structural stress generated during martensite transformation, and a composite structure of lower bainite + lath martensite + carbide + retained austenite can be obtained.

③Tempering. A high-frequency induction heating machine is used for tempering heat treatment. The process is 600℃ reduce. The retained austenite precipitates carbides, reduces the alloy degree, and relaxes the compressive stress. After tempering, it is cooled below the Ms point, and more retained austenite transforms into martensite (lath shape). Tempering at 560°C twice can further adjust the structure and reduce internal stress.

The heat treatment process directly affects the heat treatment quality of the workpiece. Therefore, it is necessary to master the heat treatment process of the workpiece. This article briefly introduces the heat treatment process of W18 steel machine woodworking blades. After many manufacturers adopt the above process, the machine woodworking blades produced have a hardness of 60-62HRC and a service life longer than imported products.