A new process for tempering M2 steel twist drills using high-frequency induction heating machine

M2 steel is a general high-speed steel widely used internationally and is mainly used to make various metal cutting tools. With the rapid development of science and technology and the continuous emergence of new materials, the requirements for the cutting life of high-speed steel tools are getting higher and higher. Therefore, people have conducted many in-depth and systematic studies on changing or adjusting the composition, smelting and thermal processing processes, etc. There is a new breakthrough. There have been reports abroad about a new tempering process for high-speed steel. It is said that after low-temperature tempering at 320-380°C, a high-frequency induction heating machine is used to perform two high-temperature temperings at 560°C, which is beneficial to improving hardness, hot hardness and toughness. , can reduce the phenomenon of brittle fracture and extend the service life of the tool. Since the 1980s, many domestic tool factories have successfully applied this process to the production of high-speed steel cutting tools, with remarkable results. The following is an introduction to the application examples of the new low and high temperature tempering technology in the production of twist drills.

1) Test method. The main chemical composition of the steel used in the test is shown in the table below. The size of the impact sample is 10mmX10mmX55mm (no notch), the size of the bending sample is 10mmx130mm in diameter, and the size of the fracture toughness sample is 10mmx10mmx100mm. The quenching process is a conventional process, that is, 850℃ preheating, 1230℃ preheating, 600℃ graded cooling, the quenching grain size is 10.5, and the tempering specifications are 360℃, 370℃, 380℃, 390℃, 400℃, 560 ℃ six groups. After the samples were processed by the above process, the metallographic structure, hardness after tempering, hot hardness (600℃xlhx4 times), impact absorbed energy AK, fracture toughness KIC and bending deflection f, fracture morphology, retained austenite were measured Observation and testing were carried out, and a cutting test was conducted on a 5mm diameter straight shank twist drill to compare their service life respectively.

Chemical composition of M2 steel (mass fraction) (%)

2) Test results

1. Combined with low and high temperature tempering, the carbide dispersion is better than conventional tempering and the tempering is sufficient.

2. Except for the hardness after tempering at 360℃xlh+560℃x1hx2 times, which is slightly lower than 66HRC, the hardness after tempering is higher than 66HRC. However, the hardness after tempering at 360℃xlhx3 times is difficult to reach 66HRC.

3) Conclusion

1. After quenching, M2 steel is tempered at low and high temperatures. Its tempering hardness and hot hardness are improved compared with conventional tempering, and its strength and toughness are also better.

2. Low and high temperature combined with tempering can promote the full precipitation of alloy carbides in steel and make them fine, dispersed and evenly distributed.

3. After low-temperature and high-temperature tempering, the amount of retained austenite increases slightly compared with conventional tempering, and is beneficial to improving toughness.

4. This process is applied to straight-shank twist drills. Compared with conventional tempering, its cutting life is increased by about 30%, and it can save energy and reduce consumption. It is a new tempering process for high-speed steel tools worth promoting.

This article briefly introduces the new process of tempering M2 steel twist drills. Many manufacturers use the above process for heat treatment. The M2 steel twist drills produced are of good quality and meet the work requirements.