How to use low-temperature annealing and tempering to stabilize the size of high-speed steel tools

After the final heat treatment of high-speed steel tools is completed, they are shaped by sharpening. The surface stress state is changed, reducing the accuracy and life of the tool during use. In Japan and some Western countries, after high-speed steel cutting tools are sharpened, they undergo low-temperature tempering at 200℃x2-3h. Several domestic factories also follow suit and add a tempering of 20℃x2h before packaging high-speed steel cutting tools. This stabilizes the tool size and improves its wear resistance.

1) The effect of low-temperature annealing and tempering on tool dimensional changes. A sample with a similar shape to the M5 gear hob was made from M2 steel. After conventional quenching, tempering, grinding, and reheat treatment, the changes in inner hole size and surface stress were measured. After quenching, tensile stress occurs on the tool surface, and after tempering, the tensile stress is close to zero. The surface state is changed during grinding, causing compressive stress on the surface, and the stress is significantly reduced during reheat treatment. After that, the residual stress gradually stabilized. Without reheat treatment, the residual stress in the grinding layer gradually becomes smaller with time, but it is higher than the residual stress after reheat treatment.

2) Reprocess the influence of tool hardness. Use 4 pieces of W18 steel specimens of 10mm The surface roughness is Ra=3.2, and the Vickers hardness is measured after grinding. Then it is reheated at 200℃x2h, and then the hardness is tested after cooling to room temperature. Finally, 0.25mm is ground off the surface.

The test results show that the hardness value of the reheat-treated sample has increased to a certain extent, but whether it is common or not requires a large amount of data to prove. If the reheat-treated sample is tempered at 560°C x lh, its hardness will drop to close to the reheat treatment properties. A large amount of data needs to be demonstrated.

3) The effect of reheat treatment on tool wear resistance. A 100mm, M2.5, A-level precision W18 steel disc shaper was used to conduct cutting tests on the Y54A machine tool. The cutting fluid is L-AN32 total loss system oil, the material to be cut is 180-200HBW 45 steel, the cutting speed v =20m/min, the rotation speed n =1.9r/min, the circumferential feed amount is 0.3mm (double stroke), The radial feed amount is 0.024mm, the total back cutting amount is 5.625mm, the total cutting length is 1500mm, and the wear amount measured after cutting is shown in Table 2-139. It can be seen that the wear amount of the reprocessed gear shaper cutter is reduced by half.

The ground high-speed steel tool has been processed into a finished product, and then undergoes a supplementary heat treatment at 200℃x2h to eliminate the grinding stress on the surface and reduce the chipping phenomenon during cutting. On the other hand, the surface hardness of the tool is improved. It's a good thing that kills two birds with one stone. However, most domestic tool manufacturers are not willing to do such a thing. There are two problems that hinder promotion: the color of the tool surface changes after stress relief treatment, whether it is oil tempering, nitrate salt, or air furnace tempering. Tempering at 200℃ will change the original color; secondly, it increases the chance of damaging the teeth during the process. But stress relief still has more advantages than disadvantages.