1. Local Carburization
When processing molds, it is important to completely eliminate local carburization or high-speed steel. High-speed steel tools may also experience local carburization uniformly. If no suitable oxidation or carburization protection is used during heat treatment, partial carburization may occur. Then, quenching will produce different temperature transformation points, resulting in different stresses in the surface and core, which often leads to cracking.
2. Sharp Edge Transition
Heat treatment causes material deformation. It will manifest as cracking in areas where there is a possibility of releasing these stresses, such as sharp corners, etc. Therefore, heat treatment work should avoid sharp corners as much as possible.
3. Pressure Marks on the Outside Surface
It is often the case that molds with sharp pressure marks on the outside surface are sent to the quenching furnace. If rough quenching medium is used, cracks may easily form on the surface. Quenching molds should be given R-angles as much as possible.
4. Incorrect Heat Treatment Temperature
The temperature experienced by each workpiece in the furnace can vary greatly, and heat treatment may cause cracks, reducing service life.
5. Annealing
Molds are often not fully annealed, assuming that the desired hardness has been achieved after quenching and the mold is immediately used. In such cases, because the temperature structure has not transformed from a square to a cubic from the beginning, there is already a hidden danger.
6. Gas nitriding (including gas soft nitriding and gas case hardening)In gas nitriding, the workpiece is placed in a nitriding furnace, which is placed in an intermittent furnace or filled with ammonia gas. Ammonia decomposes into nitrogen and hydrogen. Nitrogen diffuses into the surface of the workpiece, and hydrogen is extracted. Typically, the nitriding operation time is quite long because the nitrogen penetration rate into the workpiece is not as strong as in other processes. The advantage of gas case hardening is that the operation costs are cheap and the work surface is even under relatively simple conditions. Gas nitriding is mainly used for workpieces that are subjected to extreme wear. (Note: Gas soft nitriding penetrates about 0.1 mm in 17 hours of treatment, and gas case hardening penetrates about 0.3 mm in 70 hours of treatment) The color of the nitrided workpiece is white. If the nitrided workpiece is dark, it means that the workpiece has been oxidized, and it is possible that there is a problem with the quality of the furnace. Ion nitriding (ion soft nitriding and ion case hardening)
Ion nitriding (also known as glow discharge nitriding) operates at a slightly lower temperature. The workpiece is connected as the cathode, and the vacuum furnace wall is connected as the anode. The connection voltage is several hundred volts. As a result, low glow discharge occurs. This will produce positive nitrogen ions, which impact the surface of the workpiece with high energy. Ion nitriding uses a temperature range of 400-550°C and is very easy to control. The sharp corners of the workpiece are damaged, the impact is dulled, and it is difficult for the fluid to penetrate into the deep side position or the working bone position.