The improper heat treatment, mould processing process, cause mould cracking prematurely discarded, especially using only quenched and tempered, not for quenching, nitriding technology for appearance, in die casting for thousands of times will represent physical crack and craze.
Stress during steel quenching and cooling process is the thermal stress and phase transformation in the arrangement of the results of stress superposition, quenching stress is the cause of the form of shape, craze, there is a need for tempering to eliminate stress.
Ii. In the process of mold processing and production.
1. Quality problems of blank casting.Some of the molds produce only a few hundred of them, and the cracks begin very quickly.Is probably the only ensures that the casting exterior scale, and the dendritic crystal, mixed carbides in the steel, such as shrinkage cavity, bubble loose faults along the processing method is lengthen, streamline, the streamline on future final quenching distortion and cracking in the process of using, embrittlement, failure has enormous influence on the tendency.
2. The cutting stress occurred during the final processing of cars, milling and planing, which can be eliminated by annealing in the center.
3. The grinding stress occurs when the hardened steel is grinding, and the friction heat occurs during grinding. The softening layer and decarburization layer occur, which reduces the thermal fatigue strength, and simply causes the thermal cracking and early cracks.Of h13 steel after fine grinding, can adopt heating to 510-510 ℃, to one hour per 25 mm insulation thickness for eliminating stress annealing.
4. Stress of electrical discharge machining.The surface of the mould has a layer of enriched electrode element and dielectric element white bright layer, hard and brittle, this layer itself will have cracks, there is stress.The high frequency should be selected in the edm process to minimize the whitening layer. It is necessary to have the polishing method removed, and the tempering treatment is carried out, and the tempering is carried out at the three-stage tempering temperature.
3. In the production process of die-casting.
1, stamping die in the prenatal surely should be preheated to temperature, otherwise when chilling during high temperature liquid metal filling and the mold temperature gradient layers, thermal stress, cracks make mould appearance, and even cracking.In the process of production, the mold temperature keeps rising. When the mold temperature is overheated, the mould is simple to stick to the mold, and the moving parts fail, causing the appearance of the mold to be damaged.The cooling temperature control system should be set up and the working temperature of the mould must be kept within a certain range.