At present, China's mould life is not high, Pail Mould consumption is large, therefore, improve the life of China's mould is a very urgent task. Die heat treatment has a great influence on service life. Most of the mould damage we often come into contact with is caused by improper heat treatment. According to statistics, because the mould heat treatment is improper, and causes the mould failure to account for more than 50% of the total loss efficiency, so the foreign mould heat treatment, more and more use of vacuum furnace, semi-vacuum furnace and no oxidation protective atmosphere furnace.
The die heat treatment process includes matrix toughening and surface strengthening. The strength and toughness of the matrix is to improve the strength and toughness of the matrix and reduce the fracture and deformation, so the conventional heat treatment must be carried out strictly according to the process. The main purpose of surface strengthening is to improve the wear resistance, corrosion resistance and lubrication performance of the die surface. Surface strengthening treatment methods are many, there are mainly carburizing, carburizing, carburizing, boriding, carburizing, metal carburizing and so on. The service life of the die can be increased several times or even dozens of times by using different surface strengthening processes. In recent years, some surface strengthening processes have appeared. This paper focuses on three of them.
1, ion nitriding, in order to improve the mould corrosion resistance, wear resistance, thermal fatigue and anti-adhesion performance, can be used ion nitriding. The outstanding advantage of ionic nitriding is to significantly shorten the nitriding time, can be controlled by different gas components, reduce the nitriding layer surface brittleness, deformation is small, the hardness distribution curve of the nitriding layer is more stable, not easy to produce spallation and thermal fatigue. The permeable matrix material is wider than gas nitriding, non-toxic, will not explode, production safety, but for the shape of complex mould, it is difficult to obtain uniform heating and uniform permeation layer, and the permeation layer is shallow, the transition layer is steeper, temperature measurement and temperature uniformity are still to be solved.
Ion nitriding temperature to 450 ~ 520℃ is appropriate, after 6 ~ 9h treatment, nitriding layer depth about 0.2 ~ 0.3mm. The temperature is too low, the permeation layer is too thin; If the temperature is too high, the surface layer is easy to appear loose layer, reducing the ability of anti-adhesion mould. The thickness of the permeation layer is 0.2 ~ 0.3mm. The worn ion nitriding die can be put into use after repair and ion nitriding again, thus greatly increasing the overall service life of the die.
2, carbon and nitrogen altogether permeability, low carbon and nitrogen altogether permeability process temperature (560 ~ 570 ℃), the deformation is small, the processing of the surface of the steel hardness up to 900 ~ 1000 hv, good wear resistance, corrosion resistance is strong, have higher hot hardness, can be used in die mould, cold heading die, cold extrusion moulding, hot extrusion die, high speed forging die and plastic mould, can increase the service life of the 1 ~ 9 times respectively. However, the gas nitrocarburizing often deforms and the expansion volume accounts for about 25% of the thickness of the compound, so it is not suitable for the precision mould. Annealing and removal of residue must be carried out before treatment.
3, carbon, nitrogen and boron ternary common infiltration, ternary common infiltration can be carried out in the nitrifier, percolating agent containing boron organic percolating agent and ammonia, its ratio is 1:7, the total percolating temperature is 600℃, the total percolating time is 4h, common percolating layer compound layer thick 3 ~ 4 m, diffusion layer depth is 0.23mm, the surface hardness is HV011050. The service life of the Plastic Bucket Mould is increased remarkably after the treatment of co-permeability.