Views: 3 Author: Site Editor Publish Time: 2022-06-21 Origin: Site
In the process of mold, the custom processing heat treatment process is an indispensable part. In the heat treatment process, temperature control, heating time, cooling rate, and other factors will have different effects on the molding of the mold. The following mold accessories manufacturers Shengqi to share the mold processing heat treatment process on the mold molding factors.
The influence of the heat treatment process on the mold forming factors are mainly the following four points:
▪ Heating speed
▪ Heating temperature
▪ Quenching and cooling rate of the impact
▪ Tempering temperature
1. Heating speed
In general, quenching and heating, the faster the heating speed, the greater the thermal stress in the mold. Because of its poor thermal conductivity, it is easy to cause mold deformation and cracking, especially for alloy steel and high alloy steel, especially needs to pay attention to preheating for some complex shapes of high alloy mold but also needs to take several graded preheating. But in individual cases, using rapid heating can sometimes reduce deformation when only heating the surface of the mold. At the same time, the center remains "cold," so the corresponding reduction in tissue stress and thermal stress, and the heart deformation resistance, thus reducing the quenching deformation, according to some factory experience, is used to solve the whole distance deformation has a specific effect.
2. Heating temperature
Quenching the heating temperature of the high and low impact on the hardenability of the material, while the austenite composition and grain size play a role.
(1) from the aspect of hardenability, the high heating temperature will make the thermal stress increase, but at the same time make the hardenability increase, so the tissue stress also increases and gradually dominate. For example, in carbon tool steel T8, T10, T12, etc., the internal diameter tends to shrink in the general quenching temperature quenching. Still, tissue stress gradually dominates if the quenching temperature is increased to ≥ 850℃ due to increased hardenability. Thus the internal diameter may show a tendency to expand.
(2) from the austenite composition, quenching temperature increases the carbon content of austenite and quenching martensite squareness increases (specific volume increases), thereby increasing the volume after quenching.
(3) from the Ms point of influence on the fine view, quenching temperature is high, and the austenite grain coarse will make the parts of the deformation and cracking tendency to increase.
Comprehensive, for all the steel, especially some high-carbon medium and high alloy steel, the quenching temperature will affect the mold quenching deformation. Therefore, the correct choice of quenching heating temperature is significant.
Generally speaking, choosing too high a quenching heating temperature is not suitable for deformation. Under the premise of not affecting the use of performance, always use a lower heating temperature. But for, some quenching has more residual austenite steel (such as Cr12MoV, etc.), which can also be adjusted by adjusting the heating temperature and changing the amount of residual austenite to regulate the deformation of the mold.
3. Quenching and cooling rate of the impact
In general, increasing the cooling rate above the Ms point will make the thermal stress increase significantly. The result of thermal stress caused by the deformation tends to increase; in the Ms point below, the increase in cooling rate is mainly to make the tissue stress caused by the deformation increase.
There are different deformation tendencies for different steel grades due to the Ms point of different heights， therefore using the same quenching medium. Due to their different cooling capacity, the same steel, such as using different quenching mediums, and therefore also have different deformation tendencies. For example, the carbon tool steel in Ms point is relatively low, so the use of water cooling and thermal stress influence often prevails. By the cold, it may be tissue stress prevails.
The mold is often graded or graded in actual production- isothermal quenching is usually not completely quenched. Hence, the role of thermal stress is often dominant, so the cavity tends to shrink. Still, because the thermal stress is not very large, the total deformation is relatively small. If the use of water-oil dual-liquid quenching or oil quenching, the thermal stress caused by the more significant the cavity shrinkage will increase.
4. Tempering temperature
Tempering temperature on the impact of deformation is mainly due to the tempering process caused by the organization's transformation. Suppose the tempering process produces a "second quenching" phenomenon. In that case, the residual austenite into martensite, due to the generation of martensite than the residual austenite volume, will cause the mold cavity expansion; for some high-alloy tool steel such as Cr12MoV, etc., when the requirement of red hardness and high-temperature quenching, multiple tempering, each tempering A fire, the volume will expand once. If tempered in other temperature areas, the specific volume decreases due to quenching martensite to tempering martensite (or tempering soxhite, tempering quartzite, etc.) transformation. Therefore, the cavity tends to shrink.
In addition, tempering, the relaxation of residual stress in the mold, and the deformation also have an impact. After quenching, if the surface is in a tensile stress state, the size will increase after tempering; conversely, if the surface is in a compressive stress state, it will produce shrinkage. However, of the two effects of tissue transformation and stress relaxation, the former is the leading cause.