تأثير معالجة التسخين البلاستيكي على القالب.

1. تأثير plastic heating سرعة

بشكل عام, أثناء التبريد التدفئة, the faster the plastic heating سرعة, the greater the thermal stress generated in the قالب, والتي من المحتمل أن تسبب تشوه وتكسير القالب. خاصة بالنسبة لسبائك الصلب والفولاذ عالي السبائك, بسبب الموصلية الحرارية السيئة, وينبغي اتخاذ احتياطات خاصة. حرارة, for some complex shapes of high-alloy molds, it is necessary to take multiple preheating steps.

لكن, in individual cases, rapid heating can sometimes reduce deformation. في هذا الوقت, only the surface of the mold is heated, and the center remains “بارد”, so the structural stress and thermal stress are correspondingly reduced, and the core deformation resistance is relatively large, thereby reducing the quenching deformation. According to some factory experience, it is used to solve There is a certain effect on the hole pitch deformation.

2. تأثير plastic heating temperature

The quenching heating temperature affects the hardenability of the material, and at the same time affects the composition and grain size of austenite.

1) From the perspective of hardenability, high heating temperature will increase the thermal stress, but at the same time increase the hardenability, so the structure stress also increases, and gradually dominates. على سبيل المثال, carbon tool steels T8, T10, T12, إلخ., when quenched at general quenching temperature, the inner diameter shows a tendency to shrink, but if the quenching temperature is increased to ≥850°C, the hardenability increases and the structural stress gradually becomes dominant Status, so the inner diameter may show a tendency to bulge.

2) From the perspective of austenite composition, the increase in the quenching temperature increases the austenite carbon content, and the squareness of the martensite after quenching (increased specific volume), which increases the volume after quenching.

3) From the perspective of the influence on the Ms point, if the quenching temperature is high, the austenite grains will be coarse, which will increase the deformation and cracking tendency of the parts.

في ملخص, for all steel grades, especially some high-carbon medium and high alloy steels, the quenching temperature will obviously affect the quenching deformation of the بلاستيك قالب, so the correct selection of the quenching heating temperature is very important.

بشكل عام, choosing too high a quenching heating temperature is not good for deformation. Under the premise of not affecting the performance, the lower plastic heating temperature is always used. لكن, for some steel grades with more retained austenite after quenching (such as Cr12MoV, إلخ.), the amount of retained austenite can also be adjusted by adjusting the heating temperature to adjust the deformation of the mold.

3. The influence of quenching cooling rate

بشكل عام, increasing the cooling rate above the Ms point will significantly increase the thermal stress, and as a result, the deformation caused by the thermal stress will tend to increase; increasing the cooling rate below the Ms point will mainly increase the deformation caused by the tissue stress. Big. إلى

For different steel grades, due to the different heights of the Ms points, when the same quenching medium is used, there are different deformation tendencies. For the same steel grade, if different quenching media are used, they also have different deformation tendencies due to their different cooling capabilities.

على سبيل المثال, the Ms point of carbon tool steel is relatively low, so when water cooling is used, the influence of thermal stress tends to prevail; while when cooling is used, the structural stress may prevail.

في الإنتاج الفعلي, molds are usually not fully quenched when they are graded or graded-austempered, so thermal stress is often the main effect, which tends to shrink the cavity. لكن, because the thermal stress is not very large at this time, وبالتالي, the total deformation is relatively small. If water-oil double-liquid quenching or oil quenching is used, the thermal stress caused is greater, and the cavity shrinkage will increase.

4. The influence of tempering temperature

The effect of tempering temperature on deformation is mainly caused by the transformation of the structure during the tempering process. If the phenomenon of “secondary quenching” occurs during the tempering process, the retained austenite is transformed into martensite, and the specific volume of the martensite generated is larger than that of the retained austenite, which will cause the mold cavity to expand; For some high-alloy tool steels, such as Cr12MoV, high temperature quenching is used to require red hardness as the main requirement. When multiple tempering, the volume expands once every time the tempering is performed. إلى

If it is tempered in other temperature regions, the specific volume decreases due to the transformation of quenched martensite to tempered martensite (or tempered sorbite, tempered troostite, إلخ.), so the cavity tends to shrink.

بالإضافة الى, the relaxation of the residual stress in the mold during tempering also affects the deformation. After the mold is quenched, if the surface is in a state of tensile stress, the size will increase after tempering; على العكس تماما, if the surface is in a state of compressive stress, shrinkage will occur.

But of the two effects of organizational transformation and stress relaxation, the former is the main one. The above is only an analysis of the various factors of mold deformation from the heat treatment, which can only be used as a reference to solve the problem.

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