Die steel: What is the Effect of Heat Treatment? Heating rate, temperature, and quenching speed all affect the deformation of die steel during heat treatment, and different steel types have different cooling capacities, resulting in different deformation tendencies. So, what is the impact of die steel heat treatment? In this article, we will tell you.
Heat treatment refers to a chemical heat treatment process that uses nitrogen atom penetration into the surface of a workpiece at a certain temperature and in a certain medium. The nitriding method mainly uses a nitriding furnace, where the workpiece is placed in a material frame and lifted by a crane and placed on the furnace bottom for heating. Additionally, a nitriding furnace with a reinforced load-bearing structure for the furnace mouth can be made, and the workpiece can be hung vertically with hanging and lifting tools for heating.
The lid of the nitriding furnace is generally driven by an electric motor reducer and is electrically and automatically lifted. After closing the lid, there is another clamping bolt to ensure the vacuum seal of the nitriding furnace. Vacuum is first drawn, then nitrogen is introduced for nitriding heat treatment.
Generally speaking, the faster the heating rate during quenching, the greater the thermal stress generated in the mold, making it easy to cause deformation and cracking. Especially for alloy steel and high-alloy steel, which have poor thermal conductivity, preheating needs to be given more attention. For some complex-shaped high-alloy molds, multiple level preheating is needed.
However, in some cases, adopting rapid heating can sometimes reduce deformation. In this case, only the surface of the mold is heated, and the center remains "cold", thus corresponding to reducing the organizational stress and thermal stress, and the center has a large deformation resistance, thereby reducing quenching deformation. According to some factory experience, this has a certain effect on solving hole pitch deformation.
The height of the quenching heating temperature affects the material's hardenability and also affects the composition and grain size of the austenite.
Regarding hardenability, an increase in the heating temperature can increase the thermal stress, but also increase the hardenability, so the organizational stress also increases and gradually becomes the dominant factor. For example, carbon tool steel T8, T10, T12, etc., when quenched at ordinary quenching temperature, the inner diameter tends to shrink, but if the quenching temperature is raised to ≥850 ℃, the hardenability increases, and the organizational stress gradually becomes dominant, resulting in the possible expansion of the inner diameter.
From the perspective of austenite composition, an increase in the quenching temperature increases the carbon content of the austenite, and the martensite's squareness after quenching increases(i.e., volume increase), resulting in an increase in volume after quenching. From a microcosmic perspective, increasing the quenching temperature makes the austenite grain size larger, which increases the tendency of part deformation and cracking.
Choosing a too high quenching heating temperature is not beneficial for reducing deformation. Under the premise of not affecting the performance, a lower heating temperature should always be used. However, for some steel grades with residual austenite after quenching, such as Cr12MoV, the heating temperature can be adjusted to change the residual austenite content to adjust the mold's deformation.
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