Question from a viewer during Live Stream #301: Is cryogenic treatment necessary for DC53?
Cryogenic treatment is definitely necessary. After cryogenic treatment, DC53 has less retained austenite, resulting in better wear resistance compared to untreated DC53.
Second, retained austenite is an extremely unstable microstructure. If there is too much retained austenite in the mold steel, over time during subsequent use, this retained austenite will transform into a martensitic structure. This increases internal stress, which in turn may lead to a series of problems such as warping of the mold plates or changes in hole spacing. Furthermore, increased internal stress raises the risk of mold fracture. Therefore, it is necessary to perform deep-cold treatment on DC53.
Although DC53 has a Cr8Mo2VSi alloy composition, compared to materials such as Cr12MoV, SKD11, and D2, its carbon content is only 1.0% and its chromium content is only 8%. With both carbon and chromium contents reduced, the amount of retained austenite is lower; at the same time, the reduced chromium content also helps improve the toughness of the die steel; With a molybdenum content of 2.2%, it can be tempered at high temperatures and exhibits a secondary hardening effect, which helps reduce the residual austenite content; however, the residual austenite content remains quite high.
For DC53 with a carbon content of 1.0%, its martensitic transformation termination line is below -100°C. When cooled to room temperature, a significant amount of retained austenite cannot transform into the hard martensitic structure. Therefore, it is necessary to subject DC53 to deep cryogenic treatment to lower the temperature below 0°C—below its martensitic transformation end point—thereby reducing the amount of retained austenite and increasing the martensite content. This enhances the wear resistance of the die steel while simultaneously reducing internal stresses, preventing deformation during subsequent use and providing crack resistance.
However, there are a few points I’d like to remind everyone of: Deep cooling must be performed immediately after quenching—not after tempering or after the part has been fabricated. Performing deep cooling at that stage is pointless.
Second, deep cooling must be performed at temperatures below -100°C. Do not expect to achieve the desired effect by simply freezing the material in a freezer or refrigerator—that will be ineffective, so do not delude yourself.
Third, the benefits of cryogenic treatment for DC53 are based on the material’s inherent uniform microstructure—free of segregation and with low impurity content. Performing cryogenic treatment after quenching reduces the residual austenite content, thereby improving the mold steel’s wear resistance. Never assume that purchasing a substandard piece of DC53 and simply subjecting it to cryogenic treatment will improve its performance—this is simply not the case.
High purity, uniform microstructure, and the absence of segregation in your die steel—this is the first point mentioned earlier and forms the foundation of everything. The subsequent cryogenic treatment—the so-called “benefits”—are only relative to DC53 that hasn’t undergone cryogenic treatment; it does not bring about a dramatic improvement in the die steel’s performance. We must recognize this and not be swayed by exaggerated claims or even brainwashed.
The quality of the smelting process for mold steel is far more important than cryogenic treatment—this is undeniable. These days, mold users are quick to mention cryogenic treatment at the drop of a hat, which seems like a case of over-education—much like the situation with national standard mold steels a few years ago. Something doesn’t quite feel right here, so I’d like to remind you of this.
The quality of the smelting process is the foundation for guaranteeing the performance of die steel. Deep cryogenic treatment is merely a process for reducing the residual austenite content; it is not a magic bullet for ensuring the performance of die steel.
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Wu Dejian’s tool steel, the chief of staff of the user, bought everything he had used.