Mar 06,2026
Deep cold treatment of cast steel: the terminator of residual Oluvia
Deep cold treatment of cast steel: the terminator of residual Oluvia
Cryogenic treatment, Heat treatment, Retained austenite, Dimensional stability, Tool steel
In the heat processing chain of cast steel, tempering and refiring are well-known links. However, there is another key step that is often overlooked, but has a decisive impact on the size stability and lifespan of the cast, which is deep cold processing. Deep cold processing, as the name implies, is placing the tempered cast in an environment far below zero degrees Celsius (usually from -80°C to -196°C), transforming the unstable residual occellida in its micro-tissues into hard and stable macellida, thus completing the ultimate “tempering” of the material‘s micro-structure.
The core value of deep cold treatment lies in the complete elimination of residues of Orcs. During the tempering process, not all Orcs succeed in transforming into Ma‘s. Some Orcs are unusually stable due to oversaturation of carbon and alloy elements, and are “frozen” in microscopic tissues, which are residues of Orcs. Residues of Orcs are a soft and unstable phase. During the subsequent grinding of the mold, Electrical discharge machining, and even long service, residues of Orcs may spontaneously transform into Ma‘s under the induction of external energy (such as heat and stress). This transformation is accompanied by volume expansion, which creates microscopic stress within the mold, leading to micro-meter-scale size changes and even causing micro-cracks. For precision molds, this time-effective deformation is fatal. The deep cold treatment provides a powerful thermodynamic drive for the transformation of residual O’s into Ma’s through extremely low temperatures, making it almost completely transform, thus fundamentally eliminating this instability hazard.
The second significant effect of deep cold treatment is the extraction of ultra-fine carbonides to improve abrasion resistance. In the deep cold process, in addition to phase transition, it also encourages the migration and extraction of oversaturated carbon atoms in the steel material, forming extremely fine carbonide particles (such as vanadium carbonide, molybdenum carbonide). These ultra-fine carbonides are evenly distributed in the Ma’s body matrix, serving as diffuse reinforcement. They are like “micro bearings” and “abrasion-resistant particles” in the microscopic world, greatly improving the hardness and abrasion resistance of the mold. Research has shown that mold steel treated in deep cold can improve its abrasion resistance by 2 to 6 times. This means a dramatic increase in the life of the mold for molds that press high-strength low-alloy steel or engineered plastics containing glass fiber.
The deep cold processing process is not a simple “cooling” process, and the control of its process parameters is crucial. First is the cooling rate. Molds need to be cooled from room temperature to deep cold temperature at a controlled rate to avoid cracking due to excessive thermal stress, especially for molds with complex shapes and different thickness of walls. Temperature control is usually used to slowly cool down at a fixed rate. Second is the heat retention time. Molds need to be kept at deep cold temperature for long enough (typically 24–48 hours) to ensure that the entire section, especially the central area of the thick and large parts, can reach the target temperature and complete sufficient phase transition and carbonide removal. The third key point is the backfire joint. Deep cold processing is usually arranged after tempering, before the first backfire, or between two backfires. After the deep-cold treatment, the return fire must be carried out immediately to eliminate the huge internal stress generated during the deep-cold process and stabilize the newly formed Ma’s body tissues.
Different types of cast steel respond differently to deep cold treatment. High-alloy steel, such as high-speed steel (such as SKH51), powdered metallurgical steel (such as the ASP series), high-carbon high-chrome steel (such as D2, Cr12MoV), has the most significant response to deep cold treatment due to its large amount of alloy elements and carbonides, and its large and stable O-scale residual volume. Deep cold treatment is almost a must-pass for these steel materials to achieve their maximum performance. For low-alloy tool steel (such as O1) or pre-hardened steel (such as P20), the effects of deep cold treatment are relatively limited, and sometimes not even necessary. Therefore, the choice of whether to do deep cold treatment requires a scientific decision based on the cast steel‘s license number, the cast’s working conditions, and the lifespan requirements.
The applications of deep cold processing are becoming widespread from the cutting edge fields to mainstream manufacturing. Early on, it was mainly applied in aerospace and military industries. Today, as the requirements for mold life and precision continue to increase, as well as the cost of deep cold processing equipment and services decline, it has been widely applied in precision mold manufacturing in industries such as automotive, electronics, and household appliances. Whether it‘s the head of the press mold, the concave mold, or the shape core and fittings of the injection mold, deep cold processing has become the “standard configuration” to improve its performance and ensure long-term stability. It exchanges extremely low temperatures for the extreme enhancement of mold performance.
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