A tool steel quenched and tempered to 45 HRC offers a combination of high thermal conductivity, thermal fatigue resistance and good wear resistance, making this specialty steel particularly suitable for applications such as low-pressure die casting, high-pressure die casting (for the gate runner and biscuit area) and plastic injection molding.
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Here are three steel properties to consider when selecting your next mold material to lower cycle times, and a review of how a new specialty remelted tool steel holds up:
This specialty remelted tool steel achieves a significantly higher thermal conductivity in the hardened and tempered condition of 45 HRC to 50 HRC than conventional hot work tool steels such as 1. (AISI H11) or 1. (AISI H13) (see Figure 1).
At room temperature, the thermal conductivity is 41.5 W/mK and reaches its highest value of 44.0 W/mK at 100°C. This is about 70% higher compared to 1. and 1., which show thermal conductivities of 25.5 W/mK and 26.8 W/mK at room temperature. The thermal conductivity of this specialty remelted tool steel exceeds conventional hot work tool steels, especially in the range of 100-200°C, which is equivalent to the working temperature in injection molding applications.
Molds and inserts made of this specialty grade can dissipate the process heat from the mold surface within a shorter time, resulting in shorter cycle times and higher process efficiency. In addition, temperature differences between the surface and the mold core are minimized, lowering the mold’s thermal stresses and reducing cracking (see Figure 2).
The heat treatment (hardening and tempering) differs from conventional hot work tool steels. Molds and inserts should be hardened in the temperature range from 1,050°C to a maximum of 1,090°C, depending on their size. The hardness after quenching is approximately 52 HRC. The secondary hardness maximum of this new specialty remelted tool steel () is around 53 HRC, reaching roughly 570°C (see Figure 3).
The steel should be tempered twice, similar to other hot work tool steels. Due to its tempering resistance, it is important to temper this steel at higher temperatures to obtain hardness values comparable to those of H11 and H13. Even larger dimensions can easily be quenched and tempered and generate a homogeneous martensitic microstructure.
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Polishability is a critical tool steel property, so polishing trials were conducted to test the performance of this remelted specialty steel (the study used remelted H11 material). The processing time for standard high-gloss polishing is equivalent to H11 ESR.
Hot work tool steels have a working temperature range of 250-700 ℃. They are used as steel for hot cutting knives, steel for press extrusion molds, forging presses, steel for molds for pressurized molds, molds for the production and processing of metals in solid and liquid form.
Tool steel products are resistant to corrosion, have good toughness, fire crack resistance, heat resistance, very high strength, hardness, and abrasion resistance at high temperatures.
It is necessary to preheat the component to a suitable temperature of 200-250 ℃ in order to preserve the life of the tool steels for hot work, and to properly cool these steels after work.
For the tool life is also responsible proper heat treatment of the product, which is delivered in a softened state. The working temperature of the product should not exceed the tempering temperature. Each of the products is exposed to cracks at work, which over time grows, so it is necessary to replace the components at regular intervals.
Heat treatment of tool steels for hot work consists of multi-stage heating of the product to the austenitization temperature depending on the grade - 850- ℃. The temperature of this compartment must be chosen so that there is no grain growth in the product, which may reduce the ductility of the core of the element.
For smaller sections, hardening is carried out in oil. For larger components, hardening is carried out by spraying water mist, compressed air or with an isothermal stop. The tempering temperature is 500-600 ℃, where the treatment is repeated twice. During tempering, depending on the alloy additives in the grade, M₂C, M₄C₇, M₇C alloy carbides are responsible for the secondary hardness.
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