Mold Materials Pages 11 to 20 How to Lower Cycle Times With the Right Tool Steel By John Stocker 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 applica-tions such as low-pressure die casting, high-pressure die casting (for the gate runner and biscuit area) and plastic injection molding. 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: 1. Thermal Conductivity This specialty remelted tool steel achieves a signii-cantly higher thermal conductivity in the hardened and tempered condition of 45 HRC to 50 HRC than conventional hot work tool steels such as 1.2343 (AISI H11) or 1.2344 (AISI H13). 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 1.2343 and 1.2344, which show thermal conduc-Molds and inserts made of a remelted special steel grade can dissipate the process tivities of 25.5 W/mK and 26.8 W/mK at room tem-heat from the mold surface within a shorter time. perature. 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 The steel should be tempered twice, similar to other hot work equivalent to the working temperature in injection molding tool steels. Due to its tempering resistance, it is important to applications. temper this steel at higher temperatures to obtain hardness val-Molds and inserts made of this specialty grade can dissipate ues comparable to those of H11 and H13. Even larger dimensions the process heat from the mold surface within a shorter time, can easily be quenched and tempered and generate a homoge-resulting in shorter cycle times and higher process eficiency. neous martensitic microstructure. In addition, temperature differences between the surface and the mold core are minimized, lowering the mold’s thermal 3. Polishing stresses and reducing cracking. Polishability is a critical tool steel property, so polishing trials were conducted to test the performance of this remelted specialty 2. Heat Treatment steel (the study used remelted H11 material). The processing time The heat treatment (hardening and tempering) differs from for standard high-gloss polishing is equivalent to H11 ESR. conventional hot work tool steels. Molds and inserts should be hardened in the temperature range from 1,050°C to a maxi-FOR MORE INFORMATION FOR MORE INFORMATION mum of 1,090°C, depending on their size. The hardness after Swiss Steel International quenching is approximately 52 HRC. The secondary hardness 800-323-1233 / j.stocker@swisssteelgroup.com maximum of this new specialty remelted tool steel (2383) is John Stocker, Director of Sales around 53 HRC, reaching roughly 570°C. 20 MoldMaking Technology — — JULY 2023 Image courtesy of Swiss Steel USA.