Vacuum heat treating modified tool steels having reduced silicon content and better cleanliness using the latest vacuum furnace technology achieves uniform properties and minimizes distortion.

The use of vacuum furnaces to heat treat dies for the die-casting industry in the 1980s and 1990s had primary objectives of reducing distortion and obtaining a nice surface finish with no post cleaning combined with easy process control. Minimizing distortion saved money on post machining, especially on large H13 hot-work tool steel die inserts. The downside was that low distortion was mostly realized through a very slow gas quench (<30 F, or 17 C/min), which consequently resulted in the precipitation of grain boundary carbides, leading to shorter die life due to reduced impact toughness (Fig. 1).