Driven by the development of new tool steels—which were property-wise tailor made for applications such as aluminum die casting, drilling, and tools and dies for the plastic industry—but also due to rising dimensions of the tools, the demands on vacuum-hardening technology have changed in recent decades. One of the most important considerations that must be met is the accomplishment of highest dimensional stability with optimal microstructural properties and minimal change of the surface of the workpieces. Minimizing exposure to air during the heat treatment by reducing the quantity of oxygen in a heat treatment furnace, as with creating a vacuum, is an excellent method for preventing changes in surface appearance and chemical composition.
For more information, click on the link below (subscription required). Then scroll to Figure 14. R Schneider; R. Mesquita; W Schützenhöfer, Distortion in Tool Steels, ASM International, 2014 https://doi.org/10.31399/asm.hb.v04d.a0005958
