Metallurgical principles of microstructure formation in sub-zero treated cold-work tool steels – a review

Abstract

The beneficial influence of a sub-zero treatment on wear resistant tools and components has been known for over 100 years. On the other hand, the basic metallurgical principles being responsible for enhanced hardness and wear performance, changes in the tempering response and toughness and improved dimensional stability have become known only over the past decade. The sub-zero treatment has, thus, been changed from an art to accepted science. The topic of the current conference paper is the latest theory explaining the metallurgical background for this kind of treatment. This theory states that it is the low-temperature isothermal martensitic transformation that induces secondary microstructural effects, such as an accelerated precipitation rate for transient carbides, formation of very small globular carbides and overall refinement of the microstructure. Consequently, secondary microstructural effects have a clear impact on the most relevant properties. The extent of the improvement or deterioration of these properties may be a result of competitive microstructural effects.