Cr12MoV tool steel is a kind of die steel, and Cr12MoV tool steel has high hardenability. It can be completely hardened when the section is 300 ~ 40 0mm or less. It can maintain good hardness and wear resistance at 300 ~ 40 0 ​​°C. The toughness is higher than that of Cr12 steel, and the volume change during quenching is the smallest.

The tempering of the Cr12MoV tool steel is a heat treatment method in which the strain accumulated in the quenched workpiece is relieved by heating, and the hardness is adjusted to improve the toughness. During the tempering process, the carbide precipitates from the hard and brittle martensite formed by quenching, the quenched martensite becomes tough tempered martensite, and the retained austenite in the steel is decomposed to produce two The effect of secondary hardening.

Most of the Cr12MoV tool steels are used at high temperatures, so the secondary hardening type high temperature tempering treatment (500 to 650 ° C) is generally used to obtain the stability of the mold. However, Cr12MoV tool steel for cold work molds is sometimes treated with low temperature tempering at around 200 °C.

The change in size over the years is an important issue for cold work dies. The change in size over the years is a phenomenon in which undecomposed unstable austenite changes with time and expands to cause dimensional change. In general, for every 1% change in retained austenite, the mold size will be 0.01 to 0.015% elongation. This dimensional change will proceed slowly over a few years after heat treatment, even at room temperature. Therefore, this phenomenon becomes a big problem of a cold working die requiring high dimensional accuracy. The method of suppressing the change in size over the years is to reduce the amount of retained austenite or to stabilize austenite.

After the tempering of the Cr12MoV tool steel, the Cr12MoV tool steel is heat treated at about 400 °C to reduce the strain of the unaltered retained austenite in the quenching and tempering, so that the retained austenite is stabilized, and it is difficult to change the size over time.