Refractory hardening elements

Low—medium alloy steels contain elements such as Mo and Cr for hardenability, and W and Mo for wear resistance (Table 4) (7,16,17) (see Steel). These alloy steels, however, lose their hardness rapidly when heated above 150—340°C (see Fig. 3). Furthermore, because of the low volume fraction of hard, refractory carbide phase present in these alloys, their abrasion resistance is limited. Hence, low—medium alloy steels are used in relatively inexpensive tools for certain low speed cutting applications where the heat generated is not high enough to reduce their hardness significandy. 

More Mo is consumed annually than any other refractory metal. The major use for Mo is as an alloying element in alloy steels, tool steels, stainless steels, Ni-based and Co-based superalloys. In these materials, it increases the hardenability, toughness, high-temperature strength, and corrosion resistance. Molybdenum is important in the missile industry, where it is used for high-temperature structural parts, such as nozzles, leading edges of control surfaces, support vanes, struts, reentry cones, radiation shields and heat sinks. In the electrical and electronic industries. Mo is... 

High alumina cement is used in mortars for refractory brick walls and in refractory concretes when mixed with special aggregate, like corundum or fire clays. At present the application of high alumina cement is, in general, very restrained it is limited to non-structural elements and to refractory structures where there is no risk of high humidity. Other applications are in repair where rapid hardening is required (Barnes and Bensted 2001). 

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