Alloy steels hardened, abrasive wear

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. 

P-BN tools work satisfactorily in hardened steel up to contact temperatures of 1000°C, since there is no chemical reaction between boron nitride and iron. This, however, also depends on the binding phase of the polycrystalline materials and can lead to adhesive wear [24, 25]. In hard steel, the main wear mechanism on the tool is abrasion by hard alloy carbide particles [26]. In the case of Co-based super alloy (Vitallium), the results on hard-BN tool wear are somewhat incongruous [27, 28], while Inconel 718 can be machined under proper selection of the cutting conditions [29]. Apparently, austenitic steels containing a high percentage of Co are difficult to cut by hard-BN tools, due to the formation of cobalt nitrides which leads to high tool wear [8]. 

Prevention of abrasive wear is possible through proper material selection and the use of surface engineering treatments. A number of material families have demonstrated good resistance to abrasive wear. They are typically hard materials that resist scratching, and include ceramics, carbide materials, alloyed white cast irons containing hard chromium carbides (see Fig. 8), and hardened alloy steels. 

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