Selective surface-hardened alloy steels

Choose material couples that are resistant to interaction in sliding (metal-to-metal wear resistance). Hardfacing alloys such as cobalt-base and nickel-chromium-boron alloys have been used for many years for applications involving metal-to-metal wear. Other surfaceengineering options include through-hardened tool steels, diffusion (case)-hardened surfaces, selective surface-hardened alloy steels, and some platings. 

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. 

Water-hardening tool steels containing 0.6 wt.% to 1.4 wt.% C are widely used because they combine low cost, a good toughness, and excellent machinability. They are available as shallow, medium, or deep hardening, so the specific alloy selected depends on part cross section and required surface and core hardnesses. Common applications include drills, shear knives, chisels, hammers, and forging dies. 

If milling techniques are employed, the steel must be easily machinable and, if a harder surface is necessary, it must be heat treated after cutting the pockets. There is only a limited selection of wear-resistant alloys that can be forged or cast into rolls or segments, machined, and afterwards heat treated (hardened) without major distortion. 

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