Protective coating for metal surfaces during heat-treatment - esp. for selective carburising and nitriding in salt baths

摘要

Refractory materials in the form of foils, woven fabric and/or fibres are used on those regions which are not to be case-hardened, and the pref. material is graphite. Although many materials have been developed as masks to prevent case-hardening in the gaseous phase, none has proved satisfactory in salt baths, whereas this invention provides materials which are satisfactory. In addn. to graphite, boron nitride, silicon carbide and zirconium dioxide can be used; these materials also have an insulating effect so that the cooling rate of the coated regions is altered.