在各种机器中的零件,有许多经常活动摩擦的部份,表面需要坚硬耐磨,而内部则需柔靸,以防在运动时折断或开裂。此种零件,必须经表面硬化(Case hardening)之处理,使达到所要求之性质。表面硬化的方法很多,最常用者为渗碳(Carburizing)。其法为将含碳低之软钢(含碳<0.2％)经渗碳作用,使钢件之表面含碳量增高达「似共晶体」(Eutectoid,C=0.8％)「或过似共晶体」(Hyper-eutectoid C>0.8％)之成 Parts in a variety of machines have many parts that are often active and frictional, the surfaces need to be hard and wear resistant, and the inside to be supple to prevent breakage or cracking during exercise. Such parts must be case hardened to achieve the desired properties. There are many ways to harden the surface, the most common being Carburizing. Its method is to carbonaceous low carbon steel (carbon content <0.2%) by carburizing the surface of the steel carbon content increased up to “eutectoid” (E = 0.8%) “or similar Crystal ”(Hyper-eutectoid C> 0.8%)