Laser Hardening of Austempered Ductile Cast Iron (ADI)*

Austempered ductile cast iron (ADI) has emerged as a major engineering material in recent years. In addition to high strength and relatively light weight (compared to steel), it has high ductility, good wear resistance and good damping capacity. It has many potential applications such as automotive components (e.g. crank shafts and gear boxes) as well as aircraft components (landing gears).

In many structural applications, (e.g. aircraft landing gear) it is often required that the material be hardened at the surface while the interior of the material must remain soft or ductile. The higher hardness at the surface layer imparts excellent wear resistance while the soft inner core provides higher toughness and fracture resistance. The conventional methods of surface hardening such as carburizing and nitriding or shot peening have several limitations, e.g. retained austenite, massive carbide formations and insufficient case depth. In recent years, there has been significant interest in use of laser in surface treating of materials. Surface hardening by means of laser is a very useful technique because of self quenching and minimum of distortion. Laser hardening can also improve significantly the surface properties such as wear and fatigue resistance.