The core components (gears, shafts) of heavy machinery (such as excavators and cranes) are made of alloy structural steel (40Cr, 20CrMnTi), which has been significantly improved in hardness and wear resistance after heat treatment such as quenching and tempering and carburizing; while the bed of general machine tools is made of gray cast iron (HT250), which has both rigidity and vibration damping to ensure machining accuracy.