D_TEXTBLOCK_TEXT Gray iron contains <HL Topic=Graphite.sub>GRAPHITE</HL>, 2-4% carbon, and 1-3% <HL Topic=Silicon.sub>SILICON</HL>. It is noted for its ability to lessen vibrations, and to resist heat shock. The material can be strengthened and toughened by heat treatment. It can be used in vehicle equipment, including engine blocks, gearboxes, brake drums, and camshafts.