CAST IRON AND METHOD FOR HEAT TREATMENT OF ITS CASTINGS Russian patent published in 2007 - IPC C22C37/04 C21D5/00 

FIELD: ferrous metallurgy, namely production of high-strength cast irons with spheroidal graphite, possibly production of cast products having high strength, ductility and impact viscosity.

SUBSTANCE: cast iron contains, mass%: carbon, 3.28 - 4.03; silicon, 2.34 - 3.62; manganese, 0.22 - 0.53; copper, 1.16 - 2.34; molybdenum, 0.21 - 0.52; magnesium, 0.02 - 0.05; barium, 0.03 - 0.08; rare-earth metal, 0.02 - 0.06; iron and inevitable impurities, the balance. Cast pieces of such cast iron are subjected to heat treatment comprising stepped austenization at heating up to 820 - 830°C; soaking for 0.5 h and further heating till 870 - 900°C and soaking for 0.5 - 1.5 h. Then castings are cooled till temperature less than 500°C. Cooling rate is controlled depending upon wall thickness of cast piece. If wall thickness is less than 20 mm, cast product is cooled in air; if wall thickness is 25 -40 mm cast product is cooled in water for 4 - 5 s; if wall thickness exceeds 40 mm cast product is cooled in water for 6 - 10 s. Then casting are subjected to thermocycling in temperature range 270 - 390°C for 1.5 -3 h and to air cooling.

EFFECT: improved stable mechanical properties of castings with different wall thickness.

2 cl, 2 dwg