METHOD FOR OBTAINING BAINITIC CAST IRON AT HEAT TREATMENT Russian patent published in 2013 - IPC C21D5/00 C22C37/04 C21D1/20 C21D1/60 

FIELD: metallurgy.

SUBSTANCE: in order to obtain disperse structure of castings, which consists of bainite and spherical graphite, as well as complex of high and stable mechanical properties: strength, ductility and impact strength, a cast-iron casting containing the following components, wt %: C 3.4-4.0, Si 2.0-2.6, Mn 0.2-0.6, P ≤0.03, S ≤0.02, Cr≤0.05,Cu ≤0.4, Ni≤1.5, Mg 0.04-0.06, Ti≤0.04, Mo ≤0.3, Al ≤0.04 is subject to heat treatment that involves heating up to 900°C with exposure of 1.5-2 h and further cooling in polymer liquid to 300-500°C depending on required hardness, which provides obtainment of bainitic structure. Cooling rate is adjusted depending on cast wall thickness: at wall thickness of up to 15-20 mm, cast is cooled during 5-20 seconds, and at wall thickness of more than 20 mm, cast is cooled during 20 seconds to several minutes. After parts are cooled in polymer liquid, they are transferred to a furnace for further drawing; and by avoiding cooling-down of parts, the furnace exposure is performed during 1.5-3 h at the interval of 300-500°C.

EFFECT: improving strength.

2 cl, 2 tbl, 3 dwg