MEDIUM-ALLOY STEEL OF ENHANCED MACHINABILITY

FIELD: steels used for manufacture of heavily-loaded gears of automobile gear-boxes. ^ SUBSTANCE: proposed medium-alloy high machinability steel contains the following constituents, mass-%: carbon, 0.170.23; manganese, 0.65-0.95; silicon, 0.17-0.37; chromium, 0.35-0.65; nickel, 0.40-0.75; molybdenum, 0.15-0.25; sulfur, 0.020-0.040; phosphorus, 0.001-0.035; niobium, 0.005-0.02; vanadium, 0.005-0.08; calcium, 0.001-0.010; oxygen, 0.001-0.015; the remainder being iron and unavoidable admixtures. Oxygen-to-calcium ratio and calcium-to-sulfur ratio are determined as follows: oxygen/calcium =1-4.5 and calcium/sulfur >=0.065. Steel contains the following admixtures, mass-%: copper, no more than 0.25; arsenic, no more than 0.08; nitrogen, no more than 0.015; non-metallic inclusions have double-layer structure - sulfide with oxide envelope. ^ EFFECT: enhanced machinability of steel; full hardenability of rolled stock up to 50 mm in diameter. ^ 3 cl, 2 tbl, 1 ex