BAR MADE FROM MEDIUM-CARBON STEEL

FIELD: metallurgy; production of round merchant shapes made from medium-carbon steel of enhanced machinability for manufacture of automobile shock absorber rods. ^ SUBSTANCE: steel used for manufacture of round bars contains the following components, mass-%: carbon, 0.40-0.52; manganese, 0.40-0.95; silicon, 0.17-37; chromium, 0.01-0.25; sulfur,0.020-0.045; vanadium, 0.005-0.02; aluminum, 0.03-0.05; calcium, 0.001-0.010; nitrogen, 0.005-0.015; nickel, no more than 0.25%; copper, no more than 0.25; molybdenum, no more than 0.10; arsenic, no more than 0.08; phosphorus, no more than 0.030; the remainder being iron and unavoidable admixtures at calcium-to-sulfur ratio >=0.065. Nonmetallic inclusions of sulfides have double layer structure: sulfide with envelope. Curvature of bars does not exceed 0.5 mm/m. Shapes have laminated ferrito-pearlite structure at actual size of grain of 5-8 points; diameter of bars ranges from 10 to 300 mm; it has no decarbonized layer; hardness of billet is 229-255; rupture strength is no less than 660 Mpa; relative elongation is no less than 8% and relative reduction of area is no less than 35%. ^ EFFECT: improved ductility characteristics; low level of strain hardening at further heat treatment. ^ 1 ex