CALIBRATED ROUND MERCHANT SHAPES IN BARS Russian patent published in 2006 - IPC C21D8/06 C22C38/44 

FIELD: metallurgy; production of merchant shapes from medium-carbon steel at high machinability for manufacture of shock absorber rods for automobiles.

SUBSTANCE: proposed method enhances machinability at optimum ratio of strength, ductility and plasticity, minimum level of anisotropy at simultaneous improved characteristics of hardenability to level of through hardenability of rods to 30 mm. Proposed bars are made from medium-carbon steels containing carbon and alloying elements and possessing preset parameters of metallurgical quality, structure, mechanical properties, hardenability and machinability; medium-carbon steel contains the following components, mass-%: carbon, 0.42-0.50; manganese, 0.50-0.80; silicon, 0.17-0.37; sulfur, 0.020-0.040; phosphorus, 0.001-0.030; aluminum, 0.03-0.05; calcium, 0.001-0.010; oxygen, 0.001-0.015; chromium, no more than 0.25; nickel, no more than 0.025; copper, no more than 0.25; molybdenum, no more than 0.10; arsenic, no more than0.08; nitrogen, no more than 0.015; the remainder being iron and unavoidable admixtures. Ratio of oxygen and calcium , as well as calcium and sulfur is determined by the following dependances: oxygen/calcium= 1-4.5 and calcium/sulfur≥0.065. Nonmetallic inclusions of sulfides have double-layer structure: sulfide with oxide envelope; curvature of bars does not exceed 1.0 mm/m; rolled bars have plastic ferrite-pearlite structure at actual size of grain of 5-8; diameter of bars ranges from 10 to 30 mm; decarbonized layer is no more than 1.5% of diameter; hardness of billet is 229-255; rupture strength no less than 640 Mpa; relative elongation no less than 6% and relative reduction no less than 30%.

EFFECT: improved machinability characteristics at optimum ductility and strength; improved hardenability characteristics.

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