METHOD OF MAKING LOW-CARBON COLD-ROLLED THIN-SHEET STEEL Russian patent published in 2013 - IPC C21D8/04 C21D9/48 C22C38/04 

FIELD: metallurgy.

SUBSTANCE: method comprises cold coil rolling, annealing and tempering. Cold-rolled steel contains 0.0.6-0.09 wt % of carbon, 0.40-0.55 wt % of manganese, and not over 0.05 wt % of silicon. Annealing is carried out in bell furnaces with protective atmosphere consisting of 93%-N₂ and 7%-H₂ with heating to temperature of final curing exceeding chilling point of heated steel and interim holding at 580°C and 650°C as shown by bench thermocouple. Total duration of heating makes 36-64 h depending upon strip width and weight of bottom coil in load. Tempering is performed at rolls with surface roughness Ra 4.5-6.0 mcm and relative reduction ε_t 0.9-1.5%. DC01 cold-rolled steel is produced that features thickness of 0.60-1.20 mm, yield point σ_y of 220-260 N/mm², point of maximum load σ_t of 290-360 N/mm², elongation δ₄, smaller than 32%, and surface roughness Ra of 1.4-2.2 mcm.

EFFECT: better steel characteristics.

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