METHOD OF MAKING LOW-ALLOY COLD-ROLLED TUBE STEEL Russian patent published in 2013 - IPC C21D8/04 C21D9/663 C21D1/26 B21B1/28 

FIELD: metallurgy.

SUBSTANCE: in compliance with first version, proposed method comprises cold rolling, steel coil annealing in bell-type furnace with protective atmosphere consisting of 93% N₂ and 7% H₂ to 670°C, curing at said temperature D₆₇₀, its decrease to final curing temperature of 650°C and curing at said temperature D₆₅₀ with duration of curing defined by formulae: D₆₇₀ = 0.5D_tot, D₆₅₀ = 0.5D_tot, where D_tot is total duration of annealing. Note here that tempering is performed with 2.0-2.5%-reduction. In compliance with second version, proposed method comprises cold rolling, steel coil annealing in bell-type furnace with protective atmosphere consisting of 100% N₂ to final curing temperature of 670°C and holding thereat for time including hours from heating start to moment when difference in temperature by stand bench thermocouple and that of core makes 30°C. Note here that tempering is performed with 2.0-2.5%-reduction.

EFFECT: higher quality of cold-rolled tube 09"Г"2C-grade 2,5mm-thick steel.

2 cl, 1 tbl