METHOD OF PRODUCING COLD-ROLLED STRIPS OF EXTRA LOW CARBON STEEL Russian patent published in 2003 - IPC

FIELD: manufacture of rolled products. SUBSTANCE: method involves melting steel comprising, wt%: carbon 0.006-0.10; manganese 0.01-0.15; phosphor equal to or exceeding 0.07; nitrogen 0.0025; aluminum equal to or exceeding 0.04; niobium 0.031-0.06; sulfur equal to or exceeding 0.008; iron and inevitable contaminants the balance; pouring and heating slabs to temperature of 1,150-1,200 C; providing hot rolling with temperature at the end of hot rolling process being equal to 910-920 C; winding at temperature of 740-750 C; providing cold rolling with total squeezing of at least 70%; heating resultant cold-rolled strip to annealing temperature at rate of 10-20 C/s; providing continuous annealing, with annealing temperature being determined depending on Nb/C ratio from formulas: at C, at C, where Nb and C is niobium and carbon content in steel, wt%; holding at annealing temperature for 50-60 s and cooling strip at cooling rate of 15-25 C/s to temperature of 340-360 C. Method may be used for producing extra low carbon steel strips for automobile construction industry, possessing reinforcing effect of at least 40 MPa upon drying of paint and varnish coating. EFFECT: improved quality of cold rolled steel strips by stabilized complex of mechanical properties. 2 ex