STEEL STRIP WITH LOW RATIO OF YIELD STRENGTH TO ULTIMATE STRENGTH AND HIGH IMPACT STRENGTH AND METHOD FOR PRODUCTION THEREOF Russian patent published in 2016 - IPC C21D8/02 C22C38/60 

FIELD: metallurgy.

SUBSTANCE: invention relates to hot-rolled steel strip with high impact strength and method of its production. Steel strip for production of transport pipelines with low ratio of yield strength to ultimate strength and high impact strength has the following chemical composition, wt%: C 0.05-0.08, Si 0.15-0.30, Mn 1.55-1.85, Al 0.015-0.04, Nb 0.015-0.025, Ti 0.01-0.02, Cr 0.20-0.40, Mo 0.18-0.30, N ≤ 0.006, O ≤ 0.004, Ca 0.0015-0.0050, Ni ≤ 0.40, indigenous inclusions of P ≤ 0.015, S ≤ 0.005, wherein ratio of Ca/S ≥ 1.5, rest is Fe. Method for production of steel strip includes vacuum degassing of steel continuous casting or injection molding of molten steel, wherein with continuous casting slab is obtained, and with casting under pressure is bar. Heating of slab or bar at temperature of 1150-1220 °C, multipass rolling in area of austenite recrystallization and absence of recrystallization area, at that total reduction factor is ≥ 80 %, and rolling end temperature is ≥ 850 °C. Water cooling of rolling steel strip at rate of 15-50 °C/s to temperature within range of Bainite Bs temperature -60 °C up to Bainite Bs temperature of -100 °C. Then cooling by air for 5-60 s , fast heating of cooled steel strip in induction heating furnace at line at rate of 1-10 °C/s to Bainite Bs temperature of +20 °C. Tempering for 40-60 s with subsequent cooling air outside furnace, wherein starting point of Bainite Bs has following value: BS=830-270C-90Mn-37Ni-70Cr-83Mo, where C, Mn, Ni, Cr, Mo correspond to content of these elements in steel strip in wt%.

EFFECT: technical result consists in production of low yield strength to ultimate strength and high impact strength of steel strip.

18 cl, 3 tbl, 2 dwg