METHOD OF PRODUCTION OF ROLLED PLATES WITH STRENGTH CLASS K65, X80, L555 TO MANUFACTURE ARC WELDED PIPES OF MAIN PIPELINES Russian patent published in 2015 - IPC C21D8/02 B21B1/24 C22C38/50 

FIELD: metallurgy.

SUBSTANCE: method of production of rolled plates to manufacture arc welded pipes of main pipelines includes production of steel containing in wt %: C - 0.03-0.08, Si - 0.12-0.35, Mn - 1.65-2.10, Cr - 0.01-0.30, Ni - 0.01-0.40, Cu - 0.01-0.30, Mo - 0.01-0.30, Al - 0.02-0.05, Nb - 0.03-0.09, V - 0.001-0.10, Ti - 0.010-0.035, S - 0.0005-0.003, P - 0.002-0.015, N - 0.001-0.008, iron and inevitable admixtures - rest, at that 0.08<(Mn+Cr+Cu)/20+Si/30+Ni/60+Mo/15+V/10<0.16, -2.7<lg[Nb][C+8N]<-2 and Cr+Ni+Cu+Mo<0.8%. Continuously cast billet is subjected to austenisation at temperature at least by 100°C below temperature Ts (TiN) of dissolution of titanium nitrides according to ratio Ts(TiN)=14400/(5.0-lg[Ti][N]), where Ti and N are content of titanium and nitrogen in steel, wt %, but not below temperature Ts(Nb(C,N)) of dissolution niobium carbonitrides according to ratio: Ts(Nb(C,N))=(10100-27[Mn]+200[Si])/(4.85-lg[Nb][C+8N]), where Mn, Si, Nb, C, N are content of manganese, silicon, niobium, carbon and nitrogen in steel. Time t for holding in holding zone is selected according to equation: $$t=10\frac{1314-T}{77}\pm \mathrm{40,}$$ where t is holding time, min, T is selected holding temperature, °C. Upon preliminary deformation during last four passes the relative reductions increase as per law: ε_i=(1.05…1.35)ε_i-1±2, (%), where ε_i and ε_i-1 are reductions in previous and next passes. Temperature T_cs(°C) of accelerated cooling start is: T_cs=977-54Mn-102Ni-20Mo-866C-2.2V_cool ±30, where V_cool is roll cooling rate from rolling completion to start of accelerated cooling, °C/s, and temperature range Δ(°C) between temperature T_sc of rolling completion and temperature T_cs of accelerated cooling start is determined as follows: Δ=-2.5H+92±20, where H is plate thickness, mm.

EFFECT: meeting of the requirements for strength, plastic and tough properties characteristic for the rolled plates with strength K65, X80, L555.

4 cl, 3 tbl