METHOD OF PRODUCTION OF ROLLED STOCK FOR PIPES OF MAIN PIPELINES WITH SIMULTANEOUS PROVISION OF UNIFORM ELONGATION AND COLD RESISTANCE Russian patent published in 2019 - IPC C21D8/02 C21D1/02 

FIELD: metallurgy.

SUBSTANCE: after melting steel is continuously cast into slabs, heated to rolling temperature, controlled hot rolling is carried out with accelerated step-by-step cooling and final slow cooling of sheets in stack. At that, hot rolling is finished in austenite area at temperature T_kp±50 °C, determined depending on chemical composition of steel by formula: T_kp=880-400[C]-70[Mn]+25[Si]-35[Ni]-25[Cr]-20[Cu]±30 °C, accelerated cooling of sheets with water is performed from temperature T_kp±50 °C austenite region at rate of 10÷50 deg/s to temperature Bs±50 °C, determined by formula Bs=695-320[C]-15[Cr+Cu+Ni]-25[Mn], after stopping water supply to roll, cooling is performed in air at rate of 0.1÷3 °C/s for extraction α-phase and enrichment with carbon of unconverted austenite over time t±10 s, determined proceeding from equation t=94[Nb]+22[V]+40[Mo]+10[Cr]+5[Mn]-18[Si]-6[Ni]-3[Cu]-30[C], and final slow cooling of sheets in piles is carried out at rate of 0.01÷0.001 deg/s in air up to 100 °C.

EFFECT: method is proposed for production of rolled sheet with thickness of 12–48 mm for production of pipes of main pipelines with diameter of up to 1,420 mm with provision of a portion of viscous components making fractures in testing by falling load of not less than 85 % at test temperature of -20 °C, impact viscosity (KCV) at test temperature of -40 °C is not less than 250 J/cm², high values of uniform elongation at achievement of strength properties in pipes from this rolled stock at the level of K60-K80 (X70-X100).

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