METHOD FOR PRODUCTION OF THICK-ROLLED STEEL WITH INCREASED DEFORMATION CAPACITY (VERSIONS) Russian patent published in 2019 - IPC C21D8/02 C22C38/00 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, particularly, to production of hot-rolled stock with thickness of 7 to 50 mm. To provide high deformation capacity of rolled stock of strength class K60-K65 with preservation of its high impact viscosity and cold resistance, austenitization of workpiece from steel containing, wt%: C 0.04÷0.09; Mn 1.4÷2.2; Si 0.10÷0.50; Al 0.02÷0.06; Ti 0.003÷0.035; Nb 0.01÷0.08; V not more than 0.10; Mo not more than 0.50; Ni not more than 0.60; Cu not more than 0.30; Cr not more than 0.50; N 0.002÷0.010; S not more than 0.005; P 0.003÷0.015; Fe and unavoidable impurities – balance, having fracture resistance coefficient Pfr ≤ 0.24, roughing and finish hot rolling of billet with finish rolling end temperature T_RE=(960-310⋅C-80^.Mn-20^.Cu-15⋅Cr-55⋅Ni-80⋅Mo)±40 °C. According to the first version of the method, after finishing rolling, multistage cooling of the sheet is performed, at the first stage the sheet is cooled with water at rate of 15÷50 °C/s to temperature T₁ in range from (595-372⋅C-62⋅Mn-27⋅Ni-44⋅Cr-27⋅Mo) to (830-270⋅C-90⋅Mn-37⋅Ni-70⋅Cr-83⋅Mo) °C, at second stage – in air for 20÷60 s, then with water at rate of 15÷50 °C/s to temperature of not more than T₂=(410-37.7⋅Mn-18.9⋅Ni-37.7⋅Cr-27⋅Mo) °C and finally cooled in air or in pile. According to the second version of the method, after finishing rolling, the sheet is cooled at the first stage with water at a rate of V_R≥(17.8+50.8⋅C-8⋅Mn+0.7⋅Cr-16.8⋅Ni+7⋅Cu-22.8⋅Mo-4.9⋅Nb) °C/s, which corresponds to range 2÷13 °C/s to temperature of bainitic transformation T_BT=(830-270⋅C-90^.Mn-37⋅Ni-70⋅Cr-83⋅Mo)±20 °C, then – with water at rate of 6÷12 °C/s to temperature of not more than T₂ (°C) and finally – on air or in pile.

EFFECT: higher deformation capacity of rolled stock.

4 cl, 2 dwg, 3 tbl