SHEET STEEL FOR A THICK-STRENGTHEN HIGH-STRENGTHENING PIPE THREADING WITH EXCELLENT RESISTANCE TO ACID ENVIRONMENT, RESISTANCE TO SMOKE AND LOW-TEMPERATURE VISCOSITY AND ALSO A MAIN PIPE Russian patent published in 2017 - IPC C22C38/14 

FIELD: metallurgical engineering.

SUBSTANCE: steel contains, wt %: C: 0.04 to 0.08, Mn: 1.2 to 2.0, Nb: 0.005 to 0.05, Ti: 0.005 to 0.03, Ca: 0.0005 to 0.0050, N: 0.001 to 0.008, Si: 0.5 or less, Al: 0.05 or less, P: 0.03 or less, S: 0.005 or less, O: 0.005 or less, Fe and unavoidable impurities - The rest. The microstructure of a part of the outer zone of the sheet located at a distance from 0.9 mm to 1.1 mm from the surface in the thickness direction of the sheet contains deformed ferrite: 5% or more and S_fe1% or less, a mixture of martensite and austenite: 8% or less, the remaining polygonal ferrite and/or bainite, where S_fe1% is determined by the expression: S_fe1=0.6552×T_H-4.7826, where T_H: thickness of thick steel. The microstructure of the central part of the sheet, located at a distance of 1 mm from the centre of the sheet thickness towards the surface of the plate steel, contains a deformed ferrite: 5% or less, a mixture of martensite and austenite: 5% or less, the remaining needle ferrite and/or bainite. Said parts of the outer zone and the central part have an effective grain size, the average value of which, measured by electron diffraction backscattering, is 20 mcm or less.

EFFECT: high resistance to acidic medium, resistance to crushing and low-temperature viscosity.

7 cl, 2 dwg, 5 tbl