STEEL PLATES FOR CONSTRUCTION PIPES OR TUBES, STEEL PLATES FOR CONSTRUCTION PIPES OR TUBES MANUFACTURING METHOD, AND CONSTRUCTION PIPES OR TUBES

摘要

FIELD: metallurgy.;SUBSTANCE: invention relates to the field of metallurgy, in particular to the high-strength steel plates, having a thickness of 38 mm or more, for the structural pipes manufacturing. Steel has a chemical composition containing in wt.%: C: from 0.030 to 0.100; Si: from 0.01 to 0.50; Mn: from 1.50 to 2.50; Al: 0.080 and less; Mo: from 0.05 to 0.50; Ti: from 0.005 to 0.025; Nb: from 0.005 to 0.080; N: from 0.001 to 0.010; O: 0.0050 and less, P: 0.010 and less, S: 0.0010 and less, Fe and inevitable impurities – the rest. Chemical composition is characterized by carbon equivalent C_eq, constituting 0.42 and more. Microstructure in the middle of the steel plate thickness is the ferrite and bainite two-phase microstructure, with the ferrite surface fraction being less than 50 %. Microstructure contains ferritic grains having the grain size of 15 mcm or less, on the surface area making 80 % or more relative to the ferrite total surface area.;EFFECT: steel has the high strength of 620–825 MPa and excellent Charpy vE_-20°C toughness properties at -20 °C in the middle of the thickness, making 100 J or more.;7 cl, 3 tbl