HIGH-STRENGTH SHEET STEEL HAVING A LOW RELATIONSHIP OF THE YIELD LIMIT TO THE STRENGTH TEMPERATURE, EXCELLENT FROM THE POINT OF VIEW OF RESISTANCE TO POST-STRAIN AGING, A METHOD OF ITS BREAKDOWN FOR THEIR BREAKDOWN

摘要

1. High-strength sheet steel with a low ratio of yield strength to tensile strength, having a chemical composition in wt. % containing C: 0.03% or more and 0.08% or less, Si: 0.01% or more and 1.0% or less, Mn: 1.2% or more and 3.0% or less , P: 0.015% or less, S: 0.005% or less, Al: 0.08% or less, Nb: 0.005% or more and 0.07% or less, Ti: 0.005% or more and 0.025% or less, N: 0.010% or less, O: 0.005% or less, Fe and unavoidable impurities: the rest, and a metallographic structure, which is a two-phase structure consisting of a phase of bainite and island martensite, with the proportion of the region of island martensite being 3% or more and 15 % or less, in which the equivalent diameter of the circle of island martens this is 3.0 μm or less and the rest of the metallographic structure is represented by a bainite phase in which a change in Vickers hardness in the direction of the thickness ΔHV30 or less, a change in Vickers hardness in the direction of the width ΔHV30 or less, the maximum Vickers hardness in the surface areas of sheet steel HV230 or less, the ratio of yield strength to tensile strength of 85% or less and elongation of 22% or more in tensile tests over full thickness using a test specimen having the shape in accordance with about standards GOST.2. High-strength sheet steel with a low ratio of yield strength to tensile strength according to claim 1, which has a chemical composition additionally containing one or more elements, in wt. % selected from Cu: 0.5% or less, Ni: 1% or less, Cr: 0.5% or less, Mo: 0.5% or less, V: 0.1% or less, Ca: 0 0005% or more and 0.003% or less; and B: 0.005% or less. 3. A method for the production of high-strength sheet steel with a low ratio of yield strength to tensile strength, which includes heating steel having a chemical composition, is specified