New generation of high-strength tube steels with a ferrite-bainite structure

Effect of the structure and stress state on the magnetic properties of metal in different zones of welded pipes of large diameter

“…A finely disperse bainitic (ferritic-bainitic) structure is characteristic of steels of strength classes X80-X100 [1], which makes it possible to reach high strength and good cold resistance even for rolled sheets of large thicknesses. The formation of a ferritic-bai nitic structure is based on the following aspects [2,12]: a lowered carbon content (0.04-0.08%); the intro duction of additions of Mn, Mo, Ni, Cr, Cu, which decrease the temperature of the polymorphic γ → α transformation and which suppress the pearlitic trans formation; a complex microalloying with Nb, Ti, and V; the decrease in the content of harmful impurities (≤0.002% S; ≤0.010% of P); the use of the accelerated cooling after rolling under controlled conditions. No.…”

“…The contempo rary practice imposes more stringent requirements onto the main pipelines, which are connected with a need to increase their pipe capacity and reduce their metal content, simultaneously with the need to increase the operating pressure in the pipelines (for the gas pipelines from 75 to 100-200 atm and from 55 to 75-100 atm for oil pipelines) [1]. At the same time, a decrease in the thickness of the pipe walls is desirable, since, in the case of the rolled sheet used to produce thinner pipes, a higher level of properties can be obtained more simply [2,3]. In connection with this, a promising direction appears to be the transition to using pipes made of steels of higher strength classes (e.g., X80 and higher) [1].…”

Laboratory criteria of crack resistance of high-strength steels for gas main pipelines

“…However, the magnitude of σ y (especially for the pipes from the manufacturer A) and σ y /σ u lie at the upper limit of the required range and sometimes even exceed it. It is known [1,5] that the structure of pipe steels of the strength class under consideration consists of a ferrite matrix (~80%) and regions containing low temperature products of the decomposition of an overcooled austenite (and ~20% bainite (martensite)). The size of ferrite grains does not exceed ~5-10 μm, which leads to an increase in the stress for the start of the plastic flow σ y and, consequently, leads to a very high σ y /σ u ratio.…”

“…The operative efficiency of high strength low car bon microalloy steels for welded pipes of high pres sure gas mains is stipulated by a complex of their ser vice characteristics, in particular, by the combination of a high strength, plasticity, and ductility [1,2]. Plate steel for these pipes up to 1420 mm in diameter is pro duced on industrial scale by the controlled rolling (CR) technique with a subsequent accelerated cooling [3][4][5].…”

Structure and mechanical properties of the welded joints of large-diameter pipes

“…The efficiency of applying high strength low carbon microalloyed steels as the materials of welded pipes for high pressure main pipelines is provided by a set of the operating characteristics of a metal, in particular, a combination of a high strength, plasticity, and fracture toughness [1,2]. The strength properties of the welded joint material determine the reliability of operating main pipelines, and the aim of all manufacturers of welded pipes is to make the structures and mechanical properties of the welded joint material and the base tube material maximally close to each other.…”