OBRABOTKAMETALLOV Vol. 25 No. 4 2023 technology This review is devoted to the analysis of works related to the evaluation of the influence of the microstructure of the weld on the impact strength, as an indicator of the sensitivity of hot-rolled pipeline steels to brittle fracture. Steels for the pipes production The influence of the development of production technology and micro-alloying of pipeline steel on the strength is shown in fig. 1. Low-carbon alloy steels with ferrite-pearlite structure are widely used in pipe production [27]. Fig. 1. Effect of development of production technology and microalloying of pipeline steel on strength Increasing strength is a constant goal of the development of metallurgical alloys; currently more attention is paid to improving other important characteristics, such as toughness and weldability, each of which is negatively affected by the carbon content in steel. High-strength low-alloy (HSLA) or micro-alloyed (MA) steels, as it was later called [21–25], were already used at the beginning of the 20th century [23, 24]. Lowalloy steels, a much earlier defined class of steels than MA steels, are generally considered to contain less than 3.5 wt. % of all alloying elements and include Cr (0.5–2.5 %), Mo ≤ 3 % and V ≈ 1 %. High-strength low-alloy (HSLA) steels and the paradigm of microalloyed (MA) steels suggest that carbon may not be the best alloying element for making good steel [21–25]. In this context, HSLA steels show lower carbon content, which improves weldability and formability, but lower mechanical properties resulting from lower C content, which can be improved by the addition of alloying elements such as Nb, Mo and Ti, and an appropriate thermal and mechanical treatment. Each of these elements affects different mechanisms. On the one hand, many studies agree that Nb is capable of causing the accumulation of deformation in austenite before transformation, providing significant microstructure refining [1–3, 26–28]. Mo, in addition to the effect of solute resistance on the static kinetics of recrystallization, enhances the formation of complex non-polygonal transformation products [27, 28]. These strategies pursue finer final microstructures, which will result in a better combination of strength and toughness. On the other hand, Ti and Mo microalloyed steels have an interesting combination of high strength and good formability due to the wide dispersion of nanometer-sized titanium carbides in a thin matrix [21–23].
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