Influence of alloying by rare-earth metals on the mechanical properties of 17g1s pipe steel
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INFLUENCE OF ALLOYING BY RARE-EARTH METALS ON THE MECHANICAL PROPERTIES OF 17G1S PIPE STEEL D. Yu. Petryna,1 О. L. Kozak,1 B. R. Shulyar,1 Yu. D. Petryna,1,2 and М. I. Hredil’3
UDC 539.622:620
The positive influence of microadmixtures of rare-earth metals on the strength, plasticity, impact toughness, and cyclic crack-growth resistance of 17G1S pipe steel is discovered. The decomposition of the impact toughness into the work of crack initiation ai and the work of crack propagation a p made it possible to discover the following specific features in the temperature dependences of a p : at elevated testing temperatures guaranteeing the ductile fracture of steel, the positive effect of alloying by REM is preserved. At the same time, at lowered temperatures of brittle fracture, this effect becomes negative and the work a p decreases. Distilled water somewhat decreases the cyclic crack-growth resistance of steel and the positive effect caused by the REM admixtures manifests itself only in the increase in the cyclic fracture toughness of steel. Keywords: pipe steel, alloying by microadmixtures of rare-earth metals, strength, plasticity, impact toughness, cyclic crack-growth resistance.
The practice of long-term operation of the main pipelines demonstrates that their serviceability strongly depends on the optimal combination of the characteristics of strength, brittle fracture resistance, and corrosion resistance of steels [1, 2]. As one of the methods used to improve the quality of the metal, its mechanical and corrosion properties, one can mention the microalloying of pipe steels and welds with modifying elements and, in particular, with rare-earth and alkaline-earth metals [3–7]. The efficiency of the influence of these microadmixtures is connected with the changes in the morphology, distribution, and the range of particle sizes of the structural components of the metal, the composition of the grain boundaries, and their state. It was shown that the high resistance to general and pitting corrosion and to sulfide stress-corrosion fracture of low-alloy steels and welded joints can be attained by the lean modification of these materials with microadmixtures responsible for deep structural and phase transformations decelerating the corrosion properties. The following optimal contents of modifiers (in %) were proposed and justified for low-carbon steel in [8]: 0.01–0.03 cerium, 0.01–0.025 yttrium, 0.007–0.015 barium, 0.001–0.0025 calcium, and 0.02–0.04 zirconium. For the welds, the corresponding contents are as follows: 0.01–0.02 cerium, 0.015–0.022 yttrium, 0.0014–0.0025 barium, 0.0012–0.002 calcium, and 0.031–0.044 zirconium. However, this promising direction in the formation of a complex of mechanical properties of pipe steels requires subsequent investigation. In what follows, we study the influence of admixtures of rare-earth metals (REM) on the plasticity of 17G1S steel and its brittle-fracture resistance. 1
National Technical University of Oil and Gas, Ivano-Frankivs’k, Ukraine. Corresponding author: e-mail: mtf@nun
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