Study of the Resistance of the Near-Weld Section of the Heat-Affected Zone to Hydrogen Embrittlement

Abstract

Hydrogen embrittlement is one of the most common reasons for the premature failure of welded structures used in media that contain hydrogen. Studies have found that a high susceptibility to hydrogen embrittlement (HE) is shown by the metal of the near-weld section of the heat-affected zone ( HAZ NWS) [1, 2]. In light of this, we evaluated the effect of possibly controlling the resistance of HAZ NWS metal to embrittlement by changing the phase components and dispersity of the structure. We used normalized low-alloy steel 09G2S. Its chemical composition (%): 0.13 C; 0.74 Si; 1.61 Mn; 0.012 P; 0.11 Cr; 0.069 Ni; 0.17 Cu; 0.005 V; 0.03 Al; 0.005 Ti; 0.01 Mo. The mechanical properties: σ Y = 570 MPa; σ B = 650 MPa; δ = 21%. An HAZ NWS was simulated by using a high-frequency-current unit designed for use in a tube-rolling shop [3]. The maximum heating temperature was 1350°C and the rate of cooling w 8‐5 of the given section was varied from 3 to 30°C in order form different types of structures (Table 1) on the NWS ‐ from a coarse ferrite-pearlite structure to a bainite-marten site structure. The resistance of the different types of HAZ NWS structures to hydrogen embrittlement was evaluated on the basis of the amount of ductility lost during tests in which the method described in [4, 5] was used to subject previously hydrogenated and unhydrogenated specimens to delayed tension. We also performed such tests on specimens of the base metal ‐ steel 09G2S. Half of the flat 3-mm-thick specimens prepared in accordance with GOST 1497‐87 were hydrogenated electrolytically in a 0.1 N solution of sulfuric acid with a thiourea addition of 1.5 g/liter. Cathodic current density was 10 mA/cm 2 . After being hydrogenated, the specimens were subjected to delayed tension at room temperature in accordance with GOST 1497‐87. The testing was done on universal machine FPz-100/1. Active clamp speed was 0.3 mm/min and the load was 20 kN. The test results were compared with data obtained for similar specimens in the initial state. The degree of hydrogen embrittlement was evaluated on the basis of the decrease in the reduction of area ψ and elongation δ 5 , which were determined from the formulas