Tensile Properties of an Electrolytically Hydrogen Charged Duplex Stainless Steel Affected by Strain Rate

Abstract

To provide a reliable relationship between hydrogen embrittlement (HE) and the behavior of hydrogen in duplex stainless steels (DSSs), we evaluated the tensile behavior of electrolytically charged DSS (JIS SUS329J4L) specimens at various strain rates. Immediately after hydrogen charging, tensile tests were performed at strain rates ranging from 1.38 × 10 − 7 to 1.38 × 10 − 3 s − 1. Fracture surface was evaluated by scanning electron microscope (SEM) and the concentration of hydrogen was measured by thermal desorption spectroscopy (TDS). It was confirmed that elongation to failure was decreased with increasing charging time for testing at 1.38 × 10 − 6 s − 1 , while ultimate tensile strength was not affected markedly by hydrogen charging. The extent of HE took a maximum at a strain rate of 1.38 × 10 − 4 s − 1. Tensile test results and results of fracture surface evaluation by SEM were consistent to each other: the fraction of smooth area (area without dimples) with respect to the whole fracture area also took a maximum at the strain rate of 1.38 × 10 − 4 s − 1. These results were correlated to the balance between hydrogen diffusion and hydrogen desorption during the test. By TDS, the concentration of the diffusive hydrogen was confirmed to increase with increasing charging time. Hence, the extent of HE was strongly dependent on the concentration of the diffusive hydrogen.

Cracking Process Related to Hydrogen Behavior in a Duplex Stainless Steel

“…divided into two categories: one is non-diffusive hydrogen atoms strongly trapped by stable trapping sites such as precipitates and inclusions, and the other is diffusive hydrogen atoms that are in the interstitial site of the matrix or lightly trapped by less stable sites such as dislocations and grain boundaries. 26) In the previous study, 29) the authors investigated tensile properties of an electrolytically hydrogen-charged DSS affected by the strain rates ranging from 1.38 × 10 − 7 s − 1 to 1.38 × 10 − 3 s − 1 , and found that the susceptibility to HE becomes largest at a strain rate of 1.38 × 10 − 4 s − 1 in this charging and testing method. Furthermore, delamination type of fracture was seen in the specimen with high susceptibility to the HE.…”

“…The material used in this study is the same DSS (SUS329J4L) sheet with 1 mm thickness as in the previous study 29) annealed at 1 055°C for 18 min and then watercooled, containing 51 Vol% ferrite and 49 Vol% austenite phases. Its chemical composition is listed in Table 1.…”

“…The charging was performed at room temperature (RT) for 24 h with platinum anode in a sulfuric acid aqueous solution with pH = 2.5 containing 0.1 mass% of NH 4 SCN as a hydrogen recombination inhibitor with a current density of 100 A•m − 2 and voltage of 10 V. Figure 1 shows elongation to failure of the DSS at different strain rates ranging from1.38 × 10 − 7 s − 1 to 1.38 × 10 − 3 s − 1 , which has been already reported in the previous paper. 29) From this figure, the extent of HE took a maximum at a strain rate of 1.38 × 10 − 4 s − 1 and this strain rate has been adopted in this study. In this study as well, immediately after hydrogen charging of etched specimen, tensile test was carried out at the strain rate of 1.38 × 10 − 4 s − 1 by using a Toshin Kogyo 2LP-2R testing machine, but without simultaneous charging, i.e., charging was not made during the tests.…”

Hydrogen Distribution in a Duplex Stainless Steel Investigated by Means of Hydrogen Microprint Technique

“…[1][2][3] On the other hand, the main concern in the durability of DSSs, is their interplay with hydrogen specially in the presence of stress. [4][5][6] These combination lead to a degradation of mechanical properties and delayed fracture, known as hydrogen embrittlement (HE). [7][8][9] According to the authors, previous research, 6,7) the main cause of the fracture in the case of HE in DSS is closely related to the microstructure composed of the co-existing two phases (ferrite and austenite), combined with the local stress state in the material.…”

“…[4][5][6] These combination lead to a degradation of mechanical properties and delayed fracture, known as hydrogen embrittlement (HE). [7][8][9] According to the authors, previous research, 6,7) the main cause of the fracture in the case of HE in DSS is closely related to the microstructure composed of the co-existing two phases (ferrite and austenite), combined with the local stress state in the material. Hydrogen diffusion in the ferrite proceeds much faster than in the austenite, despite the lower solubility than in the austenite.…”