Effect of Microstructure on the Mechanical Properties and Fracture Toughness of API X65 Pipeline Steel in the Presence o
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Effect of Microstructure on the Mechanical Properties and Fracture Toughness of API X65 Pipeline Steel in the Presence of Hydrogen Meysam Ranjbar1 · Reza Miresmaeili1 · Mohammad Reza Naimi‑Jamal2 · Majid Mirzaei3 Received: 24 July 2020 / Accepted: 14 September 2020 © The Korean Institute of Metals and Materials 2020
Abstract This study investigated the influence of microstructure on the mechanical properties and fracture toughness of API X65 pipeline steel in the presence of hydrogen. In this study, electrochemical method was used for hydrogen charging and indentation technique was applied to obtain the fracture toughness. The results showed that in the presence of hydrogen, elongation (EL%), reduction of area (RA), ductile fracture percentage, and fracture toughness of all microstructures decreased. The microstructure of martensite (M) + bainite (B) + ferrite (F), had the highest hydrogen trapping and uptake ( Capp) as 8.58 × 10– 6 mol cm−3 and the lowest apparent hydrogen diffusivity (Dapp) as 5.68 × 10−10 m2 s−1; thus, the maximum decrements of 33% in fracture toughness, 40% in ductile fracture percentage, 47% in RA, and 35% in EL% were observed. However, the microstructure of ferrite (F) + degenerated perlite (DP) + martensite-austenite micro constituent (M/A), where the lowest value of 5.85 × 10–6 mol cm−3 for C app and the highest value of 8.5 × 10–10 m2 s−1 for D app had the minimum decrements as 2% in fracture toughness, 10% in ductile fracture percentage, 4% in RA, and 7% in El%. According to the obtained results, depending on the type of microstructures, hydrogen-induced work softening or hardening were observed by decreasing or increasing the yield stress respectively. Keywords Microstructure · Fracture toughness · Indentation technique · Hydrogen permeability · Hydrogen enhanced softening and hardening
1 Introduction
* Reza Miresmaeili [email protected] Meysam Ranjbar [email protected] Mohammad Reza Naimi‑Jamal [email protected] Majid Mirzaei [email protected] 1
Department of Materials Engineering, Tarbiat Modares University, Jalal Ale Ahmad Highway, 14115‑143, Tehran, Iran
2
Research Laboratory of Green Organic Synthesis and Polymers, Department of Chemistry, Iran University of Science and Technology, 16846‑13114, Tehran, Iran
3
Department of Mechanical Engineering, Tarbiat Modares University, 14115‑143, Tehran, Iran
Hydrogen embrittlement (HE) is one of major unexpected failure mechanisms in API pipeline steel. Wang [1] reported that local corrosion and cathodic protection can produce hydrogen atoms. Then, due to small atomic radius of hydrogen it can diffuse into the steel and dissolve at the interstitial sites, or be trapped at defect zones such as dislocations, grain boundaries, etc. [2]. The quantity of trapped and dissolved hydrogen in a material depends on the type of microstructure and the density of defects [1, 2]. Hejazi et al. [3] studied the influence of microstructure on the sensitivity of API X70 steel and showed that the trapping of hydr
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