Investigating the hydrogen diffusion and cracking susceptibility of pipeline steels after various heat treatments

• Published in: Engineering failure analysis 2024-07, Vol.161, p.108311, Article 108311
• Main Authors: Jack, Tonye Alaso, Nnoka, Meekness, Zhang, Jiming, Szpunar, Jerzy
• Format: Article
• Language: English
• Subjects: Heat treatment; Hydrogen diffusion; Hydrogen-induced cracking; Microstructure; Pipeline steel
• ISSN: 1350-6307
• DOI: 10.1016/j.engfailanal.2024.108311

•Modifying microstructure influences hydrogen diffusion and cracking of steels.•HIC susceptibility of steels is dependent on their diffusion characteristics.•Phase composition was seen to play the most significant role in influencing HIC.•Low local misorientaions in steels facilitates the elimination of HIC. This work examines the effect of stress-relief (SR) and quenching and tempering (QT) heat treatments on the hydrogen-induced cracking (HIC) susceptibility of pipeline steels. Two trials of a similar X65 pipeline steel were used in this study. They had distinct differences in microstructural characteristics, which significantly affected their cracking behaviour. The SR treatment reduced local misorientations, without significantly altering the microstructural appearance of the steels. Hence, this treatment resulted in a hydrogen permeation transient and cracking response similar to the as-received steels. However, the QT treatments significantly modified the microstructure of the steels, with some treatments resulting in equiaxed polygonal ferrite grains and lower local misorientations, depending on the quenchant used. These microstructural changes contributed to increasing hydrogen diffusion and permeation through the steels, as well as alleviating or eliminating HIC after hydrogen charging. Comparing the permeation transients and diffusion characteristics of the steels without cracks to those with significant cracking, a dependence of HIC susceptibility on the diffusion and trapping behavior within the steels was observed.