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<p>This study conducted a statistical analysis of the microstructural features of 9 different X70 pipeline steels, evaluated by the drop weight tear test and electrochemical hydrogen permeation test, to evaluate low-temperature toughness and hydrogen embrittlement. A cost-effective model based on grid search hyperparameter tuning was proposed and adopted to the obtained experimental results. Based on statistical analysis, key microstructural features were measured, identifying critical ranges: ferrite grain sizes of 5-9 µm, Nb content of 0.035-0.06%, NbC carbide sizes below 200 nm, kernel average misorientation values under 0.40°, {332} &lt;113&gt; fractions of 25-45%, γ-fiber fractions of 20-30%, and R-Cube fractions below 15%, all of which fall within defined ranges that contribute to improved low-temperature toughness and, subsequently, hydrogen embrittlement resistance. The proposed cost-effective model identifies {332} &lt; 113 &gt; /RC and γ/RC ratios as the most important factors influencing low-temperature toughness and hydrogen embrittlement outcomes with a synergistic effect from other microstructural features. The results are supported by a two-level full factorial analysis. Consequently, steel samples with acceptable low-temperature toughness showed improved hydrogen embrittlement resistance.</p> Graphical Abstract <p></p>

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Microstructural Observations of X70 Pipeline Steels Evaluated by Hydrogen Permeation and Drop Weight Tear Tests to Propose a Statistically Based, Cost-Effective Model

  • 期刊论文

  • 发表日期：

    2025年9月22日

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  • Reza Khatibzadeh Davani,
  • Ehsan Entezari,
  • Jerzy A. Szpunar

摘要

This study conducted a statistical analysis of the microstructural features of 9 different X70 pipeline steels, evaluated by the drop weight tear test and electrochemical hydrogen permeation test, to evaluate low-temperature toughness and hydrogen embrittlement. A cost-effective model based on grid search hyperparameter tuning was proposed and adopted to the obtained experimental results. Based on statistical analysis, key microstructural features were measured, identifying critical ranges: ferrite grain sizes of 5-9 µm, Nb content of 0.035-0.06%, NbC carbide sizes below 200 nm, kernel average misorientation values under 0.40°, {332} <113> fractions of 25-45%, γ-fiber fractions of 20-30%, and R-Cube fractions below 15%, all of which fall within defined ranges that contribute to improved low-temperature toughness and, subsequently, hydrogen embrittlement resistance. The proposed cost-effective model identifies {332} < 113 > /RC and γ/RC ratios as the most important factors influencing low-temperature toughness and hydrogen embrittlement outcomes with a synergistic effect from other microstructural features. The results are supported by a two-level full factorial analysis. Consequently, steel samples with acceptable low-temperature toughness showed improved hydrogen embrittlement resistance.

Graphical Abstract