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<p>This study investigates the effect of microalloying on the microstructure, corrosion resistance, hydrogen diffusion, and trapping behavior in three medium-Mn advanced high-strength steels (AHSSs): a base alloy (A0), Mo-V steel (A2: 0.35 wt.% Mo and 0.23 wt.% V), and high Mo-Nb steel (A4: 1.19 wt.% Mo and 0.045 wt.% Nb). Microstructural analysis revealed that A4 steel exhibits significantly refined hierarchical features compared to A0 and A2 steel. Specifically, the average sizes of blocks, packets, and prior austenite grains (PAGs) in A4 steel are approximately 3, 5, and 10&#xa0;µm, respectively; these are substantially smaller than those in A0 steel (10, 25, and 45&#xa0;µm) and A2 steel (8, 18, and 30&#xa0;µm). This refinement is primarily attributed to the microalloying effect, which promotes effective grain subdivision and variant selection during transformation. A4 steel exhibited a multiphase (ferrite/martensite) microstructure with approximately 10% retained austenite, whereas A0 and A2 steels showed a fully martensitic microstructure. Electrochemical assessments using potentiodynamic polarization and impedance spectroscopy demonstrated the superior corrosion resistance of A4 steel, as evidenced by its lower corrosion current density (15.5 µA/cm<sup>2</sup>) and higher charge transfer resistance (1522 Ω·cm<sup>2</sup>); however, localized corrosion was observed due to microgalvanic coupling between the retained austenite and ferrite/martensite phases.&#xa0;Hydrogen permeation tests indicated A4 steel had a higher apparent diffusion coefficient (2.7 × 10<sup>-7</sup>cm<sup>2</sup>/s compared to A0 (2.5 × 10<sup>-7</sup> cm<sup>2</sup>/s) and A2 (2.4 × 10<sup>-7</sup>cm<sup>2</sup>/s), attributed to its refined microstructure and retained austenite providing diffusion pathways.&#xa0;Conversely, A0 exhibited the highest diffusible hydrogen concentration (12.35&#xa0;ppm) and reversible trap density (4.11 × 10<sup>19</sup>cm<sup>-3</sup>), indicating greater susceptibility to hydrogen trapping. Quantitative analysis of decay transients revealed that A4 steels have lower diffusible hydrogen (7.23&#xa0;ppm) and trapped hydrogen density (1.97 × 10<sup>19</sup>cm<sup>-3</sup>) compared to A0 and A2 steels, correlating with their resistance to embrittlement.</p>

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Corrosion Resistance, Hydrogen Diffusion, and Trapping Behavior in Three Medium-Mn Advanced High-Strength Steels: A Comparative Study

  • 期刊论文

  • 发表日期：

    2025年10月14日

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  • Vikram Kumar S. Jain,
  • Yoganandan Govindaraj,
  • Lakshman Neelakantan,
  • V. Subramanya Sarma

摘要

This study investigates the effect of microalloying on the microstructure, corrosion resistance, hydrogen diffusion, and trapping behavior in three medium-Mn advanced high-strength steels (AHSSs): a base alloy (A0), Mo-V steel (A2: 0.35 wt.% Mo and 0.23 wt.% V), and high Mo-Nb steel (A4: 1.19 wt.% Mo and 0.045 wt.% Nb). Microstructural analysis revealed that A4 steel exhibits significantly refined hierarchical features compared to A0 and A2 steel. Specifically, the average sizes of blocks, packets, and prior austenite grains (PAGs) in A4 steel are approximately 3, 5, and 10 µm, respectively; these are substantially smaller than those in A0 steel (10, 25, and 45 µm) and A2 steel (8, 18, and 30 µm). This refinement is primarily attributed to the microalloying effect, which promotes effective grain subdivision and variant selection during transformation. A4 steel exhibited a multiphase (ferrite/martensite) microstructure with approximately 10% retained austenite, whereas A0 and A2 steels showed a fully martensitic microstructure. Electrochemical assessments using potentiodynamic polarization and impedance spectroscopy demonstrated the superior corrosion resistance of A4 steel, as evidenced by its lower corrosion current density (15.5 µA/cm2) and higher charge transfer resistance (1522 Ω·cm2); however, localized corrosion was observed due to microgalvanic coupling between the retained austenite and ferrite/martensite phases. Hydrogen permeation tests indicated A4 steel had a higher apparent diffusion coefficient (2.7 × 10-7cm2/s compared to A0 (2.5 × 10-7 cm2/s) and A2 (2.4 × 10-7cm2/s), attributed to its refined microstructure and retained austenite providing diffusion pathways. Conversely, A0 exhibited the highest diffusible hydrogen concentration (12.35 ppm) and reversible trap density (4.11 × 1019cm-3), indicating greater susceptibility to hydrogen trapping. Quantitative analysis of decay transients revealed that A4 steels have lower diffusible hydrogen (7.23 ppm) and trapped hydrogen density (1.97 × 1019cm-3) compared to A0 and A2 steels, correlating with their resistance to embrittlement.