Session: MF-02-04 Materials for Hydrogen Service (Joint with C&S)-4

Paper Number: 152165

152165 - Influence of Pre-Strain and Aging on Hydrogen Induced Cracking in Sa516 Gr. 70 Steel 

Abstract: 

This study examines the effect of pre-strain and aging on Hydrogen Induced Cracking (HIC) in SA516 Gr. 70 pressure vessel steel. Specimens were pre-strained by 2.5% to 10.0%, and some were heat-treated to simulate aging after pre-strain. HIC was induced following the NACE TM0284 standard, and analyzed using Thermal Desorption Analysis (TDA), Ultrasonic Testing (UT), and microstructural analysis. Polarization tests and Slow Strain Rate Tests (SSRT) were also conducted to determine the mechanisms behind crack formation.

No HIC was found in pre-strained, non-aged specimens (SO). In contrast, HIC occurred in strain-aged (SA) specimens with strain levels above 7.5%, with the highest amount observed at 10.0% strain. TDA results indicated hydrogen activation energy (Ea) of 20.2 kJ/mol across all specimens, related to dislocation strain fields, which were not directly related to HIC. A secondary peak with an Ea of 36.5 kJ/mol appeared in the 7.5% to 10.0% SA specimens, corresponding to microvoid formation, with hydrogen absorption proportional to the amount of HIC.

Microstructural analysis of the 10.0SA specimens showed cracks initiating in pearlite after 1 hour of immersion, accompanied by microvoid-type defects. These cracks grew with longer immersion times. Polarization testing revealed similar initial passive potentials for 10.0SO and 10.0SA, but the pitting potential of 10.0SA was lower, indicating reduced passivity. SSRT results showed no hydrogen embrittlement in electrochemically hydrogen-charged tensile specimens. The NACE TM0284 test confirmed that strain-aged specimens had lower corrosion resistance, promoting microvoid-type defects in pearlite, which facilitated hydrogen diffusion and trapping, leading to HIC.

In conclusion, strain aging affects HIC phenomenon in SA516 Gr. 70 steel, with deformation above 10.0% leading to significant crack growth.

Presenting Author: Seong Ho Hong Hyundai steel

Presenting Author Biography: Seongho Hong obtained a Master’s degree in Material Science and Engineering from Yonsei University. Since 2016, he has been working as a research engineer at Hyundai Steel R&D Center. For about 9 years, he designed chemical composition and making procedure to develop new steel product, including plates for pressure vessels and wind towers. He is currently a Senior Research Engineer in the heavy plate development team.

Authors:

Seong Ho Hong Hyundai steel
Seunghwan Chun Hyundai steel