Prevention of austenitic stainless steel from hydrogen embrittlement in hydrogen fuel cell by surface engineering

Purpose and goal:

This project explores the potential of using low temperature carburizing (LTC) to protect austenitic stainless steels from hydrogen embrittlement (HE). It evaluates the effect of hydrogen on mechanical and corrosion properties of two selected stainless steels with and without LTC.

The project has been fulfilled successfully. Some beneficial effects of LTC on HE and corrosion properties of stainless steels were demonstrated. Expected results and effects:

For cold worked 304, LTC treatment improves the resistance to HE significantly. For solution annealed 304 and 316L, cold worked 316L, HE susceptibility is improved slightly by LTC treatment. In the hydrogen environment, LTC increases open circuit potential, corrosion potential and breakdown potential compared to the samples without this treatment, except cold worked 316L.

The current project provides understanding of how hydrogen affect the mechanical and corrosion behaviour of LTC-created expanded austenite and how this can be used for industrial applications. Approach and implementation:

LTC treatment was performed on solution annealed and cold worked 304 and 316L stainless steel. Hydrogen was introduced into the materials by means of cathodic electrochemical charging. Mechanical properties and the resistance to HE were assessed by tensile tests.

The corrosion properties were evaluated by open circuit potential and potentiodynamic polarization tests in 3.5 wt.% NaCl solution. Due to long charging time, the project was extended for 1.5 month. All five work packages have been successfully completed.