Three different strain hardened austenitic corrosion resistant alloys with chemical compositions providing high pitting resistance equivalent (PREN), have been tested for susceptibility to hydrogen. The grades were UNS N08034, UNS N08935 and DIN no. 1.4675 (a proprietary grade with no UNS number).

The strain hardened corrosion resistant alloys were initially characterized by identifying the critical pitting temperature (CPT) using ASTM G48 Method C. Resistance to hydrogen embrittlement has been examined by employing the Slow Strain Rate Test and Stepwise Constant Load Test, and further supported by fractographic characterization and microstructural examination using both Optical Light Microscope and Scanning Electron Microscope.

The ASTM G48 Method C test revealed CPT for the grades tested that is higher than for e.g., 25%Cr Duplex stainless steels, a reference alloy, commonly used in seawater service.

The Stepwise Constant Load and Slow Strain Rate tests revealed little effect of hydrogen charging on yield strength and fracture strength for the tested alloys. The ductility exhibited more clear signs of hydrogen embrittlement degradation, measured as reduction in fracture strain and reduction in area reduction. However, if you compare the loss of ductility with e.g., precipitation hardened nickel alloys (PHNA) with comparable yield strength, tensile strength, and PREN, such as UNS N07716 and UNS N07725, these strain hardened alloys have superior resistance to hydrogen embrittlement degradation. Test results are supported by fractography demonstrating significant necking, less secondary cracking, and absence of intergranular facture, when compared to PHNA’s.

Subject
Test methods, Materials, Secondary cracks, Nickel based alloys, Fracture surfaces, Hydrogen charging, Elongation, Corrosion resistance, Risk reduction, Fracture, Alloys, Ductility, Hydrogen
Keywords:
Strain Harden, Cold working, Hydrogen, CRA, PHNA, UNS, N08034, N08935, 1.4675, HISC
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2023
Association for Materials Protection and Performance (AMPP)
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