Hydrogen compatibility with steel
|Understanding the fundamentals of hydrogen embrittlement is a key issue for numerous future material developments. A possible hydrogen based economy is only one of the examples showing the strategic importance of understanding the hydrogen effect in metallic materials. Indeed, thanks to its high potential as a future energy carrier, hydrogen is a hot topic these days. Here, apart from pro-active materials selection, OCAS has proven experience in advanced materials testing and characterisation.|
Hydrogen in combination with steel is a delicate topic. In-field use of certain steels in a variety of applications reveals that hydrogen sometimes causes embrittling phenomena in certain steel types. It is a known fact that many parameters play a role, which makes the embrittling effect to be dependent on the steel’s microstructure, strength level, application conditions (e.g. corrosion), stress state, etc.
For this reason, OCAS launched various studies on the hydrogen effect in steels. The major objective of one of these projects was to identify the microstructure features triggering H-embrittlement. Is it the interaction of hydrogen with dislocations that enhances brittle fracture? Can the accumulation of hydrogen at the tip of a martensite lath cause crack initiation? To what extent does chemical segregation play a role in hydrogen assisted cracking?
Read more on hydrogen economy (PDF 289 kB), hydrogen cracking and welds (PDF 280 kB) and the Disc Rupture Test (PDF 2,34 MB).
Tensile testing of in-situ H-charged samples
“For example, various steel grades were tested in our hydrogen dedicated laboratory in similar, reproducible conditions”, says Elke Leunis, Research Engineer Metallurgy at OCAS. “During the tensile test, the steel sample was H-charged electrochemically, in controlled conditions. Parallel to this tensile testing, the amount of hydrogen was determined as a function of the H-charging time. As a result it could be determined for each grade how much H is needed to be charged into the material to induce cracking.” Watch the video (WMV 481 kB).
“A specific ferrite-martensite type of steel turned out to be very sensitive to H-embrittlement. Detailed investigation of the fracture surface indicated the presence of internal cracks. The majority of the cracks was found to be located around the centerline, indicating that centerline segregations are most probably at the basis of hydrogen induced cracks due to the formation of brittle phases. These results, together with those of other research projects, provide us with an ever improving fundamental understanding of the hydrogen effect in steels and allow us to interact in the steel selection for various applications and environments.”