A team headed by Professor Mingxin Huang from the University of Hong Kong’s Department of Mechanical Engineering has achieved a significant advancement in the field of stainless steel. This recent innovation focuses on the development of stainless steel designed for hydrogen applications, known as SS-H2.
This accomplishment is part of Professor Huang’s ongoing ‘Super Steel’ Project, which previously achieved notable milestones with the creation of anti-
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The discovery has been published in the journal Materials Today. The research achievements are currently applying for patents in multiple countries, and two of them has already been granted authorisation.
Revolutionizing Corrosion Resistance
Since its discovery a century ago, stainless steel has always been an important material widely used in corrosive environments. Chromium is an essential element in establishing the corrosion resistance of stainless steel. Passive film is generated through the oxidation of chromium (Cr) and protects stainless steel in natural environments. Unfortunately, this conventional single-passivation mechanism based on Cr has halted further advancement of stainless steel. Owing to the further oxidation of stable Cr2O3 into soluble Cr(VI)
254SMO super stainless steel, for instance, is a benchmark among Cr-based anti-corrosion alloys and has superior pitting resistance in seawater; however, transpassive corrosion limits its application at higher potentials.
By using a “sequential dual-passivation” strategy, Professor Huang’s research team developed the novel SS-H2 with superior corrosion resistance. In addition to the single Cr2O3-based passive layer, a secondary Mn-based layer forms on the preceding Cr-based layer at ~720 mV. The sequential dual-passivation mechanism prevents the SS-H2 from corrosion in chloride media to an ultra-high potential of 1700 mV. The SS-H2 demonstrates a fundamental breakthrough over conventional stainless steel.
Unexpected Discovery and Potential Applications
“Initially, we did not believe it because the prevailing view is that Mn impairs the corrosion resistance of stainless steel. Mn-based passivation is a counter-intuitive discovery, that cannot be explained by current knowledge in corrosion science. However, when numerous atomic-level results were presented, we were convinced. Beyond being surprised, we cannot wait to exploit the mechanism,” said Dr Kaiping Yu, the first author of the article, whose PhD is supervised by Professor Huang.
From the initial discovery of the innovative stainless steel to achieving a breakthrough in scientific understanding, and ultimately preparing for the official publication and hopefully its industrial application, the team devoted nearly six years to the work.
“Different from the current corrosion community, which mainly focuses on the resistance at natural potentials, we specialize in developing high-potential-resistant alloys. Our strategy overcame the fundamental limitation of conventional stainless steel and established a paradigm for