Pioneering research enriches our mechanistic understanding of the unique role niobium plays in improving the properties of commercial steels.
A research team led by the Nippon Steel and Sumitomo Corporation of Japan has won the 2017 Charles Hatchett Award. The award is made annually to the best research paper on the science and technology of niobium and its alloys. This year’s illuminating paper explains how detailed atom probe tomography studies have been used to clarify the mechanism through which niobium improves the high temperature properties of a ferritic stainless steel, widely used for automotive exhaust manifolds. This innovative research has a much broader application to our understanding of the role played by niobium across the full range of commercial steels where niobium is added to enhance their properties.
2017 Charles Hatchett Award winners receiving their medals from the Institute of Materials, Minerals and Mining (IOM3). Pictured from left: IOM3 President Martin Cox, Ken Kimura, Kazuto Kawakami and Jun Takahashi.
This Institute of Materials, Minerals and Mining (IOM3) annual Award, now in its 39th year, is sponsored by Companhia Brasileira de Metalurgia e Mineração (CBMM) and makes an important contribution to the company’s activities which recognise excellence in research on niobium and its applications. The award winners were presented with their medals at the IOM3 dinner held in London on the 11th July.
It has been widely speculated that niobium atoms, in solution, segregate to grain boundaries and dislocations, initially within the gamma matrix, and that such interactions contribute to the retardation of recovery of dislocation sub-structures which then has a subsequent, important impact on the final properties of the transformed steel. This is a mechanism unique to the element niobium.
This work, using the atom probe tomography technique has, for the first time, clearly established that niobium does indeed segregate powerfully to dislocations and the authors have described the phenomenon as the ‘Niobium-Cotterell’ atmosphere. They have sought to explain its manifestation by suggesting that the size of the niobium atom plays an important role in the segregation of the element to available substitutional sites in the distorted matrix in the vicinity of dislocations.
This important observation contributes significantly to our current knowledge of the role which niobium plays in the retardation of recrystallization and thus to its ability to dramatically influence the development of enhanced mechanical properties. This mechanism is of particular importance in the processing of ferritic stainless steel that operates at high temperatures where enhanced thermal fatigue properties are required.
Prior to the medal ceremony, the lead author, Dr Jun Takahashi, presented the winning project to a select group of industry experts and CBMM representatives. This included the company’s Chief Technology Officer, Marcos Stuart, who said, “This enhanced learning helps us to understand why niobium is such a unique element and our constantly improving knowledge of its fundamental role in improving high performance steel properties opens up new uses and applications for niobium bearing steels across a range of industries. The atom probe tomography provided visualization of what could previously only be conceptualized.
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