Speaker: Roger Doherty, Professor Emeritus of Materials Science and Engineering at Drexel University
Title: Role of internally derived and externally applied axial stress on Pearlite Microstructures and their Mechanical Properties in Eutectoid Steel
Abstract: Pearlite is a micro-composite of layers of cementite, Fe3C, low carbon bcc ferrite. It is used for high strength steels cables after “patenting”. This is rapid cooling to give fine interlayer spacing, l, and then wire drawn to further refine l and to axial align the pearlite structure. A neglected aspect of the transformation, the basis for Durga’s study, was the elastic strain introduced by the locally constrained ≈ 5% volume increase of pearlite formation Industrially drawn wires of diameters 5.5 to 1.6 mm were reaustenitized and air cooled. The finer wires cooled faster giving, as expected, much finer l but unexpectedly major axial alignment of the pearlite. To study the possible roles of (i) cooling rate and (ii) axial stress during transformation, rods of constant initial microstructure and diameter were reaustenitized and cooled either (i) in a dilatometer at different cooling rates or (ii) at a constant cooling rate under applied axial stress. Both faster cooling and higher applied axial stress decreased l somewhat the spacing and also increased the alignment. Our current model is that the pearlite preferred growth direction seems close to <100> – the elastic softest ferrite direction. Interesting results were also found in comparison the mechanical properties of similar pearlite microstructure formed in either wire drawn or in undeformed pearlite. There are many unsolved problems from this project that will be briefly described.
Bio: Roger Doherty earned his undergraduate and doctorate degrees in metallurgy from Oxford University (1957-64). He then spent 2 years in a UK steel research lab before becoming a founding faculty member of the then new School of Applied Science in the University of Sussex After 17 years at Sussex he became a Professor of Materials Engineering at Drexel University where he has spent the last 40 years – since 2008 as an emeritus professor. He became a Fellow of The Materials Society (TMS) in 2007. His research has covered different aspects of materials processing – solidification, solid state phase transformations, plastic deformation including mechanical twinning, recrystallization and grain growth. His emphasis has been on their atomic mechanisms and the resulting microstructures and resulting properties of these processes. He has advised or co-advised 40+ doctorate students in 6 different countries. He has been an author or, more commonly, a co-author of over 240 research and review articles, 7 US patents and has co-authored 3 books: “Stability of Microstructure in Metallic Materials”, “Aluminum Alloys – Contemporary Research and Applications” and “Thermo-Mechanical Processing of Metallic Materials”. He has consulted widely most notably with Alcoa. Such consultancy was a major inspiration for new research projects and has spent extended time as a visiting researcher at the Brazilian Aero Space Center, at the Technical Universities of Delft (Netherlands) and of Trondheim (Norway), at the Riso Research Institute in Denmark, at The School of Mines in St Etienne in France and recently multiple visits to IIT Bombay India. After over 60 years of involvement with materials research he is still delighted by new insights from younger colleagues who continue his education.
Seminar Host: Sid Pathak
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