Striking features of microstructures in steels, by Jer-Ren Yang, Lecture 17 of 25 @bhadeshia123

Uploaded December 2021 | Updated September 2026, 2 weeks ago

Lecture 17, by Professor Jer Ren Yang of the National Taiwan University, in the series "Steel Research: A global journey", organised by Adreil Wong, Dominik Dziedzic and Steve Ooi to mark the retirement of Harry Bhadeshia.

Professor Yang describes the microscopy facilities and how they have been used to characterise detail ranging from the observation of atoms to scales that reveal the mechanical behaviour of steels. He even describes how layers of atoms can be peeled away from the surface of transmission electron microscope samples, in order to avoid moire-fringe effects. The skill demonstrated is amazing.

phase-trans.msm.cam.ac.uk

Striking features of microstructures in steels, by Jer-Ren Yang, Lecture 17 of 25

Thermodynamics of steels: the carbon-carbon interaction energy.

$Kinetics of niobium carbide precipitation in steels Kinetics and thermodynamics of niobium carbide precipitation in steels Welcome back to the channel! In this lecture, we take a deep dive into the physical metallurgy, thermodynamics, and kinetics of niobium carbide (NbC) precipitation in steels. Very often we think about niobium carbide purely in terms of equilibrium solubility products, but in real-world applications, we need to understand how fast it can precipitate and how it behaves over time. Whether you are a student, a researcher, or a professional metallurgist, this video breaks down the mathematical models and physical phenomena that control phase transformations in steel. Thermodynamics & the effect of Mmnganese: We begin by exploring thermodynamic calculations using databases and how empirical experimental data proves that adding manganese actually increases the solubility of niobium carbide in austenite. Ostwald ripening & coarsening: Discover the history of coarsening, tracing back to Ostwalds 1900 paper on interfacial energy (surface tension) and Geoffrey Greenwoods pioneering theory. Learn exactly why incredibly small particles dissolve while larger particles grow to maintain a constant volume fraction. Diffusion & particle growth: Understand the complexities of local equilibrium at the particle interface. We tackle a major problem in precipitation kinetics: how a particle can grow when carbon diffuses orders of magnitude faster than niobium, and how the ternary phase diagram provides a flat carbon concentration gradient to compensate. Nucleation & impingement: A look at the classic equations for nucleation rates, the crucial role of the number density of nucleation sites, and the beautifully simple Johnson-Mehl-Avrami-Kolmogorov theory for calculating how growing particles collide and impinge on one another. Software modelling & bold predictions: Learn the limitations of using commercial software like Dictra or MatCalc, the danger of simply fitting data without generalised parameters, and how to use these models creatively to make bold predictions—like predicting the formation of room-temperature bainite. Real-world engineering applications: We conclude with an exciting real-world application of phase transformation theory: the design of a brand new, highly resilient steel alloy for the shafts of Rolls-Royce civil aircraft engines. Free resource: Everything discussed in this video regarding phase transformations and kinetics is covered in depth in my book. You can download it entirely free of charge from my website! Also, check out the free biography of Geoffrey Greenwood available to download to learn more about the crazy, pioneering history of materials science. If you found this lecture helpful, please leave a like, subscribe for more materials science deep-dives, and let me know your thoughts in the comments below!$

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Striking features of microstructures in steels, by Jer-Ren Yang, Lecture 17 of 25