Steels: pearlite. Lecture 8 of 12 @bhadeshia123

bhadeshia123 | Steels: pearlite. Lecture 8 of 12 @bhadeshia123 | Uploaded October 2020 | Updated October 2024, 10 hours ago.
Pearlite is probably the most familiar microstructural feature in the whole
science of metallography. It was discovered by Sorby some
130 years ago, who correctly assumed it to be a lamellar mixture of iron and
iron carbide. Pearlite is an extremely common constituent of a wide variety of steels, where it provides a substantial contribution to strength, so it is
not surprising that this phase has received intensive study. Lamellar
eutectoid structures of this type are widespread in metallurgy, and
frequently, pearlite is used as a generic term to describe them. These
structures have much in common with the cellular precipitation reactions.
Both types of reaction occur by nucleation and growth and rely
on the cooperative growth of phases during diffusional growth. Pearlite nuclei occur on austenite grain boundaries, but it is
clear that they can also be associated with both pro-eutectoid ferrite and
cementite. In commercial steels, pearlite nodules can nucleate on
inclusions.

Associated teaching materials can be found on:
phase-trans.msm.cam.ac.uk/teaching.html
H. K. D. H. Bhadeshia

Steels: design of bainitic steels. Lecture 4 of 12

Characterisation of steels using modern electron microscopy techniques, by Dr Geoff West

$Steels: nanostructured alloys A nanostructured material is here defined as one containing an exceptionally large density of strong interfaces, rather than one which simply contains a minor fraction of features such as precipitates, which are small in size. The desire for such materials in the engineering context comes from the expectation of novel mechanical properties, particularly the stress that can safely be tolerated in service. It is difficult to invent such materials because any design must address three basic issues: (i) it should ideally be possible to make samples which are large in all dimensions, not simply wires or thin sheets; (ii) there are commercially available steels in which the distance between interfaces is of the order of 250 100~nm. The novelty is in approaching a structural scale in polycrystalline metals which is an order of magnitude smaller. (iii) The material concerned must be cheap to produce if it is not to be limited to niche applications. A good standard for an affordable material is that its cost must be similar to that of bottled water when considering weight or volume. An alloy system based on iron is described in which it has been possible to create a high density of interfaces by heat treatment alone. The resulting structure consists of a mixture of slender platelets of bainitic ferrite, just 20 40,nm in thickness, embedded in a matrix of carbon enriched austenite. The rate at which this structure evolves is slow by conventional standards, but this permits components to be made which are large in all three dimensions, with uniform properties throughout. The fundamental mechanisms behind this novel nanostructured steel are reviewed, along with the factors determining its strength, ductility and fracture toughness. It is argued that although reasonable toughness can be achieved in the context of strength levels exceeding 2000,MPa, the impact toughness remains poor and that it may not be possible to improve this particular parameter. Associated teaching materials can be found on: http://www.phase-trans.msm.cam.ac.uk/teaching.html H. K. D. H. Bhadeshia$

High entropy alloys - by Professor Brian Cantor

$Geiger counter output from X-ray source, at constant diffraction angle$

Mystery of MUCG46, Professor Sudarsanam Suresh Babu, Lecture 2 of 25

Real-time observations of transformations in steels

Steels: martensitic transformation, part 1. Lecture 1 of 12

Reducing automotive carbon emissions with better steels, Hongliang Yi, Lecture 22 of 25