Full Record for Micrograph 234

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Micrograph no

234

Brief description

Hypoeutectoid steel, normalised at 1100°C

Keywords

alloy

, carbon, hypoeutectoid

, iron, metal, pearlite

, steel

Categories

Metal or alloy

System

Fe-C-X

Composition

Fe, C 0.4 (wt%)

Standard codes

Reaction

Processing

Normalised 1100°C

Applications

Sample preparation

Nital

Technique

Reflected light microscopy

Length bar

200 μm

Further information

A hypoeutectoid alloy (carbon composition less than eutectoid). The first phase formed upon cooling from the austenite phase field is proeutectoid ferrite. Due to the lower solubility of carbon in ferrite, carbon is partitioned into the remaining austenite. At the eutectoid point the remaining carbon enriched austenite transforms to pearlite (a mixture of ferrite and cementite) which is the darker region of the micrograph. The proportion of pearlite is dependent upon the overall composition.

The ferrite (light areas) is a good example of an allotriomorphic ferrite. This means that its shape does not reflect its internal crystalline symmetry as it nucleates on the austenite grain boundaries and hence follows the shape of the boundaries, the remaining austenite within the ferrite then transforms to pearlite, and is surrounded by the ferrite. The large size of the areas of pearlite arises due to the high normalisation temperature which causes the austenite grains to grow large.

Contributor

Dr R F Cochrane

Organisation

Department of Materials, University of Leeds

Date

04/09/02

Licence for re-use

Attribution-NonCommercial-ShareAlike 4.0 International

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