The determination of austenite grain size in ferrous metals

Riedl, R.

doi:10.1016/0026-0800(81)90036-7

Cited by 7 publications

(2 citation statements)

References 2 publications

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“…The dilatation data were interpreted in terms of the ferrite fraction as a function of temperature by means of a lever-rule method. 22) Using optical microscopy and a thermal etching technique, 23) the re-heated austenite grain size prior to deformation was determined by the linear-intercept method to be 30 mm. This value translates to a 3D, tetrakaidecahedral diameter of approximately 50 mm.…”

Section: Methodsmentioning

confidence: 99%

The Effect of Plastic Deformation of Austenite on the Kinetics of Subsequent Ferrite Formation.

Hanlon¹,

2001

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A modeling approach to account for the effect of deformation on the austenite to ferrite transformation is described. In this approach the stored energy of deformation resulting from the formation of a dislocation substructure is considered to result in an elevation of the driving force for transformation. A scheme which accounts for the competition between softening and transformation processes is also described. Model data illustrating the effects of discrete dislocations and cell structures, with and without concurrent recovery are presented. Comparison of modeled and experimental transformation curves indicates that deformation affects the transformation principally via a reduction in the undercooling required for nucleation rather than via an acceleration of the growth kinetics.KEY WORDS: steels; austenite; phase transformations; recovery; hot deformation.edged as an accelerating effect. This has been observed in the different parameters that reflect the transformation kinetics. More specifically, in cooling experiments both the transformation start temperature and the transformation finish temperature have been found to increase, 7,9) the temperature range of the transformation to contract, 9) the final fraction of polygonal ferrite to increase 5) and the final ferrite grain size to decrease. [7][8][9] However, the exact nature of the effects that plastic deformation of austenite has on the transformation kinetics is poorly understood. A theoretical contribution by Umemoto et al. 6) postulates that three different mechanisms may affect ferrite nucleation, whilst a fourth mechanism affects ferrite grain growth. The mechanisms postulated by Umemoto et al. are: (1) accelerated nucleation kinetics as a result of an increase in grain boundary area; (2) increased nucleation potency at grain boundaries via the introduction of grain boundary ledges leading to localised increases in grain boundary energy; (3) additional nucleation sites due to a deformation substructure; (4) accelerated growth kinetics arising from the stored energy of deformation. The first three mechanisms help overcome the energy barrier for nucleation leading to a reduction of the undercooling required to bring about nucleation in a cooling experiment, and possibly also to an increase in the nucleation site density. These mechanisms thus provide plausible explanations for the observations of increased transformation start and finish temperature, and also for the refinement of microstructure. The stored energy that gives rise to mechanism (4) essentially increases the driving force for the transformation and may explain the contraction of the transformation range. Expressed in microstructural terms, the stored energy of deformation is not only a function of the dislocation density but is also dependent upon the nature of the substructure in which the dislocations are stored. Experimental observations which suggest that deformation affects the nucleation behaviour are commonly reported.6) Experimental evidence of the influence of plastic defor...

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Section: Methodsmentioning

confidence: 99%

The Effect of Plastic Deformation of Austenite on the Kinetics of Subsequent Ferrite Formation.

Hanlon¹,

2001

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“…It is believed that the sensitivity of grain boundaries to chemical etchants can be improved by heating the samples in an oxidizing atmosphere [7,14,22,29,30,32]. Moreover, it is known that some chemical etchants have the ability to reveal the austenite grain boundaries when they contain segregated elements such as phosphorus [6,24,32,40 -42].…”

Section: Ht2 Ht3 and Ht4 Heat Treatmentsmentioning

confidence: 99%