Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
On the Symmetry Among the Diffusional Transformation Products of Austenite
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0002-7656-9733
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0003-1102-4342
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
Show others and affiliations
2011 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 42A, no 6, 1558-1574 p.Article in journal (Refereed) Published
Abstract [en]

Information on the diffusional transformation products of austenite in high-carbon steels is reviewed and supplemented with new microscopic studies. A comparison with transformation products in low-carbon steels indicates that there is a symmetry with pearlite in the middle, where ferrite and cementite are equal partners, and with acicular ferrite or cementite on each side. They both form with a surface relief, and at lower temperatures, each one is the leading phase in a eutectoid microstructure, bainite and inverse bainite, respectively. However, there is an asymmetry because at low temperatures bainite appears in high-carbon steels but inverse bainite never appears in low-carbon steels. At a constant high carbon content, there is another kind of symmetry, which is related to temperature. At intermediate temperatures the eutectoid reaction results in spherical nodules in which the cementite constituent originates from Widmanstatten plates. It turns spiky at both higher and lower temperatures with the leading phase in the spikes being cementite at higher temperatures and ferrite at lower temperatures. In the first kind of symmetry, there is an abrupt change among the three reaction products; in the second kind of symmetry, there is a gradual change. Accepting that all the eutectoid microstructures form by diffusion of carbon, one may explain the existence of both symmetries by the variation of the ratio of the supersaturations of ferrite and cementite with carbon content and with temperature.

Place, publisher, year, edition, pages
2011. Vol. 42A, no 6, 1558-1574 p.
Keyword [en]
HYPEREUTECTOID STEELS; LOWER BAINITE; DECOMPOSITION; MORPHOLOGY; ALLOYS; CARBON
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-33964DOI: 10.1007/s11661-010-0539-1ISI: 000290176100021Scopus ID: 2-s2.0-79958786497OAI: oai:DiVA.org:kth-33964DiVA: diva2:420142
Note
QC 20110531Available from: 2011-05-31 Created: 2011-05-23 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Low Temperature Austenite Decomposition in Carbon Steels
Open this publication in new window or tab >>Low Temperature Austenite Decomposition in Carbon Steels
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Martensitic steels have become very important engineering materials in modern society. Crucial parts of everyday products are made of martensitic steels, from surgical needles and razor blades to car components and large-scale excavators. Martensite, which results from a rapid diffusionless phase transformation, has a complex nature that is challenging to characterize and to classify. Moreover the possibilities for modeling of this phase transformation have been limited, since its thermodynamics and kinetics are only reasonably well understood. However, the recent development of characterization capabilities and computational techniques, such as CALPHAD, and its applicability to ferrous martensite has not been fully explored yet.

In the present work, a thermodynamic method for predicting the martensite start temperature (Ms) of commercial steels is developed. It is based mainly on information on Ms from binary Fe-X systems obtained from experiments using very rapid cooling, and Ms values for lath and plate martensite are treated separately. Comparison with the experimental Ms of several sets of commercial steels indicates that the predictive ability is comparable to models based on experimental information of Ms from commercial steels.

A major part of the present work is dedicated to the effect of carbon content on the morphological transition from lath- to plate martensite in steels. A range of metallographic techniques were employed: (1) Optical microscopy to study the apparent morphology; (2) Transmission electron microscopy to study high-carbon plate martensite; (3) Electron backscattered diffraction to study the variant pairing tendency of martensite. The results indicate that a good understanding of the martensitic microstructure can be achieved by combining qualitative metallography with quantitative analysis, such as variant pairing analysis. This type of characterization methodology could easily be extended to any alloying system and may thus facilitate martensite characterization in general.

Finally, a minor part addresses inverse bainite, which may form in high-carbon alloys. Its coupling to regular bainite is discussed on the basis of symmetry in the Fe-C phase diagram.  

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xii, 77 p.
Keyword
Carbon steels, Electron backscattered diffraction, Martensite, Microscopy, Microstructure, Thermodynamic modeling
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-100993 (URN)978-91-7501-449-4 (ISBN)
Public defence
2012-09-27, F3, Lindstedsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Hero-m
Note

QC 20120824

Available from: 2012-08-24 Created: 2012-08-22 Last updated: 2012-08-24Bibliographically approved
2. Does Bainite form with or without diffusion?: The experimental and theoretical evidence
Open this publication in new window or tab >>Does Bainite form with or without diffusion?: The experimental and theoretical evidence
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With the increased interest in bainitic steels, fundamental understanding of the bainite transformationis of major importance. Unfortunately, the research on bainite has been hampered by an oldcontroversy on its formation mechanism. Over the years two quite different theories have developedclaiming to describe the bainite transformation i.e. the diffusionless and the diffusion controlledtheory. In this thesis, attention is directed towards fundamental understanding of the bainitetransformation and both experimental and theoretical approaches are used in order to reveal its truenatureIn the first part of this thesis the symmetry in the Fe-C phase diagram is studied. It is based on ametallographic mapping of microstructures using light optical microscopy and scanning electronmicroscopy in a high carbon steel. The mapping revealed symmetries both with respect to temperatureand carbon content and an acicular eutectoid with cementite as the leading phase was found andidentified as inverse bainite. By accepting that all the eutectoid microstructures forms by diffusion ofcarbon, one may explain the existence of symmetries in the Fe-C phase diagram. Additional supportof its existence is obtained from an observation of symmetries in an alloyed steel. From the performedwork it was concluded that the existence of symmetries among the eutectoid microstructures fromaustenite supports the idea that bainite forms by a diffusion controlled transformation.In the second part the growth of bainite is considered. An experimental study using laser scanningconfocal microscopy was performed and growth rates of the transformation products from austenite ina high carbon, high chromium steel was analysed. The growth rate measurements reveals the kineticrelation between Widmanstätten cementite and the acicular eutectoid previously identified as inversebainite which confirms its existence and the conclusions drawn in the first part. In addition, in-situobservations of bainite formation below Ms provide additional support for the diffusion controlledtheory for bainite formation.The final part of the work is a study of the critical conditions for the formation of acicular ferrite.Based on experimental information found in the literature a thermodynamic analysis is performed inview of the two theories. The results demonstrate that the governing process for Fe-C alloys cannot bediffusionless but both kinds of processes can formally be used for predicting Bs temperatures for Fe-Calloys.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. viii, 46 p.
Keyword
Carbon steels, Bainite, Bainitic ferrite, Widmanstätten ferrite, Microstructure, Microscopy, Thermodynamic modeling
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-121344 (URN)978-91-7501-755-6 (ISBN)
Public defence
2013-05-24, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130503

Available from: 2013-05-03 Created: 2013-04-29 Last updated: 2013-05-03Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Authority records BETA

Borgenstam, Annika

Search in DiVA

By author/editor
Borgenstam, AnnikaHedström, PeterHillert, MatsKolmskog, PeterStormvinter, AlbinÅgren, John
By organisation
Physical Metallurgy
In the same journal
Metallurgical and Materials Transactions. A
Materials Engineering

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 187 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf