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
Empirical methods to predict bainite start conditions
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
Show others and affiliations
(English)Manuscript (preprint) (Other academic)
Abstract [en]

There are many empirical equations describing the effect of alloying elements on the bainite start temperature, Bs, without using Fe-C alloys as a reference. The numerical values of the resulting coefficients do not represent the physical effects of the elements. A new empirical equation is now derived by starting from binary Fe-C alloys from high temperatures, where acicular ferrite is regarded as Widmanstätten ferrite, and extrapolated to lower temperatures. It was accepted that this is not different from bainitic ferrite. Effects of alloying elements were added separately using information from ternary alloys. Information from sets of alloys with the same alloy content but different carbon contents proved particularly useful. Lines connecting such points were regarded as  lines for the respective alloy content and the effect of alloy elements was evaluated from their distances from the Bs line for Fe-C alloys. To compare the new equation with Steven and Haynes’, Bs information was collected and organized in two tables according to the experimental method with 258 entries of critical temperatures at fixed composition and 344 entries of critical temperatures at constant alloy content. The predictive abilities were similar but the new coefficients may be closer to the physical alloying effects.

Keywords [en]
Bainite, Start temperature, Empirical model
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-227694OAI: oai:DiVA.org:kth-227694DiVA, id: diva2:1205206
Note

QC 20180518

Available from: 2018-05-11 Created: 2018-05-11 Last updated: 2018-05-18Bibliographically approved
In thesis
1. Modeling Bainite Formation in Steels
Open this publication in new window or tab >>Modeling Bainite Formation in Steels
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This study examines the fundamental aspects of bainite formation in a guided effort to lay a foundation for development of a model capable of predicting bainite formation. In the first part of this study, the tenets of an existing model for growth, developed by Zener and later modified by Hillert are examined. A number of interacting and adjustable parameters are identified namely, diffusivity, driving force, radius of the ferrite plate tip, interfacial carbon content, and thermodynamic barriers. Amongst which, there are a number of assumptions which are no longer justifiable because of the availability of software and databases from which more accurate calculations can be obtained. The approximation of the driving force is one such example. Another is the carbon content in ferrite, which was assumed negligible. The capillarity effect of the curved ferrite interface had initially been assigned by Zener as having a fixed, optimal value at the maximum growth rate. Although this principle was kept it led to quite different results when the earlier approximations were removed. It is shown that the shape of the C-curves is largely dependent on the diffusivity.

The second focus of this thesis is aimed towards developing a model for the start temperatures of bainite, WBs and is achieved twofold. The first procedure was to develop an empirical model. Experimental information on which it is based refers to the start conditions for both bainite and Widmanstätten ferrite. A systematic approach is adapted by which Fe-C is the basis and the effect of alloying elements are evaluated separately from ternary alloys. Regression analysis of data on five ternary systems with Mn, Ni, Si, Cr and Mo gives separate coefficients. A linear empirical equation for the WBs is defined from their sum which was possible because their effects were independent. Carbon had by far the largest effect and Ni the smallest. The equation has good agreement with data but further improvement can be achieved with more reliable experimental data. The second procedure is directed towards a thermodynamic description of the start condition. The critical driving forces corresponding to the critical conditions depicted in the empirical equation are calculated. The results are presented with a dependence on temperature and the same could be translated to a carbon dependence. The critical driving force increases substantially with decreasing temperature and increasing carbon content and the effect of alloying elements is varied.

In the final section, the growth model is further developed. A more generalized expression for the barrier is formulated and together with the capillarity effect, consists of the energy requirement to move the growth interface. This is balanced with the available driving force and is solved with an optimization procedure. The predicted C-curves are compared with experimental results and reasonably good agreement is found.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 51
Series
TRITA-ITM-AVL ; 2018:16TSC-MT
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-227863 (URN)978-91-7729-779-6 (ISBN)
Public defence
2018-06-15, B3, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2018-05-15 Created: 2018-05-14 Last updated: 2018-05-18Bibliographically approved

Open Access in DiVA

fulltext(4238 kB)55 downloads
File information
File name FULLTEXT02.pdfFile size 4238 kBChecksum SHA-512
17c2d28ff3ffb288283e025ed333170d70c94c82c7e0e6b40a71fce4f0fece40aea139829346fe93c4d16fda7723393c4931ac374743e1e72d092f52897f0c3f
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Leach, Lindsay
By organisation
Materials Science and Engineering
Metallurgy and Metallic Materials

Search outside of DiVA

GoogleGoogle Scholar
Total: 55 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

urn-nbn

Altmetric score

urn-nbn
Total: 48 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