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Dynamic Precipitation Behavior of Secondary M7C3 Carbides in Ti-alloyed High Chromium Cast Iron
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
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, Applied Process Metallurgy.
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2013 (English)In: ISIJ International, ISSN 0915-1559, Vol. 53, no 7, 1237-1244 p.Article in journal (Refereed) Published
Abstract [en]

In-situ observations on the dynamic precipitation behavior of secondary carbides in Ti-alloyed High Chromium Cast Iron (HCCI) were performed by using a Confocal Laser Scanning Microscope (CLSM). Moreover, the detailed characterization of the microstructure before and after heat treatment was performed by using scanning electron microscopy (SEM). The secondary carbides, which precipitate from the matrix during heat treatment, were identified as M7C3 type carbides by using transmission electron microscopy (TEM). The number, size and volume of secondary carbides during heating, holding and cooling process were quantitatively evaluated based on the in-situ observation and SEM results. It was found that ferrite (alpha) and secondary carbides start to precipitate from the matrix at around 575 degrees C and 840 degrees C, respectively, during the heating process. In addition, the in-situ results showed that the number of secondary carbides increase with an increased heating temperature and time. Moreover, it was found that the size of these secondary carbides increase at higher temperatures and longer holding times. However, the number of secondary carbides increased with a decreased temperature. Finally, it was found that the volume fraction (similar to 5%) of secondary carbides was not changed to a large extent for the different heat treatment conditions being investigated.

Place, publisher, year, edition, pages
2013. Vol. 53, no 7, 1237-1244 p.
Keyword [en]
in-situ observation, CLSM, high chromium cast iron, secondary carbides, precipitation
National Category
Metallurgy and Metallic Materials
URN: urn:nbn:se:kth:diva-126904DOI: 10.2355/isijinternational.53.1237ISI: 000322208600019ScopusID: 2-s2.0-84883239697OAI: diva2:643097

QC 20130826

Available from: 2013-08-26 Created: 2013-08-22 Last updated: 2013-09-13Bibliographically approved
In thesis
1. Microstructure Evaluation and Wear-Resistant Properties of Ti-alloyed Hypereutectic High Chromium Cast Iron
Open this publication in new window or tab >>Microstructure Evaluation and Wear-Resistant Properties of Ti-alloyed Hypereutectic High Chromium Cast Iron
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High chromium cast iron (HCCI) is considered as one of the most useful wear resistance materials and their usage are widely spread in industry. The mechanical properties of HCCI mainly depend on type, size, number, morphology of hard carbides and the matrix structure (γ or α). The hypereutectic HCCI with large volume fractions of hard carbides is preferred to apply in wear applications. However, the coarser and larger primary M7C3 carbides will be precipitated during the solidification of the hypereutectic alloy and these will have a negative influence on the wear resistance.

In this thesis, the Ti-alloyed hypereutectic HCCI with a main composition of Fe-17mass%Cr-4mass%C is studied based on the experimental results and calculation results. The type, size distribution, composition and morphology of hard carbides and martensite units are discussed quantitatively. For a as-cast condition, a 11.2μm border size is suggested to classify the primary M7C3 carbides and eutectic M7C3 carbides. Thereafter, the change of the solidification structure and especially the refinement of carbides (M7C3 and TiC) size by changing the cooling rates and Ti addition is determined and discussed. Furthermore, the mechanical properties of hypereutectic HCCI related to the solidification structure are discussed.

Mechanical properties of HCCI can normally be improved by a heat treatment process. The size distribution and the volume fraction of carbides (M7C3 and TiC) as well as the matrix structure (martensite) were examined by means of scanning electron microscopy (SEM), in-situ observation by using Confocal Laser Scanning Microscope (CLSM), Transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). Especially for the matrix structure and secondary M7C3 carbides, EBSD and CLSM are useful tools to classify the fcc (γ) and bcc (α) phases and to study the dynamic behavior of secondary M7C3 carbides. In conclusion, low holding temperatures close to the eutectic temperature and long holding times are the best heat treatment strategies in order to improve wear resistance and hardness of Ti-alloyed hypereutectic HCCI.

Finally, the maximum carbides size is estimated by using statistics of extreme values (SEV) method in order to complete the size distribution results. Meanwhile, the characteristic of different carbides types will be summarized and classified based on the shape factor. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. 76 p.
High Chromium Cast Iron, cooling rate, Ti addition, M7C3, TiC, carbides size distributions, volume fraction, heat treatment, microstructure, mechanical properties, wear resistance, statistics of extreme values (SEV), maximum carbides size.
National Category
Engineering and Technology
urn:nbn:se:kth:diva-128532 (URN)978-91-7501-842-3 (ISBN)
Public defence
2013-09-27, B1, Brinellvägen 23, Kungliga Tekniska Högskolan, Stockholm, 13:00 (English)

QC 20130913

Available from: 2013-09-13 Created: 2013-09-12 Last updated: 2013-09-13Bibliographically approved

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