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Control of Wear-Resistance Properties in Ti-added Hypereutectic High Chromium Cast Iron
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2012 (English)Licentiate 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 wear resistance and 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-added hypereutectic HCCI with a main composition of Fe-17mass%Cr-4mass%C is quantitatively studied based on the type, size distribution, composition and morphology of hard carbides and martensite units. 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) and electron backscattered diffraction (EBSD). Especially for the matrix structure, EBSD is a useful tool to classify the fcc (γ) and bcc (α) phases. 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. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , 44 p.
Keyword [en]
High Chromium Cast Iron, cooling rate, Ti addition, M7C3, TiC, carbides size distributions, volume fraction, heat treatment, microstructure, mechanical properties, wear resistance
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-105854ISBN: 978-91-7501-581-1 (print)OAI: oai:DiVA.org:kth-105854DiVA: diva2:572548
Presentation
2012-12-14, N111, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20121130

Available from: 2012-11-30 Created: 2012-11-28 Last updated: 2012-11-30Bibliographically approved
List of papers
1. Effect of cooling rate and Ti addition on the microstructure and mechanical properties in as-cast condition of hypereutectic high chromium cast irons
Open this publication in new window or tab >>Effect of cooling rate and Ti addition on the microstructure and mechanical properties in as-cast condition of hypereutectic high chromium cast irons
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2012 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 52, no 12, 2210-2219 p.Article in journal (Refereed) Published
Abstract [en]

The effect of cooling rate and Ti additions on the mechanical properties and carbides characteristics such as morphology, size distribution and composition was studied in high-chromium cast irons containing Fe-17 mass%Cr-4 mass%C. Based on the size distribution, composition and morphology, M 7C3 type carbides were roughly classified into "primary M7C3 carbides" and "eutectic M7C3 carbides" with a 11.2μ m border size. Thereafter, the change of the solidification structure and especially the refinement of carbides size were determined. It was found that both the size and number values should be summarized systematically for primary M 7C3 carbides and eutectic M7C3 carbides, respectively. Also, TiC carbides with a high formation temperature can not only act as a nuclei of M7C3 carbides, but they also contain a Ti(C, N) core. In the as-cast condition, the bulk hardness of the cast irons increases with an increased Ti content. In addition, the wear loss increases with an increased Ti content. Neither the bulk hardness nor the wear loss did change too much with an increased cooling rate.

Keyword
Carbides size distributions, Cooling rate, High chromium cast irons, M7C3, Ti addition, TiC
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-106214 (URN)10.2355/isijinternational.52.2210 (DOI)000312968000014 ()2-s2.0-84871814381 (Scopus ID)
Note

QC 20130118. Updated from accepted to published.

Available from: 2012-11-30 Created: 2012-11-30 Last updated: 2017-12-07Bibliographically approved
2. Effect of heat treatment on microstructure and mechanical properties of Ti-alloyed hypereutectic high chromium cast iron
Open this publication in new window or tab >>Effect of heat treatment on microstructure and mechanical properties of Ti-alloyed hypereutectic high chromium cast iron
Show others...
2012 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 52, no 12, 2288-2294 p.Article in journal (Refereed) Published
Abstract [en]

The effect of heat treatment on the microstructure and mechanical properties of Ti-alloyed hypereutectic High Chromium Cast Iron (HCCI) containing Fe-17 mass%Cr-4 mass%C-1.5 mass%Ti was investigated. 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) and electron backscattered diffraction (EBSD). It was found that the number of fine secondary M7C3 carbides with a size below 1 μm increases with lower holding temperatures and shorter holding times during heat treatment. The number of coarse primary M7C 3 carbides with a size above 11.2 μm increases with increasing holding temperatures and longer holding times. In addition, the number of TiC carbides increases with increasing holding times, and martensite units are more refined at longer holding times and lower holding temperatures, respectively. Moreover, the volume fraction of martensite increases with increased holding times. 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.

Keyword
Heat treatment, High Chromium Cast Iron, Mechanical properties, Microstructure, Particle size distribution, Wear resistance
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-106215 (URN)10.2355/isijinternational.52.2288 (DOI)000312968000025 ()2-s2.0-84871766093 (Scopus ID)
Note

QC 20130116. Updated from accepted to published.

Available from: 2012-11-30 Created: 2012-11-30 Last updated: 2017-12-07Bibliographically approved

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