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
Control of Alloy Composition and Evaluation of Macro Inclusions during Alloy Making
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In order to obtain a good performance and predict the properties of alloys, it is necessary to control the contents of alloying elements and to evaluate a largest inclusion in the product. Thus, improved techniques for both control of alloy elements and evaluation of the large inclusion in products will enable us to provide better qualities of the final products.

In the case of one Ni alloy, (NW2201, >99 mass%Ni), the precise control technique of Mg content is important to obtain a good hot-workability. Hereby, the slag/metal reaction experiments in a laboratory have been carried out at 1873 K, so that the equilibrium Mg content and kinetic behavior can be understood. More addition of Al in the melt as well as higher CaO/Al2O3 value of slag resulted in higher amount of Mg content in Ni. For the same conditions of Al content and slag composition, the mass transfer coefficient of Mg in molten Ni was determined as 0.0175 cm/s. By applying several countermeasures regarding the equilibrium and kinetic process to the plant trials, the value of the standard deviation for the Mg content in an alloy was decreased till 0.003 from 0.007 mass%.

The size measurements of largest inclusions in the various alloys (an Fe-10mass%Ni alloy, 17CrMo4 of low-C steel and 304 stainless steel) were carried out by using statistics of extreme values (SEV). In order to improve the prediction accuracy of this method, three dimensional (3D) observations were applied after electrolytic extraction. In addition, the relationship of extreme value distribution (EVD) in the different stages of the production processes was studied. This was done to predict the largest inclusion in the products at an early stage of the process.

A comparison of EVDs for single Al2O3 inclusion particles obtained by 2D and 3D observations has clarified that 3D observations result in more accurate EVD because of the absence of pores. Also, it was found that EVD of clusters were larger than that of single particles. In addition, when applying SEV to sulfide inclusions with various morphologies, especially for elongated sulfides, the real maximum sizes of them were able to be measured by 3D observations. Geometrical considerations of these particles clarified the possibility of an appearance of the real maximum inclusion sizes on a cross section to be low. The EVDs of deoxidation products in 304 stainless steel showed good agreement between the molten steel and slab samples of the same heat. Furthermore, the EVD of fractured inclusion lengths in the rolled steel were estimated from the initial sizes of undeformed inclusions which were equivalent with fragmented inclusions. On the other hand, from the viewpoint of inclusion width, EVD obtained from perpendicular cross section of strips was found to be useful to predict the largest inclusion in the final product with less time consumption compared to a slab sample.

In summary, it can be concluded that the improvement of the techniques by this study has enabled to precisely control of alloy compositions as well as to evaluate the largest inclusion size in them more accurately and at an earlier stage of the production process.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , 53 p.
Keyword [en]
slag/metal reaction, equilibrium, kinetics, largest inclusion, statistics of extreme values, electrolytic extraction, cross section, inclusion morphology
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-27773ISBN: 978-91-7415-846-5 (print)OAI: oai:DiVA.org:kth-27773DiVA: diva2:380922
Public defence
2011-01-14, B1、, Brinellvägen 23, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101222Available from: 2010-12-22 Created: 2010-12-22 Last updated: 2012-03-28Bibliographically approved
List of papers
1. Development of Technology to Control Mg Content in Molten Nickel Alloy of NW2201
Open this publication in new window or tab >>Development of Technology to Control Mg Content in Molten Nickel Alloy of NW2201
2009 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 49, no 6, 837-842 p.Article in journal (Refereed) Published
Abstract [en]

Technology to precisely control Mg content has been developed to improve hot-workability of NW2201 Ni alloy. Relatively high standard deviation of Mg contents, 0.007, out of average Mg content of 0.02 mass% was problem among heats. This brought poor hot-workability leading to sliver-like surface defects on the strip when Mg content was relatively high or low. Laboratory-scale experiments were performed to understand the behavior of Mg in terms of equilibrium and mass-transfer of the slag/metal reaction of 3(MgO)+2Al=(Al2O3)+3Mg. Experiments were firstly carried out to understand Mg content in molten Ni equilibrated with CaO-Al2O3-MgO-CaF, system slags. It was found that Mg content in liquid Ni depended on Al content and C/A (CaO/Al2O3 ratio in mass%) in the slag. The measured Mg contents mostly agreed with thermodynamic calculation. Further, kinetic analysis was also undertaken experimentally by approaching from both higher and lower Mg contents to the equilibrium Mg content. As a result, mass-transfer of Mg in molten Ni is considered as the rate-determining step for the above reaction. By applying the countermeasures, introduced from the view points of both equilibrium and kinetics, for practice, the standard deviation of Mg content was improved from 0.007 to 0.003 among heats. Consequently, the defects have been improved successfully.

Keyword
NW2201, nickel, hot-workability, Mg, Al, slag, equilibrium, kinetics, mass-transfer
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-27766 (URN)10.2355/isijinternational.49.837 (DOI)000267402900012 ()
Note
QC 20101222Available from: 2010-12-22 Created: 2010-12-22 Last updated: 2017-12-11Bibliographically approved
2. Application of Extreme Value Analysis for Two- and Three-Dimensional Determinations of the Largest Inclusion in Metal Samples
Open this publication in new window or tab >>Application of Extreme Value Analysis for Two- and Three-Dimensional Determinations of the Largest Inclusion in Metal Samples
2011 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, no 4, 593-602 p.Article in journal (Refereed) Published
Abstract [en]

The maximum size of single inclusion particles and clusters in an Fe-10 mass% Ni alloy deoxidized with Al or Ti/Al were examined using extreme value analysis. The results obtained from conventional two-dimensional observations of inclusions on a polished cross section of metal sample (the CS-method) were compared to those from three-dimensional investigations of inclusions on a film filter after electrolytic extraction (the EE-method). It was found that the EE-method can successfully be used as a reference method for estimation of the probable maximum size of single inclusion particles and clusters by using an extreme value distribution (EVD). The EVD results for single inclusion particles obtained from the EE-method agreed satisfactorily well with those from a conventional CS-method. However, this required identification as well as neglect of pores on an investigated cross section of a metal sample. The predicted maximum size of single inclusion particles in a 1 mm(3) volume was confirmed by results from the EE-method.

Keyword
extreme value analysis, inclusion size, cross section, electrolytic extraction, single inclusion, cluster
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-27767 (URN)10.2355/isijinternational.51.593 (DOI)000289965600011 ()2-s2.0-79961048153 (Scopus ID)
Note
QC 20101222 Uppdaterad från accepted till published (20110520).Available from: 2010-12-22 Created: 2010-12-22 Last updated: 2017-12-11Bibliographically approved
3. Analysis of Largest Sulfide Inclusions in Low Carbon Steel by Using Statistics of Extreme Values
Open this publication in new window or tab >>Analysis of Largest Sulfide Inclusions in Low Carbon Steel by Using Statistics of Extreme Values
2011 (English)In: Steel Research International, ISSN 1611-3683, Vol. 82, no 4, 313-322 p.Article in journal (Refereed) Published
Abstract [en]

The statistics of extreme values was applied for the determination of the largest sulfide inclusions with different morphology in low carbon steel samples by using both two-dimensional (2D) observations on the polished cross section and three-dimensional (3D) observations on a surface of a film filter after electrolytic extraction of the samples. It was found that the globular, rod-like and dendritic sulfides in the molten steel sample as well as the elongated sulfides in the rolled steel sample can be successfully extracted from the both samples, and analyzed precisely by using extreme value analysis in 3D. Based on the geometrical considerations of the probability for measurement of the true length of rod-like and elongated inclusions on a cross section, it was found that this probability for inclusions decreases dramatically with an increasing real aspect ratio value of them. Particularly for the determination of the true length for elongated inclusions in the rolled steel sample by 2D investigations on a metal cross section, it is required to be cut investigating section of steel sample within +/- 1 degree against rolling direction. Therefore, a 3D observation is considered to be more preferable and accurate than the conventional cross sectional observation in 2D, due to the possibility for the measurements of the real size of them.

Keyword
aspect ratio, cross section, electrolytic extraction, extreme value analysis, maximum size, sulfide inclusion
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-33942 (URN)10.1002/srin.201000141 (DOI)000290050900002 ()2-s2.0-79953685471 (Scopus ID)
Note
QC 20110609Available from: 2011-06-09 Created: 2011-05-23 Last updated: 2012-03-28Bibliographically approved
4. Application of Statistics of Extreme Values for the inclusions in Type 304 Stainless Steel throughout the Steel Making Process
Open this publication in new window or tab >>Application of Statistics of Extreme Values for the inclusions in Type 304 Stainless Steel throughout the Steel Making Process
2010 (English)Report (Other academic)
Abstract [en]

Application of statistics of extreme values was applied to determine the inclusion sizes in Type 304 stainless steel. The samples taken from a tundish, slab and hot rolled steel in one heat were examined by using a cross sectional observation. In the molten steel sample, the extreme value distribution (EVD) containing two different types of inclusions, which are deoxidation products (SiO2-CaO-MgO-Al2O3) and reoxidation products (SiO2-MnO-Cr2O3), resulted in two different slopes in one EVD. Meanwhile, the inclusions in the slab sample provided a good linearity with respect to the EVD. The correlation coefficients of the regression lines for both the slab and rolled steel samples were found to increase with an increased number of measurements between 40 and 80. Based on the EVD data obtained from the slab and rolled steel samples, it was found that the EVD data for the area of fractured inclusions on a parallel cross section of rolled steel agrees well with that for the initial undeformed inclusions area in a slab sample. According to the geometrical considerations of morphological change of inclusion during the hot rolling, the EVD for the length of fractured inclusions after the rolling is possible to estimate from their initial sizes in the case of the fracture into the equivalent particle size.

Publisher
20 p.
Keyword
extreme value analysis, largest inclusion, regression line, correlation coefficient, hot rolling, fracture
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-27770 (URN)KTH/MSE--10/74--SE+APRMETU/AVH (ISRN)
Note
QC 20101222Available from: 2010-12-22 Created: 2010-12-22 Last updated: 2010-12-22Bibliographically approved
5. Estimation of inclusion size in stainless steel coil based on statistics of extreme values
Open this publication in new window or tab >>Estimation of inclusion size in stainless steel coil based on statistics of extreme values
2006 (English)In: Sohn International Symposium Advanced Processing of Metals and Materials, Vol 2 - THERMO AND PHYSICOCHEMICAL PRINCIPLES: IRON AND STEEL MAKING, 2006, 421-430 p.Conference paper, Published paper (Refereed)
Abstract [en]

It becomes more important to control the composition of inclusions with increasing the demand for quality of products in terms of cleanliness. Along with the development of refining technology to make inclusions harmless, a study was made to develop how to predict the quality of final products. At first, observations of a number of defects revealed that the defects were caused by inclusions larger than 100 mu m in diameter. Therefore it is required to detect relatively large inclusions in steel, whose existence is quite rare, to identify the quality. In order to estimate the maximum size of inclusions in a given sample, the method with statistics of extreme values has been applied for continuously cast (CC) stabs, hot-rolled coils and cold-rolled coils of type 304 stainless steel. For the CC slabs the diameter of inclusions, which were analyzed to be mostly silicate with globular shape, in the specimens was measured. For the coils, the width of inclusions was measured at the unit section perpendicular to rolling direction because it corresponds to the diameter assuming that the width of globular inclusions does not vary with rolled. Then maximum inclusion diameter in a specimen was calculated. As a result, the obtained values in the rolled coils are larger than in the slabs. This may imply that the measurement with the coils gives the values closer to the truth. Besides, the measurement with the coils is even faster than with the slabs due to its simplicity of preparation of the specimens.

Keyword
inclusion, statistics of extreme value, stainless steel, sliver, continuous casting
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-27772 (URN)000241805400037 ()
Conference
2006 TMS Fall Extraction and Processing Division: Sohn International Symposium; San Diego, CA; 27 August 2006 through 31 August 2006
Note
QC 20101222Available from: 2010-12-22 Created: 2010-12-22 Last updated: 2010-12-22Bibliographically approved

Open Access in DiVA

fulltext(2224 kB)596 downloads
File information
File name FULLTEXT01.pdfFile size 2224 kBChecksum SHA-512
e362e5463e29c86a87922a3468de70c78efe5c73fef7db8c65eb4fa5267cb24fc094042792c4d8edc1d180a0a68f4e196e02e36974b85cf6e94bee55688f4ba4
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Kanbe, Yuichi
By organisation
Applied Process Metallurgy
Metallurgy and Metallic Materials

Search outside of DiVA

GoogleGoogle Scholar
Total: 596 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

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 530 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