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Comparative study of defect size detected by ultrasonic testing and actual size extracted by fatigue testing
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2018 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

In today’s steel industry the size and amount of defects are crucial parameters for manufacturing high quality steel. This is referred to as the cleanliness level of the material. Metallographic analysis (two-dimensional) is by far the most common method to measure this level. However, developments in ultrasonic testing (UT) has made in possible to analyze a fairly large volume (three- dimensional) for defects. The purpose of this thesis is to determine the reliability of defect sizing using 25 MHz ultrasonic testing at Erasteel Kloster AB, in Söderfors. By using a new extraction method, the actual defect size is determined by mechanical fracture using fatigue testing.

The results show that the size ratio (UT-size/actual size) varies from approximately 0.5-2 with a lot of scattered data. The scattered data could be explained by the difficulty of placing the detected inclusion in the waist of the fatigue sample. The experimental work shows, supported by theoretical claims in literature, that defects can only be detected when there is void surrounding the defect. Meaning, defects can only be detected when the degree of wetting is low. Moreover, carbides and carbide clusters in both conventional high-speed steels and powder metallurgical high-speed steels cannot be detected using ultrasonic testing due to good wetting and low acoustic impedance mismatch. This work also suggests method improvements for calibration and defect sizing using ultrasonic testing.

Due to confidentiality the report is not published. For information regarding full text report, please contact Johanna André at Erasteel Kloster AB.

Place, publisher, year, edition, pages
2018. , p. 48
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-231381OAI: oai:DiVA.org:kth-231381DiVA, id: diva2:1227851
External cooperation
Erasteel Kloster AB
Educational program
Master of Science in Engineering - Materials Design and Engineering
Supervisors
Examiners
Available from: 2018-06-27 Created: 2018-06-27 Last updated: 2018-06-27Bibliographically approved

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