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Fatigue Properties and Cleanliness of Powder Metallurgy High Speed Steel Fatigue Properties and Cleanliness of Powder Metallurgy High Speed Steel
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2012 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

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Fatigue is a phenomenon which causes failure of the material due to cyclic loads. Fatigue failure is often very sudden and catastrophic. It is the weakest point in the material that determines the fatigue strength. Fatigue failures are commonly initiated at internal defects such as inclusions and carbides in Powder Metallurgically (PM) produced High Speed Steels (HSS). The cleanliness of the steel, i.e. the inclusion content, is therefore of great importance as well as the size and distribution of the carbides.

 

The aim of this diploma work was to establish the fatigue strength of several PM HSS. The investigation was focused on understanding the dependence between fatigue strength and different cleanliness, sulfur content, carbide content, hardness, reduction rate and material anisotropy. The results were also compared to conventionally produced HSS.

 

Specimens were produced from ASP® 2023, ASP® 2005, ASP® 2005S, ASP® 2060, ASP® 2062 and M2. The material was divided into 11 test series, each containing 8-12 specimens. The role of fatigue strength was investigated for material from different capsules from a heat, in earlier produced and fatigue tested specimens of ASP® 2030 and ASP® 2023. The fatigue tests were performed using uniaxial tensile testing for 2 million cycles and the fatigue strength and standard deviation was calculated using the Dixon and Mood equations. The defects causing the fracture in the failing samples were examined using Scanning Electron Microscope (SEM). The microstructure, hardness, carbide content and surface roughness were also measured as well as the cleanliness which was measured by the use of MIC and DIN 50602 standards.

 

The fatigue tests showed that inclusions was the most common cause of fracture in PM HSS except for in one steel grade, (ASP 2062) where the failure was caused by carbide clusters. It could be seen that larger inclusions decreased the fatigue strength in steel grades where the fracture was caused by inclusions. From the fatigue tests it could also be seen that the material had better fatigue performance when tested along the rolling direction than it had when it was tested transverse to the rolling direction. By comparing PM HSS to conventionally cast HSS it could be seen that the PM production method generates a material with higher fatigue strength than what is achieved through conventional casting. This holds both for samples tested along the rolling direction and transverse to the rolling direction. Results from fatigue testing and SEM analysis were compared to results from MIC and DIN 50602 standards and it could be seen that these standards were not sufficient when trying to find inclusions that would affected the fatigue strength.

Place, publisher, year, edition, pages
2012. , 90 p.
Keyword [en]
Fatigue, powder metallutgy, HIP
National Category
Engineering and Technology Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-103216OAI: oai:DiVA.org:kth-103216DiVA: diva2:558999
Subject / course
Materials and Process Design
Educational program
Master of Science in Engineering - Materials Design and Engineering
Presentation
2012-07-23, 20:59 (Swedish)
Uppsok
Technology
Supervisors
Examiners
Available from: 2012-10-08 Created: 2012-10-05 Last updated: 2012-10-08Bibliographically approved

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