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Effects of different heat treatments on hardness of Grade 91 steel
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
2014 (English)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesisAlternative title
Effekter av olika värmebehandlingar på hårdheten hos Grade 91 stål (Swedish)
Abstract [en]

CCI Valve Technology AB is a company located in Säffle, Sweden, that manufactures and installs bypass valves. Due to requirements outside normal standards on the valve's hardness values, some measurements have had difficulties meeting such requirements. During this thesis work, tests were carried out to determine how to overcome the difficulties. The experiments focused on five different areas that may affect the components hardness, welding method, soaking temperature during post weld heat treatment, measuring procedure, component thickness and number of heat treatment cycles. The Grade 91 steel specimens that were examined consisted of five solid cylinders and three various pipes that were welded together by using shielded metal arc welding (SMAW) or gas tungsten arc welding (GTAW). Each pipe was sawed apart into three equal parts. All specimens were hardness tested and eight of the specimens' microstructure was studied with an optical microscope. The hardness measurement instruments used, LECO V-100-C2 and GE-MIC 10, are Vickers hardness testers, one stationary and the other one portable. The measuring results contain a vast number of different hardness measurement data. From the analyzed data, the conclusions were drawn that the most suitable soaking temperature during post weld heat treatment were 750° C, that the SMAW method creates a more stable hardness profile than the GTAW method, and that one heat treatment cycle is more beneficial than two or more.

Place, publisher, year, edition, pages
2014. , 32 p.
Keyword [en]
Grade 91, Post weld heat treatment, Heat treatment cycles, Hardness
National Category
Metallurgy and Metallic Materials
URN: urn:nbn:se:kau:diva-32805OAI: diva2:727769
External cooperation
CCI Valve Technology AB
Educational program
Engineering: Mechanical Engineering, spec. in Materials Engineering (300 ECTS credits)
2014-06-11, Karlstad, 09:00 (Swedish)
Available from: 2014-06-23 Created: 2014-06-23 Last updated: 2014-06-23Bibliographically approved

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