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Svetsförbandets struktur och dess mekaniska egenskaper - förhöjd arbetstemperaturs verkan vid svetsning
2004 (Swedish)Independent thesis Basic level (professional degree)Student thesis
Abstract [en]

The purpose of the theses is to see the consequences of a missing preheating and raised working temperature when welding used on a low-alloy material type SS2218 . The idea is based on the rumors that this would not affect the strength or that it is of limited importance if it does not happen. This though contradicts the facts that the steel manufacturers present and what earlier studies show. The work consists of welding together two samples with different conditions. Test 1 was welded according to the standards for the selected material, preheating temperature, suitable filler metal treated in a proper way, correct heat input and right interpass temperature. Test 2 was welded without following the proper guidelines to get a reliable result. Both samples were then sent through the standardized tests for welding and procedure. This consists of non destructive test as well as magnetic particle flaw detection and radiographic examination for cracks and internal inclusions. Destructive tests for the mechanical properties such as tensile strength, impact energy, hardness test and metallographic examination of weld was also done. In this case the result shows that preheating temperature makes no significant difference since both samples passed all tests without any remarks. Remarkable though is that the sample without preheating temperature passed the tests better regarding impact energy. This can partially be explained by the fact that the speed of cooling was faster through a critical temperature area and a small grain size was the result in the structure. Or that grain growth took place in the preheated spicemen due to lower cooling rate through the critical temperature range. The smaller grain size, the better for the impact energy. Since there is such thin line balancing the combination of cooling speed and other important parameters in the surrounding environment, such as temperature and moist the safest results will be reached following proper instructions. No preheating can in the worst case result in martensite formation. That, in combination with large grains and hydrogen, gives a brittle material, prone to crack formation.

Place, publisher, year, edition, pages
2004. , 53 p.
Identifiers
URN: urn:nbn:se:kau:diva-57129Local ID: MSK-13OAI: oai:DiVA.org:kau-57129DiVA: diva2:1121732
Subject / course
Mechanical Engineering, Bachelor of Science
Available from: 2017-07-12 Created: 2017-07-12

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