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Effect of mill quenching practises on weld HAZ properties in duplex 2205 stainless steel
2000 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

In this diploma work the properties of the Low Temperature Heat Effected Zone (LTHAZ) of duplex stainless 2205 hot rolled plate of 15mm thickness have been investigated. The steel has been studied in three different conditions: first solution heat-treated in all three cases then: air cooled in the mill, water quenched in the mill and lab quenched. The aim of the study is to examine if the longer time spent in the susceptible temperature range of 950-550°C by the air-cooled plate will increase the susceptibility to secondary phase formation during subsequent welding. The results may also be used to set the upper limit for weld energy before ductility and corrosion resistance decreases. After Gleeble simulations with different weld thermal cycles, where the peak temperature (Tp) and the time between 800 and 500°C during cooling have been varied, the impact strength at –46°C has been tested. The material has also been corrosion tested according to ASTM G150 in the Avesta Cell and according to ASTM G48 ferric chloride testing. The results show that the grade 2205 is relatively insensitive for long time spent in the 950-550°C-temperature interval, both during welding and when isothermally treated. As expected, the impact toughness and corrosion properties decrease with longer time in the temperature interval. One exception is the surface corrosion resistance measured in the Avesta cell where the properties remain unchanged even after very long time in the temperature interval. Looking at impact toughness the mill air-cooled plate is affected first which is shown by a marked drop in the impact toughness curve. The mill water-cooled and the lab water quenched plate has a similar drop in impact toughness after a longer time. The time difference correlates well with the longer time the mill air-cooled plate spent in the susceptible temperature region during cooling after solution treatment. The ferric chloride testing shows similar results, where the mill air-cooled plate shows lower values over all followed by the mill water-cooled plate. Also here the longer time spent in the susceptible temperature range during cooling after solution treatment correlates with the difference in simulated weld thermal cycle time before the drop in corrosion properties for the different plates. When connecting the simulated welding thermal cycles to welding energy, it is clear that the 2205 can take much higher weld energy, before the corrosion- and impact properties decreases, than that recommended. Due to the very long weld cycle time before any decrease in properties, the effect of letting the 15mm plate air cool instead of quenching with water will only give negligible effects on the properties on the 2205 plate. Investigations of the material have been performed with LOM to measure intermetallic phase content after different thermal cycles. SEM has been used to identify some of the precipitates and measure differences in composition in the middle of the plate and closer to the surface. There is a connection between the amount of precipitated intermetallic phase, impact toughness and corrosion properties.

Place, publisher, year, edition, pages
2000.
Keyword [en]
Technology, Stainless steel, 2205, duplex, Gleeble thermomechanical, simulator, impact toughness, corrosion testing, hot rolled, plate, SEM, LOM, segregations, thermal cycles, HAZ, welding
Keyword [sv]
Teknik
Identifiers
URN: urn:nbn:se:ltu:diva-56849ISRN: LTU-EX--00/126--SELocal ID: d97fe115-cdb8-42a3-b190-84e20fb7e80bOAI: oai:DiVA.org:ltu-56849DiVA: diva2:1030236
Subject / course
Student thesis, at least 30 credits
Educational program
Civil Engineering programmes 1997-2000, master's level
Examiners
Note
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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