Understanding Low temperature Impact Toughness of 2.25Cr-1Mo steel Submerged Arc Welds
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The Ohio State University / OhioLINK
2015
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=osu1429879752 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu14298797522021-08-03T06:30:45Z Understanding Low temperature Impact Toughness of 2.25Cr-1Mo steel Submerged Arc Welds Mohan, Soumya Engineering Submerged arc welds Charpy Impact Toughness Granular Bainite Precipitate Evolution Slag Metal reactions Phase Transformations Targeted creep strength and low-temperature toughness are required to qualify 2.25Cr- 1Mo steel welding consumables relevant to the power generation industries. Submerged arc welding of 2.25Cr-1Mo steels using the same base metal, filler, welding parameters and post weld heat treatment but different fluxes was conducted to make multipass welds. These welds exhibit a drastic variation in low temperature Charpy impact toughness in the post weld heat treated condition (114 ft-lbs to 17 ft-lbs at testing temperature of -40°F). The difference in toughness behavior was investigated using computational modeling and multi-scale microstructure characterization.The effect of flux on the recovery of alloying elements including Cr, Mo, Mn and Si into the weld metal region was analyzed using computational thermodynamic models. Single and two pass welds were made to study the microstructures as a function of thermal cycling. Another study was conducted to control and physically simulate the tempering response of the weld metal by simulating a weld cooling rate of 5 °C/s and 30 °C/s (¿t8-5 of 60 s and 10 s) on welds. Phase transformation analysis was done. Phase identification, packet size determination and precipitate characterization were done. Charpy toughness and SEM fractography was conducted to determine fracture mode.The calculated weld composition as a function of weight % ratio of filler to flux composition was found to be in good agreement with the measured composition. The predicted alloying element recovery was very sensitive to the concentration of deoxidizers in the system including Al, Si and Mn. The single and two pass welds had a solidification substructure of “ghost” delta ferrite, which led to segregation of Cr and Mo away from the ghost delta ferrite structure. The as-solidified microstructure was found to be granular bainite. The precipitates M3C, M7C3 and M23C6 formed during post weld heat treatment. Charpy toughness variation was found in the two pass PWHT welds. The fracture surface of the Charpy failures of the poor toughness weld showed fracture along prior austenite grains.The microstructure of the simulated welds was found to be granular bainite with second phase constituents identified as retained austenite. It was seen that for the same simulated cooling rate (5°C/s), solid-state phase transformation behavior (austenite to bainite) was sluggish in the case of the poor toughness weld. A difference in the initial type of retained austenite was observed, with good toughness weld consisting of film type retained austenite, and poor toughness weld consisting of blocky austenite. The sluggish transformation behavior in the poor toughness weld metal translates to sluggish precipitation kinetics of the Fe-rich cementite precipitates as good weld showed higher cementite precipitate size than bad weld. A high variation in the Charpy toughness values between post weld heat treated welds was also corroborated by fracture mode analysis. It is postulated that the optimization of microstructure due to tempering is delayed in the poor toughness weld. This is due to lower carbon content in retained austenite in its initial microstructure. Longer tempering time should be able to improve the weld toughness. 2015-05-20 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1429879752 http://rave.ohiolink.edu/etdc/view?acc_num=osu1429879752 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
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NDLTD |
| language |
English |
| sources |
NDLTD |
| topic |
Engineering Submerged arc welds Charpy Impact Toughness Granular Bainite Precipitate Evolution Slag Metal reactions Phase Transformations |
| spellingShingle |
Engineering Submerged arc welds Charpy Impact Toughness Granular Bainite Precipitate Evolution Slag Metal reactions Phase Transformations Mohan, Soumya Understanding Low temperature Impact Toughness of 2.25Cr-1Mo steel Submerged Arc Welds |
| author |
Mohan, Soumya |
| author_facet |
Mohan, Soumya |
| author_sort |
Mohan, Soumya |
| title |
Understanding Low temperature Impact Toughness of 2.25Cr-1Mo steel Submerged Arc Welds |
| title_short |
Understanding Low temperature Impact Toughness of 2.25Cr-1Mo steel Submerged Arc Welds |
| title_full |
Understanding Low temperature Impact Toughness of 2.25Cr-1Mo steel Submerged Arc Welds |
| title_fullStr |
Understanding Low temperature Impact Toughness of 2.25Cr-1Mo steel Submerged Arc Welds |
| title_full_unstemmed |
Understanding Low temperature Impact Toughness of 2.25Cr-1Mo steel Submerged Arc Welds |
| title_sort |
understanding low temperature impact toughness of 2.25cr-1mo steel submerged arc welds |
| publisher |
The Ohio State University / OhioLINK |
| publishDate |
2015 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1429879752 |
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AT mohansoumya understandinglowtemperatureimpacttoughnessof225cr1mosteelsubmergedarcwelds |
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