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dc.contributor.advisorLiu, Stephen
dc.contributor.authorSham, Kin-Ling
dc.date.accessioned2007-01-03T06:27:53Z
dc.date.accessioned2022-02-09T08:54:42Z
dc.date.available2007-01-03T06:27:53Z
dc.date.available2022-02-09T08:54:42Z
dc.date.issued2014
dc.date.submitted2014
dc.identifierT 7512
dc.identifier.urihttps://hdl.handle.net/11124/12257
dc.description2014 Spring.
dc.descriptionIncludes illustrations (some color).
dc.descriptionIncludes bibliographical references (pages 138-143).
dc.description.abstractStriving for higher strength along with higher toughness is a constant goal in material properties. Even though nickel is known as an effective alloying element in improving the resistance of a steel to impact fracture, it is not fully understood how nickel enhances toughness. It was the goal of this work to assist and further the understanding of how nickel enhanced toughness and maintained strength in particular for high strength low alloy (HSLA) steel submerged arc welding multiple pass welds in the as-welded condition. Using advanced analytical techniques such as electron backscatter diffraction, x-ray diffraction, electron microprobe, differential scanning calorimetry, and thermodynamic modeling software, the effect of nickel was studied with nickel varying from one to five wt. pct. in increments of one wt. pct. in a specific HSLA steel submerged arc welding multiple pass weldment. The test matrix of five different nickel compositions in the as-welded and stress-relieved condition was to meet the targeted mechanical properties with a yield strength greater than or equal to 85 ksi, a ultimate tensile strength greater than or equal to 105 ksi, and a nil ductility temperature less than or equal to -140 degrees F. Mechanical testing demonstrated that nickel content of three wt. pct and greater in the as-welded condition fulfilled the targeted mechanical properties. Therefore, one, three, and five wt. pct. nickel in the as-welded condition was further studied to determine the effect of nickel on primary solidification mode, nickel solute segregation, dendrite thickness, phase transformation temperatures, effective ferrite grain size, dislocation density and strain, grain misorientation distribution, and precipitates. From one to five wt. pct nickel content in the as-welded condition, the primary solidification was shown to change from primary delta-ferrite to primary austenite. The nickel partitioning coefficient increased and dendrite/cellular thickness was refined. Austenite decomposition temperatures into different ferrite products were also suppressed to refine the effective ferrite grain size with increasing nickel. Finally, dislocation density and strain increased and a more preferred orientation behavior was observed. At five wt. pct nickel, a precipitate in the form of MnNi3 or FeNi3 was observed. Its presence in both inter and intragranular regions enhanced strength and toughness by limiting the ferrite grain size and precipitation strengthening.
dc.format.mediumborn digital
dc.format.mediumdoctoral dissertations
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado School of Mines. Arthur Lakes Library
dc.relation.ispartof2014 - Mines Theses & Dissertations
dc.rightsCopyright of the original work is retained by the author.
dc.subjectHSLA steels
dc.subjectsubmerged arc welding
dc.subjectstrengthening and toughening
dc.subjectnickel
dc.subject.lcshSteel, High strength
dc.subject.lcshNickel steel
dc.subject.lcshSubmerged arc welding
dc.subject.lcshMetals -- Microstructure
dc.subject.lcshSteel -- Welding
dc.titleAdvanced characterization techniques in understanding the roles of nickel in enhancing strength and toughness of submerged arc welding high strength low alloy steel multiple pass welds in the as-welded condition
dc.typeText
dc.contributor.committeememberOlson, D. L. (David LeRoy)
dc.contributor.committeememberMishra, Brajendra
dc.contributor.committeememberFindley, Kip Owen
dc.contributor.committeememberSteele, John P. H.
dc.contributor.committeememberYoung, George
thesis.degree.nameDoctor of Philosophy (Ph.D.)
thesis.degree.levelDoctoral
thesis.degree.disciplineMetallurgical and Materials Engineering
thesis.degree.grantorColorado School of Mines


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