Show simple item record

dc.contributor.advisorDe Moor, Emmanuel
dc.contributor.authorGolden, Alex
dc.date.accessioned2017-07-20T19:38:23Z
dc.date.accessioned2022-02-03T12:59:54Z
dc.date.available2017-07-20T19:38:23Z
dc.date.available2022-02-03T12:59:54Z
dc.date.issued2017
dc.identifierGolden_mines_0052N_11288.pdf
dc.identifierT 8304
dc.identifier.urihttps://hdl.handle.net/11124/171139
dc.descriptionIncludes bibliographical references.
dc.description2017 Summer.
dc.description.abstractResearch and development by users of heavy section forgings in the oil and gas industry has found deficiencies in both strength and low temperature toughness in ASTM A694 flanges. Microalloying, specifically with vanadium, has been identified as a possible means of improving the strength and toughness combinations possible in these products. Understanding the properties of heavy section forgings is complicated due to the thermal gradient across the thickness of the forging during heat treatment, resulting in different microstructural features and different mechanical properties developing at different locations in the forging. The goal of this research is to identify the possible causes of low toughness and strength in this class of products by examining the through thickness microstructure and mechanical properties of an alloy with similar chemical composition to those commonly used for heavy section flanges. Samples with thermal profiles representing various positions of forgings were examined before and after several tempering treatments. Microstructural examination and precipitate characterization was performed to correlate strength and toughness measurements to microstructural changes during tempering. The study revealed that the conditions representative of fast post austenitizing cooling rates contained ferrite and martensite, with the martensite becoming heavily tempered even after a relatively short tempering treatment of 0.5 hour at 600 °C. Evidence of cementite spheroidization emerged after the short tempering time. These samples possessed low as-quenched toughness and a gradual ductile to brittle transition; a significant increase in toughness was observed after tempering. Tensile testing of the samples with fast post austenitizing cooling rates show roundhouse yielding in the as-quenched state associated with the presence of martensite, and a subsequent increase in yield strength, yield point elongation, and decrease in ultimate tensile strength after tempering. The samples representative of slower post austenitizing cooling rates contained microstructures of ferrite and pearlite and showed resistance to tempering even after a tempering treatment of 5 hours at 600 °C. Evidence of some breakdown of the pearlite lamellae was present during tempering but the effect was not significant. Impact testing revealed low toughness in the as-quenched state for samples representing slow post austenitizing cooling rates and a sudden ductile to brittle transition temperature. Tempering lowered the ductile to brittle transition temperature enough so that all samples would pass the ASTM standard for toughness specified for heavy section flanges. The results of tensile testing showed no appreciable effect of tempering on the yield strength or tensile strength of samples representing slow post austenitizing cooling rates. The length of the tempering treatment did not appear to have a significant effect on the yield or tensile strength of any of the slow cooled samples. A tempering treatment of 0.5 hour at 600 °C did change the yield and tensile strength of the samples representing fast post austenitizing cooling rates. The effect of tempering on the yield and tensile strength of the fast cooled samples was not increased at longer tempering times. Tempering raised the impact toughness of all samples to levels that would pass industrial standards for toughness, where as many commercially produced forgings are unable to meet these standards. The samples used in this study were machined from hot rolled bars and heat treated whereas commercially produced flanges are often pierced billets that are then ring rolled. The toughness results in this study suggest the possibility that forging reduction in commercially produced flanges is insufficient to produce the amount of refinement needed to meet the strength and toughness requirements required by end users.
dc.format.mediumborn digital
dc.format.mediummasters theses
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado School of Mines. Arthur Lakes Library
dc.relation.ispartof2017 - Mines Theses & Dissertations
dc.rightsCopyright of the original work is retained by the author.
dc.subjectmicroalloy
dc.subjectmetallurgy
dc.subjectsteel
dc.titleEffect of heat treatment on the through thickness properties of vanadium microalloyed forging steels, The
dc.typeText
dc.contributor.committeememberFindley, Kip Owen
dc.contributor.committeememberSpeer, J. G.
thesis.degree.nameMaster of Science (M.S.)
thesis.degree.levelMasters
thesis.degree.disciplineMetallurgical and Materials Engineering
thesis.degree.grantorColorado School of Mines


Files in this item

Thumbnail
Name:
Golden_mines_0052N_11288.pdf
Size:
4.599Mb
Format:
PDF

This item appears in the following Collection(s)

Show simple item record