dc.contributor.author	Yamoah, Nana Kwame Gyan	en
dc.contributor.committeechair	Murayama, Mitsuhiro	en
dc.contributor.committeemember	Druschitz, Alan P.	en
dc.contributor.committeemember	Reynolds, William T. Jr.	en
dc.contributor.department	Materials Science and Engineering	en
dc.date.accessioned	2013-06-21T08:00:29Z	en
dc.date.available	2013-06-21T08:00:29Z	en
dc.date.issued	2013-06-20	en
dc.description.abstract	Redesigning heavy components with thinner components is one way to lower automotive weight and improve fuel efficiency. Therefore, replacing thick cast iron exhaust manifolds with thinner heat resistant stainless steel one is a prime example of this approach. Material for a thin exhaust manifold must tolerate cyclic thermal fatigue. In SUS 444, this characteristic is directly related to the influence of microstructure on high temperature strength and the stability of the microstructure at the high operating temperature range. The goal of this research is to identify the cause for the drastic difference in the stress-strain behavior between two potential manufacturer heat treatments that will serve as a simplified model case for high temperature cyclic fatigue. Transmission electron microscopy (TEM) based microstructure analyses of samples which have been aged at 750"C for 100 hours and then hot-tensile tested at 750"C with a strain rate of suggest continuous recrystallization as the mechanism responsible for the stable high temperature strength. The initial high temperature strength observed in the unaged sample was due to the precipitation of fine Laves phases which pinned down the motion of dislocations. As deformation progressed the strength increased until a critical precipitate size, volume fraction and dislocation density before Laves phases begun to rapidly coarsen and resulted in the abrupt decrease in strength. Microstructure evidence suggests the absence of precipitation strengthening effect in the aged samples could be a contributing factor to the decrease in peak strength between the aged samples and the unaged samples.	en
dc.description.degree	Master of Science	en
dc.format.medium	ETD	en
dc.identifier.other	vt_gsexam:817	en
dc.identifier.uri	http://hdl.handle.net/10919/23253	en
dc.publisher	Virginia Tech	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	High Temperature Strength	en
dc.subject	Laves Phase Precipitation	en
dc.subject	Dislocation Density	en
dc.subject	Continuous Recrystallization	en
dc.title	Microstructure Characterization of SUS444 Ferritic Stainless Steel	en
dc.type	Thesis	en
thesis.degree.discipline	Materials Science and Engineering	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	masters	en
thesis.degree.name	Master of Science	en

Microstructure Characterization of SUS444 Ferritic Stainless Steel

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