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Title: Bake hardening in ultra-low and super ultra-low carbon steels
Author: Baker, L. J.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2001
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Review of the current literature identified key aspects of bake hardening steels that required further investigation. The test procedures used to characterise bake hardening steels are not standardised across the steel industry and have been investigated in this project, to ensure results obtained accurately reflect the in-service performance of the steel. The emphasis of research world-wide is on the development of super ultra-low carbon (SULC) bake hardening steel chemistries and a Nb-Ti stabilised steel of this type has been investigated in this programme. The influence of steel metallurgy and processing conditions on the properties of this steel have been studied, with an aim to optimising the bake hardening response obtained. The solute carbon content of a range of strip steels could be accurately measured using internal friction apparatus, allowing this equipment to be used as both a scientific and quality control tool. The bake hardening test procedure was investigated and it was found that variation in test parameters resulted in a 5N/mm2 variation in bake hardening response. Based on this, recommendations have been made for standardisation of the bake hardening test. The developmental Nb-Ti SULC bake hardening grade was studied to determine the metallurgical and processing areas that most influenced the bake hardening response. A two stage ageing process was identified and it was shown that this could be exploited to produce a higher bake hardening response, whilst maintaining room temperature ageing resistance. Grain size did not influence the bake hardening properties of this steel, although fine grain size did offer an improvement in room temperature ageing resistance. Continuous annealing at temperatures above 800°C improves the bake hardening response of under-stabilised Nb-Ti SULC bake hardening steel, reducing yield losses. Temper rolling of at least 1% offers adequate control of properties in this steel, ensuring it meets all of the customer specifications.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Eng.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available