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Title: The weldability of high and ultra high strength steel
Author: Anderson, C. M.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2003
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Weight reduction in body-in-white structures is necessary to make automobiles more fuel-efficient. A range of high and ultra-high strength strip steels have been developed, that will play a key role in achieving lower weights since the steels have the potential to achieve equivalent strength and crashworthiness at thinner gauges. However, the full potential of these advanced alloys can only be realised if they can be integrated into production facilities that rely on resistance spot welding as the predominant means of component joining. In particular, spot welds manufactured in these modern high strength steels will need to meet the strength and fracture resistance requirements that are based on automotive manufacturers' familiarity with low alloy steels. Dual phase steels are a range of modern alloys causing considerable excitement due to their combination of high strength, high ductility and improved crashworthiness in automotive components, compared to mild steel. Their commercial production routes rely on a metallurgical understanding of how chemical composition and thermomechanical treatments interrelate to produce appropriate microstructures. Their often complex alloy compositions mean that there is potential for significant changes to take place in the microstructure on resistance welding. This research programme has considered the important relationships from which resistance spot-welds, produced in high strength steels, derive their properties. This includes an investigation into the continuous cooling transformation behaviour of four dual phase alloys, in comparison to low alloy grades, and measurement of the mechanical properties associated with their microstructures. The thermal profiles generated within spot welds have been measured using a thermocouple technique. Advanced resistance spot welding processes, that can modify the metallurgical condition of a spot-weld, have been investigated with some success, both in terms of reductions in weld hardness following pulsed welding schedules, and an understanding of the effect of such schedules on the thermal cycle.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Eng.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available