E-Thesis 278 views
Galvanised Ultra High Strength Steel for Cold Formed Automotive Body in White Applications / JAMES AYRES
Swansea University Author: JAMES AYRES
DOI (Published version): 10.23889/SUthesis.63588
Abstract
The requirement of automotive manufacturers to downgauge material to save weight and lower vehicular emissions has led to the development of ever more complex advanced and ultra-high strength steels (AHSS/UHSS). Dual Phase (DP) steels have come to the fore in recent years due to their high strength...
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Swansea, Wales, UK
2023
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| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | EngD |
| Supervisor: | Penney, David., Evans, Peter. and Underhill, Richard. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa63588 |
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| Abstract: |
The requirement of automotive manufacturers to downgauge material to save weight and lower vehicular emissions has led to the development of ever more complex advanced and ultra-high strength steels (AHSS/UHSS). Dual Phase (DP) steels have come to the fore in recent years due to their high strength and initial strain hardening whilst achieving good elongation. Microstructurally these properties are achieved with a combination of a hard martensitic phase combined with a soft and ductile ferrite phase.This thesis focusses on silicon’s role on the microstructure and mechanical properties of DP steels whilst also optimizing the processing windows at Tata Steel’s continuous annealing processing line (CAPL), and the galvanising line, ZODIAC. Lab casts of DP800 steel with 0wt%, 0.2wt% and 0.4wt% silicon were cast and rolled to match industrial specifications, it was found that the increased silicon content led to a refined hot rolled microstructure with an increased volume fraction of pearlite. The finely dispersed pearlite allows for an increase in nucleation sites where it can transform to austenite during the soak section of the annealing cycle. This led to a more finely dispersed and higher volume fraction of austenite which on cooling transforms to martensite in the final product. The result was an increase in tensile strength from 790MPa to 900MPa with no marked change in elongation.Additionally, a DP cast chemistry with an increase in silicon produced and used in Tata Steel’s IJmuiden plant was trialled to achieve a viable DP1000 product through Zodiac. Whilst the grade did achieve the requirements in some trials, the variability when scaling to industrial processing would likely lead to mechanical property failures, outweighing the benefits. Trialling the same cast chemistry using optimized CAPL cycles led to the development of a novel high yield variant of DP1000, and a potential successful replacement to the current cast chemistry used to produce DP1000 at Tata Steel’s UK site. |
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| Keywords: |
Steel, Dual Phase, Annealing, Microstructure, Mechanical Properties |
| College: |
Faculty of Science and Engineering |