Stronger and higher strength steels are continuously being demanded by industry. A stronger steel enables less material to be used to meet structural requirements, allowing for both cost and weight savings. Through collaboration with Stelco, CanmetMATERIALS, and McMaster University, this project focused on the development of a Grade 80 (550MPa YS and 600MPa UTS) steel with elongation at fracture of 16%. The design space for the creation of the steel was limited to high-strength low-alloy and low-carbon steels that are compatible with batch-annealing processes.
To achieve this goal, two main strengthening methods were explored. The first method employed the use of precipitation hardening through microalloying additions of Mo, Nb, Ti, and V to form various metal carbide precipitates. The second method was based upon dislocation strengthening using recovery annealing and Ti to delay recrystallization.
Multi-scale characterization was used to quantify the strengthening mechanisms and to explain how the microstructural changes, features, and evolution affected the properties of the steel. Uniaxial tensile testing was performed to determine key mechanical properties, namely the yield strength, tensile strength, and elongation at fracture. Optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, electron backscatter diffraction, transmission electron microscopy, and atom probe tomography were utilized extensively for microstructural analysis to further quantify the steels.
The precipitation hardened steel reached a yield strength of 605MPa with 15.4% elongation at fracture for a 50mm gauge length. This was achieved using a cold rolling reduction of 66% followed by a heat treatment at 670°C for 24 hours.
The recovery-annealed steel obtained even better properties. It achieved a yield strength of 610MPa with a 19.6% elongation at fracture for a 25.4mm gauge length. A cold rolling reduction of 60% was used followed by a heat treatment at 550°C for 36 hours.
The strengthening mechanism for this steel is novel, and involves the slowing of recrystallization without Zener pinning nor solute decoration of dislocations. This thesis will hopefully bring upon new research into this mechanism. Furthermore, the properties of this recovery-annealed steel shows great promise for use in industry due to its high strength, good elongation, and low materials cost. Consequently, this steel could be the subject of substantial research in the near future. / Thesis / Master of Applied Science (MASc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/29397 |
| Date | January 2023 |
| Creators | Levy, Jared |
| Contributors | Zurob, Hatem, McDermid, Joseph, Materials Science and Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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