Development of a Cast 50 ksi (345 MPa) Yield Strength Low Alloy Steel with a Low Carbon Equivalent
Open Access
- Author:
- Snyder, Cody
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 08, 2019
- Committee Members:
- Robert Carl Voigt, Thesis Advisor/Co-Advisor
John C Mauro, Program Head/Chair
Allison Michelle Beese, Committee Member
Jingjing Li, Committee Member
Amy Carol Robinson, Special Signatory - Keywords:
- cast steel
HSLA cast steel
HSLA steel - Abstract:
- The purpose of this research was to develop a 50 ksi (345 MPa) Yield Strength (YS) cast steel with a carbon equivalent (CEAWS D1.1) of ≤ 0.45 wt. % CE to ensure that optimum weldability is maintained. A database of conventional C-Mn cast steel (ASTM A216 WCB grade specific cast steel) compositions and mechanical properties was analyzed to determine if these can meet YS and CE requirements, or if microalloying was needed. The database analysis found that only 0.41 % of the cast steels reached YS and CE requirements; thus, microalloying was needed to achieve YS and CE requirements. Microalloying effects of vanadium were understood further with Modified C-Mn and Modified C-Mn-V cast steels that had compositions based on previous literature work.1 These alloys were subjected to N&T and Q&T heat treatments (austenitizing at 1750 ˚F (955 ˚C) for 2 hr.), a tempering study, and special heat treatments that included: thick-section analysis, normalizing cooling rate study, and double normalizing. Optical microscopy was performed on both samples and there was precipitation hardening observed in the Modified C-Mn-V alloy for both N&T and Q&T conditions. The targeted chemistry for both alloys was not achieved by the casting foundry, this resulted in high CE for both alloys, 0.48 and 0.51 wt. % CE for Modified C-Mn and Modified C-Mn-V, respectively. Further work continued because these alloys did not meet YS and CE requirements. Next, Alloys C-F were developed with a focus on how much variation in composition is allowable to still achieve YS requirements, and they were tested for mechanical properties in the N&T and Q&T conditions. Alloy C and Alloy E met CE requirements with 0.39 and 0.44 wt. % CE, respectively. Alloy C earned a YS of 81 ksi (558 MPa) in the Q&T condition, but did not reach 50 ksi (345 MPa) in the N&T condition. Alloy E reached YS requirements in both the N&T and Q&T conditions. Thus, Alloy E has the optimum composition to achieve high weldability and 50 ksi (345 MPa) YS, with the following composition: 0.12 wt. % C, 1.04 wt. % Mn, 0.25 wt. % Si, 0.36 wt. % Cr, 0.06 wt. % Ni, 0.03 wt. % Mo, 0.06 wt. % Cu, and 0.11 wt. % V.