Abstract
HSLA-115 is a novel high-strength low-alloy structural steel derived from martensitic Cu-bearing HSLA-100. HSLA-100 is typically used in conditions with overaged Cu precipitates, to obtain acceptable impact toughness and ductility. Present work on HSLA-115 demonstrates that incorporating sub-nanometric-sized M2C carbides along with Cu precipitates produces higher strength steels that still meet impact toughness and ductility requirements. Isothermal aging at 823 K (550 °C) precipitates M2C carbides co-located with the Cu precipitates and distributed heterogeneously at lath boundaries and dislocations. 3D atom-probe tomography is used to characterize the evolution of these precipitates at 823 K (550 °C) in terms of mean radii, number densities, and volume fractions. These results are correlated with microhardness, impact toughness, and tensile strength. The optimum combination of mechanical properties, 972 MPa yield strength, 24.8 pct elongation to failure, and 188.0 J impact toughness at 255 K (−18 °C), is attained after 3-hour aging at 823 K (550 °C). Strengthening by M2C precipitates offsets the softening due to overaging of Cu precipitates and tempering of martensitic matrix. It is shown that this extended yield strength plateau can be used as a design principle to optimize strength and toughness at the same time.
Original language | English (US) |
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Pages (from-to) | 3860-3872 |
Number of pages | 13 |
Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
Volume | 47 |
Issue number | 8 |
DOIs | |
State | Published - Aug 1 2016 |
Funding
The authors gratefully acknowledge financial support for this research by the Office of Naval Research through Grant Number N00014-12-1-0475 and useful discussions with the Program Manager, Dr. William Mullins, of the Office of Naval Research. LEAP measurements were performed at the Northwestern University Center for Atom-Probe Tomography (NUCAPT). The LEAP tomograph at NUCAPT was purchased and upgraded with funding from Grants NSF-MRI (DMR-0420532) and ONR-DURIP (N00014-0400798, N00014-0610539, N00014-0910781). Instrumentation at NUCAPT was supported by the Initiative for Sustainability and Energy at Northwestern University. This research made use of Northwestern’s NUANCE-EPIC and OMM facilities. NUCAPT, EPIC, and OMM received support from the MRSEC program (NSF DMR-1121262) through Northwestern’s Materials Research Center. EPIC received support from the International Institute for Nanotechnology (IIN) and the State of Illinois, through the IIN.
ASJC Scopus subject areas
- Condensed Matter Physics
- Mechanics of Materials
- Metals and Alloys