Multi-Dimensional Site-Specific and Correlative Studies of High-Strength High-Toughness Naval Steels
Abstract
Abstract Research at the Naval Surface Warfare Center Carderock Division (NSWCCD) by Dr. X. Jie Zhang has elegantly demonstrated that a 10 wt.% Ni steel with appropriate quenchlamellarization- tempering (QLT)-type heat treatments can achieve superior mechanical properties: 130 ksi yield strength and 158 ksi ultimate tensile strength, with a 23% elongation and 42 ft-lb Charpy V-notch toughness at -320oF (78 K or -196oC). This family of 10 wt.% Ni steels therefore has the potential to deliver improved strength and blast protection for Naval applications and for additional uses in cryogenic and energy systems (for example, liquefied natural gas). We are proposing to use a fundamental physical metallurgy scientific approach to elucidate the complex microstructures in this family of 10 wt.% Ni steels, consisting of reverted or precipitated austenite, ferrite, martensite or tempered martensite, and carbide precipitates. Our studies will capture the details of the phase dispersions on all relevant length scales. Homo- and heterophase interfaces between each of the phases or precipitates present, including martensite lath boundaries and prior austenite grain boundaries, and interfacial segregation at these boundaries, will be a focus because they represent a key factor governing phase transformations and their resulting mechanical properties. We will perform studies of how the microstructures of the QLT 10Ni steels are altered by welding, and the interrelationships between microstructure and performance in low-cycle fatigue or high-speed deformation. In addition to high-resolution characterization utilizing correlated atom-probe tomography (APT) and transmission electron microscopy (TEM) we will utilize optical microscopy, scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD), focused ion-beam (FIB) microscopy, synchrotron xray diffraction, mechanical testing (microhardness, tensile and Charpy V-notch testing, lowcycle and high-speed deformation), welding and weld simulations to obtain specimens representing relevant processing and in-service conditions. Computational thermodynamics (ThermoCalc) and first-principles calculations using the Vienna ab initio simulation package (via density-functional theory and general gradient approximation) will be utilized to model the atomistic energetics underlying phase transformations and interfacial segregation. We will correlate the microstructural and atomistic results obtained from experiments, calculations and simulations with the mechanical properties (yield strength, ultimate tensile strength, plasticity, toughness, fatigue and high-speed deformation) of these steels. Specifically, we are proposing to perform sophisticated research involving the following three targeted tasks: (1) The first task focuses on a detailed characterization of the microstructural elements, at all relevant length scales, and elucidating the phase transformations responsible for the microstructures providing the beneficial mechanical properties of QLT-heattreated 10 wt.% Ni steel, in collaboration with Dr. X. Jie Zhang (NSWCCD). First-principles calculations will help us to interpret the steels’ properties, microstructural features and their temporal evolution during processing steps as detected experimentally. For comparative purposes, we will also perform selected experiments characterizing HSLA-115. (2) The second task is dedicated to an understanding of the effects of welding on the microstructures and mechanical properties of 10 wt.% Ni steels, collaborating with Prof. John DuPont (Lehigh University) and continuing our past research on welding of NUCu-140. (3) The third task, centering on low-cycle fatigue and high-speed deformation, will continue our studies of adiabatic shear band (ASB) formation and deformation modes, in collaboration with Prof. K. Sharvan Kumar (Brown University) and Dr. X. Jie Zhang (NSWCCD).
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512443
Entities
People
- David N. Seidman
Organizations
- Northwestern University
- Office of Naval Research
- United States Navy