Fundamental Principals of Phase Transformations, Strength and Toughness in High-Strength 10 wt.% Ni Steels for US Naval Applications
Abstract
Funds are provided to study the strructure-properties-processing of 10-Ni steels, and to develop integrated com engineering models and supporting data.Research problem and objectives: We are proposing to employ a scientific physical metallurgy based approach in combination with Integrated Computational Materials Engineering (ICME) to elucidate the fundamental processes of phase transformations, microstructural evolution, and strengthening and toughening mechanisms in 10 wt.% Ni high-strength high-tou samples exposed to corrosive environments. Specifically, austenite reversion, carbide precipitation, formation and tempering of martensite, will be studied with a focus on how these processes affect mechanical properties, tensile strength, plasticity, fracture toughness, as a function of processing routes. Micro-segregation, homo- and heterophase-interfaces including martensite lath boundaries and prior austenite grain boundaries, and localized interfacial segregation, will be our focus because they are key factors governing the mechanical properties. We will study the microstructure in multi-pass weldments with a focus on the fusion zone and melt-pool, effects of solidification and thermal cycling on micro-segregation and microstructure in the weld filler and base metal. We will correlate the microstructural and atomistic results obtained from experiments, calculations and simulations (ICME) with the mechanical properties (yield strength, ultimate tensile strength, plasticity, toughness, and high- strain-rate deformation). We will study susceptibility and mechanisms of hydrogen-induced embrittlement and cracking, stress-corrosion cracking, and related corrosion phenomena in typical marine (saline) environments.Technical approaches: We will utilize correlated atom-probe tomography (APT) and transmission electron microscopy (TEM), optical microscopy, scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD), focused ion-beam (FIB) microscopy, synchrotron x-ray diffraction to capture the details of the microstructure and phase dispersions at all relevant length scales in the base 10 wt.% Ni steels specimens, and in multi-pass weldments, and corrosion exposed samples, and correlate these results with mechanical testing (microhardness, tensile and Charpy V-notch testing, high-strain rate deformatil be performed to model the atomistic energetics underlying phase transformations, interfacial segregation, and atomic interactions. The investigations will be performed in close collaboration with Drs. Matt Draper, Paul Lambert, Dan Bechetti and Mr. Matthew Sinfield at the Naval Surface Warfare Center Carderock (NSWCC) Division.Anticipated outcome of the research, if successful: The results of the detailed microstructural characterization of samples after the various processing and testing treatments will be compared and correlated with their mechanical properties, primarily microhardness, tensile testing and Charpy V-notch toughness for selected samples, and the results of computer simulations (ICME) to identify the physical metallurgical principles underlying the optimized microstructure and properties. The results will provide a guide as to how beneficial properties can be achieved and preserved during fabrication, welding, and in service.Impact on DoD capabilities: A fundamental physical metallurgical understanding of microstructure and mechanical properties in 10 wt.% Ni steels and how they are affected by heat treatment, welding, and in corrosive environments will inform optimized use and further development of applications and fabrication processes of these steels for Naval applications.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2021
- Source ID
- N000142112398
Entities
People
- David N. Seidman
Organizations
- Northwestern University
- Office of Naval Research
- United States Navy