Fundamental Studies on Phase Transformations and Mechanical Properties of Fusion Welds in the 10 wt% Ni Steel System
Abstract
Fundamental Studies on Phase Transformations and Mechanical Properties of Fusion Welds in the 10 wt% Ni Steel SystemFunds are provided to study the microstructure evolution and associated physical and mechanical properties associated with fusion welds in Ni- and Cu-bearing steels.The results of this research will form the basis for further development of this alloy system for naval applications. The investigator has organized the project into four tasks.In task 1, Detailed Microstructural Characterization of Weld Samples, the investigator will characterize existing weld samples prepared at the Naval Surface Warfare Center ~ Carderock Division. These contain a wealth of information that can be used as a starting point for separating the possible effects of various microstructural features on impact toughness. In this task, the gas-tungsten-arc and gas-metal-arc welds will be obtained from Naval Surface Warfare Center ~ Carderock Division and used for detailed microstructural characterization using a variety of techniques.Task 2 is Controlled Thermal Cycle Studies. As described in Task 1, observations made to date suggest that the relatively poor toughness in the gas-metal-arc welds may be attributed to an overall coarser microstructure, the presence of coalesced martensite, and/or a high population of oxides. The objectives of Task 2 are to use the Gleeble for controlled heating/cooling studies to determine the influence of thermal cycle characteristics (heating rate, peak temperature, cooling rate) on the relative amount of lath martensite, coalesced martensite and overall microstructural scale. The investigators will then use the information from these controlled experiments to determine if the relatively low impact toughness in the gas-metal-arc welds is due to the higher oxide content or coarser microstructure.In the third task, Microstructural Modeling, the investigator will conduct several different types of simulations from their suite of capabilities to provide an improved understanding of the experimental results from Task 1 and 2. Simple phase stability vs. temperature calculations will first be conducted as a baseline case. Non- equilibrium solidification simulations will then be conducted using the Scheil-Gulliver model in ThermoCalc in order to understand the extent of microsegregation expected in the as-solidified condition. The composition profiles generated in ThermoCalc will also be used as inputs into the DICTRA kinetic modeling code to model several phenomena, including: potential relaxation of microsegregation during repetitive weld thermal cycles, influence of microsegregation on local variations in microstructural development during subsequent weld thermal cycles, and precipitate dissolution and reformation. The simulated welding cycles will be produced using the SmartWeld modeling code, which was developed based on analytical solutions to the conduction heat flow equation. The results from these simulations can be directly compared to a number of the experimental measurements described in Task 1, including retained austenite content and morphology, composition gradients in the as-solidified conditions, composition gradients after multiple thermal cycles, and amount/type of secondary phases.Task 4 consists of Studies to Optimize GMA Weld Metal Microstructure. The objective of this task is to utilize results from the research tasks described above to develop as-deposited weld microstructures with optimal toughness. The approach to this task will depend on results of Tasks 1 through 3 and will likely include systematic studies to explore the influence of composition and weld thermal cycles.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 23, 2016
- Source ID
- N000141612633
Entities
People
- John DuPont
Organizations
- Lehigh University
- Office of Naval Research
- United States Navy