10% Nickel Steel for Enhanced Platform Capability: ICME Tools for Microstructure and Toughness Optim
Abstract
A new high-strength high-toughness steel, based on the Fe-10% Ni alloy system, has been developed and made available for a wide rang,e of demanding structural applications. Yield strength in the range of 125 to 150 ksi and superior toughness are achieved through at,hree-step quenching, lamellarization, and tempering (QLT) heat treatment that provides microstructure of tempered martensite with in,terlath nano-scale austenite. A welding filler metal with matching Fe-10Ni composition was recently developed, patented, and commerc,ialized. It was demonstrated that Fe-10Ni weld metal deposited using GTAW and GMAW processes can match the base metal mechanical pro,perties.The phase transformation behavior, microstructure, and mechanical properties of base metal heat affected zone (HAZ) and weld, metal of the Fe-10Ni steel were investigated to facilitate its implementation in welded structures. The base metal HAZ exhibited a, significant impact toughness drop in the intercritical temperature range, which was related to formation of brittle high carbon mar,tensite. Improved toughness and lower strength in higher temperature HAZ regions were attributed to the competing effects of more un,iform carbon distribution in the martensitic microstructure and reduction in the retained austenite content.Fe-10Ni welds fabricated, using GTAW and GMAW processes have demonstrated excellent low temperature toughness. However, GMAW weld metal has exhibited notably, lower impact toughness than that of GTAW weld metal. It was found that the weld metal toughness is dependent on the oxide content,t,he effective grain size of the martensitic microstructure, and the presence of coarse martensite in reheated weld metal regions. Com,pared to GTAW, the coarse irregularly-shaped beads in GMAW-spray welds experienced non-uniform reheating during multipass welding.Th,is resulted in significant variations in the degree of recrystallization and tempering, which is reflected by the grain size and har,dness distribution and led to reduced toughness. Based on the results of these investigations, it is expected that reducing toughnes,s variability in groove Fe-10Ni steel groove welds, fabricated using high deposition rate process such as GMAW, through typical tri,al and error techniques would be challenging. To address this challenge, the proposed research will develop an integrated Computatio,nal Materials Engineering (ICME) tool for process-microstructure-property optimization in groove welds. This ICME tool will incorpor,ate finite element analysis (FEA) models of grove welding and predictive thermal history-microstructure-property relationships for F,e-10Ni weld metal within a module for computational design of experiment (DoE). Computational DoE studies with the ICME tool will de,velop optimized welding procedures for production of welds with improved microstructure and impact toughness. A groove weld in Fe-10,Ni steel will be fabricated using one of the optimized welding procedures and subjected to mechanical testing and metallurgical char,acterization. Successful demonstration of such weld will support the ongoing ONR-funded activities at NSWCCD under the FY22 Technica,l Candidate Program entitled: 10% Nickel Steel for Enhanced Platform Capability. Additionally, the developed ICME tool for process-m,icrostructure-property optimization in groove welds will be material-agnostic, such that it can be applied beyond the scope of this, project in optimization of other welding processes and of weld properties in other alloys.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 08, 2022
- Source ID
- N000142212708
Entities
People
- Boian S Alexandrov
Organizations
- Office of Naval Research
- Ohio State University
- United States Navy