Weldability of FeMnAl Alloys for Armor Applications
The U.S. ARMY CCDC-GVSC has been developing and optimizing a light-weight alternative to HRA armor steels currently employed by the defense industry under MIL DTL 12560. This new steel is based on the Fe-Mn-Al ternary system with additions of C to provide higher strengths. Through high additions of Al the density of the steel is decreased to allow an overall reduction in weight of armor materials without compromising its armor functionality .
GVSC has shown that FeMnAl can be adequately produced using conventional steel manufacturing methods, such as casting, forging, and hot rolling . Cast plates have also undergone ballistic testing and have shown to be on par with RHA armor steel . These results have shown that FeMnAl has the potential to be a direct replacement for current armor materials under MIL-DTL- 12560.
The heat-affected zone (HAZ) liquation cracking response of cast FeMnAl has not been fully studied and quantified, yet it has been reported by OSU and EWI based on welding mockups and simulated non-equilibrium solidification scenarios (welding). During exploratory work performed at OSU A GTAW spot weld was made on a small piece of the material, which was sectioned and analyzed using optical microscopy. It can be observed that several cracks occurred at the bottom of the weld pool, and in the HAZ of the base metal .
In conjunction with this preliminary weldability evaluation, further performance evaluation on wrought material has been conducted at GVSC. Current heats of wrought FeMnAl, while showing promising production results, has shown poor Charpy V-Notch (CVN) performance. Some of these results have pointed to the need to further optimize material chemistry and further studies.
With chemical optimization underway, potential weld metal solidification cracking and HAZ liquation cracking are a clear reality due to the alloy solidification mode and composition. Therefore, further testing is required to quantify the weldability of these alloys. Additional Cast Pin Tear Testing (CPTT) and Varestraint Testing (VT) is needed to qualify this material weldability. The results of these testing and the data analyses will support the down selection of an optimal chemistry and will inform future optimizations or modifications that may be needed for special applications.
Industry Sponsor: USARMY-CCDC-GVSC and Arcelor Mittal
Faculty: Antonio J. Ramirez (OSU)
Graduate Student: Rafael Giorjao
Faculty Contact: Dr. Katherine Sebeck and Dr. Venkata Challa