| Abstract Scope |
U.S. Army Combat Capability Development Center (CCDC) Ground Vehicle Systems Center (GVSC) is evaluating the manufacturability of a reduced-weight armor steel for military ground vehicle platforms. The material of interest is a wrought high-manganese lightweight steel alloy plate known as FeMnAl. EWI evaluated using different types of welding electrodes and parameters for gas metal arc welding (GMAW) of wrought FeMnAl plate. Different types of austenitic stainless steel electrodes were selected, along with a higher strength carbon steel, a nickel alloy, and an austenitic manganese-nickel chrome metal-cored electrode. Welding was done using eight different 0.045-in. diameter welding electrodes with tensile strengths ranging from approximately 80-100 KSI. The electrode types used were ER100S-1, ER218, ER307, ER309, ER312, ER316L, ERNiCr-3, and austenitic High Cr, High Mn (Stulz metal cored). A series of bead-on-plate welds were made using an ER316L electrode and various shielding gases to evaluate their suitability for this application. Welds made using 95% Ar/5% CO2 and 98% Ar/2% O2 resulted in rough weld bead surfaces. It was decided to use 100% argon as a baseline for further welding procedure development. A series of 124 bead-on-plate welds about 5-in. long were made on ½-in. thick FeMnAl plate with one ER316L electrode using three different heat inputs and three different preheat temperatures. Plate surfaces were ground before welding. The bead on plate welds were made using mechanized GMAW. Selected welds were sectioned, polished, etched, and examined using an optical microscope for the presence of cracks. Based on the results of this evaluation, a preferred heat input and preheat temperature were used to make between 12 and 21 bead-on-plate welds using each of the other electrodes. Selected welds were metallographically examined to determine relative performance of the electrodes and welding parameters with respect to crack formation. Test plates were prepared for double V-groove welds using 1-in. thick plate. The joint design was based on MIL-STD-22D B2V.3 with 22.5° bevels and 1/16 to 3/16-in. land. A ¼-in. diameter ceramic backing strip was used for the root bead. Mechanized or robotic test welds were made with each of the electrodes. The ER316L weld was made using a robot. The remaining welds were made using a side-beam positioner. The double V-groove test welds were radiographic tested (RT), then underwent tensile, microhardness, and Charpy impact testing. RT results were generally acceptable, although some porosity was found in the ER100S-1 weld. All but one of the welds failed in the weld metal during tensile testing. The highest tensile strengths, 111 and 113 ksi, were found in the ER316 weld. The Stulz, ER307, and ER218 welds also had tensile strengths greater than 100 ksi. The lowest tensile strengths of 26.8 and 53.6 ksi were in the ER312 weld. Steps in the ER312 tests indicated cracking occurring at lower loading. The ERNiCr-3 weld tensile test specimens failed in the HAZ. This weld was made with the lowest average heat input (8.1 kJ/in). Charpy V-Notch (CVN) impact test results showed that the ER316L and ER307 welds made without preheat had significantly higher toughness in the HAZ. The weld made using ER312 had significantly lower toughness in the base metal, HAZ, and weld metal. The CVN samples from HAZ and base metal for this weld broke at a location away from the notch indicating that the base metal was suspect. One ER100S-1 weld CVN test specimen from the base metal failed away from the notch. All ERNiCr-3 weld CVN specimens from the HAZ and base metal failed away from the notch. Hardness in the base metal ranged from 355 to 441 HV. On the high end, the base metal hardness of the ER100S-1 weld ranged from 410 to 417 HV and the Stulz weld plate ranged from 384 to 405 HV. The lowest base metal hardness of 355 to 384 HV was on the plate welded with ER312. The HAZ hardness ranged from 307 to 418 HV with the highest being on the plate welded with ER218. Weld metal hardness was highest with the ER100S-1
weld at 323 to 394 HV. The lowest hardness ranged from 254 to 295 HV in the ER307 weld. Considering the combination of tensile strength, ductility, impact toughness, and hardness, the best performing welds were made with ER316L, Stulz, and ER307. The ER218 weld had the highest yield strength and very high tensile strength, but not as much ductility and much lower impact toughness than the top three performers. The ER100S-1 weld had lower than expected tensile strength and ductility, and low toughness in the weld metal. The ERNiCr-3 weld was the only one that failed in the HAZ during tensile testing. The worst performance overall was with the ER312 weld. It must be noted that the base metal used for the ER312 weld had much lower toughness than that used for the other welds. Due to the obvious influence of base metal material properties on weld performance, none of the electrodes tested should be ruled out for use on FeMnAl based on the test results from one weld. GMA welds on FeMnAl can be made with good mechanical properties using a variety of electrode types, including austenitic stainless steel, and austenitic high chrome, high manganese. Some welding parameter sets developed with bead-on-plate welds were too cold for adequate fusion with groove welds. Base metal mechanical properties had a strong influence on weld and HAZ mechanical properties, with low toughness in the base metal an issue especially with the ER312 weld. The weld HAZ was generally not the limiting factor in performance except for the ERNiCr-3 weld that had low toughness in the HAZ and failed in the HAZ during tensile testing. HAZ impact toughness was generally higher on the ER316L and ER307 welds that were made without preheat. Keywords: FeMnAl, manganese, lightweight, armor, GMAW, ER100S-1, ER218, ER307, ER309, ER312, ER316L, ERNiCr-3 |