HSLA-115 plate was successfully evaluated for acceptable undermatched production welding performance with breakage occurring in base material. Navy Metalworking Center photo.
The goal of this project was to increase the performance and strength of HSLA-100 (high-strength, low alloy) steel through heat treatment to enable use of this new HSLA-115 (115 ksi yield strength) steel at reduced thickness, and thus, reduced weight, while meeting all performance requirements. Additional objectives were to evaluate HSLA-115 for a large-scale production plate application, to determine HSLA-115’s performance and manufacturability, and to achieve welding and shipyard practice optimization and vendor qualification.
The Navy sought solutions to reduce weight and lower the center of gravity for CVN 78 Class to improve performance at a reasonable cost.
Implementation of HSLA-115 for the target application on CVN 78 Class will result in 100 to 200 long tons of topside weight reduction per hull and achievement of a 0.05-ft KG recovery. In addition, Northrop Grumman Shipbuilding - Newport News (NGSB-NN) conducted a trade-off study and determined HSLA-115 to be cost-neutral compared to the HSLA-100 baseline. While the HSLA-115 steel cost is slightly higher than HSLA-100, the weld volumes will decrease 10% due to thickness decrease. Also, current shipyard flux-cored, SMAW, GMAW and SAW welding processes have been approved for use with HSLA-115, so a $1M acquisition cost increase was avoided. Finally, the improved minimum yield strength level of the HSLA-115 also offers enhanced factor of safety in areas where the application thickness may not be reduced, but where the design performance and strength are enhanced without a weight penalty. Additional applications may be considered in future weapon system designs.
The Future Aircraft Carriers Program Office has approved the use of HSLA-115 in the CVN 78 Class baseline design, and HSLA-115 has been incorporated into the ship specifications and the fabrication document. NGSB-NN procured the first order of HSLA-115 for CVN 78 Class in March 2009 for the first unit; construction is scheduled to begin in December 2009. More than 2000 tons of HSLA-115 will be ordered for CVN 78 Class. Implementation of HSLA-115 was achieved ahead of schedule due to the combined efforts of the Integrated Project Team (IPT). The IPT, which includes NAVSEA 05, PMS 378, Naval Surface Warfare Center - Carderock Division, Office of Naval Research, NMC, Navy Joining Center, ArcelorMittal USA and DDL Omni, was instrumental in achieving the required steps toward implementation. These steps included obtaining NAVSEA approval of the Material Selection Information (MSI) after extensive certification testing, first article testing and vendor qualification, survivability testing for both plates and weldments, and NGSB-NN’s weld cross qualification. In addition, NGSB-NN demonstrated acceptable forming and welded tie-down behavior with HSLA-115.