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A significant tonnage of HY‐100 steel has been used in the structural designs of new ships and submarines for weight reduction, where HT and HY‐80 steels had been previously used. A reduction in hull fabrication costs and higher productivity can be achieved by substitution of an HSLA steel for HY‐100. The significant factor in cost savings through use of HSLA steel in fabrication is the reduction or elimination of preheat for welding. Based on the success of the HSLA‐80 steel system, a program was initiated to develop and certify an HSLA‐100 steel as a replacement for HY‐100 in order to reduce fabrication costs. The alloy development and evaluation to support the certification of HSLA‐100 steel plate and weldments for surface combatant structural and ballistic protection applications are summarized. HSLA‐100 development consisted of three phases: (1) laboratory alloy development to formulate an interim specification; (2) trial steel mill plate production; and (3) plate production for the certification program. An interim specification for HSLA‐100 steel plate was used as the basis for the commercial production of over 200 tons of HSLA‐100 by domestic steel plate mills. The alloy design of HSLA‐100 represents a significantly different metallurgy and microstructure than HSLA‐80 steel, but retains the wettability of very low carbon steel. The certification program was conducted to establish the properties, welding characteristics, fabricability, and structural performance of HSLA‐100 steel plate over a range of gages from 1/4 to 3 3/4 inches. The certification program included the characterization of production HSLA‐100 steel plate mechanical, physical, and fracture properties; evaluation of wettability and welding process limits for structures of high restraint; studies of fatigue properties and effects of marine environments on HSLA‐100; and the fabrication and evaluation of large scale structural models to validate the laboratory developed welding process parameters. The properties and wettability demonstrated by HSLA‐100 steel resulted in certification of HSLA‐100 as a replacement for HY‐100 for surface ship structures and ballistic protection.

Fatigue crack propagation was studied in HY-130 steel base plate, as-deposited shielded metal-arc weld metal, and gas metal-arc weld metal using compact specimens. The effects of seawater, cathodic protection, frequency and hold time were investigated. The results indicated that saltwater increased crack-growth rates in HY-130 base plate at stress intensity factors below 60 ksi in. No significant effects of cyclic load-wave pattern or of frequency (0.10 to 10 cycles per min.) were evident. Cathodic potentials from zinc (−1.05 V) and magnesium couples (−1.40 V) increased fatigue crack-growth rates in seawater. Fatigue crack growth in the weld metals showed different characteristics than in wrought materials in that higher stress intensities were required to initiate crack growth, and growth rates increased over a narrow range of stress intensity. Results of the environmental effects of weld metals indicated that, even under the most severe conditions of cathodic potential in seawater, fatigue crack-growth rates in weld metal were lower than those observed with base plate in air.

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