| Summary: | Approved for public release; distribution is unlimited. === The U.S. Navy has maintained a continuous research, development and certification program in ULCB steels as a possible replacement for the HY and HSLA steels currently being used in ship construction. The overall aim of this program is to develop a high strength steel with improved weldability. Improved weldability could eliminate the requirement of preheating, (a necessary and costly step required to prevent weld metal cracking in HY steels). The strength of ULCB steel weldments can be correlated to the weld metals composition in a simple manner, however the toughness of the weldment seems to fluctuate in complex manner depending on the weld metal composition, weld power, and possibly the non-metallic inclusion size, type, number and distribution. This study attempted to correlate the embrittlement of ULCB/ULCB multipass TIG weldments to the given microstructure and to the type, size, number and distribution of the nonmetallic inclusions within the weldment. This work led to the following conclusions; (A) The embrittlement of ULCB weldments appeared to be the result of microscopic transgranular cracking, (B) There exists a need to design a process which can manufacture reproducible multipass weldments to facilitate testing, and (C) the type, size, number and distribution of the nonmetallic inclusions did not appear to be a factor in the toughness of the weldments investigated.
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