A study was conducted by welding contractors to determine the causes of cracking of low-carbon steels and to recommend preventive measures. Weld samples were analyzed for the chemical composition of deposited welds using optical emission spectroscopy (OES) and it was found that flux cored wires that produced cracks had about 0.008% boron. Hardness evaluations of cracked welds showed regions of increased hardness in the weld metal, ranging from 253-412 HVN, which was caused by the presence of boron that increase hardenability in low-carbon steels. A metallographic evaluation of the microstructures showed the presence of bainite and martensite, which was consistent with the hardness measurements obtained. The flux cored wires from five different manufacturers were also evaluated, including the wires that had been used successfully in other field repairs. It was recommended that carbon steel flux cored wire be purchased with a maximum boron content of 0.003%.