A study was made of the action of boron in relation to the hardenability of high-purity alloys varying in carbon content. The effectiveness of boron in enhancing the hardenability of these alloys and certain steels is believed to be due to its action in retarding; the rate of nucleation of ferrite and carbide while in solid solution in austenite. The hardenability of the boron-treated alloys, as determined in terms of the critical cooling rate of small specimens austenitized at a wide range of

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... emperatures, varied with the prior history and with the carbon content. The hardenability of a commercial boron-treated steel, as determined by the end-quench test, was also sensitive to prior thermal treatments. Boron was lost in the decarburized zone of commercial steels, and its rate of diffusion apparently is of the same order of magnitude as that of carbon. The heat treatment of specimens of the alloys and steels to produce a boron constituent and the microstructures of the alloys as cast and as homogenized are described. 4 212 to 24 11 4 212 to 24 13 3 2 6 to 12 13 2 26 to 12 ' ND denotes not detected. 2 Estimated. 3 The alloy also contained approximately 0.65 percent of manganese and 0.10 percent of silicon.