Substitution of Manganese for Nickel in Ni-Cr-Mo Steels

摘要

Because manganese increases the hardenability of alloy steels in a manner similar to that of nickel and because manganese is less costly than nickel, the cost of Ni-Cr-Mo HY-130/150 submarine-hull steels might be reduced by the substitution of manganese for nickel. In addition, the higher-manganese steels should be more compatible with the current experimental HY-130/150 filler metals, which contain about 2 percent manganese. Therefore, a labora¬tory study was initiated in which the manganese content of six Ni-Cr-Mo steels was increased from 0.5 to 3.0 percent and the nickel content was decreased from 4.5 to 0.5 percent to maintain a calculated hardenability index of 15 to 20. The evaluation consisted of hardenability, mechanical-property, and temperability studies on water-quenched and on blower-cooled 1/2-inch-thick plates of the six vacuum-melted, vacuum-carbon-deoxidized Mn-Ni-Cr-Mo steels.nThe results showed that the hardenability of the higher-manganese steels (1.0 to 3.0% Mn) was less than that predicted from the calculations. Thus, the yield and tensile strength of the blower-cooled 1/2-inch-thick plates (simulating water-quenched 4-inch-thick plates) decreased significantly as the manganese content increased. In addition, the notch toughness of the water-quenched and of the blower-cooled plates decreased continuously as the manga¬nese content increased. The resistance to softening upon tempering was not significantly changed by the substitution of manganese for nickel. However, compared with the other five steels, which contained 0.07 percent vanadium, , the steel containing only 0.01 percent vanadium softened rapidly when tempered above 1100 F.nThe results indicate that the base-metal properties of a Ni-Cr-Mo type HY-l30/150 steel are significantly impaired when more than about 1 percent manganese is substituted for nickel. Thus, further evaluation of high-manganese Ni-Cr-Mo steels will be confined to a limited evaluation of the compatibility improvement that may accrue when a high-manganese Ni-Cr-Mo-steel is joined with a high-manganese filler metal.