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    Effects of Manganese and Aluminum Contents on Transition Temperature of Normalized Nickel Steel

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    It has been fairly well established that fine ferrite grain size is conducive to low temperature of transition from ductile to brittle behavior in normalized carbon steels of moderate to low carbon content (1).2 The generally accepted practice for producing fine grained steels is to add aluminum to the melt after preliminary deoxidation with silicon. Although the amount of the addition will depend upon the condition of the melt, a residual or acid-soluble aluminum content of 0.015 per cent usually will ensure fine austenite grains at the temperatures associated with normalizing and fine ferrite grains after air cooling (2, 3). There has been recurring evidence, however, that the effect of aluminum on transition temperature may be more extensive than that of grain refinement alone (4); consequently, the minimum aluminum content required to obtain fine grain size might not necessarily be the optimum quantity to produce the lowest transition temperature. The transition temperature of mild carbon steel also may be lowered by increasing the manganese content (5, 6), and the addition of nickel long has been recognized as one of the most effective means of lowering the temperature of embrittlement (7). What has not been determined is whether the effects of manganese and nickel are additive and whether the optimum aluminum content for lowering the transition temperature of carbon steels is independent of the manganese content and whether the optimum aluminum addition is the same for nickel steel as for carbon steel. The plan evolved to study the effect of nickel, manganese, and aluminum on transition temperature called for 24 heats, half of which contained no nickel and the other half 21/4 per cent nickel, with each type at three manganese levels of 0.4, 0.95, and 1.5 per cent, and each of these six combinations at the four levels of acid-soluble aluminum of nil to 0.005, 0.030, 0.055 and 0.090 per cent. Carbon level of all melts was maintained at 0.15 ± 0.01 per cent. This block-type design improves validity on the effects of nickel, manganese, and aluminum because it provides data on the effect of each one at all combinations of the others and permits easy comparison when the results are presented graphically. This design has the additional advantage that the data can be analyzed statistically by the powerful “analysis of variance” technique (8) to indicate the degree of certainty of the conclusions, provided, of course, that no large uncontrolled variables are involved. Unfortunately, normalizing produced a significant quantity of martensite in four heats, and the aimed-for deoxidation practice was not quite achieved in one heat. These relatively large uncontrolled variables made it impossible to apply successfully the analysis of variance; however, several simpler statistical tests were applied to the data, as shown later in the paper.

    Author Information:

    Armstrong, T. N.
    The International Nickel Co., Inc., New York, N. Y.

    Miller, O. O.
    The International Nickel Co., Inc., New York, N. Y.

    Committee/Subcommittee: E01.01

    DOI: 10.1520/STP47575S