| 摘要 |
PURPOSE:To prevent formation of coarse crystal grains in the succeeding carburizing treatment by supressing the content of N in a case hardened steel so that AlN exists in the steel in the slight amt. to the extent of not aggregating to coarse grains during working in the stage of warm-forging the case hardened steel. CONSTITUTION:A steel consisting of the compsn. contg. 0.07-0.25% C, <0.35% Si, 0.2-1.5% Mn, 0.02-0.1% Nb, 0.01-0.05% SolAl and 0.001-0.0040% N or contg. further >=1 kind among 0.4-3% Ni, 0.4-1.5% Cr and 1.5-0.5% Mo is warm forged to produce a case hardened steel. The forging temp. in this case is lower than the temp. at which AlN solutionizes in the steel and therefore the content of N in the steel is decreased considerably as mentioned above in order to prevent the aggregation of AlN to coarse grains in the stage of a carburizing treatment and to suppress the amt. of AlN to the slight amt. to the extent of avoiding the aggregation to the coarse grains, by which the crystal grains of the case hardened steel formed by the warm forging are made extremely fine.
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