| 摘要 |
PROBLEM TO BE SOLVED: To produce medium carbon steel excellent in both strength and toughness. SOLUTION: In the process of cooling from forging, steel is transformed into pearlite in the pearlite transform temp. region, is moreover subjected to normalizing treatment at the temp. of >= the Ac3 point for one or more times, is thereafter heated to the temp. of >= the Ac3 point, is quenched and is subsequently subjected to tempering for one or more times. As its compsn., the one contg., by weight, 0.25 to 0.55% C, 2.0 to 10.0% Cr, <=2.0% Si, <=2.0% Mn, <=4.0% Ni (1/2W+Mo): <=6.0% alone or in combination of W and Mo, >=2.0% V and <=0.20% Nb is shown. The elimination of netlike carbides deteriorating the refining of the structure and its toughness is made possible, and the toughness can remarkably be improved without deteriorating its strength.
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