| 摘要 |
PROBLEM TO BE SOLVED: To improve the strength, toughness and weldability by changing the compressing direction in specified temp. range, repeating a specified quantity of the compressive deformation at specified times or more and obtaining a steel material consisting essentially of fine equiaxed ferritic grain structure having a specified value or lower of the crystal grain diameter with cooling. SOLUTION: The temp. of the compressive work of forging, swaging, rolling, etc., is regulated to 400-Ae1. Then, in the compressive work, many kinds of slippings are worked by changing the compressive direction and locally crystal lattice is rotated and thus, the fine equiaxed grains having <=2μm crystal grain diameter can be produced. In this way, even in the case the working ratio per one pass is <50%, the structure can easily be changed into the equiaxed structure. That is, the fine equiaxed ferritic grain structure having <=2μm crystal grain diameter can be obtd. by repeating the compressive deformation having >=10% per one pass at three more times.
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