| 摘要 |
PROBLEM TO BE SOLVED: To manufacture a pressed parts in which a part high in strength and rigidity and a part low in strength and rigidity can be easily formed in one parts by achieving the sub-zero treatment to a specified part of the pressed parts obtained by pressing a blank formed of a highly retained austenitic steel. SOLUTION: In sub-zero treatment, a pressed parts is cooled from the room temperature to the temperature range of -50 deg.C to -200 deg.C. The carbon content of the highly retained austenitic steel is 0.05-0.2%, and the content of the retained austenite is 5 to 20%. The remaining austenite of a cooled part is turned into martensite by the sub-zero treatment of the arbitrary position of the pressed parts consisting of highly retained austenitic steel. The cooling method in the sub-zero treatment includes the method to blow liquid oxygen (-183 deg.C) and liquid nitrogen (-196 deg.C), powder dry ice (-78 deg.C), or cooled air or alcohol to a desired part of the pressed parts, or to immerse the pressed parts in a refrigerant formed thereof.
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