| 摘要 |
PROBLEM TO BE SOLVED: To improve the proof stress to impact load by specifying the structure, etc., of the composing material of a fixture. SOLUTION: This fixture consists of an austemper nodular graphite cast iron, and the base structure is the mixture structure of a bainite and a residual austenite. Then, the bainite set having a definite directional property and the length of >=40μm is definited as <=30% in the area ratio, and <=15% in the area ratio of the residual austenite appearing near the eutectic cell grain boundary. Thus, the fixture has the machinery property of the elongation of >=7%, and the proof stress of >=800MPa. Therefor, even in the case of using the fixture as a heavy temporary structure and applying the impact load, cracks are hardly caused, also even when the structure is built by tightening a shaped steel, then the heavy load is received from the outside, since the yield strength is enough high, permanent set is not caused and the safety is ensured.
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