HIGH CHROMIUM CAST IRON HAVING EXCELLENT FATIGUE CRACK RESISTANCE AND PROCESS FOR PRODUCING THE SAME

摘要

A high Cr cast iron having excellent fatigue crack resistance that can prevents brittle fracture due to fatigue crack growth even under an atmosphere in which tensile stress can be repeatedly generated although the high Cr cast iron has high hardness, and a method for manufacturing the same are provided. A high Cr cast iron having excellent fatigue crack resistance has a composition comprising, by mass percent, 2.5 to 3.5% of C, 0.2 to 1.0% of Si, 0.6 to 2.0% of Mn, 13 to 22% of Cr, 1.0 to 3.0% of Mo, 0.01 to 0.15% of N, their contents satisfying the relational expressions of [Cr]/[C]=4.5 to 6.5 and [Mn]Î[Mo]=1.8 to 2.5, and the balance of Fe and unavoidable impurities, wherein the high Cr cast iron having excellent fatigue crack resistance has a structure in which the size of martensite when observing a cast iron structure by an optical microscope of 100 magnifications is 6,000 mum^2 or less as an average area per one martensite surrounded by carbide, and an average volume fraction of residual austenite by an X-ray peak diffraction intensity ratio in martensite, residual austenite and carbide is 5 to 40%.