Influence of Graphite on Fracture Toughness and Fatigue Crack Propagation Property in 7 mass% Chromium Ni-Hard Cast Iron

• Published in: Transactions of the Japan Society of Mechanical Engineers Series A Vol. 67; no. 660; pp. 1350 - 1355
• Main Authors: KUBO, Osamu, TANAKA, Taku, HASHIMOTO, Mitsuo, HONDA, Yoshioki, MATSUBARA, Yasuhiro
• Format: Journal Article
• Language: English; Japanese
• Published: The Japan Society of Mechanical Engineers 2001
• Subjects: Fatigue Crack Propagation; Fracture Toughness; Graphite; Ni-Hard Cast Iron; Rolling Mill Roll
• ISSN: 0387-5008; 1884-8338
• DOI: 10.1299/kikaia.67.1350

The influence of graphite volume on fracture toughness and fatigue crack propagation had been studied in 7 mass% chromium Ni-hard cast iron with 0.57∼4.52% graphite for the purpose of improving the wear and crack resistance as steel rolling mill roll materials. The main experimental results are shewn as follows ; (1) Fracture toughness (KIC) increases with an increase in graphite volume and shows the maximum KIC> value of 25.7 MPa·m0.5 at 1.90% graphite, and then it decreases as the graphite volume rises over 1.90%. (2) Threshold stress intensity factor range for fatigue crack propagation (ΔK<th) varies in the same manner as fracture toughness and it shows the maximum ΔKth value of 8.5 MPa·m0.5 at 1.90% graphite. (3) Paris-Erdogan equation da/dN= C (ΔK1)m holds good between crack propagation rate and stress intensity factor range, and there is a constant relation of C=3.89×10-4/15.8m. (4) Existence of adequate graphite volume restrains crack propagation and improves KIC and ΔKth. (5) Heat-treatment of hardening-tempering deteriorates ΔKth and hastens crack propagation.