Strain Rate and Temperature Insensitiveness of Notch-bend Strength for High Si Ductile Cast Iron

The notch-bend strength (σb,max) was investigated for High Si Solid Solution Strengthened Ferritic Ductile Cast Iron (EN-GJS-500-14) with varying the strain rate at room temperature. The notch-bend strength was also compared with the conventional ferrite-pearlite type ductile cast iron JIS-FCD500 and JIS-FCD700. Then, the application of the high Si ductile cast iron to wide industrial fields was discussed. Dynamic three-point bending tests were conducted on Charpy V-notch specimens in the range of stroke speed, 10-3~102 mm/s, at -20~22°C. The load-displacement curve for ductile fractured specimens shows that the load (P) steeply increases to the peak value (Pmax; about 10 kN) and then decreases, similar to that in the case of instrumented Charpy impact test. Even though the absorbed energy of fracture process was in the lower shelf region, the notch-bend strength did not decrease with increasing the strain rate as far as the fracture origin is ductile. It was found that the notch-bend strength is insensitive to the strain rate. The notch-bend strength (σb,max) of high Si ductile cast iron at -20°C was still equal to that at 22°C, indicating σb,max is insensitive to the temperature as well as the strain rate. High Si ductile cast iron EN-GJS-500-14 and the conventional ductile cast irons JIS-FCD500 and JIS-FCD700 show nearly the same lowest σb,max in the range of strain rate, 1.5×10-4~2.0×100s-1 at -20°C. Therefore, we think that the high Si ductile cast iron has wide industrial application potentiality