Host: The Iron and Steel Institute of Japan
Pages 185-188
The effect of loading rate on fracture toughness in hydrogen gas, KIH, of low alloy martensitic steels, JIS-SNCM439 and JIS-SNB16, was investigated using rising load tests in 85 MPa hydrogen gas at room temperature. The tests were performed at various loading rates ranging from 0.0005 to 3 MPa√m/s, and two methods based on KHKS 0220 and ASTM E399 were used to calculate KIH. In the evaluation based on KHKS 0220, no difference was recognized in the effect of the loading rate on KIH for both steels. However, in the evaluation based on ASTM E399, KIH for JIS-SNCM439 increased with increasing loading rates higher than 0.5 MPa√m/s. In contrast, KIH for JIS-SNB16 increased at loading rates higher than 0.05 MPa√m/s. This difference is probably attributed to hydrogen diffusion at the initial stage of crack propagation. Accordingly, in rising load tests, lower loading rates are required for JIS-SNB16 than those for JIS-SNCM439, and KIH for JIS-SNB16 was higher than that for JIS-SNCM439 at similar strength levels. However, no significant difference was observed in fracture surfaces of both steels after the rising load tests, and the relationship between KIH and the characteristics of their fracture surfaces was unclear.
