抄録
Fatigue crack growth characteristics in type SUS 304 stainless steel shielded-metal-arc weldments and A533 Grade B Class 1 steel submerged-arc weldments were studied using CT specimens at room temperature. The growth rates in SUS 304 stainless steel weldments were also examined at-100°C to evaluate the effect of low temperature on the growth rate of weldments. The low temperature was achieved by changing the flow quantity of liquid nitrogen. Crack closure of the weldments during fatigue crack growth was measured by a compliance method. An electron fractographic analysis was employed to determine the mechanism of crack growth and to measure striation spacings.
The resistance to crack growth in the SUS 304 stainless steel weldments was considerably higher than that of the base metal due to the presence of high compressive residual stress at the crack tip in the CT specimen. The growth rates in the stress relieved weldments in A533B steel and the base metal fell within a relatively narrow band of scatter. Therefore, the growth rates of stress relieved weldments were found not to be sensitive to the changes of microstructure or strength of materials. The fatigue crack growth rates in the SUS 304 stainless steel weldments at -100°C were slightly reduced as compared with those of the weldments at room temperature. The crack growth mechanism in the weldments of both steels was controlled by striation formation, even at -100°C. The fatigue crack growth rates and striation spacings in the base metal and the weldments with residual stress at different temperatures were closely correlated with ΔKeff based on the crack closure measurement.
