Abstract
In the authors' previous report, although effect of residual stress on fatigue crack growth rate was quite significant, that of microstructure of the weld metal was also found to he significant: The growth rate of a weld metal specimen was higher than that of a base metal when the growth rate was plotted against effective stress intensity range.
In the present study, metallurgical factors accelerating fatigue crack growth rate of weld metal specimens have been investigated. Effects of inclusions and delta ferrite are seemed to be negligible in the present range of the crack growth rate. Although effect of crystallographical heterogeneity is found to be significant, the heterogeneity may not be the factor that the fatigue crack growth rate of a weld metal specimen is higher than that of a base metal. The main factor is considered to be that dendrite structure of the weld metal is too coarse to easily cause martensitic transformation.
