Abstract
The effect of precipitation on the resistance to fatigue crack growth was investigated in rotary bending- and cyclic torsional fatigue tests, using a precipitation hardening austenitic steel, SUH 38. Matrix precipitation was found to have no marked effect on the resistance to crack growth in rotary bending fatigue, while in cyclic torsional fatigue the resistance increased considerably with an increase in proof stress or tensile strength due to matrix precipitation. It was also found that coarse grain boundary precipitation decreased the crack growth resistance of a specimen without matrix precipitation, such as an as-solution treated specimen in both fatigue tests, but this effect of coarse grain boundary precipitation disappeared remarkably with matrix precipitation.
These results are discussed in terms of Weertman's equation. It is shown that matrix precipitation which increases static strength can improve the resistance to crack growth only in such fatigue having the markedly low level of triaxiality of the stress state, as cyclic torsional fatigue, and that coarse grain boundary precipitation may have no effect on the improvement in resistance to fatigue crack growth.
