NUCLEATION AND GROWTH OF CREEP CRACKS IN AN AUSTENITIC STEEL

The cracks were counted in 20Cr 35Ni austenitic stainless steel specimens pulled in slow tension at 700°C. The number of cracks increased exponentially as straining continued up to final fracture. The size distributions, however, remained constant with an average crack size corresponding to 1.5-1.6 grain boundary facets. From these distributions it was determined that the average growth rate of the cracks remained the same during a whole test but a larger crack tended to grow faster than a smaller one, the growth rate increasing exponentially with the size. The grain boundary junctions seemed to provide the main obstacle to the growth. A life estimate was obtained assuming as a fracture criterion that a crack grows to infinite size. © 1969.