Extensive Study of Low Fatigue Crack Growth Rates in A533 and A508 Steels

For two heats of ASTM A533 Grade B Class 1 pressure vessel steel and an ASTM A508 Class 2 forged steel, an extensive study of fatigue crack growth rate characteristics was conducted within the framework of linear elastic fracture mechanics. Experimental data obtained covered a wide variation in cyclic growth rates ranging from those associated with fatigue threshold (order of 10-9 in./cycle) up to rapid fracture. The bulk of experimental information obtained was at very low cracking rates, usually 10-6 in./cycle and below. Considered in the investigation were: (1) an evaluation of the effect of stress ratio, R = σmin/σmax, on verv slow rates of fatigue crack extension; (2) an evaluation of temperature (75 to 650 F) on very slow rates of fatigue cracking; (3) an examination of the combined effects of temperature and stress ratio and their influence on fatigue crack extension; (4) an evaluation of the effect of a distilled water environment on fatigue crack propagation rates; (5) an examination of the effects of specimen thickness; and (6) a comparison of results for two separate heats of the same alloy.