Study of the fatigue crack growth in low carbon austenitic stainless steels 304L and 316L

The propagation of fatigue cracks in austenitic steels of type Z2CN1810 (304L) and Z2CND1712 (316L) was studied at room temperature. The main results are as follows: — The crack propagation rates generally follow Paris' law. — Under the same loading conditions, 304L steel exhibits a lower resistance to fatigue crack propagation than 316L steel. — The influence of the mean stress is complex. It appears that the crack length plays a more significant role than predicted by Paris' law. A formulation of this type seems more appropriate. — In comparison to results presented by various authors regarding normal carbon steels (304), a higher propagation rate is noted in the low carbon steels studied here (304L). The variation of the stress intensity factor (ΔK0) leading to a propagation rate of 10^-5 cm cycle^-1 is approximately 23 MPa √m for 304L and 27-28 for 304. — A threshold for non-propagation (after 5 x 10^6 cycles) due to fatigue (ΔKs) is observed for both materials. This threshold is generally low (5 to 10 MPa √m). It decreases linearly with R and is higher for 316L steel than for 304L steel. — The cracking is generally transgranular. However, intergranular fracture zones are encountered, corresponding to very low propagation rates, that is, close to the stopping zones determining ΔK s.