High-Temperature Fatigue Crack Growth Behaviour of SS 316LN

摘要

FCG behaviour of SS 316LN steel is evaluated in the temperature range 300-823 K. While there is a general increase in FCG rate with temperature and load ratio, specifically at low applied stress intensity factor ranges, for intermediate temperatures (623-723 K) and applied stress intensity factors (15-25 MPa m~(1/2)), a cross over in the crack growth rate is observed. The Paris exponents for different temperatures varied between 2.4 and 3.7. The variations in the crack growth rates are examined by considering the crack closure and dynamic strain ageing (DSA) effects. Attempts have been made to rationalize these variations with the temperature dependence of Young's modulus and yield strength. The stress intensity factor range normalized with yield strength gives a better correlation with FCG rates at different temperatures. The unified data for all the temperatures was fitted to a Paris-type correlation, viz., da/dN = C· (ΔK/σ_(ys)~m with C = 4.5 nm/cycle and m = 2.73.