Influence of Frequency on High-Temperature Fatigue Behavior of 17-4 PH Stainless Steels

Abstract

The effect of frequency (2 and 20 Hz) on the high-cycle fatigue and fracture behavior was investigated at 573-773 K for 17-4 PH stainless steels in three conditions: Condition A (unaged), H900 (peak-aged) and H1150 (overaged). S-N results indicated that at 573 and 673 K, there was generally no difference in fatigue strength between 2 and 20 Hz, except for H900 at 673 K where the fatigue strength at 2 Hz was lower than that at 20 Hz. At 773 K, the fatigue strength of each condition at 2 Hz was lower than that at 20 Hz due to the occurrence of creep mechanism at this low frequency. At 773 K and 2 Hz, the fatigue fracture mode exhibited a mixed mode involving transgranular and intergranular cracking and the grain boundary cavities were also observed. At a given temperature and frequency, the fatigue strength for the three conditions generally took the following order: H900 > Condition A > H1150, except for Condition A at 773 K in the long life regime where the fatigue strength was close to that of H1150 due to a precipitate-coarsening effect. With the exception of Condition A tested at 673 K, the fatigue strength of each condition was decreased with increasing temperature as a result of a reduction in yield strength. At both frequencies, the fatigue strength of Condition A at 673 K was greater than that at 573 K as a result of an in-situ precipitation-hardening effect. Fractography observations indicated that the fatigue crack initiation site, crack propagation path and fracture surface morphology were functions of testing temperature, loading frequency and applied cyclic stress level.

Effect of strain rate on high-temperature low-cycle fatigue of 17-4 PH stainless steels

“…Apparently, thermal activation of dislocations became more operative than the hardening DSA effect for the given alloys tested at 500 • C resulting in cyclic soft- ening. Moreover, the authors' previous investigations [6,7] indicated that coarsening of Cu-rich phases was observed in Conditions A and H900 tested at 500 • C and resulted in a reduction of hardness and fatigue resistance. Consequently, in addition to dynamic dislocation recovery, the coarsening of Cu-rich precipitates is believed to contribute to cyclic softening in Conditions A and H900 at 500 • C. Furthermore, due to an increase in the period of a cycle with decreasing strain rate, the coarsening effect would become more effective such that the stress level was significantly decreased with a reduction in strain rate for Conditions A and H900 tested at 500 • C. Fig.…”

“…As part of a series of studies on the high-temperature mechanical and fatigue properties of 17-4 PH stainless steels [5][6][7], the objective of the present study is to characterize the LCF behavior of such materials at high temperatures. In this study, systematic experiments were conducted to investigate the influence of strain rate (10 −2 , 10 −3 and 10 −4 s −1 ) on LCF life, cyclic stress response (CSR), and dislocation substructure at 300-500 • C for variously heat-treated 17-4 PH stainless steels.…”

High-temperature fatigue crack growth behavior of 17-4 PH stainless steels

“…Although a limited number of studies on the high-temperature characteristics of 17-4 PH alloy have been reported [8,[13][14][15][16], the high-temperature FCG behavior of this alloy has not been reported yet. As part of a series of studies on the high-temperature fatigue properties of 17-4 PH stainless steel [14][15][16], the objective of this study is therefore to characterize the high-temperature FCG behavior of variously heat-treated 17-4 PH stainless steels by conducting systematic experiments at room temperature (RT), 300, 400, and 500 o C. Mo, 0.03 S, 0.02 C, 0.016 P and Fe (balance). Three different types of heat treatments were applied, i.e.…”

Influence of Frequency on the High-Temperature Fatigue Crack Growth Behavior of 17-4 PH Stainless Steels

“…Since engineering structures often contain flaws or crack-like defects, a study on the fatigue crack growth (FCG) behavior of 17-4 PH stainless steel at high temperatures is of great importance for the design and life prediction of its various applications. Although there are a few investigations focused on the high-temperature characteristics of 17-4 PH stainless steel, 7,[12][13][14][15][16][17] study on the high-temperature FCG behavior is very limited 17) and lacks consideration of the frequency effect. Frequency is an important factor governing FCG behavior at high temperatures because time-dependent mechanisms, such as creep and oxidation, may take place during fatigue loading.…”

“…As part of a series of studies on the high-temperature fatigue and mechanical properties of 17-4 PH stainless steel, [13][14][15][16][17] the aim of this study is to characterize the influence of loading frequency on the high-temperature FCG behavior of variously heat-treated 17-4 PH stainless steels by conducting systematic experiments at 673 and 773 K.…”