Effects of R-ratio on high-temperature fatigue crack growth behavior of a precipitation-hardening stainless steel

• Published in: International journal of fatigue Vol. 30; no. 12; pp. 2147 - 2155
• Main Authors: Hsu, Kuei-Chang, Lin, Chih-Kuang
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.12.2008; Elsevier
• Subjects: 17-4 PH stainless steel; Applied sciences; Crack growth model; Exact sciences and technology; Fatigue; Fatigue crack growth; High-temperature; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; R-ratio; Crack growth model; Fatigue crack growth; 17-4 PH stainless steel; High-temperature; R-ratio; Temperature; Growth; Mechanical properties; Fatigue; High temperature; Precipitation hardening; Modeling; Fatigue crack; Crack propagation; Precipitation; Stainless steel; pH; Microstructure
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2008.05.029

The high-temperature fatigue crack growth (FCG) behavior was investigated for a precipitation-hardening stainless steel, 17-4 PH, in three differently aged conditions. FCG tests were conducted at 400 and 500 °C under various load ratios ( R-ratios) ranging from R = 0.1 to 0.7. Results indicated the fatigue crack growth rates (FCGRs) increased with R-ratio at the lower Δ K regime and merged together at the higher Δ K regime for all the given heat-treated conditions tested at 400 °C, except for Condition H900, in which the FCGRs increased with R-ratio for the entire Δ K range. At 500 °C, the FCGRs for a given heat-treated condition increased with R-ratio at lower R-ratios and became comparable at higher R-ratios for the entire Δ K range. The variations of FCGR with R-ratio could be described as an intrinsic behavior of FCG based on a Unified Approach. Accordingly, the dominating crack growth mechanism was similar to a general plastic blunting process except for Conditions A and H900 at 400 °C at the high R-ratio regime, in which the primary crack growth mechanism was associated with a crystallographic-faceted fracture mode. The variations of FCGR with R-ratio for all the given testing conditions were well correlated with a modified FCG driving force parameter, M ∗Δ K.