This paper reports on a study that investigated how low cycle fatigue (LCF) and fatigue crack propagation (FCG) properties of P92, P122, and P23 steels vary between 600°C and 700°C depending on the location relative to a cross weld. Microstructure analysis was also performed on fractured specimens. Due to its higher yield strength, P122 exhibited the best continuous LCF life. However, creep-fatigue interaction (CFI) in the weld heat-affected zone (HAZ) of P122 and P23 steels significantly reduced their lifespans compared to continuous LCF tests. This reduction is attributed to the effect of weld thermal cycles on fine precipitates. FCG tests revealed that the base metal consistently outperformed the HAZ in all tested steels and temperatures. P92 and P122 showed similar FCG rates except for P92's behavior at 600°C, which resembled P23. In both steels, the HAZ exhibited faster FCG rates at 600°C and 700°C compared to the base metal, particularly at lower stress intensity factor ranges (ΔK). Within the HAZ, the region 1 mm from the fusion line displayed the slowest FCG rates, followed by the base metal, while the fusion line and the region 2 mm from it showed the fastest. Fracture surfaces near the fusion line displayed cleavage-like features, while the region 1 mm away exhibited features associated with higher crack growth resistance.

This paper explores the low cycle fatigue (LCF) and creep-fatigue properties of a hot-forged, normalized, and tempered 9Cr-1Mo ferritic steel. This steel offers good performance in high-temperature applications (up to 873K) in power plants and reactors. The steel was forged into 70 mm diameter rods and then heat-treated with normalizing (1313K for 1 hour, air cooling) and tempering (1033K for 1 hour, air cooling). LCF tests were conducted at 300-873K with varying strain amplitudes and strain rates to understand the influence of both factors. Additionally, some specimens were aged at different temperatures for 10,000 hours before testing. Finally, creep-fatigue interaction tests were performed at 823K and 873K using tensile hold times ranging from 1 to 30 minutes.