Fatigue Strength, Crack Initiation, and Localized Plastic Fatigue Damage in VHCF of Duplex Stainless Steels

Abstract

The fatigue strength of two-duplex stainless steel grades, 2304 SRG and LDX 2101, with austenitic-ferritic microstructure is tested using ultrasonic fatigue testing equipment operating at 20 kHz. The testing is conducted in tension-compression mode with the load ratio R ¼ À1. The fatigue strength is evaluated at 10 7 , 10 8 , and 10 9 load cycles and the estimates of fatigue strength are higher for the LDX 2101 grade. The fatigue crack initiation mechanisms are analyzed using a scanning electron microscope. The fatigue cracks, in all cases, appear to initiate due to accumulation of plastic fatigue damage at the surface. In the 2304 SRG grade, accumulation of fatigue damage occurs at the external surface of fatigued specimens in the form of extrusions at the grain/phase boundaries and in the form of individual slip lines in the austenite phase. Meanwhile, in the LDX 2101 grade accumulation of plastic fatigue damage in the form of extrusions and intrusions occurs mainly within the ferrite grain. When the crack is microstructurally short, the crack growth appears to be crystallographic in nature and the crack appears to change its direction propagating from one grain into another.

Very-high-cycle fatigue crack initiation and propagation behaviours of magnesium alloy ZK60

“…For metallic materials containing internal inclusions (Type I) as classified by Mughrabi [6], the fatigue crack initiation in the VHCF regime is commonly caused by subsurface or interior inclusion surrounded by a rough region of the fine granular area (FGA) [7][8][9][10]. For the type II materials without any inclusion in the interior, fatigue failure is strongly influenced by accumulated micro-plasticity due to microstructural heterogeneity and basically initiated from slip bands at the surface or subsurface [11][12][13][14][15].…”

Computing the stress intensity factor range for fatigue crack growth testing at 20 kHz

“…In a previous study, 10 a transient dynamic analysis has been applied where the J‐integral and thereby the SIF at a crack in a fatigue crack growth (FCG) bar specimen has been computed. In References 11–13 the same simulation procedure (transient dynamic) has been used to conduct stress–strain analysis in 20 kHz fatigue strength hourglass specimens. Such analysis is computationally inefficient, especially when small values of material damping are used, and a large number of cycles are required to pass the transients and reach the steady state oscillation.…”

Reformation Behavior of Austenite in 2205 Duplex Stainless Steel with Rapid Heat Treatment

“…Meanwhile, it has been reported that the interface characteristics, which depend on the orientation relationship (OR) between the two crystals, have a great effect on the dislocation slip behavior, fatigue behavior, and dynamic restoration process of DSS . The crystallographic OR between WA and ferrite in DSS has been studied in depth.…”