Effects of Thermal Aging on the Low Cycle Fatigue Behaviors of Cast Duplex Stainless Steels

The low cycle fatigue (LCF) behaviors of cast duplex stainless steel (CDSS) thermally aged at different times were investigated under different strain amplitudes. The effects of thermal aging on the LCF lives of CDSS are closely related to the strain amplitude. At a low strain amplitude, the fatigue life of the material increases significantly after thermal aging, while the LCF life decreases with an increasing aging time at a high strain amplitude. After thermal aging at 400 °C for 10,000 h, the fatigue fracture morphologies of CDSS change from fatigue fringes to mixture features including fatigue fringes in austenite and cleavage cracks in ferrite. Severe plastic deformation in ferrite of the aged CDSS under a high strain amplitude causes the cleavage cracking of ferrite. The premature failure of ferrite accelerates the propagation of fatigue crack and shortens the fatigue life at a high strain amplitude.

Modeling of Hydrogen Embrittlement by a Ductile-Brittle Damage Model

Hydrogen embrittlement (HE) in a martensitic steel has been investigated by tensile tests. It is shown that increasing hydrogen amount results in a transition of void coalescence cracking to a mixture of intergranular and quasi-cleavage cracking. In order to reveal the mechanisms of HE, a non-local ductile-brittle damage model has been proposed to model these tests. Modeling results show that HE is caused by a combined effect of HEDE, HELP and AIDS mechanisms.