1.Fatigue Strength (Endurance Limit)
Grade 2 has a well-defined fatigue endurance limit (the stress level below which it can withstand an infinite number of cycles without failure). For smooth, polished specimens in axial loading, the typical fatigue strength is approximately 170–200 MPa at 107 cycles. This value is significantly higher than that of many steels of similar density and is superior to aluminum alloys.
2.Effect of Surface Condition
The fatigue performance of Grade 2 is highly sensitive to surface finish.
A rough surface, machining marks, or scratches act as stress raisers and can drastically reduce the fatigue life.
Processes like polishing, shot peening, or surface grinding can significantly improve fatigue resistance by introducing compressive residual stresses and removing surface defects.
3.Effect of Environment
In ambient air, Grade 2 maintains excellent fatigue properties. However, in aggressive environments (e.g., seawater, corrosive chemicals), its fatigue strength can be reduced due to the combined effects of corrosion and cyclic loading, known as Corrosion Fatigue. While it is more resistant to corrosion fatigue than many other metals, the fatigue crack growth rate can accelerate in corrosive media.
4.Notch Sensitivity
Grade 2 has low notch sensitivity compared to high-strength alloys. This means that stress concentrations at holes, threads, or fillets have a less detrimental effect on its fatigue life, making it reliable for components with complex geometries.
5.Applications
Due to its favorable fatigue properties combined with low density and high corrosion resistance, Grade 2 is widely used in cyclic load applications such as aerospace components, marine hardware, medical implants, and pressure vessels.
