Effect of Strength on Corrosion Fatigue Performance 1

[Carburize]

If a steel can be heat treated to different strength levels how does this effect fatigue performance in a corrosive environment?
For example in oil field applications it is possible to heat treat some alloys to 100,000 or 150,000 psi yield strength. Under fatigue conditions in air the higher strength material has a higher fatigue limit but what is the effect of exposing these two materials to salt water or hydrogen sulfide?

 

[Margaria]

Hi,

The fatigue limit of a steel that was heat treated in order to obtain 1000 MPa (tensile stregth) can reduce 4 or 5 times if this material work in a corrosive environment.

Margaria

 

[CoryPad]

Carburize,

The important factor to consider is presence of a flaw. In the absence of a large flaw, the majority of fatigue life is spent in the fatigue crack initiation process. High strength hinders the nucleation of critical fatigue cracks. However, in the presence of a large flaw, high strength is detrimental to fatigue crack propagation because the process zone is smaller and absorbs less energy.

In a corrosive environment, it is possible to initiate flaws such as pits, subsurface hydrogen cracks, etc. Thus, it is likely that high-strength materials will have inferior corrosion fatigue performance.

Regards,

Cory

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