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Wohler /SN curve for 42CrMo4 steel

Wohler /SN curve for 42CrMo4 steel

Wohler /SN curve for 42CrMo4 steel

I want to do some fatigue calculations on a structure. Does anyone know where I can find a Wohler or SN curve for the material 42CrMo4  in the Q+T condition?  I have done some google searches but nothing comes up. Any help would be appreciated.

RE: Wohler /SN curve for 42CrMo4 steel

This kind of information is not available for free on the Internet.

You can conduct a search of this site - many requests have been made for S-N curves for various materials.  Check the printed publications mentioned in these threads.

For a large collection of materials information, including fatigue, look at ASM International:




Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Wohler /SN curve for 42CrMo4 steel

You can find fatigue information for many materials for free at www.fatiguecalculator.com.  You can generate an S/N curve with just the fatigue strength exponent and fatigue strength coefficient.


RE: Wohler /SN curve for 42CrMo4 steel


Actually, I was able to find the fatigue values for this material in a paper on the internet at:


I didn't check if their test was specifically for quenched and tempered, but this is the normal treatment for this material when used in driveshafts or whatever.


RE: Wohler /SN curve for 42CrMo4 steel


For 42CrMo4,

sigma f' =1154 MPa
b1 = -.061

To plot the S/N curve:

plot cycle counts versus calcuated stress amplitude, where:

stress amplitude (MPa) = 1154*((2*cycle count)^(-0.061))

Using this equation:

Life (cycles)          Stress Amplitude (MPa)
1000                   725.8435
10000                  630.7293
20000                  604.6167
50000                  571.7495
200000                 525.388
300000                 512.5528
800000                 482.7858
8000000                419.5218
80000000               364.5478
1.0e+08                359.6193
2.0e+08                344.7308  <- typical cutoff for infinite life
2.0e+09                344.7308

Plot this data on a semi-log plot with the y-axis begin logarithmic.


RE: Wohler /SN curve for 42CrMo4 steel

Thanks chaps for your helpful information.

I was going to try to convert this data into a 'rolling contact SN curve' for use in a brg application. Some people believe this can be done reliably, others say it can't.

Can I ask you for your opinions ?

RE: Wohler /SN curve for 42CrMo4 steel

Rolling contact fatigue is highly dependent upon surface roughness, inclusion type and amount, case hardness, case microstructure (non-martensitic transformation products, intergranular oxidation, etc., retained austenite, carbide distribution, etc.), and residual stresses.  The S-N curve that would be generated using the method described above is really only suitable for estimating fatigue life of simple components, not bearings, gears, springs, etc.

RE: Wohler /SN curve for 42CrMo4 steel

I would agree with TVP. I would not recommend using S/N fatigue data obtained from reverse bending, uniaxial loading and attempt to extrapolate this to rolling contact fatigue under multi-axial loading conditions. There are way too many variables in rolling contact fatigue.

There are other approaches required to calculate an effective stress range for rolling contact fatigue. Here is a paper that was published on rolling contact fatigue of railway wheels as an example of the complexity of the analysis;



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