Effect of tempering temperature and frequency on fatigue crack propagation in 0.2% carbon alloy steel

Fatigue crack growth (FCG) has been investigated in air, under high and low frequencies for lower and upper tempering temperatures, on a mining chain steel. The effect of frequency over the range tested is revealed to be not negligible in the near threshold region of ΔKI. For growth rates greater than 10−5 mm/cycle, FCG rates for tests conducted at 0.6 Hz were up to 1.5 higher than FCG rates for tests conducted at 78 Hz. Tempering at 500°C produced slightly lower early stage growth rates than tempering at 200°C where the remaining residual stresses still contribute in affecting the near threshold region, for the two test frequencies. Otherwise at higher values of ΔKI, the FCG curves were coincident. Using an empirical relationship between the constants of the Paris-Erdogan law, a correlation is established for this steel taking into account both effects of frequency and tempering. The obtained results are compared to analyzed data from literature for a high tensile steel and a linear relationship between the parameters C and n is deduced for both materials.