Abstract
Abstract. In this work, the effect of the quenching media (brine, water, and two types of naphthenic mineral oils) and the tempering temperature (200, 400, 600 ∘C) on the static mechanical properties and the fatigue life has been investigated using 300 fatigue and 36 static tension tests. S–N curves and standard deviations of fatigue life under each heat treatment condition were calculated and shown. The fracture surfaces of the selected 11 specimens were observed by the scanning electron microscope and the reasons of affecting the fatigue life were discussed. To estimate the mean fatigue life under the conditions of any given tempering temperature and cycle stress amplitude based on 300 fatigue tests, the mean fatigue life estimation method based on RBF neural network was presented and verified by 12 other fatigue tests. The test results have shown that (1) the mean fatigue life decreases with the increase of tempering temperature for the same quenching media, (2) the mean fatigue life using brine is more than water which is more than naphthenic mineral oils for the same tempering temperature, and (3) the proposed method based on RBF neural network could accurately estimate the mean fatigue life when the tempering temperature and cyclic stress amplitude are given for each quenching medium.
Highlights
The fatigue life of the carbon steel could be improved by the quenched and tempered process
The effect of quenching media and tempering temperature on the fatigue life of the quenched and tempered 0.44 % carbon steel were analyzed and discussed, and the mean fatigue life estimation method based on RBF neural network was presented
The S–N curve was processed as fellows: (1) cycle stress amplitudes and means of the fatigue life were taken the logarithm with respect to base 10, (2) the linear regression model was employed to obtain the formulation between the base 10 logarithm of means of the fatigue life and cycle stress amplitudes, log N = log c − n log S, (1)
Summary
The fatigue life of the carbon steel could be improved by the quenched and tempered process. EN31 steel quenched in gingili oil have 10 times more fatigue life than the specimens quenched in the water and 100 times more than unquenched specimens in high-cycle rotating bending fatigue tests Tempering temperature is another important factor affecting the fatigue characteristics of the quenched and tempered carbon steel. It was reported by Yu et al (1988) that the fatigue limit decreased as the tempering temperature increased from 315, 482 to 649 ◦C for the centre-notched specimens, and the notch sensitivity and absolute notch fatigue strength were not significantly affected by the tempering temperature It was found by Oguma and Nakamura (2009) that in the 105–108 cycle range, the fatigue strength of the high strength steel tempered at 433 K was lower than that of the material tempered at 573 K where the uniaxial tension-compression fatigue tests were carried out.
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