Effect of grain refinement on the endurance limit of plain carbon steels at various strength levels

The relationship between the endurance limit and ferrite grain size was investigated in a wide range of ferrite grain sizes using smooth specimens of low carbon steel, medium carbon steel and low alloy steel under rotating bending. It was found that the endurance limit of ferritic pearlitic steel clearly shows the Hall-Petch type relationship when the metallurgical parameters, such as chemical compositions and microstructural morphologies are the same. The endurance limit can be determined by the additive effect of the strength level of the matrix ferrite and the grain refinement. The effect of grain refinement on the endurance limit was constant irrespective of the strength level of the matrix microstructure.