Correlation of microstructure and fatigue properties of two high-strength spring steels

Abstract

This is a study of correlation of microstructure and fatigue properties of two high-strength steels, i.e., a V- and Cr-containing alloy steel and a 0.84%C steel, used for an automotive diaphragm spring. Fatigue properties were investigated with focuses on microstructures and tensile strengths under the fixed hardness condition. The fatigue test results indicated that the fatigue limits of the two steels were the same when tensile strengths were nearly the same (over 1400 MPa), and that they were linearly decreased in the alloy steel austenitized and tempered at higher temperatures. The results were then interpreted based on the microstructural parameters such as prior austenite grain size, amount of carbides and twinnings, and martensite lath width. The alloy steel having the higher tensile strength, and the smaller amount of carbides showed better fatigue properties than the 0.84%C steel. These findings suggested that fatigue properties of the spring steels can be pre-estimated by tensile strength instead of hardness since tensile strength correlated well with the fatigue limit. (C) 1999 Elsevier Science Ltd. All rights reserved.