| Summary: | To develop higher strength spring steels with better performance for advanced automotive and transportation industries in line with the trend of lightweight, the strengthening mechanism of two practical 55SiCr and 55SiCrNbV spring steels, which represents plain and micro alloyed spring steels, has been investigated based on the systematic characterization of microstructures, hardness, and tensile test. The tensile strength and hardness were found to be correlated well in a linear relationship. Then the strengthening coefficients of C, Si, Cr and Mn were determined to quantify the solid solution strengthening. The strengthening mechanism of spring steels was found to be the summation of solid solution strengthening, grain refinement, dislocation, and precipitation strengthening, which agree well with the tensile test results. The strengthening mechanism could be used as guidance to develop next generation spring steels, which well explained the ultra-high strength spring steels over 2200 MPa class in the literature.
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