Abstract
The characteristics of cycle stress relatation for spring steels 355iMnVB, 50CrMn and 50CrVA under the conditions of various strain are investigated in the paper. The relateons between the decreasing value of cycle stress and the cycle numbers for three spring steels under the various cycle strain are measured. The microstructures of three spring steels are observed by optical microscope and TEM .The results show that the cycle stress relaxation value of new spring steel
35SiMnVB is less than that of spring 50CrMn but is more than that of spring steel 50CrVA . Some results are discussed in the paper.