DAMPING BEHAVIOR OF PRE-STRAINED HIGH MN STEELS

Effects of prestrain on internal friction (delta) at room temperature were investigated using a 28Mn-6Si-5Cr steel, in comparison with a 16Mn-5Ni steel which had been reported as a new type of damping material. A transversal vibration method with a frequency of 500 Hz and a strain amplitude of about 2x10(-5) was employed. Shape memory effect of the same 28Mn-6Si-5Cr steel was also examined to estimate the variation of deformation mode (gamma-->epsilon transformation or slip) with prestrain. With an increase in prestrain, delta changes almost parallel with the change in amount of epsilon phase in both steels. In the 28Mn-6Si-5Cr steel, moreover, nearly complete shape memory effect is observed up to 1% prestrain, while the amount of shape recovery strain exhibits a maximum at the prestrain of 5 or 6%. Considering the well known effects of epsilon phase on shape memory in high Mn-Si steels, the above results show that the increase in delta with increasing amount of prestrain up to 5 or 6% is attributed mainly to the epsilon phase which has been induced by prestraining. This suggests that the existence of epsilon phase is a major factor controlling the internal friction in high Mn steels.