An Expartmental Study of TRIP behavior in Cr-Ni-Mo-Al-Ti Managing Steel : Identification of Back Stress and Transformation Condition
Kiyokazu NAGAYAMA, Takaki TERASAKI, Fumi ISHII, Kikuaki TANAKA, F.D. FISCHER and G. CAILLETAUD
Abstract:The deformation and transformation behavior of a maraging TRIP (Transformation Induced Plasticity) steel (MAVAL X12) is studied experimentally. The stress holding test under cooling and the strain-controlled isothermal loading test are performed with the thin-walled tubular specimens in order to get the dilatation curves under a constant hold stress and the stress-strain curves. The existence of the back stress is confirmed since the dilatation curves do not close after a heating/cooling thermal cycle. Its value in the axial direction is determined to be 28.4 Mpa by means of the dilatation curves under applied hold stresses. The transformation-start condition is identified to be a linear Clausius-Clapeyron line both under tensile/compressive and shear stresses. The temperature-dependence of the yield stress determined by means of the tension, compression and torsion tests is charactered by the following: In the higher temperature range the measured values mean the yield stress of the parent phase, whereas in the low temperature range they exhibit the "composite effect," since the microstructure is consisted of the hard thermally- and stress-induced martensite phase and the soft parent phase. In the middle temperature range the measurement shows the result of the competition of both effects. Key Words:Transformation-Induced Plasticity (TRIP), Back stress, Martensite-start temperature, Ms-line, Yield stress