THE TRANSFORMATION OF AUSTENTITE UNDER EXTERNALLY APPLIED TENSILE STRESS

Results on the transformation of austenite to upper bainite in AISI 1085 and 4340 steels are presented as well as preliminary data on the mechanical properties of lower bainite resulting from stress application during isothermal transformation. Experiments on AISI 1085 indicated that an applied stress exceeding the yield stress of the austenite increased the amount of transformation. The increment in transformation was related in the same manner to a critical true strain and deformation energy value. A mechanism was suggested for bainite transformation under stress. Results on AISI 4340 revealed that a stress of 60,000 psi effects the rate of transformation in such a way as to decrease the ending time of transformation by a factor greater than 10,000. No difference was observed microscopically in the size and shape of the carbide particles in the bainite formed under no stress and 60,000 psi.