Hot Pressing of a Gas Atomized Ultrahigh Carbon Steel Powder and Superplasticity

An ultra high carbon steel powder prepared by N2-gas atomizing was hot pressed in a vacuum for 0.9-10.8 ks at 20-160 MPa at 973 K. Dense compacts having a relative density more than 99% of the theoretical value were obtained by hot pressing for 0.9 ks at 160 MPa and for 7.2 ks at 100 MPa. The analysis of the densification process by hot pressing theory indicated that sintering by a superplastic type flow mechanism occurred during the hot pressing.The flow stress-strain rate relationship obtained flom the results of change-in-strain rate test of the hot pressed specimen (>99% relative density) at 973 K yielded the high strain rate sensitivity (m=0.44). At the same time, the hot pressed compacts showed an excellent formability by compressive creep tests at 973 K. It has been concluded that superplastic flow operats during the deformation process of the hot pressed compacts of the present material.