MICROSTRUCTURE AND MECHANICAL PROPERTIES OF RAPIDLY-SOLIDIFIED WHITE-CAST IRON POWDERS AND IRON/WHITE CAST IRON PARTICULATE COMPOSITES.

摘要

The importance of microstructure on the room and elevated temperature mechanical properties of white case iron is investigated. Four different microstructures are investigated: (1) as cast, (2) thermomechanical processed, (3) rapidly solidified and warm pressed and (4) iron/white cast iron particulate composites.;White cast iron powders containing 2.4 and 3.0%C as well as a 3.0%C alloy containing 1.5%Cr, were investigated. All these powders were obtained by the rapid solidification rate process prepared by Pratt and Whitney of West Palm Beach, Florida. The as-quenched microstructures of these white cast iron powders consist basically of retained austenite and cementite.;In order to determine the influence of fine microstructure on the mechanical properties of the rapidly solidified white cast irons, intermediate and room temperature tensile and compression tests were conducted on warm pressed and rolled material. The elevated temperature tensile elongations, strain rate sensitivity exponents and activation energies for plastic flow measured on these materials are in agreement with models for superplasticity based on grain boundary sliding accommodated by slip mechanisms adjacent to the grain boundary. A tensile ductility of over 7% was obtained in rapidly solidified 3.0%C white cast iron at room temperature.;The room temperature mechanical behavior of particulate composites made from pure iron and white cast iron powders was also investigated. A unique heat treatment that allows selective hardening of the white cast iron constituent while the iron matrix is relatively unaffected is also discussed.;White cast iron containing 2.1 and 2.4%C has been thermomechanically processed to refine the microstructure. The effect of this processing on the elevated temperature and room temperature mechanical properties is discussed. The room temperature tensile strength is greatly increased over the as-cast properties. The material becomes superplastic at elevated temperatures. Elongation to failure is shown to be limited by nucleation of voids that occur at large eutectic carbides that cannot be refined by the thermomechanical processing.