HIGH-STRAIN RATE TORSIONAL BEHAVIOR OF AN ULTRAHIGH CARBON-STEEL (1.8PCT C 1.6 PCT AL) AT ELEVATED-TEMPERATURE

The elevated temperature mechanical properties of a 1.8 pct C-1.6 pct Al ultrahigh carbon steel (UHCS-1.8C-1.6Al) is described in the temper ature range from 750 degrees C to 1150 degrees C and in the strain rat e range from 0.2 to 26 s(-1). A torsion test apparatus was used which permitted rapid cooling (50 degrees C per second) immediately after fr acture to establish microstructure-processing-property relations. The strength-strain rate relation of the UHCS-1.8C-1.6Al material correlat es well with a lattice diffusion-controlled dislocation creep process. The present data, together with other high carbon steels data, predic t that austenite containing a high amount of carbon in solution has a high stacking fault energy. The ductility of the UHCS-1.8C-1.6Al is ma ximum at 1050 degrees C. This indicates that successful deep die forgi ng and other mechanical processing operations at high strain rates sho uld be performed at this temperature. The microstructure of the deform ed samples consisted of a matrix of pearlite with some undissolved sph erical,carbides when rapidly cooled from 900 degrees C and 1050 degree s C and of a thin network of proeutectoid carbides when cooled from 11 50 degrees C. High hardnesses in the range of Rockwell C 42 to 50 are obtained for such structures.