High strain rate torsional behavior of an ultrahigh carbon steel (1.8 pct 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 temperature range from 750 degrees C to 1150 degrees C and in the strain rate 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 fracture to establish microstructure-processing-property relations. The strength-strain rate relation of the UHCS-1.8C-1.6Al material correlates well with a lattice diffusion-controlled dislocation creep process. The present data, together with other high carbon steels data, predict 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 maximum at 1050 degrees C. This indicates that successful deep die forging and other mechanical processing operations at high strain rates should be performed at this temperature. The microstructure of the deformed samples consisted of a matrix of pearlite with some undissolved spherical,carbides when rapidly cooled from 900 degrees C and 1050 degrees C and of a thin network of proeutectoid carbides when cooled from 1150 degrees C. High hardnesses in the range of Rockwell C 42 to 50 are obtained for such structures.