Orientation and temperature dependence of plastic deformation processes in 3·25% silicon iron

Single crystals of a 3·25 % silicon iron were deformed in tension between 20 and 293 °K. The orientation was varied systematically between [010] and [110], to determine the orientation dependence of slip and twinning. The operative slip and twinning systems were measured by two surface analysis. At 20 °K all specimens twinned and fractured; at 77 °K crystals within 11° of [010] twinned and fractured and the remainder yielded before fracture; at 195 and 293 °K all specimens yielded. Yielding occurred by the formation and propagation of slip bands along the specimen. At 77 °K slip was confined to {011} planes but at higher temperatures slip occurred on the plane containing the <111> slip direction with the maximum resolved shear stress independent of whether or not it was a low index plane. The yield propagation stress varied with orientation in close agreement with that expected for slip on an {011} <111> system at all temperatures. Twinning occurred on those systems with the maximum resolved shear stress on the twin plane in the twinning direction and the results support a critical resolved shear stress law.