ON THE DEFORMATION MECHANISMS IN SINGLE CRYSTAL HADFIELD MANGANESE STEELS I. Karaman, Huseyin Sehitoglu and Ken Gall Department of Mechanical and Industrial Engineering University of Illinois, Urbana, IL 61801, USA Yuriy I. Chumlyakov Physics of Plasticity and Strength of Materials Laboratory Siberian Physical and Technical Institute, 634050 Tomsk, Russia (Received November 24, 1997) (Accepted in revised form December 12, 1997) Introduction Austenitic manganese steel, so called Hadfield manganese steel, is frequently used in mining and railroad frog applications requiring excessive deformation and wear resistance. Although it was discovered more than a hundred years ago by Robert Hadfield, its deformation mechanisms, particularly Its work hardening ability, are still not completely understood. Previous studies [1– 4] attributed the work-hardening characteristics of this material due to dynamic strain aging [3] or an imperfect deformation twin, a so-called pseudotwin [1]. Unfortunately, these previous studies have all focused on polycrystalline Hadfield steels. To properly study the mechanisms of deformation in the absence of grain boundary or texture effects, single crystal specimens are required. The only published study to date on single crystal Hadfield steels is by Shtremel et al. [4] who investigated orientations in which slip is principal mechanism of deformation. They observed that only one slip system dominates in the plastic deformation of the 010 and near 012 orientations. They also noted that dislocations are stopped by collisions with stacking faults, creating similar work hardening characteristics as other fcc materials undergoing multiple slip. However, it is still necessary to consider crystallographic orientations where twinning will dominate the deformation since twinned regions have been observed in deformed polycrystals [1,2]. Experiments on traditional fcc single crystal materials have demonstrated that twins normally form after considerable levels of slip strains are developed [5]. However, since the study by Copley and Kear [6] on the effect of the applied stress on the stacking fault energy and partial dislocation separation, it has been realized that twinning may play an important role on the initial yielding of the fcc materials with low stacking fault energies. Previous studies of the authors on single crystal austenitic stainless steels with high nitrogen concentrations [7], showed that an increased nitrogen concentration decreased the stacking fault energy and caused twinning to be observed at the early stages of deformation. Pergamon Scripta Materialia, Vol. 38, No. 6, pp. 1009 –1015, 1998 Elsevier Science Ltd Copyright © 1998 Acta Metallurgica Inc. Printed in the USA. All rights reserved. 1359-6462/98 $19.00 + .00 PII S1359-6462(97)00581-2 1009