Institute of Metals Division - Further Observations on Yield in Single Crystals of Iron

Studies have been made of the method of propagation of yield in iron single crystals in the range of 205' to 295OK by microscopic and X-ray techniques. 'The results show yielding in two stages, of which the second corresponds closely to the Lüders extension in polycrystalline iron. IRREGULAR macroscopic markings On the polished surface of a polycrystalline mild steel test piece during the lower yield extension were first observed by Liiders.' The lower yield stress was not very constant. Sylvestrowicz and Hall2 showed that it was possible to obtain a constant lower yield stress by using a specimen in the form of a moderately flexible thin strip; the macroscopic markings in this case then appeared as a band of deformation (Lüders' band) which propagated steadily from one or occasionally