Grain boundary strengthening in austenitic nitrogen steels

The effect of nitrogen and carbon on the strengthening of the austenitic steel Cr18Ni16Mn10 by grain boundaries is studied. It is established in accordance with previous results that, in contrast to carbon, nitrogen markedly increases the coefficient k in the Hall-Petch equation. Because of a pronounced planar slip induced by nitrogen and the absence of any noticeable segregation of nitrogen atoms at the grain boundaries, nitrogen austenite presents an excellent object for testing different existing models of grain boundary strengthening (pile-up of dislocations, grain boundary dislocation sources, work hardening). Based on the analysis of available data and measurements of interaction between nitrogen or carbon atoms and dislocations it is shown that the nitrogen effect can be attributed to a strong blocking of dislocation sources in grains adjacent to those where the slip started.