INFLUENCE OF NITRIDE (CR2N) PRECIPITATION ON THE PLASTIC-FLOW BEHAVIOR OF HIGH-NITROGEN AUSTENITIC STAINLESS-STEEL

Aging at 700 °C results in grain boundary nitride precipitation only, while aging at 900 °C results in grain boundary and cellular precipitation (40 vol%). These thermal treatments have a small but positive effect on YS, no effect on the UTS, but dramatically reduce the ability of the material to deform under localized plastic deformation (necking), leading to reduced tensile ductility. The plastic flow behavior of all annealed and aged high-nitrogen samples were modeled using the modified Ludwik relation (equation 2). Below the UTS, grain boundary nitride precipitation at 700 °C has no measurable effect on the plastic flow behavior of the material, and the modeling parameters n1, K1, n2, and K2 have values which do not deviate significantly from the behavior of the un-aged material. Cellular precipitation, caused by aging at 900 °C, does significantly affect the plastic flow behavior of the material at both low and high strains. Cellular precipitation causes both increased strengthening of the matrix in the low strain regime (0.001 < ε < 0.03) and systematic decreases in the strain hardening exponent (n1) and strength coefficient (K1) with increased aging. The rate of strain hardening ( dσ dε) measured from the σ-ε plots is unaffected by isothermal aging and nitride formation. © 1994.