Constitutive Analysis in Hot Working of a Nb Heavily Alloyed Stainless Steel

AISI 347 is an austenitic stainless steel heavily alloyed by around 0.7%Nb, which is much larger than the average content of Nb in the microalloyed steels. In this paper, hot working of AISI 347 SS was simulated by the uniaxial compression tests in a thermomechanic simulator, Thermecmaster Z. Its stress strain curves were measured at the various strain rates and deformation temperatures. All flow curves, at temperatures between 970∼1230°C and strain rates of 0.04–40/s, show a typical characteristics, i.e. stress increases with increasing strain without a peak stress observed. Numerical simulations on these flow curves shows that they can not be simulated by the well known equation in the literature σHW=σ0+Bm[1-exp(-cɛ)], but by a modified one σ=Bm[1-exp(-cɛ)]+k(ɛ-ɛs). The five coefficients in the modified equation are dependent on the strain rate and deformation temperature, such dependence has been quantified by the least square fitting method in this paper. Finally, a mathematic model is developed and can successfully describe stress-strain curves at various strain rates and temperatures for the hot working of AISI 347 SS.