The strain dependence of the flow stress-grain size relation for 70:30 brass

Abstract

The grain size dependence of the stress-strain behavior of annealed 70:30 brass was evaluated using room temperature tensile tests. The resulting data, which covered × 10-5 to 4 × 10-1, were analyzed in terms of the conventional Hall-Petch stress-grain size equation, σ∈ = σO∈ +k∈l-1/2, and, also, in terms of the extended Hall-Petch equation previously proposed for 70:30 brass, σє = σ0y+ A Єp + β(єp/l1/2 +kl−1/2 The lattice friction stress, σ0∈, increased linearly with plastic strain over nearly the full strain range. The lattice friction stress for the initiation of plastic flow, σ0y, was evaluated using two alternative double extrapolation procedures. Both extrapolation techniques, which involved the macrostrain behavior, gave the same σ0y value of 3.4 kg/mm2, which agreed with the σ0∈ value determined directly in the microstrain region (∈ <-10-3). Large grain size specimens, which yielded homogeneously, exhibited a kx2208; value of only 0.2 kg/mm3/2 at a plastic strain of 1 × 10-5; however this small kx2208; increased rapidly with increasing microstrain. For the small grain size specimens, which yielded via a Luders extension,ke was essentially constant at 0.8 kg/mm3/2 for all microstrains; however, kx03B5; did increase in the macrostrain region to a maximum value of 1.6 kg/mm3/2. When consideration was given to a grain size dependent increase in dislocation density, an intrinsic grain boundary resistance to plastic flow of approximately 0.7 kg/mm3/2 was obtained.