Ultra-fine-Grained Ferrite Prepared from Dynamic Reversal Austenite During Warm Deformation

The ultra-fine-grained ferrite(UFGF) with the size of less than 1 μm is often difficult to be obtained for low-alloyed steel in practical production processing.In this study,considering the rod and wire production process,a new method for preparing the UFGF with submicron scale is proposed by warm deformation of six passes with total strain of 2.6,followed by the cooling process in Gleeble-3500 thermo-mechanical simulator.The results show that the UFGF with an average size of 0.64 μm could be obtained via the phase transformation from austenite grains with an average size of 3.4 μm,which are achieved by the deformation-induced reversal austenization during the high strain rate warm deformation.The main driving force for the reversal transformation is the stress.And the interval between the passes also plays an important role in the reversal austenization.

Formation mechanism and organizational controlling of ultra-fine-grain copper processed by asymmetrical accumulative rolling-bond and annealing

The initial copper with large grain sizes of 60-100 μm was processed by six passes asymmetrical accumulative rolling-bond （AARB） and annealing, the ultra-fine-grained （UFG） copper with grain size of 200 nm was obtained, and the microstructures and properties were studied. The results show that there are large sub-structures and also texture component C for the UFG copper obtained by six passes AARB, possessing high strength and microhardness in company with poor elongation and conductivity. Thereafter, the UFG copper was annealed at 220 °C for 35 min, in which the sub-structures disappear, the grain boundaries are composed of big angle grain boundaries, and the textures are composed of a variety of texture components and parts of twins. Compared with the UFG copper obtained by six passes AARB, the tensile strength and yield strength for the UFG copper obtained by six passes AARB and annealing at 220 °C for 35 min are decreased slightly, the elongation and conductivity are improved obviously.

Constitutive modeling of ultra?fine?grained titanium flow stress for machining temperature prediction

This work investigates the machining temperatures of ultra-fine-grained titanium(UFG Ti),prepared by equal channel angular extrusion,through analytical modeling.UFG Ti has great usefulness in biomedical applications because of its high mechanical strength,sufficient manufacturability,and high biocompatibility.The temperatures were predicted using a physics-based predictive model based on material constitutive relation and mechanics of the orthogonal cutting process.The minimization between the stress calculated using Johnson–Cook constitutive model and the same stress calculated using mechanics model yields the estimation of machining temperatures at two deformation zones.Good agreements are observed upon validation to the values reported in the literature.The machinability of UFG Ti is investigated by comparing its machining temperature to that of Ti–6Al–4V alloy under the same cutting conditions.Significantly lower temperatures are observed in machining UFG Ti.The computational efficiency of the presented model is investigated by comparing its average computational time(~0.5 s)to that of a widely used modified chip formation model(8900 s)with comparable prediction accuracy.This work extends the applicability of the presented temperature model to a broader class of materials,specifically ultra-fine-grained metals.The high computational efficiency allows the in situ temperature prediction and optimization of temperature condition with process parameters planning.