Precipitation and flow behavior of AISI 630 stainless steel deformed at elevated temperatures

Hot compression tests were performed on the samples of AISI 630 stainless steel in the temperature range of 900-1050 C and at strain rates of 10–3- 1 s21. Single peak stress flow behavior was observed at all deformation conditions. An irregular relationship was found between the peak point of flow curves and processing condition, i.e., temperature and strain rate. The stress relaxation tests at the temperature range of 900-1050 C revealed that dynamic precipitation (DP) of carbides in the matrix and grain boundaries causes the considered irregularities in the peak stres

Enhanced grain refinement of commercial pure copper using the ECAE of Al–Cu–Al tri-layer composite

Equal channel angular extrusion (ECAE) is a promising technique for production of ultrafine grained (UFG) materials of few hundred nanometers size. In this research, the grain refinement of copper strip is accelerated to ultrafine range by sandwiching it between two aluminum strips and then subjecting the three strips to ECAE process simultaneously. After passing the aluminum–copper–aluminum laminated billet through ECAE die up to 8 passes, tensile properties of the copper layer are evaluated. The optical, scanning and transmission electron microscopes, differential scanning calorimeter, and X-ray diffraction were used to characterize the microstructural changes. The results show that the yield stress of the middle layer (Cu) is increased significantly by about eight times after application of four consecutive passes of ECAE and then it is slightly decreased when more ECAE passes are applied. An ultrafine grain within the range of 150 to 200 nm is obtained in the Cu layer

Precipitation and Flow Behavior of AISI 630 Stainless Steel Deformed at Elevated Temperatures

Hot compression tests were performed on the samples of AISI 630 stainless steel in the temperature range of 900-1050 degrees C and at strain rates of 10(-3)- 1 s(-1). Single peak stress flow behavior was observed at all deformation conditions. An irregular relationship was found between the peak point of flow curves and processing condition, i.e., temperature and strain rate. The stress relaxation tests at the temperature range of 900-1050 degrees C revealed that dynamic precipitation (DP) of carbides in the matrix and grain boundaries causes the considered irregularities in the peak stress. The FE-SEM studies also showed that DP of carbides could be responsible for the retardation of dynamic recrystallization (DRX). The phase extraction by residual testing ascertained that fine niobium carbides are the major sources for the effect of DP on the microstructural mechanisms. EBSD and optical microscopy confirmed the occurrence of continuous dynamic recrystallization by the progressive evolution of substructure toward the formation of new small grains. The enhancing rotated (cube) or slight weakening of copper and brass/ Goss texture components were mainly associated with the DRX. The hyperbolic sine equation is used in calculating the activation energy at strain of 0.4 as 485.6 kJ/mol