Sharif Digital Repository

In this study, strain ageing during and after warm rolling of a carbon steel has been investigated. At the first step, the occurrence of serrated flow was studied by means of tensile tests at different temperatures and strain rates. In the next stage, warm rolling experiments were performed under different rolling conditions and then the samples were aged at the room temperature for a period of 3 months. For both aged and non-aged samples, tensile tests were employed to evaluate their mechanical properties. The results show that static strain ageing is possible to happen in the utilized ageing period and increases the yield stress of the aged steel. However, the samples that experience both... 

In the present work, the process of equal channel angular pressing of dispersion strengthened Cu-1̇1 wt-%Al2O3 containing nanometric alumina particles was investigated by means of mathematical modelling and experimental testing. Through the modelling, deformation parameters such as hydrostatic pressure distribution and strain field were determined, and the effect of deformation path on these parameters was estimated. Equal channel angular pressing as well as mechanical and microstructural evaluations were also conducted to assess mechanical properties, grain structure and void volume fraction after deformation in different routes. The results indicate that distributions of plastic strain and... 

In this work, the flow stress behavior of a metal matrix composite AA2017-10% SiCp was studied by means of the uni-axial compression test. The composite was first produced by stir casting technique and then, hot extrusion with the ratio of 18:1 was carried out to achieve a microstructure with a homogeneous distribution of SiC particles. In the next stage, the isothermal compression tests were conducted on the cylindrical specimens up to the true strain of 0.6. The experiments were performed at temperatures between room temperature to 400°C and strain rates of 0.003, 0.03 and 0.3s-1. Negative strain rate sensitivity was observed in the temperatures less than 250°C indicating the occurrence of... 

In this study, effect of rolling speed on strain aging phenomena in warm rolling of a carbon steel has been investigated. For this purpose, by using a mathematical model and predicting temperature and strain rate fields, the possibility of occurrence of dynamic strain aging during the warm rolling was first evaluated. In the next stage, warm-rolled samples were aged up to 11 months at room temperature for studying the kinetics of static strain aging, while mechanical tests as well as microstructural evolutions have been performed to determine the effect of strain aging on material behavior. The results indicate that dynamic strain aging may not occur for the employed rolling program;... 

In this work, the phenomenon of dynamic strain aging in a high carbon steel is studied and different initial microstructures including fine and coarse pearlite structures are considered. Tensile tests at different temperatures and strain rates are performed to evaluate the occurrence of dynamic strain aging and mechanical properties as well as to calculate apparent activation energies for onset and termination of dynamic strain aging. The results show that dynamic strain aging occurs for both microstructures while the initial microstructures alters the activation energies for appearance and termination of this phenomenon. The microstructural studies illustrate that a combination of cementite...