Showing 4 results for Hot Deformation
K. Farmanesh and A. Najafi-Zadeh,
Volume 23, Issue 1 (7-2004)
Abstract
Among the titanium alloys, Ti-6Al-4V is the most widely used. In the present work, the uniaxial hot compressive behavior of Ti-6Al-4V has been investigated under constant strain rates. A series of dilatometery experiments were carried out to determine the transformation temperatures at different cooling rates. Specimens were homogenized at 1050 °C for 10 minutes followed by fast cooling to different straining temperatures from 1050 to 850°C. The cooling rate was chosen fast enough to prevent high temperature transformation during cooling. A series of isothermal compression tests were conducted at different temperatures of 850, 900, 950, 1000, 1050°C at constant true strain rates of 0.1, 0.01 and 0.001 s-1, respectively. Samples were uniaxialy compressed to a true strain of 0.55 followed by water quenching to room temperature. The apparent activation energy for compression in two phase regions was calculated at 840 KJmol-1. The partial globularization of a-phase was observed in the specimens deformed at low strain rates and at temperatures near the transformation zone followed by annealing.
R. Taherian, A. Najafi Zadeh, M. Shamanian, R. Shateri,
Volume 25, Issue 1 (7-2006)
Abstract
In this study, two CCCT diagrams are drawn to be compared with a CCT diagram. The CCCT diagrams represent continuous cooling transformations in stress assisted state. The increased Md and Bd temperatures of CCCT diagrams were also compared with those of the CCT diagrams and the cause was investigated from both thermodynamic and metallurgical viewpoints. Thermodynamic examinations revealed that stress causes the mechanical driving force to increase but the total free energy of transformation to decrease hence, Md and Bd will rise. Metallurgical investigations showed that if deformation temperatures are selected in a manner to increase the structural strength of the original austenite grains prior to deformation, the shear force required for martensite and bainite transformations will arduously obtain hence, Md and Bd will fall. However, if recrystallization or full recovery occurs during or after deformation, interior grain structure softens and the shear force required for martensite and bainite transformations will readily obtain hence, Md and Bd will rise. It was also found that the nose in CCCT curves are shifted to the left as compared to that of CCT curves. This indicates that deformation of steel enhances bainite formation more readily than that of the martensite phase.
M. Samii Zafarghandi, S. M. Abbasi,
Volume 38, Issue 2 (9-2019)
Abstract
In the present work, hot tensile behavior of Haynes 25 Co-base alloy was investigated in the temperature range of 950-1200 ˚C and 0.1 s-1. Thermodynamic calculations showed that M23C6 and M6C carbides were stable below 1000 ˚C and above 1050 ˚C, respectively. Stress-strain curves also indicated an unusual trend of strain fracture. It was observed that with increasing temperature from 950 to 1050 ˚C, the fracture strain was decreased, while it was raised above 1050 ˚C again. Increasing the volume fraction of M6C carbide rich in Tungsten resulted in the loss of ductility. Also, microstructural evaluations showed dynamic recrystallization (DRX) grains were nucleated and growth was around carbides and the initial grains at 1150 ˚C. Occurrence of DRX led to the improvement of ductility via grain refinement mechanism, so this alloy had the highest level of ductility at 1150 ˚C
F. Mostafaee Heydarloo, M. Morakabati, H. Badri ,
Volume 39, Issue 3 (12-2020)
Abstract
The aim of this study was to investigate the suitable temperature range for hot deformation of three medium carbon Ni-Cr-Mo low alloy steels by hot tensile and hot torsion tests. Hot tensile tests were carried out in the te,prature range of 850-1150°C at a constant strain rate of 0.1 s-1 until fracture. Then, the tensile flow behavior, hot ductility and microstructural evolution of the steels were studied. Hot torsion tests were performed in the temperature range of 1200-780°C at strain of 0.1 with strain rate of 1s-1. The effect of titanium and niobium on the mean flow stress and the non-recrystallization temperature were investigated. The tensile test results showed that dynamic recrystallization was the dominant mechanism at temperatures above 950°C in the base steel and temperatures above 1050°C in the microalloyed steels. The results of hot torsion tests showed that the non-recrystallization temperatures of the base, Ti containing and Nb containing steels were 1070°C, 1069°C and 1116°C, respectively. Finally, the suitable hot deformation temperature range to achieve optimum mechanical properties in the base and Ti containing steels obtained as 950-1070°C and that of Nb containing steel obtained as 950-1100°C.
