Showing 7 results for Crystallization
S. Mirzaei , A. Jazayeri Gharehbagh,
Volume 31, Issue 1 (6-2012)
Abstract
The soft magnetic nanocrystalline Fe73.5Si13.5B9Cu1Nb3 alloy (FINEMET®) is produced by heat treatment of amorphous precursor. Determining kinetic parameters of amorphous structure transformation to nanocrystalline allows the control of microstructure (e.g. size and volume fraction of nanocrystalline grains) in order to achieve desired soft magnetic properties by optimizing the heat treatment conditions. In this research, the nanocrystallization kinetics of amorphous FINEMET alloy were studied using isoconversional and isokinetic methods under non-isothermal conditions of various heating rates ranging from 5 to 20˚C/min. The changes in the microstructure and magnetic properties of amorphous ribbon during nanocrystallization process were studied using X-ray diffractometry and hysteresisgraph, respectively.
S. Ahmadi, R. Arabi Jeshvaghani, H.r. Shahverdi,
Volume 34, Issue 1 (5-2015)
Abstract
In this research, crystallization of Fe36Cr12Mo10 and α-Fe phases in devitrification of Fe51Cr18Mo7B16C4Nb4 amorphous alloy was studied using X-ray diffraction and transmission electron microscopy. For evaluation of crystallization kinetics, differential scanning calorimetric tests were carried out at different heating rates. Results showed that two-step crystallization led to the formation of Fe36Cr12Mo10 and α-Fe phases in the structure of alloy. Activation energy of crystallization of Fe36Cr12Mo10 and α-Fe phases measured according to Kissinger-Starink model were 747 and 880 kJ/mol, respectively. Results growth mechanism along with the decreasing nucleation rate in crystallization of Fe36Cr12Mo10 and α-Fe phases.
H. Chavilian, K. Farmanesh, A. Soltanipour, E. Maghsoudi,
Volume 36, Issue 3 (11-2017)
Abstract
In this research, industrial hot deformation processes was simulated for 321 austenitic stainless steel using hot compression test with the aim of acquiring technical knowledge and indigenization of stainless steel production. The obtained stress-strain curves showed the common retrieval dynamic behaviour. By microscopic studies, the main restoration mechanism during hot deformation in this steel was diagnosed as dynamic recrystallization, that due to low stacking fault energy of 321 stainless steel, this phenomenon was justified. Then, using diagrams related to real stress, real strain and strain rate, the onset point of dynamic recrystallization was determined under different conditions. Also, using the constitutive equations and Zener-Holloman parameter, hot deformation behaviour of 321 stainless steel was studied and the activation energy of hot deformation for this steel was determined as 422 (Kj/mol).
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.
R. Amirarsalani, M. Morakabati, R. Mahdavi,
Volume 40, Issue 1 (5-2021)
Abstract
In this research, the hot deformation behavior of W360 tool steel was investigated using hot compression test at 1000-1200°C and strain rates of 0.001, 0.01, 0.1, and 1 s-1. According to the results, dynamic recrystallization was found the most important restoration factor of this alloy during hot deformation. Recrystallization was enhanced with an increase in temperature and strain rate. Also, the hot working process was optimized by drawing the processing map of this steel. Microstructural images obtained from the hot compression test showed that recrystallization started at 1000°C and the strain rate of 0.01 s-1 and developed with increasing temperature and strain rate due to an increase in the stored energy and suitable regions for nucleation. The results of drawing the processing map showed that the best hot deformation region was the temperature range of 1050-1150°C and strain rates of 0.1-1 s-1.
M. Kamali Ardakani , M. Morakabati,
Volume 40, Issue 2 (9-2021)
Abstract
The aim of this study was to investigate the behavior of hot deformation and occurrence of restoration phenomena during the deformation of AISI H10 hot work tool steel. For this purpose, hot tensile test was performed on the steel in the temperature range of 900-1150 ºC with a temperature interval of 50 ºC and at a constant strain rate of 0.1s-1. The microstructures were examined and the curves of hot flow and ductility were drawn. According to the curves and microstructures, ductility was lower at temperatures of 900 ºC and 950 ºC due to inactivity of repair processes and the presence of carbides. Ductility increased in the temperature range of 1000-1100 ºC due to the occurrence of dynamic recrystallization. Finally, ductility decreased in the temperature of 1150 ºC due to the dissolution of carbide particles and grain growth. The results obtained from hot tensile test and microstructural studies at a constant strain rate of 0.1s-1 revealed that the appropriate temperature range for deformation of AISI H10 hot work tool steel was 1000-1100 ºC.
