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).
S. E. Mousavi, M. Meratian, A. Rezaeian,
Volume 36, Issue 4 (3-2018)
Abstract
Equal Channel Angular Pressing (ECAP) is currently one of the most popular methods for fabricating Ultra-Fine Grained (UFG) materials. In this study, mechanical properties of the 60-40 two phase brass processed were evaluated by ECAP. The samples were repeatedly ECAP-ed to strains as high as 2 at a temperature of 350 ◦C using route C. The microstructure of the samples showed that small grains were formed in the boundaries which indicates the occurrence of recrystallization in different passes. Observation of slip trace in the microstructure of the samples showed that even in such alloy with a low-stacking fault energy, dislocations slip trigger the deformation. Investigation of mechanical properties showed that with increasing the number of passes, tensile strength, microhardness and ducility improved at the same time.
A. Sheikhali, M. Morakkabati, S. M. Abbasi,
Volume 38, Issue 1 (6-2019)
Abstract
In this paper, in order to study the flow behavior and elongation of as-cast ingots of SP-700 titanium alloy, hot tensile test was done in α/β dual phase and β single phase regions using strain rate of 0.1 s-1. Results showed that the hot tensile behavior of SP-700 in the α/β dual phase region (700-900 ºC) was different from the β single phase one (950-1100 ºC) due to the nature of alpha and beta phases and their crystallographic structure. This was since the number of slip systems and deformation mechanism in HCP structure were different from those in BCC structure. Beside, the intensive variation of elongation in microstructural studies showed that the dominant mechanism of hot tensile deformation of SP-700 alloy was dynamic recovery (DRV). Thus, serration of grain boundaries and occurrence of DRV were the reasons for the increase of elongation with the rise of temperature. However, beta grains growth and occurrence of grain boundary fracture made a slight decrease in elongation in the temperature range of 1000-1100 ºC.
H. R. Shahverdi, R. Alipour Mogadam,
Volume 38, Issue 2 (9-2019)
Abstract
Creep age forming (CAF) process is a novel metal forming method with major benefits including improved mechanical properties and cost reduction for aviation industry applications. CAF happens due to creep phenomenon and stress-release during the artificial aging of heat-treatable aluminum alloys. In this work, the creep age forming of 7075 Aluminum alloy at 120, 150 and 180 °C for 6, 24 and 48 h was done; tensile and hardness tests were used to characterize the samples. Results on spring-back revealed that it was influenced by time and temperature; by increasing the time and temperature, it was reduced from 54.1 to 39.51. Mechanical property evaluation also showed that by increasing the time, the strength and hardness could be enhanced due to microstructural evolution and precipitation during the CAF process. According to the mechanical and CAF results, two samples were selected as the optimum ones and their work hardening behavior and fracture surfaces were investigated
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
M. H. Musazadeh, R. Vafaei, E. Mohammad Sharifi, Kh. Farmanesh,
Volume 38, Issue 3 (12-2019)
Abstract
Finite element (FE) simulations in conjunction with experimental analysis were carried out to characterize the deformation behavior of an AISI 321 austenitic stainless steel (ASS) during cold pilgering process. The effect of process parameters including feed rate (4 and 8 mm) and turn angle (15, 30 and 60°) on damage build-up were also evaluated. The Johnson-cook model was used to simulate the flow behavior of material. By considering compressive stresses, a new revised Latham-Cockcraft damage was calculated and used to determine the optimum process parameters. It was found that the radial and hoop strains in all friction conditions were compressive, while the axial strains were observed to be tensile. The amount of strain (whether it is compressive or tensile strain) was also higher on the outside of the tube compared to its inside. By considering fatigue cycles of a tube element during the process, the feed rate of 8mm, turn angle of 60° and the lowest coefficient of friction were determined as optimum parameters.
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.
M. T. Asadi Khanouki,
Volume 39, Issue 3 (12-2020)
Abstract
In this study, the influence of temperature and strain rate on plastic flow of a Zr-based bulk metallic glass (BMG) during the three-point bending test was studied to find a correlation between strain rate sensitivity (m) and flow behavior. The flexural stress-deflection curves revealed two distinct types of dynamics, serrated and non-serrated flow, related to temperature and strain rate. The serrated flow which appeared at temperatures higher than a critical value or strain rates lower than a critical value, was simultaneously due to activation of shear transformation zones (STZs) and time-dependent structural relaxations. Further results indicated negative and positive values of m at temperatures above and below 0.4 Tg, respectively. The main reason for negative strain rate sensitivity was insufficient time of structural relaxation at high strain rates which lead to generation of free volume inside shear bands making the BMG softer. Comparison of STZ activation energy with activation energy for the onset of serration indicated almost equal values and there was a close relationship between serrated flow and STZ operation.
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.
S. Shahzamani, M. R. Toroghinejad, A. Asharfi,
Volume 40, Issue 2 (9-2021)
Abstract
In this study, Al/Al2O3 composite was produced by accumulative roll bonding (ARB) process coupled with the plasma electrolytic oxidation (PEO) process. The alumina was grown on Al sheets by electrolyte technique with three different thicknesses (10, 20, and 40 µm). The results showed that incorporation of alumina up to 3.22 vol.% in aluminum matrix enhanced the yield and tensile strength of the composite, whereas increasing the amount of alumina up to 6.25 vol.% deteriorated the tensile properties. In the last part, a serial sectioning process was employed to develop a three-dimensional (3D) representation of the microstructure of Al2O3 particles reinforced Al composite for visualization and finite-element modeling (FEM).
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.
