H. Fathi, B. Mohammad Sadeghi, E. Emadoddin, H. Mohammadian Semnani,
Volume 16, Issue 3 (September 2019)
Abstract
Abstract
In the present research, the behavior of 304L austenitic stainless steel in the deep drawing process has been studied at the room temperature through experimental and finite element simulation method. Magnetic method calibrated by XRD was used to measure induced-martensite. Martensite volume fraction in the various portion of the deep drawn cup under optimum Blank Holder Force (BHF) and in the rupture location was evaluated. Findings of the present study indicated that higher martensite volume fraction occurred in the flange portion in the drawn cup due to higher strain and stress concentration in this area. Also, rupture happened at the arc portion of the wall of drawn cup with higher blank diameter due to higher strain, work hardening and martensitic transformation. Both experimental and simulation results showed that maximum LDR of 2 obtained in the forming process. All experimental procedures were simulated by LS-DYNA software, employing MAT_TRIP, and experimental results were in good agreement with the FE simulation.
F. Hosseinabadi, A. Rezaee-Bazzaz, M. Mazinani, B. Mohammad Sadeghi,
Volume 17, Issue 1 (March 2020)
Abstract
An experimental–numerical methodology was used in order to study the microstructural effects on stress state dependency of martensitic transformation kinetics in two different TRIP800 low alloy multiphase steels. Representative volume elements extracted from actual microstructure have been utilized for simulating the mechanical behavior of mentioned steels. The mechanical behavior for each constituent phases required in the model has been taken out from those reported in the literature. A stress invariant based transformation kinetics law has been used to predict the martensitic phase transformation during deformation. Crystallographic and thermodynamic theories of martensitic phase transformation have been utilized for estimating the constant parameters of the kinetics law, in a recently performed investigation, but the sensitivity of the transformation to the stress state remained as an adjusting parameter. The results of the current work show that the stress state sensitivity of martensitic phase transformation in the investigated steels is microstructure-dependent and the value of this parameter is almost equal to half of the bainite volume fraction. Therefore, the volume fraction of bainite in the low-alloy multiphase TRIP800 steels can be used as a first postulation for the value of the martensitic phase transformation sensitivity to the stress state and the microstructure based model previously developed for calculating the mechanical behavior of the TRIP800 steels can be utilized as a virtual design tool for development of TRIP steels having specific mechanical properties.
Mitra Ghannadi, Hediye Hosseini, Bagher Mohammad Sadeghi, Bahman Mirzakhani, Mohammad Tahaaha Honaramooz,
Volume 18, Issue 3 (September 2021)
Abstract
The objective of the present paper is to investigate the effects of rapid heating and cryogenic cooling on on the microstructure and tensile properties of Al-Cu-Mg. The specimens were subjected to three heat treatment cycles in which the Infrared heating (IR) were used as the heating medium at the ageing stage, and the liquid nitrogen and water were used as the quenching mediums. The ageing temperature and time were 190⁰C and from 2 hours to 10 hours, respectively.The results indicated that by using IR at the ageing stage, the hardening rate enhanced because the rapid heating via this method leads to faster diffusion of the alloying elements. Moreover, the high density of nano-sized precipitates formed during ageingleads to higher strength and suitable ductility. Cryogenic treatment showed a negligible effect on both microstructure and tensile properties; however, it improved ductility. Overall, the combination of a high heating rate and cryogenic treatment led to the highest mechanical properties. SEM micrograph of the fracture surface of alloy demonstrated that in Cryogenic treatment+Artificial Ageing (CAA) condition, the surface had been fully covered by deep dimples in contrast to the Cryogenic treatment+Infrared Heating (CIR) and Water-Quench+ Infrared Heating (QIR) conditions which their dimples were shallow and also some facets were observed.
