Showing 4 results for Bainite
Dehghan Manshadi A., Zarei Hanzaki A., Golmahalleh O.,
Volume 2, Issue 2 (6-2005)
Abstract
The presence of bainite in the microstructure of steels to obtain a proper combination of strength and toughness has always been desired. The previous works however have shown that the presence of preferred bainite morphologies in the microstructure of any steel would not be readily accessible. In addition, the appearance of different bainite morphologies in the microstructure of any steel is dictated by different factors including the steel initial microstructure, austenitization characteristics, thermomechanical processing parameters and so on. Accordingly, in the present work, the effect of prior austenite grain size and the amount of austenite hot deformation on the bainite formation characteristics were investigated in 0.12C-2.5 Ni-1.2Cr steels. The results indicated that the prior austenite grain size and the amount of deformation in the austenite no-recrystallization region resulted in significant changes of the bainite formation kinetics and morphology.
K. Ghadarghadr Jahromi, , A. Zarei-Hanzaki, O. Golmahalleh,
Volume 5, Issue 1 (3-2008)
Abstract
Abstract: In the present investigation, the effects of thermomechanical processing parameters and
the steel chemical composition on the ultra fine ferrite formation characteristics were studied.
This was programmed relying on the capabilities of strain induced transformation (SIT)
phenomenon and applying to different grades of Si-Mn TRIP (Transformation Induced Plasticity)
steels. Accordingly, wedge shaped specimens were rolled at two different temperatures, above and
below the austenite-to-ferrite transformation temperature (Ar3). An ultra fine ferrite grain size, in
the scale of some hundred nanometers, was obtained by rolling the specimens with lower Si
content at a temperature below the related Ar3 temperature. The amount of reduction, which was
resulted in the latter microstructure, was realized to be about 55%.
Khodamorad Abbaszadeh, Shahram Kheirandish, Hassan Saghafian,
Volume 7, Issue 3 (8-2010)
Abstract
The effects of lower bainite volume fraction on tensile and impact properties of D6AC ultrahigh strength steel were studied in the current work. To obtain mixed microstructures containing martensite and different volume fractions of the lower bainite, specimens were austenitized at 910° C, then quenched in a salt bath of 330°C for different holding times, finally quenched in oil. In order to obtain fully martensitic and bainitic microstructures, direct oil quenching and isothermal transformation heat treatment for 24 hours were used respectively. All specimens were double tempered at 200°C for 2 hours per tempered. Microstructures were examined by optical and scanning electron microscopes. Fracture morphologies were studied by scanning electron microscopy (SEM). Results showed that both yield and ultimate tensile strength generally decreased with an increase in volume fraction of lower bainite. However, a few exceptions were observed in the mixed microstructures containing 12% lower bainite, showing a higher strength than the fully martensitic microstructure. This can be explained on the basis of two factors. The first is an increase in the strength of martensite due to the partitioning of the prior austenite grains by lower bainite resulting in the refinement of martensite substructures. The second is a plastic constraint effect leading to an enhanced strength of lower bainite by the surrounding relatively rigid martensite. Charpy V-notch impact energy and ductility is improved with increasing the volume fraction of lower bainite.
A. Kazazi, S. M. Montazeri, S. M. A. Boutorabi,
Volume 17, Issue 4 (12-2020)
Abstract
In the present study, austempering heat treatment was performed on compacted graphite aluminum cast iron with the chemical composition of 4.8%wt Al, 3.2%wt C, 0.81%wt Ni, 0.37%wt Mn, and 0.02%wt Mg. This study aims to investigate the effect of aluminum additions and removal of silicon on the kinetics of austempering transformation of Fe-3.2%C alloy. The cast samples were austenitized at 900 °C for 120 min and the isothermal austempering heat treatment was performed at 200 °C, 300 °C and 400 °C for 5, 30, 60, 120 and 180 minutes, respectively. Kinetics of this transformation was studied by X-Ray diffraction (XRD) analysis. The effect of temperature and time on the microstructure and hardness of the austempered samples was investigated and discussed. The presence of Al was seen to prolonged formation of the carbides from high carbon austenite, and that expanded the process window in the austempering transformation. Besides, the lower bainitic ferrite phase was observed in the austempered samples at 200 °C and 300 °C. Increasing austempering temperature to 400 °C changed the lower bainite to upper bainite structure. The volume fraction of austenite reached its maximum level (34.6 %) after austempering the samples at 400 °C for 30 minutes.
