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Your search keyword '"Kheirandish, Shahram"' showing total 36 results
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36 results on '"Kheirandish, Shahram"'

26. Effect of Q&P Heat Treatment on Fine Microstructure and Mechanical Properties of a Low-alloy Medium-carbon Steel.

Author

Jafari, Rahim, Kheirandish, Shahram, and Mirdamadi, Shamsoddin

Subjects
*MICROSTRUCTURE, *LOW alloy steel, *AUSTENITE, *MARTENSITE, *BAINITE, *GRAIN size, *TENSILE tests, *MECHANICAL behavior of materials
Abstract

The current research investigates the effect of ultrafine microstructure resulted from Quench and Partitioning (Q&P) process on obtaining ultra-high strengths in a low-alloy steel with 4wt.% carbon. The purpose of Q&P heat treatment is to enrich the austenite with carbon by partitioning of carbon from supersaturated martensite to austenite, in order to stabilize it to the room temperature. The microstructure, consequently, is consists of martensite, retained austenite and in some conditions bainite. Two-step Q&P heat treatment with quench and partitioning temperatures equal to 120°C and 300°C respectively were applied to the samples at different times. Mechanical behavior was studied by tensile test. The microstructure of the samples was observed using SEM, and TEM and to quantify the amount of retained austenite X-ray diffraction was used. The retained austenite grain size was estimated to be about 0.5µm and the highest amount of retained austenite obtained was 10 vol%. All samples showed a yield strength and a tensile strength of above 900MPa and 1500MP respectively. The yield strength increased with increase in partitioning time, whereas tensile strength showed an inverse behavior. The elongation in samples varied from 5% to 9% which seemed to not have a direct connection with the amount of retained austenite, but instead it was related to the ferritic structures formed during partitioning such as coalesced martensite, bainite and tempered martensite. [ABSTRACT FROM AUTHOR]

Published
2017
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27. Mathematical-Thermodynamic Prediction and Kinetics of Eta Phase Formation in Fe-Ni-Based Superalloys.

Author

Seifollahi, Masoumeh, Sahrapour, Peyman, Abbasi, Seyed, Kheirandish, Shahram, and Razavi, Seyed

Abstract

Time-temperature-precipitation diagram of eta phase formation was established for an Fe-Ni based superalloy by means of mathematical-thermodynamic analysis, kinetic investigation, and microstructural observation. The eta phase started to precipitate at the expense of the γ′ phase after prolonged aging. On the basis of thermodynamic prediction, the interaction between Gibbs free energy of eta phase formation and activation energy for diffusion of elements, especially titanium, was considered. The tip of TTP diagram was obtained at 817 °C, on the basis of mathematical-thermodynamic prediction, and 825-840 and 840 °C, on the basis of microstructural evolution and kinetic analysis, respectively. Kinetic investigations predicted that the eta transformation started with diffusion of Ti into Ni. This indicated that, with the progress of transformation, as n in Avrami's equation predicts, other eta formation mechanisms such as γ′ to eta transformation, instant nucleation from the matrix, coincidence of eta lamellas, etc. increased n and activation energy. [ABSTRACT FROM AUTHOR]

Published
2018
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36. The precipitation of ? phase in an Fe-Ni-based superalloy with different Ti/Al ratios

Author

Seifollahi, Masoumeh, Kheirandish, Shahram, Razavi, Seyed Hossein, and Abbasi, Seyed Mahdi

Abstract

In this research, the formation and transformation mechanisms of ? (Ni3Ti) phase in an Fe-Ni-based superalloy at different Ti/Al ratios were investigated. In addition to Ti content, Ti/Al ratio also affects the ? phase. So alloys with different Ti/Al ratios were prepared and the microstructures were analysed using optical and scanning electron microscopy and X-ray diffraction. The alloy with lower Ti but higher Ti/Al ratio has a higher ? volume fraction. Time-temperature-precipitation diagrams of ? phase in the superalloys with different Ti/Al ratios are also presented. Based on the experimental results, when the Ti/Al ratio was decreased from 20 to 3, the time and temperature of ? precipitation shifted to longer and higher values, respectively, and the ? volume fraction decreased. Ti/Al of 3 could significantly retard the formation of ? phase. Depending on the Ti/Al ratio, and the time and temperature of ageing, ? was precipitated at twin and grain boundaries or inside the grains, either by ?' ? ? transformation or directly by formation of austenite. It was also shown that a high Ti/Al ratio in the alloy would reduce the fraction of twin boundaries after solution annealing which affects the ? phase nucleation.

Published
2013
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