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Showing 3 results for Phase Transformation
Thermo-Microstructural Numerical Simulation of Quenching Process of Steels
M. Eshraghi Kakhki, A. Kermanpur, M. A. Golozar,
Volume 30, Issue 1 (6-2011)
Abstract
In this work, a 3D thermo-microstructural model was developed to simulate the continuous cooling of steel. The model was employed for simulation of cooling process of the gears made from a plain carbon steel (AISI 1045) and a low alloy steel (AISI 4140). Temperature-dependent heat transfer coefficients for two different quenching media were evaluated by experimental and computational methods. The effects of latent heat releases during phase transformations, temperature and phase fractions on the variation of thermo-physical properties were investigated. The present model was validated against cooling curve measurements, metallographic analysis, and hardness tests, and good agreement was found between the experimental and simulation results. This model was used to simulate the continuous cooling process and to predict the final distribution of microstructures and hardness in steel gears.
Kinetics of Austenite Layer Growth on the Surface of Fe-23Cr-2.4Mo Ferritic Stainless Steel During Solution Nitriding
Kh. Farjam Hajiagha, A. R. Akbari, R. Mohammadzadeh,
Volume 36, Issue 2 (9-2017)
Abstract

In this study, the kinetics of austenite layer growth on the surface of Fe-23Cr-2.4Mo ferritic stainless steel during solution nitriding and the effects of nitrogen adding on microstructure and hardness of the steel have been investigated. Steel plates of 2 mm thick were solution-nitrided at 1200˚C under nitrogen pressure of 0.25 MPa for 2, 3, 6, 9, 12 hours. Microstructure, the thickness of austenite layer and the hardnes of the nitrided samples, were investigated by using optical microscope, X-ray Diffraction (XRD) and microhardness measurements. The results showed that during solution nitriding, nitrogen diffuses through the lattice and grain boundaries and transforms ferrite to austenite phase, with average nitrogen diffusion coefficient of 6.54×10-5 mm2s-1. The thickness of the austenite layer formed on the samples surfaces increased proportional to the square root of the nitriding time, so that after 12 hours niriding, the whole thickness of the ferritic sample with hardness of 262 HV0.1 transformed to austenite with hardness of 420 HV0.1.


The Effect of Boron Addition on the Microstructure, Hardness and Characteristic Temperatures of Cu-12Al-4Ni Memory Alloy Prepared by Mechanical Alloying, Pressing and Rolling
Z. Jarrahi, Sh. Raygan, M. Pourabdoli,
Volume 37, Issue 4 (3-2019)
Abstract
In this study, boron containing Cu-12wt%Al-4wt%Ni shape memory alloy was prepared by mechanical alloying, pressing and rolling. In this regard, 20 and 40 hour-milled powder was compacted and changed to the bulk alloy by cold pressing, sintering, rolling, heat treatment and quenching. Phase structure, micro-structure, micro-hardness, and transformation temperatures of the prepared samples were studied. It was found that increasing the milling time from 20 to 40 hours led to the rise of the starting temperature of martensite transformation (Ms) from 254 to 264°C. Also, the results showed that adding 0.5 wt.% B decreased the Ms temperature to 211°C and enhanced the micro-hardness from 154 (for the sample without B) to 193  vickers. These alternations were attributed to the fine structure caused by Boron rich precipitations. Moreover, two martenistic transformations with different structures were formed due to the non-homogeneity of the Al concentration in the matrix, which appeared in the form of two different transformation temperatures (Ms) in the Differential Scanning Calorimetry curves.

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