Analysis of microstructure and texture evolution in pure magnesium during symmetric and asymmetric rolling

In the present study, asymmetric rolling was carried out for incorporating a shear component during the rolling at different temperatures, and was compared with conventional (symmetric) rolling. The microstructures were investigated using electron back-scatter diffraction (EBSD). The strain incorporated was compared with the help of grain orientation spread (GOS). GOS was eventually used as a criterion to partition the microstructure for separating the deformed and the dynamically recrystallized (DRX) grains. The texture of the partitioned DRX grains was shifted by similar to 30 degrees along the c-axis from the deformed grains. The mechanism of dynamic recrystallization (DRX) has been identified as continuous dynamic recovery and recrystallization (CDRR). The partitioned deformed grains for the higher temperature rolled specimens exhibited a texture similar to the room temperature rolled specimen. The asymmetric rolling introduces a shear component which shifts the texture fibre by similar to 5-10 degrees from the conventional rolling texture. This led to an increase in ductility with little compromise on strength. (c) 2012 Elsevier B.V. All rights reserved.

Asymmetric and symmetric rolling of magnesium: Evolution of microstructure, texture and mechanical properties

The nucleation, growth, transport, and entrapment of nonmetallic inclusions during the steel casting process are briefly reviewed in this article. The current main research accomplishments as well as future topics that should be focused on in this field are summarized.

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Nucleation, Growth, Transport, and Entrapment of Inclusions During Steel Casting

On the theory of CO2 corrosion reactions – Investigating their interrelation with the corrosion products and API-X100 steel microstructure

https://era.library.ualberta.ca/items/4d12f2f3-65be-4007-a548-b12344655113/view/b65eccb7-6906-45cd-b532-bdffe51eaf34/Characterization%20of%20martensite-austenite%20constituents%20and%20micro-hardness%20in%20intercritical%20reheated%20and%20coarse-grained%20heat%20affected%20zones%20of%20API%20X70%20HSLA%20steel.pdf

Characterization of martensite-austenite constituents and micro-hardness in intercritical reheated and coarse-grained heat affected zones of API X70 HSLA steel

This study investigates the correlation among the welding heat input, microstructure and impact toughness of the simulated coarse grain heat-affected zone (CGHAZ) of a V-N microalloyed steel which contained 140 ppm of nitrogen using Gleeble simulation technique, light microscope, electron microscope and Charpy-V-Notch (CVN) testing. CVN toughness estimated at −20°C supported that a relatively low energy input is recommended for welding of low carbon V-N microalloyed steel, according to a fact that an impact energy as high as of more than 180j attained in the CGHAZ with heat input less than 25Kj-cm−1, while a CGHAZ with impact energy less than 80j was obtained at a heat input more than 40 Kj-cm−1. Quantitative metallography of samples showed that CVN toughness decreased with the increase of the amount of grain boundary ferrite (GBF). Quantitative metallography of two-stage electrolytically etched samples showed that the averaged size and ratio of lath martensite-austenite (M-A) constituent increased with increasing heat input, while the linear density and amount of M-A decreased. It is indicated that the toughness of CGHAZ was severely dependent on the characteristic parameters of M-A and the amount of GBF. Microhardness of M-A constituents estimated by nanoindentation technique were much higher than that of the neighboring matrix. Severer brittle cracking susceptibility can occur in the CGHAZ with higher heat input based on Chen et al's suggestion that the stress concentration and triaxiality of the neighboring matrix are increased by the hard phase particles such as M-A constituents.

Effect of Welding Heat Input on Simulated HAZ Microstructure and Toughness of a V-N Microalloyed Steel

An ultrafine-grained AZ31 magnesium alloy sheet was produced using three-run accumulative roll bonding (ARB) performed at a rolling temperature of 350°C and a reduction of 80% for each pass, based on examination of the bond interface influenced by reduction ranged from 10% to 80%. The microstructural change at the different ARB stages was observed and superplasticity of the final AZ31 alloy sheet was examined at a fixed temperature of 300°C and strain rates varied from 10 −4 to 10 −1 s −1 . It is shown that a good AZ31/AZ31 bond formed as a result of dynamic recrystalization (DRX) accumulation at the original separate interface, which is consistent with a high reduction. Moreover, a significant grain refinement was achieved mainly in the first run of ARB process by expanding the DRX reaction from the interface to the mass and gradual uniformity of grain size in the next by the successive DRX occurred in the AZ31 magnesium alloy. Besides, a superplastic tension with a high elongation of 316% was successfully performed at a strain rate of 10 −2 s −1 indicating a low temperature and high strain rate superplasticity in the AZ31 alloy sheet processed by ARB. The results indicate that ARB is a promising approach to produce the ultrafine-grained magnesium alloy sheet with enhanced superplasticity.

An Ultrafine-Grained AZ31 Magnesium Alloy Sheet With Enhanced Superplasticity Prepared by Accumulative Roll Bonding

There thermal cycles for the cyclic heat treatment of a bainitic steel were simulated under the different heating rate ranged from 2°C/s to 100°C/s and 1000°C/s followed by subsequent rapid cooling using a Gleeble3500 thermal-mechanical simulator equipped with the self-designed quench system. The microstructural change of the starting material imposed by the different thermal cycles was observed by optical and transmission electron microscope (TEM). The results indicate that a high degree of superheating for the reverse bainitic α→γ transformation was realized as a result of extremely rapid heating (1000°C/s) up to an elevated austenitisation temperature (1250°C), which prevent restoration of the initial coarse-grained austenite and lead to a significant refinement of austenite grain. An ultrafine-grained structure with enhanced mechanical properties then formed during the subsequent rapid γ→α reaction on cooling. The results indicate a novel microstructure refinement route for the bainitic steels.

W.W. Xu

Papers

Effect of Welding Heat Input on Simulated HAZ Microstructure and Toughness of a V-N Microalloyed Steel

An Ultrafine-Grained AZ31 Magnesium Alloy Sheet With Enhanced Superplasticity Prepared by Accumulative Roll Bonding

Refinement of Steel Austenite Grain Under an Extremely High Degree of Superheating