Macro- and microstructure analysis of SSM A356 produced by electromagnetic stirring

The objective of this work is to present the relationship between macro- and microstructure of the rheocast alloy A356 obtained by electromagnetic stirring. There is a direct relationship between grain size (macrostructure) and globule size/shape factor (microstructure): the smaller the grain size, the smaller are the globule size and shape factor. The A356 alloy was processed in a simple device, which constitutes a semi-continuous casting system, coupled with a power source. The A356 (Al-7.0 wt.%Si) alloy was electromagnetically stirred under different cooling rates (controlled by the casting speed of 1 and 3 cm/s) and different power levels (600-1200 W). Ingots with 45 mm of diameter and 3 kg with very refined and homogeneous rheocast structures were obtained. The direct relationship between macro- and microstructures of the ingots were exploited. A quality index is proposed to better characterise the rheocast structure. (C) 2002 Elsevier Science B.V. All rights reserved.1204169936537

Microstructure and mechanical properties of strip cast 1008 steel after simulated coiling and batch annealing, cold rolling

As-cast low carbon steel strips produced by twin roll strip casting process were treated by cold rolling and batch annealing. The microstructure and mechanical properties were compared to those of drawing and commercial quality strips. The mechanical properties of the as-cast strip are inferior to those of an industrial hot band due to the presence of Widmannstatten ferrite microstructure. After simulated coiling, cold rolling and batch annealing the ductility of the strip cast steel is lower than that of the industrial products, due to the hardening effect of small Cu-S precipitates and coarser iron carbides. However, for the strip cast steel processed according to a drawing quality (DQ) route, the mechanical properties are within the range of a commercial quality (CQ) product. Therefore, mechanical properties falling within the range of commercial quality steel can be obtained with strip cast steel without a hot rolling step if appropriate cold rolling and annealing treatment is used

Morphological evolution of SSM A356 during partial remelting

There is a direct relationship between grain size obtained from macrostructure characterisation and the globule size and shape factor, obtained from the microstructure characterisation: the smaller the grain size. the smaller the globule size and shape factor. Due to this relationship a Rheocast Quality Index (RQI = globule size grain size * Shape Factor) was used to evaluate the morphological evolution of the A356 alloy produced by electromagnetic stirring during the partial remelting heat treatment. The morphological structure that presents the smallest grain size, the smallest shape factor, and the most homogeneous and globular size of the primary phase, has the best behaviour in the semi-solid forming. Three different as-rheocast initial structures and one as-cast (dendrite), were partially melted at 580 degreesC at holding times of 0. 30, 90, 210. and 600 s. Both, macro and microstructure were characterised by a Clemex Image Analysis System. The morphological evolution was studied to determine an optimum holding time for thixo-forming processing. (C) 2002 Elsevier Science B.V. All rights reserved.32541671385

Thermodynamic Calculations on the Stability of Cu2S in Low Carbon Steels

Thermodynamic stability of Cu2S sulfide in low carbon steels has been investigated using a CALPHAD type thermodynamic calculation method. Thermodynamic properties of the Cu–S binary and Fe–Cu–S ternary systems were critically assessed. By combining the newly assessed thermodynamic parameters to an existing thermodynamic database for steels, a thermodynamic description for low carbon steels involving sulfur and Cu could be obtained and be used to calculate phase equilibria and thermodynamic stability of precipitating phases such as AlN, MnS, and Cu2S. It was predicted that the Cu2S sulfide often observed in low carbon steels is actually a thermodynamically unstable phase and can precipitate when thermodynamic equilibrium state is not reached during steel making processes. Probable reasons and conditions for the formation of this unstable phase are discussed