Papers by Keyword: Strip Casting

Abstract: A356 was cast into the strip by the semisolid strip casting using an unequal diameter twin roll caster. This process was one of the rheocasting. The semisolid slurry was made by a cooling slope. Solid fraction was about 5%. The casting speed was 20 m/min, and the thickness was 4.4 mm. The as-cast strip could be cold rolled down to 1 mm. The result of tension test of 1mm-thickness-T4 heat-treated strip was as below. Tensile stress was 223 MPa, 0.2 proof stress was 123 MPa and elongation was 21.8%. Deep drawing could be operated to 1 mm-thickness T4 sheet, and L.D.R was attained to 2.0. In some condition, 180 degrees bending could be operated without crack at outer surface. These results mean that semisolid roll cast A356 strip may be able to use for press forming.

Abstract: The influence of different cooling regimes on the surface microstructure of strip cast AA1XXX alloys was investigated. The cooling rate was varied over a wide range using a bench scale simulation apparatus. It was found that the type and morphology of the intermetallics varied over a wide range both at the cast surface and in the near surface regions. These observations were compared to the compounds formed in the bulk of the slab. It was found that, a surface layer containing a high concentration of alloying elements, an inverse segregation layer, forms under some conditions and can result in a high density of intermetallics. By varying casting conditions, the mechanism of formation for these structures was studied. The surface microstructure of the slabs was characterized as a function of the different local cooling regimes.

Abstract: Currently new continuous casting processes such as thin slab caster or strip casting are industrialized or under developing in the world steel makers. In these casting processes, cooling rate after solidification becomes much faster compared with thick slab caster, and hot rolling mill connected directly with casting machine tends to be installed. The present study was conducted to investigate variations of austenitic grain size and micro segregation with cooling rate after solidification and also direct hot deformation conditions in austenite immediately after solidification in HSLA steels. HSLA steels were 0.15%C-0.25%Si-1.50%Mn, 0.028%Nb and 0.028%Nb-0.015%Ti with the same basic compositions. A hot working simulator of THERMECMASTER-Z was used, and the center part of tensile specimen set up in this machine was partially or fully levitation-melted by induction heating under argon gas atmosphere. After melting, specimens were cooled at cooling rate from 0.4K/s to 40K/s, and this range covered cooling rates after solidification in heavy thick slab caster and strip casting. Direct hot tensile straining in austenite after solidification was conducted at strain rates from 1.4×10-3s-1 to 2.6s-1, corresponding to an extracting speed in a respective caster. The increase of cooling rate refined continuously as cast austenitic grain size, and it was enhanced in micro alloyed steels. Micro segregation such as Mn was improved by faster cooling. Direct straining after solidification markedly refined austenitic grain size through dynamic or static recrystallization occurring depending on strain rate.

Abstract: In this study, optimum processing conditions for strip-cast AZ31 Mg alloy was investigated on the basis of processing map and microstructural analysis. To obtain the processing map, isothermal compression tests were carried out to a strain of 0.5 at temperatures of 200 ∼ 400°C with the strain rates of 0.01 ∼ 10s-1. It was found that maximum efficiency indicating the optimum processing condition occurred at 300°C and 10s-1. The possible deformation mechanisms operating at high temperature was also discussed.

Abstract: The effect of initial microstructure on the recrystallization behaviour and texture development of low carbon (LC) steel was investigated. Steel strip samples (0.05 wt.% C) of 2 mm in thickness were heat treated to produce a microstructure consisting predominantly of either polygonal ferrite or acicular ferrite. Samples were cold rolled 50, 70 and 90% reduction then annealed for various times in the temperature range 580-640 oC. The microstructures and textures produced by deformation and annealing were studied by optical microscopy and electron backscatter diffraction in the SEM. The initial microstructure was found to have a substantial influence on the rate of recrystallization and final texture. It was found that polygonal ferrite recrystallizes more rapidly than acicular ferrite with the former generating the strongest <111>//ND recrystallization texture. The results are examined within the framework of improving the formability of LC steel produced by direct strip casting whereby controlled thermal and mechanical processing prior to cold rolling and annealing can generate the same types of initial microstructures, as studied in this work.

Abstract: AZ31 and experimental ZMA611 alloys were strip cast into 2 mm thick strips. The as-cast AZ31 alloy strip consists of columnar dendrites. On the other hand, as-cast ZMA611 alloy strip shows equiaxed dendritic structure through the thickness of strip. Strip cast AZ31 alloy in H24 condition has equivalent yield and tensile strengths with similar ductility compared to commercial ingot cast AZ31-H24 alloy, indicating that strip casting is a viable process for the fabrication of Mg alloy strips. The ZMA611 alloy has a large volume fraction of fine dispersoid particles in the microstructure, resulting from the beneficial effect of strip casting on microstructural refinement. It has been shown that the ZMA611 alloy has superior tensile properties compared to commercial ingot cast AZ31-H24 alloy, suggesting the possibility of the development of new wrought Mg alloy sheets by strip casting.

Abstract: The aim of this study is to report results of initial trials involving the strip casting process for ETPC (Electrolytic Tough Pitch Copper) and to investigate the effect of process parameters on the chemistry, microstructure evolution and mechanical properties of ETPC. A vertical twin roll strip caster used in this research was designed for manufacturing high-purity and/or reactive metal strips with a system for controlled atmosphere ranging from 103 to 10-3torr. It is expected that oxygen content can be reduced as low as 0.001wt% in as-cast strip.