Chilling Effect of Inoculation on the Microstructure and Hardness Property of Hypo-Eutectic Grey Cast Iron

The influence of varied weight percent of inoculant (ferrosilicon) on the microstructure and hardness property of hypo- eutectic grey cast iron was investigated. Four sets of chill wedge samples were produced using two chill wedge wooden patterns (W3 1/2 and W4). The first set, the control samples W3 1/2 and W4 were uninoculated. The second, third and fourth sets were inoculated with 1.0wt.%, 1.5wt.% and 2wt.% ferrosilicon respectively to give inoculated samples W3 1/2 and W4. Wedge test was conducted on the samples at the four different points (1, 2, 3 and 4) in accordance with ASTM A367. From the results, microstructures of the control and the inoculated samples were differently influenced by the varied percentage of the inoculant at the four designated points 1, 2, 3 and 4. The average hardness property of the inoculated samples decreases with increasing ferrosilicon addition. Samples W3 1/2 and W4 with 1.0wt.% ferrosilicon revealed high hardness property at chill zone, and hardness property of W3 1/2 was high relative to sample W4 with the values of 34.9 HRA and 30.6 HRA respectively. Similarly, the control samples showed the highest hardness property at the chill zone. Sample W3 1/2 revealed high hardness value of 33.0 HRA relative to sample W4 of 26.8 HRA at the chill zone. Keywords - inoculant; Microstructure; hypo- eutectic; chill zone; hardness property

Influence of Cooling Conditions on a Slab’s Chill Zone Formation During Continuous Casting of Steel

The cooling conditions of a slab during continuous casting of steel have an impact on the crystalline structure formation. Numerical methods allow real processes to be modelled. Professional computer programs are available on the market, so the results of their simulations allow us to understand the processes that occur during the casting and solidification of the slab. The study attempts to evaluate the impact of the intensity of the secondary cooling on the chilled zone size. The calculations show the differences in the structure of a slab cast with various speeds while maintaining industrial cooling parameters during operation of a continuous casting machine.

COMPLEX MODIFICATION OF GRAY CAST IRON

The influence of the complex modifier by chemical – active and surface-active additives of gray cast iron on the size of chill and on the width of molted iron zone was researched. The width of a chill zone and molted iron zones were measured at chank ends of various diameter cores. The cores were casted on a massive steel plate and also in standard chill tests. It was established that additional adding of surface-active bismuth in structure of various graphitizing modifiers promoted to reduce the width a chill zone and molted iron zones. It was established that the complex modifiers consisting of chemical – active and surfaceactive components are effective in fight with chill in cast iron castings and can be recommended for application in foundry shops of the entities of a machine-building profile for production of high-quality castings.

Determination of Crystallographic Orientation near a Chill Zone Using Ghost Lines

Many crystals nucleate on the mold surface when the molten alloy is poured in a mold cavity. Because the crystallographic orientations of these crystals are random, the solidified structure near the mold surface is very complex. The ghost lines, which are sometimes thick and the angle between them is not 90 degrees, are often observed in this region. However, if the crystallographic structure of this alloy is cubic, such as bcc or fcc, the ghost lines are very regular. In order to understand the geometry of ghost lines, Al-20 mass%Cu alloys were unidirectionally solidified with constant growth velocity. The solidified structures on the obliquely crossed section were observed. The ghost lines were quite regular and parallel to each other in a solidification grain. The angles and the ratio of the width of ghost lines were measured and crystallographic orientations were estimated using these parameters, based on the solid analytical geometry. EBSD analysis were also performed on the area, where the ghost lines were characterized, and the precise crystallographic orientations were decided. The comparison between both analytical values indicated that the differences between them are within 10 degrees and it can be safely concluded that the estimation for crystallographic orientation using ghost lines agreed well with the EBSD analysis.

The Influences on Microstructure and Segregation of the Jumbo Slab Ingot by Different Cooling Speed

Shrinkage porosity and segregation defects are often found in an air cooled jumbo steel ingot, which will influence the quality of the final rolled plates.The solidification behaviours for a 60t jumbo slab ingot under varied cooling conditions were simulated using the ProCast software.The influences of different cooling speed on dendrite distribution and segregation were studied.The results show the jumbo slab ingot could freeze layer by layer when the heat transfer coeffcients of mould increase to 1000W·K-1·m-2. The thick finer chill zone were achieved. At the same time, the columnar crystals grow preferentially parrelling to the density of heat flow, and finer equiaxied crystals are formed in the core of the ingot. They all improve the microstructure and decrease the composition segregation of jumbo slab ingot.

Chill-zone aluminum alloys with GPa strength and good plasticity

Using a cold graphite mold casting method, bulk AlNiY chill-zone alloys were prepared at hypereutectic compositions with Al content from 85 at.% to 94 at.%. It was found that ultra-hard surface layers with a thickness of about 200 μm and submicron grain size form when the melt can be undercooled without heterogeneous nucleation at the mold contact surface. This hard chill-zone forming in contact with the mold possesses Vickers microhardness Hv about 350–420 and is thus harder than fully amorphous Al alloys. In compression, ultimate strength more than 1.1 GPa and true strain more than 150% without failure were achieved simultaneously. The combination of high strength and good plasticity will be discussed in relation to the special structure of the chill-zone alloy.