Casting: An Analytical Approach (Engineering Materials and Processes)


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Two 40 metric ton MT cylindrical shape steel ingots, cm in height and cm in mean diameter, were cast in big-end-up cast iron molds using identical conditions, except for the filling rate. The hot-top, as an extension of the ingot that was 70 cm in height, was made in the mold lined inside with insulating tiles. During the production process, molten steel with the nominal composition listed in Table 1 was first produced by melting scrap material in an electric arc furnace, and then teemed into a ladle before ladle refining and vacuum degassing in an argon atmosphere.

One slice was sectioned at regularly-spaced intervals into over samples 6. It should be noted that hot-tops are commonly used in the ingot casting industry in order to provide a reservoir of molten steel for feeding the shrinkage zone as the ingot solidifies [ 1 ]. They are generally cut off from the ingot body after solidification. However, there is a growing interest in reserving at least part of the hot-top for further use [ 17 ].

Thus, in the present study, positive segregation in the hot-top was also characterized, along with the upper section of the casting body, to evaluate and validate such possibility. It is clear that, if successful, the findings could result in significant material and energy saving in the ingot casting industry. A positive R i value corresponds to positive segregation, and conversely, a negative R i to negative segregation.

The chemical distribution patterns of the principal alloying elements on the axial plane in the two ingots are shown in Figure 1. The observed section is illustrated in grey in the upper right corner of the figure. It can be seen that all the solute segregation ratio maps appear symmetric about the ingot central axis, even though minor differences are present. This indicates that the slow rise in concentration of solute in the solid was the result of bulk liquid becoming progressively concentrated in solute elements. A weak difference from nominal composition negative segregation is observed in the region next to the surface layer of the hot-tops.

This difference could be attributed to the increased local solidification time due to the presence of the refractory lining in the hot-top wall. The presence of the refractory lining decreases the cooling rate, as compared to the mold wall, and therefore reduces the segregation in these regions [ 18 ]. On top of this, some concentration islands were observed, which can be associated with possible segregation channels.

It is also noted in Figure 1 that segregation features in the two ingots were found to vary as a function of alloying elements. Carbon is the element with the highest segregation ratio.

The most intense positive segregation ratio of carbon, manganese, and chromium in both ingots was found to be sequenced in decreasing order, and reached 1. The smaller the partition coefficient of a solute element, the more solute the solid will reject into the liquid during solidification, and the more intense the resulting segregation will be [ 20 ].

Although the k value of manganese lies between carbon and chromium, as seen in Figure 2 a, its slightly lower diffusion coefficient in the liquid iron as displayed in Figure 2 b [ 21 ] results in a similar positive segregation pattern to chromium.


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In addition, as shown in Figure 1 , the most intense segregations of all the solutes the red color in the maps in LFR were observed at the top center of the hot-top, in contrast to the lower locations of positive segregates of manganese and chromium in HFR. Frequency distribution of segregation ratios were examined in the hot-top and the upper section of the casting body for the two investigated ingots.

The results are plotted in histograms in Figure 3. The above-mentioned tendency, more severe segregation in the hot-top of HFR and less severe segregation in the casting body of HFR, was more remarkable when the evolution of carbon and manganese was examined along the central axis, as shown in Figure 4 a,b.

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The axial concentration examination of chromium presented less severe segregation in both the casting body and the hot-top of HFR, as shown in Figure 4 c. Moreover, it can be seen that in both ingots, the axial concentrations of carbon present a stepped monotonic increase from the cutting section to the top center of the hot-top. In contrast, positive segregation of manganese and chromium were found to increase progressively in a fluctuating way. The fluctuation was more distinct in HFR.

The most intense positive segregation regions of manganese and chromium in HFR were found to lie about 5cm below the corresponding regions in the low filling rate case, LFR. An examination of the concentration distribution along the cutting line of the two ingots i. The above results indicate that the filling velocity has a clear influence on the resultant macrosegregation, at least in the studied zones, of large size ingots.

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The obtained results confirm the observations of Yadav et al. Considering the large size of the ingots, the solid percentage formed at the end of filling was not expected to induce changes in the melt density, temperature, and viscosity. Thus, the influence of filling velocity on the flows of the liquid steel during the filling stage considered as isothermal flow of a single phase material was analyzed using the dimensionless Reynolds number Re [ 22 , 23 ]. The proposed approach is similar to the ones used by Marx et al. The mean filling speed was taken as the characteristic velocity and the average diameter of the cylinder mold cavity as characteristic length.

After calculation with all the determined parameters, Reynolds numbers of for LFR and for HFR during the pouring process were obtained. This flow instability is expected to result in some residual flow up to the initial stage of solidification under HFR condition. Macroetch analysis of the zones near the surface of the ingot first solidified zones , as reported in Figure 6 , revealed columnar grains in the casting body of LFR Figure 6 a and equiaxed grains in the same position of HFR Figure 6 b.

The examined region is encircled in red in the upper right corner of Figure 6. A schematic views of the grain morphologies are also provided for clarification due to the large size of the blocks and the grains, it is difficult to capture high quality images with uniform light and shade in one single picture. Campbell [ 26 ] found that a dampened fluid flow promotes columnar growth, while an unsteady liquid movement promotes the development of equiaxed grain structure [ 27 ].

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Toggle navigation Additional Book Information. Summary Introducing a new engineering product or changing an existing model involves making designs, reaching economic decisions, selecting materials, choosing manufacturing processes, and assessing its environmental impact. Author s Bio Author. Mahmoud M. Reviews "This third edition of the bestselling Materials and Process Selection for Engineering Design has been comprehensively revised and reorganized to reflect changes [in the fields and teaching of materials and manufacturing]. Carr, Northwestern University, Evanston, IL, USA "Many of the topics in the book, especially the relationship between design, materials, and manufacturing are increasingly discussed in the curricula of materials engineering and mechanical engineering.

It is clear that, if successful, the findings could result in significant material and energy saving in the ingot casting industry. A positive R i value corresponds to positive segregation, and conversely, a negative R i to negative segregation. The chemical distribution patterns of the principal alloying elements on the axial plane in the two ingots are shown in Figure 1.

The observed section is illustrated in grey in the upper right corner of the figure. It can be seen that all the solute segregation ratio maps appear symmetric about the ingot central axis, even though minor differences are present. This indicates that the slow rise in concentration of solute in the solid was the result of bulk liquid becoming progressively concentrated in solute elements.

A weak difference from nominal composition negative segregation is observed in the region next to the surface layer of the hot-tops. This difference could be attributed to the increased local solidification time due to the presence of the refractory lining in the hot-top wall. The presence of the refractory lining decreases the cooling rate, as compared to the mold wall, and therefore reduces the segregation in these regions [ 18 ]. On top of this, some concentration islands were observed, which can be associated with possible segregation channels. It is also noted in Figure 1 that segregation features in the two ingots were found to vary as a function of alloying elements.

Carbon is the element with the highest segregation ratio. The most intense positive segregation ratio of carbon, manganese, and chromium in both ingots was found to be sequenced in decreasing order, and reached 1.

Casting by Reikher, Alexandre; Barkhudarov, Michael

The smaller the partition coefficient of a solute element, the more solute the solid will reject into the liquid during solidification, and the more intense the resulting segregation will be [ 20 ]. Although the k value of manganese lies between carbon and chromium, as seen in Figure 2 a, its slightly lower diffusion coefficient in the liquid iron as displayed in Figure 2 b [ 21 ] results in a similar positive segregation pattern to chromium. In addition, as shown in Figure 1 , the most intense segregations of all the solutes the red color in the maps in LFR were observed at the top center of the hot-top, in contrast to the lower locations of positive segregates of manganese and chromium in HFR.

Frequency distribution of segregation ratios were examined in the hot-top and the upper section of the casting body for the two investigated ingots. The results are plotted in histograms in Figure 3. The above-mentioned tendency, more severe segregation in the hot-top of HFR and less severe segregation in the casting body of HFR, was more remarkable when the evolution of carbon and manganese was examined along the central axis, as shown in Figure 4 a,b. The axial concentration examination of chromium presented less severe segregation in both the casting body and the hot-top of HFR, as shown in Figure 4 c.

Moreover, it can be seen that in both ingots, the axial concentrations of carbon present a stepped monotonic increase from the cutting section to the top center of the hot-top. In contrast, positive segregation of manganese and chromium were found to increase progressively in a fluctuating way.

The fluctuation was more distinct in HFR.

Casting: An Analytical Approach (Engineering Materials and Processes)
Casting: An Analytical Approach (Engineering Materials and Processes)
Casting: An Analytical Approach (Engineering Materials and Processes)
Casting: An Analytical Approach (Engineering Materials and Processes)
Casting: An Analytical Approach (Engineering Materials and Processes)

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