the Mg content from 5.8 to 4.6 to even 4.1wt% Mg, without any need to add more alloy. Final Mg levels remain similar or sometimes even higher with the lower Mg content MgFeSi.
Case 1:
In a foundry with a 2,900 lb. tundish treatment 44 lb. of an alloy with 5.8wt% Mg, 0.8 to 1.2wt% Ca, 0.4 to 1wt% Al, and 0.35 to 0.65wt% La (as pure La metal) was replaced by 38 lb. of another alloy with the same specification except for a lower Mg content of 4.1wt% Mg. Similar final Mg con- tents were obtained with 39% less Mg input.
Case 2:
In a foundry with 4,000 lb. treatment 58 lb. of MgFeSi con- taining 5.9wt% Mg were replaced by an equal amount of MgFeSi containing 4.1wt% Mg covered with 25 lb. of Ca and Ba containing FeSi inoculant. Final Mg levels jumped 20% higher, necessitating a compensating reduction in us- age of the lower Mg content alloy.
Summary:
It appears that from 4.1wt% Mg to 5.9wt% Mg, lower Mg content alloys provide a high enough increase in Mg recov- ery to compensate for the lower Mg content. The low Mg level versions react far more calmly with much lower slag generation. Similar experiments have been reproduced nu- merous times, often including intermediate content alloys in the series with a similar trend.
Treat and Pour from Same Ladle Case 1:
A foundry switched from a tundish ladle Mg treatment fol- lowed by inoculation on iron transfer into the pouring ladle to use of the first ladle as simply a transfer ladle, doing the Mg treatment and inoculation simultaneously in the pour- ing ladle. The cover alloy also provides the inoculation ef- fect. This change takes advantage of several Mg recovery improvement effects:
• While the furnace tap temperature is the same, the Mg treatment is done at a much lower temperature.
• The fill time in the treatment ladle was reduced to less than 10 seconds, so most of the Mg is released into a full ladle of iron. Previously fill time was variable, with especially long fill times as the last taps were made from the medium frequency fur- naces. In the prior process, Mg was being evolved long before the ladle was filled.
• Mg losses during transport of the first ladle to the pouring area have been eliminated.
• To accommodate the reaction in a pouring ladle a lower reactivity lower Mg type alloy is used. This increases % Mg recovery reducing flare, smoke, and slag formation.
International Journal of Metalcasting/Volume 8, Issue 2, 2014
• The MgFeSi alloy uses pure La as the RE type pro- viding a reduced shrinkage effect.
Case 1 Data:
Medium frequency coreless induction furnaces Base iron sulfur level: 0.010 to 0.015% Final iron sulfur level: 0.008 to 0.011%
MgFeSi grade: 4.1wt% Mg typical and ½” x 8 mesh size MgFeSi addition rate: 1.1 to 1.2wt%
Cover/inoculant: 50wt% FeSi with 1wt% Ca and 1wt% Ba Treatment temperature: Approx. 2650˚F Treatment size: 1,300 lb. to 1,500 lb. Final iron Mg level: 0.030 to 0.040% Final iron silicon level: 2.2 to 2.5%
Casting types: truck parts: front mounting brackets, hubs Case 2:
A jobbing foundry had been treating and pouring in the same ladle for some time with their Mg treat and inoculation si- multaneously in the pouring ladle. Low Mg alloys had been used for some time to try to minimize splashing when the ladle was full. However, the foundry had identified room for improvement. Steel cover and 75% FeSi FG were used to try to delay the onset of the reaction and to provide inoculation effect. This process allowed reduced MgFeSi usage due to the lower treatment temperature, and reduced costs by elimi- nating the expense of the first ladle from the process. Mg recovery was 72%, and further gains were sought.
The pouring ladle was fitted with an improved alloy pocket. The design was taller with a reduced area. The same 1.1% by weight addition of 4.3wt% Mg content MgFeSi was used. This steel cover and 75wt% FeSi FG were eliminated and re- placed by a 50wt% FeSi based cover/inoculant alloy contain- ing 1wt% Ca and 1wt% Ba. The treatment temperature was reduced by over 100˚F. Part of this was due to the elimination of the chilling effect of cold steel in the iron. Additionally, im- provements to the alloy pocket design were made to optimize alloy covering.
The results of the above changes made profound differenc- es in the treatment and final %Mg recovery. The Mg reac- tion was delayed until after the ladle was filled with iron, as compared to early into the filling process. The reaction was very calm with only a small fraction of the flare previously observed. The reaction continued for twice the time of the prior process, demonstrating a more gradual release of the Mg into the iron. Using the same amount of the same lot of MgFeSi alloy, the final Mg level jumped from 0.034% Mg to 0.047% Mg corresponding to a calculated % Mg recovery increase from 72% to 99%. While this is a very significant improvement in Mg recovery, it represents only one tap. In ongoing production the foundry now experi- ences recoveries in the range of 85 to 95% since changing to the new process.
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