the carburizing method for casting

As one of the most important elements in cast iron, carbon is more difficult to adjust than other elements, because the dense of carbon is much less than molten iron, so the absorption efficiency will be low if without vigorous stirring. Usually, when batching, the carbon is calculated according to the upper limit of the process requirements, and the burning loss of carbon in the smelting process is considered, so that after the metal charge is cleared, the carbon content is basically within the process range, even if it slightly exceeds the upper limit, you can add a small amount of ( clean, dry) scrap steel to bring it down, and decarburization in smelting is much simpler than a carburization operation.

There are two ways to add the carbon, the most commonly used is the in-furnace carburizing method, the other is ladle carburizing method.

1.In-furnace carburizing method

Feeding order

(1)First lay a certain amount of returning material (or a small amount of molten iron) on the bottom of the furnace, so that the new material can be immersed in the molten iron to reduce oxidation.

(2)Add scrap, and then add recarburizer. At this time, the melting point of the molten iron is low, which can be quickly melted to increase the height of the liquid level, so that the recarburizer can be infiltrated in the molten iron. The synchronization of carbon increase and iron melting does not increase the smelting time nor consume much power. Since the ability of C to reduce FeO is higher than that of Si and Mn, the addition of recarburizer at low temperature can also reduce the burning loss of Si and Mn; try to use the recarburizer packed in quantitative packaging bags into the electric furnace, and do not use a shovel to put it into the electric furnace to avoid fine particles are sucked up by the dust collector.

(3)When the scrap steel melted and then add the return charge. To ensure that the recarburizer has been completely absorbed before the slag removal, a high-power electric furnace (>600kW/t) is particularly important because the time required to melt the material may be less than the time for the recarburizer to be completely absorbed. At the same time, the stirring function of the electric furnace should be used as much as possible during the absorption of the recarburizer.

(4)If the recovery rate of the recarburizer and the control of the carbon content in the molten iron are certain, the recarburizer can be added with the scrap steel at one time. If  not sure, 5%~10% of the recarburizer can be added for the second time. The recarburizer added for the second time belongs to fine-tuning the carbon amount (or supplementing the amount of carbon lost by burning), and should be added after the molten iron is cleared. The slag on the surface of the molten iron must be cleaned before the recarburizer is added to avoid the recarburizer being involved in the slag as much as possible, and then the high-power power transmission uses the stirring function of the electric furnace to improve the absorption rate.

(5)Add ferrosilicon and other alloys, sample and analyze, adjust the composition, and release. It need to avoid long-term high temperature storage of molten iron. Long-term high-temperature storage of molten iron (especially long-term heat preservation above 1450 °C) is likely to lead to oxidation of carbon, increase of silicon content (silicon dioxide is reduced) and loss of crystal nuclei in molten iron.