Carburization

1. Enrichment of the carbon content in molten cast iron by addition of carburizing compounds. In the electric furnace process, coke is not used as energy carrier so that the molten metal generally requires carburization; thus, carburization is of particular importance for this process, compared to the cupola furnace process. The carburization agent may be added both in the furnace (MF and NF smelting furnaces) and in the ladle. The carburization effect strongly depends on the quality of the carburization agent (carbon content, ash content, volatile constituents, hydrogen, nitrogen, sulfur), on the molten iron temperature at the time of carburization, on the chemical composition of the molten bath (in particular C content), on bath agitation inside the smelting furnace (degree of stirring, NF or MF furnace), and on quantity and composition of the slag. Molten cast iron baths with low carbon contents and high smelting temperatures are better suitable for carburization than baths with high carbon contents and low temperatures since carburization is a diffusion process that is both temperature- and time-dependent. The driving or triggering force of diffusion is the concentration gradient between the C content at the phase boundary between carbon carrier and molten bath and the C content in the molten bath.

2. Annealing treatment of case-hardening steel in carbon-releasing agents (s. a. Case hardening). Thus, in this context carburization is understood as the addition of carbon to steel with carbon contents of less than 0.2 %. From the carbonaceous atmosphere in the furnace, carbon diffuses into the surface area of a workpiece and make it hardenable. The major advantage is that in the hardening process only the surface is hardened but not the core of the component. The toughness of the core, which is often a beneficial property, is maintained.

Additional references:

Carburization depth

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