The application of CALPHAD in the process of steel making

11.06.2014 Benjamin Gubler

There are various applications of CALPHAD, especially in steel making and in the various stages of ore extraction. The focus will be mostly on the various uses of CALPHAD in steel making and processing. Oxygen is an important solute in the process of steelmaking, actually it is the main refining agent and therefore it is important for the subsequent control in order to have a clean atmosphere and also enhance workability.

It is here that a crucial process will be determined that describes the relationship in Fe-O. This is achieved by the various models of CALPHAD where there is calculation by comparison of the metal–gas equilibrium. The next application is in the non-metallic inclusions engineering; the non metallic inclusions does affect the properties and processing ability of steel. The inclusions that form before solidifications are easier to remove than those that form after solidification – they can only be tailored to suit the needs.

The idea is to be ready for any eventuality when it comes to inclusions (even if they are not found in the process), they must be controlled to help in their removal. Due to this, the process of computational thermodynamics finds a place in steelmaking.

The other application is the silicon-aluminium equilibrium; most of the times silicon tends to be undesirable in flat products for forming operations. These kinds of steel are then deoxidized by aluminium, the process of deoxidation is done in conjunction with ladle metallurgy operations whereby slag metal equilibrium is favored. There must be consideration that silica doesn’t revert back to slag. Because of that possibility, it is important to understand the silicon distribution in the metal and also in the slag.

Then there is the slag refractory interaction; the saturation of steelmaking converter slag in MgO is vital to avoid refractory dissolution and add to the lining life. So, the addition of MgO must be controlled since it plays a part in increase the cost of the processes and decreases the dephosphorization power of the slag in comparison with CaO. The converter slags are complex systems and there have been different trials in creating statistical correlation between slag compositions, temperature and MgO solubility have been done with certain level of success.

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