Grain refinement in iron-based materials

A process for manufacturing an iron-based alloy comprising, in sequence:

• a) feeding iron-bearing material into a melting furnace and melting the iron-bearing material into molten metal;
• b) introducing elements into the molten metal to react with dissolved oxygen and/or carbon in the molten metal to form targeted oxide and/or carbide dispersoids in the molten metal;
• c) after said forming of the targeted oxide and/or carbide dispersoids in the molten metal, maintaining the molten metal at a temperature above a liquidus temperature of the molten metal and introducing one or more metal grain refiner elements into the molten metal to precipitate metal nitrides of the metal grain refiner elements to yield a molten metal containing the metal nitrides;
• and
• d) cooling the molten metal with said metal nitrides therein to a temperature below the solidus temperature of the molten metal to form solidified iron-based alloy, wherein:
• the elements added in step (b) are selected from the group consisting of Al and Mg to form oxide dispersoids of MgO and magnesium aluminate in a form of MgAl2O4 and/or MgO—Al2O3 which facilitate precipitation of the nitrides;
• the process further comprises, after step (b) and prior to initiating step (c), terminating addition of the elements selected from Al and Mg and subjecting the molten metal to a dwell time of at least 10 seconds before initiating step (c);
• the solidified iron-based alloy is an austenitic steel which has a microstructure which is between 60 and 85 vol % equiaxed structure having an average grain size of between about 0.5 and 3 mm.