Feasibility of Solid-state Steelmaking from Cast Iron -Decarburization of Rapidly Solidified Cast Iron-

Abstract

To meet the unprecedented demand of environmental issues and tightened production cost, steel industry must develop the disruptively innovative process. In the present study, totally new steelmaking process of 'Solid State Steelmaking' (or S-3 process) without BOF process or liquid state oxidation process is proposed. The overview of the new process is as follows: (1) High carbon liquid iron from the ironmaking processes is directly solidified by using a strip casting process to produce high carbon thin sheets. (2) Then, the produced cast iron sheet is decarburized by introducing oxidizing gas of H2O or CO2 in a continuous annealing line to produce low carbon steel sheets. The most beneficial aspect of the S-3 process is the elimination of several steps such as BOF, and secondary refinement processes and no formation of inclusions. To investigate the feasibility of S-3 process, the cast iron strips with various high carbon content produced by a centrifugal slip casting method are decarburized at 1 248 K and 1 373 K by using H2O-H-2 gas mixture and its kinetics of the decarburization is investigated. In the decarburization process, the carbon diffusion through the decarburized austenite phase but not the decomposition of cementite is the rate controlling step of the decarburizing process. It is found that 0.5 mass% C sheets can be produced from 3.89 mass% C sheets with the thickness of 1.0 mm within 30 min at 1 373 K. Based on these results, S-3 process is confirmed to be feasible as an alternative low cost steelmaking process although the further improvement of the process will be necessary.