The Effect of Temperature and Carbon to Hematite Ratio on the Formation of Cementite During the Couple of STMA and Partial Melting Processes

Abstract

In this research, the role of the couple of simultaneous thermal-mechanical activation (STMA) and partial melting (PM) processes in the carbothermic reduction of hematite and cementite formation was studied. For this purpose, the STMA process was performed for 6 hours at 1073 K (800 °C) on the mixture of hematite and graphite with stoichiometry ratio (22 wt pct C) in argon atmosphere in the first stage, and then this process was coupled to the PM process at 1453 K (1180 °C) for 25 minutes. The results obtained showed that the percentage of cementite phase in the product of the STMA process was only about 24 wt pct and after carrying out the PM process, this value reached 77 wt pct in the final product. In the second stage, the effect of the ratio of the parameters of carbon to hematite on the initial mixture (1:1, 1:25, and 1:5 times the stoichiometry ratio) and STMA process temperature [1073 K, 1123 K, and 1173 K (800 °C, 850 °C, and 900 °C)] was studied. The results were indicative of the fact that by an increase in the ratio of carbon to hematite and at STMA temperature, the percentage of cementite in the final product obtained from the PM process significantly increased. In fact, the specimens obtained from the couple of the STMA and PM processes with a carbon to hematite ratio of 1.5:1 at 1073 K (800 °C) and that of 1.25:1 at 1173 K (900 °C) showed the greatest percentage of cementite. The mechanism regarding the processes showed that by controlling the amount and manner of free carbon distribution in the STMA product based on the parameters of the ratio of carbon to hematite and temperature, it was possible to obtain pure cementite. Therefore, the couple of STMA and PM processes can also be brought up as a new method in the production of pure cementite.