The effect of direct reduced iron (DRI) addition in metallic charge on the different steel making parameters and consumption figures have been studied. Data obtained from industrial heats carried out in 185-ton electric arc furnace (EAF) were used to study. The present study carried out in a wide range of DRI percentage, 0 - 50% of metallic charge, and the results have been statistically analyzed to correlate the percentage of DRI with the different consumption figures of electric energy, oxygen, coke and fluxing materials. In addition, the influence of DRI percentage on contents of tramp and detrimental elements affecting on steel quality has been also investigated.
The results reveal improving the steel quality by increasing DRI percentage, as the tramp elements (Cu, Sn, Ni, Cr) and detrimental elements (P, S) and also nitrogen, all decrease by increasing the percentage of DRI in the metallic charge. On the other hand, the increase in DRI percentage leads to increase in the consumptions (per ton of liquid steel) of electric energy, oxygen, coke and fluxing materials. Furthermore, the metallic yield decreases and the power on time and hence the tap-to-tap time increase as DRI percentage increases. With using higher DRI percentage in the charge, the yield strength and ultimate tensile strength of produced hot rolled bars of low carbon steel slightly decrease whereas elongation increases.

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Factorial design was used to investigate the contribution effect of cooling rate of stage between rolling and coiling and cooling rate after coiling on grain size, pearlite lamellar spacing, mechanical properties and hardness of hot rolled narrow 65Mn strip. The contribution of both cooling rates before and after coiling process, and the interaction combination effect of both rates were determined for each measured property. The regression models were built up to identify grain size, pearlite lamellar spacing, mechanical properties and hardness as a function in cooling rates before and after coiling process.
It was found that the contribution effect of cooling rate before coiling on grain size growth, enlargement of pearlite lamellar spacing, Ultimate Tensile Strength (UTS) and elongation is negative with different magnitude and it has positive effect on Yield Strength (YS) and hardness. Cooling rate after coiling has negative effect on grain size growth, enlargement of pealite lamellar spacing and elongation while it has positive contribution on UTS, YS, and hardness. The interaction combination effect of both two rates has very small positive contribution on YS and elongation, it has small positive effect on grain size growth, enlargement pearlite lamellar spacing, and it has large negative contribution on UTS and hardness. Factorial design technique is a successful technique to analysis the effecting parameters.

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