December 2011 - SIMA

Above data are shown graphically also in figure - 3:It is clearly evident from above data and the graphthat % metallization is comparatively higher by about4-5% in case of DRI Pellets for the same Fe(M)contents. This higher metallization resulted in lowerFeO content of Pellet based DRI compared to ironore based DRI as shown below:(i)Iron ore based DRI = 10.23 – 14.02 % FeO in Agrade.(ii) Pellet based DRIgrade.Fig.-3= 5.19 – 9.42 % FeO in ANormally A grade DRI having metallization of 88-92%is used in steel making for smooth furnace operation.But with A grade DRI Pellets lower FeO contentresulted in inadequate boiling and hence, dense slag,causing difficulty in its removal and other relatedproblems as mentioned above.CORRECTIVE MEASURES:As there is no Oxygen injection in induction furnaces,some measures were taken to feed extra FeOthrough some additives in the furnaces as indicatedbelow:a) MILL SCALE ADDITION:As mill scale contains high FeO, the same was addedin the furnaces when slag was getting jammed, but itwas not found to be very effective. It is felt that millscale gets lost in the slag, as it is a very fine material.b) IRON ORE ADDITION:Attempts were also made to charge sized Iron ore inthe furnaces in place of mill scale but its effect wasfound to be very slow in the furnaces. Hence it wasdiscarded.c) ADDITION OF ABOUT 10 - 15% B GRADESPONGE IRON IN CHARGE – MIX:With B grade S.I. [76%> Fe(M) < 80% ] charge mixcomposition was changed as follows:A grade DRI Pellets = 80 - 85%B grade sponge iron = 10 - 15% (approx.)Scrap = 5%It was observed that furnace operation was smoothwith the above charge mix composition. Problems ofslag jamming, high heat duration & excessive powerconsumption were resolved by this measure. Thereafter it has been put to regular practice in our plant.QUALITY OF STEEL OUTCOME:Output steel quality of induction furnaces is a matterof concern as silica lined induction furnaces areunable to carry out any refining operation. They arepresently treated as merely melting furnaces. So bothde-phosphorization and desulphurization cannot becarried out in induction furnaces. Though Sulphur canbe reduced by installation of LRF but, the processfor Phos removal is always difficult although undercontinuous development through IRF (InductionRefining Furnace) as claimed by M/s. Electrotherm.In EAF Phos and Sulphur can be controlled by makingoxidizing and reducing slag practice as well as byoxygen blowing.However Monnet manages to produce quality mildsteel billets and finished structural steel sections bycontrolling raw material quality strictly to maintain anaverage quality range as achieved with DRI Pelletsis as follows:%C %Mn %S %P %Si0.12-0.25 0.50-0.80 0.040-0.045 0.050-0.060 0.15-0.35DECEMBER-2011/19