| The characters of the inclusions in the molten steel affect the quality of the steel directly,therefore,it is one of the key tasks to reduce inclusions in making steel.This paper combining with the case of a certain enterprise,the content of inclusions in the casting is over standard,which makes the Hot-rolled productions peeling more frequently.In order to promote the cleanness level of the molten steel,provide current steel making procedure with the theory and experiment gist,this paper probe into the transformation about the inclusions in whole procedure of steel making,which are about the inclusions' type,morphology,size,and distribution,especially for Q195L and SPHD steel.According to the experiments and the theory analysis,the results are as follows:(1)Among all kinds of the steels,three kinds of aluminum killed steel-Q195L,SPHC,and SPHD peel more seriously.After the research and the analysis on the whole procedure,a preliminary conclusion has been drawn:the top-slag of high oxidizability that without the procedure of making white slag is the primary reason of peeling.(2)The thesis contrapose the cause of peeling carried out top slag modification experiments,modification scheme determined by the analysis of slag composition.Except for the basis of the original alloying operation,adding 200 kg of lime after the steel tapping a quarter.After that,adding 30kg aluminum to restore the top slag at the end of the steel tapping.At this point,attention should be given to control the Ar flow rate,in order to prevent sloshing and avoid aluminium deoxidizing the molten steel.(3)During the experiments about modification of top-slag on SPHD steel,it turns out that,when employing the original procedure,the involving of the top-slag,re-oxidization between slag and the molten steel,and the polymerization and growth of inclusions happens more easily in the process of RH refining.So,during the process of "Ar—RH—CC",the size of the inclusions follows a regular pattern:it becomes big first and then small.While,employing the modification of steel ladle's top-slag will avoid the RH refining procedure and the re-oxidization exerted by top-slag of high oxidizability on molten steel in the following continuous casting.So the quantity and the size of inclusions will decrease,and the cleanness level of the molten steel will be improved dramatically.(4)During the experiments about modification of top-slag on Q195L steel,it turns out that,when employing the original procedure,the size of the inclusions will become smaller during the "Ar-RH-CC" process.While through the comparison,we can find that,the inclusions in the modified molten steel is smaller and fewer and the spheroidization is more obvious and there are little compound inclusions.After the modification,we find that the oxidizability of the top-slag becomes obviously lower,and the phenomena of oxygen transfer in the process of conveying molten steel are less than before.In addition,the slag has better flowability and the adsorbability now,and the cleanness level of the molten steel is improved.(5)High melting point CaO·6Al2O3 is the main composition of submerged nozzle nodulation.In view of the impact of submerged nozzle clogging on the flow field of crystallizer,and the impact of nodule's detachment on peeling.Calcium treatment on Q195L steel and SPHC steel should be given to.In consideration of the high costs,abnormal furnaces should be given calcium treatment at least,and controlling Als to its minimum as far as possible.(6)Improving the cleanness level of the molten steel and reducing peeling are systematic projects,which can not be achieved only by modification on the top-slag.So all the links in steel-making need to be promoted,such as the process of steel tapping,deoxidation alloying,RH refining,and the protection for casting in continuous casting.In future work,the procedures of blowing Ar to the ladle,the RH refining and the improvement on the flow field of tundish still need further researches,then the removal of inclusions can promote a step further. |
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