Method for manufacturing ferritic stainless steel slabs with equiaxed grain structures and the ferritic stainless steel manufactured by it

Abstract

Disclosed is a method for manufacturing ferritic stainless steel slabs with equiaxed grain structures and the ferritic stainless steel manufactured by it, which control concentration of alumina inclusions in molten steel to maximize an available TiN generation effect serving as a non-uniform nucleating site of ferrite when solidifying it, thereby improving equiaxed crystal ratio, the method comprising the steps of: performing oxygen decarburization reaction by blowing oxygen from the upper part of the molten steel in a vacuum oxygen decarburization ladle; injecting Al in the molten steel to which the oxygen decarburization reaction is made for Cr₂O₃ reduction; making composite deoxidation by injecting deoxidizer in the molten steel into which the Al is injected for the Cr₂O₃ reduction; making alloying process by injecting alloying metal in the molten steel; first judging for judging whether Al concentration is in the range of a setting value by analyzing the Al concentration in the molten steel; if the Al concentration satisfies the setting value, stirring it using inert gas and second judging for judging whether alumina inclusion concentration in the final molten steel corresponds to a target value; and if the alumina inclusion concentration satisfies the target value, continuously casting the molten steel.

Description

BACKGROUND ART[0001]1. Field of the Invention[0002]The present invention relates to a method for manufacturing ferritic stainless steel slabs with equiaxed grain structures and the ferritic stainless steel manufactured by it, and more specifically to a method for manufacturing ferritic stainless steel slabs with equiaxed grain structures and the ferritic stainless steel manufactured by it which control concentration of alumina inclusions in molten steel to maximize an available TiN generation effect serving as a non-uniform nucleating site of ferrite when solidifying it, thereby improving equiaxed crystal ratio.[0003]2. Description of Related Art[0004]In general, there is a case that Ti of 0.2-0.5% is added to a ferritic stainless steel with Cr concentration of 10-30% in order to improve its corrosion-resistance. In this case, TiN is formed by the following equation from a steel making process to a continuous casting process, wherein when its size and distribution are proper, it ser...

AI Technical Summary

Benefits of technology

[0020]In contrast to a method for manufacturing steel slabs with equiaxed grain structures depending on techniques such as a casting temperature control and an electromagnetic mixing power control and the like made in the prior art, a method for manufacturing ferritic stainless steel slabs with equiaxed grain structures and the ferritic stainless steel manufactured by it according to the present invention as described above precisely controls components of molten steel, such as Si and Mn, etc., and concentration of alumina inclusions to effectively generate available TiN so that it can manufacture ferritic stainless steel slabs with equiaxed grain structures and high equiaxed crystal ratio while improving operating stability, thereby obtaining ferritic stainless steel slabs with equiaxed grain structures having excellent formability, that is, low ridging defect.

Problems solved by technology

Also, since the generation of excessive TiN oxide can arise the clogging of a submerged entry nozzle in a continuous casting process and the defect of steel making ability in a slab surface, simply the application of Ti deoxidation has any limitation.

However, in this case, when it is impossible to simultaneously control the concentration of each oxide, that is, even when the concentration of a specified component such as Al2O3 is very high or the concentration of MgAl2O4 is very low, the above equation can be satisfied, however, the equiaxed grain structures cannot easily be obtained.

This is because if the concentration of Al2O3 in the inclusions is excessively high, the difference of lattice mismatched degree between Al2O3 / TiN or Al2O3 / ferrite becomes very large, that is, interface energy becomes large so that these inclusions have a difficulty to serve as the non-uniform nucleating site of ferrite when solidifying the molten steel.

However, when operating with the compositions of high Ti and low Al within the range of the concentration, there is risk of generating a large amount of Ti oxide.

This may be a factor causing a nozzle clogging or a defect of a slab surface during a casting process.

However, it is not easy to properly form TiN independently from oxidation-inclusions in the stainless molten steel over which the inclusions in the form of oxide is distributed.

However, it is judged that whenever stainless molten steel is refined, it takes relatively much time to measure the oxygen activity in the molten steel using the oxygen sensor, its accuracy is slightly degraded, and a concrete kind of the deoxidizer is not specified so that it becomes slightly ambiguous in applying it to an actual operation.

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