Metallurgical method for refining grains of steel by modifying inclusions through addition of magnesium and aluminum

Abstract

A metallurgical method for refining grains of steel includes adding aluminum into molten steel obtained from a secondary refining process. Aluminum reacts with oxygen and sulfur in the molten steel to reduce the total oxygen content in the molten steel to 15-120 ppm, to reduce a sulfur content in the molten steel to 15-150 ppm, and to produce aluminum oxide, obtaining cleaner molten steel. Magnesium is added into the cleaner molten steel and reacts with oxygen, sulfur, and aluminum oxide in the cleaner molten steel to reduce the total oxygen content in the molten steel to 10-60 ppm, to reduce the sulfur content in the molten steel to 5-100 ppm, and to produce inclusions including magnesium oxide, magnesium sulfide, and magnesium-aluminum spinel. Precipitates of the inclusions can serve as crystalline cores in a subsequent crystallization process to obtain fine-grained steel.

What is claimed is: 
     
         1 . A metallurgical method for refining grains of steel obtained from a secondary refining process, with the method comprising:
 a pre-processing step, with the pre-processing step including adding aluminum into the molten steel obtained from the secondary refining process, with aluminum reacting with oxygen and sulfur in the molten steel to reduce a total oxygen content in the molten steel to 15-120 ppm, to reduce a sulfur content in the molten steel to 15-150 ppm, and to produce aluminum oxide, obtaining a cleaner molten steel; and   a modification step, with the modification step including adding magnesium into the cleaner molten steel, with magnesium reacting with oxygen, sulfur, and aluminum oxide in the cleaner molten steel to reduce the total oxygen content in the molten steel to 10-60 ppm, to reduce the sulfur content in the molten steel to 5-100 ppm, and to produce inclusions, with the inclusions including magnesium oxide, magnesium sulfide, and magnesium-aluminum spinel, with precipitated inclusions serving as crystalline cores in a subsequent crystallization process following the modification step, obtaining fine-grained steel in the crystallization process.   
     
     
         2 . The metallurgical method as claimed in  claim 1 , wherein 0.01-0.06 kilograms of magnesium per ton of the cleaner molten steel is added in the modification step. 
     
     
         3 . The metallurgical method as claimed in  claim 1 , wherein a magnesium-iron alloy wire is added into the cleaner molten steel in the modification step, with the magnesium-iron alloy wire including 5-80 wt % of magnesium. 
     
     
         4 . The metallurgical method as claimed in  claim 1 , wherein each of the pre-processing step and the modification step is carried out at 1843K to 1903K. 
     
     
         5 . The metallurgical method as claimed in  claim 1 , wherein the molten steel obtained from the secondary refining process is medium carbon steel or low carbon steel.