In many fields such as automobile molding, aerospace, rail transit, instrumentation, medical equipment, household appliances, new energy, etc., 60% to 80% of the parts are molded by mold. Therefore, the quality level of the mold is a important measure of the industrial level of a country.
At present, China's mold steel output has leapt to the world's first, but the vast majority of low-end products, high-end high-quality mold steel still needs to be imported from Germany, the United States, Japan and other developed countries. The quality and cleanliness of foreign high-end cold-worked die steel is very high. The grades of non-metallic inclusions of A, B, C, D coarse/fine and Ds are all ≤1.0, and the oxygen content in steel is ≤20ppm.
The process of producing cold work die steel is: 40 ton electric furnace (adding carbon powder and ferrosilicon block / powder reduction) → electric furnace tapping → ladle slag removal → 40 ton LF furnace (adding lime, refining slag and other slag and steel slag friends) Reduction)→40 tons VD→argon protection cast ingot→red delivery→825 rolling mill rolling slab or 4500 ton fast forging machine forging blanking→annealing→grinding→700 rolling mill forming→annealing→straightening→shotping→ Check the warehouse. The percentage of Class B fine inclusions in the cold work die steel produced by the production is ≥2.0, which is 43.7%, and the average oxygen content in the steel is 0.00344%. Therefore, the cold work die steel smelted by the original process has poor cleanliness. In order to improve the cleanliness of steel, an experimental study on the effect of the new process of electric furnace reduction on the cleanliness of cold work die steel was carried out.
The new process uses aluminum ingots and steel slag friends (the main component is Al2O3 30% ~ 45%, Al 40% ~ 50%) instead of the original process of ferrosilicon block / powder, strengthen the electric furnace reduction. The differences between the slag composition of the new and old process electric furnace reduction slag and the refining final slag composition of the VD sling steel before and after the new and old process were analyzed and discussed. The dissolution rate of the refining furnace slag system Al2O3 was compared with the old and new technology, and the SiO2 content in the new and old refining slag system and steel. The relationship between the oxygen content, the cleanliness of the new and old process cold work die steel (non-metallic inclusion grade and oxygen content in steel).
The results show that the new process of intensifying reduction of electric furnace adopts strong deoxidizer aluminum ingot and steel slag friend instead of the weak deoxidizer ferrosilicon or powder in the original process, which improves the alkalinity of slag, strengthens deoxidation, and greatly reduces Cr2O3 in slag. content. After the electric furnace is tapped, the slag has good fluidity, and the ladle can remove the high SiO2 content electric furnace reducing slag, effectively reduce the SiO2 content in the LF slag, and control the final slag composition of the refining cold work die steel to the low SiO2 content calcium. Within the required range of aluminum slag, the dissolution rate of slag Al2O3 is effectively increased, thereby reducing the total amount of Al2O3 inclusions in the steel and reducing the class B oxide inclusions. The proportion of ≥2.0 grade B oxide fine inclusions in the cold-worked die steel smelted by the new process was reduced by 30.4% compared with the original process, and the average oxygen content decreased by 48.0%, which improved the cleanliness of the cold work die steel. (Source: Metallurgical Information Network）
