Thu, 19 Jul 2018 03:17:07 +0000
Smelting process in industrial steel manufacturing
It is an important method to improve the rolling contact fatigue life of bearing steel to reduce the total oxide inclusion in steel by improving the steelmaking process. In order to obtain high quality steel, it is a common method to increase the amount of molten iron and select high quality scrap steel for smelting. In the process of ladle metallurgy, the content of aluminum, silicon or calcium added into steel can be precisely controlled to promote the deoxidation and desulfurization.
Isotope tracking tests show that 70% of the oxide inclusions in steel come from vacuum degassing and aluminum deoxygenation, and the rest from refractory materials or protective slag. It has been reported that acidic smelting can reduce the content of non-metallic inclusions (mainly silicates) and make them better shaped and deformed.
Vacuum smelting is also an important way to reduce the content of inclusions. At a high vacuum, the oxygen content in steel can be reduced to less than 10×10-6. Electroslag refining can obtain better than vacuum smelting smelting effect, due to the small size of inclusions in the process of electroslag refining, under the same oxygen concentration, electroslag refined steel than other refining technology in the production of steel to fatigue failure of the sensitivity of the weak.
By electroslag refining is not just simply reduces the oxygen content in steel, also reduced the size of inclusions in the steel, the inclusions distribution more uniform, after remelting can provide opportunities for large inclusion floatation. Ultra-high cycle fatigue tests were conducted on GCr15 bearing steel prepared by vacuum smelting and electroslag refining respectively. Stainless bearing steel such as 9Cr18 and 9Cr18Mo can be smelted by arc furnace smelting and electroslag remelting.
The oxygen content in the steel smelted by electroslag remelting is 0.28 * 10-4% ~ 0.4 * 10-4%, and the oxide inclusion in the steel is small, but the content is large, which affects the service life of the bearing. The total content of oxygen, titanium and sulfur in steel can be controlled below 80×10-4% by using argon stirring, electromagnetic stirring and vacuum degassing in ladle.
At present, the use of bearing steel is more important to adopt vacuum induction and vacuum consumable (double vacuum smelting, the production of this new type of stainless bearing steel purity of 6 cr14mo increased sharply, oxygen content is only 5 x 10-4% (usually less than 10 by 10-4%), and less number of oxide inclusions, the size is small, distribution more uniform