Inclusion in steel is one of the main factors affecting the contact fatigue life of bearing steel.The key to control inclusion in steel is to control the oxygen content and oxide in steel.The main idea of reducing oxide inclusion in steel is as follows.
First, the carbon content of the end of the steel furnace is controlled.
When the carbon content is too low, the dissolved oxygen is high in the steel, resulting in a large amount of aluminum consumed in subsequent deoxygenation, and the total amount of inclusions will increase, which will bring difficulties to the later refining.In addition, the oxidation of slag will also increase obviously, and it is difficult to refine and control the composition of steel slag.However, the high carbon content of the end point of steel will bring pressure to the process control of the furnace.When the arc furnace is smelting, the end carbon content is generally controlled at about 0.2%.
Choose the right deoxidizer.
In the process of bearing steel production, the oxygen content in steel can be reduced and the amount of acid soluble aluminum can be reduced with aluminum.When the content of acid soluble aluminum is too high, the protection of molten steel can easily lead to secondary oxidation, thus increasing the content of brittle Al2O3 inclusion.When the content of acid soluble aluminum is low, the dissolution of the dissolved oxygen due to the secondary oxidation of silicon and the lower temperature of molten steel leads to the formation of large silicate inclusions rich in SiO2.According to the research, the content of acid soluble aluminum in steel can be controlled at 0.02%~0.04%, and the grain of steel can be refined to obtain high toughness.
Barium is an ideal deoxidizing agent, and the barium alloy is not only deoxidized, but also can make the residual inclusions in steel very well denatured.According to research, using silicon - aluminum - barium alloy after deoxidation of bearing steel, the total oxygen content in steel rapidly to a stable value, in the end point without containing barium globular inclusions in steel, and residual inclusions in steel is modified, the inclusions fine dispersion, uniform distribution.
Magnesium has a significant effect on the deterioration of Al2O3 inclusions in bearing steel.Acid soluble was 0.03%, according to research, there are 2 in steel 10-4% of magnesium is Al2O3 inclusions can be metamorphosed into MgO style, Al2O3, greater than 10 microns of Al2O3 inclusions in steel into small, spherical magnesium aluminate spinel inclusions, and more than 99.46% less than 5 microns of inclusions, the inclusions for 5 ~ 10 microns.
3. Optimize the composition of refined slag.
The study found that the binary basicity refining slag increased from 2.0 to 4.5, the total oxygen content of molten steel end by 20 10-6 to 11 10 -, inclusion of total quantity and total area is reduced.The typical inclusions in the steel liquid of high alkalinity slag are Al2O3 and alumina magnesium spinel and other brittle inclusions. The size is not greater than 5 mu m.To increase the content of Al2O3 or to add CaF2 and reduce the content of MgO can significantly improve the speed and capacity of the adsorption inclusions of refined slag.
Optimize the smelting process.
In order to obtain high quality steel, it is commonly used to increase the amount of molten iron and select high-quality scrap steel.In the process of ladle metallurgy, the aluminum, silicon or calcium content in the steel can be precisely controlled to promote deoxygenation and desulfurization, and the whole process adopts protective pouring, and the inclusion content will be greatly reduced.Vacuum is an important approach to reduce the content of inclusions, under high vacuum degree, the oxygen content in steel can be dropped to 10 10-6 below.Electroslag refining can improve the smelting effect of vacuum smelting.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 is more even, after remelting can provide opportunities for large inclusion floatation.
At present, the use of bearing steel is more important to adopt vacuum induction smelting and vacuum consumable, the production of this new type of stainless bearing steel purity of 6 cr14mo is increased sharply, oxygen content is only 5 10-4, the quantity is less, and the oxide inclusions size is small, distribution more uniform.