TItle：How to achieve the so-called “three-layer structure” of mold powder powder?
Description：Briefly explain the formation of the “three-layer structure” of mold powder
To play the 5 functions of the mold powder, it is necessary to form a “three-layer structure” with the powder added to the mold slag. The key to forming a “three-layer structure” is to control the melting speed of the powder, that is to say, the slag powder added to the molten steel level should not be melted into liquid all at once, but gradually melted. For this reason, carbon particles are generally added to the mold flux as a regulator of the melting rate.
The speed at which carbon particles control the melting rate depends on the type and quantity of carbon particles added. Carbon is a high-temperature resistant material, and extremely fine carbon powder is adsorbed around the slag particles, which separates the slag particles from each other to hinder the contact and fusion between the slag materials and slow down the melting speed. If the carbon powder is insufficient and the temperature of the slag layer has not reached the sintering temperature of the slag material, the carbon particles have been burned out, the sintering layer is developed, the melting rate is too fast, and the liquid slag layer is too thick. If too much carbon powder is added, some carbon particles will still exist after the slag is completely melted, and the sintered layer will shrink and the thickness of the sintered layer will be too thin. When the amount of carbon powder is moderate, some of the carbon particles in the sintered layer are burned out, and the remaining part of the slag material is still effectively controlled by the carbon particles, so that a sintered layer and a liquid slag layer of appropriate thickness will be obtained.
There are two types of carbon materials: graphite and carbon black. Graphite particles are coarse, with a particle size of 60-80μm, and their separation and retarding effects are poor, but the initial oxidation temperature is higher (about 560°C), the oxidation speed is slow, and the ability to control the melting rate in the high temperature zone is strong. Carbon black has an amorphous structure, with very fine particles (0.06～0.10μm), strong separation and retardation, low initial oxidation temperature (500℃), and fast oxidation speed. Therefore, carbon black is in the lower temperature zone of the slag layer. The melting rate is strong, and the control efficiency is low in the high temperature zone. Even if the dosage is increased, the improvement effect is limited.
Generally, the amount of carbon powder added is 4 to 7%.