Effect of refractory materials on non-metallic inclusions in steel

In the application of refractory materials, different substances will produce different properties under the interaction, according to the source of non-metallic inclusions in steel is divided into 3 groups:

(1) Endogenous – the metal itself, when it deoxidizes, crystallizes and cools, forms an internal origin due to various physicochemical processes;

(2) Exogenetic – composed of refractory materials and slag of external origin, when the liquid metal is exiled and poured, mechanically induced and may solidify in the steel. The most dangerous is the liquid metal induced refractory small particles, because large particles are easy to float;

(3) Endogenous – exogenous secretion on exogenous, when endogenous inclusions. Visually evaluate the pollution of non-metallic inclusions in steel according to the level of the standard grade table (Figure 11-18). The polished microgrinding plate is observed under a microscope with an increase of 100 to 125 times, and the rolled steel sample is compared with the standard grade table. This method is used primarily to identify exogenous inclusions, which are relatively small in the share of all inclusions.

In normal metallurgical process, the external inclusion does not exceed 5% to 10% of the total inclusion. This compelling indicator has been studied many times using radioisotopes (tracer atoms). The mass fraction of all inclusions is generally 0.01%~0.02%.

The least dense nonmetallic inclusions can float. Buoyancy generally follows what is known as Stocker’s rule. But in fact, when the inclusion size is not large, the adhesion force has a great effect. The smaller the degree of wettability (the large interphase energy of the metal-inclusions), the smaller the force that restrains the contact between the inclusions and the metal, and the easier it is to separate from the metal and float. As an example of inclusion, liquid iron is not well wetted and may suffer from alumina inclusion (σ-al2o3 ≈1J/m2); As an example of an inclusion, liquid iron is well wetted (so is not well separated from it) and may suffer from an inclusion of iron silicate (σ-au ≈0.4J/m2). Inclusions with a size of 1-2 μm rise very slowly and, due to airflow convection, may be transferred in the liquid metal volume for a long time, while the end result remains in the metal. The bubbles emitted through the molten pool (metal boiling, inert gas blowing molten pool, etc.) and the inclusion have a smaller phase energy than the phase energy between the inclusion and the metal, that is, (σ-gas < σ-gold – impurity), so the inclusion sticks to the bubble and disappears with it in the slag.

On the effect of exclusion rate of inclusions from metal:

(1) the size of the inclusion, its composition (melting temperature) and density;

(2) the ability to increase inclusions;

(3) interphase energy at metal-inclusion and slag-inclusion boundaries;

(4) stirring intensity of the molten pool;

(5) Physical properties of metals.

First, the impact of the steel groove lining The steel groove lining is a lot of damage: 1t steel is 2~6kg. The discharge of a furnace is extended from 10min to 20min. The fragments of refractory material washed out at this time float due to the small thickness of the metal layer. Therefore, the possibility of contaminating the steel by the refractory lining of the steel groove is very small.

Second, the impact of ladle lining has shown that ladle refractory material consumption is large, and large and deep inclusions float. In addition, the steel in the ladle rotates. The steel cools in the outer part and moves down, while it goes up in the center part. At the same time, some parts of non-metallic inclusions remain in the steel, as shown in Table 11-5.

The statistical data show that the ingot cast by the method of flowing steel bricks has less non-metallic inclusions than the ingot cast. Porous flow steel bricks even absorb some parts of endogenous nonmetallic inclusions formed by aluminum deoxidation of steel; But there is another point of view, because of the low thermal stability of the flow steel brick, so the crack is the fault of the flow steel brick to produce non-metallic inclusions. In order to reduce non-metallic inclusions, it is recommended to use semi-silicon materials when pouring silicon steel, and use bricks with small free silicon oxide content when pouring steel with high manganese content. In any case, the cast steel brick should be heat stable, only the glass phasor is minimal, its structure is in line with the desire, that is, the flow steel brick should be low temperature fired into porous, or not fired.

Although the refractory material is severely damaged during the refining process of the molten steel furnace, it is involved in the formation of non-metallic inclusions in the steel, which is the minimum here, because the development direction of the refining process itself is to reduce all types of non-metallic inclusions. When the refractory is dissolved in the metal, the refractory elements change into ionic or atomic form. In metals, these elements interact with gases to form nonmetallic inclusions, thus forming nitrides, oxides, sulfides, etc. In this way, any dissolution of the refractory in the steel forms non-metallic inclusions.