Serial-IV: Knowledge about Steel Production

1. How to classify steelmaking slag according to chemical composition?

1) Acidic oxides: such as SiO2, P2O5;

2) Basic oxides: such as CaO, MgO, MnO, FeO;

3) Amphoteric oxides: such as Al2O3, Fe2O3;

4) Other substances: CaS, FeS, MnS, if added fluorite and CaF2.

2. What is the role of converter slag in the steelmaking process?

1) Removing P and S from the molten metal;

2) Reduce the degree of erosion of the refractory material;

3) Dispersing metal droplets creates favorable conditions for decarburization;

4) Prevent a large amount of heat loss, avoid the oxygen flow strands from strongly impacting the molten pool; reduce metal splashing;

5) Prevent the molten steel from absorbing harmful gases;

6) Adsorption of foreign and intrinsic fine non-metallic inclusions.

3. What is the root cause of the splash?

1) The C-O reaction in the molten pool develops unevenly, and a large amount of CO gas is instantaneously discharged to the outside, which is the root cause of explosive splashing;

2) Severe foam slag, large slag layer, etc., hinder the smooth discharge of CO gas, is another important cause of splashing.

4. What is the cause of the lining erosion?

1) The role of high temperature heat flow. The high temperature action from the liquid metal and slag, especially in the primary reaction zone, may soften and melt the surface of the lining.

2) The role of quenching and rapid heat. The lining is subjected to quenching and rapid heat, which reduces the high temperature strength of the lining.

3) Mechanical damage. The movement of liquid and solid in the furnace and the collision of large scrap during feeding will accelerate the damage of the lining.

4) Chemical attack. Mainly from furnace gas and slag.

5. What are the measures to prevent phosphorus reversion?

1) The tapping is as far as possible to reduce the slag when tapping;

2) Using alkaline lining to reduce the slag alkalinity caused by ladle erosion;

3) Put a small amount of lime powder into the ladle during the tapping process, and thicken the slag to maintain alkalinity;

4) When the tapping is completed, minimize the residence time of the molten steel in the ladle.

6. In the hot metal pretreatment, why does dephosphorization of molten iron must be desiliconized first?

The hot metal pre-desiliconization technology was developed based on the hot metal pre-dephosphorization technology. Since the affinity of oxygen and silicon in molten iron is larger than that of phosphorus, when deoxidizing by adding oxidant, silicon is preferentially oxidized than phosphorus, and the formed SiO2 greatly reduces the alkalinity of the slag. For this purpose, the silicon content must be reduced to less than 0.15% before dephosphorization. This value is much lower than the silicon content of the blast furnace molten iron. That is to say, only when the silicon in the molten iron is mostly oxidized, the phosphorus can be rapidly oxidized and removed. Therefore, it is necessary to remove silicon before dephosphorization.

7. What is the converter type and what are the basis for selecting the converter type?

1) Conducive to the physical and chemical reaction of the steelmaking process;

2) Conducive to the movement of furnace liquid and furnace gas;

3) Conducive to uniform mixing of the molten pool.

4) Splash is small and metal consumption is small.

5) The furnace shell is easy to manufacture and manufacture;

6) The furnace lining brick is easy to masonry;

7) Easy maintenance and long service life of the lining.

8) It is beneficial to improve working conditions and increase the operating rate of the converter.

8. What is the effect of slag oxidation on the smelting process?

1) affecting dephosphorization and desulfurization, which is beneficial to dephosphorization and is not conducive to desulfurization

2) Influence of lime dissolution rate on residual and manganese content in molten steel

3) Oxygen content affecting the end of molten steel

4) Affect the yield of metals and alloys

5) Affect the generation of foam slag and the occurrence of splashing

6) Affect the life of the converter lining

9. Where does the steelmaking slag come from?

An oxide formed by oxidation of various impurity elements (such as Si, Mn, P, etc.) contained in steel materials (hot metal, scrap steel); slagging materials (lime, etc.) added to remove sulfur and phosphorus in molten iron Flux (fluorite, etc.); ore, sinter, iron oxide skin and other materials added as oxidant or coolant to bring in impurities; lining refractory material that is eroded or washed away; sediment impurities brought in by various raw materials.

10. What is the role of adding Nb, V, Ti elements to the steel for microalloying?

Adding Nb, V, and Ti elements to steel can combine with [C] and [N] to form carbides, nitrides, and carbonitrides. These compounds dissolve at high temperatures and precipitate at low temperatures to inhibit grain growth and precipitation strengthening. effect. The result is a reduction in carbon equivalent, a significant increase in the strength and toughness of the steel, and a significant cost advantage.

11. Blowing medium slag characteristics and mineral composition?

In the middle of blowing, the furnace [C], [O] reacts fiercely, and the slag is prone to "back to dry". Its characteristics are high alkalinity and low ferrous oxide content. The slag mineral composition is: the main phase is dicalcium silicate and tricalcium silicate. When the lime is added, there is more free CaO. The higher the alkalinity, the larger the amount of tricalcium carbonate and the more free CaO, which is unfavorable for the smelting effect.

12. What is the slag "back to dry"? Why is the slag "back to dry"?

Back-drying refers to the phenomenon that the slag that has been melted or partially melted becomes sticky or even formed. In the middle of blowing, the carbon is violently oxidized, and the iron oxide in the slag is reduced, and high-melting 2CaO·SiO2, FeO and MnO are reduced, and the precipitate is precipitated. The solid material makes the slag sticky, and when it is serious, it forms a large block.

13. What are the main measures to increase the age of the converter?

1) Improve the quality of lining refractory materials.

2) Adopt integrated furnace technology.

3) The slag is mixed with an appropriate amount of magnesium oxide (MgO).

4) Using computer dynamic control, that is, optimal smelting control, to improve the end point hit rate, that is, shorten the smelting cycle.

5) Perform effective spray cleaning and maintenance.

6) Improve the structure of the spray gun.

7) Reduce the tapping temperature as much as possible.

8) Reduce the time of shutdown.

14. What is the role of the carbon-oxygen reaction during steelmaking?

1) Increase the steel-slag interface and accelerate the physical and chemical reactions.

2) Stir the molten pool, uniform composition and temperature.

3) It is advantageous for the floating of non-metallic inclusions and the discharge of harmful gases.

4) Conducive to the formation of slag.

5) The exotherm heats up.

6) Explosive carbon and oxygen reactions can cause splashing.

15. Does slag oxidation affect the smelting process?

1) It affects dephosphorization and desulfurization, which is beneficial to dephosphorization and is not conducive to desulfurization.

2) The speed of the solution that affects the lime.

3) Affect the residual manganese content of steel grades.

4) The oxygen content that affects the end of the molten steel.

5) Affect the yield of metals and ferro alloys.

6) Affect the generation of foam slag and the occurrence of splashing.

7) Affect the life of the converter lining.

#steelmaking #steelproduction #steelplant #ladlerefractories #EAFrefractories #converterrefractories #cxrefractories