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89 common sense of steelmaking

Attention:     Issuing time:2020-09-09 09:11
89 common sense of steelmaking

1. Ways to accelerate lime slagging?
Answer: ①Improve the quality of lime and use soft-burned active lime.
②Properly improve the composition of the flux ③Increase the blowing temperature. ④Control the appropriate gun position ⑤Use synthetic slag
2. Why should molten steel be deoxidized?
Answer: If the molten steel is not deoxidized, the continuous casting billet cannot get the correct solidification structure. High oxygen content in steel can also produce defects such as subcutaneous bubbles and looseness, and aggravate the harmful effects of sulfur. The generated oxide inclusions remaining in the steel will reduce the mechanical properties such as plasticity and impact toughness of the steel. Therefore, the excess oxygen in the steel must be removed.
3. Which aspects should be taken to prevent explosive splashing during the blowing process?
Answer: (1) Control the temperature of the molten pool. ⑵Control (TFe) does not appear aggregation phenomenon. ⑶ Do not drop the gun easily once splashing occurs during blowing. ⑷When the furnace temperature is very high, white ash can be added to thicken the slag while lifting the gun.
4. The reason for the damage of the lining?
Answer: (1) The impact of scrap steel and molten iron on the furnace lining and mechanical wear. (2) The agitation of molten steel and slag and gas flushing.
(3) The chemical attack of the slag on the furnace lining. (4) The lining temperature is chilled, heated, and the structure is changed.
(5) Mechanical peeling at the beginning of furnace opening. (6) Oxidation of the carbon inside the lining brick.
5. Briefly describe the characteristics and mineral composition of the slag in the middle smelting process?
Answer: In the middle of smelting, the carbon and oxygen in the furnace react violently, and the slag is prone to "dry back". Its characteristics: high alkalinity and low iron oxide content. When the slag is composed of minerals: the main phases are dicalcium silicate and tricalcium silicate. When the lime is added, there is more free CaO. The higher the alkalinity, the greater the amount of tricalcium silicate and the more free CaO, which is unfavorable for the smelting effect.
6. Briefly describe the principle of selecting raw materials for steelmaking?
Answer: Mass production at home and abroad proves that implementing the concentrate policy is an important way to automate the converter steelmaking process and improve various technical and economic indicators. The raw materials are mainly molten iron, scrap steel, slag-making materials, ferroalloys, and oxygen. Reasonable selection of raw materials is based on the principle of low input and high quality output based on smelting steel grades, operating techniques and equipment levels.
7. The main way to reduce blow loss?
Answer: ⑴Finished material policy, reduce the amount of slag. ⑵Reasonable slagging system. ⑶Use a reasonable oxygen supply system and loading system to reduce mechanical splashing. ⑷Adopt thermal compensation technology to eat more scrap steel and reduce chemical burn loss. ⑸ Use reasonable combined blowing technology.
8. What is less slag operation, and what are the advantages of less slag operation?
Answer: When the amount of lime added per ton of metal material is less than 20kg/t, the slag formed per ton of metal is less than 30kg/t, which is a low-slag operation
⑴The amount of lime added is small, which reduces the slag material and energy consumption, and reduces the emission of pollutants.
⑵The utilization rate of oxygen is high, the end point oxygen content is low, the residual manganese is high, and the alloy yield is high.
⑶ Reduce corrosion to the furnace lining and reduce splashing.
9. What are the ways to reduce oxide inclusions in steel?
Answer: To reduce oxide inclusions in steel, foreign inclusions should be minimized. Improve the purity of raw materials; adopt reasonable smelting technology, deoxidation system and molten steel refining technology according to the requirements of steel types; improve the quality and performance of refractory materials used in converters and pouring systems; reduce and prevent secondary oxidation of molten steel to maintain normal Pouring temperature, full protective pouring, selection of good performance mold powder; selection of reasonable steel thermal processing and heat treatment processes are beneficial to improve the nature of inclusions and improve steel quality.
10. Why use argon instead of nitrogen for blowing and stirring?
Answer: The argon in the inert gas does not dissolve in molten steel, and does not react with any element. It is a very ideal stirring gas, so it is widely used. In terms of stirring, nitrogen is the same as argon, and nitrogen is cheap, but nitrogen can dissolve in molten steel at high temperature, and the amount of nitrogen increase increases with the increase of temperature and the extension of nitrogen blowing time. When the temperature is higher than 1575℃ At this time, the nitrogen content in the steel can be increased by 0.003%, which affects the quality of the steel. Therefore, the use of nitrogen as a stirring gas is restricted. Only a small amount of nitrogen-containing steel can be used as a stirring gas, and there is also an unstable nitrogen increase problem.
11. What is the significance of the decarburization reaction to the steelmaking process?
Answer: ① The carbon in the molten iron is oxidized to be close to or equal to the specification range of the carbon in the molten steel through the decarburization reaction.
②Circular stirring effect on the molten pool ③The generated CO is necessary to remove the gas in the steel. ④Conducive to the elimination of non-metallic inclusions in steel. ⑤Provide heat source for steelmaking reaction. ⑥ Conducive to the reaction between slag and steel in the blowing process.
12. Why does steelmaking need to create slag?
Answer: To make good steel, slag must be made first. The completion of all steelmaking tasks is almost related to slag. The purpose of steelmaking and slagging is to ①remove the harmful elements P and S in the steel ②steel-making slag covers the surface of molten steel to protect the molten steel from excessive oxidation, absorption of harmful gases, heat preservation, and reduction of beneficial element burning. ③ Absorb the floating inclusions and reaction products. ④Ensure the smooth progress of carbon-oxygen reaction. ⑤It can reduce the corrosion loss of furnace lining.
13. What is the relationship between aluminum and steel properties?
Answer: Aluminum is added to steel as a deoxidizer or alloying element, and its deoxidizing ability is much stronger than that of silicon and manganese. The main role of aluminum in steel is to refine the grains and fix the nitrogen in the steel, thereby significantly improving the impact toughness of the steel, reducing the tendency to cold brittleness and the tendency to age. Aluminum can also improve the corrosion resistance of steel, especially when used in conjunction with elements such as molybdenum, copper, silicon, and chromium, the effect is better.
14. What effect does oxygen have on the performance of steel?
Answer: The solubility of oxygen in solid iron is very small, mainly in the form of oxide inclusions. Therefore, except for some sulfides, most of the inclusions in steel are oxides. Non-metallic inclusions are the main source of damage to steel, and have significant adverse effects on the fatigue strength, processability, ductility, toughness, welding performance, HIC resistance, and corrosion resistance of steel. With high oxygen content, the continuous casting slab will also produce defects such as subcutaneous bubbles, which will deteriorate the surface quality of the continuous casting slab.
15. Why do we need to stop slag tapping?
Answer: Less slag or slag stop tapping is one of the necessary methods for producing pure steel. Its purpose is to help accurately control the composition of molten steel, effectively reduce the rephosphorization of molten steel, increase the absorption rate of alloy elements, and reduce alloy consumption. It is beneficial to reduce the content of inclusions in steel and improve the ladle scouring effect. It is also beneficial to reduce corrosion damage to the ladle refractory materials. At the same time, the life span of the tap hole of the converter is also improved.
16. What are the basic tasks of steelmaking? By what means?
Answer: The basic tasks of steelmaking are decarburization, dephosphorization, desulfurization, and deoxidation, removing harmful gases and non-metallic inclusions, increasing the temperature, and adjusting the composition of molten steel. Oxygen supply, slagging, stirring, and alloying are the means to complete steelmaking tasks.
17. Briefly describe the main function of adding dolomite to converter steelmaking.
Answer: Dolomite is a slag adjuster, which can be divided into raw dolomite and light burned dolomite. According to the need of slag splash protection technology, add appropriate amount of dolomite to keep the MgO content in the slag saturated or supersaturated, so as to reduce the corrosion loss of the initial acidic slag to the furnace lining, so that the final slag can be sticky, and reach the slag splash after tapping. Requirements.
18. Combining the conditions before, during and after blowing, briefly describe the operation of constant pressure changing gun.
Answer: The constant flow variable lance position operation means that the oxygen supply flow remains unchanged during the blowing process of a furnace of steel, and the blowing is controlled by adjusting the lance position to change the interaction between the oxygen flow and the molten pool. Most manufacturers in our country use staged constant flow change gun position operation. Due to the different conditions of converter tonnage, nozzle structure, raw material conditions and steel types, the operation of the oxygen lance is not exactly the same. There are currently two operating modes of the oxygen lance as follows. ①High-low-high-low gun position mode. The blowing gun position is relatively high, and the initial slag is formed early. After the second batch of rice is added, the gun can be lowered in time. When the slag is returned to dry in the middle of the blowing, the gun can be lifted or an appropriate amount of flux can be added to adjust the slag fluidity to shorten the blowing time. Pull carbon out of steel. ⑵High-low-low gun position mode. The blowing gun position is higher, and the initial slag is formed as soon as possible; the gun position is gradually reduced during the blowing process, and an appropriate amount of flux is added in the middle of the blowing process to adjust the fluidity of the slag, and the end point is carbon steel.
19. Write down the chemical reaction formula of carbon oxidation in converter steelmaking, and indicate the carbon-oxygen reaction produced by splashing.
Answer: [C]+½{O2}={CO} [C]+(FeO)={CO}+[Fe] (carbon-oxygen reaction caused by splashing) [C]+[O]={CO}
20. What are non-metallic inclusions? Where does it come from?
Answer: The non-metallic phases produced or mixed in during smelting, casting and solidification of molten steel are called non-metallic inclusions. The non-metal phase is a compound formed by combining some metal elements and Si with non-metal elements, such as oxides, nitrides, and sulfides. Due to the presence of inclusions, the continuity of the steel matrix is ​​destroyed, resulting in uneven steel structure, which affects the mechanical properties and processing properties of the steel. However, non-metallic inclusions also have beneficial effects on steel, such as controlling intrinsic fine grains, precipitation hardening, promoting grain orientation, and improving the cutting performance of steel.
twenty one. How to classify steel according to room temperature organization and carbon content?
Answer: (1) Hypoeutectoid steel: 0.0218<C<0.77%; (2) Eutectoid steel: C=0.77%; 3) Hypereutectoid steel: 0.77%<C<2.11%.
twenty two. Name 10 common quality defects of hot rolled strip steel?
Answer: scars, bubbles, surface inclusions, delamination, cracks, oxide scale, roll marks, indentations, scratches, waves, edge cracks, pitting.
twenty three. What are the statistical methods commonly used in quality management?
Answer: Commonly used statistical methods are: ① Histogram; ② Permutation diagram; ③ Cause and effect diagram; ④ Correlation diagram; ⑤ Management diagram; ⑥ Survey diagram; ⑦ Stratification method.
twenty four. What are the advantages of ferrite rolling technology?
Answer: (1) Reduce heating energy consumption; (2) Increase metal yield; (3) Reduce roll consumption per ton of steel; (4) Improve the surface quality of strip steel; (5) Cold rolling is not required for subsequent processing; (6) ) Reduce the rolling force of cold rolling.
25. What is the meaning of quality management?
Answer: The significance of quality management is: (1) Improve product quality; (2) Improve product design; (3) Speed ​​up the production process;
(4) Improve employees' enthusiasm and quality awareness; (5) Improve product after-sales service; (6) Improve market acceptance;
(7) Reduce operating quality costs; (8) Reduce operating losses; (9) Reduce on-site maintenance costs; (10) Reduce liability accidents.
26. What are the distribution characteristics of the as-cast structure of the continuous casting slab?
Answer: The edge is a small equiaxed chilled crystal area, the adjacent columnar crystal area, and the center is an equiaxed crystal area.
27. How is the iron-carbon equilibrium phase diagram applied in the rolling process?
Answer: According to the iron-carbon equilibrium phase diagram, the heating temperature range, open rolling temperature range and final rolling temperature range of each steel can be formulated. This is the relationship between the temperature and the structure of the iron-carbon equilibrium phase diagram and provides a reference for people. It ensures that the processing of various steel grades is carried out in a reliable state, and the ideal structure and performance are finally obtained.
28. What is magnetic testing and ultrasonic testing?
Answer: Place the test piece in a strong magnetic field of the flaw detector to make it magnetize, and then apply a suspension of iron oxide powder mixed with gasoline or alcohol on the surface of the test piece. At this time, the iron oxide powder gathers on those surfaces or under the skin Where there is a defect, this is the magnetic flaw detection.
Ultrasonic flaw detection uses the physical properties of ultrasound to inspect macrostructure defects. This method can be used to directly inspect the internal defects of steel, such as inspection of boiler tubes, and the internal quality of large forgings.
These two kinds of flaw detection belong to non-destructive inspection.
29. What is the significance of the iron-carbon alloy phase diagram for steel rolling production?
Answer: Through the iron-carbon alloy phase diagram, we can know what phase the carbon steel heated to a certain temperature is, and can analyze the structure transformation of the steel during the slow heating and slow cooling process. Therefore, the iron-carbon alloy phase diagram is to determine the carbon Reference basis for steel heating, open rolling, final rolling temperature and carbon steel heat treatment process.
30. Briefly describe the behavior of unburned pulverized coal in the blast furnace.
Answer: (1) Participate in the carbon gasification reaction (2) Participate in the carburizing reaction (3) Mixed in the slag, affecting the fluidity of the slag (4) Depositing in the reflow zone and material column, worsening the gas permeability (5) Gas escapes out of the furnace
31. Which aspects should be used to evaluate the quality of iron ore?
Answer: First, the iron content of the ore is the most important criterion for evaluating the quality of iron ore; second, the chemical composition of the gangue; third, the harmful impurities in the ore, including S, P, Pb, Zn, As, The content of Cu, K, Na, F, etc.; fourth, the reducibility of the ore; fifth, the softening characteristics of the ore; sixth, the particle size composition of the ore; seventh, the mechanical strength of the ore; eighth, It is the stability of the chemical composition of the ore.
32. What are the requirements for coke quality during blast furnace smelting?
Answer: 1) The fixed carbon content should be high and the ash content should be low;
2) There should be less impurities containing S and P; 3) the mechanical strength of coke should be good, and the thermal strength should be high; 4) the particle size should be uniform, and the powder should be less; 5) the water content should be stable.
33. What are the differences between sinter and pellets?
Answer: Both sintering and pelletizing are methods of agglomerating fine ore, but their production process and the basic principle of solid joint agglomeration are quite different, and the smelting effect on the blast furnace also has its own characteristics. The difference between sinter and pellets is mainly manifested in the following aspects: 1) different requirements for the particle size of raw materials; 2) different mechanisms of solid joints and agglomeration; 3) different shapes of finished ore; 4) different production processes.
34. Why is [Si] often used to express furnace temperature in blast furnace production?
Answer: Whether Si is reduced from the liquid state or from the gaseous state, a very high temperature is required. The higher the hearth temperature, the more Si is reduced into the pig iron. On the contrary, the less Si in the pig iron. Production statistics show that the hearth temperature (slag iron temperature) has a linear relationship with the Si content of pig iron. Therefore, [Si] is often used to express furnace temperature in blast furnace production, and [Si] has become synonymous with hearth temperature. Of course, there are sometimes incomplete matches, which indicates that the hearth works abnormally, and it only appears in very rare cases.
35. What is the oxidation of molten steel?
Answer: Oxygen can be dissolved in molten steel in a small amount in the atomic state. The oxygen content of molten steel at the end of converter blowing is called the oxidizing property of molten steel.
36. What is the basic principle of gun position control in converter steelmaking?
Answer: Make corresponding adjustments in time according to the specific conditions that occur in the blowing process, and strive to achieve neither "splashing" nor "back-drying", so that the smelting process has reached the end smoothly.
37. What are the metallurgical effects of out-of-furnace refining?
Answer: (1) To homogenize the composition and temperature of molten steel; (2) Fine-tune the composition to reduce the range of chemical composition of finished steel; (3) Reduce the content of sulfur, hydrogen and nitrogen in steel; (4) Change the form of inclusions in steel And composition; (5) Remove harmful elements in steel and adjust the temperature of molten steel.
38. What is calcium treatment?
Answer: Calcium treatment is to add calcium or calcium alloy to steel in different ways to improve the steelmaking process, desulfurization, improve the shape of inclusions, improve cutting performance, improve the transverse mechanical properties along the rolling direction, and improve the molten steel Flow performance.
39. What are the functions of continuous casting tundish?
Answer: The functions of the continuous casting tundish are: (1) reduce the static pressure of the molten steel, keep the tundish stable and inject the molten steel into the mold steadily; (2) promote the floating of inclusions in the molten steel; (3) divert the molten steel; 4) Store molten steel to realize continuous casting of multiple furnaces.
40. What is the adverse effect of phosphorus on steel properties?
Answer: Phosphorus has a large segregation in steel. In the parts with high phosphorus content, the plasticity and toughness are greatly reduced, especially at low temperature, "cold brittleness" is even less obvious. Generally, as the content of C, N, and O in steel increases, this harmful effect of phosphorus increases. Phosphorus also has an adverse effect on the welding performance of steel.
Briefly describe the characteristics and mineral composition of the slag in the middle of converting.
[C] and [O] in the furnace during the mid-conversion stage have fierce reactions, and the slag is prone to "dry back". Its characteristics: high alkalinity and low iron oxide content. The mineral composition of the slag is: mainly dicalcium silicate and dicalcium silicate. When the lime is added, there is more free CaO. The higher the alkalinity, the greater the amount of dicalcium silicate and the more free CaO, which is unfavorable for the smelting effect.
41. How to improve the quality of molten steel when smelting high and medium carbon steel?
Answer: (1) High-strength carbon, the end-point carbon is controlled above 0.15% to reduce carbon increase;
(2) Reduce the content of P and S in molten steel as much as possible;
(3) Control the composition of molten steel to ensure that Mn/Si≥3.0;
(4) When the continuous casting temperature allows, reduce the tapping temperature as much as possible to reduce the amount of slag during tapping.
42. Why is Mn/Si>2.5 required in the production of high-quality carbon structural steel?
Answer: (1) Improve the fluidity of continuous casting molten steel;
(2) In order to control the deoxygenation product into a liquid state;
(3) Ensure that the oxygen content in the steel is low, so as not to produce bubble defects in the cast slab
43. What are the requirements for lime in converter steelmaking?
Answer: (1) CaO content is high, but SiO2 content is low. Because the combination of SiO2 and CaO will reduce the effective CaO content of lime.
(2) The sulfur content should be low, and the sulfur content is too high, which will affect the desulfurization ability of lime, and even increase sulfur.
(3) The green burning rate should be small and the green burning rate is large, indicating that there is still a large amount of CaCO3 in the lime that has not turned into CaO. After being added to the furnace, the CaCO3 decomposes and absorbs heat, which affects the thermal efficiency of the furnace and makes slagging and temperature control difficult. .
(4) The degree of lump into the furnace should be moderate.
44. What is the purpose of controlling the oxygen converter converting process?
Answer: The purpose of the oxygen converter blowing process control is to stabilize the operation, shorten the smelting time, reduce various energy consumption, and increase the end point hit rate, so as to achieve "high yield, high quality, low consumption and labor saving". Specifically, the blowing control requires the formation of alkaline slag as much as possible to reduce carbon and accelerate the slag formation rate. Under the condition of adding as little auxiliary material consumption as possible, ensure the full desulfurization and dephosphorization of molten steel; minimum splashing and slag overflow in the converting process, long furnace age, high metal recovery rate, product indicators meet requirements, and energy consumption less.
Is it true that the more deoxidizers are added to the molten steel, the less oxygen in the steel must be? why?
Answer: Incorrect, because after the deoxidizing element is added to the steel, it can deoxidize with oxygen on the one hand to reduce the oxygen concentration, and on the other hand, it affects the oxygen activity coefficient. When the concentration of deoxidizing elements is very high, because it reduces the activity coefficient of oxygen, it hinders the progress of deoxidation reaction, and as a result, the oxygen content in the steel increases instead.
45. What are the basic tasks of converter steelmaking?
Answer: In order to turn pig iron into steel, the main tasks are: (1) decarburization; (2) temperature rise; (3) alloying; (4) deoxidation; (5) removal of impurities
46. How to ensure the composition of molten steel during the tapping process when blowing after the end point?
Answer: (1) Block the tap hole to prevent slag. (2) Add a part of deoxidizer before adding alloy material when tapping. (3) The total amount of deoxidizer should be added more than usual. (4) The amount of alloy material is appropriately increased. (5) Enough argon blowing time must be guaranteed.
47. How to deal with molten steel by slag during the tapping process?
Answer: (1) Take a package sample in time to confirm the composition, and observe the deoxidation effect for ordinary carbon steel. (2) When the composition of the package sample is indeed low, the molten steel is sent to the refining station for composition adjustment to ensure the argon blowing time. (3) If there is poor deoxidation of normal carbon steel due to the slag, it is necessary to add a deoxidizer and ensure the argon blowing time. (4) After processing and confirming that the molten steel is normal, the master can go to the next process.
48. What are the main sources of non-metallic inclusions in steel?
① Endogenous inclusions. Refers to the oxides formed by the oxidation of elements during the smelting process, the deoxidation products formed during deoxidation, and the compounds that are not melted in the steel due to the temperature drop and component segregation during the solidification of molten steel.
② Foreign inclusions. Refers to the inclusions that are eroded from the furnace lining and refractory materials of the casting equipment and enter the molten steel during the smelting and pouring process, the dirt brought by the furnace charge, and the slag mixed into the molten steel.
49. How to deal with the blow-drying process?
Answer: (1) Increase the gun position to reduce slag. (2) Appropriately reduce the oxygen pressure to achieve "soft blowing". (3) When the temperature is high, iron sheet or ore can be added to force the slag. (4) After the flame is adjusted, the gun should be lowered gradually, and the range should not be too large.
50. What is active lime?
Answer: The SiO2 and sulfur content is low, the particle size is small, the reaction capacity is strong, and the lime is easy to melt during smelting.
51. What are the main aspects of the source of slag?
Answer: There are three main sources of slag: (1) Oxides formed by oxidation of elements in molten iron and scrap steel, such as silicomanganese, phosphorus and iron oxides. (2) Refractory material whose lining has been corroded. (3) Added slag-making materials and coolants, such as lime, dolomite, ore, etc.
52. Briefly describe the formation mechanism of molten steel vapor bubbles.
Answer: As the temperature of the molten steel drops, the balance between C and [O] in the steel is broken, and the reaction proceeds in the direction of generating CO gas. If the CO cannot rise and be removed in time, bubbles may form. In addition, [H] and [N] dissolved in steel decrease with the decrease of temperature and their saturation solubility decreases, and they may also precipitate from molten steel to form bubbles.
53. What are the factors that affect the oxidation of molten steel at the end of blowing?
Answer: ①End point carbon. The lower the end point carbon, the stronger the oxidation. ②Terminal temperature. The higher the end temperature, the stronger the oxidation. ③Gun position control. High gun position means strong oxidation. ④ Number of blows. If the number of blows is large, the oxidation is strong.
54. Briefly describe the classification method of slag.
Answer: The slag can be divided into acidic slag and alkaline slag according to the basicity. R<1 is called acidic slag, and R>1 is called alkaline slag.
The slag is divided into oxidation slag and reduced slag according to its oxidizing property. TFe<0.5% is reduced slag.
Slag is also divided into converter slag, slag washing slag and refined slag according to its purpose.
55. How is steelmaking slag classified by chemical composition? for example.
Answer: Steelmaking slag is divided into:
(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, and CaF2 if fluorite is added.
56. What is the role of converter slag in the steelmaking process?
Answer: The role of converter slag in the steelmaking process: (1) Remove P and S from molten metal; (2) Reduce the corrosion degree of refractory materials; (3) Disperse metal droplets to create favorable conditions for decarburization; ( 4) Prevent a large amount of heat loss, avoid the strong impact of oxygen stream on the molten pool; reduce metal splash; (5) prevent molten steel from absorbing harmful gases; (6) adsorb foreign and internal small non-metallic inclusions.
57. What is the root cause of splashing?
Answer: The root causes of splashing are: (1) The CO reaction in the molten pool develops unevenly, and a large amount of CO gas is emitted out of the instant, which is the root cause of explosive splashing; (2) The amount of serious foam slag is large , The thickness of the slag layer, etc., hinder the smooth discharge of CO gas, which is another important cause of splashing.
58. What is the cause of furnace lining corrosion?
Answer: (1) The role of high temperature heat flow. The high temperature from the liquid metal and slag, especially the primary reaction zone, may soften and melt the surface of the furnace lining. (2) The role of rapid cold and rapid heat. The furnace lining undergoes rapid cooling and heating, which reduces the high temperature strength of the furnace lining. (3) Mechanical damage. The movement of liquids and solids in the furnace, and the collision of large pieces of scrap steel during feeding will accelerate the damage of the furnace lining. (4) Chemical attack. Mainly from furnace gas and slag.
59. What are the measures to prevent phosphorus reversion?
Answer: The measures to prevent phosphorus reversion include: (1) Minimize slag during tapping when tapping; (2) Use alkaline lining to reduce the alkalinity of slag due to ladle erosion; (3) In the process of tapping, Put a small amount of lime powder into the ladle to maintain the alkalinity of the thickened slag; (4) When tapping is completed, minimize the residence time of molten steel in the ladle.
60. What role does the secondary combustion oxygen lance play? What are the types?
Answer: The post-combustion oxygen lance is divided into single-channel and double-channel. The use of a secondary combustion oxygen lance is also a kind of thermal compensation technology. By supplying oxygen, the CO gas discharged from the molten pool is partially burned, and supplementing the heat in the furnace is the secondary combustion.
The oxygen enters the nozzle from one channel and is divided into two streams. One stream of oxygen flows through the main orifice channel of the Laval nozzle, and the other stream enters the auxiliary channel of the straight orifice. The oxygen flow entering the main channel of Lavalcone is used for smelting; the oxygen entering the auxiliary flow channel is used for the combustion of CO gas in the furnace, also called end-type secondary combustion oxygen lance; its gun body is still three Layer concentric circular casing.
The oxygen of the dual-channel post-combustion oxygen lance is separately supplied to the molten pool through the main oxygen channel and the auxiliary oxygen channel. The gun body is a four-layer concentric sleeve, the center tube is the main oxygen flow channel, and oxygen is supplied to the Laval nozzle; the tube adjacent to the center tube is auxiliary
61. What is active lime, what are the characteristics of active lime, and what are the benefits of using active lime?
Answer: Usually the lime that is roasted in a rotary kiln or a new type of shaft kiln (sleeve kiln) at a temperature of 1050-1150°C has high reactivity, small bulk density, high porosity, large specific surface area, and fine grains. The high-quality lime is called active lime, also called soft burnt lime.
The water activity of activated lime is greater than 310ml, the volume density is small, about 1.7-2.0g/cm3, the porosity is as high as 40%, the specific surface area is 0.5-1.3cm2/g; the crystal grains are small, the melting speed is fast, and the reaction capacity is strong . The use of active lime can reduce the consumption of lime and fluorite and the amount of converter slag, which is beneficial to improve the desulfurization and dephosphorization effects, and reduce the heat loss of the converter and the corrosion of the furnace lining. It is also difficult to form dense dicalcium silicate on the surface of the lime. The shell helps to accelerate the slagging of lime.
62. In the hot metal pretreatment, why must the hot metal dephosphorization be desiliconized first?
Answer: Hot metal pre-desiliconization technology is developed based on hot metal pre-dephosphorization technology. Since the affinity of oxygen and silicon in molten iron is greater than that of phosphorus, when an oxidant is added for dephosphorization, silicon is oxidized preferentially than phosphorus, and the formed SiO2 greatly reduces the alkalinity of the slag. For this reason, the silicon content must be reduced to below 0.15% before dephosphorization, which is far lower than the silicon content of the molten iron in the blast furnace. Therefore, it must be desiliconized before dephosphorization.
63. What is a converter furnace type and what are the basis for choosing a converter furnace type?
Answer: The converter furnace type refers to the geometric shape of the inner shape of the converter after bricklaying. The following factors should be considered when choosing a converter type:
(1) Conducive to the progress of physical and chemical reactions in the steelmaking process; conducive to the movement of furnace liquid and furnace gas; and conducive to uniform stirring of the molten pool.
(2) Splashing should be small and metal consumption should be small. (3) The furnace shell is easy to process and manufacture; the furnace lining bricks are easy to build; the maintenance is convenient and the furnace lining has a long service life. (4) Conducive to improving working conditions and increasing the operating rate of the converter.
64. What is the effect of slag oxidation on the smelting process?
Answer: (1) Affect dephosphorization and desulfurization, which is beneficial to dephosphorization, but not conducive to desulfurization. (2) Affect the dissolution rate of lime
(3) Affect the residual and manganese content in molten steel (4) Affect the oxygen content at the end of molten steel (5) Affect the yield of metals and alloys
(6) Affect the generation of foamed slag and the occurrence of splashing (7) Affect the life of the converter lining
65. Where does the steelmaking slag come from?
Answer: The main source of steelmaking slag is: oxides formed by oxidation of various impurity elements (such as Si, Mn, P, etc.) contained in iron and steel materials (hot metal, scrap steel); added to remove sulfur and phosphorus in molten iron Slag-making materials (lime, etc.) and fluxes (fluorite, etc.); ore, sintered ore, iron oxide scale and other materials added as oxidants or coolants bring impurities; lining refractories that are eroded or washed down; Sediment impurities brought in by raw materials.
66. What is the effect of adding Nb, V and Ti elements to steel for microalloying?
Answer: 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. As a result, the carbon equivalent is reduced, but the strength and toughness of steel are greatly improved, and it has a significant cost advantage.
67. What are the characteristics and mineral composition of the slag in the middle stage of converting?
Answer: In the middle of converting, the [C] and [O] reactions in the furnace are fierce, and the slag is prone to "dry back". Its characteristics: high alkalinity and low ferrous oxide content. The slag mineral composition is: the main phases are dicalcium silicate and tricalcium silicate. When the lime is added, there is more free CaO. The higher the alkalinity, the greater the amount of tricalcium carbonate and the more free CaO, which is unfavorable for the smelting effect.
68. What is slag "drying back"? Why does the slag "dry back"?
Answer: Back-drying refers to the phenomenon that the slag that has been melted or partially melted becomes sticky or even becomes large. In the middle of converting, the carbon is violently oxidized, and the iron oxide in the slag is reduced, resulting in high melting point 2CaO·SiO2, FeO and MnO reduction. Part of the solid matter is precipitated, which makes the slag sticky, and in severe cases, it forms large pieces.
69. What are the main measures to improve the life of the converter?
Answer: (1) Improve the quality of refractory linings. (2) Adopt comprehensive furnace building technology. (3) The slag is equipped with an appropriate amount of magnesium oxide (MgO). (4) Using computer dynamic control, that is, the best smelting control, to increase the end-point hit rate, that is, to shorten the smelting cycle. (5) Carry out effective gunning and maintenance. (6) Improve the spray gun structure. (7) Lower the tapping temperature as much as possible. (8) Reduce the shutdown time.
70. What is the role of carbon-oxygen reaction in the steelmaking process?
Answer: ①Enlarge the steel-slag interface to accelerate the progress of physical and chemical reactions. ② Stir the molten pool to make the composition and temperature uniform.
③It is beneficial to the floating of non-metallic inclusions and the discharge of harmful gases. ④ Conducive to the formation of slag. ⑤Exothermic heat up. ⑥ Explosive carbon-oxygen reaction will cause splashing.
71. How does slag oxidation affect the smelting process?
Answer: ① Affect dephosphorization and desulfurization, which is beneficial to dephosphorization, but not conducive to desulfurization. ②Affect the speed of lime dissolution.
③Affect the residual manganese content of steel. ④ Affect the oxygen content at the end of molten steel. ⑤ Affect the yield of metals and ferroalloys.
⑥ Affect the generation of foam slag and the occurrence of splashing. ⑦Affect the life of converter lining.
72. Please briefly describe the 6 main hazards of non-metallic inclusions to steel?
Answer: 1) Stress concentration and cracks are generated in the internal structure of steel. 2) Reduce the plasticity of steel. 3) Reduce the toughness of steel.
4) Reduce the fatigue limit of steel. 5) Reduce the cold bending performance of steel. 6) Reduce the electromagnetic properties of steel.
73. Please write down the reaction equation of the converter dephosphorization and briefly describe the basic factors that affect the dephosphorization effect of the converter?
Answer: 1) The effect of slag alkalinity: Increasing alkalinity can improve dephosphorization ability, but too high alkalinity affects slag viscosity and is not conducive to dephosphorization.
2) The influence of (FeO): increasing the content of (FeO) in the slag can improve the dephosphorization ability.
3) Influence of temperature: Dephosphorization is an exothermic reaction, and lowering the temperature is beneficial to dephosphorization.
4) The influence of slag amount: increasing the slag can dilute the (P2O5) concentration in the slag and increase the amount of dephosphorization.
5) Influence of slag viscosity: proper slag viscosity is easy to mix with slag and steel, which improves the slag dephosphorization ability.
74. Briefly describe the task of deoxidizing molten steel.
Answer: 1. Reduce the oxygen content in the steel to the required level to ensure that the normal surface and different structural types of ingots are obtained during solidification. 2. Reduce the content of non-metallic inclusions in the finished steel, with proper distribution and proper shape to ensure the various properties of the steel. A fine grain structure is obtained.
75. Briefly describe the characteristics and mineral composition of the slag in the middle stage of converter conversion?
Answer: In the middle of converting, the reaction of [C] and [O] in the furnace is fierce, and the slag is prone to "dry back". Its characteristics are: high alkalinity and low iron oxide content.
The slag mineral composition is: the main phases are dicalcium silicate and tricalcium silicate. When the lime is added in a large amount, there is more free CaO. The higher the alkalinity, the larger the tricalcium silicate and the more free CaO, which is unfavorable for the smelting effect.
76. Why is it required to reduce the amount of slag in the ladle?
Answer: 1) Since the slag contains iron oxide, a part of the ferroalloy added will react with the iron oxide in the slag and burn out. If there is less slag in the ladle, the less ferroalloy will burn, which means saving alloy. 2) Reduce the phosphorus recovery during the tapping process and the phosphorus recovery during the secondary refining. 3) Reduce the erosion of the ladle bricks and increase the life of the ladle. 4) Reduce the overflow of slag in the ladle during the tapping process and the secondary refining to avoid accidents. 5) Good for the quality of steel.
77. Analyze the characteristics and mineral composition of the slag in the middle of converting?
Answer: In the middle of converting, the reaction of [C] and [O] in the furnace is fierce, and the slag is prone to "back-drying". Features: high alkalinity, low iron oxide content, and slag mineral composition: the main phase is dicalcium silicate And tricalcium silicate, when the lime is added large, there will be more free CaO. The higher the alkalinity, the greater the amount of tricalcium silicate and the more free CaO, which is unfavorable for the smelting effect.
78. Under what circumstances need to adjust slag after tapping?
Answer: (1) The slag superheat is high; (2) The final slag FeO is high, the slag is thin and the MgO in the slag reaches the required value for slag splashing, so it is not easy to splash slag directly.
79. Briefly describe the content of carbon in steel and its effect on the performance of steel?
Answer: Generally, [C]<2.11% in Fe-C melt is called steel, and [C]<0.02 is called industrial pure iron, so [C] in steel is between 0.02% and 2.11%.
C in steel generally has the following effects on its performance: C hardness increases, strength increases, toughness and plasticity decrease, welding performance is poor, and corrosion resistance also deteriorates.
80. Try to analyze the favorable conditions of the P removal reaction?
Answer: [P]+5[FeO]+4[CaO]=4CaO.P2O5+5[Fe]+Q. If you want the reaction to facilitate the dephosphorization process, you must increase the reactant concentration and reduce the product concentration. That is, increase the content of CaO (that is, increase the alkalinity R), increase the content of (FeO) in the slag, and reduce the concentration of (4CaO.P2O5)-discharge slag or increase the amount of slag, and then see that the reaction is an exothermic reaction, a reaction that lowers the temperature Favorable, but when the temperature is too low, slag cannot be formed and has no fluidity. Therefore, the favorable conditions for P removal are high alkalinity, high (FeO), large amount of slag, and appropriate low temperature.
81. Why is there back phosphorus in steel tapping?
Answer: In the converter, the removal of phosphorus is relatively sufficient, because the conditions are more favorable, the alkalinity is high, the content of (FeO) is high, the amount of slag is large, and the slag fluidity is very good, but in the case of steel tapping, with the deoxidizer Adding, the oxygen in the slag can be reduced, and SiO2 and AhO3, etc. continue to increase, that is, the basicity of the slag is decreasing, and the (FeO) is decreasing. Therefore, under the action of the strong reducing agent SiAL, the unstable P2O5 in the slag quickly Is reduced into molten steel.
82. Briefly describe the corrosion mechanism of Mg-C brick lining?
Answer: When the furnace lining works in the furnace, firstly, a brittle decarburization reaction occurs on the surface and a "reaction layer" is formed on the surface. The carbon in the reaction layer has been oxidized, and Fe2O3 and SiO2 in the slag invade the bricks to form a low level of MgO and CaO. Melting point substances, the more intrusives Fe2O3 and SiO2, the more severely the fire resistance and high-temperature strength of the lining brick will decrease, and even become a molten contact film state in the steelmaking state, which cannot withstand the mechanical erosion of steel slag and furnace gas, making bricks and furnace linings It will fall off crisply.
83. What is the bottom rise? What is the main reason for the bottom rise?
Answer: The so-called rise of the furnace bottom means that the furnace bottom gradually increases during the smelting process, as if a new layer of refractory is applied to the original furnace lining. This is a new problem caused by improper dolomite slagging operations. As the furnace bottom increases, the slag line moves, which threatens the furnace cap and affects the gun position control. Therefore, it must be eliminated during the smelting process. The main reason for the increase is that the slag is too sticky.
84. How does the print head work?
Answer: The nozzle of the oxygen lance is a pressure-speed energy converter. The high-pressure and low-speed air flow is converted into a low-pressure and high-speed oxygen jet. The oxygen outlet flow rate generally reaches the supersonic machine. The basic condition is: the nozzle must have a throat, that is, it must be a contraction-expansion type, and the outlet oxygen pressure must be less than the throat oxygen pressure ( Requires P outlet/P throat <0.528).
85. In the slag splashing, which aspects should be paid attention to in the maintenance of the bottom air supply element?
Answer: (1) Adjustment of slag composition during slag splashing process; (2) Reasonable selection of slag splashing operation process parameters; (3) Controlling the thickness of the covering slag layer; (4) Grasp the slag splashing time and discard the slag in time; (5) Dredge the bottom air supply element; (6) Reduce the slag splash rate, Reduce the tendency of furnace bottom rising or bottom air supply element blockage; ⑺Develop the technology of quick replacement of bottom air supply element to increase the ratio of reblowing.
86. What are the advantages of the subgun device?
Answer: ⑴ There are many functions, and the probe type structure with external probe can be equipped with probes of different functions as needed to achieve different functions of the probe and achieve different detection purposes; ⑵ The gun body adopts water-cooled structure, so it has a longer service life; ⑶ There are many measures taken for safety purposes in the organization, so the operation is safe and reliable; ⑷The measurement speed is fast and the accuracy is high. After the operation is proficient, the bidirectional hit rate of carbon content and temperature can reach more than 90%.
87. Briefly describe the erosion of each part of the converter lining?
Answer: (1) Furnace cap: composition of molten metal spray, heat radiation, furnace gas scour; (2) Molten pool and furnace bottom: in contact with the churning molten metal, oxygen flow hits the surrounding area of ​​the ventilated bricks to be hot and cold; (3) Furnace body: slag erosion, air flow The comprehensive effect of molten metal and slag (the lower side of the charging side is mechanically damaged) ⑷Tap: the temperature of the working surface rises sharply during tapping, and it is worn by molten metal and slag.
88. What are the measures to improve the purity of molten steel?
Answer: Measures to improve the purity of molten steel include:
(1) Improve the quality of raw materials and reduce the amount of inclusions brought by the raw materials; (2) Strengthen and improve the process operation, increase the composition and temperature hit rate, and reduce the number of blows; (3) Improve the deoxidation alloying system to facilitate the elimination of inclusions (4) Strengthen the maintenance of the tapping hole, reduce the oxidation and slag of the tapping; (5) Improve the quality of refractory materials and strengthen the stirring of the molten pool; (6) Seal the molten steel during the tapping and pouring process Protective measures to avoid direct contact between molten steel and air; (7) Adopt techniques such as refining outside the furnace to improve the purity of molten steel.
89. Briefly describe the role of bottom blowing in the converter smelting process?
Answer: (1) Increase the early stage stirring to accelerate the melting of scrap steel, improve the smelting reaction, and facilitate the formation of early slag; (2) Make the blowing process more balanced, reduce splashing, and increase the metal recovery rate; (3) Late stage It can balance the CO reaction, reduce the oxygen content in the steel, and can blow ultra-low carbon steel.

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