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Steelmaking must understand the problem!
1. ways to accelerate lime slagging?
Answer: ① improve the quality of lime by using soft burning active lime ② Properly improve the composition of flux ③ increase the blowing temperature ④ Control proper gun position ⑤ use synthetic slag
2. why should molten steel be deoxidized?
Answer: if the molten steel is not deoxidized, the continuous casting slab will not have the correct solidification structure. High oxygen content in steel will also produce subcutaneous bubbles, looseness and other defects, and aggravate the harmful effect of sulfur. The residual oxide inclusions in the steel will reduce the mechanical properties of the steel, such as plasticity and impact toughness. Therefore, the excess oxygen in the steel must be removed.
3. what aspects should be taken to prevent explosive splashing during converting?
Answer: ⑴ control the temperature of molten pool. (2) control (TFE) does not appear aggregation. (3) in case of splashing during blowing, do not drop the gun easily. (4) when the furnace temperature is very high, lime can be appropriately added to thicken the slag while lifting the gun.
4. why is the furnace lining damaged?
Answer: (1) impact of scrap steel and molten iron on furnace lining and mechanical wear. (2) Stirring and gas scouring of molten steel and slag. (3) Chemical attack of slag on furnace lining. (4) Cracking and spalling of furnace lining due to temperature quenching, heat shock change and microstructure change. (5) Mechanical spalling at the initial stage of furnace opening. (6) Oxidation of carbon inside the lining brick.
5. briefly describe the characteristics and mineral composition of slag in the medium-term smelting process?
Answer: in the middle stage of smelting, the reaction between carbon and oxygen in the furnace is intense, and the slag is prone to "back drying". Its characteristics are high alkalinity and low content of ferrous oxide. Mineral composition of slag: the main phase is dicalcium silicate and tricalcium silicate. When 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 to the smelting effect.
6. briefly describe the principle of selecting raw materials for steelmaking?
Answer: mass production at home and abroad has proved that implementing the fine material policy is an important way to realize the automation of converter steelmaking process and improve various technical and economic indicators. The raw materials are mainly molten iron, scrap steel, slag making materials, ferroalloy, oxygen, etc. The reasonable selection of raw materials is based on the principle of low input and high quality output according to the smelting steel type, operation process and equipment level.
7. main ways to reduce blowing loss?
Answer: ⑴ concentrate policy, reduce slag amount ⑵ reasonable slag making system ⑶ adopt reasonable oxygen supply system and loading system to reduce mechanical splash. (4) adopt thermal compensation technology, eat more scrap, and reduce chemical burning loss. (5) adopt 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 is less than 20kg/t, the slag formed per ton of metal is less than 30kg/t, which is a less slag operation
(1) the amount of lime added is small, which reduces the slag and energy consumption, and reduces the emission of pollutants.
⑵ high oxygen utilization rate, low terminal oxygen content, high residual manganese and high alloy yield.
(3) reduce erosion to furnace lining and splash.
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; Reasonable smelting process, deoxidation system and refining process of molten steel shall be adopted according to the requirements of steel grade; Improve the quality and performance of refractory materials used in converter and gating system; Reduce and prevent secondary oxidation of molten steel, maintain normal pouring temperature, implement whole process protective pouring, and select protective slag with good performance; Reasonable selection of steel hot working and heat treatment process is beneficial to improve the properties of inclusions and improve the quality of steel.
10. why is argon used instead of nitrogen for blowing and stirring?
Answer: argon in the inert gas, which does not dissolve in molten steel and does not react with any element, is a very ideal stirring gas, so it is widely used. In terms of mixing, nitrogen is the same as argon, and nitrogen is cheap. However, nitrogen can be dissolved in molten steel at high temperature, and its nitrogen increase increases with the increase of temperature and the extension of nitrogen blowing time. When the temperature is higher than 1575 ℃, the nitrogen content in steel can be increased by 0.003%, affecting the quality of steel. Therefore, the use of nitrogen as a stirring gas is limited, and only a small amount of nitrogen-containing steel can be used as a stirring gas, There is also the problem of unstable nitrogen increase.
11. what is the significance of decarburization reaction for steelmaking process?
Answer: ① the carbon in molten iron is oxidized through decarburization reaction to be close to or equal to the specification range of carbon in molten steel at tapping. ② Circulating stirring of molten pool ③ the generated CO is necessary for removing gas from steel. ④ It is beneficial to the elimination of non-metallic inclusions in steel. ⑤ Provide heat source for steelmaking reaction. ⑥ It is beneficial to the reaction between slag and steel in the converting process.
12. why slagging in steelmaking?
Answer: to make good steel, we must first make good slag. The completion of all steelmaking tasks is almost related to slag. The purpose of steelmaking and slagging is ① to remove harmful elements P and s in steel ② to cover the surface of molten steel with steelmaking slag, so as to protect the molten steel from excessive oxidation, absorption of harmful gases, heat preservation and reduce the burning loss of beneficial elements. ③ Absorb floating inclusions and reaction products. ④ Ensure the smooth progress of carbon oxygen reaction. ⑤ It can reduce the erosion of furnace lining.
13. What is the relationship between aluminum and steel properties?
Answer: when aluminum is added to steel as a deoxidizer or alloying element, its deoxidizing ability is much stronger than that of silicon and manganese. The main function of aluminum in steel is to refine the grain size and fix the nitrogen in steel, so as to significantly improve the impact toughness of steel and reduce the tendency of cold embrittlement and aging. Aluminum can also improve the corrosion resistance of steel, especially when used with molybdenum, copper, silicon, chromium and other elements.
14. what is the effect of oxygen on the properties of steel?
Answer: the solubility of oxygen in solid iron is very small, mainly in the form of oxide inclusions. Therefore, most of the inclusions in steel are oxides except partial sulfides. Nonmetallic inclusions are the main damage source of steel, which have significant adverse effects on the fatigue strength, processability, ductility, toughness, weldability, HIC resistance and corrosion resistance of steel. When the oxygen content is high, the continuous casting slab will also produce subcutaneous bubbles and other defects, which will deteriorate the surface quality of the continuous casting slab.
15. why should slag blocking and tapping be done?
Answer: less slag or slag blocking tapping is one of the necessary means to produce pure steel. Its purpose is to help accurately control the composition of molten steel, effectively reduce the dephosphorization of molten steel, improve the absorption rate of alloy elements and reduce alloy consumption. It is beneficial to reduce the content of inclusions in steel and improve the refining effect of ladle. It also helps to reduce the corrosion of ladle refractory. At the same time, the service life of converter taphole is also increased.
16. what is the basic task 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 temperature and adjusting the composition of molten steel. Oxygen supply, slagging, stirring and alloying are the means to complete the steelmaking task.
17. briefly describe the main function of dolomite in converter steelmaking.
Answer: dolomite is a slag adjusting agent, which can be divided into raw dolomite and lightly burned dolomite. According to the needs of slag splashing technology, add an appropriate amount of dolomite to keep the MgO content in the slag saturated or supersaturated, so as to reduce the corrosion of the initial acid slag on the furnace lining, so that the final slag can be sticky and meet the requirements of slag splashing after tapping.
18. Combined with the situation before, during and after converting, the operation of constant pressure variable lance is briefly described.
Answer: the constant flow and variable lance position operation is to control the blowing process by changing the interaction between the oxygen flow and the molten pool by adjusting the lance position while the oxygen supply flow remains unchanged during the blowing process of a furnace of steel. Most manufacturers in our country adopt the operation of changing gun position with constant flow in stages. Due to different converter tonnage, nozzle structure, raw material conditions and types of steelmaking, the operation of oxygen lance is not exactly the same. At present, there are two oxygen lance operation modes. ① High low high low gun position mode. The starting position of the blowing gun is high, so the initial slag can be formed as soon as possible. After the second batch of rice is added, the gun can be lowered in time. When the slag returns to dry in the middle of blowing, the gun can be raised or an appropriate amount of flux can be added to adjust the fluidity of the slag, so as to shorten the blowing time and pull out the carbon at the end. (2) high low low gun position mode. The blowing gun is at a high position to form initial slag as soon as possible; During the blowing process, the gun position gradually decreases. In the middle of the blowing process, an appropriate amount of flux is added to adjust the fluidity of the slag, and the carbon is drawn out at the end.
19. write the chemical reaction formula of carbon and oxygen in converter steelmaking and indicate the carbon and oxygen reaction caused by splashing.
Answer: [c]+ ½ {o2}={co} [c]+ (FeO) ={co}+[fe] (carbon oxygen reaction generated by splashing) [c]+[o]={co}
20. what are non-metallic inclusions? Where does it mainly come from?
Answer: the non-metallic phases produced or mixed in the process of smelting, casting and solidification of molten steel are called non-metallic inclusions. Nonmetallic phase is a compound formed by the combination of some metal elements and Si with nonmetallic elements, such as oxides, nitrides, sulfides, etc. Because of the existence of inclusions, the continuity of the steel matrix is destroyed, resulting in the uneven structure of the steel, and affecting the mechanical properties and processability of the steel. However, non-metallic inclusions also have beneficial effects on the steel, such as controlling the intrinsic fine grain, precipitation hardening, promoting grain orientation, improving the machinability of the steel, etc.
21. how are steels classified according to the room temperature structure and carbon content?
Answer: (1) hypoeutectoid steel: 0.0218
22. name 10 common quality defects of hot rolled strip steel?
Answer: scar, bubble, surface inclusion, delamination, crack, iron oxide scale, roll mark, indentation, scratch, wave, edge crack, pitting.
23. what are the commonly used statistical methods for quality management?
Answer: common statistical methods are: ① histogram; ② Arrangement diagram; ③ Cause and effect diagram; ④ Correlation diagram; ⑤ Management chart; ⑥ Survey map; ⑦ Layered method.
24. what are the advantages of ferrite rolling technology?
Answer: (1) reduce heating energy consumption; (2) Improve metal yield; (3) Reduce the consumption of per ton steel roll; (4) Improve the surface quality of strip steel; (5) Cold rolling is not required for subsequent processing; (6) Reduce the cold rolling force.
25. what is the significance of quality management?
Answer: the significance of quality management lies in: (1) improving product quality; (2) Improve product design; (3) Accelerate the production process; (4) Improve employees' work enthusiasm and quality awareness; (5) Improve product after-sales service; (6) Improve market acceptance; (7) Reduce the cost of operation quality; (8) Reduce operating losses; (9) Reduce on-site maintenance cost; (10) Reduce liability accidents.
26. what are the distribution characteristics of as cast microstructure of continuous casting slab?
Answer: the edge is a small equiaxed cooling crystal region, the adjacent is a columnar crystal region, and the center is an equiaxed crystal region.
27. how can iron carbon equilibrium phase diagram be applied to rolling process?
Answer: according to the iron carbon equilibrium phase diagram, the heating temperature range, start rolling temperature range and finish rolling temperature range of each steel type can be formulated, which provides a reference basis for the relationship between temperature and microstructure in the iron carbon equilibrium phase diagram, and ensures that the processing of each steel type is carried out in a reliable state, and finally obtains the ideal microstructure and properties.
28. what are magnetic flaw detection and ultrasonic flaw detection?
Answer: place the test piece in the strong magnetic field of the flaw detector to magnetize it, and then apply the suspension mixed with iron oxide powder and gasoline or alcohol on the surface of the test piece. At this time, iron oxide powder will gather in those defective places on the surface or under the skin, which is magnetic flaw detection. Ultrasonic flaw detection is to use the physical properties of ultrasonic to inspect macrostructure defects. This method can be used to directly inspect the internal defects of steel, such as boiler tubes, and the internal quality of large forgings.
These two types of flaw detection belong to non-destructive inspection.
29. what is the significance of 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 analyze the structural transformation of the steel during the slow heating and slow cooling process. Therefore, the iron carbon alloy phase diagram is the reference basis for determining the heating, start rolling and final rolling temperatures of carbon steel and the thermal treatment process of carbon steel.
30. describe the behavior of unburned pulverized coal in blast furnace.
Answer: (1) participate in the carbon gasification reaction (2) participate in the carburization reaction (3) mix in the slag and affect the fluidity of the slag (4) deposit in the soft melt zone and material column and deteriorate the permeability (5) escape out of the furnace with the gas
31. what should be done to evaluate the quality of iron ore?
Answer: first of all, the iron content of ore is the most important standard to evaluate the quality of iron ore; Secondly, the chemical composition of gangue; The third is the content of harmful impurities in the ore, including s, P, Pb, Zn, as, Cu, K, Na, F, etc; Fourth, the reducibility of ore; The fifth is the softening characteristic of the ore; The sixth is the particle size composition of the ore; Seventh, the mechanical strength of the ore; Eighth, the stability of ore chemical composition.
32. what are the requirements for coke quality in blast furnace smelting process?
Answer: 1) high fixed carbon content and low ash content; 2) Less s and P impurities; 3) Coke has better mechanical strength and higher thermal strength; 4) The particle size should be uniform and the powder should be less; 5) The moisture should be stable.
33. what are the differences between sinter and pellet?
Answer: both sintering and pelletizing are methods for making blocks of fine ore, but their production processes and basic principles of solid joint and block forming are very different, and their smelting effects on blast furnaces also have their own characteristics. The main differences between sinter and pellet are as follows: 1) different requirements for raw material particle size; 2) The mechanism of solid joint forming is different; 3) Different shapes of finished ore; 4) The production process is different.
34. why is [si] commonly used to represent furnace temperature in blast furnace production?
Answer: whether Si is reduced from liquid state or gas state, it needs a very high temperature. The higher the hearth temperature is, the more Si will be reduced into pig iron. On the contrary, the less Si will be in pig iron. The production statistics results show that the hearth temperature (slag iron temperature) has a linear relationship with the content of Si in pig iron. Therefore, [si] is commonly used to represent the hearth temperature in blast furnace production, and [si] has become a synonym of hearth temperature. Of course, sometimes there are not completely consistent phenomena, which indicates that the hearth works abnormally, which only occurs in rare cases.
35. what is the oxidizability of molten steel?
Answer: oxygen can be dissolved in a small amount of molten steel in atomic state. The oxygen content of molten steel at the end of converter blowing is called the oxidizability of molten steel.
36. what are the basic principles of gun position control in converter steelmaking?
Answer: make corresponding adjustment in time according to the specific conditions in the blowing process, and strive to achieve neither "splashing" nor "back drying", so that the smelting process can reach the end point smoothly.
37. what are the metallurgical functions of off furnace refining?
Answer: (1) homogenize the composition and temperature of molten steel; (2) Fine adjustment of composition reduces the range of chemical composition of finished steel; (3) Reduce the content of sulfur, hydrogen and nitrogen in steel; (4) Changing the shape and composition of inclusions in steel; (5) Remove harmful elements in steel and adjust molten steel temperature.
38. what is calcium treatment?
Answer: calcium treatment is to add calcium or calcium alloy into steel in different ways to improve steelmaking process, desulfurization, inclusion morphology, cutting performance, transverse mechanical properties along rolling direction and molten steel flow performance.
39. what are the functions of continuous casting tundish?
Answer: the functions of continuous casting tundish are as follows: (1) reduce the static pressure of molten steel, keep the stable liquid level of tundish and inject molten steel into the mold smoothly; (2) Promote the floating of inclusions in molten steel; (3) Shunting molten steel; (4) Store molten steel to realize multi furnace continuous casting.
40. what are the adverse effects of phosphorus on steel properties?
Answer: phosphorus has large segregation in steel. In the parts with high phosphorus content, the plasticity and toughness are greatly reduced, especially at low temperature, the "cold brittleness" is not obvious. Generally, the harmful effect of phosphorus increases with the increase of C, N and O contents in steel. Phosphorus also has an adverse effect on the weldability of steel. The characteristics and mineral composition of slag in the middle stage of blowing are briefly described. The [c] and [o] reactions in the furnace during the medium-term blowing are intense, and the slag is prone to "back drying", which is characterized by high alkalinity and low content of ferrous oxide. The mineral composition of 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 to the smelting effect.
41. how to improve molten steel quality when smelting high and medium carbon steel?
Answer: (1) high carbon, control the end carbon at more than 0.15% and 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) If the continuous casting temperature permits, the tapping temperature shall be reduced as far as possible to reduce the amount of slag.
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 deoxidation product into liquid state; (3) Ensure that the oxygen content in the steel is low, so as not to produce bubble defects in the slab
43. what are the requirements for lime in converter steelmaking?
Answer: (1) high CaO content, low SiO2 content. Because the combination of SiO2 and Cao will reduce the effective CaO content of lime. (2) The sulfur content shall be low and too high, which will affect the desulfurization capacity of lime and even increase sulfur. (3) The green burning rate should be small and large, indicating that there is still a large amount of CaCO3 in lime that has not changed into Cao. After being added to the furnace, CaCO3 decomposes and absorbs heat, which affects the thermal efficiency of the furnace and makes slagging and temperature control difficult. (4) The lump size shall be moderate.
44. what is the purpose of oxygen converter blowing process control?
Answer: the purpose of oxygen converter blowing process control is to make the operation stable, shorten the smelting time, reduce various energy consumption, and improve the target hit rate, so as to achieve "high yield, high quality, low consumption and labor saving". Specifically, the blowing control requires to form alkaline slag as much as possible, so as to reduce carbon and speed up slag formation. Ensure full desulfurization and dephosphorization of molten steel under the condition that the consumption of auxiliary materials is reduced as much as possible; During the converting process, the splashing and slag overflow are the least, the furnace life is long, the metal yield is high, the product indicators meet the requirements, and the energy consumption is small.
Is it correct to say that the more deoxidizer is added to the molten steel, the less oxygen is in the steel? Why? Answer: incorrect, because after deoxidizing elements are added to steel, on the one hand, they can deoxidize with oxygen, reducing the concentration of oxygen, on the other hand, they can affect the activity coefficient of oxygen. When the concentration of deoxidizing element is very high, the deoxidizing reaction is hindered because of its low oxygen activity coefficient, and the oxygen content in steel increases instead.
45. what is the basic task 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) Remove impurities
46. how to ensure the composition of molten steel during tapping during end point post blowing?
Answer: (1) block the tapping hole to prevent slag. (2) A part of deoxidizer shall be added before alloy material is added during tapping. (3) The total amount of deoxidizer should be increased than usual. (4) The amount of alloy material shall be increased appropriately. (5) Sufficient argon blowing time must be ensured.
47. how to treat molten steel with slag during tapping?
Answer: (1) take the package sample in time to confirm the composition, and observe the deoxidation effect for ordinary carbon steel. (2) When the composition of the ladle sample is really low, the molten steel shall be sent to the refining station for composition adjustment to ensure the argon blowing time. (3) In case of poor deoxidization of plain carbon steel due to slagging, Deoxidizer must be added and argon blowing time must be guaranteed. (4) After the molten steel is confirmed to be normal after treatment, the master can go to the next process.
48. what are the main sources of non-metallic inclusions in steel?
① Endogenous inclusions. It refers to oxides formed by element oxidation during smelting, deoxidation products formed during deoxidation, and compounds that do not melt in steel due to temperature drop and component segregation during solidification of molten steel. ② Foreign inclusions. It refers to the inclusions in molten steel washed and eroded from the refractory materials of furnace lining and casting equipment during smelting and pouring, the dirt brought in by furnace charge, and the slag mixed in molten steel.
49. how to deal with the drying back in the converting process?
Answer: (1) improve slag melting at gun position. (2) Reduce the oxygen pressure properly to realize "soft blowing". (3) When the temperature is high, iron sheet or ore can be added to force slag. (4) After the flame is adjusted, the gun shall be lowered gradually, and the range shall not be too large.
50. what is active lime?
Answer: lime with low SiO2 and sulfur content, small particle size, strong reaction ability and easy melting during smelting.
51. what are the main sources of slag?
Answer: there are three main sources of slag: (1) oxides generated by the oxidation of elements in molten iron and scrap steel, such as silicon manganese, phosphorus and iron oxides. (2) Refractory material whose lining has been eroded. (3) Slagging materials and coolants added, such as lime, dolomite, ore, etc.
52. briefly describe the formation mechanism of bubble in molten steel.
Answer: as the temperature of molten steel drops, the balance between C and [o] in steel is destroyed, and the reaction proceeds in the direction of generating CO gas. If co cannot float up and be eliminated in time, bubbles may be formed. In addition, the saturated solubility of [h] and [n] dissolved in steel decreases with the decrease of temperature, and bubbles may also be formed from the molten steel.
53. what are the factors that affect the oxidizability of molten steel at the end of blowing?
Answer: ① terminal carbon. The lower the end carbon, the stronger the oxidation. ② End point temperature. The higher the terminal temperature, the stronger the oxidation. ③ Gun position control. High gun position makes it highly oxidizing. ④ Point blowing times. If the number of point blowing 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 alkalinity. The slag with R < 1 is called acidic slag, and the slag with R > 1 is called alkaline slag. The slag is divided into oxidation slag and reduction slag according to oxidizability, and TFE < 0.5% is reduction slag. The slag is also divided into converter slag, slag washing slag and refining slag.
55. how to classify steel-making slag according to chemical composition? Examples.
Answer: steelmaking slag is divided into:
(1) Acid oxides: such as SiO2 and P2O5; (2) Alkaline oxides: such as Cao, MgO, MnO, FeO; (3) Amphoteric oxides: such as Al2O3 and 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 steelmaking: (1) remove P and s from molten metal; (2) Reduce the erosion degree of refractory materials; (3) Dispersing metal droplets creates favorable conditions for decarburization; (4) Prevent a large amount of heat loss and avoid the strong impact of oxygen flow on the molten pool; Reduce metal splashing; (5) Prevent liquid steel from absorbing harmful gas; (6) Adsorption of foreign and internal small non-metallic inclusions.
57. What is the root cause of splashing?
Answer: the root causes of splashing are: (1) the uneven development of C-O reaction in the molten pool, which instantaneously produces a large amount of CO gas to be discharged, which is the root cause of explosive splashing; (2) Large amount of foam slag and thick slag layer hinder the smooth discharge of CO gas, which is another important reason for splashing.
58. what is the cause of furnace lining erosion?
Answer: (1) the role of high temperature heat flow. The high temperature action from liquid metal and slag, especially in the primary reaction zone, may soften and melt the lining surface. (2) The function of quenching and heating. The furnace lining undergoes the action of rapid cooling and heating, which reduces the high-temperature strength of the furnace lining. (3) Mechanical damage. The movement of liquid and solid in the furnace and the collision of large scrap during charging will accelerate the damage of 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 return are: (1) try to reduce slag during tapping; (2) Alkaline ladle lining is adopted to reduce the basicity of slag due to ladle erosion; (3) During tapping, a small amount of lime powder is put into the ladle to keep the alkalinity of thickened slag; (4) When the tapping is completed, the residence time of molten steel in the ladle shall be minimized.
60. what is the function of the secondary combustion oxygen lance? What types?
Answer: the secondary combustion oxygen lance can be divided into single channel and double channel. The use of 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 the secondary combustion is to supplement the heat in the furnace.
After entering the nozzle from one channel, the oxygen is divided into two streams, one stream of oxygen flows through the main hole channel of Laval nozzle, and the other stream enters the auxiliary channel of straight hole. The oxygen flow entering the main channel of Laval hole is for smelting; The oxygen entering the auxiliary channel is used for the combustion of CO gas in the furnace, also known as the end type secondary combustion oxygen lance; The gun body is still a three-layer concentric casing.
The oxygen of the double channel secondary combustion oxygen lance is supplied to the molten pool through the main oxygen channel and the auxiliary oxygen channel respectively. The gun body is a four layer concentric casing, the central pipe is the main oxygen flow channel, and the oxygen is supplied to the Laval nozzle; The pipe adjacent to the central pipe is auxiliary
61. what is active lime, what are the characteristics of active lime, and what are the benefits of using active lime?
Answer: generally, lime calcined in rotary kiln or new shaft kiln (sleeve kiln) at 1050-1150 ℃, that is, high-quality lime with high reaction capacity, small bulk density, high porosity, large specific surface area and fine grains, is called active lime, also known as soft calcined lime.
The water activity of activated lime is more than 310ML, the volume density is small, about 1.7-2.0g/cm3, the porosity is more than 40%, and the specific surface area is 0.5-1.3cm2/g; Fine grain, fast melting speed and strong reaction ability. The use of active lime can reduce the consumption of lime, fluorite and converter slag, improve the effect of desulfurization and dephosphorization, reduce converter heat loss and corrosion to furnace lining, and it is difficult to form a dense dicalcium silicate hard shell on the surface of lime, which is conducive to accelerating the slagging of lime.
62. why is desilication necessary for hot metal dephosphorization in hot metal pretreatment?
Answer: the hot metal pre desilication technology is developed based on the hot metal pre dephosphorization technology. Since the affinity between oxygen and silicon in molten iron is greater than that of phosphorus, when oxidant is added for dephosphorization, silicon is oxidized preferentially than phosphorus, and the formed SiO2 greatly reduces the basicity of slag. Therefore, before dephosphorization, the silicon content must be reduced to less than 0.15%, which is far lower than the silicon content of blast furnace molten iron. That is to say, phosphorus can be rapidly oxidized and removed only after most of the silicon in molten iron is oxidized. Therefore, desilication must be carried out before dephosphorization.
63. what is the converter type and what is the basis for selecting the converter type?
Answer: the converter type refers to the geometric shape of the internal type of the converter after bricklaying. The following factors shall be considered in the selection of converter type:
(1) It is conducive to the physical and chemical reactions in the steelmaking process; It is conducive to the movement of furnace liquid and gas; It is conducive to uniform mixing of molten pool. (2) Less splash and less metal consumption. (3) The furnace shell is easy to process and manufacture; Furnace lining bricks are easy to build; Easy maintenance and long service life of furnace lining. (4) It is beneficial to improve working conditions and operation rate of converter.
64. Impact of slag oxidizability on smelting process?
Answer: (1) affect dephosphorization and desulfurization, which is conducive 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 formation and splashing of foam slag (7) affect the life of converter lining
65. where does the steelmaking slag come from?
Answer: the main source of steel-making slag is: oxides generated by oxidation of various impurity elements (such as Si, Mn, P, etc.) contained in steel materials (hot metal, scrap); Slagging materials (lime, etc.) and fluxes (fluorite, etc.) added to remove sulfur and phosphorus from molten iron; Impurities brought by ore, sinter, iron oxide scale and other materials added as oxidant or coolant; Furnace lining refractory materials eroded or washed down; Sediment impurities brought in by various raw materials.
66. what is the effect of microalloying with Nb, V and Ti in steel?
Answer: adding Nb, V and Ti to steel can combine with [c] and [n] to form carbides, nitrides and carbonitrides. These compounds dissolve at high temperature and precipitate at low temperature to inhibit grain growth and precipitation strengthening. As a result, the carbon equivalent is reduced, but the strength and toughness of the steel are greatly improved, and it has a significant cost advantage.
67. characteristics and mineral composition of slag in the middle of blowing process?
Answer: in the middle of blowing, the [c] and [o] reactions in the furnace are intense, and the slag is prone to "back drying", which is characterized by high alkalinity and low content of ferrous oxide. The mineral composition of the slag 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 greater the amount of tricalcium carbonate and the more free CaO, which is unfavorable to the smelting effect.
68. what is slag "back drying"? What is the reason for slag "drying back"?
Answer: back drying refers to the phenomenon that the melted or partially melted slag becomes sticky or even forms large. In the middle of blowing, the carbon is oxidized violently, the iron oxide in the slag is reduced, and 2CaO · SiO2, FeO and MnO with high melting point are generated for reduction, and some solid substances are precipitated, making the slag sticky. In serious cases, it forms large blocks.
69. what are the main measures to improve the converter life?
Answer: (1) improve the quality of furnace lining refractory. (2) Comprehensive furnace building technology is adopted. (3) Appropriate amount of magnesium oxide (MgO) is added to the slag. (4) Computer dynamic control, i.e. optimal smelting control, is adopted to improve the hit rate of the end point, i.e. shorten the smelting cycle. (5) Carry out effective gunning and maintenance. (6) Improve the structure of spray gun. (7) Lower the tapping temperature as much as possible. (8) Reduce the shutdown time.
70. what is the role of carbon oxygen reaction in steelmaking process?
Answer: ① increase the steel slag interface and accelerate the physical and chemical reaction. ② Stir the molten pool to uniform the composition and temperature. ③ It is conducive to the floating of non-metallic inclusions and the discharge of harmful gases. ④ It is conducive to the formation of slag. ⑤ Exothermic heating. ⑥ Explosive carbon oxygen reactions can cause splashing.
71. effect of slag oxidizability on smelting process?
Answer: ① affect dephosphorization and desulfurization, which is conducive to dephosphorization but not conducive to desulfurization. ② Affect the lime dissolving rate. ③ Affect the residual manganese content of steel grade. ④ Affect the oxygen content at the end of molten steel. ⑤ It affects the yield of metals and ferroalloys. ⑥ It affects the formation of foam slag and the occurrence of splashing. ⑦ The service life of converter lining is affected.
72. please briefly describe the six main hazards of non-metallic inclusions to steel?
Answer: 1) make the internal structure of steel produce stress concentration and cracks. 2) Reduce the plasticity of steel. 3) Reduce the toughness of steel. 4) Reduce the fatigue limit of steel. 5) Reduce the cold bending property of steel. 6) Reduce the electromagnetic properties of steel.
73. please write down the reaction equation of converter dephosphorization and briefly describe the basic factors that affect the effect of converter dephosphorization?
Answer: 1) influence of slag alkalinity: increasing the alkalinity can improve the dephosphorization capacity, but too high alkalinity affects the slag viscosity and is not conducive to dephosphorization. 2) (FeO): increasing the content of (FeO) in slag can improve the dephosphorization capacity. 3) Effect of temperature: dephosphorization is an exothermic reaction, and reducing the temperature is conducive to dephosphorization. 4) Influence of slag amount: increasing slag can dilute the (P2O5) concentration in slag and increase dephosphorization amount. 5) Effect of slag viscosity: proper slag viscosity is easy to mix slag and steel, and improves slag dephosphorization capacity.
74. briefly describe the task of deoxidizing molten steel.
Answer: 1. Reduce the oxygen content in the steel to the required level to ensure the normal surface and ingots of different structural types during solidification. 2. The content of non-metallic inclusions in the finished steel is reduced, the distribution is appropriate, and the shape is appropriate to ensure the properties of the steel. Fine grain structure was obtained.
75. briefly describe the characteristics and mineral composition of slag in the medium-term converter blowing process?
Answer: in the middle of blowing, the [c] and [o] reactions in the furnace are intense, and the slag is prone to "drying back", which is characterized by high alkalinity and low iron oxide content.
The mineral composition of slag is: the main phase is dicalcium silicate and tricalcium silicate. When the amount of lime is large, there is more free CaO. The higher the alkalinity, the greater the tricalcium silicate and the more free CaO, which is unfavorable to the smelting effect.
76. why is it required to reduce the amount of slag in the ladle?
Answer: 1) because the slag contains iron oxide, a part of the ferroalloy is added to act with the iron oxide in the slag and burned. If there is less slag in the ladle, the less the burning loss of the ferroalloy, that is, saving the alloy. 2) Reduce the dephosphorization during tapping and secondary refining. 3) Reduce the erosion of ladle bricks and improve the service life of ladle. 4) Reduce the overflow of slag in ladle during tapping and secondary refining to avoid accidents. 5) It is good for the quality of steel.
77. analyze the characteristics and mineral composition of slag in the middle of blowing process?
Answer: in the middle of blowing, the [c] and [o] reactions in the furnace are intense, and the slag is prone to "back drying". Its characteristics are: high alkalinity, low content of ferrous oxide, and the mineral composition of the slag is: the main phase is dicalcium silicate and tricalcium silicate. When the lime is added, there is more free CaO. When the alkalinity is higher, the greater the amount of tricalcium silicate, the more free CaO, which is unfavorable to the smelting effect.
78. under what circumstances is slag mixing required after tapping?
Answer: ⑴ high superheat of slag; ⑵ 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 directly splash the slag.
79. briefly describe the content of carbon in steel and its influence on the properties of steel?
Answer: generally, those with [c]<2.11% in Fe-C melt are called steel, and those with [c]<0.02 are called industrial pure iron, so [c] in steel is between 0.02% and 2.11%.
C content in steel generally has the following effects on its performance: C hardness increases, strength increases, toughness and plasticity decreases, welding performance is poor, and corrosion becomes poor.
80. Try to analyze the favorable conditions for dep reaction?
Answer: [p]+5[feo]+4[cao]=4cao P2o5+5[fe]+q, if the reaction is beneficial to the dephosphorization direction, it is necessary to increase the reactant concentration, reduce the product concentration, that is, increase the CaO content (i.e., increase the alkalinity R), increase the content of (FeO) in the slag, and reduce the concentration of (4cao.p2o5) - slag discharge or increase the slag amount. The reaction is exothermic, and the reaction of reducing the temperature is beneficial, but the slag cannot form and has no fluidity when the temperature is too low. Therefore, the favorable conditions for dephosphorization are, High alkalinity, high FeO, large amount of slag and appropriate low temperature.
81. why does back phosphorus occur in tapping?
Answer: in the converter, the removal of phosphorus is sufficient because the conditions are favorable, with high alkalinity, (FeO) content, large slag volume and good slag fluidity. However, in the tapping process, with the addition of deoxidizer, the oxygen in the slag decreases, and SiO2 and aho3 continue to increase, that is, the slag alkalinity is decreasing, (FeO) is decreasing. Therefore, under the action of strong reductant sial element, Unstable P2O5 in slag is quickly reduced into molten steel.
82. briefly describe the erosion 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. Fe2O3 and SiO2 in the slag invade the brick to form low melting point substances with MgO and Cao. The more Fe2O3 and SiO2 invade, the worse the fire resistance and high-temperature strength of the furnace lining brick will decline. Even in the steel-making state, it will become a molten contact film, which can not withstand the mechanical scouring of steel slag and furnace gas, so that the bricks The lining of the furnace is about to crumble down.
83. what is furnace bottom rise? What are the main reasons for the rise of furnace bottom?
Answer: the so-called furnace bottom rise means that the furnace bottom gradually rises during the smelting process. It seems that a new layer of refractory is applied to the original furnace lining. This is a new problem caused by improper operation of dolomite slagging. As the furnace bottom increases, the slag line moves up, threatening the furnace cap and affecting the gun position control. Therefore, it must be eliminated in the smelting process. The main reason for the increase is that the slag is too sticky.
84. how does the nozzle work?
Answer: the oxygen lance nozzle is a pressure velocity energy converter. The high-pressure low-speed air flow is transformed into low-pressure high-speed oxygen jet, and the oxygen outlet flow rate generally reaches the supersonic machine. The basic conditions are: the nozzle must have a throat, that is, it must be of contraction expansion type, and the outlet oxygen pressure must be less than the throat oxygen pressure (P outlet / P throat <0.528).
85. during slag splashing, what aspects should be paid attention to in the maintenance of the bottom air supply element?
Answer: ⑴ slag composition adjustment during slag splashing; (2) reasonable selection of slag splashing operation process parameters; (3) control the thickness of covering slag layer; (4) grasp the slag splashing time and dump the slag in time; (5) dredge the bottom air supply element; (6) reduce the slag splashing rate and the tendency of furnace bottom rising or bottom air supply element blocking; (7) develop the technology of quickly replacing the bottom air supply element to improve the combined blowing ratio.
86. what are the advantages of the auxiliary gun device?
Answer: ⑴ there are many functions. The external probe type structure can be equipped with probes with different functions as required to achieve different functions and different detection purposes; (2) the gun body adopts water-cooled structure, so it has a long service life; ⑶ there are many measures taken for the purpose of safety in the organization, so the operation is safe and reliable; (4) the measurement speed is fast and the accuracy is high. After skilled operation, the two-way hit rate of carbon content and temperature can reach more than 90%.
87. briefly describe the corrosion of various parts of converter lining?
Answer: ⑴ furnace cap: composition of metal liquid spray, thermal radiation, furnace gas scouring; (2) molten pool and furnace bottom: contact with the churning liquid metal, and the oxygen flow impacts the surrounding of the permeable brick, causing rapid cooling and heating; (3) furnace body: slag erosion, combined action of molten metal and slag (below the charging side, mechanical damage) ⑷ tapping hole: the temperature of the working surface rises sharply during tapping and is worn by molten metal and slag.
88. what are the measures to improve the purity of molten steel?
Answer: the measures to improve the purity of molten steel are:
(1) Improve the quality of raw materials and reduce the amount of inclusions brought in by raw materials; (2) Strengthen and improve the process operation, improve the hit rate of composition and temperature, and reduce the number of point blowing; (3) Perfect deoxidation and alloying system to facilitate inclusion removal and floatation; (4) Strengthen the maintenance of tapping hole to reduce the amount of oxidation and slag; (5) Improve the quality of refractory materials and strengthen the mixing of molten pool; (6) Sealing protection measures shall be taken for molten steel during tapping and pouring to avoid direct contact between molten steel and air; (7) To improve the purity of molten steel by adopting technologies such as refining outside the furnace.
89. briefly describe the role of combined bottom blowing in converter smelting process?
Answer: (1) increase early-stage agitation to accelerate scrap melting and improve smelting reaction, which is conducive to early slag formation; (2) It makes the converting process more balanced, reduces splashing and improves metal yield; (3) In the later stage, the C-O reaction can be balanced, the oxygen content in the steel can be reduced, and the ultra-low carbon steel can be blown.
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