Chemical heating cleanliness control method for low-carbon alloy aluminum deoxidized and killed steel

Abstract

The invention relates to the field of steelmaking refining, in particular to a low-carbon alloy aluminum deoxidized and killed steel chemical heating cleanliness control method which comprises the following steps: (1) for low-carbon alloy aluminum deoxidized and killed steel, the converter tapping amount is 240 t, the steel grade liquidus temperature is 1515 DEG C, the pouring superheat degree is 15-30 DEG C, the pouring period of a casting machine is 50 min, the temperature of molten steel is reduced to 1.2 DEG C / min in the RH treatment process, and the temperature of molten steel is reduced to be 40 DEG C / min; the end-point carbon content of the converter is 0.048%, the end-point oxygen content is 0.053%, and the end-point temperature is 1655 DEG C; (2) the oxygen blowing amount of chemical heating is calculated, a steel ladle is jacked, and vacuumizing is conducted; (3) the Al particles are conveyed to a vacuum hopper to be vacuumized according to the calculation result of the chemical heating oxygen blowing amount; (4) after Al particles are added into the vacuum chamber, oxygen blowing operation is started immediately; (5) carrying out molten steel vacuum treatment after oxygen blowing; according to the method, the technological process of the low-carbon alloy aluminum deoxidized and killed steel can be shortened, the temperature loss is reduced, and the cleanliness of molten steel is controlled through temperature rising.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking and refining, and in particular to a chemical heating cleanliness control method for low-carbon alloy aluminum deoxidized killed steel. Background Art

[0002] As the competition in the steel market becomes more intense, steel mills are forced to research new processes and technologies to develop high-quality, low-cost products to seize the market. At present, the production process of low-carbon aluminum-killed steel generally adopts the deoxidation alloying production process of adding medium-carbon ferromanganese and argon station aluminum wire in converter steelmaking. This method not only increases the consumption of aluminum deoxidizer and medium-carbon ferromanganese, but also increases the generation of aluminum deoxidation products, reduces the purity of molten steel, increases the cost of deoxidation alloying, and the manganese absorption rate of carbon-manganese alloy is low, while reducing the deep stamping performance of steel.

[0003] The steel industry is facing a severe market situation with poor benefits. All enterprises are seeking ways to reduce processing and manufacturing costs. In order to reduce the impact of high hydrogen concentration in steel on the internal quality of medium and thick plates (especially those with a thickness of ≥40mm), the process route of low-carbon (especially 0.07%-0.25% carbon content) alloy aluminum deoxidized killed steel in the steelmaking process of medium and thick plate products is usually BOF-LF-RH-CC. Because the steel is deoxidized and alloyed after the converter is discharged (where Als ≥ 0.010%, completely deoxidized), if the molten steel is not treated in the LF refining furnace, the temperature cannot meet the casting conditions of the continuous casting machine. At the same time, the industry unanimously believes that when low-carbon alloy aluminum deoxidized killed steel is chemically heated by oxygen blowing under RH vacuum, Als in the molten steel will be oxidized first, and then other easily oxidized elements. This process will have an adverse effect on the composition, cleanliness and RH process treatment cycle of the molten steel. Summary of the invention

[0004] In the prior art, when low-carbon alloy aluminum deoxidized killed steel is chemically heated by blowing oxygen under RH vacuum, Als in the molten steel is first oxidized, and this process will have adverse effects on the composition, cleanliness and RH process treatment cycle of the molten steel. The present invention provides a chemical heating cleanliness control method for low-carbon alloy aluminum deoxidized killed steel, which can control the cleanliness of the molten steel through heating operation by shortening the process flow of low-carbon alloy aluminum deoxidized killed steel, reducing process temperature loss and reducing production costs.

[0005] A method for controlling the cleanliness of low-carbon alloy aluminum deoxidized killed steel, wherein the molten steel is sequentially subjected to a converter, RH vacuum treatment, oxygen blowing, and Ca treatment processes, specifically comprising the following steps: (1) Low-carbon alloy aluminum deoxidized killed steel, converter output is 240t, steel grade liquidus temperature is 1515℃, pouring superheat is 15-30℃, casting cycle is 50min, RH treatment process molten steel temperature drops to 1.2℃ / min, converter end carbon content is 0.037-0.048%, end oxygen content is 0.0435-0.053%, and end temperature is 1649-1655℃; (2) Calculate the oxygen blowing amount required for chemical heating, lift the ladle and start vacuuming; (3) According to the calculation result of the amount of oxygen required for chemical heating and blowing, the Al particles are transported to the vacuum hopper for vacuuming; (4) After Al particles are added to the vacuum chamber, the oxygen blowing operation is started immediately; (5) After oxygen blowing, the molten steel is vacuum treated. After the vacuum treatment of the molten steel is completed and the vacuum system is broken, Ar is first blown through the bottom of the ladle for soft blowing with a small amount of gas, and then Ca treatment is carried out. The Ca line feed amount is fed at 0.8-1m / t steel. The purpose is to allow the Al2O3 inclusions generated by the chemical heating process of oxygen blowing to be fully floated before Ca treatment, so as to avoid the Al2O3 inclusions caused by direct Ca treatment from being liquefied and spheroidized and then retained in the molten steel.

[0006] Furthermore, the ratio of oxygen blowing amount to Al particles is 0.8, and the unit of oxygen blowing amount is m 3 The unit of Al particle dosage is kg, and no unit conversion is performed during calculation, i.e. oxygen blowing volume (m 3 ) / weight of added Al particles (kg) = 0.8. The above formula is the perfect ratio of oxygen blowing amount to Al reaction. If it is greater than 0.8, Al in the molten steel will be oxidized. If it is less than 0.8, the expected heating effect will not be achieved.

[0007] Furthermore, the amount of oxygen blown during chemical heating is calculated based on the RH operation process, the temperature drop of the molten steel is 1.2℃ / min, the outlet temperature is 1575℃, and the Als of the molten steel is added at 0.035%. Therefore, 48kg of Al particles are needed for compounding, and the total weight of Al particles for chemical heating and compounding is 168kg.

[0008] Furthermore, the oxygen blowing operation should be carried out under a vacuum of 3-8kpa, the gun position should be controlled at 5.2-5.8m, and the oxygen blowing intensity should be 2000-2500Nm 3 / h.

[0009] Furthermore, the addition of Al particles should be carried out under a vacuum degree of 8 kPa.

[0010] Furthermore, when the vacuum degree reaches 8kPa, oxygen blowing begins and the oxygen blowing volume is set to 140-160m 3 .

[0011] Furthermore, after meeting the RH vacuum treatment requirements for 8 minutes, the molten steel breaks through the air.

[0012] Furthermore, the molten steel is soft-blown for 5 minutes after breaking through the air, fed with Ca wire for 200-210m, and then soft-blown for another 6-7 minutes before being put on the machine.

[0013] The beneficial effects of the present invention are: (1) It can effectively shorten the process flow of low-carbon alloy aluminum deoxidation killed steel, reduce process temperature loss, and reduce production costs without affecting the cleanliness of the molten steel. The cleanliness of the molten steel can be controlled by heating operation.

[0014] (2) After adding Al particles during the RH vacuum treatment process, oxygen is blown to chemically heat the steel through the Al-O exothermic reaction. After chemical heating, in order to avoid excessive inclusions, the timing of Ca treatment is optimized and adjusted to promote the floating of inclusions, so as to achieve the purpose of improving the cleanliness of molten steel.

[0015] (3) The oxygen blowing operation will not cause burn damage to easily oxidized elements such as Als in the molten steel, will not deteriorate the cleanliness of the molten steel due to the chemical temperature rise caused by oxygen blowing, and will not affect the RH vacuum treatment operation cycle. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0017] Example 1 The process of smelting low-carbon alloy aluminum killed steel is that the molten steel passes through the converter, RH vacuum treatment, oxygen blowing, and Ca treatment in turn; the low-carbon alloy A ship plate steel with a target carbon content of 0.17% is smelted by combined blowing converter-RH refining-continuous casting. The converter output is 240t, the liquidus temperature of the steel grade is 1515℃, the pouring superheat requirement is 15-30℃, the casting cycle of the casting machine is 50min, the temperature drop of the molten steel during the RH treatment process is about 1.2℃ / min, the carbon content of the converter is 0.048%, the oxygen content of the end point is 0.053%, and the end point temperature is 1655℃. During the steel tapping process, 1630kg of silicon manganese iron, 1000kg of top slag lime, 360kg of deoxidized alloy aluminum manganese iron, and 240kg of graphite recarburizer are added. The molten steel is sampled and tested in the RH furnace, and C=0.165%, Als=0.016%, and the temperature is 1602℃. After the molten steel reaches the processing position, the ladle is lifted and the vacuum operation is started. The amount of oxygen blown for chemical heating and the Al particles required for the added components are calculated and weighed.

[0018] The calculation of oxygen blowing amount for chemical heating is carried out according to the reverse method. For example: ① If the liquidus temperature of molten steel is 1515℃, the temperature drop of molten steel during pouring is 25℃ with a ladle capacity of 240t and a pouring cycle of 50 minutes, the average superheat of molten steel during pouring is 25℃, and the average temperature drop of molten steel during transfer from RH to continuous casting machine is 12℃, then the RH molten steel outlet temperature needs to reach 1577℃. ② The average temperature drop of molten steel during RH vacuum treatment is 1.2℃ / min, and the average time of RH vacuum treatment is 40min, then the process temperature drop is 1.2×40=48℃. Therefore, the temperature of molten steel to RH should be ≥1625℃ (1577℃+48℃), while the actual temperature of molten steel to RH is 1602℃, which requires chemical heating of 1625-1602=23℃.

[0019] If Als is added to molten steel at 0.035%, 48kg of Al particles are needed for compounding. A total of 168kg of Al particles are weighed for chemical heating and compounding, and transported to the vacuum hopper. When the vacuum degree reaches 8kPa, add the weighed Al particles in the vacuum hopper to the vacuum tank, lower the RH top gun position to 5.5m, start blowing oxygen, and set the oxygen blowing intensity to 2300Nm 3 / h, oxygen blowing volume is set to 140m 3 . After the vacuum degree dropped to less than 100Pa and ran stably for 5 minutes, the samples were C=0.17%, Als=0.035%, and the other components were consistent with the entry temperature and met the steel grade requirements. The temperature was measured at 1573℃. After pure degassing met the process requirements for 8 minutes, the molten steel system was broken. After the molten steel system was broken, it was soft-blown for 5 minutes, fed with Ca line for 200m, and then soft-blown for another 6 minutes before being put on the machine.

[0020] Example 2 The target carbon content of low-carbon alloy A ship plate steel with a target carbon content of 0.17% was smelted by combined blowing converter-RH refining-continuous casting. The converter tapping capacity was 240t, the liquidus temperature of the steel grade was 1515℃, the pouring superheat requirement was 15-30℃, the casting cycle of the casting machine was 50min, and the temperature drop of the molten steel during the RH treatment process was about 1.2℃ / min. The carbon content of the converter was 0.037%, the oxygen content of the end point was 0.0435%, and the end point temperature was 1649℃. During the steel tapping process, 1900kg of ferrosilicon manganese, 1000kg of top slag lime, 470kg of deoxidized alloy ferroalloy aluminum manganese, and 270kg of graphite recarburizer were added. The molten steel was sampled and tested in the RH furnace, and the composition was C=0.172%, Als=0.013%, and the temperature was measured at 1598℃. After the molten steel arrived at the treatment position, the ladle was lifted and the vacuum operation was started, and the Al particles required for chemical heating and addition of components were calculated and weighed. Among them, the calculation of chemical heating is based on the RH operation process, the temperature of the molten steel drops by 1.2℃ / min, and the exit temperature is 1575℃, so 135kg of Al particles are needed for chemical heating; the molten steel Als is added according to the target 0.035%, so 55kg of Al particles are needed for proportioning. The total weight of Al particles for chemical heating and proportioning is 190kg, and they are transported to the vacuum hopper; when the vacuum degree reaches 8kPa, the weighed Al particles in the vacuum hopper are added to the vacuum tank, the RH top gun position is lowered to 5.3m, and oxygen blowing is started, and the oxygen blowing intensity is set to 2500Nm 3 / h, oxygen blowing volume is set to 160m 3 . After the vacuum degree dropped to less than 100Pa and ran stably for 5 minutes, the sample was taken, C=0.175%, Als=0.037%, and the other components were consistent with the incoming sample and met the steel grade requirements. The temperature was measured at 1575℃. After pure degassing met the process requirements for 8 minutes, the molten steel broke through the air. After the molten steel broke through the air, it was soft-blown for 5 minutes, fed with Ca line for 210m, and then soft-blown for another 7 minutes before being put on the machine.

[0021] From the data of Example 1 and Example 2, it can be seen that: (1) by precise oxygen blowing, it can be ensured that the oxygen blowing process does not affect the composition change of molten steel, especially the Al in the molten steel, which will not be oxidized by oxygen blowing and thus deteriorate the quality of the molten steel. Oxygen blowing volume (m 3 ) / weight of added Al particles (kg) = 0.8. The above formula is the perfect ratio of oxygen blowing amount and Al reaction. If it is greater than 0.8, Al in the molten steel will be oxidized; if it is less than 0.8, the expected heating effect will not be achieved.

[0022] (2) The oxygen blowing operation needs to be carried out in the vacuum range of 3-8 kPa, the gun position is controlled at 5.2-5.8 m, and the oxygen blowing intensity is 2000-2500 Nm 3 / h is to avoid the splashing phenomenon caused by the violent Al-O reaction in the furnace when blowing oxygen under high vacuum, which causes the splashing slag to adhere to the top gun sealing channel, affecting the vacuuming efficiency and good vacuum degree. At the same time, it ensures the highest efficiency of Al-O reaction.

[0023] (3) First, blow Ar through the bottom of the ladle for 5-8 minutes to make the pure Al2O3 inclusions float. If Ca treatment is done first, the pure Al2O3 will be transformed into low-melting point (liquid) calcium aluminate inclusions. The floating time of such inclusions is 4-8 hours, which is difficult to be effectively removed.

[0024] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A chemical heating cleanliness control method for low carbon alloy aluminum deoxidation killed steel, characterized in that: The molten steel goes through the converter, RH vacuum treatment, oxygen blowing, and Ca treatment process in sequence, which specifically includes the following steps: (1) Low-carbon alloy aluminum deoxidized killed steel, converter output is 240t, steel grade liquidus temperature is 1515℃, pouring superheat is 15-30℃, casting cycle is 50min, RH treatment process molten steel temperature drops to 1.2℃ / min, converter end carbon content is 0.037-0.048%, end oxygen content is 0.0435-0.053%, and end temperature is 1649-1655℃; (2) Calculate the oxygen blowing amount required for chemical heating, lift the ladle and start vacuuming; (3) According to the calculation result of the amount of oxygen required for chemical heating and blowing, the Al particles are transported to the vacuum hopper for vacuuming; (4) After Al particles are added to the vacuum chamber, the oxygen blowing operation is started immediately; (5) After oxygen blowing, the molten steel is vacuum treated. After the vacuum treatment of the molten steel is completed and the vacuum system is broken, Ar is first blown through the bottom of the ladle for soft blowing with a small amount of gas, and then Ca treatment is carried out. The Ca line feed amount is fed at 0.8-1m / t steel.

2. A chemical heating cleanliness control method for low carbon alloy aluminum deoxidation killed steel as claimed in claim 1, characterized in that: In step (2), the ratio of oxygen blowing amount to Al particles is 0.8, and the unit of oxygen blowing amount is m 3 The unit of Al particle consumption is kg, and no unit conversion is performed during calculation.

3. A chemical heating cleanliness control method for low carbon alloy aluminum deoxidation killed steel as claimed in claim 1, characterized in that: In step (3), the amount of oxygen blown during chemical heating is calculated based on the temperature drop of molten steel during the RH operation at 1.2°C / min and the outlet temperature at 1575°C, and the molten steel is added at 0.035%.

4. A chemical heating cleanliness control method for low carbon alloy aluminum deoxidation killed steel as claimed in claim 1, characterized in that: In step (4), the oxygen blowing operation is carried out at a vacuum degree of 3-8 kPa, the gun position is controlled at 5.2-5.8 m, and the oxygen blowing intensity is 2000-2500 Nm 3 / h.

5. A chemical heating cleanliness control method for low carbon alloy aluminum deoxidation killed steel as claimed in claim 1, characterized in that: In step (4), the addition of Al particles is carried out under a vacuum degree of 8 kPa.

6. A chemical heating cleanliness control method for low carbon alloy aluminum deoxidation killed steel as claimed in claim 1, characterized in that: When the vacuum degree reaches 8kPa, oxygen blowing begins and the oxygen blowing volume is set to 140-160m 3 .

7. A chemical heating cleanliness control method for low carbon alloy aluminum deoxidation killed steel as claimed in claim 1, characterized in that: After meeting the RH vacuum treatment requirements for 8 minutes, the molten steel breaks through the air.

8. A chemical heating cleanliness control method for low carbon alloy aluminum deoxidation killed steel as claimed in claim 8, characterized in that: After the molten steel breaks through the air, it is soft-blown for 5 minutes, fed with Ca wire for 200-210m, and then soft-blown for another 6-7 minutes before being put on the machine.