CN105986055A - Multi-tank molten steel continuous casting method for ultra-low phosphorus and sulfur high alloy steel in single LF furnace - Google Patents

Abstract

The invention provides a method for continuous pouring of molten steel in multiple tanks in a single LF furnace for ultra-low-phosphorus-sulfur high-alloy steel. For ultra-low-phosphorus-sulfur high-alloy steel with phosphorus <0.005% and sulfur <0.002%, the converter process is optimized to control the tapped phosphorus content and tapping temperature, adopt phosphorus return control technology, reduce molten steel tank, RH vacuum phosphorus return, cancel molten steel slag removal process, shorten LF treatment cycle, control the phosphorus content in tapping at 10-20ppm, and control phosphorus return within 15ppm. The phosphorus content of the finished product is controlled within 35ppm. The LF treatment cycle was shortened from 150min to 70min, matching the pouring time of the casting machine, and increased from the original 1-2 pot pouring to 6 pots or even more than 6 pots in a row. Simultaneously, the present invention can reduce steel material 52kg/t steel, the cost of steel material per ton of steel can be saved by 520 yuan, and the processing cost can be saved by 200 yuan/ton of steel.

Description

A method for continuous pouring of molten steel in multiple tanks in a single LF furnace for extremely low-phosphorus-sulfur high-alloy steel

technical field

The invention belongs to the field of steelmaking technology. In particular, it relates to a method for continuously pouring multiple tanks of molten steel in a single LF furnace of extremely low phosphorus and sulfur high alloy steel with phosphorus < 0.005% and sulfur < 0.002%.

Background technique

Very low phosphorus and sulfur high alloy steel, such as ultra-low temperature pressure vessel steel 9Ni, requires its composition: nickel 9%, phosphorus content less than 0.005%, sulfur content less than 0.002%. Low temperature operation, the smelting end temperature is not higher than 1550°C, and the phosphorus content of the tapping is controlled at about 20ppm. In order to control the phosphorus content of the finished product to meet the quality requirements, the tapping slag + molten steel slag removal process is adopted to control the phosphorus return of molten steel. After adopting this process, the LF treatment is forced to be divided into two steps: 1) the temperature is raised first when entering the station, but the steel slag is not modified to prevent phosphorus return after modification, 2) the molten steel slag is removed after the temperature is raised;

The processing cycle of the above-mentioned LF is particularly long, which does not match the pouring time of the casting machine. Therefore, only one can can be poured separately, and at most 2 cans can be poured continuously. Nanjing Iron and Steel Co., Ltd. adopts the multiple slag pouring method of the converter to control the phosphorus in the tapped steel at 30ppm, and the latter method is the same as that adopted by Anshan Iron and Steel Co., Ltd. Taiyuan Iron and Steel Converter is blown according to the normal smelting method. Before tapping the steel, the dephosphorization agent is added to the ladle, and the dephosphorization is carried out in the ladle through the tapping process of the converter. 9Ni steel. Angang and Nanjing Iron and Steel LF refining takes an average of 150 minutes, and Taiyuan Iron and Steel LF furnace treatment time is more than 150 minutes. These traditional methods, first of all, due to the long processing time of molten steel, the pollution of molten steel is serious, and the quality of steel grades deteriorates. Secondly, because the number of single-casting tanks is too small, there are many waste products, and the consumption of various materials is large, and the production cost per ton of steel is very high.

Contents of the invention

The invention provides a method for continuous pouring of multiple tanks of molten steel in a single LF furnace for ultra-low phosphorus and sulfur high alloy steel. , RH vacuum phosphorus return, cancel the molten steel slag removal process, shorten the LF treatment cycle, realize continuous pouring of 6 tanks or more, and reduce the production cost per ton of steel.

For this reason, the solution that the present invention takes is:

A method for continuous pouring of multiple tanks of molten steel in a single LF furnace for extremely low-phosphorus-sulfur high-alloy steel, characterized in that the continuous pouring of multiple tanks of molten steel in a single LF furnace for extremely low-phosphorus-sulfur high-alloy steel with phosphorus < 0.005% and sulfur < 0.002% The method is:

(1) Before production, first arrange to cast low-silicon aluminum-killed steel once, control the converter tapping P≤0.015%, and rinse the RH vacuum tube for more than 2 times;

(2) The ladle uses low-silicon aluminum-killed steel to rinse the tank more than 2 times to control the rephosphorization of the ladle;

(3) According to the chemical blowing loss of the dephosphorization furnace of 2.7%, and the physical blowing loss of 2.1%, the target charge of the dephosphorization furnace is: the charge of the decarburization furnace/(1-4.8%)±2 tons;

(4) The molten iron Si content is required to be 0.2-0.6%, the temperature is 1280-1400°C, the scrap steel is light and pure scrap steel, and the scrap steel ratio is 80kg/ton of iron; the charging sequence is to add scrap steel first and then add molten iron;

(5) Control the sulfur ≤ 0.0010% after the pre-desulfurization of the molten iron, remove the slag thoroughly, and there is no block of slag on the surface of the molten iron;

(6) The converter is smelted by a double-link method. For the dephosphorization furnace, during the desiliconization and dephosphorization period, the oxygen blowing intensity of the top lance is set to 90% of the normal blowing intensity, and the flow rate of the bottom blowing is set to the maximum flow rate; Active lime is 12-16kg/ton of steel, lightly burned dolomite is 4-8kg/ton of steel, ore is added to 2/3 of the total amount according to heat balance, and blowing is carried out for 4-5 minutes. Release the phosphorous slag; then continue blowing with guns, re-slagging, add active lime 14-18kg/ton steel, lightly burnt dolomite 2-4kg/ton steel and the remaining ore; at the same time, control the first half of the converter to dephosphorize When the furnace is blowing for 8.8-9 minutes, the tapping temperature is 1400-1450°C, the carbon content of the tapping is 2.00-2.30%, and the phosphorus of the tapping furnace is below 0.025%;

(7) Add 11-13kg/ton of carburizer for temperature raising before the blowing of the decarburization furnace, the oxygen blowing intensity of the top lance is the normal oxygen blowing intensity, and the flow rate of the bottom blowing is set to the maximum flow rate; after the blowing is started, add active lime 39 ～41kg/ton of steel, 8～10kg/ton of light-burned dolomite and 3.5～4.5kg/ton of slagging agent for steel; the end point carbon is controlled at 0.03～0.05%, the tapping temperature is controlled at 1600～1620℃, hanging tank The temperature is controlled above 1580°C;

(8) Before tapping the taphole plug brick, confirm whether it is firmly plugged, and plug another plug outside the original taphole plug brick to prevent the slag from entering the molten steel tank in the early stage of tapping. slag;

(9) During the desulfurization process of the LF refining furnace, calcium carbide and molten slag are not allowed to be added to the slagging material; the argon blowing flow rate at the bottom of the ladle is based on the fact that the molten steel surface does not violently turbulent, and the amount of Als generated during the top slag modification process is controlled at 0.015～0.020%;

(10) During the RH vacuum refining and degassing process, the vacuum degree is ≤200Pa, and the cycle time is ≥30min. After the void is broken, the molten steel is blown with argon at the bottom with a small flow rate for 15-20min, and then it is taken out of the machine for pouring.

Positive effects and beneficial effects of the present invention are:

1. The phosphorus content of the molten iron in the decarburization furnace is less than 0.025%, which reduces the P ₂ O ₅ content in the decarburization slag. Adding a carburizing agent to raise the temperature ensures the carbon at the end of the converter and reduces the degree of peroxidation of the molten steel, which is beneficial Control the slag and phosphorus return during the tapping process.

2. Increase the temperature of the converter, cancel the molten steel slag removal process, make the LF heating and upgrading desulfurization proceed at the same time, shorten the LF treatment cycle, match it with the pouring cycle of the casting machine, and realize continuous pouring of 6 or even more than 6 pots.

3. Due to the realization of the multi-tank continuous pouring technology, the energy consumption of the process is greatly saved, the steelmaking capacity is released, and the adverse effects of severe iron pressing caused by the production of extremely low-phosphorus and high-sulfur alloy steel are eliminated.

4. Since the pouring of 1-2 pots is increased to 6 pots or even more than 6 pots, the loss of waste products is reduced, and the consumption of refractory materials such as tundishes is also significantly reduced, thereby effectively reducing the smelting cost of this type of steel.

5. Because the temperature of the steel hanging can in the converter is increased by more than 30 °C compared with the traditional process, the LF heating time is shortened by more than half, the number of molten steel inclusions is reduced, and the quality of molten steel is improved.

Therefore, the present invention can control the phosphorus content of tapping within 10-20ppm, control the phosphorus returning within 15ppm, and control the phosphorus content of the finished product within 35ppm. The LF treatment period is shortened from the original 150min to 70min, matching the pouring time of the casting machine, and the number of continuous pouring cans is increased from 1 to 2 cans to 6 cans or even more than 6 cans; at the same time, the invention can reduce the steel material by 52kg/t steel , 520 yuan can be saved for steel materials per ton of steel, and 200 yuan/ton of steel can be saved for processing costs.

detailed description

The continuous pouring method of multiple tanks of molten steel in a single LF furnace for ultra-low phosphorus and sulfur high alloy steel of the present invention mainly controls the phosphorus content and temperature of tapping by optimizing the converter process, and adopts the phosphorus return control technology to reduce the return of phosphorus in molten steel tanks and RH vacuum , cancel the molten steel slag removal process, shorten the LF treatment cycle, realize continuous pouring of 6 or more tanks, and reduce the production cost per ton of steel.

The present invention will be further described below by taking 260 tons of top-bottom combined blowing converter smelting ultra-low temperature pressure vessel steel 9Ni as an example.

Example 1:

1. Before the production of 9Ni steel, arrange for a sprue of SPHC steel, control the converter tapping P≤0.015%, and rinse the RH vacuum tube for 3 times to reduce the amount of phosphorus returned during the RH treatment process.

2. The ladle uses low-silicon aluminum-killed steel to rinse the tank for 4 times to control the rephosphorization of the ladle.

3. According to the chemical blowing loss of the dephosphorization furnace is 2.7%, the physical blowing loss is 2.1%, and the target charging capacity of the decarburization furnace is 265 tons: then the charging capacity of the dephosphorizing furnace is 278±2 tons.

4. Hot metal Si 0.4%, temperature 1350°C, 21.6 tons of light and pure steel scrap; according to the target loading capacity of the dephosphorization furnace 278±2 tons: 258 tons of molten iron is controlled, and the charging sequence is to add scrap steel first and then add molten iron to prevent scrap steel Sticky big noodles.

5. After the pre-desulfurization of molten iron, the sulfur content is 0.0010%, and the slag is removed thoroughly, and there is no block of slag on the surface of the molten iron.

6. The converter is smelted by double-link method. For the dephosphorization furnace, during the desiliconization and dephosphorization period, the top lance oxygen blowing intensity is set to 90% of the normal blowing intensity, that is, 48000m ³ /h, and the bottom blowing flow rate is set to the maximum 26Nm ³ /h. After starting blowing, add 3500kg of active lime, 1500kg of lightly burned dolomite, add 2/3 of the total amount of ore according to the heat balance, and blow for 4 minutes. When the slag is active, lift the slag gun to release part of the high phosphorus slag in the furnace. Then continue blowing with guns, adding 4000kg of active lime, 500kg of lightly burned dolomite, and re-slagging with the remaining ore. When the blowing reaches 8.8 minutes, the gun is lifted to tap the steel, the tapping temperature is 1440°C, the carbon content of the tapping steel is 2.10%, and the phosphorus content of the tapping steel is 0.018%.

7. Add carburant 3500kg before blowing, top lance oxygen blowing intensity is 53700m ³ /h, bottom blowing flow rate is set to 26Nm ³ /h. Add 11,000kg of active lime, 2,000kg of lightly burned dolomite, and 1,000kg of slagging agent after blowing is started; raise the gun when the secondary automatic control system of converter smelting shows that the carbon content at the end point is within the range of 0.03-0.05%, and the carbon content at the end point is 0.05% , temperature 1618°C.

8. Double plug brick technology is adopted. Check whether the plug brick of the tapping hole is firm before tapping, and then plug another plug brick outside the original plug brick of the tapping hole to prevent the slag from entering the molten steel tank in the early stage of tapping, and use the slag stopper at the end Mark to block slag, and strictly prohibit dropping slag. The temperature of the hanging tank after the converter furnace is 1593°C.

9. During the desulfurization process of the LF refining furnace, calcium carbide and flux slag are not allowed to be added to the slagging material; the argon blowing flow rate at the bottom of the ladle is based on the fact that the steel surface does not violently turbulent, and the Als after the top slag is modified is 0.018%.

10. During the RH vacuum refining and degassing process, the vacuum degree is ≤200Pa, and the cycle time is 30 minutes. After the void is broken, the molten steel is blown with argon at the bottom with a small flow rate for 16 minutes, and then it is moved out of the machine for pouring.

Example 2:

1. Before the production of 9Ni steel, arrange for a sprue of SPHC steel, control the converter tapping P≤0.015%, and rinse the RH vacuum tube for 5 times to reduce the amount of phosphorus returned in the RH treatment process.

2. The ladle uses low-silicon aluminum-killed steel to rinse the tank for 4 times to control the rephosphorization of the ladle.

3. According to the chemical blowing loss of the dephosphorization furnace is 2.7%, the physical blowing loss is 2.1%, and the target charging capacity of the decarburization furnace is 265 tons: then the charging capacity of the dephosphorizing furnace is 278±2 tons.

4. Hot metal Si 0.5%, temperature 1300°C, 20.4 tons of light and pure steel scrap; according to the target loading capacity of the dephosphorization furnace 278±2 tons: 258 tons of molten iron is controlled, and the charging sequence is to add scrap steel first and then add molten iron to prevent scrap steel Sticky big noodles.

5. After the pre-desulfurization of molten iron, the sulfur content is 0.0008%, the slag is removed thoroughly, and there is no block of slag on the surface of the molten iron.

6. The converter is smelted by double-link method. For the dephosphorization furnace, during the desiliconization and dephosphorization period, the top lance oxygen blowing intensity is set to 90% of the normal blowing intensity, that is, 48000m ³ /h, and the bottom blowing flow rate is set to the maximum 26Nm ³ /h. After blowing, add 3800kg of active lime, 1300kg of lightly burned dolomite, add 2/3 of the total amount of ore according to the heat balance, and blow for 4.5 minutes. When the slag is active, lift the slag gun to release part of the high phosphorus slag in the furnace. Then continue blowing with guns, add 3650kg of active lime, 900kg of lightly burned dolomite, and re-slag the remaining ore. When the blowing reaches 9 minutes, the gun is lifted to tap the steel, the tapping temperature is 1420°C, the carbon content of the tapping steel is 2.15%, and the tapping phosphorus content is 0.021%.

7. Add 3200kg of recarburizer before the blowing of the decarburization furnace, the oxygen blowing intensity of the top lance is 53700m ³ /h, and the flow rate of the bottom blowing is set at 26Nm ³ /h. After blowing, add 10400kg of active lime, 2500kg of lightly burned dolomite, and 920kg of slagging agent; when the secondary automatic control system of converter smelting shows that the end point carbon content is in the range of 0.03-0.05%, raise the gun, and the end point carbon content is 0.035% , temperature 1610°C.

8. Double plug brick technology is adopted. Check whether the plug brick of the tapping hole is firm before tapping, and then plug another plug brick outside the original plug brick of the tapping hole to prevent the slag from entering the molten steel tank in the early stage of tapping, and use the slag stopper at the end The slag is marked to stop, and the slag is strictly prohibited. The temperature of the hanging tank after the converter is 1598 ° C.

9. During the desulfurization process of the LF refining furnace, calcium carbide and flux slag are not allowed to be added to the slagging material; the argon blowing flow rate at the bottom of the ladle is based on the fact that the steel surface does not turbulently, and the Als after the top slag is modified is 0.016%.

10. During the RH vacuum refining and degassing process, the vacuum degree is ≤200Pa, and the cycle time is 37 minutes. After breaking the air, the molten steel is blown with argon at the bottom with a small flow rate for 18 minutes, and then it is moved out of the machine for pouring.

Claims (1)

1. a pole low phosphor and sulfur high-alloy steel list LF stove multiple tank molten steel even waters method, it is characterised in that for phosphorus ＜ 0.005%, Single LF stove multiple tank molten steel of the pole low phosphor and sulfur high-alloy steel of sulfur ＜ 0.002% even method of watering is:

(1), before producing, first arrange one to water time low silicon aluminium killed steel, control converter tapping P≤0.015%, RH vacuum tube is entered Row rinses pipe more than 2 times；

(2) ladle uses low silicon aluminium killed steel to carry out rinsing tank more than 2 times, controls ladle rephosphorization；

(3) according to dephosphorization stove chemistry blow loss 2.7%, physics blow loss 2.1%, dephosphorization stove target charge weight is: decarbonizing furnace charge weight/ (1-4.8%) ± 2 tons；

(4) requiring molten iron Si 0.2～0.6%, temperature 1280～1400 DEG C, steel scrap is frivolous pure steel scrap, and scrap ratio is 80kg/ Ton ferrum；Loading sequence is for first adding hot metal charging after steel scrap；

(5) controlling sulfur≤0.0010% after molten iron pre-desulfurization, skim thoroughly, molten iron face does not has in bulk accumulated slag；

(6) converter uses duplex method to smelt, and for dephosphorization stove, desiliconizing and dephosphorizing phase, top gun oxygen blast intensity settings is normal blowing The 90% of intensity, bottom blowing flow set is maximum stream flow；Open after blowing add activity white lime 12～16kg/ ton steel, light dolomite 4～ 8kg/ ton steel, Ore adds the 2/3 of total amount according to thermal balance, and blowing 4～5min, blunderbuss slagging when slag enlivens, by furnace interior High phosphorus slag is divided to bleed off；Then proceed to lower rifle blowing, slag making again, add activity white lime 14～18kg/ ton steel, light dolomite 2～ 4kg/ ton steel and remaining Ore；Meanwhile, the half steel i.e. dephosphorization stove tapping temperature when blowing is to 8.8～9min before converter is controlled Degree is 1400～1450 DEG C, carbon content 2.00～2.30% of tapping, and dephosphorization stove tapping phosphorus is below 0.025%；

(7) adding temperature raising carburant 11～13kg/ ton steel before decarbonizing furnace is opened and blown, top gun oxygen blast intensity is normal oxygen blast intensity, Bottom blowing flow set is maximum stream flow；Open and after blowing, add activity white lime 39～41kg/ ton steel, light dolomite 8～10kg/ ton steel And 3.5～4.5kg/ slagging agents of ton steel；Aim carbon controls 0.03～0.05%, and tapping temperature controls 1600～1620 DEG C, hanging pot temperature controls more than 1580 DEG C；

(8) tapping hole plug brick is confirmed whether that before tapping plug firmly, fills in one outside tapping hole former plug brick again, before avoiding tapping The slag of phase enters in ladle, and latter stage with pushing off the slag mark pushing off the slag, forbids slag；

(9) LF refining furnace is in desulfurization processing procedure, and slag making materials does not allows to add carbide and fluxing slag；Steel ladle bottom argon blowing flow The most acutely seething as standard with molten steel face, in the slag upgrading processes of control top, the growing amount of Als is 0.015～0.020%；

(10) in RH vacuum refining degassing processing procedure, vacuum≤200Pa, circulation time >=30min, after broken sky, steel Water low discharge BOTTOM ARGON BLOWING 15～20min, then takes out of machine cast.