Method for smelting low-carbon, low-silicon and high-sulfur molten iron in converter at low cost

Abstract

The invention discloses a method for smelting low-carbon, low-silicon and high-sulfur molten iron in a converter at low cost. According to the method, 109-111t of low-carbon, low-silicon and high-sulfur molten iron is added into a 120t converter, 14-16t of dry high-carbon, high-silicon and low-sulfur pig iron is added, after smelting ignition is normal, the lance position is lowered to 1100-1300mm, the oxygen supply flow is controlled to be 400-450Nm < 3 > / min, after smelting is carried out for 240S, the lance position is raised to 1300-1500mm, the oxygen supply flow is controlled to be 400-410Nm < 3 > / min, and the lance position and the flow can be finely adjusted according to the slagging condition; the lance position is gradually reduced to 800-900 mm when the smelting is close to the end point, the oxygen supply flow is controlled according to 430-450 Nm < 3 > / min, and the end point pressure time is gt; 30S, 30S; the final temperature is controlled to be 1630-1650 DEG C, the final C content is controlled to be 0.03-0.07%, the final P content is less than or equal to 0.025%, and the final S content is less than or equal to 0.030%; by the adoption of the method, the process requirement for smelting the steel grade with S smaller than or equal to 0.035% through the low-carbon low-silicon high-sulfur molten iron can be met, cost is reduced, energy consumption is reduced, stable production is facilitated, safety risks are eliminated, and good application and popularization value is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a method for smelting low-carbon, low-silicon and high-sulfur molten iron in a converter at low cost. Background Art

[0002] The desulfurization rate of the converter steelmaking process is usually 20%~40%. In actual production, when the S content of molten iron is 0.040%~0.050%, the Si content is 0.07%~0.15%, the C content is 3.60%~3.90%, and the Mn content is <0.20%, the converter desulfurization rate is only 10%~20%. When the converter-continuous casting process route is used to produce steel with S≤0.035% by smelting low-carbon, low-silicon, high-sulfur molten iron, the converter-LF refining-continuous casting process route must be used to meet the steel grade process requirements. However, in the current situation of steelmaking pursuing low energy consumption and low consumption, this process undoubtedly increases the cost of steelmaking. At present, the technologies commonly used in converters to produce steel with S≤0.035% using low-carbon, low-silicon, high-sulfur molten iron are: 1. Hot metal pre-desulfurization method: This method has the disadvantages of extended production cycle, large cooling of hot metal, increased solvent consumption and energy consumption, and large metal loss during hot metal slagging, which increases the cost.

[0003] 2. Refining treatment outside the furnace: Refining treatment outside the furnace has the problems of long production cycle, large temperature drop of the system, affecting the normal production rhythm, increasing the consumption of energy, electrodes, spare parts and other inputs, and increasing costs.

[0004] 3. Slag washing in the converter steel-making process: There is an unstable desulfurization phenomenon in the slag washing in the converter steel-making process, which has a certain impact on product quality.

[0005] 4. Hot metal mixing and smelting: Currently, most steel mills do not use mixing furnaces and iron tank mixing devices. They need to put two tanks of molten iron into the furnace at the same time. This poses a safety risk of long iron tank lifting time and affects the normal production rhythm. At the same time, the composition of blast furnace molten iron basically remains relatively stable for a period of time, and the effect of molten iron mixing is poor.

[0006] In view of the problems and shortcomings of the prior art in producing S≤0.035% steel using low-carbon, low-silicon, high-sulfur molten iron (S content 0.040%~0.050%, C content 3.60%~3.90%, Si content <0.15%, Mn content <0.20%), the present invention aims to provide a method for low-cost smelting low-carbon, low-silicon, high-sulfur molten iron using a converter-continuous casting process. Summary of the invention

[0007] The purpose of the present invention is to provide a method for smelting low-carbon, low-silicon and high-sulfur molten iron in a converter at low cost.

[0008] The object of the present invention is achieved by a method for smelting low-carbon, low-silicon, high-sulfur molten iron in a converter at low cost, which is achieved by the following steps: 1) Converter charging: Add 109-111t of low-carbon, low-silicon, high-sulfur hot metal into a 120t converter, and then add 14-16t of dry high-carbon, high-silicon, low-sulfur pig iron blocks; 2) Converter smelting: After the smelting ignition is normal, the gun position is lowered to 1100-1300mm, and the oxygen flow rate is controlled to 400-450Nm 3 / min, add the first batch of active lime 1500-1700kg, light-burned dolomite 800-1000kg, after the primary slag is basically formed, add the second batch of materials: active lime 500-700kg, light-burned dolomite 300-450kg, according to the smelting slag situation, add 3-4 batches of materials: active lime 300-400kg / batch, and complete the feeding before smelting 570S; among them, after smelting 240S, the gun position is raised to 1300-1500mm, and the oxygen supply flow rate is controlled at 400~410Nm 3 / min, the gun position and flow rate can be fine-tuned according to the slag-forming conditions; the gun position is gradually lowered to 800-900mm as the smelting approaches the end point, and the oxygen flow rate is 430-450Nm 3 / min control, end point pressure time>30S; The endpoint temperature is controlled at 1630-1650℃, the endpoint C content is controlled at 0.03~0.07%, the endpoint P content is ≤0.025%, the endpoint S content is ≤0.030%, and the molten steel meets the steel grade process control conditions; 3) Carry out steel tapping, deoxidation and alloying, and argon blowing operations according to the key points of steel grade process control; 4) Molten steel is hoisted into continuous casting machine for casting.

[0009] The present invention utilizes low-sulfur molten iron obtained by melting high-silicon, high-carbon, low-sulfur pig iron blocks to dilute the sulfur content of the molten metal in the converter molten pool, thereby reducing the sulfur content of the molten metal in the molten pool by 0.003%, and further reducing the desulfurization load of the converter; by increasing the silicon content of the molten metal in the converter molten pool by 0.010%, the basicity of the converter slag is increased, and a large amount of slag is provided for converter desulfurization; the present invention utilizes high-silicon, high-carbon, low-sulfur pig iron blocks to replace normal process scrap steel, and the chemical elements oxidize and release heat to increase the molten pool temperature, thereby avoiding the converter from heating up, and providing high temperature and low oxidation conditions for converter desulfurization; after increasing the silicon content and carbon content of the molten metal in the converter molten pool, the molten iron sulfur activity coefficient f can be increased. (s) At the same time, extend the oxygen supply time, strengthen the molten pool stirring, strengthen the converter desulfurization mass transfer, and improve the converter desulfurization rate.

[0010] The beneficial effects of the present invention are as follows: (1) The present method solves the problem of the S activity coefficient f of low-carbon, low-silicon and high-sulfur molten iron. (s)(2) This method solves the technical problem of converter slag formation when the Si content of molten iron is less than 0.15%; (3) This method improves the kinetic and thermodynamic conditions of the converter desulfurization molten pool, so that the slag can simultaneously achieve large slag volume, high temperature, high basicity, low oxidation, and improve the S activity coefficient f of the molten metal liquid when the converter smelts low carbon, low silicon and high sulfur molten iron. (s) ; (4) The method of the present invention solves the problem of slow mass transfer of sulfur at the slag-metal interface during converter smelting, thereby gaining time for converter desulfurization. When converter smelts low-carbon, low-silicon, high-sulfur hot metal to produce steel with S≤0.035%, the converter-continuous casting process route can meet the steel process requirements, reduce costs, reduce energy consumption, and be conducive to stabilizing production and eliminating safety risks, and has good promotion and application value. DETAILED DESCRIPTION

[0011] The present invention is further described below in conjunction with the embodiments, but the present invention is not limited in any way. Any changes or substitutions made based on the teachings of the present invention belong to the protection scope of the present invention.

[0012] The present invention provides a method for smelting low-carbon, low-silicon, high-sulfur molten iron in a converter at low cost, which is achieved by the following steps: 1) Converter charging: Add 109-111t of low-carbon, low-silicon, high-sulfur molten iron into a 120t converter, and then add 14-16t of dry high-carbon, high-silicon, low-sulfur pig iron blocks; first add molten iron to the converter, and then add high-Si pig iron blocks (to avoid pig iron blocks from piling up in the furnace, affecting the melting of pig iron blocks in the early stage of smelting, and causing adverse effects on smelting and desulfurization); 2) Converter smelting: After the smelting ignition is normal, the gun position is lowered to 1100-1300mm, and the oxygen flow rate is controlled to 400-450Nm 3 / min, add the first batch of active lime 1600-1700kg, light-burned dolomite 890-960kg, after the primary slag is basically formed, add the second batch of materials: active lime 600-650kg, light-burned dolomite 340-380kg, according to the smelting slag situation, add 3-4 batches of materials: active lime 300-400kg / batch, and complete the feeding before smelting 570S; after testing, the Si of molten iron in the molten pool increased by about 0.10%, according to the basicity of 5.0, the slag material is added, and the effective lime number is 0.85. Based on the original process, 1570kg more active lime can be added to create conditions for large slag volume for converter desulfurization, and can solve the technical problem of difficult converter slag when the Si of molten iron is <0.15%, the basicity of converter slag reaches 5, the amount of converter slag is still small, the basicity of converter slag is >5 or above, and the converter slag is difficult.

[0013] Among them, after smelting for 240S, the gun position is raised to 1300-1500mm, and the oxygen flow rate is controlled to 400~410Nm 3 / min, the gun position and flow rate can be fine-tuned according to the slag-forming conditions; the gun position is gradually lowered to 800-900mm as the smelting approaches the end point, and the oxygen flow rate is 430-450Nm 3 / min control, the end pressure time> 30S; compared with the normal process, the Si of the molten iron in the molten pool increased by about 0.10%, the C of the molten iron increased by about 0.10%, and the oxygen supply increased by about 225Nm 3 The oxygen flow rate is about 30Nm lower than the normal process 3 / min, the oxygen supply time can be extended by about 80S, and the desulfurization mass transfer time can be extended by forming a high-temperature, high-basicity slag with better desulfurization conditions during converter smelting.

[0014] The endpoint temperature is controlled at 1630-1650℃, the endpoint C content is controlled at 0.03~0.07%, the endpoint P content is ≤0.025%, the endpoint S content is ≤0.030%, and the molten steel meets the steel grade process control conditions; 3) Carry out steel tapping, deoxidation and alloying, and argon blowing operations according to the key points of steel grade process control; 4) Molten steel is hoisted into continuous casting machine for casting.

[0015] In step 1), the chemical composition of the low-carbon, low-silicon, high-sulfur molten iron is: S 0.040%-0.050%, Si 0.07%-0.15%, C 3.60%-3.90%, Mn<0.20%. The chemical composition of the high-carbon, high-silicon, low-sulfur pig iron block is: Si>1.00%, C>4.60%, S<0.020%.

[0016] Example 1 The smelting furnace number of this embodiment is: 24F01257, the steel grade is Q235B, and the molten steel volume is 118.3 tons.

[0017] After the slag splashing of the converter is completed, 110.765 tons of low-carbon, low-silicon, high-sulfur molten iron are added to the 120t converter by a crane, and then 15.2 tons of high-Si pig iron blocks are added. After the loading is completed, the converter is shaken to -20° behind the furnace, and then the converter is shaken to "zero position". The temperature of the molten iron entering the furnace: 1384℃; the composition of the molten iron entering the furnace is C: 3.65%; Si: 0.08%; Mn: 0.17%; S: 0.050%. The composition of high-Si pig iron is C: 5.20%; Si: 1.43%; S: 0.011%. Smelting with the lower oxygen lance, the oxygen flow rate is set to 300Nm 3 / min, the gun position is lowered to 2460mm, stay for 10S, and confirm that the ignition is normal by observing the flame state at the furnace mouth. The gun position is lowered to 1220mm, and the oxygen flow rate is set to 380Nm 3 / min, add the first batch of lime 1660kg, lightly burned dolomite 960kg, high-level purified steel particles 500kg, smelt 186S, avoid the conditions of opening and venting explosion, and set the oxygen flow rate to 430Nm3 / min; After smelting for 258S, the molten pool began to enter the intense carbon-oxygen reaction period through furnace flame observation, the gun position was adjusted to 1456mm, and the oxygen flow rate was set to 405Nm 3 / min; smelting 330S, the early slag is well formed, add the second batch of active lime 604kg, light-burned dolomite 380kg, smelting 480S, add the third batch of active lime 400kg, smelting 510S, adjust the gun position to 1580mm, and add 480kg of temperature-adjusting and purified steel particles, smelting 540S, add light-burned dolomite 390kg, smelting 600S, adjust the gun position to 1440mm, smelting 630S, adjust the gun position to 1180mm, smelting to 660S, adjust the gun position to 1060mm, smelting to 690S, adjust the gun position to 796mm, smelting to 730S, and stop blowing. The furnace was poured to measure the temperature and take samples, the end temperature was 1635℃, the end C: 0.06%, the end P: 0.022%, and the end S: 0.029%.

[0018] After the molten steel is smelted, it is tapped, and 112kg of ferrosilicon, 123kg of silicon calcium barium, 636kg of manganese silicon, and 50kg of iron core aluminum are added for deoxidation and alloying; after the tapping is completed, the molten steel is transported to the argon station for argon blowing, and finally the molten steel is hoisted to the casting machine for casting. The composition of the molten steel sample at the argon station is: C 0.11%, Si 0.20%; Mn 0.49%, S 0.036%, P 0.030%; the composition of the molten steel sample is: C 0.11%, Si 0.18%; Mn 0.47%, S 0.035%, P 0.031%, the converter desulfurization rate reaches 42%, and the product quality meets the internal control requirements.

[0019] Example 2 The smelting furnace number of this embodiment is: 24E03929, the steel grade is Q235B, and the molten steel volume is 118.3 tons.

[0020] After the converter slag splashing is completed, a crane is used to lift 110.5 tons (920.1 kg / t 钢水 ) low carbon, low silicon and high sulfur hot metal is added to the 120t converter, and then 15.9 tons (132.4kg / t 钢水 ) High Si pig iron block, after loading, the converter is shaken to -24° behind the furnace, and then the converter is shaken to "zero position". The temperature of the molten iron entering the furnace is 1344℃; the composition of the molten iron entering the furnace is C: 3.8%; Si: 0.16%; Mn: 0.14%; S: 0.042%. The composition of high Si pig iron is C: 4.74%; Si: 1.08%; S: 0.015%. Smelting with oxygen lance, the oxygen flow rate is set to 300Nm 3 / min, the gun position is lowered to 2520mm, stay for 10S, and confirm that the ignition is normal by observing the flame state at the furnace mouth. The gun position is lowered to 1180mm, and the oxygen flow rate is set to 380Nm3 / min, add the first batch of lime 1700kg, lightly burned dolomite 890kg, high-level purified steel particles 400kg, smelt for 200S, avoid the conditions of opening the blower to vent the explosion, and set the oxygen flow rate to 430Nm 3 / min (measured flow rate 425-436Nm 3 / min); After smelting for 246S, the molten pool began to enter the intense carbon-oxygen reaction period through furnace mouth flame observation, the gun position was adjusted to 1425mm, and the oxygen flow rate was set to 410Nm 3 / min (measured flow rate 401-410Nm 3 / min); smelting 360S, the slag is well formed in the early stage, the second batch of active lime 650kg, light burned dolomite 340kg are added, smelting 450S, the gun position is adjusted to 1600mm, smelting 490S, adding the third batch of active lime 300kg; smelting 520S, adding the fourth batch of active lime 320kg, smelting 580S, the gun position is adjusted to 1400mm, smelting gradually lowered the position in the later stage, smelting to 670S, the gun position is adjusted to 750mm, smelting to 705S, the blowing is terminated. The temperature of the furnace was measured and sampled, and the end point temperature was 1642℃, the end point C: 0.06%, the end point P: 0.016%, and the end point S: 0.030%; 112kg of ferrosilicon, 123kg of silicon calcium barium, 636kg of manganese silicon, and 50kg of iron core aluminum were added for deoxidation and alloying; after the steelmaking was completed, the molten steel was transported to the argon station for argon blowing, and finally the molten steel was hoisted to the casting machine for casting.

[0021] After testing, the composition of the argon station molten steel sample was: C 0.08%, Si 0.18%; Mn 0.43%, S 0.034%, P 0.019%; the composition of the smelting sample was: C 0.10%, Si 0.17%; Mn 0.46%, S 0.033%, P 0.021%. The converter desulfurization rate reached 28.6%, and the product quality met the internal control requirements.

[0022] Low-carbon, low-silicon and high-sulfur molten iron (molten iron S content 0.040%~0.050%, molten iron Si content 0.07%~0.15%, molten iron C content 3.60%~3.90%, molten iron Mn content <0.20%) of a certain factory accounts for 5% of the total molten iron, of which 30% is used to produce steel with S≤0.035%. The cost of smelting molten iron by the method of the present invention is 30 yuan / ton lower than that of LF refining for off-furnace desulfurization. Calculated based on a monthly output of 250,000 tons: annual benefit = 25×10000×5%×30%×30×12=1.35 million yuan.

Claims

1. A method for smelting low-carbon, low-silicon, high-sulfur hot metal in a converter at low cost. It is characterized in that To do this, follow these steps: 1) Converter charging: Add 109-111t of low-carbon, low-silicon, high-sulfur hot metal into a 120t converter, and then add 14-16t of dry high-carbon, high-silicon, low-sulfur pig iron blocks; 2) Converter smelting: After the smelting ignition is normal, the gun position is lowered to 1100-1300mm, and the oxygen flow rate is controlled to 400-450Nm 3 / min, add the first batch of active lime 1500-1700kg, light-burned dolomite 800-1000kg, after the primary slag is basically formed, add the second batch of materials: active lime 500-700kg, light-burned dolomite 300-450kg, according to the smelting slag situation, add 3-4 batches of materials: active lime 300-400kg / batch, and complete the feeding before smelting 570S; among them, after smelting 240S, the gun position is raised to 1300-1500mm, and the oxygen supply flow rate is controlled at 400~410Nm 3 / min, the gun position and flow rate can be fine-tuned according to the slag-forming conditions; the gun position is gradually lowered to 800-900mm as the smelting approaches the end point, and the oxygen flow rate is 430-450Nm 3 / min control, end point pressure time>30S; The endpoint temperature is controlled at 1630-1650℃, the endpoint C content is controlled at 0.03~0.07%, the endpoint P content is ≤0.025%, the endpoint S content is ≤0.030%, and the molten steel meets the steel grade process control conditions; 3) Carry out steel tapping, deoxidation and alloying, and argon blowing operations according to the key points of steel grade process control; 4) Molten steel is hoisted and transported to the continuous casting machine for casting.

2. According to claim 1, a method for smelting low-carbon, low-silicon, high-sulfur hot metal in a converter at low cost, It is characterized in that In step 1), the chemical composition of the low-carbon, low-silicon, high-sulfur molten iron is: S 0.040%~0.050%, Si 0.07%~0.15%, C 3.60%~3.90%, Mn<0.20%.

3. According to claim 1, a method for smelting low-carbon, low-silicon, high-sulfur molten iron in a converter at low cost is used. It is characterized in that In step 1), the chemical composition of the high carbon, high silicon and low sulfur pig iron block is: Si>1.00%, C>4.60%, S<0.020%.