A smelting method for improving converter dephosphorization efficiency

Abstract

The present invention relates to a smelting method for improving the dephosphorization efficiency of a converter. The raw materials for converter steelmaking are scrap steel and molten iron. The smelting process controls a suitable oxygen supply system and slag making system to improve the slag-making effect of the smelting process. In addition, an iron-carbon agent is added in the late stage of converter smelting to increase the stirring energy of the molten pool through the carbon-oxygen reaction between slag and metal, promote the dephosphorization reaction, improve the dephosphorization effect, and reduce the oxidizability of the terminal slag and iron loss. The present invention is simple to operate and easy to promote and apply. It is especially suitable for converters with poor bottom blowing effects and can improve the dephosphorization effect.

Description

Technical Field

[0001] The invention belongs to the technical field of converter steelmaking, in particular to a smelting method for improving the dephosphorization efficiency of a converter, and belongs to the technical field of smelting. Background Art

[0002] Phosphorus is generally considered to be a harmful impurity in steel. It is easy to segregate at the grain boundary, causing the steel to be "cold brittle" and significantly reducing the low-temperature impact toughness of the steel. The reaction equation for dephosphorization in converter steelmaking is 2[P]+3(CaO)+5(FeO)= 3CaO·P 2 O 5 +5[Fe], the phosphorus in the molten steel reacts with the iron oxide and calcium oxide in the liquid slag to generate stable tricalcium phosphate and enter the slag to achieve the dephosphorization task. From this reaction, it can be seen that the dephosphorization reaction is mainly concentrated at the slag-metal interface. Improving the kinetic conditions of the molten pool can promote the dephosphorization reaction and improve the dephosphorization effect. In the later stage of the converter campaign, the bottom blowing components are seriously corroded and blocked. At the same time, in order to protect the furnace lining, it is necessary to increase the thickness of the furnace bottom by replenishing the furnace material, resulting in the failure of the bottom blowing, the deterioration of the kinetic conditions of the molten pool, and the dephosphorization of the converter becomes difficult. Due to the lack of relevant equipment and taking into account the production cost and rhythm issues, the low-phosphorus steel grades such as cord steel produced by our company are mainly smelted by the converter single slag method. In the later stage of the campaign, when the kinetic conditions deteriorate, the dephosphorization efficiency is unstable and re-blowing treatment is often required. In the prior art, there is an operation of adding iron-carbon agent for dephosphorization, among which CN202110174017.9 is an iron-carbon briquette and its use method. In the converter smelting process, 0.1-3kg / t of iron-carbon briquette is added at the end of smelting. After adding the iron-carbon briquette, the converter is bottom-blown. The dissolved oxygen content in the molten steel at the end of smelting is ≥500ppm, and then the steel tapping operation is performed. The chemical composition and weight percentage of the iron-carbon briquette are: C: 5%-50%, Mn≤2%, S≤0.060%, P≤0.060%, Si≤0.60%, and the rest are iron and unavoidable impurity elements. At the end of smelting, iron-carbon briquettes are added. The carbon content of the iron-carbon briquettes is between 5.0% and 50.0%, which should not be too high. Otherwise, adding it at the end of smelting will easily lead to excessive carbon content in molten steel, and the smelting cycle will be extended. At the same time, in order to prevent the carbon content of the finished product from exceeding the standard, the carbon content of the converter end is required to be ≤0.04%, the oxygen content is ≥500ppm, and the carbon content of the finished product is required to be ≥0.06%, indicating that the carbon return amount is about 0.02%, and the carbon increase is obvious. When the bottom blowing of the converter fails, the iron-carbon briquettes will not be usable. CN201711134097.5 A process for preparing mechanical briquette of carbon-containing iron materials for direct converter steelmaking. By adding carbon-iron materials, FeO is promoted to improve the slag-removing effect, and carbon increases the heat, but the specific dephosphorization effect is not studied.

[0003] In view of this situation, the present invention provides a smelting method for improving the dephosphorization efficiency of the converter. In the later stage of converter smelting, as the carbon content of molten steel gradually decreases, the oxidizability of slag gradually increases, and the temperature of the molten pool is relatively high at this time, the calcium oxide in the slag is basically melted, forming a high-basicity liquid slag with good fluidity, which has a strong dephosphorization ability. At this time, the limiting factor of dephosphorization is mainly the kinetic conditions of the molten pool. After research, 85% to 95% oxygen is blown into the converter, and a specific proportion of components and a density iron-carbon agent are added. Since the density of the iron-carbon agent is between the slag and the molten steel, the added iron-carbon agent is at the slag-metal interface, and the iron scale on the surface of the iron-carbon agent is quickly melted, and the carbon powder inside reacts with the slag FeO to generate CO gas and be discharged. This process can improve the kinetic conditions of the slag-metal interface, promote the dephosphorization reaction, and improve the dephosphorization efficiency. Summary of the invention

[0004] The object of the present invention is to provide a smelting method for improving the dephosphorization efficiency of a converter. When the dynamic conditions of the molten pool deteriorate in the later stage of the converter service, an iron-carbon agent is added in the later stage of converter smelting to increase the stirring intensity of the molten pool, promote the dephosphorization reaction, and improve the dephosphorization effect.

[0005] The specific method steps and control method parameters are as follows:

[0006] A smelting method for improving converter dephosphorization efficiency, wherein the converter steelmaking raw materials are scrap steel and molten iron, wherein the scrap steel accounts for 10% to 25% of the total mass of the steelmaking raw materials, and the molten iron accounts for 75% to 90% of the total mass of the steelmaking raw materials. The smelting process controls the appropriate oxygen supply system and slag making system, and adds an iron-carbon agent when the oxygen blowing is 85% to 95%.

[0007] Furthermore, from the start of blowing to the total oxygen supply of 20%, the oxygen lance position is controlled at 1.4~1.5m; from blowing oxygen to the total oxygen supply of 20%~85%, the oxygen lance position is controlled at 1.5~2.0m; from blowing oxygen 85% to the end of blowing, the oxygen lance position is controlled at 1.3~1.5m. The oxygen supply intensity throughout the process is controlled at 4.0~4.5Nm 3 / t / min.

[0008] Furthermore, as a preferred method, the amount of lime and ore is calculated according to the target slag basicity and temperature using a two-stage steelmaking model; 60% to 70% of the lime and 50% to 60% of the ore are added when the oxygen blowing rate is 0% to 30%, and the remaining amount of lime and ore (Fe 2 O 2 ) is added in batches according to the principle of small amounts and multiple batches when the oxygen blowing rate is 30% to 85%. 2 O 3 Content greater than 90%).

[0009] Furthermore, a layer of iron sheet is wrapped around the carbon powder. The carbon content of the iron-carbon agent is 55%~70%, the iron content is 30%~45%, and the rest are unavoidable impurities; the particle size of the iron-carbon agent is controlled at 20~50mm, and the specific gravity (density) is controlled at 4.0~7.0g / cm 3 The addition amount is controlled at 1.5~3.0kg / t. Furthermore, the density of the iron-carbon agent is controlled at 4.0~5.0g / cm 3 At this time, the iron-carbon agent is between the slag and the steel. Due to the oxidation reaction of the iron-carbon agent between the slag and the steel, a large amount of CO gas is released, which stirs the molten pool and increases the dephosphorization effect. This solves the problem of decreased dephosphorization effect when the kinetic conditions of the molten pool are greatly weakened after the bottom blowing of the converter fails.

[0010] The advantages of the present invention are: (1) when the dynamic conditions of the molten pool deteriorate in the later stage of the converter service, the stirring intensity of the molten pool is increased by adding an iron-carbon agent in the later stage of the converter smelting, the dephosphorization reaction is promoted, and the dephosphorization effect is improved; (2) since the iron-carbon agent is added at the end of the converter smelting and the added iron-carbon agent reacts with the iron oxide in the slag, the oxidation of the final slag can be reduced, thereby reducing iron loss. Implementation Example 1

[0011] The smelting method for improving the dephosphorization efficiency of the converter adopts the following specific process steps.

[0012] The 130t converter smelted LX72A steel with a furnace age of 6125, at which time the bottom blowing was completely ineffective; 25t scrap steel + 120t molten iron were added, the silicon content of the molten iron was 0.35%, and the phosphorus content of the molten iron was 0.11%. The conditions not specifically required during the smelting process are the normal conditions for LX72A production.

[0013] Control points:

[0014] (1) Oxygen supply intensity control method during smelting process: The oxygen supply intensity is controlled at 33000 Nm 3 / h;

[0015] (2) Lance position control method: from the start of blowing to 20% oxygen supply, the oxygen lance position is controlled at 1.5m; from 20% to 50% oxygen blowing, the oxygen lance position is controlled at 1.65m; from 50% to 90% oxygen blowing, the oxygen lance position is controlled at 1.8m; from 90% oxygen blowing to the end of blowing, the oxygen lance position is controlled at 1.4m.

[0016] (3) Feeding system: add 65% of lime and 60% of ore when blowing oxygen 0-30%, add the remaining amount in small batches when blowing oxygen 30% to 85%, and add 200kg of iron-carbon agent (the carbon content of iron-carbon agent is 65%, the iron content is 35%, and the density is 4.2g / cm 3 ).

[0017] The molten pool temperature at the end of converter smelting is 1615℃, the composition of molten steel is C: 0.05%, P: 0.006%, slag basicity is 3.5, slag FeO: 14.6%, and the overall dephosphorization rate is 94.5%. Example 2

[0018] A 130t converter was used to smelt LX72A steel with an age of 8230 years and all bottom blowing failed. 26t scrap steel and 120t molten iron were added, with silicon content of 0.56% and phosphorus content of 0.12%.

[0019] Control points:

[0020] (1) Oxygen supply intensity control method during smelting process: The oxygen supply intensity is controlled at 33000 Nm 3 / h;

[0021] (2) Lance position control method: from the start of blowing to 20% oxygen supply, the oxygen lance position is controlled at 1.45m; from 20% to 50% oxygen blowing, the oxygen lance position is controlled at 1.7m; from 50% to 90% oxygen blowing, the oxygen lance position is controlled at 1.85m; from 90% oxygen blowing to the end of blowing, the oxygen lance position is controlled at 1.45m.

[0022] (3) Feeding system: add 65% of lime and 60% of ore when blowing oxygen 0-30%, add the remaining amount in small batches when blowing oxygen 30% to 85%, and add 300kg of iron-carbon agent (the carbon content of iron-carbon agent is 60%, the iron content is 40%, and the density is 4.6g / cm 3 ).

[0023] The molten pool temperature at the end of converter smelting was 1608℃, the molten steel composition was C: 0.06%, P: 0.006%, slag basicity was 3.6, slag FeO: 14.0%, and the overall dephosphorization rate was 95.0%.

[0024] Comparative Example 1

[0025] Compared with Example 1, the difference is that no iron-carbon agent is added.

[0026] A 130t converter was used to smelt LX72A steel with an age of 6126 furnaces and all bottom blowing failed. 25t scrap steel + 120t molten iron were added, with silicon content of 0.35% and phosphorus content of 0.11%.

[0027] Control points:

[0028] (1) Oxygen supply intensity control method during smelting process: The oxygen supply intensity is controlled at 33000 Nm 3 / h;

[0029] (2) Lance position control method: from the start of blowing to 20% oxygen supply, the oxygen lance position is controlled at 1.5m; from 20% to 50% oxygen blowing, the oxygen lance position is controlled at 1.65m; from 50% to 90% oxygen blowing, the oxygen lance position is controlled at 1.8m; from 90% oxygen blowing to the end of blowing, the oxygen lance position is controlled at 1.4m.

[0030] (3) Feeding system: add 65% of lime and 60% of ore when blowing oxygen 0-30%, and add the remaining amount in small batches when blowing oxygen 30% to 85%.

[0031] The molten pool temperature at the end of converter smelting was 1613°C, the molten steel composition was C: 0.05%, P: 0.012%, slag basicity was 3.6, slag FeO: 18.9%, and the overall dephosphorization rate was 89.1%.

[0032] Comparative Example 2

[0033] Compared with Example 2, the difference is that the iron-carbon agent is added too early.

[0034] A 130t converter was used to smelt LX72A steel with an age of 8232 furnaces and all bottom blowing failed. 26t scrap steel + 120t molten iron were added, with a silicon content of 0.56% and a phosphorus content of 0.11%.

[0035] Control points:

[0036] (1) Oxygen supply intensity control method during smelting process: The oxygen supply intensity is controlled at 33000 Nm 3 / h;

[0037] (2) Lance position control method: from the start of blowing to 20% oxygen supply, the oxygen lance position is controlled at 1.45m; from 20% to 50% oxygen blowing, the oxygen lance position is controlled at 1.7m; from 50% to 90% oxygen blowing, the oxygen lance position is controlled at 1.85m; from 90% oxygen blowing to the end of blowing, the oxygen lance position is controlled at 1.45m.

[0038] (3) Feeding system: add 65% of lime and 60% of ore when blowing oxygen 0-30%, add the remaining amount in small batches when blowing oxygen 30% to 85%, and add 300kg of iron-carbon agent (the carbon content of the iron-carbon agent is 60%, the iron content is 40%, and the density is 4.6g / cm 3 ).

[0039] The molten pool temperature at the end of converter smelting is 1610℃, the molten steel composition is C: 0.06%, P: 0.013%, slag basicity is 3.62, slag FeO: 17.6%, and the overall dephosphorization rate is 88.2%.

[0040] Comparative Example 3

[0041] Compared with Example 1, the difference is that the density of the iron-carbon agent is 2.0 g / cm 3 The dephosphorization effect is higher than that without adding iron-carbon agent, but lower than that of iron-carbon agent with a density of 4.0 g / cm 3 The above dephosphorization effect.

[0042] A 130t converter was used to smelt LX72A steel with an age of 6126 furnaces and all bottom blowing failed. 25t scrap steel + 120t molten iron were added, with silicon content of 0.35% and phosphorus content of 0.11%.

[0043] Control points:

[0044] (1) Oxygen supply intensity control method during smelting process: The oxygen supply intensity is controlled at 33000 Nm 3 / h;

[0045] (2) Lance position control method: from the start of blowing to 20% oxygen supply, the oxygen lance position is controlled at 1.5m; from 20% to 50% oxygen blowing, the oxygen lance position is controlled at 1.65m; from 50% to 90% oxygen blowing, the oxygen lance position is controlled at 1.8m; from 90% oxygen blowing to the end of blowing, the oxygen lance position is controlled at 1.4m.

[0046] (3) Feeding system: When blowing oxygen at 0-30%, add 65% of lime and 60% of ore; when blowing oxygen at 30% to 85%, add the remaining amount in small batches; when blowing oxygen at 92%, add 200kg of iron-carbon agent.

[0047] The molten pool temperature at the end of converter smelting was 1616℃, the molten steel composition was C: 0.052%, P: 0.010%, slag basicity was 3.52, slag FeO: 14.5%, and the overall dephosphorization rate was 90.9%.

Claims

1. A smelting method for improving converter dephosphorization efficiency, characterized in that: Dephosphorization of the converter is carried out when the bottom blowing of the converter fails; the raw materials for converter steelmaking are scrap steel and molten iron, the oxygen supply system and the material addition and slag making system are controlled during the smelting process, and iron-carbon agent is added when the oxygen blowing reaches 85%~95% of the total oxygen supply; the carbon content of the iron-carbon agent is 55%~70%, the iron content is 30%~45%, and the rest is impurities; the dephosphorization rate reaches more than 94.5%; Among them, scrap steel accounts for 10% to 25% of the total mass of the steelmaking raw materials, and molten iron accounts for 75% to 90% of the total mass of the steelmaking raw materials; the oxygen supply system refers to: from the start of blowing to 20% of the total oxygen supply, the oxygen lance position is controlled at 1.4~1.5m; oxygen is blown to 20%~85% of the total oxygen supply, and the oxygen lance position is controlled at 1.5~2.0m; from 85% of oxygen to the end of blowing, the oxygen lance position is controlled at 1.3~1.5m, and the oxygen supply intensity throughout the process is controlled at 4.0~4.5Nm 3 / (t·min); The slag-making system is as follows: first, the amount of lime and ore is calculated according to the target slag basicity and temperature using the secondary steelmaking model; 60% to 70% of the total mass of lime and 50% to 60% of the total mass of ore are added when the oxygen blowing rate is 0% to 30%, and the oxygen blowing rate is 30% to 85%, and the remaining amount of lime and ore are added in small quantities and multiple batches; Among them, the iron-carbon agent is a layer of iron sheet wrapped around the carbon powder. The particle size of the iron-carbon agent is controlled at 20~50mm and the density is controlled at 4.0~5.0g / cm 3 The addition amount is controlled at 1.5~3.0kg / t.