WO2018014752A1

WO2018014752A1 - Production process for dephosphorization outside of furnace of molten steel

Info

Publication number: WO2018014752A1
Application number: PCT/CN2017/092404
Authority: WO
Inventors: 周志立; 彭光辉; 王凯; 李春远; 丁广友
Original assignee: 唐山正丰钢铁有限公司
Priority date: 2016-07-22
Filing date: 2017-07-10
Publication date: 2018-01-25
Also published as: CN106011381B; CN106011381A

Abstract

A production process for dephosphorization outside of a furnace of molten steel, comprising the following process steps: (1) medium-frequency induction furnace smelting: adding steel scrap into a medium-frequency induction furnace for smelting, wherein the smelting end-point is that chemical components in mass percentage are C: 0.05-0.30% and P: ≤ 0.050%, and the temperature of the molten steel is 1550-1650ºC; and (2) dephosphorization and smelting outside of the furnace: pouring the molten steel into a ladle, and blowing the molten steel using a lime injection lance and an oxygen lance, wherein the injection rate of the lime injection lance is 10-100 kg/min, the injection amount of lime (Kg) is (the phosphorus content in % at the smelting end-point of the medium-frequency induction furnace smelting - a target phosphorus content in %) * 100 * 3.4 * the weight of the molten steel, and the injection rate of oxygen is 1-10 m³/min. The process can reduce the phosphorus content in the molten steel to the target content at a low cost by means of optimizing the production process and the injection process.

Description

Production process of dephosphorization outside molten steel furnace

Technical field

The invention relates to a dephosphorization production process outside a molten steel furnace, in particular to a dephosphorization production process outside an electric furnace steelmaking furnace, and belongs to the technical field of electric furnace steelmaking production in the metallurgical industry.

Background technique

Phosphorus is easily segregated at the grain boundary of steel to cause cold brittleness of steel, which can significantly reduce the low temperature impact properties of steel. It is therefore considered a harmful component in most steel grades. How to reduce phosphorus to the limit at low cost has always been the direction of steel workers.

At present, there are two main steelmaking processes: one is the long steel process of the steelmaking process centered on the converter steelmaking process, and the other is the short steel process of steel centered on the electric steelmaking process. With the development of environmental protection requirements, green steelmaking is gaining more and more attention. Electric steelmaking is an important green smelting method. Most of the world's major steel-making countries are mainly electric steelmaking. The output of electric furnace steel is mostly higher than that of converter steel. The proportion of electric furnace steel in the United States and India has reached more than 60%. At present, China's electric furnace steel production accounts for only about 10%, far below the world average of 29.3%. In recent years, long-process enterprises have large pollutant emissions and high energy consumption, which are important factors for the decline of air quality in China. Therefore, it is imperative to develop green short-flow enterprises with low emissions and low energy consumption.

The medium frequency induction furnace is a green short-flow smelting equipment with high efficiency, low energy consumption and low emission of scrap steel resources. However, because it does not have the thermodynamic and dynamic conditions for removing phosphorus, it greatly limits the expansion of smelting varieties.

The phosphorus content of high-quality steel is generally controlled at ≤0.025%, and some requirements are ≤0.015% or even lower. Therefore, in today's market economy, how to reduce the phosphorus content in molten steel to the target content at a low cost, enterprises can have a competitive advantage.

The medium-frequency furnace induction furnace is the center of the short-flow enterprise, smelting low-phosphorus high-quality steel, currently through the matching The dephosphorization electric arc furnace is carried out, so that the cost of smelting steel per ton will increase by 120-150 yuan/ton, making the enterprise products uncompetitive and difficult to survive. Therefore, it is necessary to seek an economical and effective means of dephosphorization outside the furnace, which is the basis for the survival of the short-flow steelmaking process centered on the intermediate frequency induction furnace. Through an effective, low-cost dephosphorization process outside the furnace, the phosphorus content is reduced to the target value, which has high promotion value for such high efficiency, low energy consumption, low emission, green short process enterprises.

Summary of the invention

The object of the present invention is to provide a dephosphorization production process outside the molten steel furnace. On the basis of ensuring the performance of the steel and the quality of the product, the phosphorus content in the molten steel can be reduced to the target content at a low cost by optimizing the production process and the blowing process. Solve the problems in the background art.

The technical solution of the utility model is:

A process for dephosphorization outside the molten steel furnace, comprising the following process steps:

(1) Medium frequency induction furnace smelting: adding scrap steel to medium frequency induction furnace for smelting, smelting end point: chemical composition mass percentage: C: 0.05 ~ 0.30%, P: ≤ 0.050%, molten steel temperature: 1550 ~ 1650 ° C;

(2) Dephosphorization smelting outside the furnace: the above molten steel is poured into a ladle, and is blown by a lime spray gun and an oxygen lance, the lime spray gun:

a. Gun position: 200 to 1000 mm from the bottom of the ladle;

b. blowing speed: 10 ~ 100kg / min;

c. Lime injection volume: calculated according to the following formula

W=(U-V)*100*3.4*G;

W: lime spray amount, unit: Kg;

U: the mass percentage of phosphorus content in the smelting end point of the intermediate frequency induction furnace;

V: the percentage of the target phosphorus content;

G: weight of molten steel, unit: tons;

The oxygen lance:

a. Gun position: 300 ~ 1800mm from the liquid surface;

b. Oxygen blowing flow rate: 1 ~ 10m ³ / min;

c. Oxygen injection volume: calculated according to the following formula

Q=(U-V)*100*0.2*G;

Q: oxygen injection amount, unit: Nm ³ ;

V: the percentage of the target phosphorus content;

In the above-mentioned molten steel furnace dephosphorization production process, the lime particle size in the step (2) is 200 mesh or more, and the mass percentage of the CaO content in the lime is more than 85%.

For the above-mentioned molten steel after dephosphorization and smelting, according to the smelted steel grade, different slag systems and different deoxidizers are used for LF furnace refining to achieve the purpose of deoxidation, desulfurization, composition adjustment and temperature adjustment.

After refining through the LF furnace, depending on the type of steel, it is decided whether to enter the VD furnace for refining and holding time.

Finally, the molten steel refined by the LF furnace or the VD furnace is cast into a steel billet by full-protection casting, low-heating and constant-speed drawing steel for rolling steel production.

By adopting the invention, the comprehensive cost of dephosphorization and smelting outside the furnace is 15 to 35 yuan/ton of steel, which is 115 yuan/ton of steel lower than that by using an electric arc furnace for dephosphorization.

The invention has the beneficial effects that the phosphorus content in the molten steel can be reduced to the target content at a low cost by optimizing the production process and the blowing process on the basis of ensuring the performance of the steel and the quality of the product.

detailed description

The invention is further illustrated by the following examples.

(1) Medium frequency induction furnace smelting: adding scrap steel to medium frequency induction furnace for smelting, smelting end point: chemical composition mass percentage: C: 0.05~0.30%, P: ≤ 0.050%, molten steel temperature: 1550~ 1650 ° C;

a. Gun position: 200 to 1000 mm from the bottom of the ladle;

b. blowing speed: 10 ~ 100kg / min;

c. Lime injection volume: calculated according to the following formula

W=(U-V)*100*3.4*G;

W: lime spray amount, unit: Kg;

V: the percentage of the target phosphorus content;

G: weight of molten steel, unit: tons;

The oxygen lance:

a. Gun position: 300 ~ 1800mm from the liquid surface;

b. Oxygen blowing flow rate: 1 ~ 10m ³ / min;

c. Oxygen injection volume: calculated according to the following formula

Q=(U-V)*100*0.2*G;

Q: oxygen injection amount, unit: Nm ³ ;

V: the percentage of the target phosphorus content;

Example:

Smelting steel grade: Q345B, target phosphorus mass percentage: 0.005%. The process of dephosphorization outside the molten steel furnace includes the following process steps:

(1) Medium-frequency induction furnace smelting: 60-ton medium-frequency induction furnace is used. In the smelting process, 45250kg of unloaded scrap steel and 18790kg of briquetting scrap are added, totaling 64,040kg. The smelting process is sampled three times. The chemical composition percentage is as follows:

Smelting end point: molten steel temperature: 1630 ° C.

(2) Dephosphorization and smelting outside the furnace: the molten steel at the end of the above smelting is subjected to a tapping operation, and argon gas is blown at the bottom of the ladle during the tapping process. After the tapping is completed, the crane is used to weigh: 62.430t of molten steel, the steel ladle is sampled at the dephosphorization station, and the bottom of the argon gas system is adjusted to 35L/min. After the ladle is dumped, the molten steel level is measured at 875mm. Lower the lime spray gun and the oxygen lance for blowing.

The lime spray gun:

a. Gun position: 620mm from the bottom of the ladle;

b. blowing speed: 30kg / min;

c. Lime injection volume:

W=(U-V)*100*3.4*G=(0.032-0.005)*100*3.4*62.430=573kg.

The lime has a particle size of 200 mesh or more, and the mass percentage of CaO content in the lime is more than 85%.

The oxygen lance:

a. gun position: 1250mm from the liquid surface;

b. Oxygen injection flow rate: 3m ³ /min;

c. Oxygen injection volume:

Q=(UV)*100*0.2*G=(0.032-0.005)*100*0.2*62.430=33.7Nm ³

After the end of the blowing, slag is smashed, and the residue is removed as much as possible, and then sampled and tested. The percentage of chemical composition of molten steel after the end of the refining process is the following:

Calculation of dephosphorization and smelting cost outside the furnace: lime: 573kg*1 yuan/kg=573 yuan; oxygen 33.7m ³ *1.2 yuan/m ³ = 40.44 yuan; spray gun cost: 420 yuan / furnace; nitrogen cost: 400m ³ / furnace * 0.6 yuan / m ³ = 240 yuan; a total of 1273.44 yuan, equivalent to steel material costs 20.39 yuan / ton of steel. Reduced by 115 yuan / ton of steel than dephosphorization using an electric arc furnace.

(3) The molten steel after the above-mentioned dephosphorization and smelting is subjected to LF furnace refining. LF furnace refining process:

CaO-SiO ₂ -CaF ₂ slag system is adopted. After the molten steel enters the heating position, argon is stirred, and 600Kg of lime, 100Kg of fluorite and the first batch of alloy material (900kg of silicomanganese alloy, 250kg of high carbon manganese iron) are added in two batches. 30 kg of silicon carbide powder, 35 kg of ferrosilicon powder (dispersed), and a reduced electrode heating slag. When the slag is added for 4 minutes, the amount of lime and fluorite is added, and the slag is further added. After the slag is finished, the temperature is measured and sampled. The slag is used to observe the deoxidation of the slag. After the refining and slag-reducing agent is added, the ferro-smelting of the ladle slag is supplemented with ferrosilicon powder and carbonization. Silicon powder; then according to the S content of molten steel and the slag condition, the amount of slag added can be appropriately adjusted. After the ladle slag is controlled to be light grayish white or white, the amount of the alloy is added according to the content of the steel element in the station, and heating is continued to the target temperature; Calcium water treatment and argon blowing operation: After the end of heating, the argon gas flow rate is adjusted to soft argon (the strength is slightly blown to the molten steel surface but not the steel flower). The ladle car was sampled after soft blowing of argon for 3 minutes, and the silicon calcium line was 100-150 m/furnace (150-200 m/furnace in the furnace). The silicon calcium wire feed speed is 2.5 to 3.0 m/s. It is required to feed the silicon calcium wire and softly blow argon for 3 to 5 minutes.

The percentage of chemical composition of molten steel in the LF furnace refining process is shown in the following table:

(4) continuous casting: continuous pouring temperature 1575 ° C, the drawing speed is 2.15m / min;

After rolling into finished products, the tensile strength is 530 MPa, the yield strength is 435 MPa, the elongation is 32%, and the 20°C impact toughness is 105 J, which fully meets the standard requirements.

Claims

The invention discloses a process for dephosphorization outside the molten steel furnace, which is characterized in that the following process steps are included:

(1) Medium frequency induction furnace smelting: adding scrap steel to medium frequency induction furnace for smelting, smelting end point: chemical composition mass percentage: C: 0.05 ~ 0.30%, P: ≤ 0.050%, molten steel temperature: 1550 ~ 1650 ° C;

(2) Dephosphorization smelting outside the furnace: the above molten steel is poured into a ladle, and is blown by a lime spray gun and an oxygen lance, the lime spray gun:

a. Gun position: 200 to 1000 mm from the bottom of the ladle;

b. blowing speed: 10 ~ 100kg / min;

c. Lime injection volume: calculated according to the following formula

W=(U-V)*100*0.34*G;

W: lime spray amount, unit: Kg;

U: the mass percentage of phosphorus content in the smelting end point of the intermediate frequency induction furnace;

V: the percentage of the target phosphorus content;

G: weight of molten steel, unit: tons;

The oxygen lance:

a. Gun position: 300 ~ 1800mm from the liquid surface;

b. Oxygen blowing flow rate: 1 ~ 10m 3 / min;

c. Oxygen injection volume: calculated according to the following formula

Q=(U-V)*100*0.2*G;

Q: oxygen injection amount, unit: Nm 3 ;

U: the mass percentage of phosphorus content in the smelting end point of the intermediate frequency induction furnace;

V: the percentage of the target phosphorus content;
The process for dephosphorization outside the molten steel furnace according to claim 1, characterized in that in the step (2), the lime has a particle size of 200 mesh or more, and the mass percentage of CaO in the lime is greater than 85%.