Control method for straight continuous casting of low-carbon aluminum killed steel

Abstract

The invention belongs to the technical field of steelmaking, and particularly discloses a low-carbon aluminum killed steel direct continuous casting control method which comprises the following steps: molten iron is desulfurized, converter oxygen blowing smelting is carried out, a slag former is added according to the alkalinity of slag and the content of MgO in the slag, a silicon-calcium alloy is added to the bottom of a steel ladle, and the molten iron is subjected to continuous casting; and adding a silicon-calcium alloy at the beginning of tapping, carrying out medium stirring argon blowing treatment, adding aluminum particles on the surface of the steel slag, adding a deoxidizing agent according to the end-point oxygen content of molten steel in the steel ladle, feeding the steel ladle into an argon blowing station, and rapidly finishing top slag modification by using strong stirring. The method aims at solving the problems that in the treatment process of three modes, additional equipment is needed, and consequently the production cost and the operation complexity are increased. The silicon-calcium alloy is used for replacing calcium carbide to conduct pre-deoxidation treatment on the molten steel, the recarburization phenomenon caused by the calcium carbide in the deoxidation process is completely eradicated, meanwhile, the silicon-calcium alloy and aluminum particles conduct deoxidation on the molten steel and steel slag, wire feeding treatment is not conducted in an argon station, and the alloy cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking, and in particular to a control method for direct continuous casting of low-carbon aluminum killed steel. Background Art

[0002] As one of the main steel grades for producing cold-rolled thin plates, low-carbon aluminum-killed steel is widely used in the automotive, home appliance, packaging and other industries. In order to obtain good formability, it needs to have low carbon, low silicon and low nitrogen properties, among which strict control of silicon content is particularly critical. Although increasing the silicon content in the molten steel can improve the strength of the thin plate, it will reduce the stamping performance. When the silicon content is high, oxide "red rust" is easily generated on the surface of the cold-rolled thin plate, which brings difficulties to the subsequent production process.

[0003] In the traditional production process, low-carbon aluminum-killed steel is usually required to have an appropriate aluminum content in order to improve the organizational structure and eliminate the generation of subcutaneous bubbles. The number of inclusions in the steel should be small, the size should be small and plastic. A large amount of aluminum is used for deoxidation in production, which will cause the excess oxygen in the molten steel to produce a large amount of spherical A1203. In order to ensure the purity of the molten steel and make the spherical inclusions float effectively, LF+calcium treatment, CAS+calcium treatment or LF+non-calcification treatment are usually used for treatment.

[0004] However, the above treatment method requires refining through an LF furnace during the treatment process, and the amount of calcium added must be controlled, otherwise it will lead to unsatisfactory control of inclusion morphology and affect the quality of steel. If improperly controlled, new types of inclusions may be generated, which not only increases equipment costs but also increases the complexity of operations. Summary of the invention

[0005] The purpose of the present invention is to provide a control method for direct continuous casting of low-carbon aluminum killed steel to solve the problem that the three methods require additional equipment during the processing, which leads to increased production costs and operational complexity.

[0006] To achieve the above object, the basic scheme provided by the present invention is: a control method for direct continuous casting of low-carbon aluminum killed steel, comprising the following steps:

[0007] S1. Desulfurize the molten iron and skim the molten iron. The skimming standard is that 3 / 4 of the molten iron surface is exposed;

[0008] S2, pouring 108-115t of desulfurized molten iron into a converter, adding 15-20t of scrap steel, and carrying out oxygen blowing smelting. The amount of slag-making agent added is adjusted according to the target slag basicity and MgO content in the slag to ensure that the TFe content in the final slag is ≤16%;

[0009] S3, after the blowing is completed, before the steel is tapped, 90-110 kg of silicon-calcium alloy is added to the ladle without molten iron, and then the steel is tapped out. During the tapping, oxygen determination operation and temperature measurement and sampling are performed. From the start of tapping to the addition of the alloy, 40-60 kg of silicon-calcium alloy is added to the ladle, and argon blowing treatment is performed during the stirring. The stirring time is 4-6 minutes. After the steel is tapped, 40-60 kg of aluminum particles are added to the surface of the molten steel in the ladle;

[0010] S4. Add deoxidizer according to the final oxygen content of the molten steel in the ladle. When the oxygen content is abnormal, add deoxidizer according to the final carbon content. The target aluminum content of the molten steel is 0.03-0.05%;

[0011] S5. Then send the ladle to the argon blowing station, use strong stirring to quickly complete the top slag reform, the strong stirring time is ≥5min, and after the top slag deoxidation on the inner surface of the ladle is completed, soft blowing treatment is carried out, and the soft blowing time is ≥8min;

[0012] S6. Finally, the molten steel is fed into the continuous casting machine for casting.

[0013] The beneficial effects of the present invention are as follows: using silicon-calcium alloy instead of calcium carbide to pre-deoxidize molten steel can, on the one hand, prevent the inevitable carbon increase caused by calcium carbide in the deoxidation process, and on the other hand, the residual Ca element in the alloy after deoxidation enters the molten steel, providing a certain Ca content in the molten steel. The appropriate calcium-aluminum ratio can effectively improve the castability of the molten steel and ensure the continuous production of continuous casting; at the same time, the silicon-calcium alloy + aluminum particles are used to deoxidize the molten steel and slag, and the argon station does not perform wire feeding treatment, thereby lowering the steel tapping temperature of the converter, reducing the erosion of the furnace lining due to high-temperature, low-carbon, high-oxygen slag, reducing the amount of aluminum-iron alloy added, and reducing the alloy cost. At the same time, the argon station does not perform wire feeding treatment. After the new process of deoxidation of low-carbon, low-silicon steel, the converter process operation flow is stabilized, making the on-site furnace machine production more matched, and further improving production efficiency.

[0014] Scheme 2 is the preferred basic scheme. In S1, the composition of the molten iron entering the furnace is as follows: Si content is 0.10-0.85%, Mn content is 0.20-0.50%, P content is <0.120%, S content is <0.045%, and the molten iron temperature is >1280°C.

[0015] Scheme 3 is a preferred option of the basic scheme. In S2, the target basicity of the slag is R=3.0-3.5, and the target MgO content in the slag is 9-10%.

[0016] Scheme 4: This is the preferred basic scheme. In S2, the opening position of the blow gun is 1300-1500 mm from the liquid surface, and the oxygen supply flow rate is 27500-28500 m 3 / h, the gun position in the carbon fire stage is adjusted to 1650-1750mm from the liquid surface, and the oxygen supply flow rate is reduced to 25500-26500m 3 / h, the gun position in the middle stage of oxygen blowing is 1600-1800mm from the liquid surface, and the oxygen supply flow rate is 25500-26500m 3 / h, the gun position in the carbon pulling stage is lowered to 950-1050mm from the liquid surface, and the oxygen supply flow rate is 27500-28500m 3 / h, carbon pulling and gun lowering time ≤40s; in different stages of steelmaking, by strictly controlling the gun position and oxygen supply flow, the steelmaking reaction process can be accurately regulated, the removal of impurities and the homogenization of the steel liquid composition can be promoted, the decarburization efficiency can be improved, and the carbon content of the molten steel can be accurately controlled.

[0017] Scheme 5 is the preferred option of the basic scheme. In S3, the tapping temperature is 1655-1670°C, and the tapping time is 3min-5.5min.

[0018] Scheme 6 is the preferred basic scheme. In S3, the composition of the silicon-calcium alloy is: carbon content is 0.03-0.05%, silicon content is 20.15-22.15%, sulfur content is 0.006-0.08%, phosphorus content is 0.033-0.53%, and calcium content is 30-32%. Through the appropriate alloy composition, the silicon-calcium alloy can better play its role in deoxidation and improving the castability of molten steel.

[0019] Option seven, which is the preferred option of the basic option, the diameter of the strong stirring blowing is 500-600mm, the diameter of the medium stirring blowing is 300-400mm, and the diameter of the soft blowing is 150-200mm. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below through specific embodiments:

[0021] A control method for direct continuous casting of low-carbon aluminum killed steel comprises the following steps:

[0022] S1. Desulfurize the molten iron and skim the molten iron. The skimming standard is that 3 / 4 of the molten iron surface is exposed. The composition of the molten iron entering the furnace is as follows: Si content is 0.30%, Mn content is 0.20%, P content is 0.10%, S content is 0.038%, and the molten iron temperature is 1300°C;

[0023] S2. Pour 110t of desulfurized molten iron into the converter, and then add 15t of scrap steel. It is forbidden to add high-sulfur scrap steel such as slag, oil, radiator, etc. into the converter. Oxygen blowing smelting is carried out. The amount of slag-making agent added is based on the target slag basicity R=3.2 and the MgO content in the slag is 9.5%. The TFe content in the terminal slag is ensured to be 15%. The opening position of the blowing gun is 1400mm from the liquid surface, and the oxygen supply flow rate is 28000m 3 / h, the gun position in the carbon fire stage was adjusted to 1700mm from the liquid surface, and the oxygen supply flow rate was reduced to 26000m3 / h, the gun position in the middle stage of oxygen blowing is 1700mm from the liquid surface, and the oxygen supply flow rate is 26000m 3 / h, the gun position in the carbon pulling stage is lowered to 1000mm from the liquid surface, the oxygen supply flow rate is 28000m3 / h, the carbon pulling gun lowering time is 38s, and the end point C is determined according to the flame shape;

[0024] S3, after the blowing is completed, before the steel is tapped, 100kg of silicon-calcium alloy is added to the ladle without adding molten iron, and then the steel is tapped out of the furnace. When the steel is tapped out, the oxygen determination operation and temperature measurement sampling are performed. From the beginning of the steel tapping to the addition of the alloy, 50kg of silicon-calcium alloy is added to the ladle, and the medium stirring argon blowing treatment is performed. The diameter of the medium stirring blow is 400mm, and the medium stirring time is 5min. After the steel is tapped, 50kg of aluminum particles are added to the surface of the molten steel in the ladle. The slag blocking method is the slide plate slag blocking. The silicon-calcium alloy composition: carbon content is 0.04%, silicon content is 21.15%, sulfur content is 0.07%, phosphorus content is 0.43%, and calcium content is 31%;

[0025] Table 1 Alloy types and dosage

[0026] Consumption Pre-deoxidizer (Silicon calcium alloy Low carbon ferromanganese (alloy) Deoxidizer (aluminum iron) Top slag reforming agent (aluminum particles) Single furnace kg 150 50-100 350-500 50 Ton of steel kg / t 1.25 0.4-0.8 2.9-4.2 0.42

[0027] Table 2 Steel tapping temperature control requirements for various steel grades

[0028] Casting conditions Steel tapping℃(reference) Ar station ℃ Upper steel temperature ℃ Tundish (superheat 20-30℃) Continuous pouring 1660 1615 1595 1550-1555 Power on / plug in 1670 1620 1600 1550-1560

[0029] S4. Add deoxidizer according to the final oxygen content of the molten steel in the ladle. When the oxygen content is abnormal, add deoxidizer according to the final carbon content (see Table 3 for details). The target aluminum content of the molten steel is 0.04%;

[0030] Table 3: End point oxygen content / carbon content and deoxidizer addition

[0031] End point [C]% End point temperature ℃ End point [O] ppm Deoxidizer addition amount kg 0.04 1660 738 300 0.045 1660 665 300 0.05 1660 599 280 0.055 1660 544 250 0.06 1660 499 250 0.065 1660 461 250 0.07 1660 428 200 0.075 1660 400 200 0.08 1660 375 200

[0032] S5, then send the ladle to the argon blowing station, use strong stirring to quickly complete the top slag reform, the strong stirring blows open the diameter of 600mm, the strong stirring time is 5min, after the top slag deoxidation on the inner surface of the ladle is completed, soft blowing treatment is carried out, the soft blowing blows open the diameter of 200mm, the soft blowing time is 8min, and the ladle turnover time is 1.5h;

[0033] S6. Finally, the molten steel is fed into the continuous casting machine for casting.

[0034] A direct operation method for low-carbon aluminum-killed steel without calcification treatment is adopted. Silicon-calcium alloy + aluminum ingots are used to deoxidize molten steel and slag. The argon station does not perform wire feeding treatment. After the new process of low-carbon and low-silicon steel deoxidation, the converter process operation flow is stabilized, making the on-site furnace machine production more matched and further improving production efficiency.

[0035] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A control method for direct continuous casting of low-carbon aluminum killed steel, characterized in that: The following steps are involved: S1. Desulfurize the molten iron and skim the molten iron. The skimming standard is that 3 / 4 of the molten iron surface is exposed; S2, pouring 108-115t of desulfurized molten iron into a converter, adding 15-20t of scrap steel, and carrying out oxygen blowing smelting. The amount of slag-making agent added is adjusted according to the target slag basicity and MgO content in the slag to ensure that the TFe content in the final slag is ≤16%; S3, after the blowing is completed, before the steel is tapped, 90-110 kg of silicon-calcium alloy is added to the ladle without molten iron, and then the steel is tapped out. During the tapping, oxygen determination operation and temperature measurement and sampling are performed. From the start of tapping to the addition of the alloy, 40-60 kg of silicon-calcium alloy is added to the ladle, and argon blowing treatment is performed during the stirring. The stirring time is 4-6 minutes. After the steel is tapped, 40-60 kg of aluminum particles are added to the surface of the molten steel in the ladle; S4. Add deoxidizer according to the final oxygen content of the molten steel in the ladle. When the oxygen content is abnormal, add deoxidizer according to the final carbon content. The target aluminum content of the molten steel is 0.03-0.05%; S5. Then send the ladle to the argon blowing station, use strong stirring to quickly complete the top slag reform, the strong stirring time is ≥5min, and after the top slag deoxidation on the inner surface of the ladle is completed, soft blowing treatment is carried out, and the soft blowing time is ≥8min; S6. Finally, the molten steel is fed into the continuous casting machine for casting.

2. The control method for direct continuous casting of low-carbon aluminum killed steel according to claim 1, characterized in that: In S1, the composition of the molten iron entering the furnace is as follows: Si content is 0.10-0.85%, Mn content is 0.20-0.50%, P content is less than 0.120%, S content is less than 0.045%, and the molten iron temperature is greater than 1280°C.

3. The control method for direct continuous casting of low-carbon aluminum killed steel according to claim 1, characterized in that: In S2, the target basicity of the slag is R=3.0-3.5, and the target MgO content in the slag is 9-10%.

4. The control method for direct continuous casting of low-carbon aluminum killed steel according to claim 1, characterized in that: In S2, the opening position of the blow gun is 1300-1500mm from the liquid surface, and the oxygen supply flow rate is 27500-28500m 3 / h, the gun position in the carbon fire stage is adjusted to 1650-1750mm from the liquid surface, and the oxygen flow rate is reduced to 25500-26500m3 / h. The gun position in the middle stage of oxygen blowing is 1600-1800mm from the liquid surface, and the oxygen flow rate is 25500-26500m3 / h. 3 / h, the gun position in the carbon pulling stage is lowered to 950-1050mm from the liquid surface, and the oxygen supply flow rate is 27500-28500m 3 / h, carbon pulling and gun lowering time ≤40s.

5. The control method for direct continuous casting of low-carbon aluminum killed steel according to claim 1, characterized in that: In S3, the tapping temperature is 1655-1670°C, and the tapping time is 3min-5.5min.

6. The control method for direct continuous casting of low-carbon aluminum killed steel according to claim 1, characterized in that: In S3, the silicon-calcium alloy composition is as follows: carbon content is 0.03-0.05%, silicon content is 20.15-22.15%, sulfur content is 0.006-0.08%, phosphorus content is 0.033-0.53%, and calcium content is 30-32%.

7. The control method for direct continuous casting of low-carbon aluminum killed steel according to claim 1, characterized in that: The diameter of the strong stirring blowing is 500-600mm, the diameter of the medium stirring blowing is 300-400mm, and the diameter of the soft blowing is 150-200mm.