Smelting control method of steel Q345RRE for high-cleanliness rare earth container

Abstract

The invention discloses a smelting control method of steel Q345RRE for a high-cleanliness rare earth container, which comprises the steps of deep desulfurization of KR molten iron, smelting in a converter, LF (ladle furnace) refining, RH (relative humidity) furnace and continuous casting, and parameter control of each process is optimized. According to the method, stable industrial production of the rare earth container steel is achieved through research and practice, the rare earth container steel Q355RE is developed, the quality of a steel-clad container steel product is improved, a foundation is laid for expanding a wider container steel market, and therefore considerable sales performance and economic benefits can be generated.

Description

Technical Field

[0001] The invention belongs to the technical field of steel metallurgy and steelmaking technology, and in particular relates to a smelting control method of Q345RRE steel for high-purity rare earth containers. Background Art

[0002] In recent years, Baosteel has carried out trial production of rare earth steel in multiple varieties, among which it has independently developed steel for rare earth microalloy containers. After rare earths are added to container steel products, rare earth elements react with O and S in molten steel to form high-melting-point rare earth oxides, which improve the size and morphology of molten steel inclusions and further purify the molten steel. It is of great significance to produce container steel with high purity, high strength, high toughness, good welding performance and corrosion resistance to meet engineering needs. In order to optimize container steel products, the smelting process fully applies the smelting technology of clean steel to ensure the high purity of steel. In the continuous casting process, crystallizer electromagnetic stirring, light pressure reduction and other technologies are used to ensure the uniformity of the composition and organization of container steel products. Summary of the invention

[0003] The purpose of the present invention is to provide a smelting control method for Q345RRE steel for high-cleanliness rare earth containers, which utilizes rare earth to deform molten steel inclusions to improve the cleanliness of molten steel, and improves the cleanliness of container steel products by adding rare earth, thereby providing a guarantee for improving the quality of container steel.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention discloses a smelting control method for high-clean rare earth container steel Q345RRE, comprising KR molten iron deep desulfurization → converter smelting → LF refining → RH furnace → continuous casting, wherein:

[0006] KR hot metal deep desulfurization: After the hot metal is treated by KR, the sulfur content of the hot metal entering the furnace is controlled at 0.005%. After the hot metal is desulfurized, slag removal is carried out;

[0007] Converter smelting: The carbon content of the steel tapped at the converter end is controlled to be ≥0.03%, and the oxygen content at the converter end is controlled to be ≤600ppm. The converter is required to pull carbon successfully in one go, and spot blowing operation is avoided. The converter end temperature is controlled above 1620℃;

[0008] LF refining process: After the ladle is in place and heated, temperature measurement, sampling and oxygen determination are carried out, and alloy composition adjustment and aluminum supplementation are carried out according to the sampled composition; for deep deoxidation operation in the LF refining process, it is recommended to add aluminum all at once, and try not to add aluminum in the later stage of refining to ensure sufficient floating time for inclusions after aluminum deoxidation; in the early stage of refining and when adjusting the composition, appropriate stirring and argon blowing intensity is used to strengthen desulfurization and uniform composition, and soft argon blowing is maintained for the rest, and calcium treatment is carried out in the LF furnace;

[0009] The RH process requires that the vacuum treatment time of RH should be ≥15min at a vacuum degree below 2.6Kpa. 30% rare earth ferrocerium alloy should be added in the later stage of RH vacuum treatment. After the alloy is added, the pure degassing time should be ensured to be more than 5min. After the RH treatment, soft blowing should be performed for more than 6min.

[0010] Continuous casting process: During the continuous casting process, the sealing protection of the shroud and the tundish must be ensured to prevent the secondary oxidation of the molten steel. The continuous casting nitrogen addition amount is required to be no more than 4ppm; the superheat control is increased by 10℃ based on the lower limit of the quality plan.

[0011] Furthermore, the test casting and production furnace tapping operation used a slide plate to block the slag, and the front and rear double gears controlled the slag amount to minimize the slag discharged from the ladle and reduce the total amount of inclusions in the molten steel.

[0012] Furthermore, lime, slag-reducing agent and aluminum particles are added during the converter steelmaking process to modify the top slag and pre-deoxidize the molten steel.

[0013] Furthermore, after adding the rare earth alloy, the cyclic pure degassing time is guaranteed to be 5 minutes.

[0014] Furthermore, the RH treatment was terminated by soft blowing for 8 min.

[0015] Furthermore, the casting machine uses hollow stopper rods and formulates protective pouring measures to prevent steel from accumulating in the sprue. The castability of the casting machine is significantly improved. The liquid level is stable during the pouring process without steel accumulating. The sealing protection of the long sprue and the tundish is ensured during the continuous casting process to prevent the secondary oxidation of the molten steel. The continuous casting nitrogen addition amount is required to be within 3ppm, and the rare earth alloy yield reaches more than 45%.

[0016] Furthermore, all kinds of inclusions in the ingot are within level 1.0.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are:

[0018] Through research and practice, we have achieved stable industrial production of rare earth container steel, developed rare earth container steel Q355RE, improved the quality of Baosteel's container steel products, and laid the foundation for expanding a broader container steel market, which will generate very considerable sales performance and economic benefits.

[0019] Through cost estimation and market research, the price of rare earth container steel Q355RRE is increased by 50 yuan / ton, with an annual production of 40,000 tons, and an expected profit of 2 million yuan. DETAILED DESCRIPTION

[0020] The following examples are used to specifically illustrate the present invention. These examples are only general descriptions of the present invention and do not limit the present invention.

[0021] Embodiment 1:

[0022] Through small furnace smelting and laboratory rolling of Q345R with different rare earth types and contents, the influence of different rare earth types and contents on the mechanical properties, inclusions, chemical composition, etc. of the product was studied.

[0023] 1. Production process route

[0024] 25kg vacuum smelting → rolling → mechanical properties, inclusions, chemical composition inspection.

[0025] 2. Small furnace smelting test results

[0026] A small furnace smelting plan for container steel Q345R was formulated. The smelting adopted 25kg vacuum smelting while ensuring that the smelting conditions were basically the same. A total of 4 furnaces were planned. The specific small furnace smelting plan for container steel Q345R is shown in Table 1.

[0027] Table 1 Small furnace smelting scheme for container steel Q345R (ppm)

[0028]

[0029]

[0030] 40ppm, 90ppm and 100ppm of rare earth ferrocerium alloy were added to the container steel Q345R, and the detected rare earth Ce contents were 35ppm, 82ppm and 94ppm respectively. The specific composition is shown in Table 2.

[0031] Table 2 Small furnace smelting composition of container steel Q345R

[0032]

[0033] 3. Rolling test results

[0034] The soaking temperature is 1200±20℃, and the soaking time is 30-60min; the starting rolling temperature is 1030±20℃, the first pass reduction is greater than 20%, the final rolling temperature is 850±15℃, and the steel plate thickness is 12mm.

[0035] 4. Conclusion

[0036] After adding rare earth element Ce, the impact performance of Q345R at 0℃, -20℃ and -40℃ is improved to a certain extent.

[0037] Embodiment 2:

[0038] Based on the results of the small furnace experiment, industrial production experiments were carried out. In the industrial production experiments, industrial experiments were completed on container steel products with and without the addition of rare earths under the same process production conditions.

[0039] 1. Converter smelting situation

[0040] 1. Supply of molten iron to converter

[0041] The Si content of the molten iron produced in this casting is 0.38%~0.59%; the S content of the molten iron entering the furnace is ≤0.003% after KR desulfurization, the P content of the molten iron entering the furnace is ≤0.133%, the temperature of the molten iron entering the furnace is 1349℃~1388℃, and the molten iron is stably controlled (as shown in Table 3), which is beneficial to the control of the converter smelting process and improves the hit rate of the converter terminal temperature.

[0042] Table 3: Hot metal entering the furnace

[0043] Smelting number Si(%) Mn(%) P(％) S(％) Temperature(℃) 24206787 0.48 0.39 0.133 0.002 1382 24206788 0.38 0.36 0.133 0.002 1388 24307580 0.52 0.45 0.132 0.003 1361 24307581 0.59 0.47 0.132 0.003 1365 24107697 0.58 0.45 0.127 0.001 1349

[0044] 2. Converter treatment

[0045] During the converter smelting process, lime and dolomite are added to increase the slag basicity and adjust the molten steel temperature, stabilize the smelting process temperature and meet the MgO content of the slag to avoid severe erosion of the furnace lining. The specific smelting charge addition conditions are shown in Table 4.

[0046] Table 4: Amount of iron-containing material and slag added

[0047]

[0048] The converter endpoint temperature is controlled at 1622℃~1642℃, the converter endpoint temperature is controlled above 1620℃, the oxygen content is 422ppm~559ppm, the converter endpoint oxygen content is controlled within 600ppm, the converter endpoint tapping carbon content is ≥0.03%, and the carbon content is 0.031%~0.043%. During the tapping process, lime and modifier are added to perform top slag modification operation. The converter endpoint control is shown in Table 5.

[0049] Table 5 Converter endpoint control and modifier addition amount

[0050]

[0051] The steel is discharged by sliding plate to block the slag, and the front and rear double gears are used to control the amount of slag. Aluminum iron, ferromanganese and ferrosilicon alloys are added for deoxidation and alloying. The composition of the LF furnace meets the requirements as shown in Table 6.

[0052] Table 6 Composition for LF furnace (%)

[0053] Smelting number C Si Mn P S Alt 24206787 0.15 0.13 1.26 0.010 0.012 0.080 24206788 0.15 0.13 1.34 0.012 0.004 0.042 24307580 0.16 0.18 0.81 0.013 0.003 0.043 24307581 0.16 0.14 0.76 0.009 0.006 0.051 24107697 0.17 0.13 0.74 0.011 0.009 0.040

[0054] 2. Refining Process

[0055] 1.LF furnace treatment

[0056] After heating in the LF furnace for 5 minutes, the temperature was measured and samples were taken. Aluminum was added once and the composition was adjusted according to the sampling composition. Appropriate stirring and argon blowing intensity was used to strengthen desulfurization and uniform composition. No aluminum was added in the later stage of refining to ensure sufficient floating time for inclusions after aluminum deoxidation. Calcium treatment was carried out after deoxidation and alloying in the LF furnace. The LF off-site refining composition met the planned requirements (see Table 7).

[0057] Table 7 LF furnace off-site composition (%)

[0058] Smelting number C Si Mn P S Alt Ca 24206787 0.18 0.14 1.45 0.011 0.007 0.036 0.0017 24206788 0.17 0.14 1.43 0.012 0.004 0.039 0.0012 24307580 0.19 0.14 1.44 0.012 0.002 0.024 0.0013 24307581 0.18 0.15 1.41 0.012 0.004 0.034 0.0015 24107697 0.19 0.15 1.39 0.014 0.004 0.032 0.0021

[0059] 2.RH vacuum treatment process control

[0060] During the RH vacuum treatment, temperature measurement, sampling and fine-tuning of composition are performed. The RH process is controlled according to this treatment mode, the vacuum degree is required to be ≤2.6mbar, and the vacuum time is maintained for ≥10min. Rare earth alloy is added in the later stage of vacuum treatment, and the cycle pure degassing time is guaranteed to be 5min after adding rare earth alloy. Soft blowing is performed for 8min at the end of RH treatment, and the end composition of RH furnace is shown in Table 8.

[0061] Table 8 RH furnace end point composition (%)

[0062]

[0063]

[0064] 3. Casting machine casting situation

[0065] The casting machine uses hollow stopper rods and formulates protective pouring measures to prevent steel from accumulating at the sprue. The castability of the casting machine is significantly improved. The liquid level is stable during the pouring process and no steel is accumulating. During the continuous casting process, the sealing protection of the long sprue and the tundish is guaranteed to prevent the secondary oxidation of the molten steel. The continuous casting nitrogen addition amount is required to be within 3ppm. The rare earth alloy recovery rate reaches more than 45%, which further improves the rare earth recovery rate. The casting machine production process parameters are shown in Table 9.

[0066] Table 9 Casting machine production process parameters

[0067]

[0068] 4. Inclusions and product performance

[0069] After inspection, it was found that all kinds of inclusions after adding rare earth were within level 1.0, meeting the quality plan requirements. The specific inclusions are shown in Table 10.

[0070] Table 10 Inclusions

[0071]

[0072] After adding rare earth element Ce, the impact performance of product Q345R at 0℃, -20℃ and -40℃ is improved to a certain extent.

[0073] Through a smelting control method for high-purity rare earth container steel Q345RRE, the rare earth added recovery rate of rare earth container steel Q345RRE is steadily improved, and precise control of the composition is achieved, providing a guarantee for the control of the product performance of rare earth container steel Q345RRE.

[0074] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A smelting control method for high-purity rare earth container steel Q345RRE, characterized in that: Including KR hot metal deep desulfurization → converter smelting → LF refining → RH furnace → continuous casting, including: KR hot metal deep desulfurization: After the hot metal is treated by KR, the sulfur content of the hot metal entering the furnace is controlled at 0.005%. After the hot metal is desulfurized, slag removal is carried out; Converter smelting: The carbon content of the steel tapped at the converter end is controlled to be ≥0.03%, and the oxygen content at the converter end is controlled to be ≤600ppm. The converter is required to pull carbon successfully in one go, and spot blowing operation is avoided. The converter end temperature is controlled above 1620℃; LF refining process: After the ladle is in place and heated, temperature measurement, sampling and oxygen determination are carried out, and alloy composition adjustment and aluminum supplementation are carried out according to the sampled composition; for deep deoxidation operation in the LF refining process, it is recommended to add aluminum all at once, and try not to add aluminum in the later stage of refining to ensure sufficient floating time for inclusions after aluminum deoxidation; in the early stage of refining and when adjusting the composition, appropriate stirring and argon blowing intensity is used to strengthen desulfurization and uniform composition, and soft argon blowing is maintained for the rest, and calcium treatment is carried out in the LF furnace; The RH process requires that the vacuum treatment time of RH should be ≥15min at a vacuum degree below 2.6Kpa. 30% rare earth ferrocerium alloy should be added in the later stage of RH vacuum treatment. After the alloy is added, the pure degassing time should be ensured to be more than 5min. After the RH treatment, soft blowing should be performed for more than 6min. Continuous casting process: During the continuous casting process, the sealing protection of the shroud and the tundish must be ensured to prevent the secondary oxidation of the molten steel. The continuous casting nitrogen addition amount is required to be no more than 4ppm; the superheat control is increased by 10℃ based on the lower limit of the quality plan.

2. The smelting control method of high-purity rare earth container steel Q345RRE according to claim 1 is characterized in that: The test casting and production furnace tapping operation uses a slide plate to block the slag, and the front and rear double gears control the slag amount to minimize the slag discharge from the ladle and reduce the total amount of inclusions in the molten steel.

3. The smelting control method of high-purity rare earth container steel Q345RRE according to claim 1 is characterized in that: During the converter steelmaking process, lime, slag-reducing agent and aluminum particles are added to modify the top slag and pre-deoxidize the molten steel.

4. The smelting control method of high-purity rare earth container steel Q345RRE according to claim 1 is characterized in that: After adding rare earth alloy, the circulating pure degassing time is guaranteed to be 5 minutes.

5. The smelting control method of high-purity rare earth container steel Q345RRE according to claim 1 is characterized in that: After RH treatment, soft blowing was performed for 8 minutes.

6. The smelting control method of high-purity rare earth container steel Q345RRE according to claim 1 is characterized in that: The casting machine uses hollow stopper rods and formulates protective pouring measures to prevent steel from accumulating in the sprue. The castability of the casting machine is significantly improved. The liquid level is stable during the pouring process without steel accumulating. During the continuous casting process, the sealing protection of the long sprue and the tundish is guaranteed to prevent the secondary oxidation of the molten steel. The continuous casting nitrogen addition amount is required to be within 3ppm, and the rare earth alloy recovery rate reaches more than 45%.

7. The smelting control method of high-purity rare earth container steel Q345RRE according to claim 1 is characterized in that: All kinds of inclusions in the ingot are within level 1.0.

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