A method for producing low temperature Hi-B steel with enhanced AlN suppression capability

Abstract

The present invention relates to a method for producing low-temperature Hi-B steel with enhanced AlN suppression capability, comprising the steps of calculating the AlN solid solution temperature and the AlN solid solution amount at the heating temperature of the billet through a hot rolling process, wherein the billet heating temperature is 1199-1229°C, the heating time is 120-135min, the temperature of 1050-1150°C when the austenite phase content is the largest is selected as the normalizing heating temperature, the holding time is 2-4min, and then air cooling is started, and when the air cooling reaches 890±10°C, quenching is started in 95-100°C water for rapid cooling, and the infiltration The nitrogen process adjusts the actual nitrogen content infiltrated in the nitriding process to ensure the constancy of the total amount of innate and acquired AlN inhibitors. The nitriding temperature is 750-820°C, the nitriding time is determined according to the N content to be infiltrated, and the nitriding atmosphere is dry 75% H2+25% N2 plus 4-14% NH3. The present invention adjusts the N content infiltrated in the nitriding annealing process according to the Al and N contents in the low-temperature Hi-B steel composition and the ingot heating temperature to ensure the stability of the total amount of innate and acquired nitride inhibitors and the method of inhibition ability.

Description

Technical Field

[0001] The invention relates to the technical field of cold-rolled oriented silicon steel production, and in particular to a method for producing low-temperature Hi-B steel with enhanced AlN suppression capability. Background Art

[0002] Grain-oriented silicon steel is a special type of steel with high consumption and high investment. The future trend of producing grain-oriented silicon steel is to develop energy-saving and environmentally friendly processes. The heating temperature of the low-temperature slab heating process to produce Hi-B steel is 1150-1250℃, and the inhibitors used are "innate inhibitors + acquired inhibitors". Compared with the traditional high-temperature method, the low-temperature slab heating process has the advantages of low equipment performance requirements and low equipment maintenance frequency, so it can save energy, reduce costs and increase production.

[0003] The congenital inhibitor method is to add inhibitor-forming elements during smelting, heat to dissolve the coarse second-phase particles in the slab, and precipitate them as fine dispersed second-phase particles during subsequent hot rolling or normalizing, playing the role of inhibitor. The acquired inhibitor method generally adopts the nitriding process to form (Al, Si) N precipitates after decarburization annealing and before secondary recrystallization annealing. The method of nitriding treatment is not specified. In order to reduce the complexity of the production process, decarburization annealing and nitriding treatment can be carried out simultaneously for rapid nitriding treatment. In addition, nitriding treatment can also be carried out by adding CrN, MnN, etc. to the MgO separator.

[0004] As the main inhibitor of Hi-B steel, AlN can still have a strong inhibitory effect when annealing at higher temperatures. At the beginning of decarburization annealing and secondary recrystallization, AlN not only inhibits the growth of primary grains, but also promotes the development of secondary recrystallization grains and makes the grains grow preferentially, which has the effect of improving the secondary recrystallization texture. The regular shapes of AlN particles include rectangles and close-packed hexagons. Generally, AlN is divided into three categories according to size: A, B, and C. Class A has the smallest size, which is a precipitated particle less than 10nm, which is a fine needle-shaped; Class B has a size of 20-50nm fine disc-shaped precipitates, which plays a major inhibitory role; Class C has a size of 200-300nm coarse block-like aggregation state, which does not have an inhibitory effect.

[0005] The present invention provides a method for adjusting the N content infiltrated in the nitriding annealing process according to the Al and N contents in the low-temperature Hi-B steel composition and the heating temperature of the casting billet, so as to ensure the stability of the total amount of innate and acquired nitride inhibitors and the method for inhibiting the ability, thereby improving the grade of the magnetic properties of the low-temperature Hi-B steel finished product and ensuring the stability of the magnetic properties of the finished product. Summary of the invention

[0006] The present invention provides a method for producing low-temperature Hi-B steel with enhanced AlN inhibition capability, a method for adjusting the N content infiltrated in the nitriding annealing process according to the Al and N contents in the low-temperature Hi-B steel composition and the heating temperature of the ingot, and a method for ensuring the stability of the total amount of innate and acquired nitride inhibitors and the inhibition capability.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for producing low-temperature Hi-B steel with enhanced AlN suppression capability includes the following process steps: smelting, continuous casting, hot rolling, normalizing, cold rolling, decarburization annealing, nitriding, coating with MgO separator, high-temperature annealing and testing magnetic properties, wherein:

[0009] 1) Hot rolling:

[0010] Calculate the solid solution temperature of AlN and the solid solution amount of AlN at the heating temperature of the billet. The billet heating temperature is 1199-1229°C and the heating time is 120-135min.

[0011] 2) Normalization:

[0012] The temperature of 1050-1150℃ when the austenite content is the highest is selected as the normalizing heating temperature, and the holding time is 2-4 minutes. Then, air cooling is started. When the air cooling reaches 890±10℃, quenching is started in 95-100℃ water for rapid cooling.

[0013] 3) Nitriding:

[0014] Nitriding annealing and decarburization annealing are carried out on the same continuous furnace production line. The actual nitrogen content infiltrated in the nitriding process is adjusted according to the Al and N content in the composition and the innate AlN content that can be dissolved in the billet heating process to ensure the constant total amount of innate and acquired AlN inhibitors. The nitriding temperature is 750-820°C, and the nitriding time is determined according to the N content that needs to be infiltrated. The nitriding atmosphere is dry 75% H2+25% N2 plus 4-14% NH3.

[0015] Furthermore, the chemical composition of the low-temperature Hi-B steel is as follows by weight percentage: 0.035%≤C≤0.065%, 3.00%≤Si≤3.40%, 0.075%≤Mn≤0.095%, 0.001%≤S≤0.010%, 0.002%≤P≤0.015%, 0.022%≤Als≤0.032%, 0.004%≤N≤0.010%, 0.06%≤Cu≤0.16%, 0.05%≤Cr≤0.15%, and the rest is Fe and impurities.

[0016] Furthermore, the smelting process adopts converter smelting, RH refining, argon blowing throughout the process, and the end point control after the converter is: C≤0.056%; P≤0.010%; S≤0.028%; Mn≤0.035%.

[0017] Furthermore, the continuous casting process adopts near-liquidus pouring, the superheat is 10-30°C, a constant speed is maintained during the pouring process, the pulling speed of the ingot is controlled at 0.52-0.92m / min, electromagnetic stirring is added during the continuous casting process, the ingot is hot transported after continuous casting, and the slab thickness is 150-250mm.

[0018] Furthermore, during the hot rolling process, the thickness of the rough rolled billet is 46±4 mm, and the target thickness of the hot rolled plate is 1.60 to 2.60 mm.

[0019] Furthermore, the cold rolling process adopts a Sendzimir single-stand twenty-roller reversible rolling mill for 5 passes, and the thickness of the cold-rolled plate is 0.265-0.275 mm.

[0020] Furthermore, during the decarburization annealing process, the decarburization annealing temperature is 805-855°C, the time is 2.5-4.5 min, the protective atmosphere is wet 75% H2+25% N2, and the dew point temperature is 35-65°C.

[0021] Furthermore, in the process of applying the MgO separator, the MgO separator is applied by roller coating after nitriding annealing, and the MgO drying temperature is 300-660°C.

[0022] Furthermore, the high-temperature annealing process adopts a ring furnace for high-temperature annealing, firstly introducing 75% N2+25% H2 gas, heating to 600-720°C at a rate of 45-55°C / h, and keeping warm for 4-9 hours to discharge crystal water; then heating to 910-1100°C at a rate of 18-22°C / h for secondary recrystallization; heating to 980-1050°C to form a magnesium silicate bottom layer; heating to 1200°C and keeping warm in a pure H2 atmosphere for 6-12 hours to purify S and N in the matrix.

[0023] Furthermore, the magnetic property detection process is carried out after the high temperature annealing coil is hot stretched and flattened, and then coated with an insulating coating.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) Design the composition of low-temperature Hi-B steel, use nitriding method to increase the inhibitory ability of acquired inhibitors, reduce the heating temperature of the ingot, and greatly save energy;

[0026] 2) Adjust the nitriding amount according to the Al and N contents in the composition and the heating temperature of the ingot, so as to ensure that sufficient nitride inhibitors are formed after nitriding and the content of nitride inhibitors is constant;

[0027] 3) The present invention comprehensively considers the composition, the heating process of the ingot and the nitriding process, not only improving the magnetic property level of the low-temperature Hi-B steel product, but also ensuring the stability of the magnetic properties. DETAILED DESCRIPTION

[0028] The specific embodiments of the present invention are further described below:

[0029] The chemical components of the qualified low-temperature Hi-B steel of the present invention are as follows by weight percentage: 0.035%≤C≤0.065%, 3.00%≤Si≤3.40%, 0.075%≤Mn≤0.095%, 0.001%≤S≤0.010%, 0.002%≤P≤0.015%, 0.022%≤Als≤0.032%, 0.004%≤N≤0.010%, 0.06%≤Cu≤0.16%, 0.05%≤Cr≤0.15%, and the rest are Fe and impurities.

[0030] A method for producing low-temperature Hi-B steel with enhanced AlN suppression capability includes the following process:

[0031] 1) Smelting: converter smelting, RH refining, argon blowing throughout the process, converter end point control: C ≤ 0.056%; P ≤ 0.010%; S ≤ 0.028%; Mn ≤ 0.035%.

[0032] 2) Continuous casting: Near-liquidus casting is adopted, the superheat is 10-30℃, the casting speed is kept constant, the pulling speed of the ingot is controlled at 0.52-0.92m / min, electromagnetic stirring is used during the continuous casting process, the ingot is hot transported after continuous casting, and the slab thickness is 150-250mm.

[0033] 3) Hot rolling: Calculate the solid solution temperature of AlN and the solid solution amount of AlN at the heating temperature of the billet. The billet heating temperature is 1199-1229°C, the heating time is 120-135min, the rough rolling billet thickness is 46±4mm, and the target thickness of the hot rolled plate is 1.60-2.60mm.

[0034] 4) Normalizing: Select the temperature of 1050~1150℃ when the austenite content is the highest as the normalizing heating temperature, keep warm for 2~4min, then start air cooling, and start quenching in 100℃ water for rapid cooling after air cooling to 890±10℃.

[0035] 5) Cold rolling: The cold rolled plate is rolled 5 times using a Sendzimir single-stand twenty-roller reversible rolling mill, and the thickness of the cold rolled plate is 0.27 mm.

[0036] 6) Decarburization annealing: Decarburization annealing temperature is 805-855°C, time is 2.5-4.5min, protective atmosphere is wet 75% H2+25% N2, dew point temperature is 35-65°C.

[0037] 7) Nitriding: Nitriding annealing and decarburization annealing are carried out on the same continuous furnace production line. The actual nitrogen content in the nitriding process is adjusted according to the Al and N content in the composition and the innate AlN content that can be dissolved in the billet heating process to ensure the constant total amount of innate and acquired AlN inhibitors and achieve stable magnetic properties of the finished product;

[0038] If the total amount of nitrogen infiltrated is adjusted according to the N content in the composition: on the one hand, the nitride inhibitor content is insufficient, because AlN is not completely dissolved in the billet heating process, and the AlN that is not dissolved is large in size and cannot play an inhibitory role, so a part of the nitride inhibitor is lost; on the other hand, the total content of the N-oxide inhibitor is not equal, because in addition to N, the Al content also has a relatively large impact on the total AlN inhibitor content, causing the magnetic properties of the finished product to fluctuate with the Al content in the actual smelting composition;

[0039] The nitriding temperature is 750-820°C, and the nitriding time is determined according to the N content to be infiltrated. The nitriding atmosphere is dry 75% H2+25% N2 plus 4-14% NH3.

[0040] 8) Apply MgO isolation agent: After nitriding annealing, apply MgO isolation agent by roller coating. The MgO drying temperature is 300-660℃.

[0041] 9) High temperature annealing: A ring furnace is used for high temperature annealing. First, 75% N2 + 25% H2 gas is introduced, and the temperature is raised to 600-720°C at a rate of 45-55°C / h, and kept warm for 4-9 hours to discharge the crystal water; then the temperature is slowly raised to 910-1100°C at a rate of 18-22°C / h to cause secondary recrystallization; the temperature is raised to 980-1050°C to form a magnesium silicate bottom layer; after the temperature is raised to 1200°C, it is kept warm in a pure H2 atmosphere for 6-12 hours to purify the S and N in the matrix.

[0042] 10) Detection of magnetic properties: After high temperature annealed coils are hot stretched and flattened, they are coated with insulating coatings and the magnetic properties of the finished products are detected.

[0043] The density of AlN particles precipitated from low-temperature Hi-B steel during hot rolling and normalizing is low, which is not enough to inhibit the growth of primary recrystallized grains. Therefore, nitriding treatment must be carried out after decarburization. Nitriding treatment greatly increases the amount of AlN precipitation and strengthens the ability to inhibit the growth of primary grains. The amount and distribution of nitrogen infiltrated into the oriented silicon steel strip during the nitriding process directly determines the distribution, quantity and fraction of the nitride inhibitors formed, thereby affecting the evolution and orientation of the Goss texture grains during the subsequent high-temperature annealing process, and thus determines the final magnetic properties.

[0044] AlN is the main inhibitor of Hi-B steel. The acid-soluble aluminum (Als) is stipulated to be 0.022%~0.032%, and the nitrogen is 0.004%~0.010%. The acid-soluble aluminum = total aluminum content - aluminum content in Al3O2. The Als and N content in the smelting composition are combined to form AlN. The AlN dissolved at the heating temperature of the ingot is dispersed and precipitated during the hot rolling process. This part of AlN is the innate AlN that can play an inhibitory role. The actual composition has different Als and N contents, and the solid solution temperature of AlN is different. When the heating temperature is the same, the actual solid solution AlN is different. The content of innate AlN that can play an inhibitory role dispersed and precipitated during hot rolling is different. The acid-soluble aluminum content not only affects the innate AlN inhibitor, but also affects the nitriding amount, thereby affecting the acquired nitride inhibitor. If the nitriding process is adjusted only by detecting the total N content in the nitrided plate in actual production, the total amount of inhibitors will be different, resulting in differences in the magnetic properties of the finished plate. At the same time, adding the alloy element Cu to the composition expands the austenite phase region, and the transformation of austenite to ferrite occurs during finishing rolling, and a large amount of (Cu, Mn) 1.8S inhibitors are precipitated.

[0045] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified. Example

[0046] The chemical composition of a low temperature Hi-B steel is shown in Table 1 by weight percentage:

[0047] Table 1 Element content, wt%

[0048]

[0049] A method for producing low-temperature Hi-B steel with enhanced AlN suppression capability includes the following process:

[0050] 1) Smelting: converter smelting, RH refining, argon blowing throughout the process, converter end point control: C ≤ 0.052%; P ≤ 0.010%; S ≤ 0.022%; Mn ≤ 0.022%.

[0051] 2) Continuous casting: Near-liquidus casting is adopted. The liquidus temperature of the composition shown in Table 1 is calculated to be 1490°C, and the superheat is 25°C, so the pouring temperature is 1515±5°C. The pouring process maintains a constant speed, and the pulling speed of the billet is controlled to be 0.72m / min. Electromagnetic stirring is used during the continuous casting process. The billet is hot transported after continuous casting. The slab thickness is 210mm.

[0052] 3) Hot rolling:

[0053] (1) The heating temperature of the ingot is 1229°C. The solid solution temperature of AlN and the amount of AlN dissolved in the ingot at the heating temperature are calculated. The solid solution temperature of AlN with different Al and N contents, as well as the AlN that can be dissolved in the ingot at the heating temperature of 1229°C, are shown in Table 2:

[0054] Table 2 AlN solid solution temperature corresponding to Al and N content and N in AlN solid solution at 1229℃

[0055]

[0056] (2) The heating time is 128 min, the rough rolled slab thickness is 48 mm, and the target thickness of the hot rolled plate is 2.3 mm.

[0057] 4) Normalization: Select 1120℃, the temperature with the highest austenite content, as the normalization heating temperature. Keep warm for 3 minutes, then start air cooling. When the temperature reaches 890℃, start quenching in 100℃ water for rapid cooling.

[0058] 5) Cold rolling: The cold rolled plate is rolled 5 times using a Sendzimir single-stand twenty-roller reversible rolling mill, and the thickness of the cold rolled plate is 0.27 mm.

[0059] 6) Decarburization annealing: Decarburization annealing temperature is 825℃, time is 3min, protective atmosphere is wet 75%H2+25%N2, dew point temperature is 52℃.

[0060] 7) Nitriding: To ensure that the nitrogen content in the total amount of innate and acquired nitride inhibitors is 140ppm, the nitriding temperature is 810℃, and the nitriding atmosphere is dry 75%H2+25%N2 plus 10%NH3;

[0061] In the embodiment, the amount of N infiltrated is determined based on the Al and N contents in the composition and the AlN content dissolved at the heating temperature of the ingot. The total N content of the nitriding plate is not less than 140 ppm, and the N content of the nitride inhibitor acting as an inhibitor is 140 ppm, which ensures both the content of the nitride inhibitor and the constant inhibitory ability.

[0062] Comparative Example The amount of nitrogen infiltrated is determined based on the N content in the composition. The total N content after nitriding is the sum of the N content in the composition and the amount of N infiltrated. The total N content of the nitrided plate is 140ppm.

[0063] The Al and N contents in the actual composition, the nitriding time of the embodiment and the comparative example, and the N content required to be infiltrated are shown in Table 3:

[0064] Table 3 Composition, N content and nitriding time

[0065]

[0066] 8) Apply MgO isolation agent: After nitriding annealing, apply MgO isolation agent by roller coating, and the MgO drying temperature is 500℃.

[0067] 9) High temperature annealing: A ring furnace is used for high temperature annealing. First, 75% N2 + 25% H2 gas is introduced, and the temperature is raised to 680°C at a rate of 50°C / h, and kept warm for 8 hours to discharge the crystal water; then the temperature is slowly raised to 940°C at a rate of 18°C / h for secondary recrystallization; the temperature is raised to 1000°C to form a magnesium silicate bottom layer; after the temperature is raised to 1200°C, it is kept warm in a pure H2 atmosphere for 10 hours to purify the S and N in the matrix.

[0068] 10) Testing of magnetic properties: After the high temperature annealed coil is hot stretched and flattened, an insulating coating is applied and the magnetic properties of the finished product are tested; the magnetic properties of the finished products of the embodiment and the comparative example are shown in Table 4.

[0069] Table 4 Magnetic properties of finished products of embodiments and comparative examples

[0070]

[0071] From the comparison results in Table 4, it can be seen that by using the method of the present invention to control the infiltrated N content, the magnetic properties of the finished product of 27-specification high magnetic induction oriented silicon steel can be stably controlled at the level of 110 grades. However, when the infiltrated N content is controlled based on the N content in the composition, it is difficult to ensure the magnetic properties of the finished product to be 110 grades, and the magnetic properties fluctuate.

Claims

1. A method for producing low temperature Hi-B steel with enhanced AlN suppression capability, characterized in that: The process includes: smelting, continuous casting, hot rolling, normalizing, cold rolling, decarburization annealing, nitriding, MgO isolation agent coating, high temperature annealing and magnetic property testing, among which: 1) Hot rolling: Calculate the solid solution temperature of AlN and the solid solution amount of AlN at the heating temperature of the billet. The billet heating temperature is 1199-1229°C and the heating time is 120-135min. 2) Normalization: The temperature of 1050-1120℃ when the austenite content is the highest is selected as the normalizing heating temperature, and the holding time is 2-4 minutes. Then, air cooling is started. When the air cooling reaches 890±10℃, quenching is started in 95-100℃ water for rapid cooling. 3) Nitriding: Nitriding annealing and decarburization annealing are carried out on the same continuous furnace production line. The actual nitrogen content infiltrated in the nitriding process is adjusted according to the Al and N content in the composition and the innate AlN content that can be dissolved in the billet heating process to ensure the constant total amount of innate and acquired AlN inhibitors. The nitriding temperature is 750-820°C, and the nitriding time is determined according to the N content that needs to be infiltrated. The nitriding atmosphere is dry 75% H2+25% N2 plus 4-14% NH3.

2. The method for producing low temperature Hi-B steel with enhanced AlN suppression capability according to claim 1, characterized in that: The chemical composition of the low-temperature Hi-B steel is as follows by weight percentage: 0.035%≤C≤0.065%, 3.00%≤Si≤3.40%, 0.075%≤Mn≤0.095%, 0.001%≤S≤0.010%, 0.002%≤P≤0.015%, 0.022%≤Als≤0.032%, 0.004%≤N≤0.010%, 0.06%≤Cu≤0.16%, 0.05%≤Cr≤0.15%, and the rest is Fe and impurities.

3. The method for producing low temperature Hi-B steel with enhanced AlN suppression capability according to claim 1, characterized in that: The smelting process adopts converter smelting, RH refining, argon blowing throughout the process, and the end point control after the converter is: C≤0.056%; P≤0.010%; S≤0.028%; Mn≤0.035%.

4. The method for producing low temperature Hi-B steel with enhanced AlN suppression capability according to claim 1, characterized in that: The continuous casting process adopts near-liquidus pouring, the superheat is 10-30°C, a constant speed is maintained during the pouring process, the pulling speed of the ingot is controlled at 0.52-0.92m / min, electromagnetic stirring is added during the continuous casting process, the ingot is hot transported after continuous casting, and the slab thickness is 150-250mm.

5. The method for producing low temperature Hi-B steel with enhanced AlN suppression capability according to claim 1, characterized in that: During the hot rolling process, the thickness of the rough rolled billet is 46±4 mm, and the target thickness of the hot rolled plate is 1.60-2.60 mm.

6. The method for producing low temperature Hi-B steel with enhanced AlN suppression capability according to claim 1, characterized in that: The cold rolling process adopts a Sendzimir single-stand twenty-roller reversible rolling mill for five rolling passes, and the thickness of the cold-rolled plate is 0.265-0.275 mm.

7. The method for producing low temperature Hi-B steel with enhanced AlN suppression capability according to claim 1, characterized in that: During the decarburization annealing process, the decarburization annealing temperature is 805-855°C, the time is 2.5-4.5 minutes, the protective atmosphere is wet 75% H2+25% N2, and the dew point temperature is 35-65°C.

8. The method for producing low temperature Hi-B steel with enhanced AlN suppression capability according to claim 1, characterized in that: The MgO isolating agent coating process comprises the following steps: coating the MgO isolating agent by roller coating after nitriding annealing, and the MgO drying temperature is 300-660°C.

9. The method for producing low temperature Hi-B steel with enhanced AlN suppression capability according to claim 1, characterized in that: The high-temperature annealing process adopts a ring furnace for high-temperature annealing, firstly introducing 75% N2+25% H2 gas, heating to 600-720°C at a rate of 45-55°C / h, and keeping warm for 4-9 hours to discharge crystal water; then heating to 910-1100°C at a rate of 18-22°C / h to cause secondary recrystallization; heating to 980-1050°C to form a magnesium silicate bottom layer; heating to 1200°C and keeping warm in a pure H2 atmosphere for 6-12 hours to purify S and N in the matrix.

10. The method for producing low temperature Hi-B steel with enhanced AlN suppression capability according to claim 1, characterized in that: The magnetic property detection process is carried out after the high temperature annealing coil is hot stretched and flattened, and then coated with an insulating coating.

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