Low-coercivity hot-rolled pure iron and preparation method thereof

Abstract

The low-coercivity hot-rolled pure iron comprises the following components in percentage by mass: less than or equal to 0.005% of C, less than or equal to 0.01% of Si, more than or equal to 0.05% and less than or equal to 0.08% of Mn, 0.45-0.75% of Al, 0.035-0.045% of N, less than or equal to 0.015% of P, less than or equal to 0.005% of S, less than or equal to 0.005% of O, less than or equal to 0.03% of Cr, less than or equal to 0.02% of Ni, less than or equal to 0.02% of Cu and the balance of Fe and inevitable impurities. Wherein the mass ratio of Al to N is (8-14): 1, and the mass ratio of Mn to S is greater than or equal to 9. The coercive force of the produced low-coercive-force hot-rolled pure iron reaches the 20A / m level, and the low-coercive-force hot-rolled pure iron has the advantages of low coercive force, high residual magnetic flux density, excellent yield strength and tensile strength, high percentage elongation after fracture and excellent processability.

Description

Technical Field

[0001] The present invention relates to the technical fields of materials and metallurgy, and more specifically, to a hot-rolled pure iron with low coercivity and a preparation method thereof. Background Art

[0002] Pure iron is an excellent soft magnetic material, which has the advantages of low cost and easy processing, and is widely used in the electrical appliances, instruments and national defense high-tech industries to manufacture electromagnetic components, electromagnet cores, etc. For soft magnetic materials, they have the characteristics of low coercivity, high magnetic induction intensity and high magnetic permeability. Under the action of an external magnetic field, soft magnetic materials are easily magnetized and can quickly change their internal magnetization state with the change of the external magnetic field. When the external magnetic field is removed, the magnetism of the soft magnetic material will also quickly disappear, showing good demagnetization performance.

[0003] After annealing, the general coercivity value Hc of the existing hot-rolled pure iron using the continuous casting process is greater than 30 A / m, which cannot meet some use scenarios with higher requirements. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects existing in the prior art, and provide a hot-rolled pure iron with low coercivity and a preparation method thereof. Through the production process of "hot metal pretreatment + converter smelting + LF refining + RH vacuum refining + continuous casting + hot rolling + magnetic annealing" combined with alloy design, the coercivity of the produced hot-rolled pure iron with low coercivity reaches the 20 A / m level, and the magnetic induction intensities B 200 、B 500 、B 1000 ,B 2500 ,B 5000 ,B 10000 (magnetic induction intensity at 200 A / m, magnetic induction intensity at 500 A / m, magnetic induction intensity at 1000 A / m, magnetic induction intensity at 2500 A / m, magnetic induction intensity at 5000 A / m, magnetic induction intensity at 10000 A / m) are respectively ≥ 1.21 T, 1.42, 1.51, 1.64, 1.73, 1.81 T, the maximum magnetic permeability is not less than 0.02 H / m, the yield strength ≥ 110 MPa, the tensile strength ≥ 250 MPa, the elongation at break ≥ 50%, having low coercivity, high residual magnetic induction intensity, excellent yield strength and tensile strength, relatively high elongation after fracture, and excellent processing performance.

[0005] To achieve the above purpose, the technical solution of the present invention is as follows:

[0006] A low coercivity hot-rolled pure iron, comprising components in the following mass percentages: C ≤ 0.005%, Si ≤ 0.01%, 0.05% ≤ Mn ≤ 0.08%, Al: 0.45% - 0.75%, N: 0.035% - 0.045%, P ≤ 0.015%, S ≤ 0.005%, O ≤ 0.005%, Cr ≤ 0.03%, Ni ≤ 0.02%, Cu ≤ 0.02%, the balance being Fe and unavoidable impurities; wherein, the mass ratio of Al to N is (8 - 14):1, and the mass ratio of Mn to S ≥ 9.

[0007] Optionally, the coercivity of the low coercivity hot-rolled pure iron is 20 A / m - 30 A / m, the magnetic induction intensity is ≥ 1.21 T at 200 A / m, ≥ 1.42 T at 500 A / m, ≥ 1.51 T at 1000 A / m, ≥ 1.64 T at 2500 A / m, ≥ 1.73 T at 5000 A / m, ≥ 1.81 T at 10000 A / m, the maximum magnetic permeability ≥ 0.02 H / m, the yield strength ≥ 110 MPa, the tensile strength ≥ 250 MPa, and the elongation rate ≥ 50%.

[0008] Optionally, the metallographic structure of the low coercivity hot-rolled pure iron is ferrite; the thickness of the low coercivity hot-rolled pure iron is 1.2 mm - 12.7 mm.

[0009] The present invention also discloses a preparation method of the low coercivity hot-rolled pure iron as described above, comprising the following steps:

[0010] Hot metal pretreatment, converter smelting, LF refining, RH vacuum refining, continuous casting, hot rolling, and magnetic annealing;

[0011] In the converter smelting, the furnace charge includes hot metal after the hot metal pretreatment and low alloy content scrap steel, and the proportion of scrap steel is 10% - 20%;

[0012] In the LF refining, the molten steel discharged from the converter smelting enters the LF furnace for refining treatment;

[0013] In the continuous casting, the molten steel subjected to the RH vacuum refining treatment is continuously cast to obtain a continuous casting billet;

[0014] In the hot rolling, the continuous casting billet is rolled to obtain the hot-rolled pure iron;

[0015] In the magnetic annealing, the hot-rolled pure iron is subjected to magnetic annealing in an atmosphere of nitrogen or hydrogen. It is heated in the furnace at a heating rate of 50°C / h to 100°C / h to 910°C to 950°C, and held for 80 min to 150 min. Subsequently, it is slowly cooled to room temperature at a rate of 30°C / h to 50°C / h and taken out of the furnace. The average grain size after magnetic annealing is 150 μm to 200 μm, and the low coercivity hot-rolled pure iron is obtained.

[0016] Optionally, in the hot rolling, the continuous casting billet is heated to 1250°C to 1275°C and then taken out of the furnace for rolling. After descaling with high-pressure water, rough rolling is carried out, and the rough rolling temperature is 1100°C to 1150°C. After descaling again, finish rolling is carried out, and the finish rolling temperature is 1000°C to 1050°C. It is cooled to 790°C to 810°C by laminar cooling and then coiled, and then slowly cooled. The slow cooling temperature is 600°C to 800°C, and the slow cooling time is 10 h to 20 h.

[0017] Optionally, in the continuous casting, the drawing speed is 1.2 m / min to 1.4 m / min, the superheat is 25°C to 30°C, the dynamic soft reduction and electromagnetic stirring processes are put into use. The electromagnetic stirring current is 350 A to 450 A, and the frequency is 2.2 Hz to 2.9 Hz.

[0018] Optionally, in the hot metal pretreatment, the hot metal is desiliconized, and the silicon in the hot metal is removed by the desiliconizing agent to ≤0.16%, and the slag is removed cleanly; desulfurization: magnesium powder and lime powder are added to make S in the hot metal ≤0.03%; the molten bath is stirred to remove P by FeO slag to make P ≤0.03%.

[0019] Optionally, in the LF refining, the molten steel is heated in the LF furnace after leaving the station. To promote the reaction of the steel slag, lime and bauxite are heated in batches during the period when the slag maintains good fluidity. During the tapping process, 3.5 Kg / t to 4.0 Kg / t of steel of small-grained quicklime is added to the molten steel, and the tapping temperature of the molten steel is controlled to ensure the temperature of the RH process is 1660°C to 1670°C.

[0020] Optionally, in the RH vacuum refining, the RH deep vacuum degassing is ensured to be >18 min, and calcium treatment is carried out with pure calcium wire. After wire feeding, the soft blowing time of the molten steel is >12 min.

[0021] Implementing the embodiments of the present invention will have the following beneficial effects:

[0022] (1) By controlling the contents of elements C, Si, Mn, P, S, Al and N, and cooperating with the production process of "hot metal pretreatment + converter smelting + LF refining + RH vacuum refining + continuous casting + hot rolling + magnetic annealing", the average grain size after annealing is 150 to 200 μm, and coarse AlN precipitates are formed. The magnetic properties are improved by using AlN inclusions. The coercivity of the produced hot-rolled pure iron reaches the 20 A / m level, B 200 、B500 , B 1000 , B 2500 , B 5000 , B 10000 (Magnetic induction intensity at 200 A / m, magnetic induction intensity at 500 A / m, magnetic induction intensity at 1000 A / m, magnetic induction intensity at 2500 A / m, magnetic induction intensity at 5000 A / m, magnetic induction intensity at 10000 A / m) The magnetic induction intensity is respectively ≥ 1.21 T, 1.42, 1.51, 1.4, 1.73, 1.81 T, the maximum magnetic permeability is not less than 0.02 H / m, the yield strength is ≥ 110 MPa, the tensile strength is ≥ 250 MPa, the elongation is ≥ 50%, having low coercivity, high residual magnetic induction intensity, excellent yield strength and tensile strength, higher elongation after fracture, excellent processing performance, significantly improving the market competitiveness of the product.

[0023] (2) The process of the present invention is based on conventional production equipment, having the characteristics of strong process applicability and controllability, and no additional investment is required. Description of the Drawings

[0024] Figure 1 It is the metallographic structure diagram of the low coercivity hot-rolled pure iron of Example 1 of the present invention. Detailed Embodiments

[0025] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0026] I. Chemical Composition and Mechanical Properties

[0027] The present invention discloses a low coercivity hot-rolled pure iron, including the following components in mass percentage: C ≤ 0.005%, Si ≤ 0.01%, 0.05% ≤ Mn ≤ 0.08%, Al: 0.45% - 0.75%, N: 0.035% - 0.045%, P ≤ 0.015%, S ≤ 0.005%, O ≤ 0.005%, Cr ≤ 0.03%, Ni ≤ 0.02%, Cu ≤ 0.02%, and the balance is Fe and unavoidable impurities; wherein, the mass ratio of Al to N is (8 - 14):1, and the mass ratio of Mn to S is ≥ 9.

[0028] Specifically, the action mechanism of each alloy component in the pure iron of the present invention is as follows:

[0029] C is an interstitial atom solid solution in steel. C has a relatively high solid solubility in steel at high temperatures. As the temperature decreases, C atoms precipitate, and the non-magnetic phase formed after precipitation reduces the magnetic properties, and the lower the content, the better. Therefore, in this application, C ≤ 0.005%.

[0030] Cr, Ni, Cu, and O form compounds and non-magnetic phases in steel, which hinder the movement of magnetic domain walls and reduce magnetic properties. Therefore, it is necessary to control O ≤ 0.005%, Cr ≤ 0.03, Ni ≤ 0.02, and Cu ≤ 0.02.

[0031] Si exists in pure iron in the form of a solid solution. Although Si has a certain deoxidizing effect, can inhibit eddy current losses caused by magnetic field changes by increasing resistance, and also has a certain effect on reducing coercivity, too high content of S will cause a decrease in saturation magnetic induction B. Therefore, control Si ≤ 0.01%.

[0032] Mn and S elements: The Mn element in hot-rolled pure iron plays a certain role in solid solution strengthening, but the content should not be too high, as too high content will reduce magnetic properties; the S element forms FeS, resulting in hot brittleness, reducing the ductility and toughness of steel, hindering the movement of magnetic domain walls and reducing magnetic properties, and increasing the crack risk during forging, rolling, and welding of steel. Therefore, in this application, 0.05% ≤ Mn ≤ 0.08% and S ≤ 0.005% are controlled; further control the mass ratio of Mn and S ≥ 9, aiming to add an appropriate amount of Mn to eliminate the harmful effects of S in steel and coarsen MnS, making it easier for grains to grow.

[0033] The Al element in hot-rolled pure iron can narrow the austenite region, increase the phase transformation point between austenite and ferrite, reduce the residence time in the austenite region during hot rolling, and make pure iron enter the ferrite region at a higher temperature during the cooling process, promoting grain growth to obtain larger ferrite grains. Therefore, the Al content in this invention is controlled at 0.45% - 0.75%.

[0034] The N element in hot-rolled pure iron can improve the strength of steel materials and improve the toughness and welding performance of steel. However, too high N element makes the pure iron steel plate more brittle and prone to cracking. Therefore, the N element content is controlled at 0.035% - 0.045%.

[0035] This invention further sets the mass ratio of Al and N to be (8 - 14):1, preferably (11 - 14):1. Controlling the contents of N element and Al element can form coarse AlN inclusions, which precipitate concentratedly at grain boundaries, reduce the inhibition of crystal growth, and reduce the hindrance to the irreversible movement of magnetic domain walls, reduce coercivity, and increase magnetic induction intensity and permeability.

[0036] In a specific embodiment, the coercivity of the low-coercivity hot-rolled pure iron of this invention is 20 A / m - 30 A / m, B 200 、B 500 、B 1000 ,B 2500 ,B 5000 ,B 10000(Magnetic induction intensity at 200 A / m, magnetic induction intensity at 500 A / m, magnetic induction intensity at 1000 A / m, magnetic induction intensity at 2500 A / m, magnetic induction intensity at 5000 A / m, magnetic induction intensity at 10000 A / m) The magnetic induction intensity is respectively ≥ 1.21 T, 1.42, 1.51, 1.4, 1.73, 1.81 T, the maximum magnetic permeability is not less than 0.02 H / m, the yield strength is ≥ 110 MPa, the tensile strength is ≥ 250 MPa, and the elongation is ≥ 50%.

[0037] In a specific embodiment, the metallographic structure of the low coercivity hot-rolled pure iron is coarse ferrite.

[0038] In a specific embodiment, the thickness of the low coercivity hot-rolled pure iron is 1.2 mm to 12.7 mm.

[0039] II. Production process technology

[0040] The present invention also discloses a preparation method of low coercivity hot-rolled pure iron according to any embodiment of the present invention, including the following steps: hot metal pretreatment, converter smelting, LF refining, RH vacuum refining, continuous casting, hot rolling and magnetic annealing.

[0041] Furthermore, it specifically includes the following steps:

[0042] S1. In hot metal pretreatment, desiliconize the hot metal, and use the desiliconizing agent to remove the silicon in the hot metal ≤ 0.16%, and skim the slag clean; desulfurize: add magnesium powder and lime powder to make the sulfur in the hot metal ≤ 0.03%; use FeO slag for phosphorus removal by molten pool stirring to make the phosphorus ≤ 0.03%.

[0043] S2. In converter smelting, the furnace charge includes the hot metal after hot metal pretreatment and scrap steel with a low alloy content, and the proportion of scrap steel is 10% - 20%.

[0044] S3. In LF refining, the molten steel after converter smelting is put into the LF furnace for refining treatment.

[0045] In a specific embodiment, in LF refining, after the molten steel leaves the station, it is heated in the LF furnace. To promote the reaction between the molten steel and the slag, lime and bauxite are heated in batches during the period when the slag maintains good fluidity. During the tapping process, 3.5 Kg / t - 4.0 Kg / t of the molten steel of small-grained white lime is added to the molten steel, and the tapping temperature of the molten steel is controlled to ensure the temperature in the RH process is 1660 °C - 1670 °C.

[0046] S4. In RH vacuum refining, the molten steel after LF refining is put into RH vacuum refining treatment.

[0047] In a specific embodiment, in RH vacuum refining, the RH deep vacuum degassing is guaranteed to be > 18 min, and calcium treatment is carried out using pure calcium wire, and the soft blowing time of the molten steel after wire feeding is > 12 min.

[0048] S5. In continuous casting, the molten steel treated by RH vacuum refining is subjected to continuous casting to obtain a continuous casting billet.

[0049] In a specific embodiment, during continuous casting, the casting speed is 1.2 m / min to 1.4 m / min, the superheat is 25°C to 30°C, the dynamic soft reduction and electromagnetic stirring processes are applied, the electromagnetic stirring current is 350 A to 450 A, and the frequency is 2.2 Hz to 2.9 Hz.

[0050] S6. In hot rolling, the continuous casting billet is rolled to obtain hot-rolled pure iron.

[0051] In a specific embodiment, during hot rolling, the continuous casting billet is heated to 1250°C to 1275°C and then taken out of the furnace for rolling. After descaling with high-pressure water, rough rolling is carried out, and the rough rolling temperature is 1100°C to 1150°C. After descaling again, finish rolling is carried out, and the finish rolling temperature is 1000°C to 1050°C. It is cooled to 790°C to 810°C by laminar cooling and then coiled, and then slowly cooled. The slow cooling temperature is 600°C to 800°C, and the slow cooling time is 10 h to 20 h.

[0052] S7. In magnetic annealing, the hot-rolled pure iron is subjected to magnetic annealing in an atmosphere of nitrogen or hydrogen. It is heated in the furnace at a heating rate of 50°C / h to 100°C / h to 910°C to 950°C, preferably 935°C to 950°C, and held for 80 min to 150 min. Then it is slowly cooled to room temperature at a rate of 30°C / h to 50°C / h and taken out of the furnace. The average grain size after magnetic annealing is 150 μm to 200 μm, and low coercivity hot-rolled pure iron is obtained.

[0053] The following are specific embodiments

[0054] Example 1

[0055] The low coercivity hot-rolled pure iron of this example comprises the following components by mass percentage: C: 0.0043%, Si < 0.01%, Mn: 0.05%, Al: 0.52%, N: 0.039%, P < 0.005%, S: 0.0052%, O: 0.047%, Cr: 0.016%, Ni: 0.01%, Cu: 0.0067%, and the balance is Fe and unavoidable impurities.

[0056] The preparation method of the low coercivity hot-rolled pure iron of this example comprises the following steps:

[0057] S1. In hot metal pretreatment, desiliconization of hot metal is carried out. The silicon in the hot metal is removed by the desiliconizing agent to ≤0.16%, and the slag is removed cleanly; desulfurization: magnesium powder and lime powder are added to make S in the hot metal ≤0.03%; the molten bath is stirred to remove P by FeO slag to make P ≤0.03%.

[0058] S2. During converter smelting, the furnace charge includes hot metal after hot metal pretreatment and scrap steel with a low alloy content, and the proportion of scrap steel is 15%.

[0059] S3. During LF refining, after the molten steel leaves the station, it is heated up in the LF furnace. To promote the reaction between the molten steel and the slag, lime and bauxite are heated in batches during the period when the slag maintains good fluidity. During the tapping process, 3.75 Kg / t of molten steel of small-grained quicklime is added to the molten steel, and the tapping temperature of the molten steel is controlled to ensure the temperature of the RH process is 1665 °C.

[0060] S4. During RH vacuum refining, the RH deep vacuum degassing is guaranteed to be > 18 min, and calcium treatment is carried out using pure calcium wire. After wire feeding, the soft blowing time of the molten steel is > 12 min.

[0061] S5. During continuous casting, the casting speed is 1.3 m / min, the superheat is 25 °C - 30 °C, the dynamic soft reduction and electromagnetic stirring processes are put into use. The electromagnetic stirring current is 350 A - 450 A, and the frequency is 2.2 Hz - 2.9 Hz.

[0062] S6. During hot rolling, the continuous casting billet is heated to 1262 °C and then discharged from the furnace for rolling. After descaling with high-pressure water, rough rolling is carried out, and the rough rolling temperature is 1137 °C. After descaling again, finish rolling is carried out, and the finish rolling temperature is 1032 °C. It is cooled to 801 °C by laminar cooling and then coiled, and then slowly cooled. The slow cooling temperature is 700 °C, and the slow cooling time is 15 h.

[0063] S7. During magnetic annealing, the hot-rolled pure iron is subjected to magnetic annealing in an atmosphere of nitrogen or hydrogen. It is heated to 940 °C at a heating rate of 80 °C / h along with the furnace and held for 100 min, and then slowly cooled to room temperature at a rate of 30 °C / h and discharged from the furnace. The average grain size after magnetic annealing is 150 μm - 200 μm, and low coercivity hot-rolled pure iron is obtained. As Figure 1 shown, the metallographic structure is ferrite.

[0064] Examples 2 - 12

[0065] Compared with Example 1, Examples 2 - 12 are different in that: the chemical compositions of the steel grades and some process parameters in Examples 2 - 12 are different, and the rest are the same. Details are not elaborated here. Specifically, see Table 1 and Table 2. The process parameters not mentioned in Table 2 are the same as those in Example 1. The product performances of the examples are shown in Table 3.

[0066] Table 1 Chemical Compositions (%) of Examples 1 - 12

[0067] Serial number C Si Mn P S N Al O Cr Ni Cu 1 0.0043 ＜0.01 0.05 ＜0.005 0.0032 0.039 0.52 0.0047 0.016 0.01 0.0067 2 0.0029 ＜0.01 0.08 ＜0.005 0.0042 0.040 0.53 0.0048 0.019 0.012 0.0089 3 0.0040 ＜0.01 0.07 ＜0.005 0.0033 0.044 0.58 0.0046 0.014 0.013 0.0076 4 0.0038 ＜0.01 0.08 ＜0.005 0.0040 0.036 0.47 0.0039 0.018 0.014 0.0063 5 0.0031 ＜0.01 0.06 ＜0.005 0.0041 0.039 0.51 0.0044 0.014 0.016 0.0067 6 0.0035 ＜0.01 0.07 ＜0.005 0.0031 0.036 0.48 0.0044 0.015 0.009 0.0081 7 0.0047 ＜0.01 0.06 ＜0.005 0.0043 0.035 0.49 0.0045 0.016 0.008 0.0088 8 0.0043 ＜0.01 0.07 ＜0.005 0.0041 0.040 0.55 0.0038 0.019 0.009 0.0062 9 0.0033 ＜0.01 0.05 ＜0.005 0.0039 0.042 0.54 0.0047 0.014 0.014 0.0059 10 0.0035 ＜0.01 0.05 ＜0.005 0.0041 0.045 0.59 0.0049 0.018 0.012 0.0071 11 0.0037 ＜0.01 0.06 ＜0.005 0.0042 0.045 0.61 0.0042 0.017 0.013 0.0074 12 0.0041 ＜0.01 0.06 ＜0.005 0.0037 0.038 0.50 0.0043 0.018 0.009 0.0056

[0068] Table 2 Process Parameters of Examples 1 - 12

[0069]

[0070] Table 3 Product Performance of Examples 1-12

[0071]

[0072]

[0073] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of this invention patent shall be subject to the appended claims.

Claims

1. A low coercivity hot-rolled pure iron, characterized in that, Comprising components with the following mass percentages: C ≤ 0.005%, Si ≤ 0.01%, 0.05% ≤ Mn ≤ 0.08%, Al: 0.45% - 0.75%, N: 0.035% - 0.045%, P ≤ 0.015%, S ≤ 0.005%, O ≤ 0.005%, Cr ≤ 0.03%, Ni ≤ 0.02%, Cu ≤ 0.02%, the balance being Fe and unavoidable impurities; wherein, the mass ratio of Al to N is (8 - 14):1, and the mass ratio of Mn to S ≥ 9.

2. The low coercivity hot-rolled pure iron according to claim 1, characterized in that, The coercivity of the low coercivity hot-rolled pure iron is 20 A / m - 30 A / m, the magnetic induction intensity is ≥ 1.21 T at 200 A / m, ≥ 1.42 T at 500 A / m, ≥ 1.51 T at 1000 A / m, ≥ 1.64 T at 2500 A / m, ≥ 1.73 T at 5000 A / m, ≥ 1.81 T at 10000 A / m, the maximum magnetic permeability ≥ 0.02 H / m, the yield strength ≥ 110 MPa, the tensile strength ≥ 250 MPa, and the elongation rate ≥ 50%.

3. The low coercivity hot-rolled pure iron according to claim 1, characterized in that, The metallographic structure of the low coercivity hot-rolled pure iron is ferrite; The thickness of the low coercivity hot-rolled pure iron is 1.2 mm - 12.7 mm.

4. A method for preparing a low coercivity hot-rolled pure iron as described in any one of claims 1-3, characterized in that, Including the following steps: Hot metal pretreatment, converter smelting, LF refining, RH vacuum refining, continuous casting, hot rolling, and magnetic annealing; In the converter smelting, the furnace charge includes hot metal after the hot metal pretreatment and scrap steel with a low alloy content, and the proportion of scrap steel is 10% - 20%; In the LF refining, the molten steel discharged from the converter smelting enters the LF furnace for refining treatment; In the continuous casting, the molten steel subjected to the RH vacuum refining treatment is continuously cast to obtain a continuous casting billet; In the hot rolling, the continuous casting billet is rolled to obtain hot-rolled pure iron; In the magnetic annealing, the hot-rolled pure iron is magnetically annealed in an atmosphere of nitrogen or hydrogen, heated in the furnace at a heating rate of 50 °C / h - 100 °C / h to 910 °C - 950 °C, and held for 80 min - 150 min, and then slowly cooled to room temperature at a rate of 30 °C / h - 50 °C / h and taken out of the furnace. The average grain size after magnetic annealing is 150 μm - 200 μm to obtain the low coercivity hot-rolled pure iron.

5. The preparation method according to claim 4, characterized in that, In the hot rolling, the continuous casting billet is heated to 1250 °C - 1275 °C and then taken out of the furnace for rolling. After descaling with high-pressure water, rough rolling is carried out, and the rough rolling temperature is 1100 °C - 1150 °C. After descaling again, finish rolling is carried out, and the finish rolling temperature is 1000 °C - 1050 °C. It is cooled to 790 °C - 810 °C by laminar cooling and coiled, and then slowly cooled. The slow cooling temperature is 600 °C - 800 °C, and the slow cooling time is 10 h - 20 h.

6. The preparation method according to claim 4, wherein In the continuous casting, the casting speed is 1.2 m / min - 1.4 m / min, the superheat is 25 °C - 30 °C, the dynamic soft reduction and electromagnetic stirring processes are applied, the electromagnetic stirring current is 350 A - 450 A, and the frequency is 2.2 Hz - 2.9 Hz.

7. The preparation method according to claim 4, characterized in that, In the hot metal pretreatment, desiliconization of the hot metal is carried out, and the silicon in the hot metal is removed by the desiliconizing agent to ≤0.16%, and the slag is removed cleanly; desulfurization: magnesium powder and lime powder are added to make S in the hot metal ≤0.03%; the molten bath is stirred to remove P with FeO slag to make P ≤0.03%.

8. The preparation method according to claim 4, characterized in that, In the LF refining, the molten steel is heated up in the LF furnace after leaving the station. To promote the reaction of the molten steel and slag, lime and bauxite are heated in batches during the period when the slag maintains good fluidity. During the tapping process, small-grained quicklime of 3.5 Kg / t - 4.0 Kg / t of steel is added to the molten steel, and the tapping temperature of the molten steel is controlled to ensure the temperature in the RH process is 1660°C - 1670°C.

9. The preparation method according to claim 4, characterized in that, In the RH vacuum refining, the RH deep vacuum degassing is guaranteed for >18 min, and calcium treatment is carried out with pure calcium wire. After wire feeding, the soft blowing time of the molten steel is >12 min.

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