Low coercivity wire and method for manufacturing the same

Abstract

The present invention discloses a low remanence magnetic wire containing Fe and inevitable impurities, and further contains each chemical element represented by the following mass percentage contents: C: 0 < C ≤ 0.003%, Si: Si ≤ 0.01%, Mn: 0.1 - 0.2%, Al: 0.30 - 0.45%, O: 0.0015 - 0.0035%, N: 0.001 - 0.003%, Ca: 0.0005 - 0.0015%. Correspondingly, the present invention also discloses a manufacturing method of the above wire. The present invention can obtain a wire with low remanence magnetic force through reasonable chemical composition design and tissue control.

Description

Technical Field

[0001] The present invention relates to steel materials and their manufacturing methods, and particularly to wire rods and their manufacturing methods.

Background Art

[0002] Soft magnetic materials refer to materials in which magnetization mainly occurs when the magnetic field strength H is 1000 A / m or less, and they have low coercive force and high magnetic permeability. Soft magnetic materials are easy to magnetize and demagnetize. Electromagnetic pure iron is a typical kind of soft magnetic material. As the industries such as electronics and telecommunications develop rapidly, the application fields of electromagnetic pure iron continue to expand and the demand is increasing rapidly.

[0003] The main magnetic properties of electromagnetic pure iron include coercive force, coercive force aging increase value, maximum magnetic permeability, maximum magnetic induction intensity, etc. Among them, the magnitude of the maximum magnetic induction intensity depends on the composition of the material, and the corresponding physical state is a state where the magnetization vectors inside the material are arranged neatly. This is the number of magnetic flux lines passing through the unit cross-sectional area of the iron core, also called magnetic flux density, which represents the magnetization ability of the material, and the unit is T. Coercive force is a quantity indicating the ease of magnetization of the material and depends on the composition and defects (impurities, stress, etc.) of the material. Magnetic permeability is the ratio of B to H corresponding to any point on the magnetic hysteresis loop and is closely related to the material structure and the operating state of the device. Coercive force means that after a magnetic material is saturatedly magnetized, even if the external magnetic field returns to zero, its magnetic induction intensity B does not return to zero, and the magnetic induction intensity can only be returned to zero by applying a magnetic field of a certain magnitude in the opposite direction to the original magnetization field. In this case, this magnetic field is called the retaining magnetic field or coercive force. The smaller the coercive force of a soft magnetic material, the easier it is to magnetize and demagnetize. In actual applications, it can more quickly realize the conversion of circuit power parameters and improve the response speed. Therefore, it is desirable to reduce the coercive force of electromagnetic pure iron materials.

[0004] For example, in the Chinese patent document titled "Low Coercivity High Permeability Electromagnetic Pure Iron Cold-Rolled Thin Sheet Material," publication number CN100457385C, published on February 4, 2009, a component ratio of C≦0.010%, Si≦0.10%, Mn≦0.20%, P≦0.015%, S≦0.010%, Al=0.50%~0.80%, [O], [N]<40ppm, electrolytic inclusions<60ppm, remaining Fe is adopted to obtain a DT4C class product with low coercivity and high permeability. [Overview of the project] [Problems that the invention aims to solve]

[0005] One of the objectives of the present invention is to provide a low-coercivity wire that has low coercivity, is easier to magnetize and demagnetize, and improves the response speed and magnetic properties of electronic components by obtaining a soft magnetic material through optimized design of alloy components and control of microstructure. [Means for solving the problem]

[0006] To achieve the above objectives, the present invention proposes a low coercivity wire containing Fe and unavoidable impurities, and further 0 <C≦0.003%、 Si ≤ 0.01%, Mn: 0.1~0.2%, Al: 0.30-0.45%, O: 0.0015~0.0035%, N: 0.001~0.003%, Ca: 0.0005~0.0015% It contains each chemical element as indicated by its mass percentage content.

[0007] Furthermore, the present invention also provides low coercivity wires, the mass percentage content of each chemical element being as follows: 0 <C≦0.003%、 Si ≤ 0.01%, Mn: 0.1~0.2%, Al: 0.30-0.45%, O: 0.0015~0.0035%, N: 0.001~0.003%, Ca: 0.0005~0.0015%, The remainder consists of Fe and other unavoidable impurities.

[0008] The design principles for each chemical element in the low-coercivity wire of the present invention are as follows.

[0009] Carbon (C) is an important element used in the steel production process, and remains in the final product after blast furnace, converter, or electric furnace smelting. After rolling and cooling or annealing heat treatment of the steel, carbon precipitates in the form of cementite. The presence of cementite provides pinning for magnetic domain movement and increases the coercivity of the material, and the present invention controls its upper limit to 0.003%. In some embodiments, the mass percentage content of C in the low coercivity wire of the present invention is 0.001 to 0.003%.

[0010] Si: Si is a nonmetallic element, and in this invention, if its content is too high, the magnetic properties of the alloy will decrease. However, it is impossible to completely remove the Si element in the steel smelting process. Furthermore, considering smelting costs and performance, this invention controls the upper limit to 0.01%. In some embodiments, the mass percentage content of Si in the low coercivity wire of this invention is 0.001 to 0.01%.

[0011] Mn: The element Mn readily combines with the harmful element S to form MnS, thereby reducing its harmfulness. At the same time, the solid solution of Mn in the steel is advantageous for grain growth during the annealing process. To fully utilize the effects of Mn, this invention controls the Mn content to 0.1% or more. However, for this invention, if the Mn content is too high, it becomes difficult to control the controlled cooling structure of the wire, and the magnetic properties deteriorate. Therefore, the amount of Mn added is controlled to 0.20% or less.

[0012] Al: The element Al is often added to steel as a deoxidizing element, and the addition of Al simultaneously affects the phase transformation of the alloy. When Al is dissolved in ferrite, it raises the austenite transformation temperature, but the addition of Mn expands the austenite phase region and lowers the phase transformation temperature. This invention considers the interaction between Al and Mn simultaneously, and through calculations and experimental studies, it was discovered that when the amount of Al added exceeds 0.3%, the alloy transformation point of this material exceeds 930°C. This is advantageous for the growth of equiaxed ferrite grains during the annealing process after wire drawing. However, if the Al content in the steel is too high, Al will replace iron, reducing the magnetic properties of the alloy, and at the same time, it will promote the grain growth of oxides and increase coercivity, so the amount of Al added should be controlled to 0.45% or less.

[0013] O:O is an element that is inevitably present in the steel smelting process. In this invention, O combines with Al in molten steel to form aluminum oxide precipitates. By adding Al in 2 to 3 separate additions during the refining process, the size of aluminum oxide particles can be controlled to 3 μm or less. This provides nucleation points for the solidification of the steel molten metal during the continuous casting process, promotes the formation of an equiaxed crystal structure, prevents excessive segregation of residual elements due to excessive growth of columnar crystals which degrades the material's workability and magnetic properties, and is advantageous for structural uniformity. Therefore, this invention controls the O content in steel to 0.0015% or more. However, if the oxygen content is too high, the number of inclusions in the steel increases, their size increases, and this significantly affects the material's drawability and magnetic properties, increasing coercivity. Therefore, it is necessary to control the O content to 0.0035% or less.

[0014] N: In this invention, when element N is dissolved in ferrite, the phase transformation temperature and magnetic properties decrease, so its content must be controlled to 0.003% or less. During the cooling process of the alloy, N readily precipitates by bonding with element Al, and residual element C combines with other alloying elements to form carbides. These precipitates are small in size and, when controlled within the nanometer scale, prevent abnormal grain growth during the heating process, promote uniform growth of ferrite grains, and improve the uniformity of the material's structure and properties. Based on this, in order to fully exert the effects of element N, its content is controlled to 0.001% or more.

[0015] Ca: In this invention, while a Ca content of 0.0005% or more is advantageous for the dispersion distribution of aluminum oxide particles, if the Ca content is too high, the smelting of the alloy becomes difficult and costs increase. Therefore, the Ca content is controlled to 0.0015% or less.

[0016] Furthermore, other unavoidable impurities in the low-coercivity wire of the present invention are Ti ≤ 0.003%, P ≤ 0.015%, and S ≤ 0.008%.

[0017] The unavoidable impurities in this invention are mainly P, S, and Ti. Of these, since Ti readily combines with N to form coarse TiN, it is preferable to control the Ti content to 0.003% or less. If P and S elements remain in the steel, the brittleness of the steel increases and the formability of the material decreases, so it is preferable to control the P content to 0.015% or less and the S content to 0.008% or less.

[0018] Furthermore, in the low coercivity wire of the present invention, the mass percentage content of the chemical elements satisfies at least one of the following conditions: (Al+100Ca) / (Ti+N)≧85, Mn / S≧20, and the numerical value before the percentage sign of the mass percentage content of the corresponding chemical element is substituted for each chemical element in the formula.

[0019] In order to promote sufficient precipitation of aluminum nitride and carbon element and exert the function of calcium element, the present invention further controls the mass percentage content of each chemical element in the material to satisfy (Al + 100Ca) / (Ti + N) ≥ 85. In some embodiments, 85 ≤ (Al + 100Ca) / (Ti + N) ≤ 170.

[0020] Since the Mn element is likely to combine with the harmful element S to form MnS, in order to reduce its harmfulness, the present invention controls Mn / S ≥ 20. In some embodiments, 20 ≤ Mn / S ≤ 200.

[0021] The microstructure of the low coercivity wire material of the present invention includes ferrite crystal grains. Furthermore, in the low coercivity wire material of the present invention, the size of the ferrite crystal grains is 200 - 800 μm. This tissue characteristic can effectively reduce the coercivity of the material and endow good soft magnetic properties.

[0022] The microstructure of the low coercivity wire material of the present invention includes aluminum oxide and aluminum carbonitride precipitates. Furthermore, in the low coercivity wire material of the present invention, the size of the aluminum oxide and aluminum carbonitride precipitates is 3 μm or less. This tissue characteristic can effectively reduce the coercivity of the material and endow good soft magnetic properties. In some embodiments, the size of the aluminum oxide and aluminum carbonitride precipitates in the low coercivity wire material of the present invention is 0.1 - 3 μm.

[0023] Furthermore, the coercivity of the low coercivity wire material of the present invention is 25 A / m or less. In some embodiments, the coercivity of the low coercivity wire material of the present invention is 5 - 25 A / m, for example, it is 10 A / m, 15 A / m, or 20 A / m.

[0024] Another object of the present invention is to provide a manufacturing method of a low coercivity wire material that can manufacture a soft magnetic material wire satisfying low coercivity by adopting a relatively simple processing process.

[0025] Based on the above objectives, the present invention further provides a method for manufacturing low coercivity wires, comprising the following steps: (1) Smelting, (2) Continuous casting, (3) Initial rolling, (4) Heating: Heat to 900-1150°C, for example, 950-1150°C, and keep warm for 1.5-2.5 hours. (5) Wire rod rolling, (6) Cooling by a Stermore fan, (7) Pull out the wire rod, (8) Annealing: The annealing heating temperature shall be 870-910°C, the holding time shall be 1-2 hours, and thereafter it shall be cooled to below 500°C at a cooling rate of 50°C / h or less.

[0026] In some embodiments, in the initial rolling step of the manufacturing method of the present invention, smelting is carried out using an electric furnace or converter smelting, followed by LF (Ladler Furnace) furnace smelting and VD (Vacuum Degassing) or RH (Ruhrstahl-Heraeus) degassing treatment, after which calcium wire is supplied.

[0027] Furthermore, in the initial rolling step of the manufacturing method of the present invention, the billet or slab is heated to 1100-1250°C and then rolled into small billets of 140-220 mm.

[0028] Furthermore, in the wire rod rolling step of the manufacturing method of the present invention, the rolling speed is controlled to 20 to 110 m / s.

[0029] Furthermore, in the wire rod rolling step of the manufacturing method of the present invention, the finish rolling mill group inlet temperature is controlled to 900-980°C, the diameter reduction / constant diameter rolling mill group inlet temperature is controlled to 900-980°C, and the discharge temperature is controlled to 890-960°C.

[0030] Furthermore, in the cooling step using the Stermore fan in the manufacturing method of the present invention, the airflow of the F1-F3 fans in the Stermore fan group is controlled to 0-50%.

[0031] Furthermore, in the wire rod drawing step of the manufacturing method of the present invention, the drawing reduction ratio is controlled to 10-30%.

[0032] Furthermore, in the annealing step of the manufacturing method of the present invention, the cooling rate is controlled to 30-50°C / h.

[0033] The low-coercivity wire of the present invention has the following advantages and beneficial effects.

[0034] The low-coercivity wire of the present invention has a uniform microscopic weave, a ferrite grain size of 200-800 μm, a coercivity of 25 A / m or less, excellent magnetic properties, can meet the processing requirements for iron cores of high-performance, high-speed switching relays and communication electronic components, and has a wide range of application prospects. [Modes for carrying out the invention]

[0035] The low-coercivity wire and its manufacturing method of the present invention will be further interpreted and explained below with reference to specific examples, but this interpretation and explanation will not unduly limit the technical solutions of the present invention.

[0036] Examples 1-10 and Comparative Examples 1-3 The low-coercivity wires of Examples 1 to 10 were all manufactured using the following steps.

[0037] (1) After electric furnace smelting, LF furnace refining and RH degassing treatment were performed to control the P element content in the steel to 0.015% or less, the S element content to 0.008% or less, and the Ti element content to 0.003% or less, while controlling the O content in the steel to 0.0015-0.0035% and the N content to 0.001-0.003%. After refining, calcium wire was supplied to control the Ca content in the steel to 0.0005-0.0015%.

[0038] (2) Casting was performed using a continuous bloom casting machine under argon gas protection to obtain continuous cast blooms or slabs. The size of the blooms was 450 mm or less, and the thickness of the slabs was 400 mm or less. By adjusting the drawing speed, cooling, and end reduction parameters in the continuous casting process, the uniform distribution of precipitates was controlled, and elemental segregation in the center of the billet was reduced. The chemical composition of the blooms or slabs is shown in Table 1.

[0039] (3) The slab was cut longitudinally to obtain billets of size 400 mm or less. Of these, 400 mm billets were used in Examples 6-7, 350 mm billets in Examples 8-9, and 250 mm billets in Example 10. The continuous casting bloom or slab was cut into billets and heated to 1100-1250°C, then rolled into small billets of 140-220 mm. The small billets underwent eddy current testing, magnetic particle testing, grinding with a grinder, and additional magnetic particle testing and grinding to remove defects such as cracks and depressions from the ingot surface, with a defect depth of 0.5 mm or less.

[0040] (4) The small billets were heated to 900-1150°C, for example, 950-1150°C, and kept warm for 1.5-2.5 hours.

[0041] (5) The wire rods were rolled, with the rolling speed controlled to 20-110 m / s, the finish rolling mill inlet temperature controlled to 900-980°C, the diameter reduction / constant diameter rolling mill inlet temperature controlled to 900-980°C, and the discharge temperature controlled to 890-960°C. The size specifications of the wire rods obtained by rolling were Φ5.5-16 mm.

[0042] (6) Cooling with Stelmore fans: The airflow of fans F1 to F3 was set to 0 to 50%. 27 3m insulation covers were installed on the Stelmore line, of which insulation covers 1 to 5 were left open, and insulation covers 6 to 27 were closed.

[0043] (7) Hot-rolled wire rods were subjected to single-pass drawing, and the drawing reduction ratio was controlled to 10-30%.

[0044] (8) Annealing: The annealing heating temperature was 870-910°C, the holding time was 1-2 hours, and then it was cooled to below 500°C at a cooling rate of 50°C / h or less.

[0045] Although the control wires of Comparative Examples 1 to 3 were manufactured using the same process as described above, their chemical composition and specific process parameters at each step all failed to meet the design requirements of the present invention.

[0046] Table 1 shows the mass percentages of each chemical element in the low-coercivity wires of Examples 1 to 10 and the control wires of Comparative Examples 1 to 3.

[0047] [Table 1]

[0048] Tables 2-1 and 2-2 show the specific process parameters in the above steps for the low-coercivity wires of Examples 1 to 10 and the control wires of Comparative Examples 1 to 3.

[0049] [Table 2-1] TIFF2026514478000003.tif58170

[0050] [Table 2-2]

[0051] The wires from Examples 1-10 and the control wires from Comparative Examples 1-3 were sampled, and the microstructure (ferrite grain size, size of aluminum oxide and aluminum carbonitride precipitates) of the steel sheet samples from each example was observed and analyzed using GB / T 13298-2015 "Method for Microscopic Examination of Metallurgical Structures". The relevant observation and analysis results are shown in Table 3 below.

[0052] Furthermore, the wires from Examples 1 to 10 and the control wires from Comparative Examples 1 to 3 obtained through the above process steps were sampled again, and the coercivity was measured based on GB / T 13012-2008 "Method for Measuring DC Magnetic Properties of Soft Magnetic Materials: Permeability and Saturated Magnetic Flux Density - Annular Sampling Method and Magnetometer Method," and the measurement results are shown in Table 3.

[0053] Table 3 shows the microstructure characteristics and coercivity measurement results of the wires from Examples 1 to 10 and the control wires from Comparative Examples 1 to 3.

[0054] [Table 3]

[0055] As shown in Table 3, the ferrite grain size range of the wires in Examples 1 to 10 was 200 to 800 μm, while the ferrite grain size of the comparative examples was smaller than that of the present invention. Furthermore, the size of the aluminum oxide and aluminum carbonitride precipitates in the wires of Examples 1 to 10 of the present invention was 3 μm or less.

[0056] As can be seen from Table 3, the coercivity of the wires in Examples 1 to 10 of the present invention was all less than 25 A / m. On the other hand, the coercivity of Comparative Examples 1 to 3 was at least 41 A / m.

[0057] Furthermore, the combination methods of each technical feature in this application are not limited to the combination methods described in the claims of this application or the combination methods described in the specific embodiments, and all technical features described in this application can be freely combined or combined in any manner, as long as they do not contradict each other.

[0058] Furthermore, the embodiments described above are merely specific examples of the present invention. The present invention is not limited to the above embodiments, and similar changes or modifications can be obtained from or easily conceived by those skilled in the art from the content disclosed herein, and are within the scope of protection of the present invention.

Claims

1. A low coercivity wire containing Fe and unavoidable impurities, further 0＜C≦0.003%、 Si ≤ 0.01%, Mn: 0.1–0.2%, Al：0.30～0.45%、 O：0.0015～0.0035%、 N：0.001～0.003%、 Ca: 0.0005–0.0015% A low-coercivity wire characterized by containing each chemical element as indicated by its mass percentage content.

2. The mass percentage content of each chemical element is 0＜C≦0.003%、 Si ≤ 0.01%, Mn: 0.1–0.2%, Al：0.30～0.45%、 O：0.0015～0.0035%、 N：0.001～0.003%、 Ca: 0.0005–0.0015%, The low coercivity wire material according to claim 1, characterized in that the remainder is Fe and other unavoidable impurities.

3. The low coercivity wire material according to claim 1, characterized in that, among other unavoidable impurities, Ti ≤ 0.003%, P ≤ 0.015%, and S ≤ 0.008%.

4. The mass percentage content of that chemical element is (Al+100Ca) / (Ti+N)≧85, Mn / S ≥ 20, The low coercivity wire according to claim 3, characterized in that it satisfies at least one of the following items, and each chemical element in the formula is replaced with the numerical value before the percentage sign of the mass percentage content of the corresponding chemical element.

5. The low coercivity wire according to claim 1, characterized in that the ferrite crystal grain size in the low coercivity wire is 200 to 800 μm.

6. The low coercivity wire according to claim 1, characterized in that the size of aluminum oxide and aluminum carbonitride precipitates in the low coercivity wire is 3 μm or less.

7. The low-coercivity wire material according to claim 1, characterized in that its coercivity is 25 A / m or less.

8. A method for manufacturing a low coercivity wire according to any one of claims 1 to 7, (1) Smelting, (2) Continuous casting, (3) Initial rolling, (4) Heating: Heat to 900-1150°C and keep warm for 1.5-2.5 hours. (5) Wire rod rolling, (6) Cooling by a Stermore fan, (7) Pull out the wire rod, (8) Annealing: The annealing heating temperature is 870-910°C, the holding time is 1-2 hours, and then it is cooled to below 500°C at a cooling rate of 50°C / h or less. A manufacturing method characterized by including the following step.

9. The manufacturing method according to claim 8, characterized in that, in the initial rolling step, the billet or slab is heated to 1100 to 1250°C and then rolled into small billets of 140 to 220 mm.

10. The manufacturing method according to claim 8, characterized in that the rolling speed is controlled to 20 to 110 m / s in the wire rod rolling step.

11. The manufacturing method according to claim 8, characterized in that, in the wire rod rolling step, the inlet temperature of the finishing rolling mill group is controlled to 900 to 980°C, the inlet temperature of the diameter reduction / constant diameter rolling mill group is controlled to 900 to 980°C, and the discharge temperature is controlled to 890 to 960°C.

12. The manufacturing method according to claim 8, characterized in that, in the cooling step using a Stermore fan, the airflow of the F1 to F3 fans of the Stermore fan group is controlled to 0 to 50%.

13. The manufacturing method according to claim 8, characterized in that the wire rod drawing step controls the drawing reduction ratio to 10 to 30%.

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