A low coercivity wire and its manufacturing method

Abstract

This invention discloses a low coercivity wire containing Fe and unavoidable impurities, and further containing the following chemical elements in the following mass percentages: O < 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%. Accordingly, this invention also discloses a method for manufacturing the above-mentioned wire. Through rational chemical composition design and microstructure control, this invention can obtain a wire with low coercivity.

Description

Technical Field

[0001] This invention relates to a steel material and its preparation method, and more particularly to a wire and its preparation method. Background Technology

[0002] Soft magnetic materials refer to materials whose magnetization mainly occurs in a magnetic field strength H of no more than 1000 A / m, exhibiting low coercivity and high permeability. Soft magnetic materials are easily magnetized and demagnetized. Electromagnetic pure iron is a typical example of a soft magnetic material. With the rapid development of industries such as electronics and telecommunications, the application areas of electromagnetic pure iron are constantly expanding, and demand is growing very rapidly.

[0003] The main magnetic properties of electromagnetic pure iron include coercivity, the increase in coercivity over time, maximum permeability, and maximum magnetic flux density. The maximum magnetic flux density depends on the material composition and corresponds to a physical state where the magnetization vectors within the material are neatly aligned. It is the number of magnetic field lines passing through a unit cross-sectional area of ​​the iron core, also known as magnetic flux density, representing the material's magnetization capability, and is measured in tons (T). Coercivity is a quantity indicating the ease with which a material can be magnetized, and it depends on the material's composition and defects (impurities, stress, etc.). Permeability is the ratio of B to H at any point on the hysteresis loop, and it is closely related to the material's microstructure and the device's operating state. Coercivity refers to the fact that after a magnetic material is saturated with magnetization, its magnetic flux density (B) does not return to zero when the external magnetic field returns to zero. Only when a magnetic field of a certain magnitude is applied in the opposite direction of the original magnetization field can the magnetic flux density return to zero. This magnetic field is called the coercive magnetic field, also known as coercivity. The lower the coercivity of soft magnetic materials, the easier they are to magnetize and demagnetize. In practical applications, this allows for faster transformation of electrical parameters in circuits and improves response speed. Therefore, it is desirable to reduce the coercivity of electromagnetic pure iron materials.

[0004] For example, Chinese patent document CN100457385C, published on February 4, 2009, entitled "A Cold-Rolled Sheet Material of Electromagnetic Pure Iron with Low Coercivity and High Permeability", uses a composition 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, with the remainder being Fe, to obtain a product of grade DT4C with low coercivity and high permeability. Summary of the Invention

[0005] One of the objectives of this invention is to provide a low coercivity wire, which obtains a soft magnetic material through alloy composition optimization and microstructure control, resulting in low coercivity, easier magnetization and demagnetization, and improved response speed and magnetic performance of electronic components.

[0006] To achieve the above objectives, the present invention provides a low coercivity wire containing Fe and unavoidable impurities, and further containing the following chemical elements in the following mass percentages:

[0007] 0 < C ≤ 0.003%;

[0008] Si≤0.01%;

[0009] Mn: 0.1-0.2%;

[0010] Al: 0.30-0.45%;

[0011] O: 0.0015-0.0035%;

[0012] N: 0.001-0.003%;

[0013] Ca: 0.0005-0.0015%.

[0014] Furthermore, the present invention also provides a low coercivity wire, wherein the mass percentage content of each chemical element is as follows:

[0015] 0 < C ≤ 0.003%;

[0016] Si≤0.01%;

[0017] Mn: 0.1-0.2%;

[0018] Al: 0.30-0.45%;

[0019] O: 0.0015-0.0035%;

[0020] N: 0.001-0.003%;

[0021] Ca: 0.0005-0.0015%;

[0022] The balance consists of Fe and other unavoidable impurities.

[0023] In the low coercivity wire described in this invention, the design principles of each chemical element are as follows:

[0024] C: C is an important element used in the steel production process. After blast furnace ironmaking, converter or electric furnace smelting, carbon is retained in the final product. After the steel is rolled and cooled or after annealing heat treatment, carbon will precipitate in the form of cementite. The presence of cementite will provide pinning for magnetic domain movement and improve the coercivity of the material. Therefore, the present invention controls its upper limit to 0.003%.

[0025] Si: Si is a non-metallic element. In this invention, its excessive content will lead to a decrease in the magnetic properties of the alloy. However, Si cannot be completely removed during the steel smelting process. Considering the smelting cost and performance, this invention controls its upper limit to 0.01%.

[0026] Mn: Mn readily combines with harmful element S to form MnS, reducing its hazard. Simultaneously, Mn dissolved in steel promotes grain growth during annealing. To fully utilize the role of Mn, this invention controls the Mn content to be higher than 0.1%. However, for this invention, excessively high Mn content increases the difficulty of controlling the controlled cooling structure of the wire and reduces magnetic properties; therefore, the Mn addition is controlled to be lower than 0.20%.

[0027] Al: Al is often added to steel as a deoxidizing element. At the same time, the addition of Al will affect the phase transformation of the alloy. Al dissolved in ferrite will increase the austenite transformation temperature, but the addition of Mn will expand the austenite phase region and reduce the phase transformation temperature. This invention considers the interaction between Al and Mn elements. Through calculation and experimental research, it was found that when the Al addition is higher than 0.3%, the phase transformation point of the alloy can be higher than 930℃. During the annealing process after wire drawing, it will be beneficial to the growth of equiaxed ferrite grains. However, when the Al content in the steel is too high, Al will replace iron and reduce the magnetic properties of the alloy, while promoting the growth of oxide size and increasing coercivity.

[0028] O: O is an element that is inevitably present in the steelmaking process. In this invention, O will combine with Al in molten steel to form alumina precipitates. By adding Al in 2-3 stages during the refining process, the alumina particle size can be controlled to not exceed 3μm. This provides nucleation sites for the solidification of molten steel during continuous casting, promotes the formation of equiaxed crystal structure, and prevents excessive segregation of residual elements due to excessive growth of columnar crystals, which would reduce the material's processing performance and magnetic properties. It is also beneficial for the homogenization of the structure. Therefore, this invention controls the O content in the steel to be higher than 0.0015%. However, excessively high oxygen content will lead to an increase in the number and size of inclusions in the steel, which will greatly affect the material's drawing and magnetic properties and improve coercivity. Therefore, it is necessary to control the O content to be lower than 0.0035%.

[0029] Nitrogen (N): In this invention, nitrogen dissolved in ferrite lowers the phase transformation temperature and magnetic properties; therefore, its content must be controlled below 0.003%. During alloy cooling, N readily combines with Al to precipitate, and together with residual carbon, it combines with other alloying elements to form performance carbides. These precipitates are small, controlled within the nanometer range, which prevents abnormal grain growth during heating, promotes uniform ferrite grain growth, and improves the uniformity of material microstructure and properties. Therefore, to fully utilize the role of nitrogen, its content is controlled above 0.001%.

[0030] Ca: In this invention, the addition of Ca element above 0.0005% is beneficial to the dispersion and distribution of alumina particles. However, excessive Ca element will lead to increased difficulty and cost in alloy smelting. Therefore, the Ca content is controlled to be below 0.0015%.

[0031] Furthermore, in the other unavoidable impurities of the low coercivity wire described in this invention: Ti≤0.003%, P≤0.015%, S≤0.008%.

[0032] The unavoidable impurities in this invention are mainly P, S, and Ti. Ti readily combines with N to form coarse-sized TiN, therefore, the Ti content is preferably controlled to not exceed 0.003%. Residual P and S in the steel will increase its brittleness and reduce its formability; therefore, the P content is preferably controlled to be below 0.015%, and the S content below 0.008%.

[0033] Furthermore, in the low coercivity wire described in this invention, the mass percentage content of its chemical elements also satisfies at least one of the following: (Al+100Ca) / (Ti+N)≥85; Mn / S≥20; where each chemical element is represented by the value before the percentage sign of its corresponding mass percentage content.

[0034] In order to promote the full release of Al nitrides and carbon elements and give full play to the role of Ca, this invention further controls the mass percentage content of each chemical element in the material to meet the requirement of (Al+100Ca) / (Ti+N)≥85.

[0035] Mn element readily combines with harmful element S to form MnS. In order to reduce its harm, this invention controls Mn / S ≥ 20.

[0036] Furthermore, in the low coercivity wire described in this invention, the ferrite grain size is 200-800 μm. This microstructure effectively reduces the coercivity of the material, giving it excellent soft magnetic properties.

[0037] Furthermore, in the low coercivity wire described in this invention, the size of its alumina and aluminum carbonitridium precipitates is ≤3 μm. This microstructure effectively reduces the coercivity of the material, giving it excellent soft magnetic properties.

[0038] Furthermore, the coercivity of the low coercivity wire described in this invention is ≤25A / m.

[0039] Another objective of this invention is to provide a method for manufacturing low coercivity wire, which employs a relatively simple processing technology to produce soft magnetic material wire that meets the requirements of low coercivity.

[0040] To achieve the above objectives, the present invention also provides a method for manufacturing a low coercivity wire, comprising the steps of:

[0041] Smelting;

[0042] Continuous casting;

[0043] Initial rolling;

[0044] Heating: Heat to 950-1150℃ and hold for 1.5-2.5 hours;

[0045] Wire rod rolling;

[0046] Stelmore fan cooling;

[0047] Wire rod drawing;

[0048] Annealing: The annealing heating temperature is 870-910℃, the holding time is 1-2h, and then the temperature is cooled to below 500℃ at a cooling rate of less than 50℃ / h.

[0049] Furthermore, in the initial rolling step of the manufacturing method described in this invention, the billet is heated to 1100-1250°C and then rolled into a small billet of 140-220 mm.

[0050] Furthermore, in the wire rod rolling step of the manufacturing method described in this invention, the rolling speed is controlled to be 20-110 m / s.

[0051] Furthermore, in the wire rod rolling step of the manufacturing method described in this invention, the inlet temperature of the finishing mill is controlled at 900-980℃, the inlet temperature of the reducing and sizing mill is controlled at 900-980℃, and the wire drawing temperature is controlled at 890-960℃.

[0052] Furthermore, in the Steyrmore fan cooling step of the manufacturing method described in this invention, the air volume of the F1-F3 fans of the Steyrmore fan unit is controlled to be 0-50%.

[0053] Furthermore, in the wire drawing step of the manufacturing method described in this invention, the drawing area reduction rate is controlled to be 10-30%.

[0054] The low coercivity wire described in this invention has the following advantages and beneficial effects:

[0055] The low coercivity wire described in this invention has a uniform microstructure, with ferrite grain size of 200-800μm, coercivity of less than 25A / m, and excellent magnetic properties. It can meet the processing requirements of high-performance, fast-switching relay cores and communication electronic device parts, and has broad application prospects. Detailed Implementation

[0056] The low coercivity wire and its preparation method described in this invention will be further explained and described below with reference to specific embodiments. However, this explanation and description do not constitute an improper limitation on the technical solution of this invention.

[0057] Examples 1-10 and Comparative Examples 1-3

[0058] The low coercivity wires in Examples 1-10 were all prepared using the following steps:

[0059] (1) After smelting in an electric furnace or converter, the steel undergoes LF furnace refining and VD or RH degassing treatment to control the P content to be below 0.015%, S content to be below 0.008%, and Ti content to be below 0.003%, while simultaneously controlling the O content to be 0.0015-0.0035% and the N content to be 0.001-0.003%. After refining, calcium wire is fed to control the Ca content in the steel to be 0.0005-0.0015%.

[0060] (2) A large billet continuous casting machine is used to cast billets under argon protection to obtain large billets or slabs. The size of the large billet is ≤450mm and the thickness of the slab is ≤400mm. By adjusting the casting speed, cooling and end light pressing parameters during the continuous casting process, the uniform distribution of precipitates and the reduction of element segregation in the core of the billet are controlled. The chemical composition of the large billet or slab is shown in Table 1.

[0061] (3) The slab is longitudinally cut into square billets with a size ≤ 400 mm. Specifically, in Examples 6-7, the billets are cut into 400 mm square billets, in Examples 8-9, they are cut into 350 mm square billets, and in Example 10, they are cut into 250 mm square billets. The square billets cut from the continuous casting large square billets or slabs are heated to 1100-1250℃ and then rolled into small square billets of 140-220 mm. The small square billets are subjected to eddy current testing, magnetic particle testing, grinding wheel mold repair, supplementary magnetic particle testing, and grinding to remove defects such as cracks and pits on the surface of the billet. The defect depth is ≤ 0.5 mm.

[0062] (4) Heat the small square billet to 950-1150℃ and keep it warm for 1.5-2.5h.

[0063] (5) Wire rod rolling: control the rolling speed to 20-110m / s, control the inlet temperature of the finishing mill to 900-980℃, control the inlet temperature of the reducing mill to 900-980℃, control the wire drawing temperature to 890-960℃, and control the wire rod size to Ф5.5-16mm.

[0064] (6) Cooling of Steilmo blowers: The air volume of F1-F3 blowers is 0-50%. In some implementations, 27 3m insulation covers can be installed on the Steilmo line, of which 1-5# insulation covers are open and 6-27# insulation covers are closed.

[0065] (7) Perform single-pass drawing on hot-rolled wire rod, and control the drawing area reduction rate to be 10-30%.

[0066] (8) Annealing: The annealing heating temperature is 870-910℃, the holding time is 1-2h, and then the temperature is cooled to below 500℃ at a cooling rate of less than 50℃ / h.

[0067] The comparative wires of Comparative Examples 1-3 were prepared using the same steps and processes described above, but their chemical composition and specific process parameters in each step failed to meet the design requirements of this invention.

[0068] Table 1 lists the mass percentage of each chemical element for the low coercivity wires of Examples 1-10 and the comparative wires of Comparative Examples 1-3.

[0069] Table 1. (wt%, balance Fe and other unavoidable impurities besides P, S, and Ti)

[0070]

[0071]

[0072] Note: In the above formulas (Al+100Ca) / (Ti+N) and Mn / S, each chemical element should be replaced with the value before the percentage sign of its mass percentage content.

[0073] Tables 2-1 and 2-2 list the specific process parameters for the low coercivity wires of Examples 1-10 and the comparative wires of Comparative Examples 1-3 in the above steps.

[0074] Table 2-1.

[0075]

[0076]

[0077] Table 2-2.

[0078]

[0079]

[0080] Samples of the wires obtained in Examples 1-10 and the comparative wires of Comparative Examples 1-3 were taken respectively. The microstructure of the steel plate samples of each example was observed and analyzed using GB / T13298-2015 Metal Microstructure Inspection Method. The relevant observation and analysis results are listed in Table 3 below.

[0081] In addition, the wires of Examples 1-10 and the comparative wires of Comparative Examples 1-3 obtained through the above process steps were sampled again, and the coercivity was tested according to GB / T 13012-2008 Measurement Method of DC Magnetic Properties of Soft Magnetic Materials - Permeability and Saturation Magnetic Induction - Ring Sample Method and Permeability Meter Method, and the test results are listed in Table 3.

[0082] Table 3 lists the microstructure characteristics and coercivity test results of the wires in Examples 1-10 and the comparative wires in Comparative Examples 1-3.

[0083] Table 3.

[0084]

[0085]

[0086] As shown in Table 3, the ferrite grain size of the wires in Examples 1-10 ranges from 200 to 800 μm, while the ferrite grain size of the comparative examples is smaller than that of the present invention. Furthermore, the size of the alumina and aluminum carbonitriding precipitates in the wires in Examples 1-10 of the present invention is ≤3 μm.

[0087] As can be seen from Table 3, the coercivity of the wires in Examples 1-10 of the present invention is all below 25 A / m. In contrast, the lowest coercivity of Comparative Examples 1-3 is 41 A / m.

[0088] Furthermore, the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0089] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A low coercivity wire, characterized in that, Its mass percentage content of each chemical element is 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 balance is Fe and other unavoidable impurities, of which: Ti ≤ 0.003%, P ≤ 0.015%, S ≤ 0.008%; Its chemical element mass percentage content also meets at least one of the following conditions: (Al+100Ca) / (Ti+N)≥85;Mn / S≥20;Substitute the values ​​before the percentage sign of the corresponding chemical element into the formula; The size of the alumina and aluminum carbonitridium precipitates is ≤3μm.

2. The low coercivity wire as described in claim 1, characterized in that, Its ferrite grain size is 200-800μm.

3. The low coercivity wire as described in claim 1, characterized in that, Its coercivity is ≤25A / m.

4. The method for manufacturing low coercivity wire as described in any one of claims 1-3, characterized in that, It includes the following steps: Smelting; Continuous casting; Initial rolling; Heating: Heat to 950-1150℃ and hold for 1.5-2.5 hours; Wire rod rolling; Stelmore fan cooling; Wire rod drawing; Annealing: The annealing heating temperature is 870-910℃, the holding time is 1-2h, and then the temperature is cooled to below 500℃ at a cooling rate of less than 50℃ / h.

5. The manufacturing method as described in claim 4, characterized in that, In the initial rolling step, the billet is heated to 1100-1250℃ and then rolled into a small billet of 140-220mm.

6. The manufacturing method as described in claim 4, characterized in that, In the wire rod rolling process, the rolling speed is controlled at 20-110 m / s.

7. The manufacturing method as described in claim 4, characterized in that, In the wire rod rolling process, the inlet temperature of the finishing mill is controlled at 900-980℃, the inlet temperature of the reducing and sizing mill is controlled at 900-980℃, and the wire drawing temperature is controlled at 890-960℃.

8. The manufacturing method as described in claim 4, characterized in that, In the Steyrmore fan cooling process, the air volume of fans F1-F3 of the Steyrmore fan unit is controlled to be 0-50%.

9. The manufacturing method as described in claim 4, characterized in that, In the wire rod drawing process, the reduction rate of the drawing surface area is controlled to be 10-30%.

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