A uniform steel belt for needle making and its preparation method

Abstract

The present application relates to the technical field of high-carbon precision stamping steel, and in particular to a steel strip for needle making with uniform structure and a preparation method thereof; the method comprises: refining smelted molten iron, and then performing continuous casting, rolling, laminar cooling, coiling and leveling to obtain a hot-rolled steel coil; pickling the hot-rolled steel coil, and then performing annealing and cold rolling, and then leveling to obtain a steel strip for needle making with uniform structure and a small hardness fluctuation range; wherein, annealing and cold rolling comprises a first annealing, a first cold rolling, a second annealing and a second cold rolling; the chemical composition of the steel strip comprises: C, Si, Mn, P, S, Alt, Cr, Nb, and the rest are Fe and unavoidable impurity elements; by alternating the pickled steel in an "annealing + rolling" mode, using two annealings to ensure that the carbides are spheroidized and the diameter of the spheroidizes is ensured, and then by two cold rollings, the hardness is uniformly controlled to ensure that the hardness fluctuation of the steel is within a relatively low range.

Description

Technical Field

[0001] The present application relates to the technical field of high-carbon precision stamping steel, and in particular to a steel strip with uniform structure for needle making and a preparation method thereof. Background Art

[0002] Textile needles are a kind of consumables in the textile industry. Their service life is generally 6 to 8 months. They are made of steel coils through dozens of processes such as slitting, stamping, grinding, bending, heat treatment and fine grinding. In order to ensure the performance of textile needles, the processed steel coils are generally required to have high uniformity of organization and hardness. Therefore, the diameter of the carbide in the ferrite and carbide organization of the steel coil is required to be about 1μm, and the hardness fluctuation is required to be within 30 HV (HV5).

[0003] At present, the preparation process of steel coils generally requires multiple cold rolling and annealing. Generally, the last process is annealing. However, it is difficult to control the hardness by annealing alone. Therefore, in order to reduce the difficulty, low-temperature annealing is required. However, low-temperature annealing will cause the hardness to fluctuate around 50 HV, and the hardness fluctuation cannot be guaranteed. The hardness fluctuation will make the product quality uncontrollable and affect the product performance.

[0004] Therefore, how to reduce the hardness fluctuation of the steel coil while ensuring the diameter of the carbide is a technical problem that needs to be solved urgently. Summary of the invention

[0005] The present application provides a needle-making steel strip with uniform structure and a preparation method thereof, so as to solve the technical problem in the prior art that the hardness fluctuation of the steel coil is too large on the basis of ensuring the carbide diameter.

[0006] In a first aspect, the present application provides a method for preparing a uniform steel strip for needle making, the method comprising:

[0007] The smelted molten iron is refined, and then continuously cast, rolled, laminar cooled, coiled and leveled to obtain hot rolled steel coils;

[0008] The hot-rolled steel coil is pickled, annealed and cold-rolled, and then flattened to obtain a needle-making steel strip with uniform structure and small hardness fluctuation range;

[0009] Wherein, the annealing and cold rolling includes a first annealing, a first cold rolling, a second annealing and a second cold rolling.

[0010] Optionally, the endpoint temperature of the first annealing = Ac1 temperature - first preset lowering temperature;

[0011] The first preset lowering temperature is 10°C to 40°C.

[0012] Optionally, the endpoint temperature of the second annealing = Ac1 temperature - second preset lowering temperature;

[0013] The second preset lowering temperature is 20°C to 50°C.

[0014] Optionally, the first annealing time is ≥14 h, and the second annealing time is ≥14 h.

[0015] Optionally, both the first annealing and the second annealing are hood annealing.

[0016] Optionally, the reduction ratio of the first cold rolling is ≥40%, and the reduction ratio of the second cold rolling is 15% to 35%.

[0017] Optionally, the hardness fluctuation of the needle-making steel strip is ≤20HV.

[0018] In a second aspect, the present application provides a uniform steel strip for needle making, wherein the steel strip is prepared by the method described in the first aspect, and the chemical composition of the steel strip, measured by mass fraction, includes:

[0019] C: 0.80% ~ 1.2%, Si: 0.22% ~ 0.70%, Mn: 0.25% ~ 1.00%, P ≤ 0.015%, S ≤ 0.010%, Alt ≤ 0.013%, Cr: 0.20% ~ 0.50%, Nb: 0.03% ~ 0.15%, the rest are Fe and unavoidable impurity elements.

[0020] Optionally, the metallographic structure of the steel strip includes spheroidized matter, the diameter of the spheroidized matter is 0.85 μm to 1.2 μm, and the spheroidization rate of the metallographic structure is ≥96%.

[0021] Optionally, the ratio of the single-sided decarburization layer depth of the needle-making steel strip to the thickness of the needle-making steel strip is ≤0.4%.

[0022] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0023] The embodiment of the present application provides a method for preparing a needle-making steel strip with uniform structure, wherein the pickled steel is subjected to an "annealing + rolling" mode alternately to form a process of first annealing and first cold rolling, second annealing and second cold rolling. The two annealings are used to ensure that the annealing energy is sufficient to ensure the spheroidization of carbides in the metallographic structure, thereby ensuring the diameter of the spheroidized products and improving the yield of the steel. The first cold rolling is used to ensure the spheroidization effect of the carbides and promote complete spheroidization of the carbides. The second cold rolling is used to promote the uniform distribution of the spheroidized products in the metallographic structure. The uniformly distributed spheroidized products can ensure the uniform distribution of the mechanical properties of the steel. Therefore, compared with the traditional process, the hardness can be controlled more evenly to ensure that the hardness fluctuation of the steel is within a lower range, thereby achieving the reduction of the hardness fluctuation of the steel coil on the basis of ensuring the diameter of the carbides, and at the same time ensuring the uniformity of the structure of the final steel product. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0026] Figure 1 A schematic diagram of a process for a method provided in an embodiment of the present application;

[0027] Figure 2 A schematic diagram of the annealing and cold rolling process provided in an embodiment of the present application;

[0028] Figure 3 This is a result diagram of the metallographic structure of the steel strip provided in the embodiment of the present application. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below in conjunction with specific implementations and examples, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific implementations and examples are for illustrating the present invention, rather than limiting the present invention.

[0030] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. In the event of a conflict, the present specification takes precedence.

[0031] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0032] The technical solution provided by the embodiment of the present invention is to solve the above technical problems, and the overall idea is as follows:

[0033] In one embodiment of the present application, Figure 1 As shown, a method for preparing a needle-making steel strip with uniform structure is provided, the method comprising:

[0034] S1. Refining the molten iron after smelting, and then performing continuous casting, rolling, laminar cooling, coiling and flattening to obtain a hot-rolled steel coil;

[0035] S2. The hot-rolled steel coil is pickled, annealed and cold-rolled, and then flattened to obtain a needle-making steel strip with uniform structure and small hardness fluctuation range;

[0036] Wherein, the annealing and cold rolling includes a first annealing, a first cold rolling, a second annealing and a second cold rolling;

[0037] The rolling includes descaling before rough rolling, rough rolling, descaling before finish rolling and finish rolling.

[0038] In some optional embodiments, such as Figure 2 As shown, the endpoint temperature of the first annealing = Ac1 temperature - the first preset lowering temperature;

[0039] The first preset lowering temperature is 10°C to 40°C; wherein the Ac1 temperature is 720-750°C.

[0040] In the embodiment of the present application, the positive effect of the first preset temperature reduction of 10°C to 40°C is that within this temperature range, it can ensure that carbides in the metallographic structure of the steel initially form spheroidized products; when the temperature value is greater than or less than the end point value of this range, it will lead to incomplete morphological changes of the spheroidized products, and the spheroidization rate of the carbides cannot be guaranteed, and thus the carbide diameter of the steel cannot be guaranteed, and thus the hardness of the steel cannot be guaranteed to change uniformly.

[0041] In some optional embodiments, the endpoint temperature of the second annealing = Ac1 temperature - second preset lowering temperature;

[0042] The second preset lowering temperature is 20°C to 50°C; wherein the Ac1 temperature is 720-750°C.

[0043] In the embodiment of the present application, the positive effect of the second preset lowering temperature of 20°C to 50°C is that within this temperature range, it can be ensured that after the second annealing, the carbides in the metallographic structure of the steel can completely form spheroidized products; when the temperature value is greater than or less than the end point value of this range, it will lead to incomplete morphological transformation of the spheroidized products, and the spheroidization rate of the carbides cannot be guaranteed, and then the carbide diameter of the steel cannot be guaranteed, and thus the hardness of the steel cannot be guaranteed to change uniformly.

[0044] In some optional embodiments, the first annealing time is ≥14 h, and the second annealing time is ≥14 h.

[0045] In the embodiment of the present application, the positive effect of the first annealing time being ≥ 14h is that within the annealing time range and under the temperature conditions of the first annealing, it can be ensured that the carbides in the metallographic structure of the steel have sufficient time to initially form spheroidized substances; when the time value is less than the endpoint value of the range, the carbides in the metallographic structure will not have sufficient time to form spheroidized substances.

[0046] The positive effect of the second annealing time being ≥ 14h is that within this annealing time range and under the temperature conditions of the second annealing, it can ensure that the carbides in the metallographic structure of the steel have enough time to completely form spheroidizes; when the time value is less than the endpoint value of this range, the carbides in the metallographic structure will not have enough time to form spheroidizes.

[0047] In some optional embodiments, the first annealing and the second annealing are both hood annealing, wherein the annealing furnace is a full hydrogen hood annealing furnace.

[0048] In the embodiment of the present application, the annealing forms of the first annealing and the second annealing are limited, which can effectively ensure the surface quality of the steel strip and further ensure the mechanical properties of the steel strip.

[0049] In some optional embodiments, the reduction ratio of the first cold rolling is ≥40%, and the reduction ratio of the second cold rolling is 15% to 35%.

[0050] In the embodiment of the present application, the positive effect of the first cold rolling reduction rate ≥ 40% is that within the range of the reduction rate, it can ensure that the steel has sufficient mechanical energy storage and carbon diffusion channels, thereby ensuring a higher spheroidization rate; when the reduction rate is less than the endpoint value of the range, the adverse effect that will result is that too low a reduction rate will lead to insufficient mechanical energy storage of the steel, thereby failing to ensure a carbon diffusion channel.

[0051] The positive effect of the second cold rolling reduction ratio of 15% to 35% is that within the range of the reduction ratio, the hardness of the steel can be ensured to be uniform, thereby ensuring a lower hardness fluctuation of the steel as a whole.

[0052] In some optional embodiments, the hardness fluctuation of the needle-making steel strip is ≤20 HV.

[0053] In a second aspect, the present application provides a uniform steel strip for needle making, wherein the steel strip is prepared by the method described in the first aspect, and the chemical composition of the steel strip, measured by mass fraction, includes:

[0054] C: 0.80% ~ 1.2%, Si: 0.22% ~ 0.70%, Mn: 0.25% ~ 1.00%, P ≤ 0.015%, S ≤ 0.010%, Alt ≤ 0.013%, Cr: 0.20% ~ 0.50%, Nb: 0.03% ~ 0.15%, the rest are Fe and unavoidable impurity elements.

[0055] In the embodiment of the present application, the positive effect of the mass fraction of C being 0.80% to 1.2% is that sufficient C content ensures the wear resistance of the needle-making steel; too low C content will make it difficult to ensure the wear resistance of the needle-making steel, and too high C content will lead to insufficient toughness of the finished textile needles, affecting their service life.

[0056] The positive effect of Si mass fraction of 0.22% to 0.70% is that within this mass fraction range, Si element can contribute to the improvement of hardness and strength; too high Si content may cause the surface quality of the steel plate to deteriorate, and too low Si content may cause insufficient hardness of the steel plate.

[0057] The positive effect of a Mn mass fraction of 0.25% to 1.00% is to ensure hardness and hardenability; too much Mn content may cause aggravated segregation and deterioration of plasticity, and too low Mn content may cause insufficient hardness.

[0058] The positive effect of P≤0.015% is to ensure the plasticity, toughness and fatigue properties of the parts after heat treatment; when the mass fraction is greater than the end point of this range, the adverse effect will be that the service life of the parts after heat treatment will be shortened.

[0059] The positive effect of S≤0.010% is to ensure the plasticity and toughness after heat treatment; when the mass fraction is greater than the endpoint value of this range, the adverse effect will be insufficient plasticity of the parts after heat treatment and a shorter service life.

[0060] The positive effect of Alt≤0.013% is to ensure the toughness after quenching, and the Al element can also be added to the steel as a deoxidizer or alloying element; when the mass fraction is greater than the end point of this range, the adverse effect will be the increase in the brittleness of the parts after quenching.

[0061] The positive effect of Cr mass fraction of 0.20% to 0.50% is due to the fact that the addition of Cr element is beneficial to inhibiting decarburization and intergranular oxidation of annealed steel coils and improving the uniformity of spheroidized products; too much Cr element will increase the risk of ingot cracks, and too low Cr element will cause insufficient hardness.

[0062] The positive effect of Nb mass fraction of 0.03% to 0.15% is due to the fact that the addition of Nb element is beneficial to refine ferrite grains, control decarburization and improve the uniformity of distribution of spheroidized products; too much Nb element will increase production costs, and too low Nb element will not guarantee sufficient effects of refining grains, improving decarburization and improving the uniformity of distribution of spheroidized products.

[0063] In some optional embodiments, the metallographic structure of the steel strip includes spheroidizes, and the diameter of the spheroidizes is 0.85 μm to 1.2 μm.

[0064] In the embodiment of the present application, the positive effect of the spheroidizer having a diameter of 0.85 μm to 1.2 μm is that within the diameter range, the spheroidizer can improve the performance of the steel, and at the same time, the spheroidizer with uniform particle size can promote the uniform distribution of the metallographic structure and ensure the appropriate hardness of the steel; when the particle size is greater than or less than the end point value of the range, the adverse effect will be the dimensional accuracy, wear resistance and fatigue performance of the parts after heat treatment.

[0065] In some optional embodiments, the spheroidization rate of the metallographic structure is ≥96%.

[0066] In the embodiment of the present application, the positive effect of the spheroidization rate of the metallographic structure being ≥ 96% is that within the range of the spheroidization rate, it can ensure that the carbides in the metallographic structure can be fully converted into spheroidized substances, which can not only further improve the uniformity of the structure but also further improve the hardness of the steel.

[0067] In some optional embodiments, the ratio of the single-sided decarburized layer depth of the needle-making steel strip to the thickness of the needle-making steel strip is ≤0.4%.

[0068] In the embodiment of the present application, the positive effect of the ratio of the depth of the single-sided decarburization layer to the thickness of the steel strip being ≤0.4% is that within this ratio range, the surface hardness, wear resistance and fatigue strength of the parts after the final heat treatment can be guaranteed; when the ratio is greater than the endpoint value of the range, it indicates that the depth of the single-sided decarburization layer is too large, which will lead to adverse effects such as low surface hardness of the parts after heat treatment, insufficient wear resistance and low fatigue performance.

[0069] The chemical compositions of the embodiments and comparative examples are shown in Table 1.

[0070] Table 1

[0071]

[0072]

[0073] The process parameters of annealing and cold rolling of various embodiments and comparative examples are shown in Table 2.

[0074] Table 2

[0075]

[0076] The mechanical properties and spheroidization rates of the finished products of the embodiments and comparative examples are shown in Table 3.

[0077] Test methods for related experiments:

[0078] Yield strength (R p0.2 ): Determined according to the national standard GB / T 228.1-2010;

[0079] Tensile strength (R m ): Determined according to the national standard GB / T 228.1-2010;

[0080] Total elongation: measured according to the national standard GB / T 228.1-2010, using a measuring gauge length of 50 mm.

[0081] Hardness (HV5): Determined according to the national standard GB / T 4340.1-2009, using the HV5 test method.

[0082] Table 3

[0083]

[0084]

[0085] Detailed analysis of Tables 1 to 3:

[0086] Yield strength (R p0.2 ) refers to the elongation strength of steel when the non-proportional elongation is 0.2%. The more the yield strength conforms to the standard, the better the mechanical properties of the steel.

[0087] Tensile strength (R m ) refers to the maximum stress per unit area before the specimen is broken. The closer the tensile strength meets the standard, the better the mechanical properties of the steel.

[0088] The total elongation refers to the percentage of the total deformation ΔL of the gauge section after the specimen is tensile fractured to the original gauge length L. The more the total elongation conforms to the standard, the better the mechanical properties of the steel.

[0089] The spheroidization rate refers to the probability of carbides forming spheroidized products in the metallographic structure of steel. The higher the spheroidization rate, the more spheroidized products are formed by carbides.

[0090] From the data of Examples 1-5, it can be seen that:

[0091] If the method of the present application is adopted, the pickled steel is subjected to an annealing + rolling mode alternately, and two annealings are used so that the energy of annealing and cold rolling is sufficient to ensure the spheroidization of carbides in the metallographic structure, thereby ensuring the diameter of the spheroidizes. Then, through two cold rollings, the hardness can be controlled more evenly, ensuring that the hardness fluctuation of the steel is within a lower range, thereby achieving the reduction of the hardness fluctuation of the steel coil on the basis of ensuring the diameter of the carbides.

[0092] From the data of Comparative Examples 1-5, it can be seen that:

[0093] From Comparative Example 1, it can be seen that:

[0094] The addition of Nb element contributes to the improvement of spheroidization rate, ensuring that the spheroidization rate is ≥96%;

[0095] From Comparative Example 2, it can be seen that:

[0096] The addition of Cr element contributes to the improvement of spheroidization rate, ensuring that the spheroidization rate is ≥96%;

[0097] From Comparative Example 3, it can be seen that:

[0098] Sufficient annealing temperature is critical to ensure the spheroidization rate. Sufficient temperature can make the carbides spheroidized and evenly distributed.

[0099] From Comparative Example 4, it can be seen that:

[0100] Sufficient annealing time is critical to ensure the spheroidization rate. Sufficient annealing time can provide enough energy to spheroidize the carbides and distribute them evenly.

[0101] From Comparative Example 5, it can be seen that:

[0102] Sufficient first cold rolling reduction is critical to ensure spheroidization rate. Mechanical energy storage and carbon diffusion channels during cold rolling are the key to spheroidization.

[0103] One or more technical solutions in the embodiments of the present application also have at least the following technical effects or advantages:

[0104] (1) The method provided in the embodiment of the present application is to perform annealing + rolling mode alternately on the pickled steel. First, two annealing processes are used to ensure that the carbides are spheroidized and the diameter of the spheroidized products is ensured. The spheroidization effect of the carbides is ensured by the first cold rolling, and the carbides are completely spheroidized. Then, the second cold rolling is performed to promote the uniform distribution of the spheroidized carbides in the metallographic structure, thereby ensuring that the hardness fluctuation of the steel is within a relatively low range and the uniformity of the structure of the final steel product is ensured.

[0105] (2) The method provided in the embodiment of the present application can finally obtain a finished steel plate with a thickness of 0.1 mm to 2.8 mm, a yield strength of 700 MPa to 800 MPa, a tensile strength of 750 MPa to 850 MPa, an elongation after fracture (A50) of 7% to 14%, a hardness (HV5) of 230 HV to 250 HV, a spheroidization rate of ≥96%, and an average diameter of spheroidized products of 0.85 μm to 1.2 μm.

[0106] (3) The method provided in the embodiment of the present application can obtain a uniform structure, uniform spheroidized material and uniform structure by combining annealing and cold rolling processes.

[0107] (4) The steel strip provided in the embodiment of the present application can comprehensively control the decarburization of the steel coil and improve the distribution uniformity of the spheroidized material by adding Cr and Nb elements to the chemical composition.

[0108] Explanation of the attached figure:

[0109] Figure 3 A schematic diagram of the metallographic structure of the steel strip provided in Example 1 of the present application, comprising Figure 3 It can be seen that the steel strip obtained by the method and chemical composition defined in the present application contains a large amount of spheroidized materials in its metallographic structure.

[0110] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "include..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0111] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0112] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a uniform steel strip for needle making, characterized in that: The method comprises: The molten iron after smelting is refined, and then continuous casting, rolling, laminar cooling, coiling and leveling are performed to obtain hot-rolled steel coils; The hot-rolled steel coil is pickled, annealed and cold-rolled, and then flattened to obtain a needle-making steel strip with uniform structure and small hardness fluctuation range; Wherein, the annealing and cold rolling includes a first annealing, a first cold rolling, a second annealing and a second cold rolling; The endpoint temperature of the first annealing=Ac1 temperature-first preset lowering temperature; The first preset lowering temperature is 10°C to 40°C; The end point temperature of the second annealing=Ac1 temperature-second preset lowering temperature; The second preset lowering temperature is 20°C to 50°C; The first annealing time is ≥14h, and the second annealing time is ≥14h; The reduction rate of the first cold rolling is ≥40%, and the reduction rate of the second cold rolling is 15% to 35%; The chemical composition of the steel strip includes, by mass fraction: C: 0.80%~1.2%, Si: 0.22%~0.70%, Mn: 0.25%~1.00%, P≤0.015%, S≤0.010%, Alt≤0.013%, Cr: 0.20%~0.50%, Nb: 0.03%~0.15%, and the rest are Fe and unavoidable impurity elements.

2. The method according to claim 1, characterized in that The first annealing and the second annealing are both hood annealing.

3. The method according to claim 1, characterized in that The hardness fluctuation of the needle-making steel strip is ≤20HV.

4. A uniform steel belt for needle making, characterized in that: The steel strip is prepared by the method according to any one of claims 1 to 3, the metallographic structure of the steel strip includes spheroidized matter, the diameter of the spheroidized matter is 0.85 μm to 1.2 μm, and the spheroidization rate of the metallographic structure is ≥96%.

5. The steel strip according to claim 4, characterized in that The ratio of the single-side decarburized layer depth of the needle-making steel strip to the thickness of the needle-making steel strip is ≤0.4%.

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