A cold-heading steel wire for non-quenched and tempered high-strength bolts and its preparation method

Abstract

The present invention particularly relates to a preparation method and wire of cold-heading wire for non-quenched and tempered high-strength bolts, belonging to the technical field of wire preparation. A preparation method of cold-heading wire for non-quenched and tempered high-strength bolts includes the following steps: pickling and first film coating the wire rod to obtain a pretreated wire rod; drawing the pretreated wire rod to obtain a prefabricated wire; cleaning and second film coating the prefabricated wire to obtain a film-coated wire; drying the film-coated wire to obtain the cold-heading wire for non-quenched and tempered high-strength bolts. By optimizing the wire drawing passes and reduction ratio, the cold upsetting performance of the wire is effectively improved; and by optimizing the wire film coating process, the film coating is decomposed into the first film coating and the second film coating, and the two film coatings are respectively located before and after drawing, effectively improving the lubrication effect during the cold heading forming process of the bolts, significantly reducing the die consumption, and realizing the high-efficiency and low-cost production of non-quenched and tempered 8.8-grade flange bolts with large deformation amount.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel wire preparation, and particularly relates to a preparation method and steel wire of cold-heading steel wire for non-quenched and tempered high-strength bolts. Background Art

[0002] In the cold-heading steel industry, cold-heading steel with a C content < 0.25% is usually referred to as low-carbon cold-heading steel, and cold-heading steel with a C content of 0.25 - 0.50% is referred to as medium-carbon cold-heading steel. Generally, fasteners below grade 6.8 are mostly made of non-heat-treated medium-carbon and low-carbon cold-heading steel, and the finished fasteners do not require quenching and tempering treatment. However, low-carbon cold-heading steel is difficult to meet the requirements of grade 8.8 high-strength fasteners due to its low strength. High-strength cold-heading steel usually refers to steel used for producing bolt products above grade 8.8 or nut products above grade 8. The fasteners of different strength grades need to select different cold-heading steel grades and adopt different processing technologies. Currently, the steel for grade 8.8 high-strength bolts usually uses medium-carbon high-quality carbon structural steel or medium-carbon alloy steel hot-rolled wire rods as raw materials, and is manufactured through processes such as pickling - phosphating - saponification - drawing - spheroidizing annealing - pickling - phosphating - saponification - drawing - cold-heading forming - quenching and tempering heat treatment - surface treatment. Among them, the steel wire manufacturing requires two pickling, phosphating, and drawing processes, and spheroidizing annealing is required, and the mechanical properties of the finished bolts need to be ensured through quenching and tempering heat treatment.

[0003] Currently, there is also an application of using non-quenched and tempered cold-heading steel wire rods as raw materials to produce grade 8.8 bolt products through processes such as drawing, cold-heading forming, and stabilization heat treatment. Since there is almost no work hardening effect generated by cold-heading deformation in the screw part of the bolt, in order to ensure the performance of the bolt rod part, it is necessary to increase the drawing reduction ratio. However, increasing the reduction ratio will cause problems such as a decrease in the cold-heading performance of the steel wire, a decrease in surface quality, and a reduction in the film coating effect. Summary of the Invention

[0004] The purpose of the present application is to provide a cold-heading steel wire for non-quenched and tempered high-strength bolts and its preparation method, so as to solve the technical problems in the prior art that after increasing the drawing reduction ratio, the cold-heading performance of the steel wire decreases, the surface quality decreases, and the film coating effect decreases.

[0005] The embodiment of the present invention provides a preparation method of a cold-heading steel wire for non-quenched and tempered high-strength bolts, including the following steps:

[0006] Obtain wire rods;

[0007] Pickle the wire rods and perform the first film coating to obtain pre-treated wire rods;

[0008] Draw the pre-treated wire rods to obtain prefabricated steel wires;

[0009] Clean the prefabricated steel wires and perform the second film coating to obtain film-coated steel wires;

[0010] Dry the coated steel wire to obtain the cold-heading steel wire for non-quenched and tempered high-strength bolts;

[0011] Wherein:

[0012] The number of drawing passes is 3 passes,

[0013] The cumulative area reduction rate of the drawing is 28-30%.

[0014] Optionally, industrial hydrochloric acid is used for the pickling.

[0015] Optionally, both the first coating and the second coating are phosphating-saponification treatments.

[0016] Optionally, the drawing includes a first pass, a second pass and a third pass,

[0017] Wherein:

[0018] The area reduction rate of the first pass is 16-18%;

[0019] The area reduction rates of the second pass and the third pass are both 6%.

[0020] Optionally, a continuous precision drawing machine is used for the drawing, and the die for the drawing is a diamond die.

[0021] Optionally, potassium permanganate solution is used for the cleaning.

[0022] Optionally, the drying temperature is 80-100 °C, and the drying time is 30-45 min.

[0023] Optionally, a box-type annealing furnace is used for the drying.

[0024] Based on the same inventive concept, an embodiment of the present invention also provides a steel wire, which is prepared by using the preparation method of the cold-heading steel wire for non-quenched and tempered high-strength bolts described in any one of the above, and the chemical composition of the steel wire includes, by mass percentage:

[0025] C: 0.15-0.20%, Si: ≤0.01%, Mn: 1.20-1.40%, P: ≤0.015%, S: ≤0.015%, Nb: 0.020-0.030%, V: 0.040-0.060%, Cr: ≤0.20%, Ni: ≤0.20%, Cu: ≤0.20%, and the rest are Fe and unavoidable impurities.

[0026] Optionally, the diameter of the steel wire is 7.60-7.70 mm.

[0027] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0028] The preparation method of cold-heading steel wire for non-quenched and tempered high-strength bolts provided by the embodiments of the present invention effectively improves the cold heading performance of the steel wire by optimizing the wire drawing passes and the reduction ratio of cross-sectional area; and by optimizing the wire coating process, the coating is decomposed into the first coating and the second coating, and the two coatings are respectively located before and after drawing, effectively improving the lubrication effect during the cold heading forming process of the bolts, significantly reducing the die consumption, and realizing the high-efficiency and low-cost production of non-quenched and tempered 8.8-grade flange bolts with large deformation.

[0029] The above description is only an overview of the technical solutions of the present invention. In order to be able to understand the technical means of the present invention more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention are specifically given below. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to these drawings without creative efforts.

[0031] Figure 1 is a flowchart of the method provided by the embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention will be specifically described below in combination with the specific embodiments and examples, and the advantages and various effects of the present invention will be presented more clearly therefrom. Those skilled in the art should understand that these specific embodiments and examples are used to illustrate the present invention, rather than to limit the present invention.

[0033] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as having the meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as the general understanding of those skilled in the technical field to which the present invention belongs. In case of contradiction, this specification shall prevail. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention. For example, room temperature may refer to the temperature in the range of 10 to 35 °C.

[0034] Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0035] The technical solution of the embodiment of the present application for solving the above technical problems is generally as follows:

[0036] According to a typical embodiment of the present invention, a method for preparing cold-heading steel wire for non-quenched and tempered high-strength bolts is provided, including the following steps:

[0037] S1. Obtain wire rods.

[0038] S2. Pickle and perform the first film coating on the wire rods to obtain pretreated wire rods.

[0039] The mechanism of this step is as follows: By pickling, the scale on the surface of the hot-rolled wire rods is removed; by the first film coating, the surface of the wire rods is protected, and the friction between the wire rods and the dies during the drawing process is reduced to form effective lubrication.

[0040] As an alternative embodiment, industrial hydrochloric acid is used for the pickling.

[0041] As an alternative embodiment, the first film coating is phosphating-saponification treatment.

[0042] S3. Draw the pretreated wire rods to obtain prefabricated steel wires.

[0043] Among them: The number of drawing passes is 3 passes, and the cumulative area reduction rate of the drawing is 28-30%.

[0044] In step S3, by optimizing the wire drawing passes and area reduction rate of the steel wires, the cold heading performance of the steel wires is effectively improved.

[0045] As an alternative embodiment, the drawing includes the first pass, the second pass and the third pass, and the area reduction rate of the first pass is 16-18%; the area reduction rates of the second pass and the third pass are both 6%.

[0046] As an alternative embodiment, a continuous precision drawing machine is used for the drawing, and the dies for the drawing are diamond dies.

[0047] S4. Clean and perform the second film coating on the prefabricated steel wires to obtain film-coated steel wires.

[0048] The mechanism of this step lies in that: during the wire drawing process, a large amount of phosphating film will fall off, resulting in severe consumption of the dies during the cold heading forming process of the bolts, and frequent die replacement cannot be carried out for normal industrial production. Therefore, it is necessary to perform the second film coating after the wire drawing. Before the film coating, through cleaning, the fragmented residues of the film formed by the first film coating are effectively removed, so that the second film coating can be carried out evenly, flatly and effectively.

[0049] As an alternative embodiment, potassium permanganate solution is used for the cleaning.

[0050] As an alternative embodiment, the second film coating is phosphating-saponification treatment.

[0051] S5. Dry the coated steel wire to obtain the cold-heading steel wire for non-quenched and tempered high-strength bolts.

[0052] As an alternative embodiment, the drying temperature is 80 - 100 °C, and the drying time is 30 - 45 min.

[0053] As an alternative embodiment, a box-type annealing furnace is used for the drying.

[0054] According to another typical embodiment of the present invention, a steel wire is provided, which is prepared by using the preparation method of the cold-heading steel wire for non-quenched and tempered high-strength bolts described in any one of the above, and the chemical composition of the steel wire includes, by mass percentage:

[0055] C: 0.15 - 0.20%, Si: ≤0.01%, Mn: 1.20 - 1.40%, P: ≤0.015%, S: ≤0.015%, Nb: 0.020 - 0.030%, V: 0.040 - 0.060%, Cr: ≤0.20%, Ni: ≤0.20%, Cu: ≤0.20%, and the balance is Fe and inevitable impurities.

[0056] As an alternative embodiment, the diameter of the steel wire is 7.60 - 7.70 mm.

[0057] The present application will be described in detail below with reference to examples, comparative examples and experimental data.

[0058] Example 1

[0059] This example provides a preparation method of a cold-heading steel wire for non-quenched and tempered high-strength bolts, including the following steps:

[0060] S1. Obtain a wire rod with a diameter of 9.0 mm.

[0061] S2. Subject the wire rod to pickling and the first film coating to obtain a pretreated wire rod.

[0062] Among them:

[0063] Industrial hydrochloric acid is used for the pickling.

[0064] The first film coating is phosphating-saponification treatment.

[0065] S3. Draw the pretreated wire rod to obtain a prefabricated steel wire.

[0066] Among them:

[0067] The number of drawing passes is 3, and the cumulative area reduction rate of the drawing is 28%.

[0068] The drawing includes a first pass, a second pass, and a third pass. The area reduction rate of the first pass is 16%; the area reduction rates of the second pass and the third pass are both 6%.

[0069] The drawing is carried out by a continuous precision drawing machine, and the die for the drawing is a diamond die.

[0070] S4. Clean and perform a second film coating on the prefabricated wire to obtain a film-coated wire.

[0071] Wherein:

[0072] The cleaning is carried out using a potassium permanganate solution.

[0073] The second film coating is phosphating-saponification treatment.

[0074] S5. Dry the film-coated wire to obtain the cold-heading wire for non-quenched and tempered high-strength bolts.

[0075] Wherein:

[0076] The temperature of the drying is 85°C, and the time of the drying is 35 min.

[0077] The drying is carried out using a box-type annealing furnace.

[0078] This embodiment also provides a kind of wire, which is prepared by the above preparation method. The chemical composition of the wire is shown in Table 1 by mass percentage.

[0079] Table 1 Chemical composition of the wire in Example 1

[0080] C Si Mn Nb V P S Cr Ni Cu Example 1 0.16 0.06 1.28 0.022 0.043 0.010 0.009 0.06 0.02 0.05

[0081] The diameter of the wire is 7.65 mm.

[0082] Example 2

[0083] The difference from Example 1 is only that the chemical composition of the wire is different. The chemical composition of the wire is shown in Table 2 by mass percentage.

[0084] Table 2 Chemical composition of the wire in Example 2

[0085] C Si Mn Nb V P S Cr Ni Cu Example 2 0.19 0.03 1.37 0.028 0.050 0.011 0.012 0.04 0.01 0.02

[0086] Example 3

[0087] The difference from Example 1 is only that:

[0088] In step S5, the temperature of the drying is 95°C, and the time of the drying is 45 min.

[0089] Comparative Example 1

[0090] The difference from Example 1 is only that: in step S3, the drawing method is: using a vertical drawing machine to assemble a polycrystalline die and drawing to Φ7.65mm in a single pass, with a drawing area reduction rate of 28%.

[0091] Comparative Example 2

[0092] The difference from Example 1 is only that: step S4 is cancelled.

[0093] Comparative Example 3

[0094] The difference from Example 1 is only that: in step S5, the drying method is natural air drying.

[0095] Experimental Example

[0096] The 1 / 4 cold heading performance, cold heading bolt cracking rate, and cold heading die wear of the steel wires provided in Examples 1 - N and Comparative Examples 1 - 3 were respectively detected. The specific detection results are shown in the following table.

[0097]

[0098]

[0099] Remark: 1. The qualified rate of the 1 / 4 cold heading performance of the steel wire ≥95% can meet the cold heading forming requirements of high - deformation bolts.

[0100] 2. The cold heading bolt cracking rate ≤5% is an acceptable ratio for the cold heading cracking rate in the fastener industry. If the cold heading cracking rate >10%, normal production cannot be carried out.

[0101] 3. The cold heading die life refers to the number of cold heading forming processes that a set of dies can perform (i.e., how many bolts are cold - headed). The fastener industry requires the die life to be not less than 50,000 times per set, otherwise industrial production cannot be carried out due to frequent die replacement.

[0102] 4. The mechanical property requirements for 8.8 - grade bolts are tensile strength ≥800MPa and yield strength ≥640MPa.

[0103] As can be seen from the above table, the performance of the steel wires provided in Embodiments 1-3 of the present invention is significantly better than that of the steel wires in Comparative Examples 1-3. Among them, the qualification rate of the 1 / 4 cold heading performance is 100%, which is greater than 95%, and can meet the cold heading forming requirements of bolts with large deformation; the highest cracking rate of cold heading bolts is 1.5%, which is much less than 5%; the minimum life of cold heading dies is 101,000 times per set, which is much greater than 50,000 times per set; the minimum value of the yield strength of the bolts is 793 MPa, which is much greater than 640 MPa. At the same time, the minimum value of the mechanical tensile strength of the bolts is 835 MPa, which is greater than 800 MPa, meeting the mechanical property requirements of 8.8 grade bolts.

[0104] Finally, it should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0105] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0106] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A preparation method of cold-heading steel wire for non-quenched and tempered high-strength bolts, characterized in that, it includes the following steps: Obtain wire rods; Pickle and apply the first film coating to the wire rods to obtain pretreated wire rods; Draw the pretreated wire rods to obtain prefabricated steel wires; Clean and apply the second film coating to the prefabricated steel wires to obtain film-coated steel wires; Dry the film-coated steel wires to obtain the cold-heading steel wire for non-quenched and tempered high-strength bolts; wherein: Both the first film coating and the second film coating are phosphating-saponifying treatments; The drawing includes the first pass, the second pass and the third pass, The area reduction rate of the first pass is 16-18%; The area reduction rates of the second pass and the third pass are both 6%; The chemical composition of the steel wire includes by mass percentage: C: 0.15-0.20%, Si: ≤0.01%, Mn: 1.20-1.40%, P: ≤0.015%, S: ≤0.015%, Nb: 0.020-0.030%, V: 0.040-0.060%, Cr: ≤0.20%, Ni: ≤0.20%, Cu: ≤0.20%, and the rest are Fe and inevitable impurities; The diameter of the steel wire is 7.60-7.70 mm.

2. The preparation method of cold-heading steel wire for non-quenched and tempered high-strength bolts according to claim 1, characterized in that, Industrial hydrochloric acid is used for the pickling.

3. The preparation method of cold-heading steel wire for non-quenched and tempered high-strength bolts according to claim 1, characterized in that, A continuous precision drawing machine is used for the drawing, and the die for the drawing is a diamond die.

4. The preparation method of cold-heading steel wire for non-quenched and tempered high-strength bolts according to claim 1, characterized in that, Potassium permanganate solution is used for the cleaning.

5. The preparation method of cold-heading steel wire for non-quenched and tempered high-strength bolts according to claim 1, characterized in that, The temperature of the drying is 80-100 °C, and the time of the drying is 30-45 min.

6. The preparation method of cold-heading steel wire for non-quenched and tempered high-strength bolts according to claim 1, characterized in that, A box-type annealing furnace is used for the drying.

7. A steel wire, characterized in that, It is prepared by using the preparation method of cold-heading steel wire for non-quenched and tempered high-strength bolts described in any one of claims 1-6.

Images