Production method for online softening of high-strength cold heading steel wire rod

Abstract

The invention discloses a production method for online softening of a high-strength cold heading steel wire rod. The wire rod comprises the following chemical components in percentage by mass: 0.33-0.38% of C, 0.15-0.35% of Si, 0.60-0.90% of Mn, less than or equal to 0.025% of P, less than or equal to 0.020% of S, 0.9-1.20% of Cr, 0.15-0.30% of Mo, more than or equal to 0.02% of Al and the balance of Fe and inevitable impurities. The key process steps comprise a rolling procedure and a heat preservation vestibule online softening procedure. According to the on-line softening production method for the high-strength cold heading steel wire rod, the phase change rule of the high-strength cold heading steel wire rod is mastered through thermal simulation and research, and the high-strength cold heading steel wire rod is obtained under the high-speed wire rod equipment conditions of a reducing and sizing unit, a short heat collection coil Stelmor air cooling line and a heat preservation vestibule. And the pearlite and ferritic structure wire rod with the tensile strength being smaller than or equal to 820 MPa in the hot rolling state and refined and uniform grains is obtained, the softening annealing procedure before rough drawing of a fastener user is omitted, rough drawing production with the large reducing rate can be achieved, and energy consumption is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a production method for online softening of a high-strength cold heading steel wire rod. Background Art

[0002] The tensile strength of conventionally produced high-strength cold heading steel wire rods is generally between 800 and 1100 MPa, and the wire rod structure is generally dominated by bainite + ferrite. In order to ensure the cold heading performance of the fine wire material and prevent cracking during the cold heading forming process, users all adopt the "two-drawing and two-balling" process for production, that is, first softening annealing, large diameter reduction rate rough drawing, spheroidizing annealing, and fine drawing. This production process has a long production cycle, high energy consumption, high production cost, and great environmental pollution. From the development trend of cold heading steel, simplifying the production process, shortening the production cycle, reducing energy consumption, and reducing production costs are the inevitable trends of future development. Therefore, users hope to use the more economical "two-drawing and one-balling" process to replace the traditional "two-drawing and two-balling" process to produce high-strength fasteners. That is, the softening annealing process is omitted, and the large diameter reduction rate rough drawing is directly performed.

[0003] Therefore, research and development of online softening high-strength cold heading steel wire rod has broad application prospects and huge economic benefits. Summary of the invention

[0004] To achieve the above-mentioned purpose, the present invention provides a production method for online softening of high-strength cold heading steel wire rod, which can realize online softening production of high-strength cold heading steel wire rod by using a high-speed wire equipment production line with a heavy-loaded sizing unit, a relatively short hot-rolled Stelmor air cooling line and a heat-insulating corridor. The principle is that through low-temperature large-deformation hot machine rolling, a large number of dislocations and deformation bands are formed at the extremely deformed austenite grain boundaries and inside the grains, and online softening is achieved in combination with the subsequent sufficient slow cooling process phase change control.

[0005] The technical solution adopted by the present invention is:

[0006] A production method for online softening of high-strength cold heading steel wire rod, characterized in that the chemical composition of the wire rod includes, by mass percentage: C: 0.33-0.38%, Si: 0.15-0.35%, Mn: 0.60-0.90%, P≤0.025%, S≤0.020%, Cr: 0.9-1.20%, Mo: 0.15-0.30%, Al≥0.02%, and the rest is Fe and unavoidable impurities; the key process steps include:

[0007] (1) During the rolling process: low temperature rolling, the temperature of the reducing and sizing mill is 780-800°C, the spinning temperature is 740-770°C, the fans are all turned off, the insulation hoods are all closed, the insulation hood inlet temperature is 730-750°C, the insulation hood outlet temperature is 700-720°C, and the hot wire rods are collected in the insulation corridor;

[0008] (2) In the online softening process in the insulation corridor: the preheating temperature is 350-450℃, the wire rod enters the insulation corridor, the preheating device is turned off, the insulation softening time is ≥90min, the cooling rate in the insulation corridor is ≤0.15℃ / s, and the hook temperature of the wire rod out of the corridor is 350-400℃.

[0009] Preferably, the chemical composition of the wire rod includes, by mass percentage: C: 0.35%, Si: 0.18%, Mn: 0.69%, P: 0.015%, S 0.0031%, Cr: 0.98%, Mo: 0.16%, Al: 0.032%, and the rest is Fe and unavoidable impurities.

[0010] Further preferably, the chemical composition of the wire rod includes, by mass percentage: C: 0.34%, Si: 0.19%, Mn: 0.67%, P: 0.013%, S 0.0026%, Cr: 0.99%, Mo: 0.16%, Al: 0.029%, and the rest is Fe and unavoidable impurities.

[0011] Preferably, in the rolling process, the temperature of the reducing and sizing mill is 780-790°C, and the spinning temperature is 750-770°C.

[0012] In the online softening process of the insulation corridor, the preheating temperature is 370-430℃, the insulation softening time is 100min, the cooling rate of the wire rod in the insulation corridor is 0.09℃ / s, and the hook temperature of the wire rod out of the corridor is 380-400℃.

[0013] Further preferably, in the online softening process in the insulation corridor, the preheating temperature is 370-420°C, the insulation softening time is 97 minutes, the cooling rate of the wire rod in the insulation corridor is 0.10°C / s, and the hook temperature of the wire rod out of the corridor is 380-390°C.

[0014] Furthermore, the hot-rolled tensile strength of the wire rod is ≤820MPa, and the metallographic structure is pearlite+ferrite.

[0015] The beneficial effects of the present invention are as follows: according to the user's requirements for the use of high-strength cold heading steel, combined with the existing equipment capabilities, rolling and cooling process research is carried out to achieve online softening of the wire rod, thereby eliminating the user's softening annealing before rough drawing, simplifying subsequent processing procedures, and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 Metallographic structure diagram of wire rod according to Example 1 of the present invention;

[0018] Figure 2 Metallographic structure diagram of wire rod according to Example 2 of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] Embodiment 1:

[0021] A production method for online softening of high-strength cold-heading steel wire rod, with a rolling specification of Φ8.0mm.

[0022] The chemical composition by mass percentage includes: C: 0.35%, Si: 0.18%, Mn: 0.69%, P: 0.015%, S0.0031%, Cr: 0.98%, Mo: 0.16%, Al: 0.032%, as shown in Table 1.

[0023] The key process steps are as follows:

[0024] During the rolling process: the steel billet is taken out of the furnace, descaled by high-pressure water and then enters the continuous rolling mill for rolling. The temperature entering the reducing and sizing mill is 780-790℃, the water tank is quickly cooled, the wire-spinning temperature is 750-770℃, and loose coils are formed on the roller table. The fans are all turned off, the insulation covers are all closed, the insulation cover inlet temperature is 730-750℃, the insulation cover outlet temperature is 700-720℃, and the hot wire rods are collected in the insulation corridor.

[0025] In the online softening process of the insulation corridor: the insulation corridor is preheated online in advance, the ambient temperature in the insulation corridor is 370-430℃, and the doors at both ends of the corridor are closed. The wire rod enters the insulation corridor and the preheating device is turned off. The wire rod is preheated to achieve online softening. The insulation and softening time of the wire rod in the insulation corridor is 100min. The cooling rate of the wire rod in the insulation corridor is 0.09℃ / s. The hook temperature of the wire rod out of the corridor is 380-400℃. The outlet end is closed when the wire rod enters the insulation corridor, and the inlet end is closed when the wire rod leaves the insulation corridor.

[0026] The metallographic structure of the wire rod in this embodiment is pearlite + ferrite. Figure 1 As shown, the tensile strength of the hot-rolled wire rod is shown in Table 2.

[0027] Embodiment 2:

[0028] A production method for online softening of high-strength cold-heading steel wire rod, with a rolling specification of Φ12.0mm.

[0029] The chemical composition by mass percentage includes: C: 0.34%, Si: 0.19%, Mn: 0.67%, P: 0.013%, S0.0026%, Cr: 0.99%, Mo: 0.16%, Al: 0.029%, as shown in Table 1.

[0030] The key process steps are as follows:

[0031] During the rolling process: the steel billet is taken out of the furnace, descaled by high-pressure water and then enters the continuous rolling mill for rolling. The temperature entering the reducing and sizing mill is 780-790℃, the water tank is quickly cooled, the wire-spinning temperature is 750-770℃, and loose coils are formed on the roller table. The fans are all turned off, the insulation covers are all closed, the insulation cover inlet temperature is 730-750℃, the insulation cover outlet temperature is 700-720℃, and the hot wire rods are collected in the insulation corridor.

[0032] In the online softening process of the insulation corridor: the insulation corridor is preheated online in advance, the ambient temperature in the insulation corridor is 370-420℃, and the doors at both ends of the corridor are closed. The wire rod enters the insulation corridor and the preheating device is closed. The wire rod is preheated to achieve online softening. The insulation and softening time of the wire rod in the insulation corridor is 97 minutes. The cooling rate of the wire rod in the insulation corridor is 0.10℃ / s. The hook temperature of the wire rod out of the corridor is 380-390℃. The outlet end is closed when the wire rod enters the insulation corridor, and the inlet end is closed when the wire rod leaves the insulation corridor.

[0033] The metallographic structure of the wire rod in this embodiment is pearlite + ferrite. Figure 2 As shown, the tensile strength of the hot-rolled wire rod is shown in Table 3.

[0034] Table 1 Chemical composition content

[0035] chemical composition C％ Si% Mn% P％ S％ Cr％ Mo% Al％ Example 1 0.35 0.18 0.69 0.015 0.0031 0.98 0.16 0.032 Example 2 0.34 0.19 0.67 0.013 0.0026 0.99 0.16 0.029

[0036] Table 2 Hot rolled tensile strength of wire rod

[0037] Serial number 1 2 3 4 Tensile strength / MPa 754 732 748 744

[0038] Table 3 Hot rolled tensile strength of wire rod

[0039] Serial number 1 2 3 4 Tensile strength / MPa 738 736 742 742

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A production method for online softening of high-strength cold heading steel wire rod, characterized in that: The chemical composition of the wire rod includes, by mass percentage: C: 0.33-0.38%, Si: 0.15-0.35%, Mn: 0.60-0.90%, P≤0.025%, S≤0.020%, Cr: 0.9-1.20%, Mo: 0.15-0.30%, Al≥0.02%, and the rest is Fe and unavoidable impurities; the key process steps include: During the rolling process: low temperature rolling, the temperature of the reducing and sizing unit is 780-800℃, the spinning temperature is 740-770℃, the fans are all turned off, the insulation covers are all closed, the insulation cover inlet temperature is 730-750℃, the insulation cover outlet temperature is 700-720℃, and the hot wire rods are collected in the insulation corridor; In the online softening process of the insulation corridor: the preheating temperature is 350-450℃, the wire rod enters the insulation corridor, the preheating device is turned off, the insulation softening time is ≥90min, the cooling rate in the insulation corridor is ≤0.15℃ / s, and the hook temperature of the wire rod out of the corridor is 350-400℃.

2. The method for producing online softening of high-strength cold heading steel wire rod according to claim 1, characterized in that: The chemical composition of the wire rod includes, by mass percentage, C: 0.35%, Si: 0.18%, Mn: 0.69%, P: 0.015%, S0.0031%, Cr: 0.98%, Mo: 0.16%, Al: 0.032%, and the rest is Fe and unavoidable impurities.

3. The method for producing online softening of high-strength cold heading steel wire rod according to claim 1, characterized in that: The chemical composition of the wire rod includes, by mass percentage, C: 0.34%, Si: 0.19%, Mn: 0.67%, P: 0.013%, S0.0026%, Cr: 0.99%, Mo: 0.16%, Al: 0.029%, and the rest is Fe and unavoidable impurities.

4. The method for producing online softening of high-strength cold heading steel wire rod according to claim 2, characterized in that: During the rolling process, the temperature of the sizing unit is 780-790°C, and the wire drawing temperature is 750-770°C.

5. The method for producing online softening of high-strength cold heading steel wire rod according to claim 2, characterized in that: In the online softening process of the insulation corridor, the preheating temperature is 370-430℃, the insulation softening time is 100min, the cooling rate of the wire rod in the insulation corridor is 0.09℃ / s, and the hook temperature of the wire rod out of the corridor is 380-400℃.

6. The method for producing online softening of high-strength cold heading steel wire rod according to claim 3, characterized in that: In the online softening process in the insulation corridor, the preheating temperature is 370-420℃, the insulation softening time is 97min, the cooling rate of the wire rod in the insulation corridor is 0.10℃ / s, and the hook temperature of the wire rod out of the corridor is 380-390℃.

7. A method for producing high-strength cold heading steel wire rod by online softening according to any one of claims 1 to 6, characterized in that: The hot-rolled tensile strength of the wire rod is ≤820MPa, and the metallographic structure is pearlite+ferrite.

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