Cold hardening non-quenched and tempered cold heading steel wire rod and production method thereof

Abstract

The invention relates to the technical field of metallurgy, in particular to a cold hardening non-quenched and tempered cold heading steel wire rod and a production method thereof, and the cold hardening non-quenched and tempered cold heading steel wire rod comprises the following chemical components in percentage by weight: 0.12-0.28% of C, 0.05-0.35% of Si, 1.00-1.80% of Mn, 0.10-0.25% of Cr, 0.10-0.50% of Nb, 0.10-0.80% of V, 0.007-0.025% of Ti, 0.020-0.060% of Al, less than or equal to 50PPm of N, and the balance of Fe and trace impurities. According to the cold hardening non-quenched and tempered cold heading steel wire rod and the production method thereof, the surface quality of the produced wire rod is excellent, the tensile strength of the wire rod ranges from 620 Mpa to 750 Mpa, the percentage reduction of area is larger than or equal to 52%, the ductility is larger than or equal to 16%, the structure is a fine grain F + P structure, the performance of a 8.8-9.8-grade fastener is achieved after drawing, meanwhile, the heat treatment procedure is omitted, the machining cost is reduced, and the product quality is improved. And the production efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a cold-work hardening non-quenched and tempered cold heading steel wire rod and a production method thereof. Background Art

[0002] Traditional high-strength (8.8, 9.8 grade) bolts are all made of medium carbon steel, low carbon alloy steel or medium carbon alloy steel for quenching and tempering (quenching + tempering). The use of cold-worked hardened non-quenched and tempered cold heading steel to manufacture high-strength bolt products can save the annealing treatment before cold drawing of steel and the quenching and tempering treatment after bolt forming, and greatly simplify the production process, shorten the production cycle, reduce energy consumption, and avoid surface oxidation, decarburization and workpiece deformation caused by heat treatment. Therefore, it has significant economic and social benefits. Cold-worked hardened non-quenched and tempered cold heading steel is a new process route for high-strength fasteners and is the future development direction.

[0003] Non-quenched and tempered steel is produced by adding micro-alloying elements such as Nb and V and adopting the TMCP thermomechanical rolling process to achieve the performance of quenched and tempered steel after quenching and tempering, which can save heat treatment processes and achieve energy saving and consumption reduction in the production process.

[0004] Since this type of steel billet contains Nb alloying elements, the strength increment generated by the precipitation of Nb (C, N) is 50-100MPa, and it has both solute dragging and secondary pinning effects, preventing the occurrence of recrystallization and refining the grains. However, during the continuous casting process, Nb forms Nb (C, N) compounds with C and N at 1050-1100℃, which precipitate along the austenite grain boundaries, weakening the bonding force at the grain boundaries. The continuous casting straightening temperature is mostly around 900℃, causing the steel billet to crack during the straightening process, forming transverse cracks at the corners, affecting the surface quality and cold heading performance of the hot-rolled material.

[0005] There are many studies on cold-work-strengthened non-quenched and tempered high-strength bolt steel, mainly including the following types of organization, including ferrite-pearlite type, ferrite-bainite type, ferrite-martensite dual-phase type and ultrafine grain type steel. Although there are patents proposing the rolling method of 8.8-10.9 grade non-quenched and tempered cold heading steel and its hot-rolled wire rod, there is no research on the method of controlling the surface quality of cold-work-strengthened non-quenched and tempered cold heading steel billet. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a cold-work hardened non-quenched and tempered cold heading steel wire rod and a production method thereof, so as to solve the problem of controlling the surface quality of the cold-work hardened non-quenched and tempered cold heading steel billet.

[0007] Based on the above-mentioned purpose, one aspect of the present invention provides a cold work hardening non-quenched and tempered cold heading steel wire rod, the weight percentage of each chemical component is C: 0.12-0.28%, Si: 0.05-0.35%, Mn: 1.00-1.80%, Cr: 0.10-0.25%, Nb: 0.10-0.50%, V: 0.10-0.80%, Ti: 0.007-0.025%, Al: 0.020-0.060%, N≤50PPm, and the rest is Fe and trace impurities.

[0008] Furthermore, the weight percentage of the chemical components of the cold-work hardened non-tempered cold-heading steel wire rod is C: 0.13%, Si: 0.05%, Mn: 1.1%, Cr: 0.12%, Nb: 0.2%, V: 0.2%, Ti: 0.007%, Al: 0.03%, N: 45PPm, and the rest is Fe and trace impurities.

[0009] Furthermore, the weight percentage of the chemical components of the cold-work hardened non-tempered cold-heading steel wire rod is C: 0.25%, Si: 0.33%, Mn: 1.6%, Cr: 0.2%, Nb: 0.50%, V: 0.80%, Ti: 0.025%, Al: 0.055%, N: 40PPm, and the rest is Fe and trace impurities.

[0010] Another aspect of the present invention provides a method for producing a cold-work hardened non-quenched and tempered cold heading steel wire rod, comprising at least the following steps: Billet continuous casting: During the cooling stage, the first cooling water is water pipe cooling with a water flow of 1800L / min, the second cooling water is water mist cooling with a specific water volume of 0.68L / kg, and the billet straightening temperature is ≥950℃; the continuous casting speed is 2.2-2.4m / min; Billet rolling temperature control: starting rolling temperature is 960-1020℃, finishing rolling inlet temperature is 880-950℃, sizing inlet temperature is 800-860℃, and wire laying temperature is 780-860℃; Cooling after spinning: After spinning, the silk goes into the heat preservation cover, which is cooled by air. The temperature of entering the heat preservation cover is 700-800℃, and the temperature of leaving the heat preservation cover is ≤600℃. Finished wire rod products are packaged.

[0011] Optionally, the tensile strength of the wire rod is between 620-750 MPa, the cross-sectional shrinkage is ≥52%, the elongation is ≥16%, and the structure is a fine-grained F+P structure.

[0012] Beneficial effects of the invention: The invention proposes a cold-work hardened non-quenched and tempered cold heading steel wire rod and a production method thereof. The produced wire rod has excellent surface quality, and its tensile strength is between 620-750Mpa, its cross-sectional shrinkage rate is ≥52%, its elongation is ≥16%, its structure is a fine-grained F+P structure, and after drawing, it reaches the performance of 8.8-9.8 grade fasteners. At the same time, it eliminates the heat treatment process, reduces the processing cost, and improves the production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the present invention or 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 in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 This is the appearance of the finished wire rod in Example 1 after 1 / 5 cold forming; Figure 2 This is the metallographic image of the wire rod of Example 1. DETAILED DESCRIPTION

[0015] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0016] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. Example 1

[0017] A cold work hardening non-quenched and tempered cold heading steel wire rod, the weight percentage of each chemical component is C: 0.13%, Si: 0.05%, Mn: 1.1%, Cr: 0.12%, Nb: 0.2%, V: 0.2%, Ti: 0.007%, Al: 0.03%, N: 45PPm, and the rest is Fe and trace impurities.

[0018] The production method comprises the following steps: Billet continuous casting: During the cooling stage, the first cooling water is water pipe cooling with a water flow rate of 1800L / min, the second cooling water is water mist cooling with a specific water volume of 0.68L / kg, and the billet straightening temperature is 950℃; the continuous casting speed is 2.2m / min.

[0019] Billet rolling temperature control: starting rolling temperature is 960℃, finishing rolling inlet temperature is 900℃, sizing inlet temperature is 800℃, and wire laying temperature is 800℃; Cooling after spinning: After spinning, the wire rods are put into the heat preservation cover, and two heat preservation covers are opened for heat preservation. Fans are used in the heat preservation cover for air cooling. The temperature entering the heat preservation cover is 700℃, and the temperature leaving the heat preservation cover is 600℃. The finished wire rods are packaged.

[0020] The finished wire rod of this embodiment is as follows Figure 1 As shown in the figure, it can be seen that the surface quality of the wire rod produced by this embodiment is excellent, the finished wire rod does not crack after 1 / 5 cold forming, and its tensile strength is 650MPa, the cross-sectional shrinkage rate is 52%, the elongation is 17%, and the organization is a fine-grained F+P organization. The metallographic diagram is as shown in Figure 2 As shown, after drawing, the performance of 8.8-9.8 grade fasteners is achieved, eliminating the heat treatment process, reducing processing costs and improving production efficiency. Example 2

[0021] A cold-work hardening non-quenched and tempered cold heading steel wire rod, wherein the weight percentages of the chemical components are C: 0.25%, Si: 0.33%, Mn: 1.6%, Cr: 0.2%, Nb: 0.50%, V: 0.80%, Ti: 0.025%, Al: 0.055%, N: 40PPm, and the rest are Fe and trace impurities.

[0022] The production method comprises the following steps: Billet continuous casting: During the cooling stage, the first cooling water is water pipe cooling with a water flow rate of 1800L / min, the second cooling water is water mist cooling with a specific water volume of 0.68L / kg, and the billet straightening temperature is 960℃; the continuous casting speed is 2.3m / min.

[0023] Billet rolling temperature control: starting rolling temperature is 1000℃, finishing rolling inlet temperature is 950℃, sizing inlet temperature is 850℃, and wire laying temperature is 860℃; Cooling after spinning: After spinning, the wire rods are put into the heat preservation cover, and 6 heat preservation covers are opened for heat preservation. Fans are used for air cooling in the heat preservation cover. The temperature entering the heat preservation cover is 800℃, and the temperature leaving the heat preservation cover is 550℃. The finished wire rods are packaged.

[0024] The wire rod produced in this embodiment has excellent surface quality. The finished wire rod does not crack after 1 / 5 cold forming, and its tensile strength is 750MPa, the cross-sectional shrinkage rate is 54%, the elongation is 18%, and the structure is a fine-grained F+P structure. After drawing, it reaches the performance of 8.8-9.8 grade fasteners, eliminating the heat treatment process, reducing processing costs, and improving production efficiency.

[0025] Comparative Example A cold heading steel wire rod, whose composition and mass percentage are: C: 0.22%, Si: 0.08%, Mn: 0.80%, Cr: 0.05%, Ti: 0.025%, Al: 0.045%, B: 0.0020%, N: 63PPm, the rest is Fe and trace impurities, and the rest is Fe and unavoidable impurities.

[0026] The mechanical properties data of Example 1 and Example 2 are compared with those of the comparative example, as shown in Table 1: Table 1 Mechanical properties data of Example 1, Example 2 and Comparative Example

[0027] From the above comparison results, it can be seen that the wire rod produced by this embodiment has excellent surface quality, and its tensile strength is between 620-750Mpa, the cross-sectional shrinkage rate is ≥52%, the elongation is ≥16%, the structure is a fine-grained F+P structure, and after drawing, it reaches the performance of 8.8-9.8 grade fasteners. At the same time, the heat treatment process is eliminated, the processing cost is reduced, and the production efficiency is improved.

[0028] It should be understood by those skilled in the art that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention (including the claims) is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the above aspects of the present invention, which are not provided in detail for the sake of simplicity.

[0029] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A cold-work hardened non-quenched and tempered cold heading steel wire rod, characterized in that: The weight percentage of each chemical component is C: 0.12-0.28%, Si: 0.05-0.35%, Mn: 1.00-1.80%, Cr: 0.10-0.25%, Nb: 0.10-0.50%, V: 0.10-0.80%, Ti: 0.007-0.025%, Al: 0.020-0.060%, N≤50PPm, and the rest is Fe and trace impurities.

2. The cold work hardening non-quenched and tempered cold heading steel wire rod according to claim 1, characterized in that: The weight percentages of each chemical component are C: 0.13%, Si: 0.05%, Mn: 1.1%, Cr: 0.12%, Nb: 0.2%, V: 0.2%, Ti: 0.007%, Al: 0.03%, N: 45PPm, and the rest are Fe and trace impurities.

3. The cold-work-hardened non-quenched and tempered cold-headed steel wire rod according to claim 1, characterized in that: The cold work hardening non-quenched and tempered cold heading steel wire rod has the following chemical components in weight percentage: C: 0.25%, Si: 0.33%, Mn: 1.6%, Cr: 0.2%, Nb: 0.50%, V: 0.80%, Ti: 0.025%, Al: 0.055%, N: 40PPm, and the rest is Fe and trace impurities.

4. A method for producing a cold-work hardened non-quenched and tempered cold heading steel wire rod according to any one of claims 1 to 3, characterized in that: At least the following steps are included: Billet continuous casting: During the cooling stage, the first cooling water is water pipe cooling with a water flow of 1800L / min, the second cooling water is water mist cooling with a specific water volume of 0.68L / kg, and the billet straightening temperature is ≥950℃; the continuous casting speed is 2.2-2.4m / min; Billet rolling temperature control: starting rolling temperature is 960-1020℃, finishing rolling inlet temperature is 880-950℃, sizing inlet temperature is 800-860℃, and wire laying temperature is 780-860℃; Cooling after spinning: After spinning, the silk goes into the heat preservation cover, which is cooled by air. The temperature of entering the heat preservation cover is 700-800℃, and the temperature of leaving the heat preservation cover is ≤600℃. Finished wire rod products are packaged.

5. The production method according to claim 4, characterized in that: The tensile strength of the wire rod is between 620-750 MPa, the cross-sectional shrinkage is ≥52%, the elongation is ≥16%, and the structure is a fine-grained F+P structure.

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