12.9-grade annealing-free cold forging steel and rolling method thereof

Abstract

The invention relates to the technical field of metallurgy, in particular to 12.9-grade annealing-free cold forging steel and a rolling method thereof, and the 12.9-grade annealing-free cold forging steel comprises the following components in percentage by mass: 0.25 to 0.29 percent of C, less than or equal to 0.10 percent of Si, 0.35 to 0.60 percent of Mn, less than or equal to 0.030 percent of P, less than or equal to 0.030 percent of S, 0.40 to 0.60 percent of Cr, 0.0015 to 0.0035 percent of B, 0.12 to 0.21 percent of Mo, 0.010 to 0.020 percent of V, 0.010 to 0.015 percent of La and the balance of Fe and inevitable impurities. The strength and hardness of the material are reduced and the plasticity is improved by properly reducing the contents of Si and Mn, and meanwhile, the hardenability of the material is improved by adding a proper amount of B, V and Re (La) elements. And after the annealing process of downstream users is reduced, the time cost is saved, and the energy consumption cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a 12.9-grade annealing-free cold heading steel and a rolling method thereof. Background Art

[0002] The main processing technology for 12.9-grade bolts during wire rod reform is one ball and two draws or two balls and two draws, that is, pickling and phosphorus saponification → drawing → annealing → drawing, or annealing → pickling and phosphorus saponification → drawing → annealing → drawing. The steel used for 12.9-grade bolts has a high C content, so the material hardness is high and the plastic deformation ability is poor. Fastener manufacturers need to perform spheroidizing annealing before cold heading to soften the material, reduce the hardness of the material, and reduce the cracking that may be caused during the cold heading process. The manufacturer's annealing process increases the time cost and also increases the energy cost. Summary of the invention

[0003] In view of this, the purpose of the present invention is to propose a 12.9 grade annealing-free cold heading steel and a rolling method thereof, so as to solve the problem that annealing treatment is required before the existing cold heading process, which increases the time cost and energy consumption cost.

[0004] Based on the above purpose, one aspect of the present invention provides a 12.9 grade annealing-free cold heading steel, whose composition and mass percentage are: C: 0.25-0.29%, Si: ≤0.10%, Mn: 0.35-0.60%, P: ≤0.030%, S: ≤0.030%, Cr: 0.40-0.60%, B: 0.0015-0.0035%, Mo: 0.12-0.21%, V: 0.010-0.020%, La: 0.010-0.015%, and the rest are Fe and unavoidable impurities.

[0005] Furthermore, the composition and mass percentage of the 12.9 grade annealing-free cold heading steel are: C: 0.26%, Si: 0.8%, Mn: 0.4%, P: 0.020%, S: 0.025%, Cr: 0.45%, B: 0.0016%, Mo: 0.13%, V: 0.013%, La: 0.011%, and the rest are Fe and unavoidable impurities.

[0006] Furthermore, the composition and mass percentage of the 12.9 grade annealing-free cold heading steel are: C: 0.28%, Si: 0.6%, Mn: 0.55%, P: 0.020%, S: 0.020%, Cr: 0.56%, B: 0.0032%, Mo: 0.2%, V: 0.018%, La: 0.015%, and the rest are Fe and unavoidable impurities.

[0007] Another aspect of the present invention provides a rolling method for 12.9 grade annealing-free cold heading steel, comprising at least the following steps: Billet heating: The billet is heated in three stages in the heating furnace. The temperature of the first stage is 840-890℃, the temperature of the second stage is 1000-1100℃, and the temperature of the soaking stage is 1120-1180℃. High-pressure water dephosphorization: The steel billet is dephosphorized by high-pressure water, the dephosphorization water pressure is ≥14MPa, and the rolling temperature is controlled at 1020-1080℃; Controlled rolling and controlled cooling: finishing rolling inlet temperature is 880-940℃, sizing inlet temperature is 830~870℃, and spinning temperature is 830~880℃; Insulation after rolling: After the wire rod is formed, it enters the insulation channel for insulation to ensure that the outlet temperature is within 550℃.

[0008] Optionally, the post-rolling insulation specifically includes: after spinning, the hot coil is quickly rolled down through three-stage rollers and enters the insulation channel, ensuring that the temperature entering the insulation channel is 700-800°C, the insulation channel runs at a speed of 0.04m / s, and the outlet temperature of the channel is ensured to be within 550°C.

[0009] Optionally, the tensile strength of the wire rod is 650-750 MPa, the cross-sectional shrinkage is ≥45%, the hardness is ≤82 HRB, and the hardness of the wire rod after being drawn into a fine wire is 90-95 HRB.

[0010] Beneficial effects of the present invention: The 12.9-grade cold heading steel and the rolling method thereof proposed in the present invention reduce the hot-rolled hardness and the cold working hardening index by appropriately reducing the contents of Si and Mn, reduce the hardness increase during the drawing and rounding process of the wire rod, and simultaneously add trace amounts of B, V, and La elements to increase the hardenability, so that after the wire rod is drawn into a fine wire, the hardness of the fine wire can be controlled within 93HRB. During the rolling process, the wire rod forms a relatively fine and spheroidized pearlite structure by appropriately reducing the sizing temperature and the wire drawing temperature and keeping the wire drawing temperature in a heat preservation channel for a long time after the wire drawing, thereby ensuring that the wire rod has excellent cold drawing and cold heading properties. The cold heading steel fastener manufacturer produced by the present invention does not need to perform spheroidizing annealing treatment and can directly perform cold heading processing, saving time cost and reducing energy consumption cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 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.

[0012] Figure 1is the metallographic diagram of the wire rod in Example 1; Figure 2 This is the metallographic image of the wire rod in Example 2. DETAILED DESCRIPTION

[0014] 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.

[0015] 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

[0016] A 12.9 grade annealing-free cold heading steel, whose composition and mass percentage are: C: 0.26%, Si: 0.8%, Mn: 0.4%, P: 0.020%, S: ≤0.025%, Cr: 0.45%, B: 0.0016%, Mo: 0.13%, V: 0.013%, La: 0.011%, and the rest are Fe and unavoidable impurities.

[0017] The cold heading steel is rolled by first heating the steel billet in a heating furnace in three stages, with the first stage heating temperature at 850°C, the second stage heating temperature at 1000°C, and the soaking stage temperature at 1150°C; The heated steel billet is first descaled by high-pressure water and then rolled, where the descaling water pressure is 15MPa and the rolling temperature is 1050℃; After the initial rolling, the steel billet is subjected to finishing rolling, sizing reduction and wire drawing. A 1# cooling water section is provided between the initial rolling and finishing rolling, a 2# cooling water section is provided between the finishing rolling and sizing reduction, and a 3# cooling water section is provided between the sizing reduction and wire drawing. The temperature is controlled according to the parameters in Table 1.

[0018] Table 1

[0019] After spinning, the wire is quickly rolled down through three rollers and enters the insulation channel to ensure that the temperature entering the insulation channel is 720°C. The running speed of the insulation channel is 0.04m / s, ensuring that the temperature out of the channel is 550°C. This embodiment reduces the content of Si and Mn, thereby reducing the strength and hardness of the material, improving plasticity, and at the same time improving the hardenability of the material by adding appropriate amounts of B, V, and Re elements. The wire rod produced in this embodiment has a tensile strength of 660MPa, an elongation of 15%, a cross-sectional shrinkage of 46%, a hardness of 79HRB, a ferrite grain size of 10, and a hardness of 90HRB after the wire rod is drawn into a fine wire. The metallographic diagram is shown in the figure. Example 2

[0020] A 12.9 grade annealing-free cold heading steel, whose composition and mass percentage are: C: 0.28%, Si: 0.6%, Mn: 0.55%, P: 0.020%, S: 0.020%, Cr: 0.56%, B: 0.0032%, Mo: 0.2%, V: 0.018%, La: 0.015%, and the rest are Fe and unavoidable impurities.

[0021] The cold heading steel is rolled by first heating the steel billet in a heating furnace in three stages, with the first stage heating temperature at 880°C, the second stage heating temperature at 1060°C, and the soaking stage temperature at 1170°C. The heated steel billet is first descaled by high-pressure water and then rolled. The descaling water pressure is 16MPa and the rolling temperature is 1070℃. After the initial rolling, the steel billet is subjected to finishing rolling, sizing reduction and wire drawing. A 1# cooling water section is provided between the initial rolling and finishing rolling, a 2# cooling water section is provided between the finishing rolling and sizing reduction, and a 3# cooling water section is provided between the sizing reduction and wire drawing. The temperature is controlled according to the parameters in Table 2.

[0022] Table 2

[0023] After spinning, the wire is quickly rolled down through three rollers and enters the insulation channel to ensure that the temperature entering the insulation channel is 780°C. The running speed of the insulation channel is 0.04m / s, ensuring that the temperature out of the channel is 550°C. This embodiment reduces the content of Si and Mn, thereby reducing the strength and hardness of the material and improving the plasticity. At the same time, by adding appropriate amounts of B, V, and Re elements, the hardenability of the material is improved. The wire rod produced in this embodiment has a tensile strength of 730MPa, an elongation of 14%, a cross-sectional shrinkage of 47%, and a hardness of 76HRB. The hardness of the wire rod after being drawn into a fine wire is 93HRB. The metallographic diagram is as follows Figure 2 shown.

[0024] Comparative Example A 12.9 grade cold heading steel, whose composition and mass percentage are: C: 0.34%, Si: 0.18%, Mn: 0.70%, P: 0.022%, S: 0.021%, Cr: 0.98%, Mo: 0.17%, and the rest is Fe and unavoidable impurities.

[0025] The mechanical properties data of Example 1 and Example 2 are compared with those of the comparative example, as shown in Table 3: Table 3 Mechanical properties data of Example 1, Example 2 and Comparative Example

[0026] From the above comparison results, it can be seen that the 12.9 grade cold heading steel and the rolling method thereof proposed in the present invention, by appropriately reducing the content of Si and Mn to reduce the hot-rolled hardness and the cold work hardening index, reduce the hardness increase during the drawing and rounding process of the wire rod, and at the same time add trace amounts of B, V, and La elements to increase the hardenability, so that after the wire rod is drawn into a fine wire, the hardness of the fine wire can be controlled within 93HRB. During the rolling process, by appropriately reducing the sizing temperature and the wire drawing temperature and keeping the wire in a heat preservation channel for a long time after the wire drawing, the wire rod forms a finer and spheroidized pearlite structure, thereby ensuring that the wire rod has excellent cold drawing and cold heading properties. The cold heading steel fastener manufacturer produced by the present invention does not need to perform spheroidizing annealing treatment, and can directly perform cold heading processing, saving time cost and reducing energy consumption cost.

[0027] 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.

[0028] 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 12.9 grade annealing-free cold heading steel, characterized in that: Its composition and mass percentage are: C: 0.25-0.29%, Si: ≤0.10%, Mn: 0.35-0.60%, P: ≤0.030%, S: ≤0.030%, Cr: 0.40-0.60%, B: 0.0015-0.0035%, Mo: 0.12-0.21%, V: 0.010-0.020%, La: 0.010-0.015%, and the rest are Fe and unavoidable impurities.

2. The 12.9 grade annealing-free cold heading steel according to claim 1, characterized in that: The composition and mass percentage of the 12.9 grade annealing-free cold heading steel are: C: 0.26%, Si: 0.8%, Mn: 0.4%, P: 0.020%, S: 0.025%, Cr: 0.45%, B: 0.0016%, Mo: 0.13%, V: 0.013%, La: 0.011%, and the rest are Fe and unavoidable impurities.

3. The 12.9 grade annealing-free cold heading steel according to claim 1, characterized in that: The composition and mass percentage of the 12.9 grade annealing-free cold heading steel are: C: 0.28%, Si: 0.6%, Mn: 0.55%, P: 0.020%, S: 0.020%, Cr: 0.56%, B: 0.0032%, Mo: 0.2%, V: 0.018%, La: 0.015%, and the rest are Fe and unavoidable impurities.

4. A rolling method for the 12.9 grade annealing-free cold heading steel according to any one of claims 1 to 3, characterized in that: At least the following steps are included: Billet heating: The billet is heated in three stages in the heating furnace. The temperature of the first stage is 840-890℃, the temperature of the second stage is 1000-1100℃, and the temperature of the soaking stage is 1120-1180℃. High-pressure water dephosphorization: The steel billet is dephosphorized by high-pressure water, the dephosphorization water pressure is ≥14MPa, and the rolling temperature is controlled at 1020-1080℃; Controlled rolling and controlled cooling: finishing rolling inlet temperature is 880-940℃, sizing inlet temperature is 830~870℃, and spinning temperature is 830~880℃; Insulation after rolling: After the wire rod is formed, it enters the insulation channel for insulation to ensure that the outlet temperature is within 550℃.

5. The rolling method according to claim 4, characterized in that: The post-rolling insulation specifically includes: after spinning, the hot coil is quickly lowered through three-stage rollers and enters the insulation channel, ensuring that the temperature entering the insulation channel is 700-800°C, the insulation channel runs at a speed of 0.04m / s, and the outlet temperature of the channel is ensured to be within 550°C.

6. The rolling method according to claim 4, characterized in that: The tensile strength of the wire rod is 650-750MPa, the cross-sectional shrinkage is ≥45%, the hardness is ≤82HRB, and the hardness of the wire rod after being drawn into a fine wire is 90-95HRB.

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