Manufacturing method of a non-quenched and tempered bolt

Abstract

The present invention belongs to the technical field of fastener manufacturing, and particularly relates to a manufacturing method of a non-quenched and tempered bolt. The present invention uses hot-rolled wire rods as raw materials, and through cold drawing, hot upsetting and air cooling, a non-quenched and tempered bolt with a performance grade of 8.8-10.9 is obtained. Step 1, the hot-rolled wire rods are pre-treated and cold drawn into precision wires; Step 2, the precision wires obtained in Step 1 are heated to not less than 800 °C, and the heated precision wires are hot upset into bolt blanks; Step 3, the bolt blanks obtained in Step 2 are air cooled; Step 4, the bolt blanks obtained in Step 3 are processed into bolt finished products through processes such as thread rolling and surface treatment. By optimizing the manufacturing process of 8.8-10.9 grade high-strength bolts, the present invention obtains a non-quenched and tempered bolt with a sorbite microstructure, effectively improving the plasticity of the bolt and reducing the fracture failure of the bolt.

Description

Technical Field

[0001] The present invention belongs to the technical field of fastener manufacturing, and particularly relates to a manufacturing method for non-quenched and tempered bolts. Background Art

[0002] At present, there are mainly two categories of production processes for manufacturing 8.8 - 10.9 grade bolts in China: The first category of production process is relatively traditional, usually using medium carbon steel hot-rolled wire rods as raw materials, including boron steel, high-quality carbon steel, and alloy steel. After being processed into bolts, quenching and tempering heat treatment is carried out to obtain quenched and tempered bolts with a tempered structure as the metallographic structure. The second category of production process is relatively new, usually using non-quenched and tempered cold-heading steel hot-rolled wire rods as raw materials, and obtaining non-quenched and tempered bolts with a work-hardened structure as the metallographic structure through material properties and work hardening. The representative process of the first category of production process is: wire rod - pickling - phosphating - saponification - drawing - spheroidizing annealing - pickling - phosphating - saponification - drawing - cold heading forming - thread rolling - quenching and tempering heat treatment - surface treatment. Among them, the wire rod pretreatment uses pickling, phosphating, and saponification. The preparation of fine wire requires two wire rod pretreatments and drawing, and one spheroidizing annealing is carried out to obtain quenched and tempered bolts with a tempered structure as the metallographic structure. The mechanical properties of the bolts are ensured through quenching and tempering heat treatment. The representative process flow of the second category of production process is: wire rod - pickling - phosphating - saponification - drawing - cold heading forming - thread rolling - artificial aging - surface treatment. Among them, the wire rod pretreatment uses pickling, phosphating, and saponification. The preparation of fine wire only requires one wire rod pretreatment and drawing, and there is no need for spheroidizing annealing and quenching and tempering heat treatment, obtaining non-quenched and tempered bolts with a work-hardened structure as the metallographic structure. The mechanical properties of the bolts are ensured through material properties and work hardening (processing such as cold drawing, cold heading, and cold extrusion of materials at room temperature). Work hardening is to improve the strength and hardness of materials, and artificial aging is also to further improve the strength and hardness. Relying on work hardening will inevitably reduce the plasticity of materials; if work hardening is cancelled, the traditional idea can only follow the route of quenching and tempering heat treatment.

[0003] It can be seen that although the mechanical properties of non-quenched and tempered bolts can meet the standard requirements, the production process that relies on work hardening to ensure mechanical properties greatly reduces the plasticity of the bolts, resulting in the problem of bolt fracture and failure, and thus unable to meet the actual internal control requirements of fastener manufacturing enterprises and using enterprises.

[0004] By optimizing the manufacturing process of 8.8 - 10.9 grade high-strength bolts, the present invention develops a manufacturing method for non-quenched and tempered bolts with low energy consumption, low cost, less pollution, and easy operation, effectively improving the plasticity of the bolts, reducing bolt fracture and failure, meeting the actual internal control requirements of fastener manufacturing enterprises and using enterprises, realizing the replacement of traditional quenched and tempered bolts, and then realizing industrial application, which is an urgent problem to be solved at present. Summary of the Invention

[0005] To solve the above problems, the present invention optimizes the manufacturing process of 8.8 - 10.9 grade high-strength bolts, obtaining non-quenched and tempered bolts with a sorbite metallographic structure, effectively improving the plasticity of the bolts and reducing bolt fracture failure. The manufacturing method of the non-quenched and tempered bolts of the present invention has the advantages of low energy consumption, low cost, less pollution, and easy operation.

[0006] A manufacturing method of non-quenched and tempered bolts uses hot-rolled wire rods as raw materials, and through cold drawing, hot upsetting, and air cooling, non-quenched and tempered bolts with a performance grade of 8.8 - 10.9 are obtained.

[0007] The stabilization treatment process of the present invention is described in detail below.

[0008] The specific manufacturing steps of the non-quenched and tempered bolts of the present invention are as follows:

[0009] Step 1, the hot-rolled wire rod undergoes pretreatment and is cold-drawn into fine wire; the chemical composition of the hot-rolled wire rod is: by weight percentage, C: 0.37 - 0.55%, Si: ≤0.35%, Mn: 1.35 - 1.65%, Al: 0.010 - 0.050%, P, S ≤0.025%, Cr, Ni, Cu ≤0.10%; the wire rod pretreatment method is shot peening and lime water immersion;

[0010] The specification of the hot-rolled wire rod is Φ5.0 - 42.5mm, and the specification of the fine wire cold-drawn is Φ4.2 - 40.0mm fine wire;

[0011] Step 2, the fine wire obtained in Step 1 is heated to 800 - 900°C, and the heated fine wire is hot-upset into bolt blanks;

[0012] Step 3, the bolt blanks obtained in Step 2 are air-cooled (the temperature after hot upsetting is basically the same as the temperature of the fine wire), cooled at a cooling rate of 16 - 18°C / s to 450 ± 10°C, and then placed in the air to cool naturally to room temperature;

[0013] Step 4, the bolt blanks obtained in Step 3 are processed into bolt finished products through conventional processes such as thread rolling and surface treatment.

[0014] The manufacturing process flow of the non-quenched and tempered bolts of the present invention is: wire rod - shot peening - lime water immersion - drawing - fine wire heating - hot upsetting - air cooling - thread rolling - surface treatment, which has the advantages of low energy consumption, low cost, less pollution, and easy operation compared with the existing bolt manufacturing process flow.

[0015] The wire rod pretreatment scheme uses "shot peening + lime water immersion" instead of "pickling + phosphating + saponification", simplifying the wire rod pretreatment operation, avoiding chemical waste liquid pollution, and reducing the pretreatment cost;

[0016] Select ordinary medium-high carbon steel hot-rolled wire rods with lower cost as raw materials, which can reduce the cracking rate of bolt forming; directly perform air cooling after hot upsetting forming, realizing the utilization of waste heat, ensuring the mechanical properties of bolts by obtaining sorbite structure. Sorbite has high strength and good plasticity, thereby effectively improving the plasticity of bolts and reducing bolt fracture failure. Brief Description of the Drawings

[0017] Figure 1 It is the metallographic structure diagram of the bolt prepared in Example 1. Detailed Embodiments

[0018] The non-quenched and tempered bolts in the present invention use hot-rolled wire rods as raw materials, and after cold drawing, hot upsetting and air cooling, non-quenched and tempered bolts with performance grades of 8.8 - 10.9 are obtained. The specific manufacturing process flow is: wire rod - shot peening - soaking in lime water - drawing - heating of fine wire - hot upsetting forming - air cooling - thread rolling - surface treatment.

[0019] The specifications of the hot-rolled wire rods used as raw materials are Φ5.0 - 42.5mm, and the chemical composition is: by weight percentage, C: 0.37 - 0.55%, Si: ≤0.35%, Mn: 1.35 - 1.65%, Al: 0.010 - 0.050%, P, S ≤0.025%, Cr, Ni, Cu ≤0.10%, and the rest is Fe and inevitable impurities.

[0020] The following takes the actual manufacturing of 10.9-grade M16 non-quenched and tempered flange bolts as examples and comparative examples.

[0021] Example 1

[0022] The chemical composition of the raw material hot-rolled wire rod is by weight percentage: C: 0.49%, Si: 0.20%, Mn: 1.60%, Al: 0.021%, P: 0.018%, S: 0.017%, Cr: 0.05%, Ni: 0.05%, Cu: 0.03%.

[0023] Step 1, the Φ18.0mm hot-rolled wire rod is pretreated by shot peening and soaking in lime water, and is cold drawn into Φ17.2mm fine wire by a drawing machine;

[0024] Step 2, heat the fine wire obtained in Step 1 to 880°C, and the heated fine wire is hot upset into the blank of M16 flange bolts;

[0025] Step 3, air cool the blank of M16 flange bolts obtained in Step 2, cool it to 443°C at a cooling rate of 17.5°C / s, and then place it in the air to cool naturally to room temperature;

[0026] Step 4: Process the bolt blanks obtained in Step 3 into finished M16 flange bolts through processes such as thread rolling and surface treatment.

[0027] Example 2

[0028] The chemical composition of the raw material hot-rolled wire rod is, by weight percentage: C: 0.53%, Si: 0.32%, Mn: 1.52%, Al: 0.040%, P: 0.022%, S: 0.015%, Cr: 0.07%, Ni: 0.01%, Cu: 0.02%.

[0029] Step 1: The Φ18.0mm hot-rolled wire rod is pretreated by shot peening and soaking in lime water, and then cold-drawn into Φ17.2mm fine wire through a drawing machine.

[0030] Step 2: Heat the fine wire obtained in Step 1 to 850°C, and the heated fine wire is hot-forged into M16 flange bolt blanks.

[0031] Step 3: Blow-cool the M16 flange bolt blanks obtained in Step 2, cool them at a cooling rate of 16.5°C / s to 455°C, and then place them in the air to cool naturally to room temperature.

[0032] Step 4: Process the bolt blanks obtained in Step 3 into finished M16 flange bolts through processes such as thread rolling and surface treatment.

[0033] Comparative Example 1

[0034] Replace Step 2 in Example 1 with: Cold-forge the fine wire obtained in Step 1 into M16 flange bolt blanks, cancel Step 3, and keep other conditions the same as in Example 1.

[0035] Comparative Example 2

[0036] Replace Step 3 in Example 1 with: Place the M16 flange bolt blanks obtained in Step 2 in the air to cool naturally to room temperature, and keep other conditions the same as in Example 1.

[0037] Comparative Example 3

[0038] Replace the Φ18.0mm hot-rolled wire rod in Step 1 of Example 1 with: Φ20.0mm hot-rolled wire rod; that is, the Φ20.0mm hot-rolled wire rod is pretreated by shot peening and soaking in lime water, and then cold-drawn into Φ17.2mm fine wire through a drawing machine. Replace Step 2 in Example 1 with: Cold-forge the fine wire obtained in Step 1 into M16 flange bolt blanks, cancel Step 3, and keep other conditions the same as in Example 1.

[0039] Replace the Φ18.0mm hot-rolled wire rod with Φ20.0mm, increase the reduction rate of drawing processing to improve the strength of the drawn wire, but the plasticity of the material drops sharply and the forming cracking rate rises linearly.

[0040] The comparison between the example of the present invention and the 10.9 grade M16 non-quenched and tempered flange bolts produced in the comparative example is shown in Table 1 as follows:

[0041] Table 1

[0042]

Claims

1. A manufacturing method of a non-quenched and tempered bolt, characterized in that: Using hot-rolled wire rods as raw materials, through cold drawing, hot upsetting and air cooling, non-quenched and tempered bolts with performance grades of 8.8 to 10.9 are obtained; The chemical composition of the hot-rolled wire rod is as follows: by weight percentage, C: 0.37~0.55%, Si: ≤0.35%, Mn: 1.35~1.65%, Al: 0.010~0.050%, P, S ≤0.025%, Cr, Ni, Cu ≤0.10%, and the rest is Fe and inevitable impurities; The specific manufacturing steps are as follows: Step 1, the hot-rolled wire rod undergoes pretreatment and is cold-drawn into fine wire; Step 2, the fine wire obtained in Step 1 is heated to not less than 800 °C, and the heated fine wire is hot-upset into bolt blanks; Step 3, the bolt blanks obtained in Step 2 are air-cooled; the bolt blanks are air-cooled at a cooling rate of 16~18 °C / s to 450 ± 10 °C, and then placed in the air to cool naturally to room temperature; Step 4, the bolt blanks obtained in Step 3 are processed into bolt finished products through thread rolling and surface treatment processes.

2. The manufacturing method of the non-quenched and tempered bolt according to claim 1, characterized in that: The method for preprocessing the wire rod in Step 1 is shot peening and lime water immersion.

3. The manufacturing method of the non-quenched and tempered bolt according to claim 1, characterized in that: The heating temperature of the fine wire in Step 2 is 800~900 °C.

4. The manufacturing method of the non-quenched and tempered bolt according to claim 1, characterized in that: The specifications of the hot-rolled wire rod are Φ5.0~42.5 mm, and the specifications of the fine wire cold-drawn are Φ4.2-40.0 mm.

5. The manufacturing method of the non-quenched and tempered bolt according to claim 1, characterized in that: The metallographic structure of the bolt is sorbite.

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