High-strength high-toughness corrosion-resistant cold heading rivet and preparation method thereof

Abstract

The preparation method comprises the following steps: (1) carrying out acid pickling, phosphorization and saponification on a hot-rolled wire rod, and then carrying out low-speed single-pass micro-reducing cold drawing to obtain a fine wire; (2) performing cold heading on the cold-drawn fine wire to form the shape and the size of a rivet; and (3) carrying out heat treatment on a finished product subjected to cold heading forming. The rivet is good in corrosion resistance, high in strength, high in toughness, high in plasticity and low in yield ratio, meanwhile, the cold heading rivet is high in size precision, a tiny variable-diameter step is formed, the installation efficiency is high during riveting, the mold filling effect is good after riveting, the shear load bearing capacity of a steel structural part after riveting is guaranteed, and the service life of the steel structural part is prolonged. And the installation manufacturability and the service reliability of the steel structural part are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metallurgy, and particularly relates to a high-strength high-toughness corrosion-resistant cold upsetting rivet and a preparation method thereof. BACKGROUND

[0002] At present, rivets for steel structures such as mechanical equipment, bridges, rail transit, wind power, petrochemical industry, aerospace, and construction are mainly made of carbon steel materials such as Q235, ML10, and BL3. These materials have low strength, and their components are not specially designed for corrosion resistance. With the progress of science and technology, the design of steel structures requires higher bearing capacity and corrosion resistance, and higher strength, toughness, and corrosion resistance of rivets used for connecting steel structures.

[0003] At present, the rivets for steel structures on the market are shaped according to GB / T863.1 "Half-round head rivets (rough) ". The rivet shank is completely equal in diameter. During riveting, the metal at the riveting end is directly subjected to the riveting force of the riveter, and the riveting hole is easily filled. However, the shank at the non-riveting end (rivet head end) is more difficult to fill, and for high-strength materials with poor fluidity, voids may be formed, which can cause the rivet shank near the non-riveting end to loosen under shear force, affecting the bearing capacity of the steel structure.

[0004] At present, rivets on the market are mainly formed by hot forging (commonly known as red beating) process, which has low production efficiency, poor size accuracy, and surface oxidation. Before riveting, a large installation allowance is left in the rivet hole, resulting in a large gap between the rivet shank and the riveting hole after installation, which is not conducive to the filling of the metal in the riveting hole after riveting, and affects the ability of the steel structure to withstand shear load after riveting. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the deficiencies and defects mentioned in the above background technology, and to provide a high-strength high-toughness corrosion-resistant cold upsetting rivet and a preparation method thereof.

[0006] To solve the above technical problems, the technical solution provided by the present application is as follows: A preparation method of a high-strength high-toughness corrosion-resistant cold upsetting rivet, comprising the following steps: (1) Slow single-pass micro-diameter cold drawing of hot-rolled wire rod after pickling, phosphating, and saponification to obtain fine wire; The hot-rolled wire rod is steel material, including the following components in percentage by mass: C 0.04~0.05%, Si 0.2~0.3%, Mn 0.8~0.9%, P 0.01~0.02%, S 0.002~0.003%, Ni 1.2~1.4%, Cu 0.4~0.5%, Mo 0.2~0.3%, Nb 0.01~0.02%, Al 0.02~0.03%, Ti 0.01~0.02%, and the balance of Fe and inevitable impurities; (2) cold heading the fine wire after cold drawing to the shape and size of the rivet; The finished rod part after cold heading forming includes two parts with different rod diameters, and the rod diameter of the enlarged part near the head end is larger than that of the remaining part; (3) heat treating the finished product after cold heading, the heat treatment holding temperature is 770~830℃, the holding time is 10-15h, after holding, the furnace is cooled to 450~550℃, then the product is taken out of the furnace and air cooled, to obtain the high-strength high-toughness corrosion-resistant cold heading rivet.

[0007] As a further improvement, the hot-rolled wire rod in step (1) includes the following components in percentage by mass: C 0.047%, Si 0.25%, Mn 0.88%, P 0.013%, S 0.0025%, Ni 1.34%, Cu 0.46%, Mo 0.25%, Nb 0.015%, Al 0.026%, Ti 0.014%, and the balance of Fe and inevitable impurities.

[0008] As a further improvement, in step (1), pickling is carried out with hydrochloric acid with a mass concentration of 17%-23%, and a hexamethylenetetramine corrosion inhibitor with a mass concentration of 0.2%-0.5% is added during pickling; the phosphating treatment is spraying the phosphating liquid for 2-3.2 minutes, and then soaking for 4-10.4 minutes, with the temperature controlled at 44-52℃; saponification is carried out with soap powder with a mass concentration of 7%-13%, and the saponification temperature is controlled at 75℃-90℃.

[0009] As a further improvement, in step (1), the slow single-pass micro-reduction cold drawing has a reduction ratio of 2.5%-3.0%, and the cold drawing speed is 8.5-10.5m / min.

[0010] As a further improvement, in step (2), the cold heading forming is two-step cold heading forming, the first step is to pre-form the rivet head, and the rod part length is to be to the final product length L1, and the second step is to be to the required shape and size of the final product.

[0011] As a further improvement, in the first step of the cold upsetting forming of step (2), the diameter of the shank part φY is larger than the diameter of the precision wire φX by more than 0 and less than or equal to 0.1 mm, the height L3 of the preformed part of the head is larger than the height L4 of the semi-circular head of the final product rivet, the bottom diameter D1 of the preformed part of the head is smaller than the diameter D3 of the semi-circular head of the final product rivet, and the top diameter D2 of the preformed part of the head is smaller than D1.

[0012] As a further improvement, in the second step of the cold upsetting forming of step (2), the diameter φZ1 of the shank part is larger than φY by more than 0 and less than or equal to 0.15 mm; the diameter of the enlarged part of the shank part near the head end is formed in the second step, and the diameter φZ2 of the enlarged part is larger than the diameter φZ1 of the rest of the shank part by 0-0.6 mm, excluding 0.

[0013] As a further improvement, the length L2 of the enlarged part of the shank part near the head end in step (2) is 4-15 mm.

[0014] As a further improvement, after the heat treatment of step (3), compared with before the heat treatment: the tensile strength of the rivet is improved, the elongation is improved, and the yield strength ratio is decreased.

[0015] A high-strength and high-toughness corrosion-resistant cold upsetting rivet is prepared by the preparation method.

[0016] Compared with the prior art, the present application has the following beneficial effects: (1) The corrosion-resistant rivet has good corrosion resistance, the weathering V index is above 1.29, the service life and corrosion resistance of the rivet are equal to those of the main structure material of the steel structure, and the use performance of the steel structure part is improved.

[0017] (2) The rivet has high strength, high toughness, low yield strength ratio, and high plasticity, the typical process tensile strength can reach 639 MPa, the yield strength can reach 378 MPa, the elongation can reach 26%, the yield strength ratio can reach 0.592, and the carrying capacity is 1.73 times that of ordinary rivets (tensile strength 370 MPa).

[0018] (3) The cold upsetting rivet has high dimensional accuracy and forms a small variable-diameter step, so that the installation efficiency is high during riveting, the filling effect is good after riveting, the ability of the steel structure part to bear shear load after riveting is guaranteed, and the installation process and service reliability of the steel structure part are improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0020] Figure 1 is a schematic diagram of a step-by-step micro-diameter cold upsetting forming; Figure 2 is the effect after rivet riveting; Figure 3 is the rivet head; Figure 4 is a comparative diagram of the metallographic structure before and after heat treatment of Example 1. DETAILED DESCRIPTION

[0021] In order to facilitate the understanding of the present application, the following will be more fully and specifically described in conjunction with the drawings and preferred embodiments of the present application, but the protection scope of the present application is not limited to the following specific embodiments.

[0022] Unless otherwise defined, all the professional terms used in the following have the same meaning as generally understood by those skilled in the art. The professional terms used in the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the protection scope of the present application.

[0023] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0024] The rivet of the present application adopts a low-carbon high-copper high-nickel weather-resistant steel hot-rolled wire rod, adds elements such as Ni, Cu, Mn, Mo, Nb, Al, Ti, and optimizes the element ratio, so that the rivet forms a protective rust layer on the surface during use, has good corrosion resistance, and at the same time has high strength, high toughness, low yield ratio, good riveting performance, is formed and manufactured by a cold upsetting process, realizes steel structure connection by a riveting process, the weather-resistant V index of the rivet reaches 1.29 or more, so that the rivet has superior corrosion resistance and super-long service life, and the calculation of the weather-resistant V index is V=1 / {(1.0-0.16[C])×(1.05-0.05[Si])×(1.04-0.016[Mn])×(1.0-0.5[P])×(1.0+1.9[S])×(1.0-0.1[Cu])×(1.0-0.12[Ni])×(1.0-0.3[Mo])×(1.0-1.7[Ti])}.

[0025] In some embodiments, the hot-rolled wire rod comprises the following components in mass percentage: C 0.04~0.05%, Si 0.2~0.3%, Mn 0.8~0.9%, P 0.01~0.02%, S 0.002~0.003%, Ni 1.2~1.4%, Cu 0.4~0.5%, Mo 0.2~0.3%, Nb 0.01~0.02%, Al 0.02~0.03%, Ti 0.01~0.02%, and the balance of Fe and inevitable impurities. If the carbon content is higher than the above range, it is not conducive to rivet forming, and if the copper and nickel content is lower than the above range, it is not conducive to corrosion resistance.

[0026] Slow single pass micro-diameter precision cold drawing of the hot-rolled wire rod: after the hot-rolled wire rod is subjected to pickling, phosphating and saponification treatment, it is subjected to single pass cold drawing at a drawing speed of 8.5-10.5 m / min, and the cold drawing reduction ratio is 2.5%-3.0%, to obtain a fine wire. The diameter reduction ratio=(original diameter-cold drawn diameter) / original diameter. On the one hand, the above diameter reduction ratio can ensure that the outer surface of the hot-rolled wire rod can be in contact with the inner surface of the cold drawing die, and the outer surface of the fine wire after cold drawing is smooth, the diameter tolerance is ≤0.25%, and the out-of-roundness is ≤0.025; on the other hand, it can avoid excessive work hardening and insufficient plastic deformation capacity of the material. If the diameter reduction ratio is higher than the above range, significant cold drawing hardening and processing stress will be generated, and cold heading cracking is prone to occur. Within the above slower drawing speed range, the drawing hardening can be greatly reduced. By controlling the diameter reduction ratio and the cold drawing speed, the cold drawing hardening is reduced, and the cold heading cracking is avoided.

[0027] Stepwise micro-diameter high-precision cold heading forming of the fine wire after cold drawing: the fine wire diameter φX (such as Figure 1 a) is subjected to two-step cold heading forming, the first step is to pre-form the rivet head (such as Figure 1 b), and the length of the shank is upset to the final product length L1, and the shank diameter φY is thicker than the fine wire by more than 0 and less than or equal to 0.1 mm, and the second step is to upset the rivet to the required shape and size of the final product (such as Figure 1 c), wherein the shank diameter φZ1 is thicker than φY by more than 0 and less than or equal to 0.15 mm, and the diameter of the rivet shank near the head end is increased by 0-0.6 mm (not including 0) compared to the diameter of the rest of the shank. The final rivet shank is designed to be discontinuous and slightly variable in diameter, with the diameter near the head end being slightly larger than the diameter of the rest of the shank. Through two-step forming and high-precision cold heading process, a small variable diameter step is formed, and the diameter near the head end is slightly increased, which can ensure that the rivet can be smoothly inserted into the riveting hole, and the metal near the head end can be filled into the riveting hole, which is beneficial to improve the load bearing of the riveted steel structure.

[0028] The cold upsetting process is adopted to form the rivet, the size precision of the rod part is high, the installation gap left by the rivet hole is small, a small interference is formed between the rod part and the rivet hole after riveting, the metal is well filled after riveting, the riveting structure is not easy to loosen, the bearing capacity is strong, and the riveting effect is as shown in Figure 2 .

[0029] Finally, a high-strength and high-toughness heat treatment process is performed: after the material is subjected to hot rolling, cold drawing and cold upsetting, work hardening is generated, and the degree of work hardening of the head part and the rod part is inconsistent, meanwhile, residual stress exists, the grain size is uneven, and the yield strength ratio is high, which is not conducive to actual service. In order to further improve the comprehensive performance of the rivet, a finished product heat treatment is performed, and an inert atmosphere protection process is adopted for heat treatment, so as to avoid the generation of oxide skin on the surface and affect the size precision and the installation effect of the rivet.

[0030] In order to develop a heat treatment process suitable for the material with the element composition and content of the present application, and a rivet shape suitable for the above discontinuous variable-diameter design, eliminate residual stress, and achieve optimal comprehensive performance of the rivet, a large number of tests are performed to determine that the heat treatment holding temperature is 770-830℃, the holding time is 10-15h, the temperature is cooled to 450-550℃ in the furnace after holding, and then the furnace is discharged for air cooling, and the performance is best. After heat treatment, the ferrite is recrystallized and softened, and a hard phase structure with uniform size and uniform distribution is generated. After heat treatment, the hardness of the rivet decreases, the strength increases, the elongation increases, the yield strength ratio decreases, the grain structure is more uniform, and no oxide skin is generated on the surface, and the size precision after cold upsetting is maintained, high strength, high toughness, low yield strength ratio, high plasticity, excellent comprehensive performance, and better service performance are achieved. If the furnace cooling is not performed and the air cooling is directly performed, due to the high discharge temperature, the surface will react with air to generate oxide skin, and the rapid cooling speed will increase the residual stress and cause rivet deformation, and even cracking during riveting. If the heat treatment holding temperature is lower than the above range, the elongation is improved after heat treatment, but the hardness does not change obviously, and the yield strength ratio is relatively high. If the heat treatment holding temperature is higher than the above range, the elongation is significantly improved after heat treatment, but the tensile strength and yield strength are greatly reduced.

[0031] Embodiment (1) High weather resistance index material composition and performance: the rivet adopts a low-carbon high-copper high-nickel weather resistance steel hot rolled wire rod, the material composition and content of the hot rolled wire rod are as shown in Table 1, and the performance is as shown in Table 2.

[0032] Table 1

[0033] Table 2

[0034] (2) Single pass micro-diameter precision cold-drawing of hot-rolled wire rod: The hot-rolled wire rod is treated by pickling, phosphating and saponifying, and then is subjected to single pass cold-drawing in a cold-drawing die. The cold-drawing reduction ratio is 2.5%, and the cold-drawing speed is 8.5 m / min. After cold-drawing, the precision wire diameter tolerance is ≤0.22%, and the out-of-roundness is ≤0.025%.

[0035] The pickling, phosphating and saponifying treatments include: The pickling is performed using hydrochloric acid with a concentration of 17%-23% (w / w). A hexamethylenetetramine corrosion inhibitor with a concentration of 0.2%-0.5% (w / w) is added during pickling to inhibit corrosion of the base metal by the acid, reduce iron loss and hydrogen evolution (reduce the risk of hydrogen embrittlement), help remove the oxide scale, and improve the pickling efficiency.

[0036] The phosphating treatment is performed using a conventional zinc-manganese-nickel system phosphating solution for 2-3.2 minutes of spraying and 4-10.4 minutes of immersion at a temperature of 44-52°C to obtain a denser and more protective film layer with a target film weight of 2.7-4.2 g / m².

[0037] The saponification is performed using a conventional composite soap powder with a concentration of 7%-13% (w / w) at a saponification temperature of 75-90°C to generate a lubricating metal soap film on the clean wire rod surface.

[0038] (3) Stepwise micro-diameter cold heading forming: After the precision wire is unwound and straightened by the cold heading machine, it is automatically cut to the same weight as the rivet. The cut wire is then formed into a rivet in multiple steps on a multi-station continuous cold heading machine and a matching die. The rivet is formed in two steps. In the first step, the rivet head is pre-formed, and the rod length is upset to the final product length L1. The rod diameter φY is 0-0.1 mm larger than the precision wire. The pre-formed part of the head has a vertical cross-section similar to a trapezoid. The height L3 of the pre-formed part of the head is greater than the height L4 of the final product rivet semi-circular head. The bottom diameter D1 of the pre-formed part of the head is smaller than the final product rivet semi-circular head diameter D3. The top diameter D2 of the pre-formed part of the head is smaller than D1. In the second step, the rivet is upset to the required shape and size of the final product. The rod diameter φZ1 is 0-0.15 mm larger than φY. The rod diameter increase part (length L2) is formed in the second step. The rod diameter increase part diameter φZ2 is 0-0.6 mm larger than the rest of the rod diameter φZ1. The typical dimensions of the rivet rod are shown in Table 3 as Real Object 1, Real Object 2 and Real Object 3. Table 3 (units: mm)

[0039] The rivet head is subjected to metal flow line inspection. The head metal flow line is normal, and there is no turbulent backflow phenomenon, as shown in Figure 3 .

[0040] (4) High strength and high toughness heat treatment process of finished product: The physical object 1 in Table 3 above is heat treated. The heat treatment is protected by an inert atmosphere to avoid the formation of oxide scale on the surface, which affects the surface quality and dimensional accuracy. The heat treatment holding temperature is 800℃ and the holding time is 12h. After holding, it is cooled to 500℃ in the furnace and then air-cooled after being taken out of the furnace. The performance is shown in Table 4.

[0041] Table 4

[0042] The comparative process 1 is a heat treatment at a lower temperature, with a temperature range of 450-550℃ and a holding time of 12 hours. The heat treatment is carried out in a non-atmosphere protected furnace, followed by air cooling after heating and holding.

[0043] Comparative process 2 involves a higher temperature heat treatment, where the furnace is heated to above 900°C for 0.5-1 hour in the first high temperature range, and then cooled in the furnace to above 750°C for 9.5-12 hours for heat preservation. The heating and heat preservation are carried out in an atmosphere-protected furnace, and the furnace is then cooled in the furnace to below 500°C for air cooling.

[0044] It can be seen that after heat treatment by the heat treatment process of the present invention, the tensile strength of the rivet is improved, the elongation is significantly improved, and the yield strength ratio is reduced. The improvement in tensile strength is conducive to improving the load capacity of the rivet, while the improvement in elongation and the reduction in yield strength ratio are both conducive to the plastic forming of the rivet and the riveting process is better. The rivet has a low yield strength ratio, and its energy absorption capacity, safety reserve, overload resistance, fatigue resistance and impact resistance are all better, which is conducive to the structure bearing dynamic loads and fatigue impact loads.

[0045] Compared to process 1, the elongation is improved after heat treatment, but the hardness does not change significantly, maintaining a relatively high yield strength ratio, which is not conducive to riveting construction and the fatigue and impact resistance of the structure. Compared to process 2, the elongation is significantly improved after heat treatment, but the tensile strength and yield strength are greatly reduced, which is not conducive to rivet load-bearing. In summary, the heat treatment process of this invention has the characteristics of high strength, high toughness, and low yield strength ratio, and has the best overall performance.

[0046] Comparison of metallographic structures before and after heat treatment in this embodiment ( Figure 4 (a represents before heat treatment, b represents after heat treatment) It can be observed that after heat treatment, the ferrite grains recrystallize, causing the matrix to soften. The yield strength and hardness of the rivet decrease, while the elongation increases. However, at the same time, the hard phase structure distributed along the grain boundaries changes from two types to one, and the size is more uniform and the distribution is more even. This makes the tensile strength of the rivet slightly improved after heat treatment. This metallographic structure with soft and hard phases gives the rivet excellent comprehensive mechanical properties.

[0047] The above is only the preferred embodiment of the present application, and does not limit the present application in any form. Therefore, any simple modification, equivalent change and modification of the above embodiment according to the technical essence of the present application, without departing from the technical scheme of the present application, shall fall within the protection scope of the technical scheme of the present application.

Claims

1. A method for preparing a high-strength high-toughness corrosion-resistant cold-upset rivet, characterized by comprising the steps of: The steps include the following: ​ (1) after pickling, phosphating and saponification, the hot-rolled wire rod is slowly single-pass micro-diameter cold-drawn to obtain fine wire; The hot-rolled wire rod is steel material, including the following components by mass percentage: C 0.04~0.05%, Si 0.2~0.3%, Mn 0.8~0.9%, P 0.01~0.02%, S 0.002~0.003%, Ni 1.2~1.4%, Cu 0.4~0.5%, Mo 0.2~0.3%, Nb 0.01~0.02%, Al 0.02~0.03%, Ti 0.01~0.02%, and the balance of Fe and inevitable impurities; (2) the fine wire after cold-drawing is cold-upset formed to the shape and size of the rivet; The finished rod after cold-upset forming includes two parts with different diameters, and the diameter of the enlarged part near the head end is larger than the rest; (3) the finished product after cold-upset forming is heat treated, the heat treatment holding temperature is 770~830℃, the holding time is 10-15h, after holding, the furnace is cooled to 450~550℃, then the product is taken out of the furnace and air-cooled, to obtain the high-strength high-toughness corrosion-resistant cold-upset rivet.

2. The production method according to claim 1, characterized by, The hot-rolled wire rod in step (1) includes the following components by mass percentage: C 0.047%, Si 0.25%, Mn 0.88%, P 0.013%, S 0.0025%, Ni 1.34%, Cu 0.46%, Mo 0.25%, Nb 0.015%, Al 0.026%, Ti 0.014%, and the balance of Fe and inevitable impurities.

3. The production method according to claim 1 or 2, characterized by, In step (1), the pickling is performed with hydrochloric acid with a mass concentration of 17%-23%, and a hexamethylenetetramine corrosion inhibitor with a mass concentration of 0.2%-0.5% is added during pickling; the phosphating treatment is spraying phosphating liquid for 2-3.2 minutes, then soaking for 4-10.4 minutes, and the temperature is controlled at 44-52℃; the saponification is performed with soap powder with a mass concentration of 7%-13%, and the saponification temperature is controlled at 75℃-90℃.

4. The production method according to claim 1 or 2, characterized by, In step (1), the slow single-pass micro-diameter cold-drawing has a diameter reduction ratio of 2.5%-3.0%, and the cold-drawing speed is 8.5-10.5m / min.

5. The production method according to claim 1 or 2, characterized by, In step (2), the cold-upset forming is two-step cold-upset forming, the first step is to pre-form the rivet head and to pound the rod length to the final product length L1, and the second step is to pound to the required shape and size of the final product.

6. The production method according to claim 5, wherein In the first step of the cold-upset forming in step (2), the rod diameter φY is larger than the fine wire diameter φX by more than 0 and less than or equal to 0.1mm, the pre-formed head part height L3 is larger than the final product rivet semi-circular head height L4, the pre-formed head part bottom diameter D1 is smaller than the final product rivet semi-circular head diameter D3, and the pre-formed head part top diameter D2 is smaller than D1.

7. The production method according to claim 6, characterized by, In the second step of the cold-upset forming in step (2), the rod diameter φZ1 is larger than φY by more than 0 and less than or equal to 0.15mm; the diameter of the enlarged part of the rod near the head end is formed in the second step, and the diameter φZ2 is larger than the diameter φZ1 of the rest of the rod by 0-0.6mm, excluding 0.

8. The preparation method according to claim 7, characterized in that, Step (2) the length L2 of the enlarged diameter part near the head end of the rod is 4-15 mm.

9. The production method according to claim 1 or 2, characterized by, Step (3) after heat treatment, compared with before heat treatment: the tensile strength of the rivet is improved, the hardness is decreased, the elongation is improved, and the yield ratio is decreased.

10. A high-strength high-toughness corrosion-resistant cold upset rivet, characterized by, The rivet is prepared by the method of any one of claims 1-9.

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