A non-nickel annealing-free high-strength weather-resistant bolt wire rod, bolt and manufacturing method thereof

Abstract

The application discloses a nickel-free and annealing-free high-strength weather-resistant bolt wire rod, which contains Fe and inevitable impurity elements, and also contains the following chemical elements with mass percentage as follows: C: 0.05-0.14%, Si: 0.01-2.0%, Mn: 0.3-2.2%, Cr: 2.4-4.5%, Cu: 0.2-0.6%, Al: 0.01-0.1%; and the mass percentage of Cr and C satisfies Cr / C>20; and the nickel-free and annealing-free high-strength weather-resistant bolt wire rod does not contain Ni. Correspondingly, the application also discloses a manufacturing method of the nickel-free and annealing-free high-strength weather-resistant bolt wire rod, which specifically comprises the following steps: (1) smelting and casting; (2) heating; (3) rolling; (4) cooling: after rolling, the wire rod is cooled to 900-920 DEG C at a cooling speed of 4-5 DEG C / s, and then the wire rod is continuously cooled to room temperature at a cooling speed of less than 0.4 DEG C / s.

Description

TECHNICAL FIELD

[0001] The present application relates to a wire rod, a bolt and a manufacturing method thereof, in particular to a wire rod for high-strength weather-resistant bolt, a bolt and a manufacturing method thereof. BACKGROUND

[0002] Weathering steel refers to a low-alloy high-strength steel with good corrosion resistance in the atmosphere by adding a small amount of alloying elements. When phosphorus, copper, chromium and other elements are added to the steel, an amorphous spinel oxide layer about 50-100 μm thick is formed between the rust layer and the substrate. The oxide layer is dense and has good adhesion to the substrate metal, preventing oxygen and water in the atmosphere from penetrating into the steel substrate, slowing down the development of rust into the steel material, and improving the atmospheric corrosion resistance of the steel material. The atmospheric corrosion resistance of weathering steel is 2-8 times that of ordinary carbon steel, and the longer the service time, the more prominent the corrosion resistance. Weathering steel has good mechanical properties, welding properties and other use properties in addition to good weather resistance.

[0003] Bolts, as important connecting parts, can cause serious harm to the safety of the structure when they rust. In order to delay and control the corrosion of the bolt, prevent the degradation and deterioration of the bolt material, and ensure the reliability, safety and service life of the bolt, the bolt is usually subjected to surface corrosion protection treatment to improve the corrosion resistance of the bolt. Surface corrosion protection treatment refers to applying a protective layer to the surface of the metal to separate the metal from the corrosive environment to prevent or inhibit the occurrence of the corrosion process.

[0004] At present, high-strength bolts are mainly used for connection in steel structures such as buildings, bridges and power transmission towers. These bolts generally use coating methods such as hot plating, electroplating and mechanical plating to achieve corrosion resistance. However, high-strength bolts have a large pre-tightening torque and a large friction between threads, and the coating itself cannot resist the large friction. During the pre-tightening process of the bolt, the coating is often damaged, resulting in thinning of the coating, and in severe cases, the base material of the bolt is exposed to the service environment, reducing the corrosion resistance of the bolt.

[0005] Using surface coating methods, the corrosion-resistant coating needs to be maintained every 3-5 years, and re-coated every 10-15 years. Coating maintenance not only increases the cost, but also causes health hazards and environmental pollution during the coating process. Moreover, some coating processes introduce hydrogen sources into the bolt, which increases the hydrogen embrittlement sensitivity of high-strength bolts, and further induces delayed fracture and other safety hazards. Therefore, it is of great significance to develop high-strength weather-resistant bolts without coating. SUMMARY

[0006] One of the purposes of the present application is to provide a nickel-free and annealing-free high-strength weather-resistant bolt wire rod, which can obtain stronger weather resistance and atmospheric corrosion resistance to meet the requirements of free coating under the premise of not adding Ni elements.

[0007] In order to achieve the above-mentioned purpose, the present application provides a nickel-free and annealing-free high-strength weather-resistant bolt wire rod containing Fe and inevitable impurities, and further containing the following chemical elements with mass percentage as follows:

[0008] C: 0.05-0.14%, Si: 0.01-2.0%, Mn: 0.3-2.2%, Cr: 2.4-4.5%, Cu: 0.2-0.6%, Al: 0.01-0.1%, the balance being Fe and other inevitable impurities;

[0009] And the mass percentage of Cr and C satisfies: Cr / C>20.

[0010] The nickel-free and annealing-free high-strength weather-resistant bolt wire rod does not contain Ni.

[0011] Correspondingly, the present application also provides a nickel-free and annealing-free high-strength weather-resistant bolt wire rod, each chemical element of which has a mass percentage as follows:

[0012] C: 0.05-0.14%, Si: 0.01-2.0%, Mn: 0.3-2.2%, Cr: 2.4-4.5%, Cu: 0.2-0.6%, Al: 0.01-0.1%, the balance being Fe and other inevitable impurities;

[0013] And the mass percentage of Cr and C satisfies: Cr / C>20.

[0014] The design principle of each chemical element in the nickel-free and annealing-free high-strength weather-resistant bolt wire rod is as follows:

[0015] C: In the nickel-free and annealing-free high-strength weather-resistant bolt wire rod, C is an important element for forming fine and dispersed carbides after subsequent quenching and tempering, which plays a crucial role in improving the strength of the bolt. However, it should be noted that the content of C element in the steel should not be too high. When the content of C element in the steel is too high, on the one hand, it will affect the atmospheric corrosion resistance of the material, and on the other hand, it will increase the strength of the hot-rolled wire rod, which cannot meet the strength requirements of free annealing. Therefore, in order to ensure that the material of the present application has good atmospheric corrosion resistance and appropriate strength, the content of C element in the steel needs to be controlled within a reasonable range, and in the present application, the mass percentage of C element is controlled between 0.05-0.14%.

[0016] Si: In the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application, the Si element has a high solid solubility in the steel, and the addition of an appropriate amount of Si element in the steel can effectively increase the ferrite volume fraction in the steel and refine the grains, thereby facilitating the improvement of the toughness of the steel. Therefore, in order to exert the beneficial effects of the Si element, the mass percentage content of the Si element in the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application is controlled to be between 0.01-2.0%.

[0017] Mn: In the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application, the Mn element has a strong solid solution strengthening effect, and it is also an important toughening element. The addition of an appropriate amount of Mn element in the steel can significantly reduce the phase transition temperature of the steel and refine the microstructure of the steel. Based on this, considering the beneficial effects of the Mn element, the mass percentage content of the Mn element in the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application is controlled to be between 0.3-2.2%.

[0018] Cr: In the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application, the presence of Cr element can significantly accelerate the development of electrochemical corrosion products to a thermodynamic stable state. In the rust layer analysis, the Cr element can significantly accelerate the conversion process of (Fe X H Y O Z )→γ-FeOOH→α-FeOOH→α-Fe2O3, promoting the generation of spinel compounds. At the same time, the Cr element in the steel can partially replace Fe to form chromium-iron hydroxyl oxide Cr X Fe 1-X OOH, thereby making the α-FeOOH rust layer have cation selectivity and preventing Cl - , SO4 2- from penetrating into the substrate surface, so that the rust layer has a protective effect. Therefore, in order to exert the beneficial effects of the Cr element and ensure the significant improvement of the atmospheric corrosion resistance of the steel, the mass percentage content of the Cr element in the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application is controlled to be between 2.4-4.5%.

[0019] Of course, it should be noted that the Cr element will inevitably combine with the C element to form precipitates Cr 23 C6, and the precipitates Cr 23 C6 cannot improve the weather resistance of the steel. Therefore, in the present application, while controlling the mass percentage content of a single chemical element, the contents of Cr and C elements in the steel are further controlled to satisfy Cr / C>20, so as to ensure that there is enough Cr element in the steel to improve the weather resistance.

[0020] Cu: In the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application, among all alloying elements, the influence of Cu element on the weather resistance of the material is the most significant. The addition of an appropriate amount of Cu element in the steel can effectively delay the anodic dissolution of Fe or reduce the electronic conductivity of the rust layer, reducing the rate of electron flow to the cathode area. At the same time, the Cu element in the steel can also cooperate and form a small amount of insoluble copper hydroxysulfate, such as Cu4(SO4)(OH) and Cu4(SO4)(OH)4, which can precipitate in the pores of the rust layer and improve the barrier effect of the corrosion product film. However, it should be noted that the content of Cu element in the steel should not be too high, and too high Cu will cause the steel to be hot brittle, increasing the production difficulty. Therefore, in order to exert the beneficial effect of Cu element, the mass percentage content of Cu element in the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application is controlled between 0.2-0.6%.

[0021] Al: In the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application, Al is a deoxidizing agent added to the steel, which can play a deoxidizing role. In the present application, the mass percentage content of Al element is controlled between 0.01-0.1%, which is beneficial to grain refinement and improvement of the strength and toughness of the steel.

[0022] Further, in the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application, P≤0.012%, S≤0.005%.

[0023] In the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application, P element and S element are both impurity elements in the steel, and in the case of technical conditions, in order to obtain steel with better performance and quality, the content of impurity elements in the steel should be as low as possible.

[0024] S, P: In the present application, the presence of impurity element S will deteriorate the atmospheric corrosion resistance of the steel and cause the steel to be hot brittle; while P can improve the atmospheric corrosion resistance of the steel, but when the content of P element in the steel is too high, it will significantly reduce the toughness and plasticity of the steel, and also cause cold brittleness. Therefore, the content of P and S elements in the steel should be as low as possible, and in the design of the present application, very low S and P content is adopted, and the mass percentage content of P element can be controlled to P≤0.012%, and the mass percentage content of S element can be controlled to S≤0.005%.

[0025] Further, in the nickel-free annealing-free high-strength weather-resistant bolt wire rod described in the application, the microstructure is ferrite + pearlite.

[0026] Further, in the nickel-free annealing-free high-strength weather-resistant wire rod for bolts according to the present application, the weather resistance index I is greater than or equal to 8.5, where I = 26.01xCu+3.88xNi+1.20xCr+1.49xSi+17.28xP-7.29xCu xNi-9.10xNi xP-33.39xCu xP 2 ; in the formula, each chemical element is substituted by the value before the mass percentage, and for the nickel-free steel according to the present application, the value of Ni in the formula is 0.

[0027] It should be noted that for steel, the greater the value of I, the higher the atmospheric corrosion resistance of the steel. In general, a material with a weather resistance index I greater than 6 has very good atmospheric corrosion resistance.

[0028] Further, in the nickel-free annealing-free high-strength weather-resistant wire rod for bolts according to the present application, the yield strength is less than or equal to 400 MPa, the tensile strength is less than or equal to 600 MPa, the elongation is greater than or equal to 25%, and the reduction of area is greater than or equal to 60%.

[0029] In addition, another object of the present application is to disclose a bolt made of the above-mentioned nickel-free annealing-free high-strength weather-resistant wire rod for bolts. The bolt made of the nickel-free annealing-free high-strength weather-resistant wire rod for bolts not only has a mechanical property of grade 8.8-10.9, but also has very excellent atmospheric corrosion resistance. It can be applied to the fields of bridge structure, power transmission tower, photovoltaic support, etc. without coating, and has good application prospect.

[0030] To achieve the above-mentioned object, the present application provides a bolt made of the above-mentioned nickel-free annealing-free high-strength weather-resistant wire rod for bolts by at least quenching and tempering treatment. The yield strength of the bolt is greater than or equal to 720 MPa, the tensile strength is greater than or equal to 870 MPa, the elongation is greater than or equal to 16%, and the reduction of area is greater than or equal to 55%.

[0031] In the above technical solution, based on the nickel-free annealing-free high-strength weather-resistant wire rod for bolts according to the present application, the downstream user can further perform pickling, phosphorus saponification, drawing, cold heading, quenching and tempering treatment, thread rolling, etc. on the nickel-free annealing-free high-strength weather-resistant wire rod for bolts when preparing the bolt, so as to process the bolt with high strength and high weather resistance.

[0032] In some embodiments, the quenching and tempering heat treatment process specifically adopted by the downstream user can be: quenching at a temperature of 850-880℃, oil quenching after holding for 80 min; tempering at a temperature of 420-600℃, air cooling after holding for 1 h.

[0033] Accordingly, another object of the present application is to provide a manufacturing method of the above-mentioned nickel-free and annealing-free high-strength weathering bolt wire rod, which combines the component design with the control of the wire rod rolling process to inhibit the formation of copper-rich phase, and reduces the strength of the hot-rolled wire rod through the controlled cooling process to produce the required hot-rolled wire rod.

[0034] In order to achieve the above-mentioned object, the present application proposes the above-mentioned manufacturing method of the nickel-free and annealing-free high-strength weathering bolt wire rod, which comprises the following steps:

[0035] (1) smelting and casting;

[0036] (2) heating;

[0037] (3) rolling;

[0038] (4) cooling: after rolling, cooling to 900-920℃ at a cooling rate of 4-5℃ / s, and then continuing to cool to room temperature at a cooling rate of less than 0.4℃ / s.

[0039] Further, in the manufacturing method described in the present application, in step (2), the heating temperature is controlled to be 1050-1100℃, and the furnace time is controlled to be within 120min.

[0040] In this manufacturing method designed in the present application, after smelting the molten steel according to the chemical composition designed in the present application, the molten steel can be poured into ingots or billets under protective conditions after the molten steel is settled.

[0041] Accordingly, the obtained ingots or billets also need to be further subjected to the processes of heating, rolling and cooling. It should be noted that the temperature of the billet should be strictly controlled during rolling to avoid the precipitation of copper-rich phase caused by excessively high heating temperature, and therefore the process can be specifically controlled as follows: the heating temperature of the billet before rolling should be controlled to be 1050-1100℃, and the furnace time is controlled to be within 120min.

[0042] The temperature of the wire rod should be strictly controlled during cooling to avoid excessively high strength of the hot-rolled wire rod caused by too fast cooling below 900℃, and therefore after rolling, the wire rod is cooled to 900-920℃ at a cooling rate of 4-5℃ / s, and then cooled to room temperature at a cooling rate of less than 0.4℃ / s, so as to obtain the nickel-free and annealing-free high-strength weathering bolt wire rod described in the present application.

[0043] The nickel-free and annealing-free high-strength weathering bolt wire rod, bolt and manufacturing method thereof described in the present application have the following advantages and beneficial effects:

[0044] The nickel-free high-strength weather-resistant bolt wire rod without annealing provided by the present application has high strength and high weather resistance by reasonable component matching and process design, and the atmospheric corrosion resistance (weather resistance index I≥8.5) is enough to meet the requirements of free coating and plating. The yield strength of the nickel-free high-strength weather-resistant bolt wire rod without annealing is ≤400 MPa, the tensile strength is ≤600 MPa, the elongation is ≥25%, and the reduction of area is ≥60%.

[0045] The bolt made of the nickel-free high-strength weather-resistant bolt wire rod without annealing provided by the present application has yield strength ≥720 MPa, tensile strength ≥870 MPa, elongation ≥16%, and reduction of area ≥55%. The bolt not only has high strength, but also has very excellent atmospheric corrosion resistance, and can be applied in the fields of bridge structure, power transmission tower, photovoltaic support, etc. without coating. DETAILED DESCRIPTION

[0046] The nickel-free high-strength weather-resistant bolt wire rod without annealing, the bolt and the manufacturing method thereof provided by the present application will be further explained and described below in combination with specific examples, but the explanation and description do not constitute undue limitation on the technical solutions of the present application.

[0047] Examples 1-6

[0048] Table 1-1 lists the mass percentage of each chemical element of the nickel-free high-strength weather-resistant bolt wire rod without annealing in examples 1-6.

[0049] Table 1-1. (wt%, the balance is Fe and other unavoidable impurities except P and S)

[0050]

[0051] Table 1-2 lists the content relationship between some chemical elements in the nickel-free high-strength weather-resistant bolt wire rod without annealing in examples 1-6.

[0052] Table 1-2.

[0053]

[0054]

[0055] Note: In the above table 1-2, Cr and C in the formula "Cr / C" are substituted by the mass percentage of the corresponding chemical elements; and I = 26.01 × Cu + 3.88 × Ni + 1.20 × Cr + 1.49 × Si + 17.28 × P - 7.29 × Cu × Ni - 9.10 × Ni × P - 33.39 × Cu 2 , and each chemical element in the formula is substituted by the value before the percentage sign of the mass percentage of the corresponding element.

[0056] In the present application, the nickel-free annealing-free high-strength weather-resistant bolt wire rod of Examples 1-6 is prepared by the following steps:

[0057] (1) Smelting and casting according to the chemical composition shown in Table 1-1 and Table 1-2: smelting according to the designed composition, and after the molten steel is settled, pouring into 142mmx142mm square billets under protective conditions.

[0058] (2) Heating: the prepared 142mmx142mm square billets are transported to the heating furnace for heating, and the heating temperature is controlled at 1050-1100℃, and the furnace time is controlled within 120min.

[0059] (3) Rolling.

[0060] (4) Cooling: after rolling, cooling to 900-920℃ at a cooling rate of 4-5℃ / s, and then continuing to cool to room temperature at a cooling rate of less than 0.4℃ / s, to obtain the corresponding nickel-free annealing-free high-strength weather-resistant bolt wire rod.

[0061] In the present application, six steel furnaces are smelted according to the chemical composition designed in Table 1-1 and Table 1-2, i.e. Examples 1-6, and the chemical element composition and related process design of the nickel-free annealing-free high-strength weather-resistant bolt wire rod of Examples 1-6 meet the design specification requirements of the present application.

[0062] Table 2 lists the specific process parameters of the nickel-free annealing-free high-strength weather-resistant bolt wire rod of Examples 1-6 in the above process steps.

[0063] Table 2

[0064]

[0065] The obtained finished nickel-free annealing-free high-strength weather-resistant bolt wire rod of Examples 1-6 is sampled and observed, and the inventors observe that the microstructure of the nickel-free annealing-free high-strength weather-resistant bolt wire rod of Examples 1-6 is ferrite+pearlite.

[0066] Correspondingly, after the above observation and analysis, the obtained finished nickel-free annealing-free high-strength weather-resistant bolt wire rod of Examples 1-6 can be further sampled, and the wire rod samples of each example are tested for related mechanical properties, and the obtained mechanical property test results are listed in Table 3.

[0067] The related mechanical property test method is as follows:

[0068] Tensile test: under the condition of room temperature, according to GBT228-2002 metal material room temperature tensile test method, to detect the yield strength, tensile strength, elongation and reduction of area of the nickel-free annealing-free high-strength weather-resistant bolt wire rod of examples 1-6.

[0069] Table 3 lists the mechanical property test results of the finished product nickel-free annealing-free high-strength weather-resistant bolt wire rod of examples 1-6.

[0070] Table 3.

[0071]

[0072] As shown in Table 3, combined with Tables 1-2, it can be seen that the nickel-free annealing-free high-strength weather-resistant bolt wire rod of examples 1-6 has excellent corrosion resistance (weather resistance index I is greater than 8.5) while the yield strength is less than 400 MPa, the tensile strength is less than 600 MPa, the elongation is greater than 25%, and the reduction of area is greater than 60%. The atmospheric corrosion resistance of the nickel-free annealing-free high-strength weather-resistant bolt wire rod of examples 1-6 can meet the requirements of free coating.

[0073] In order to further illustrate that the annealing-free high-strength weather-resistant bolt wire rod of the application can further prepare bolts with excellent performance. Based on the annealing-free high-strength weather-resistant bolt wire rod of examples 1-6 of the application, subsequent processes such as pickling, phosphorus saponification, drawing, cold heading, quenching and tempering, and thread rolling can be further carried out to obtain high-strength weather-resistant bolts with excellent performance.

[0074] It should be noted that in some embodiments of the application, the quenching and tempering process used is: quenching temperature 850-880℃, holding for 80min and then oil quenching; tempering temperature 420-600℃, holding for 1h and then air cooling.

[0075] Therefore, for the high-strength weather-resistant bolts prepared from examples 1-6, the inventors tested the mechanical properties of each bolt, and the mechanical property test results are listed in Table 4 below. When testing the mechanical properties of the high-strength weather-resistant bolts prepared from examples 1-6, the inventors used the same tensile test method as described above in Table 3, which will not be repeated here.

[0076] Table 4 lists the mechanical properties of the high-strength weather-resistant bolts prepared from examples 1-6.

[0077] Table 4.

[0078]

[0079] As shown in Table 4 above, the yield strength Rp0.2 of the bolts prepared in Examples 1-6 are all greater than 720 MPa, the tensile strength is all greater than 870 MPa, the elongation is all greater than or equal to 16%, and the reduction of area is all greater than or equal to 55%, the mechanical properties are excellent, and the strength reaches 8.8-10.9 grade, thus being free of painting and applied in the fields of bridge structure, power transmission tower, photovoltaic support and the like.

[0080] It should be noted that the combination of the technical features in the present case is not limited to the combination manner described in the claims of the present case or the combination manner described in the specific embodiments, and all the technical features described in the present case can be freely combined or combined in any manner, unless contradictory to each other.

[0081] It should also be noted that the above-mentioned examples are only specific embodiments of the present application. Obviously, the present application is not limited to the above examples, and similar changes or modifications made in accordance with the disclosure of the present application are directly derived or easily conceived by those skilled in the art, and should all fall within the protection scope of the present application.

Claims

1. A non-nickel, non-annealed high-strength weathering bolt wire rod characterized by, The mass percentage of each chemical element is as follows: C: 0.05-0.14%, Si: 0.01-2.0%, Mn: 0.3-2.2%, Cr: 2.4-4.5%, Cu: 0.2-0.6%, Al: 0.01-0.1%; the balance is Fe and inevitable impurities; The mass percentage of Cr and C satisfies Cr / C>20; The nickel-free high-strength weather-resistant bolt wire rod without annealing has a weather resistance index I of 8.5 or more, wherein I = 26.01xCu+3.88xNi+1.20xCr+1.49xSi+17.28xP-7.29xCu xNi-9.10xNi xP-33.39xCu 2 ; each chemical element in the formula is substituted by the value before the mass percentage; The yield strength of the nickel-free annealing-free high-strength weather-resistant bolt wire rod is ≤400 MPa, the tensile strength is ≤600 MPa, the elongation is ≥25%, and the reduction of area is ≥60%.

2. The nickel-free, non-annealed high-strength weather resistant bolt wire rod of claim 1, wherein, In the inevitable impurities, P≤0.012%, S≤0.005%.

3. The nickel-free, non-annealed high-strength weather resistant bolt wire rod of claim 1, wherein, The microstructure thereof is ferrite+pearlite.

4. A bolt made of the nickel-free annealing-free high-strength weather-resistant bolt wire rod of any one of claims 1-3 at least after quenching and tempering treatment, the yield strength of the bolt is ≥720 MPa, the tensile strength is ≥870 MPa, the elongation is ≥16%, and the reduction of area is ≥55%.

5. The method of producing a nickel-free, non-annealed high-strength weather-resistant wire rod for bolts according to any one of claims 1 to 3, characterized in that, It comprises the steps of: (1) smelting and casting; (2) heating; (3) rolling; (4) cooling: after rolling, cooling to 900-920℃ at a cooling rate of 4-5℃ / s, and then continuing to cool to room temperature at a cooling rate of less than 0.4℃ / s.

6. The production method according to claim 5, wherein In step (2), the heating temperature is controlled to be 1050-1100℃, and the furnace time is controlled to be within 120 min. In step (2), the heating temperature is controlled to be 1050-1100℃, and the furnace time is controlled to be within 120 min.

Images