Weathering resistant steel, preparation method thereof and weather resistant bolt

Abstract

The invention provides weathering resistant steel, a preparation method thereof and a weathering resistant bolt, and belongs to the technical field of weathering resistant steel. According to the preparation method of the weathering resistant steel, by adding Cu, Ni and Cr, the low-temperature toughness and the fracture toughness of the steel are improved, meanwhile, the hardenability is improved, and the corrosion resistance and the high-temperature strength of the material are improved; by reducing the contents of P, S and Mn, non-metallic inclusions in the steel are reduced, the delayed fracture sensitivity of the steel is reduced, and the strength and toughness of the steel are improved; by controlling the rolling temperature, the internal structure of the material is improved, and the strength and toughness of the material are improved; and a tempered sorbite structure is formed in the material by controlling the quenching and tempering temperatures, so that the strength and toughness of the material are improved, and the mechanical properties of the material meet the use requirements of the weather-resistant bolt.

Description

Technical Field

[0001] The invention belongs to the technical field of weathering steel, and in particular relates to weathering steel and a preparation method thereof, and a weathering bolt. Background Art

[0002] In modern society, the stability and safe operation of the power system plays a vital role. As the infrastructure of the power system, the stability and durability of the transmission tower have a direct impact on the reliability of the power grid. For a long time, the materials used for transmission towers in my country are mainly hot-rolled angle steel profiles of carbon structural steel and low-alloy high-strength structural steel, which rely on hot-dip galvanizing anti-corrosion technology. However, the hot-dip galvanizing process will produce a large amount of water, gas, solid waste and noise, bringing serious environmental pollution problems; in addition, the rust removal, pickling, galvanizing and other processes of hot-dip galvanizing will cause material waste and require later maintenance. The use of weather-resistant angle steel in transmission towers can effectively solve the problems of the above materials. At present, there are relevant standards for weather-resistant angle steel in transmission towers to ensure its durability and safety in harsh environments.

[0003] However, there is a lack of weather-resistant bolts that match weather-resistant angle steels on the market, and traditional galvanized bolts are still used, making it difficult to form a complete anti-corrosion solution for weather-resistant steel structures in practical applications: Since the tower structure is mainly composed of weather-resistant angle steels connected by bolts, conventional hot-dip galvanized bolts often encounter galvanic corrosion problems when in contact with weather-resistant angle steels due to differences in electrochemical properties, which not only affects the reliability of the connection, but also shortens the service life of the entire tower structure.

[0004] In order to reduce the corrosion of bolts and increase the service life of towers, the existing technology adds an appropriate amount of element Cu to carbon steel. The grains are refined by the reaction of Cu with other elements, thereby improving the corrosion resistance of the material. However, its strength and toughness are only level 5.8, which does not meet the requirements for bolts for transmission towers. Summary of the invention

[0005] The object of the present invention is to provide a weather-resistant bolt material and a preparation method thereof and a weather-resistant bolt. The preparation method provided by the present invention can improve the strength and toughness of the weather-resistant bolt material and meet the requirements of bolts for transmission towers.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing weathering steel, comprising the following steps:

[0008] 1) hot rolling the continuous casting billet to obtain a formed billet; the hot rolling temperature is 860-1240° C.;

[0009] 2) processing the formed steel billet obtained in step 1) into a preform, and then quenching and tempering in sequence to obtain weathering steel; the quenching temperature is 860-880° C., and the tempering temperature is 450-650° C.;

[0010] The weathering steel comprises, by mass percentage, C 0.15-0.35%, Si 0.10-0.35%, Mn 0.60-1.20%, Cr 0.40-1.20%, Ni 0.40-1.20%, Cu 0.30-0.50%, P≤0.020%, S≤0.010%, and the balance Fe.

[0011] Preferably, the tempering temperature in step 2) is 550-650°C.

[0012] Preferably, the tempering temperature in step 2) is 450-500°C.

[0013] Preferably, the holding time of tempering in step 2) is 70 to 100 minutes.

[0014] Preferably, the quenching holding time in step 2) is 70 to 100 minutes.

[0015] Preferably, the cooling rate of quenching in step 2) is 12 to 18 minutes to cool to 40°C.

[0016] Preferably, in step 2), the initial rolling temperature of the hot rolling is 1000-1150° C., the final rolling temperature is 900-1050° C., and the deformation amount is 10-80%.

[0017] Preferably, in step 2), soaking is performed before hot rolling, and the soaking time is 40 to 50 minutes.

[0018] The present invention also provides weathering steel prepared by the preparation method described in the above technical solution, wherein the microstructure of the weathering steel includes tempered troostite.

[0019] The present invention also provides weather-resistant bolts prepared using the weather-resistant steel described in the above technical solution.

[0020] The invention provides a method for preparing weathering steel, comprising the following steps: 1) hot rolling a continuous casting billet to obtain a shaped steel billet; the hot rolling temperature is 860-1240°C; 2) processing the shaped steel billet obtained in the step 1) into a preform, and then quenching and tempering are performed in sequence to obtain weathering steel; the quenching temperature is 860-880°C, and the tempering temperature is 450-650°C; the weathering steel has the following components by mass percentage: C 0.15-0.35%, Si 0.10-0.35%, Mn 0.60-1.20%, Cr 0.40-1.20%, Ni 0.40-1.20%, Cu 0.30-0.50%, P≤0.020%, S≤0.010%, and the balance Fe. The invention improves the low-temperature toughness and fracture toughness of the steel by adding Cu, Ni and Cr, and improves the hardenability at the same time, which is beneficial to improving the corrosion resistance and high-temperature strength of the material; reduces the content of P, S and Mn, reduces the non-metallic inclusions in the steel, reduces the delayed fracture sensitivity of the steel, and improves the strength and toughness of the steel; controls the rolling temperature to improve the internal structure of the material, and improves the strength and toughness of the material; controls the quenching and tempering temperatures to form a tempered bainite structure in the material, thereby improving the strength and toughness of the material, and making the mechanical properties of the material meet the use requirements of weather-resistant bolts. The results of the embodiments show that the yield strength of the 6.8-grade weather-resistant bolts prepared by the preparation method provided by the present invention is 556 MPa, the tensile strength is 661 MPa, the elongation after fracture is 24.50%, and the end shrinkage rate is 74%; the yield strength of the 8.8-grade weather-resistant bolts prepared by the preparation method provided by the present invention is 808 MPa, the tensile strength is 870 MPa, the elongation after fracture is 15%, and the end shrinkage rate is 72%; the mechanical properties of the two grades of bolts meet the requirements of DL / T284-2012, the potential is -0.69 to -0.704 V, which is close to the potential of Q345NHB weather-resistant angle steel, and the potential change after coupling is within 14 mV, and no galvanic corrosion effect (higher than 50 mV) will be generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The microstructure of the weather-resistant bolt prepared in Example 1 is magnified 100 times;

[0022] Figure 2 The microstructure of the weather-resistant bolt prepared in Example 1 is magnified 500 times;

[0023] Figure 3 The microstructure of the weather-resistant bolt prepared in Example 2 is magnified 100 times;

[0024] Figure 4 The microstructure of the weather-resistant bolt prepared in Example 2 is magnified 500 times;

[0025] Figure 5 This is the galvanic corrosion potential diagram of weathering angle steel and hot-dip galvanized bolts;

[0026] Figure 6 This is the galvanic corrosion potential diagram of the weather-resistant angle steel and the weather-resistant bolt prepared in Example 1. DETAILED DESCRIPTION

[0027] All raw materials of the present invention have no particular limitation on their sources and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0028] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses high-purity or conventional purity in the field of weathering steel alloys.

[0029] The present invention provides a method for preparing weathering steel, comprising the following steps:

[0030] 1) hot rolling the continuous casting billet to obtain a formed billet; the hot rolling temperature is 860-1240° C.;

[0031] 2) processing the formed steel billet obtained in step 1) into a preform, and then quenching and tempering in sequence to obtain weathering steel; the quenching temperature is 860-880° C., and the tempering temperature is 450-650° C.;

[0032] The weathering steel comprises, by mass percentage, C 0.15-0.35%, Si 0.10-0.35%, Mn 0.60-1.20%, Cr 0.40-1.20%, Ni 0.40-1.20%, Cu 0.30-0.50%, P≤0.020%, S≤0.010%, and the balance Fe.

[0033] In the present invention, the mass percentage of C in the composition of the weathering steel is 0.15-0.35%, preferably 0.20-0.30%; as an embodiment of the present invention, the mass percentage of C in the composition of the weathering steel can be 0.18%, 0.20%, 0.23%, 0.25%, 0.28%, 0.30% or 0.32%. C is the most effective element for improving the strength and hardness of steel, but too high a content of C will reduce the plasticity and toughness of steel. The present invention limits the amount of C to the above range, which can ensure sufficient strength and maintain a certain plasticity and toughness.

[0034] In the present invention, the mass percentage of Si in the composition of the weathering steel is 0.10-0.35%, preferably 0.20-0.30%; as an embodiment of the present invention, the mass percentage of Si in the composition of the weathering steel can be 0.15%, 0.18%, 0.20%, 0.23%, 0.25%, 0.28%, 0.30% or 0.32%. Si is beneficial to improving the corrosion resistance and high temperature oxidation resistance of steel, but the increase of Si content has a greater impact on the surface quality of steel; and, with the increase of tensile strength and hardness of steel, the elongation and end shrinkage rate decrease significantly, and the cold heading performance decreases significantly. Therefore, the content of Si in bolt steel is generally required to be as small as possible, generally below 0.10%, but the bolts used for transmission towers are generally larger in specifications (M10-M64), and the cold heading performance requirements can be appropriately relaxed. The present invention limits the amount of Si to the above range, which can improve the corrosion resistance while ensuring the cold heading performance of the steel.

[0035] In the present invention, the mass percentage of Mn in the composition of the weathering steel is 0.60-1.20%, preferably 0.80-1.00%; as an embodiment of the present invention, the mass percentage of Mn in the composition of the weathering steel can be 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.00%, 1.05%, 1.10% or 1.15%. Mn can improve the strength and toughness of steel, but if its content is too high, it will form a more serious banded structure with C. The present invention limits the amount of Mn to the above range, which can improve the strength and toughness of steel and avoid the formation of banded structure.

[0036] In the present invention, the mass percentage of Cr in the composition of the weathering steel is 0.40-1.20%, preferably 0.60-1.00%; as an embodiment of the present invention, the mass percentage of Cr in the composition of the weathering steel can be 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.05% or 1.10%. Cr can improve the strength, hardness and hardenability of steel, and is beneficial to improve the corrosion resistance and high temperature strength of steel, but Cr will promote the coarsening of steel structure, resulting in increased brittleness. The present invention limits the amount of Cr to the above range, which can improve the corrosion resistance without increasing the brittleness of the steel.

[0037] In the present invention, the mass percentage of Ni in the composition of the weathering steel is 0.40-1.20%, preferably 0.60-1.00%; as an embodiment of the present invention, the mass percentage of Ni in the composition of the weathering steel can be 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.00%, 1.05%, 1.10% or 1.15%. Ni can avoid the negative impact of Cu on the surface quality of steel, and can also improve the low temperature toughness and fracture toughness of steel. The present invention limits the amount of Ni to the above range, which can improve the toughness and surface quality of steel.

[0038] In the present invention, the mass percentage of Cu in the composition of the weathering steel is 0.30-0.50%, preferably 0.35-0.45%; as an embodiment of the present invention, the mass percentage of Cu in the composition of the weathering steel can be 0.30%, 0.33%, 0.38%, 0.44%, 0.46% or 0.48%. Cu can significantly improve the weathering resistance of steel, but the surface defects of the continuous casting billet of steel increase, affecting the surface quality of the billet after hot rolling, and further affecting the cold heading performance of the steel. The present invention limits the amount of Cu to the above range, which can improve the weathering resistance on the basis of ensuring the surface quality of the steel.

[0039] In the present invention, the mass percentage of P in the weathering steel is not higher than 0.020%. P will reduce the low temperature toughness of the steel. The present invention limits the amount of P to the above range to ensure the low temperature toughness of the steel.

[0040] In the present invention, the mass percentage of S in the composition of the weathering steel is not higher than 0.010%. S is a harmful element in steel, which will reduce the toughness, impact performance and corrosion resistance of the steel. The present invention limits the amount of S to the above range, which can ensure the toughness, impact performance and corrosion resistance of the steel.

[0041] In the present invention, the composition of the weathering steel also includes a balance of Fe.

[0042] The present invention hot-rolls the continuous casting billet to obtain a formed steel billet.

[0043] The present invention has no special requirements for the refining of the continuous casting billet, and the conventional refining method in the art can be used. As an embodiment of the present invention, the temperature of the converter steel can be 1645-1665°C, the LF inlet temperature can be 1615-1635°C, the LF end temperature can be 1635-1655°C, the RH end temperature can be 1585°C, and the tundish temperature can be 1535°C.

[0044] As another embodiment of the present invention, during the steelmaking process, by adding deoxidizer and performing vacuum treatment, the hydrogen in the molten steel is controlled to be no higher than 2 ppm, and the oxygen is controlled to be no higher than 16 ppm.

[0045] In the present invention, soaking is preferably performed before hot rolling, and the soaking time is preferably 40 to 50 minutes, more preferably 42 to 45 minutes. The present invention improves the processing performance of the steel billet through soaking, is beneficial to hot rolling, and is beneficial to improving the surface quality of the steel billet formed after hot rolling.

[0046] In the present invention, the hot rolling temperature is 860-1240°C, preferably 900-1100°C, and more preferably 950-1050°C. In the present invention, the initial rolling temperature of the hot rolling is preferably 1000-1150°C, the final rolling temperature is preferably 900-1050°C, and the deformation is preferably 10-80%. The present invention controls the hot rolling parameters within the above range to improve the toughness of the steel.

[0047] The present invention has no special requirements for the specific operation of the hot rolling, and conventional operation means in the art can be used. As an embodiment of the present invention, the heating time of the hot rolling can be 3 to 4 hours, the heating temperature can be 1200 to 1240°C, the steel tapping temperature can be 1180 to 1220°C, the final rolling speed can be 16 to 20 m / s, the wire laying temperature can be 900 to 950°C, and the coiling temperature can be 500 to 600°C.

[0048] In the present invention, the shaped steel billet is preferably a wire rod or a bar, the specification of the wire rod is preferably φ16 or φ18, and the specification of the bar is preferably φ30 or φ40. The shaped steel billet of the present invention is a wire rod or a bar, which is conducive to processing the shaped steel billet into bolts.

[0049] After obtaining the formed steel billet, the present invention processes the formed steel billet into a preform and then sequentially performs quenching and tempering to obtain weathering steel.

[0050] The present invention has no special requirements on the processing method for the prefabricated parts, and any processing method well known to those skilled in the art may be used.

[0051] In the present invention, the quenching temperature is 860-880°C, preferably 865-875°C; the quenching holding time is preferably 70-100 min, more preferably 80-90 min; the quenching cooling rate is preferably 12-18 min to cool to 40°C. The present invention limits the quenching parameters within the above range, which can further improve the strength and hardness of the steel.

[0052] In the present invention, the quenching is preferably carried out in a protective gas atmosphere, and the protective gas is preferably nitrogen, argon or helium. The present invention can reduce oxidation by quenching in a protective gas, which is beneficial to improving the surface quality of the steel.

[0053] The present invention has no special requirements for the quenching device, and a quenching device commonly used in the art can be used. In an embodiment of the present invention, the quenching is performed in a quenching furnace.

[0054] In the present invention, the quenching cooling is preferably water cooling. The present invention has no special requirements for the water cooling coolant, and the coolant commonly used in the art can meet the required cooling rate.

[0055] In the present invention, the tempering temperature is 450-650° C., preferably 450-500° C. or 550-650° C. The present invention forms a tempered bainite structure in the weathering steel through tempering, thereby improving the strength and toughness of the steel material, so that it can meet the use requirements of iron tower bolts.

[0056] In a technical solution of the present invention, the tempering temperature is preferably 450-500° C., more preferably 460-490° C. When tempered at this temperature, the microstructure of the weathering steel is tempered troostite, which can make the steel have higher strength and toughness and meet the performance requirements of 8.8 grade bolts.

[0057] In another technical solution of the present invention, the tempering temperature is preferably 550-650° C., more preferably 580-630° C. When tempered at this temperature, the microstructure of the weathering steel is ferrite and tempered troostite, which can improve the strength and toughness of the steel and meet the performance requirements of grade 6.8 bolts.

[0058] In the present invention, the holding time of the tempering is preferably 70 to 100 minutes, more preferably 80 to 90 minutes. The holding time of the tempering within the above range is beneficial to further improve the strength and toughness of the steel.

[0059] In the present invention, the heating time of the tempering is preferably 15 to 25 minutes, more preferably 18 to 22 minutes. The heating time of the tempering within the above range is beneficial to further improve the strength and toughness of the steel.

[0060] The present invention has no special requirements for the tempering device, and a tempering device commonly used in the art can be used. In an embodiment of the present invention, the tempering is performed in a tempering furnace.

[0061] As an implementation mode of the present invention, the cooling method of the tempering is furnace cooling.

[0062] After tempering, the present invention preferably performs dehydrogenation treatment on the obtained tempered steel to obtain weathering steel. In the present invention, the dehydrogenation treatment is preferably performed by vacuum baking at 170-200°C for 3-6 hours. The dehydrogenation treatment of the present invention is beneficial to improving the crack resistance of the steel and reducing hydrogen embrittlement damage.

[0063] The invention improves the low-temperature toughness and fracture toughness of the steel by adding Cu, Ni and Cr, and improves the hardenability at the same time, which is beneficial to improving the corrosion resistance and high-temperature strength of the material; reduces the content of P, S and Mn, reduces the non-metallic inclusions in the steel, reduces the delayed fracture sensitivity of the steel, and improves the strength and toughness of the steel; controls the rolling temperature to improve the internal structure of the material, and improves the strength and toughness of the material; controls the quenching and tempering temperatures to form a tempered bainite structure in the material, thereby improving the strength and toughness of the material, and making the mechanical properties of the material meet the use requirements of weather-resistant bolts.

[0064] The present invention also provides weathering steel prepared by the preparation method described in the above technical solution, wherein the microstructure of the weathering steel includes tempered troostite.

[0065] The present invention also provides weather-resistant bolts prepared using the weather-resistant steel described in the above technical solution.

[0066] In the present invention, the preparation of the weather-resistant bolt preferably includes: in the preparation process of the weather-resistant steel, processing the obtained formed steel billet into a bolt profile, and then sequentially quenching and tempering to obtain the weather-resistant bolt.

[0067] In the present invention, the operations of processing the formed steel billet into the bolt profile may be pickling, drawing, forming, thread rolling and surface treatment performed in sequence. The present invention has no special limitation on the operations of pickling, drawing, forming, thread rolling and surface treatment, and a technical solution for bolt processing well known to those skilled in the art may be used.

[0068] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0069] Example 1

[0070] A method for preparing weathering steel, comprising the following specific steps:

[0071] The composition of the material is, by mass percentage, C 0.15%, Si 0.20%, Mn 0.80%, Cr 0.50%, Ni 0.40%, Cu 0.30%, P ≤ 0.020%, S ≤ 0.010%, and the balance Fe.

[0072] Steelmaking: Mix all raw materials in proportion and refine them into continuous casting billets. The steel tapping temperature of the converter is 1655℃, the LF entering temperature is 1625℃, the LF ending temperature is 1645℃, the RH ending temperature is 1585℃, and the tundish temperature is 1535℃. The hydrogen element in the molten steel is not higher than 2ppm, and the oxygen element is not higher than 16ppm.

[0073] Rolling: The continuous casting billet is rolled into wire rod, with a heating time of 3.2h, a heating section temperature of 1220℃, a steel tapping temperature of 1200℃, and a soaking time of 43min; the starting temperature of rough rolling is 1060℃, the final rolling speed is 16m / s, the deformation is 30%, the wire drawing temperature is 930℃, the coiling temperature is 560℃, and the wire rod specification is φ16.

[0074] Processing prefabricated parts: Process the wire rod into bolt prefabricated parts. The specific steps are as follows:

[0075] Pickling: ① Immerse the entire wire rod in a 25% hydrochloric acid tank at room temperature for 8 minutes to remove the oxide scale on the surface; ② Rinse the hydrochloric acid corrosion products on the wire rod surface with clean water; ③ Immerse in oxalic acid for pretreatment; ④ Immerse in phosphate treatment to form an insoluble phosphate film on the surface; ⑤ Rinse with clean water; ⑥ Apply lubricant on the surface;

[0076] Drawing: cold drawing the wire rod to the required diameter (M16);

[0077] Forming: ① Cut the wire rod into the required blank; ② One punch: The back punch presses the blank, the punch extrudes the blank, and initially forms it, and the back punch pushes the blank out; ③ Two punches: The blank enters the second die, the second die extrudes, the blank becomes oblate, and then the back punch pushes the blank out; ④ Three punches: The blank enters the third die, and is sheared by the hexagonal three-die blade, and the hexagonal head of the blank is initially formed, and then the back punch pushes the leather out, cuts it, and the hexagonal head is formed;

[0078] Thread rolling: one tooth plate is fixed, and the other movable tooth plate drives the product to move, and the surface of the blank rod is plastically deformed by extrusion to form threads;

[0079] Surface treatment: Use NaOH solution, concentration 600g / L, temperature 140℃, soak for 20min.

[0080] Quenching and tempering: Place the bolt preform in a quenching furnace, pass nitrogen for protection, heat up to 870°C in 15 minutes, keep warm for 90 minutes, take out the bolt preform and place it in a quenching liquid at 40°C, and cool the bolt preform to 40°C in 15 minutes; Place the bolt preform in a tempering furnace, heat up to 600°C in 20 minutes, keep warm for 90 minutes, and then cool with the furnace to obtain weathering steel, which is the weathering bolt.

[0081] Dehydrogenation treatment: vacuum baking at 180°C for 4 h.

[0082] Oil coated packaging.

[0083] The microstructure of the weather-resistant bolts was observed using a metallographic microscope. Figure 1 , Figure 2 As shown. Figure 1 and Figure 2 It can be seen that the microstructure of the weather-resistant bolts is ferrite and tempered troostite (tempered after quenching, the higher the tempering temperature, the lower the strength and the higher the plasticity).

[0084] According to DL / T284-2012, the mechanical properties of weather-resistant bolts were tested, with a yield strength of 556MPa, a tensile strength of 661MPa, an elongation of 24.5%, and a section shrinkage of 74%.

[0085] Example 2

[0086] A method for preparing weathering steel, comprising the following specific steps:

[0087] The composition of the material is, by mass percentage, C 0.15%, Si 0.20%, Mn 0.80%, Cr 0.50%, Ni 0.40%, Cu 0.30%, P ≤ 0.020%, S ≤ 0.010%, and the balance Fe.

[0088] Steelmaking: Mix all raw materials in proportion and refine them into continuous casting billets. The steel tapping temperature of the converter is 1655℃, the LF entering temperature is 1625℃, the LF ending temperature is 1645℃, the RH ending temperature is 1585℃, and the tundish temperature is 1535℃. The hydrogen element in the molten steel is not higher than 2ppm, and the oxygen element is not higher than 16ppm.

[0089] Rolling: The continuous casting billet is rolled into wire rod, with a heating time of 3.2h, a heating section temperature of 1220℃, a steel tapping temperature of 1200℃, and a soaking time of 43min; the starting temperature of rough rolling is 1060℃, the final rolling speed is 16m / s, the deformation is 30%, the wire drawing temperature is 930℃, the coiling temperature is 560℃, and the wire rod specification is φ18.

[0090] Processing prefabricated parts: Process the wire rod into bolt prefabricated parts. The specific steps are as follows:

[0091] Pickling: ① Immerse the entire wire rod in a 25% hydrochloric acid tank at room temperature for 8 minutes to remove the oxide scale on the surface; ② Rinse the hydrochloric acid corrosion products on the surface with clean water; ③ Immerse in oxalic acid for pretreatment; ④ Immerse in phosphate treatment to form an insoluble phosphate film on the surface; ⑤ Rinse with clean water; ⑥ Apply lubricant on the surface;

[0092] Drawing: cold drawing the wire rod to the required diameter (M20);

[0093] Forming: ① Cut the wire rod into the required blank; ② One punch: The back punch presses the blank, the punch extrudes the blank, and initially forms it, and the back punch pushes the blank out; ③ Two punches: The blank enters the second die, the second die extrudes, the blank becomes oblate, and then the back punch pushes the blank out; ④ Three punches: The blank enters the third die, and is sheared by the hexagonal three-die blade, and the hexagonal head of the blank is initially formed, and then the back punch pushes the leather out, cuts it, and the hexagonal head is formed;

[0094] Thread rolling: one tooth plate is fixed, and the other movable tooth plate drives the product to move, and the surface of the blank rod is plastically deformed by extrusion to form threads;

[0095] Surface treatment: Use NaOH solution, concentration 600g / L, temperature 140℃, soak for 20min.

[0096] Quenching and tempering: Place the bolt preform in a quenching furnace, pass nitrogen for protection, heat up to 870°C in 15 minutes, keep warm for 90 minutes, take out the bolt preform and place it in a quenching liquid at 40°C, and cool the bolt preform to 40°C in 15 minutes; Place the bolt preform in a tempering furnace, heat up to 470°C in 20 minutes, keep warm for 90 minutes, and then cool with the furnace to obtain weathering steel, which is the weathering bolt.

[0097] Dehydrogenation treatment: vacuum baking at 180°C for 4 h.

[0098] Oil coated packaging.

[0099] The microstructure of the weather-resistant bolts was observed using a metallographic microscope. Figure 3 , Figure 4 As shown. Figure 3 and Figure 4 It can be seen that the microstructure of the weather-resistant bolts is tempered troostite.

[0100] According to DL / T284-2012, the mechanical properties of weather-resistant bolts were tested, with a yield strength of 808MPa, a tensile strength of 870MPa, an elongation of 15%, and a cross-sectional shrinkage of 72%.

[0101] Test Case

[0102] The commercially available galvanized bolts (M16 / 6.8 grade, Hebei Xinde Electric Power Parts Co., Ltd.) and the weather-resistant bolts prepared in Example 1 were respectively tested with Q345NHB weather-resistant angle steel for galvanic corrosion potential. The results are as follows: Figure 5 , Figure 6 As shown. Figure 5 It can be seen that when not coupled, the potentials of Q345NHB weathering angle steel and hot-dip galvanized bolts are -0.7V (vs. SCE) and -1.1V (vs. SCE) respectively. After coupling, the mixed potential varies between -0.98 and -1.07V (vs. SCE), with a potential variation range of 90mV. The hot-dip galvanized bolts act as anodes and the Q345NHB weathering angle steel acts as cathodes, forming galvanic corrosion. Figure 6 It can be seen that the galvanic corrosion potential test data of Q345NHB weathering angle steel and weathering bolts, the uncoupled potential and the mixed potential after coupling vary between -0.69 and -0.704 V (vs. SCE), the potential change range is within 14 mV, and when the corrosion potential difference of dissimilar metals is within 50 mV, the galvanic corrosion effect can be ignored.

[0103] It can be seen from the above embodiments that the weathering steel provided by the present invention can be used to manufacture grade 6.8 and grade 8.8 weathering bolts, and the manufactured weathering bolts and weathering angle steels do not suffer from galvanic corrosion, thus meeting the use requirements of transmission towers.

[0104] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing weathering steel, comprising the following steps: 1) hot rolling the continuous casting billet to obtain a formed billet; the hot rolling temperature is 860-1240° C.; 2) processing the formed steel billet obtained in step 1) into a preform, and then quenching and tempering in sequence to obtain weathering steel; the quenching temperature is 860-880° C., and the tempering temperature is 450-650° C.; The weathering steel comprises, by mass percentage, C 0.15-0.35%, Si 0.10-0.35%, Mn 0.60-1.20%, Cr 0.40-1.20%, Ni 0.40-1.20%, Cu 0.30-0.50%, P≤0.020%, S≤0.010%, and the balance Fe.

2. The preparation method according to claim 1, characterized in that: The tempering temperature in step 2) is 550-650°C.

3. The preparation method according to claim 1, characterized in that: The tempering temperature in step 2) is 450-500°C.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The holding time of tempering in step 2) is 70 to 100 minutes.

5. The preparation method according to claim 1, characterized in that: The holding time of quenching in the step 2) is 70 to 100 minutes.

6. The preparation method according to claim 1, characterized in that: The cooling rate of quenching in the step 2) is 12 to 18 minutes to cool to 40°C.

7. The preparation method according to claim 1, characterized in that: In the step 2), the initial rolling temperature of the hot rolling is 1000-1150° C., the final rolling temperature is 900-1050° C., and the deformation amount is 10-80%.

8. The preparation method according to claim 1 or 7, characterized in that: In the step 2), soaking is performed before hot rolling, and the soaking time is 40 to 50 minutes.

9. Weathering steel prepared by the preparation method according to any one of claims 1 to 8, wherein the microstructure of the weathering steel comprises tempered troostite.

10. Weather-resistant bolts made using the weather-resistant steel according to claim 9.

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