Production method of marine climate resistant steel for bridge rivets

Abstract

The invention discloses a production method of marine climate resistant steel for bridge rivets. The steel comprises the following chemical components in percentage by weight: 0.03%-0.06% of C, 0.15%-0.30% of Si, 0.80%-1.00% of Mn, less than or equal to 0.015% of P, less than or equal to 0.003% of S, 1.3%-1.4% of Ni, 0.45%-0.50% of Cu, 0.20%-0.30% of Mo, 0.01%-0.03% of Nb, 0.02%-0.05% of Al, 0.01%-0.02% of Ti and the balance of Fe and inevitable impurities. The marine climate-resistant bridge rivet steel adopting a special finished product design has the characteristic of better marine climate corrosion resistance. A produced wire rod is good in surface quality and good in cold extrusion deformation capacity, and the performance of a produced rivet can meet the use requirement. According to the innovative production, the rivet resistant to marine climate corrosion can be produced and used for connecting bridges nearby the coastal area, connection failure caused by marine climate can be remarkably relieved, the safety performance of the bridges is improved, and the comprehensive maintenance cost of the bridges is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a production method of steel for ocean-weather-resistant bridge rivets. Background Art

[0002] The wetting time of the metal surface is a complex variable that determines the duration of the electrochemical corrosion process. When the metal surface is in air that is higher than its temperature, the water vapor contained in the air will condense on the metal surface as liquid. This phenomenon is called condensation. Whether the metal surface can condense is related to the humidity of the air. The higher the air humidity, the easier it is for the metal surface to condense, the longer the electrolyte film on the surface exists, and the corrosion rate increases accordingly. In the atmosphere near the ocean, seawater droplets containing sodium chloride are mixed into the atmosphere when the sea spray disperses, so there are more Cl- or NaCl particles in the atmosphere. If NaCl particles fall on the metal surface, it has a hygroscopic effect, which increases the conductivity of the surface liquid film layer. The chloride ions themselves are very corrosive, making the corrosion more serious.

[0003] The rapid development of bridge construction in coastal areas has also put forward higher requirements on the comprehensive performance of steel used in bridges, that is, the steel used on bridges must have good mechanical properties and suitable atmospheric corrosion resistance. Riveting, as an important connection method in bridge structures, has a wide range of application scenarios. In marine climates, it is difficult for traditional rivets to form a protective rust layer on the surface, and it is impossible to effectively prevent the corrosion of the steel matrix by corrosive media in the atmosphere. Therefore, it is necessary to research and develop a weather-resistant rivet steel that can be used safely and for a long time in a marine atmospheric environment. Summary of the invention

[0004] The purpose of the present invention is to provide a method for producing marine weather resistant steel for bridge rivets. The produced marine weather resistant steel for bridge rivets is formed into rivets by cold extrusion, has good comprehensive performance, meets customer requirements, and has a weather resistance index of more than 1.30.

[0005] The technical solution of the present invention: A method for producing marine weather resistant bridge rivet steel, wherein the chemical composition of the steel is C=0.03%-0.06%, Si=0.15%-0.30%, Mn=0.80%-1.00%, P≤0.015%, S≤0.003%, Ni=1.3%-1.4%, Cu=0.45%-0.50%, Mo=0.20%-0.30%, Nb=0.01%-0.03%, Al=0.02%-0.05%, Ti=0.01%-0.02%, and the rest is Fe and unavoidable impurities. The production is carried out according to the process flow of converter-LF-RH-continuous casting-rolling, and the process steps are as follows: (1) Converter: endpoint control C≤0.05%, P≤0.010%; (2) LF: Use Al particles for diffusion deoxidation to make the LF refined slag white and ensure a certain Al content; (3) RH: vacuum degassing, maintain vacuum time ≥ 8 min, blow Ar gas from the bottom after breaking the vacuum, soft blowing time ≥ 10 min; (4) Continuous casting: Use a casting speed of 2.2 m / min, low secondary cooling water ratio, the billet is placed in the slow cooling pit for ≥ 24 hours, and the billet is ground to a depth of 1.0-1.5 mm; (5) Rolling: The temperature of the soaking section is 1150±20℃, the descaling pressure after the furnace is not less than 15MPa, the temperature of the finishing rolling is 850±20℃, the water tank is cooled after finishing rolling, and the coiling temperature is 850±20℃.

[0006] Principle of the invention: In the step (1) converter, the final C content is ≤0.05%, and the P content is ≤0.010%, so as to ensure that the C content of the finished product can reach a relatively low target. The low P content of the steel produced ensures that the steel has low P content, thereby improving the cold extrusion performance of the steel.

[0007] In step (2) LF, Al particles are used for diffusion deoxidation to make the LF refined slag white and ensure a certain Al content; Al can refine the grains, improve the plasticity of the steel, and ensure the processing performance of the steel in the subsequent cold extrusion process.

[0008] In step (3) RH, vacuum degassing is performed, and the vacuum time is maintained for ≥8 min. After breaking the vacuum, Ar gas is blown from the bottom, and the soft blowing time is ≥10 min. Maintaining the vacuum time can reduce the hydrogen content in the steel to below 2 ppm, thereby improving the purity of the steel and reducing the risk of hydrogen-induced cracking of the steel during long-term use.

[0009] In step (4), during continuous casting, a pulling speed of 2.2 m / min and a low secondary cooling water ratio are used, the straightening temperature of the steel billet corner is controlled to be ≥ 900 degrees, and the billet is placed in a slow cooling pit for ≥ 24 hours. The effect is that a high pulling speed and low secondary cooling water are used to ensure the straightening temperature of the steel billet and prevent cracks from forming on the surface of the steel billet. The slow cooling of the billet releases the hydrogen content in the steel and reduces the probability of cracks forming on the surface of the steel.

[0010] During the rolling of step (5), the temperature of the soaking section is 1150±20°C, the descaling pressure after the furnace is not less than 15MPa, the temperature of the finishing rolling is 850±20°C, the steel is cooled in a water tank after finishing rolling, and the coiling temperature is 850±20°C to ensure that the steel grains are fine and uniform.

[0011] The advantages of the present invention are as follows: the steel for bridge rivets resistant to marine climates, which is designed with special finished products, has good marine climate corrosion resistance. The produced wire rod has good surface quality and good cold extrusion deformation ability, and the performance of the produced rivets can meet the use requirements. This innovative production can produce rivets resistant to marine climate corrosion with a weather resistance index of more than 1.30, which can be used for bridge connections near the coast, significantly slowing down the connection failure caused by marine climate, improving the safety performance of bridges and saving the comprehensive maintenance cost of bridges. DETAILED DESCRIPTION

[0012] The present invention will be further described below in conjunction with the embodiments. Example 1

[0013] A method for producing marine weather resistant bridge rivet steel, which is produced according to the process flow of converter-LF-RH-continuous casting-rolling, and the rolling specification is Φ23mm. The chemical composition of the steel is C=0.04%, Si=0.20%, Mn=0.91%, P=0.012%, S=0.002%, Ni=1.34%, Cu=0.47%, Mo=0.25%, Nb=0.021%, Al=0.032%, Ti=0.015%, and the rest is Fe and unavoidable impurities; the production process is as follows: (1) Converter: final P content 0.009%, C content 0.04%; (2) LF: Al particles are used for diffusion deoxidation, LF becomes white slag, the white slag retention time is 20 minutes, and the Al content in the steel is 0.035%; (3) RH: vacuum degassing, maintain vacuum time for 8 minutes, blow Ar gas from the bottom after breaking the vacuum, and soft blowing time for 12 minutes; (4) Continuous casting: The casting speed is 2.2 m / min, the straightening temperature of the steel billet corner is 920 degrees, the steel billet is put into the slow cooling pit for 32 hours; the full grinding depth of the steel billet is 1.2 mm; (5) Rolling: The temperature of the soaking section is 1150-1160°C, the descaling pressure after the furnace is 15 MPa, the finishing rolling temperature is 850-860°C, the water tank is cooled after finishing rolling, and the coiling temperature is 850-860°C. Example 2

[0014] A method for producing marine weather resistant bridge rivet steel, which is produced according to the process flow of converter-LF-RH-continuous casting-rolling, and the rolling specification is Φ23mm. The chemical composition of the steel is as follows by weight: C=0.05%, Si=0.21%, Mn=0.92%, P=0.011%, S=0.002%, Ni=1.35%, Cu=0.46%, Mo=0.25%, Nb=0.022%, Al=0.031%, Ti=0.014%, and the rest is Fe and unavoidable impurities. The production process is as follows: (1) Converter: final P content 0.010%, C content 0.04%; (2) LF: Al particles are used for diffusion deoxidation, LF becomes white slag, the white slag retention time is 22 minutes, and the Al content in the steel is 0.038%; (3) RH: vacuum degassing, maintaining vacuum time for 8 minutes, bottom blowing Ar gas after breaking the vacuum, soft blowing time for 14 minutes; (4) Continuous casting: The casting speed is 2.2 m / min, the straightening temperature of the steel billet corner is 910 degrees, the steel billet is put into the slow cooling pit for 35 hours; the full grinding depth of the steel billet is 1.2 mm; (5) Rolling: The temperature of the soaking section is 1150-1170°C, the descaling pressure after the furnace is 15 MPa, the finishing rolling temperature is 850-860°C, the water tank is cooled after finishing rolling, and the coiling temperature is 840-850°C.

[0015] The performance of rivets made of steel for marine weather resistant bridge rivets is shown in Table 1.

[0016] Table 1 Performance test results of marine weather resistant bridge rivet steel produced in Example .

[0017] As shown in Table 1, the marine weather resistant bridge rivets produced in the embodiment have a marine weather resistant index V of more than 1.30, good mechanical properties, and can fully meet the actual use requirements.

Claims

1. A method for producing marine weather resistant bridge rivet steel, characterized in that: The chemical composition of steel by weight percentage is C=0.03%~0.06%, Si=0.15%~0.30%, Mn=0.80%~1.00%, P≤0.015%, S≤0.003%, Ni=1.3%~1.4%, Cu=0.45%~0.50%, Mo=0.20%~0.30%, Nb=0.01%~0.03%, Al=0.02%~0.05%, Ti=0.01%~0.02%, and the rest is Fe and unavoidable impurities; The key process steps include: (1) Converter: endpoint control P≤0.008%, C≥0.10%; (2) LF: Use Al particles for diffusion deoxidation to make the LF refined slag white, ensuring that the residual Al content in the steel is above 0.03%; (3) RH: vacuum degassing, maintain vacuum time ≥ 8 min, blow Ar gas from the bottom after breaking the vacuum, soft blowing time ≥ 10 min; (4) Continuous casting: Use a casting speed of 2.2 m / min, a low secondary cooling water ratio of 0.2 L / kg, control the straightening temperature of the steel billet corners to ≥ 900 °C, and place the billet in the slow cooling pit for ≥ 24 hours; (5) Rolling: The temperature in the soaking section is 1150±20℃, the descaling pressure after the furnace is not less than 15MPa, the finishing rolling temperature is 850±20℃, the water tank is cooled after finishing rolling, and the coiling temperature is 850±20℃ to obtain marine weather resistant bridge rivet steel with a weather resistance index of more than 1.30.