Rare earth modified seawater corrosion resistant steel bar and production process thereof

Abstract

The invention provides a rare earth modified seawater corrosion resistant steel bar and a production process thereof, and belongs to the technical field of corrosion resistant steel bars. The steel bar is composed of the following components in percentage by mass: 0.08%-0.15% of C, 0.30%-0.45% of Si, 1.25%-1.32% of Mn, 0.85%-0.94% of Cr, less than or equal to 0.035% of P, less than or equal to 0.035% of S, 0.008%-0.012% of rare earth alloy and the balance of Fe and inevitable impurities. The rare earth alloy is composed of, by mass, 45%-55% of Ce, 25%-30% of La and the balance Fe. Rare earth alloy elements are added in the steel bar preparation process, the size and distribution behavior of inclusions in steel are improved, meanwhile, fine and dispersively distributed rare earth inclusions are used for refining grains, and therefore the pitting corrosion resistance of the steel bar is improved, and the service life of the steel bar is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of corrosion-resistant steel bars, and in particular relates to a rare earth modified seawater corrosion-resistant steel bar and a production process thereof. Background Art

[0002] Reinforced concrete is the most common structural form in infrastructure. However, cases of reinforced concrete failure caused by steel corrosion are widespread, causing huge economic losses. Among all types of steel failure cases, accidents caused by steel corrosion account for more than 50%, and may even be higher in some areas or under specific conditions. This is because steel corrosion directly affects the strength and bonding properties of the steel, which in turn affects the bearing capacity and durability of the entire structure. Among the many cases of steel corrosion failure, local corrosion problems caused by non-metallic inclusions and stress corrosion problems under stress also account for a high proportion. Therefore, it is of great significance to effectively control non-metallic inclusions in corrosion-resistant steel bars while providing steel manufacturers with low-cost and high-efficiency inclusion modification measures.

[0003] In natural chloride corrosion environments such as oceans, salt lakes, and saline-alkali lands, as well as roads and bridges where deicing salt is spread, concrete steel bars will be corroded by chloride ions, causing concrete cracks and reducing the bond strength between the steel bars and concrete; this will in turn lead to changes in the stress state of the concrete structure, reduced durability, and even various accidents.

[0004] At present, there are two main ways to improve the corrosion resistance of steel bars: coating treatment and adding alloy elements. Among them, adding alloy elements is an economical and convenient method. By adding alloy elements such as chromium (Cr), nickel (Ni), phosphorus (P) and molybdenum (Mo) to steel bars, a dense inner rust layer can be formed, thereby preventing further corrosion. For example, the Chinese patent announcement text CN107099734B provides a corrosion-resistant steel bar for marine building structures and a manufacturing method thereof. The chemical composition of the corrosion-resistant steel bar is: C: 0.12% to 0.22%, Si: 0.25% to 0.70%, Mn: 0.50% to 0.80%, P: ≤0.012%, S: ≤0.012%, Cr: 0.65% to 1.20%, V: 0.06% to 0.12%, N: 0.013% to 0.017%, and the remainder is Fe and unavoidable impurities. The manufacturing method of the corrosion-resistant steel bar is to refine the steel bar structure and improve its hardenability by adding alloy elements, effectively reduce the segregation, looseness and shrinkage of the ingot by adopting electromagnetic stirring, light pressure reduction and other methods during the smelting process, and combine the rolling and cooling process control to finally produce corrosion-resistant steel bars with good mechanical properties and corrosion resistance, which can meet the needs of marine environment building structure engineering. However, the method involves the addition of relatively high Cr and V elements, which increases the alloying cost. CN108251746B discloses a high weather-resistant, low-cost seawater corrosion-resistant steel bar and production process, and the steel bar has the following elemental composition by weight: C: 0.04% to 0.10%, Si: 0.10% to 0.50%, Mn: 0.5% to 1.6%, P: ≤0.03%, S: ≤0.02%, Cr: 2% to 4%, Cu: 0.3% to 0.5%, Ni: 0.2% to 0.6%, and the rest is Fe and unavoidable impurities. The mechanical properties of this steel bar meet the requirements of corrosion-resistant steel bars, with low aging effects and a corrosion rate lower than 70% of ordinary steel bars. However, this scheme did not conduct research on local corrosion resistance, and the Cr content was high, which increased the production cost. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a rare earth modified seawater corrosion resistant steel bar and its production process. In the present invention, rare earth alloy elements are added to improve the size and distribution behavior of inclusions in steel, and small dispersed rare earth inclusions are used to refine grains, thereby improving the pitting corrosion resistance and service life of the steel bar.

[0006] Specifically, the present invention adopts the following technical solutions to achieve the above objectives:

[0007] A rare earth modified seawater corrosion resistant steel bar is composed of the following components in percentage by mass: C: 0.08%-0.15%, Si: 0.30%-0.45%, Mn: 1.25%-1.32%, Cr: 0.85%-0.94%, P≤0.035%, S≤0.035%, rare earth alloy: 0.008%-0.012%, and the balance is Fe and unavoidable impurities; the rare earth alloy is composed of the following elements in percentage by mass: 45%-55% Ce, 25%-30% La, and the balance is Fe.

[0008] Carbon (C) is a key strengthening element in steel, usually in the form of carbides, which can enhance the strength of steel by precipitation strengthening and grain refinement. However, carbon has a strong affinity with chromium (Cr), and the combination of the two can form various complex carbides. Although these carbides can increase the hardness of steel, they also reduce the corrosion resistance of steel. In addition, too high a carbon content will weaken the plasticity and toughness of steel and affect its welding performance.

[0009] Silicon (Si) is an important reducing agent and deoxidizer. After being added to steel, silicon can significantly improve the elastic limit, yield point and tensile strength of steel. Silicon combined with chromium (Cr) can improve the corrosion resistance and oxidation resistance of steel to a certain extent, but too high silicon content will reduce the welding performance of steel.

[0010] Manganese (Mn) is a good deoxidizer and desulfurizer, mainly acting through solid solution strengthening. It is an important element for improving the toughness and strength of steel, and is also a key element for forming austenite. However, too high a manganese content will significantly increase the hardenability of steel and reduce its plasticity and weldability. In terms of corrosion resistance, the role of manganese is relatively limited.

[0011] Chromium (Cr) is a key element to improve the oxidation resistance and corrosion resistance of steel. Under appropriate conditions, it can promote the formation of a stable passivation film on the steel surface, thereby improving corrosion resistance. However, in non-oxidizing media, adding chromium alone cannot significantly improve the seawater corrosion resistance of steel, and it is easy to increase the tendency of pitting corrosion.

[0012] Cerium (Ce) can refine the grain structure of steel and improve the organizational properties of steel. Cerium can form stable compounds with impurity elements in steel (such as S, P, O, etc.). These compounds can change the shape and distribution of inclusions and reduce the adverse effects of harmful inclusions on steel properties. Cerium can effectively modify sulfide inclusions in steel, changing their shape from long strips to spheres, thereby improving the plasticity and toughness of steel. Cerium can form a dense oxide film on the surface of steel, which can effectively block the penetration of corrosive media, thereby improving the corrosion resistance of steel; especially in high temperature and acidic environments, the addition of cerium can significantly improve the corrosion resistance of steel.

[0013] Lanthanum (La) can inhibit grain growth, making the microstructure of steel more uniform and dense. Lanthanum can form stable compounds with impurity elements in steel (such as sulfur, phosphorus, oxygen, etc.), thereby changing the shape and distribution of inclusions and reducing the negative impact of harmful inclusions on steel performance. Lanthanum can turn sulfide inclusions into spherical ones, which helps to improve the plasticity and toughness of steel. Lanthanum can form a dense oxide film on the surface of steel to prevent the penetration of corrosive media, thereby improving the corrosion resistance of steel; especially in acidic and seawater environments, the addition of lanthanum can significantly improve the corrosion resistance of steel.

[0014] The present invention also provides a method for preparing the rare earth modified seawater corrosion resistant steel bar, comprising the following steps:

[0015] S1. The raw materials are mixed uniformly according to the mass percentage, wherein the molten iron accounts for 10% to 50% of the total mass of the raw materials, and the remaining raw materials are scrap steel; the raw materials are smelted in an electric furnace, and oxygen supply is strengthened and a slag-making agent is added during the smelting process; a composite deoxidizer is added at the beginning of steel tapping and before the alloy is added; steel is tapped when there is no slag at the eccentric furnace bottom, and then alloying treatment is performed in a ladle; when the amount of steel tapped reaches 1 / 5 of the total mass of the molten steel, FeSi alloy is added, and when the amount of steel tapped reaches 2 / 3 of the total mass of the molten steel, all FeSi alloys are added; when tapping, the temperature of the molten steel is controlled to be 1630 to 1650°C, the carbon content in the molten steel is 0.07wt% to 0.10wt%, and the P content in the molten steel is ≤0.030wt%;

[0016] S2. Refining the reducing slag by LF furnace refining and alloying operation, the slag binary basicity CaO / SiO2 ratio is 3.5-5.0, T.Fe in the slag is ≤0.5%; the LF furnace tapping temperature is 1650℃-1690℃, the S content in the final molten steel is 0.002wt%-0.004wt%, and the O content is 0.003wt%-0.005wt%;

[0017] S3, produced by arc-shaped billet continuous casting machine;

[0018] S4. A walking beam heating furnace is used to heat the continuous casting billet in three stages, wherein the heating temperature in the first stage is lower than the heating temperature in the second stage, and the heating temperature in the second stage is lower than the heating temperature in the third stage.

[0019] In a preferred embodiment, the main components of the slag-forming agent are lime and light-burned dolomite.

[0020] In a preferred embodiment, the composite deoxidizer is a silicon-calcium alloy, wherein the Ca content is 24wt% to 30wt%, the Si content is 55wt% to 65wt%, and the balance is Fe.

[0021] In a preferred embodiment, in step S2, alloy raw materials are added after the LF furnace is vacuum degassed, and the order of addition is Si, Mn and rare earth alloy.

[0022] In a preferred embodiment, in step S2, argon is blown into the bottom of the LF furnace, the argon flow rate is controlled at 12-20 NL / min, and the blowing time of argon is 10-18 min.

[0023] In a preferred embodiment, in step S3, the superheat degree of the pouring process is 16-32°C.

[0024] In a preferred solution, in step S3, an argon sealing protection pouring technology is adopted, and a slag retaining wall is provided in the tundish; at the same time, an argon blowing process is performed in the tundish, and the argon flow rate is controlled at 7-22 NL / min.

[0025] In a preferred embodiment, in step S3, the temperature of the continuous casting furnace is 1570-1620°C.

[0026] In the preferred embodiment, in step S3, electromagnetic stirring and automatic control technology of the crystallizer liquid level are used, and the crystallizer water flow rate is controlled to 135-150m 3 / h.

[0027] In the preferred solution, in step S3, a secondary cooling dynamic water distribution and aerosol cooling process are adopted, and the water volume of the secondary cooling zone is 14-16m 3 / h, one roller water volume is 9.5~11m 3 / h, the water volume of the two rollers is 17.5~19m 3 / h, three-roller water volume is 4~6m 3 / h.

[0028] In a preferred embodiment, in step S3, the continuous casting speed is controlled to be 2.0-2.6 m / min.

[0029] In a preferred embodiment, in step S4, the first stage heating temperature is 830°C to 930°C.

[0030] In a preferred embodiment, in step S4, the second stage heating temperature is 1080°C to 1180°C.

[0031] In a preferred embodiment, in step S4, the third stage heating temperature is 1150°C to 1250°C.

[0032] In a preferred embodiment, in step S4, the first heating period is 45 to 100 minutes.

[0033] In a preferred embodiment, in step S4, the heating time of the second stage is 45 to 100 minutes.

[0034] In a preferred embodiment, in step S4, the third heating period is 30 to 80 minutes.

[0035] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: in the present invention, rare earth alloy elements are added during the steelmaking process to improve the size and distribution behavior of inclusions in the steel, and at the same time, fine and dispersed rare earth inclusions are used to refine the grains. The distribution of the refined inclusions is also relatively uniform. On the one hand, small-sized inclusions can improve the pitting corrosion resistance of the steel bars; on the other hand, small-sized inclusions can reduce the stress concentration behavior of the steel bars under external loads and increase the service life of the steel bars. At the same time, rare earth elements can also improve the stability of the corrosion passivation film, which can effectively block the penetration of corrosive media, thereby improving the corrosion resistance of steel. The addition of rare earth alloy elements provides a method that can effectively improve the corrosion resistance of steel bars without significantly improving the production process. It is an economical and effective way to improve the comprehensive performance of steel bars. DETAILED DESCRIPTION

[0036] The following content is combined with the embodiments to clearly and completely describe the technical solution of the present application so that those skilled in the art can fully understand the present application. Obviously, the described embodiments are only some preferred embodiments of the present application, rather than all embodiments. Any equivalent transformation or substitution made to the following implementation modes by those of ordinary skill in the art without creative work belongs to the protection scope of the present application.

[0037] In the following examples, unless otherwise specified, all percentages are by mass.

[0038] Example 1

[0039] A rare earth modified seawater corrosion resistant steel bar is composed of the following components in percentage by mass: C: 0.12%, Si: 0.36%, Mn: 1.28%, Cr: 0.90%, P: 0.030%, S: 0.035%, rare earth alloy: 0.01%, and the balance is Fe and unavoidable impurities; wherein the rare earth alloy is composed of the following elements in percentage by mass: 50% Ce, 28% La, and the balance is Fe.

[0040] The method for preparing the rare earth modified seawater corrosion resistant steel bar comprises the following steps:

[0041] S1. Use an electric furnace to smelt, mix the raw materials according to the mass percentage, add 10% of the molten iron, and the rest is scrap steel. During the smelting process, the raw materials are melted by electric heating, and decarburization is achieved by strengthening the oxygen supply. In this process, a slag-making agent with lime and light-burned dolomite as the main components is added to remove phosphorus and other harmful impurities in the steel. When there is no slag at the eccentric furnace bottom, the steel is tapped, and then alloying treatment is carried out in the ladle. At the beginning of tapping, before the alloy is added, a composite deoxidizer (silicon-calcium alloy, Ca content is 25%, Si content is 60%, and the balance is Fe) is added. When the tapping reaches 1 / 5 of the total mass of the molten steel, FeSi alloy is added, and when the tapping reaches 2 / 3 of the total mass of the molten steel, all FeSi alloys are added. The composition of the molten steel during tapping is controlled at a C content of 0.08wt%, a P content of ≤0.030wt% (for example, 0.020wt%), and the temperature of the molten steel is controlled at 1640°C.

[0042] S2. Use LF (Ladle Furnace) furnace refining to refine the reducing slag and implement alloying operations. The binary basicity CaO / SiO2 ratio of the slag is 4.0, and the T.Fe (total iron content) in the slag is ≤0.5% (for example, 0.2%). The LF furnace is subjected to arc heating treatment, and alloy raw materials are added 6 minutes before the end of LF. The order of addition is Si, Mn and rare earth alloy. After adding the alloy, argon is blown into the bottom of the LF refining furnace. The argon flow rate is controlled at 16NL / min, and the argon blowing time is 15 minutes. The LF furnace tapping temperature is 1670°C, the S content in the steel is controlled to be 0.002%, and the O content is controlled to be 0.003%.

[0043] S3, adopts arc-shaped billet continuous casting machine, the pouring superheat is controlled at 25℃, argon sealing protection pouring technology is adopted, and slag retaining wall is set in the tundish; at the same time, argon gas is blown into the tundish throughout the whole process, and the argon gas flow rate is controlled at 14NL / min. The temperature of the continuous casting furnace is 1570℃; electromagnetic stirring and automatic control technology of crystallizer liquid level are adopted, and the crystallizer water distribution control is 135m 3 / h; the secondary cooling zone uses dynamic water distribution and mist cooling technology, and the water volume of the secondary cooling zone is 14m 3 / h, one roller water volume is 9.5m 3 / h, the water volume of the second roller is 17.5m 3 / h, three-roller water volume is 4m 3 / h, and the continuous casting speed is controlled at 2.0m / min.

[0044] S4. Use a walking beam heating furnace to perform three-stage temperature heating on the continuous casting billet. The first stage heating temperature is 880°C, and the holding time is 75 minutes; the second stage heating temperature is 1150°C, and the holding time is 75 minutes; the third stage heating temperature is 1200°C, and the heating time is 55 minutes.

[0045] Example 2

[0046] A rare earth modified seawater corrosion resistant steel bar is composed of the following components in percentage by mass: C: 0.08%, Si: 0.3%, Mn: 1.25%, Cr: 0.85%, P: 0.032%, S: 0.030%, rare earth alloy: 0.008%, and the balance is Fe and unavoidable impurities; wherein the rare earth alloy is composed of the following elements in percentage by mass: 45% Ce, 25% La, and the balance is Fe.

[0047] The method for preparing the rare earth modified seawater corrosion resistant steel bar comprises the following steps:

[0048] S1. Use an electric furnace to smelt, mix the raw materials according to the mass percentage, add 20% of the molten iron, and the rest is scrap steel. During the smelting process, the raw materials are melted by electric heating, and decarburization is achieved by strengthening the oxygen supply. In this process, a slag-making agent with lime and light-burned dolomite as the main components is added to remove phosphorus and other harmful impurities in the steel. When there is no slag at the eccentric furnace bottom, the steel is tapped, and then alloying treatment is carried out in the ladle. At the beginning of steel tapping, before the alloy is added, a composite deoxidizer (silicon-calcium alloy, Ca content is 28%, Si content is 55%, and the balance is Fe) is added. When the steel tapping reaches 1 / 5 of the total mass of the molten steel, FeSi alloy is added, and when the steel tapping reaches 2 / 3 of the total mass of the molten steel, all FeSi alloys are added. The composition of the molten steel during steel tapping is controlled to be 0.10wt% C, P content ≤0.030wt% (for example, 0.025wt%), and the temperature of the molten steel is controlled to be 1630℃.

[0049] S2. Use LF (Ladle Furnace) furnace refining to refine the reducing slag and implement alloying operations. The binary basicity CaO / SiO2 ratio of the slag is 3.5, and the T.Fe (total iron content) in the slag is ≤0.5% (for example, 0.3%). The LF furnace is subjected to arc heating treatment, and alloy raw materials are added 5 minutes before the end of LF. The order of addition is Si, Mn and rare earth alloy. After adding the alloy, argon is blown into the bottom of the LF refining furnace. The argon flow rate is controlled at 12NL / min, and the argon blowing time is 18 minutes. The LF furnace tapping temperature is 1650°C, the S content in the steel is controlled to be 0.003%, and the O content is controlled to be 0.003%.

[0050] S3, adopts arc-shaped billet continuous casting machine, the pouring superheat is controlled at 16℃, argon sealing protection pouring technology is adopted, and slag retaining wall is set in the tundish; at the same time, argon gas is blown into the tundish throughout the whole process, and the argon gas flow rate is controlled at 7NL / min. The temperature of the continuous casting furnace is 1620℃; electromagnetic stirring and automatic control technology of crystallizer liquid level are adopted, and the crystallizer water distribution control is 150m3 / h; the secondary cooling dynamic water distribution and aerosol cooling process are adopted, and the water volume of the secondary cooling zone is 16m 3 / h, one roller water volume is 11m 3 / h, the water volume of the second roller is 19m 3 / h, three-roller water volume is 6m 3 / h, and the continuous casting speed is controlled at 2.6m / min.

[0051] S4. Use a walking-beam heating furnace to heat the continuous casting billet in three stages. The first stage heating temperature is 830°C, and the holding time is 100 min; the second stage heating temperature is 1080°C, and the holding time is 100 min; the third stage heating temperature is 1150°C, and the heating time is 80 min.

[0052] Example 3

[0053] A rare earth modified seawater corrosion resistant steel bar is composed of the following components in percentage by mass: C: 0.15%, Si: 0.45%, Mn: 1.32%, Cr: 0.94%, P: 0.035%, S: 0.035%, rare earth alloy: 0.012%, and the balance is Fe and unavoidable impurities; wherein the rare earth alloy is composed of the following elements in percentage by mass: 55% Ce, 30% La, and the balance is Fe.

[0054] The method for preparing the rare earth modified seawater corrosion resistant steel bar comprises the following steps:

[0055] S1. Use an electric furnace to smelt, mix the raw materials according to the mass percentage, add 50% of the molten iron, and the rest is scrap steel. During the smelting process, the raw materials are melted by electric heating, and decarburization is achieved by strengthening the oxygen supply. In this process, a slag-making agent with lime and light-burned dolomite as the main components is added to remove phosphorus and other harmful impurities in the steel. When there is no slag at the eccentric furnace bottom, the steel is tapped, and then alloying treatment is carried out in the ladle. At the beginning of tapping, before the alloy is added, a composite deoxidizer (silicon-calcium alloy, Ca content is 28%, Si content is 60%, and the balance is Fe) is added. When the tapping reaches 1 / 5 of the total mass of the molten steel, FeSi alloy is added, and when the tapping reaches 2 / 3 of the total mass of the molten steel, all FeSi alloys are added. The composition of the molten steel during tapping is controlled at a C content of 0.07wt%, a P content of ≤0.030wt% (for example, 0.030wt%), and the temperature of the molten steel is controlled at 1650℃.

[0056] S2. Use LF (Ladle Furnace) furnace refining to refine the reducing slag and implement alloying operations. The binary basicity CaO / SiO2 ratio of the slag is 5.0, and the T.Fe (total iron content) in the slag is ≤0.5% (for example, 0.5%). The LF furnace is subjected to arc heating treatment, and alloy raw materials are added 8 minutes before the end of LF. The order of addition is Si, Mn and rare earth alloy. After adding the alloy, argon is blown into the bottom of the LF refining furnace. The argon flow rate is controlled at 20NL / min, and the argon blowing time is 10 minutes. The LF furnace tapping temperature is 1690°C, the S content in the steel is controlled to be 0.004%, and the O content is controlled to be 0.005%.

[0057] S3, adopts arc-shaped billet continuous casting machine, the pouring superheat is controlled at 32℃, argon sealing protection pouring technology is adopted, and slag retaining wall is set in the tundish; at the same time, argon gas is blown into the tundish throughout the process, and the argon gas flow rate is controlled at 22NL / min. The temperature of the continuous casting furnace is 1580℃; electromagnetic stirring and automatic control technology of crystallizer liquid level are adopted, and the crystallizer water distribution control is 140m 3 / h; the secondary cooling zone uses dynamic water distribution and aerosol cooling technology, and the water volume of the secondary cooling zone is 15m 3 / h, one roller water volume is 10m 3 / h, the water volume of the two rollers is 18m 3 / h, three-roller water volume is 5m 3 / h, and the continuous casting speed is controlled at 2.4m / min.

[0058] S4. Use a walking beam heating furnace to perform three-stage temperature heating on the continuous casting billet. The first stage heating temperature is 930°C, and the holding time is 45 minutes; the second stage heating temperature is 1180°C, and the holding time is 45 minutes; the third stage heating temperature is 1250°C, and the heating time is 30 minutes.

[0059] Comparative Example 1

[0060] A modified seawater corrosion-resistant steel bar is composed of the following components in percentage by mass: C: 0.17%, Si: 0.46%, Mn: 1.30%, Cr: 1.1%, P: 0.032%, S: 0.032%, rare earth alloy: 0.004%, and the balance is Fe and unavoidable impurities; wherein the rare earth alloy is composed of the following elements in percentage by mass: 50% Ce, 25% La, and the balance is Fe.

[0061] The preparation method of the modified seawater corrosion-resistant steel bar comprises the following steps:

[0062] R1. Use an electric furnace to smelt, mix the raw materials according to the mass percentage, add 50% of the molten iron, and the rest is scrap steel. During the smelting process, the raw materials are melted by electric heating, and decarburization is achieved by strengthening the oxygen supply. In this process, a slag-making agent with lime and light-burned dolomite as the main components is added to remove phosphorus and other harmful impurities in the steel. When there is no slag at the eccentric furnace bottom, the steel is tapped, and then alloying treatment is carried out in the ladle. At the beginning of tapping, before the alloy is added, a composite deoxidizer (silicon-calcium alloy, Ca content is 30%, Si content is 55%, and the balance is Fe) is added. When the tapping reaches 1 / 5 of the total mass of the molten steel, FeSi alloy is added, and when the tapping reaches 2 / 3 of the total mass of the molten steel, all FeSi alloys are added. The composition of the molten steel during tapping is controlled to be 0.75wt% C, P content ≤ 0.030wt% (for example, 0.030wt%), and the temperature of the molten steel is controlled to be 1675℃.

[0063] R2. Use LF (Ladle Furnace) furnace refining to refine the reducing slag and implement alloying operations. The binary basicity CaO / SiO2 ratio of the slag is 5.0, and the T.Fe (total iron content) in the slag is ≤0.5% (for example, 0.5%). The LF furnace is subjected to arc heating treatment, and alloy raw materials are added 7 minutes before the end of LF. The order of addition is Si, Mn and rare earth alloy. After adding the alloy, argon is blown into the bottom of the LF refining furnace. The argon flow rate is controlled at 20NL / min, and the argon blowing time is 10 minutes. The LF furnace tapping temperature is 1680°C, the S content in the steel is controlled to be 0.004%, and the O content is controlled to be 0.003%.

[0064] R3, produced by arc-shaped billet continuous casting machine, the pouring superheat is controlled at 31℃, argon sealing protection pouring technology is adopted, and slag retaining wall is set in the tundish; at the same time, argon gas is blown into the tundish throughout the process, and the argon gas flow rate is controlled at 22NL / min. The temperature of the continuous casting furnace is 1580℃; electromagnetic stirring and automatic control technology of crystallizer liquid level are adopted, and the crystallizer water distribution control is 150m 3 / h; the secondary cooling zone uses dynamic water distribution and aerosol cooling technology, and the water volume of the secondary cooling zone is 15m 3 / h, one roller water volume is 10.5m 3 / h, the water volume of the second roller is 19m 3 / h, three-roller water volume is 5m 3 / h, and the continuous casting speed is controlled at 2.4m / min.

[0065] R4. A walking beam heating furnace is used to heat the continuous casting billet in three stages. The first stage heating temperature is 920°C and the holding time is 43 minutes. The second stage heating temperature is 1185°C and the holding time is 43 minutes. The third stage heating temperature is 1240°C and the heating time is 32 minutes.

[0066] Comparative Example 2

[0067] A modified seawater corrosion-resistant steel bar is composed of the following components in percentage by mass: C: 0.16%, Si: 0.48%, Mn: 1.36%, Cr: 0.75%, P: 0.04%, S: 0.04%, rare earth alloy: 0.002%, and the balance is Fe and unavoidable impurities. The rare earth alloy is composed of the following elements in percentage by mass: 52% Ce, 32% La, and the balance is Fe.

[0068] The preparation method of the modified seawater corrosion-resistant steel bar comprises the following steps:

[0069] P1. Use an electric furnace to smelt, mix the raw materials according to the mass percentage, add 50% of the molten iron, and the rest is scrap steel. During the smelting process, the raw materials are melted by electric heating, and decarburization is achieved by strengthening the oxygen supply. In this process, a slag-making agent with lime and light-burned dolomite as the main components is added to remove phosphorus and other harmful impurities in the steel. When there is no slag at the eccentric furnace bottom, the steel is tapped, and then alloying treatment is carried out in the ladle. At the beginning of steel tapping, before the alloy is added, a composite deoxidizer (silicon-calcium alloy, Ca content is 24%, Si content is 60%, and the balance is Fe) is added. When the steel tapping reaches 1 / 5 of the total mass of the molten steel, FeSi alloy is added, and when the steel tapping reaches 2 / 3 of the total mass of the molten steel, all FeSi alloys are added. The composition of the molten steel during steel tapping is controlled at a C content of 0.72wt%, a P content of ≤0.030wt% (for example, 0.030wt%), and the temperature of the molten steel is controlled at 1680℃.

[0070] P2. Use LF (Ladle Furnace) furnace refining to refine the reducing slag and perform alloying operations. The binary basicity CaO / SiO2 ratio of the slag is 5.0, and the T.Fe (total iron content) in the slag is ≤0.5% (for example, 0.5%). The LF furnace is subjected to arc heating treatment, and alloy raw materials are added 7 minutes before the end of LF. The order of addition is Si, Mn and rare earth alloy. Argon is blown into the bottom of the LF refining furnace. The argon flow rate is controlled at 20NL / min, and the argon blowing time is 10 minutes. The LF furnace tapping temperature is 1680°C, the S content in the steel is controlled to 0.004%, and the O content is controlled to 0.003%.

[0071] P3, adopts arc-shaped billet continuous casting machine, the pouring superheat is controlled at 16℃, argon sealing protection pouring technology is adopted, and slag retaining wall is set in the tundish; at the same time, the argon gas blowing process is combined with the tundish, and the argon gas flow rate is controlled at 22NL / min. The temperature of the continuous casting furnace is 1590℃; electromagnetic stirring and automatic control technology of crystallizer liquid level are adopted, and the crystallizer water distribution control is 145m 3 / h; the secondary cooling zone uses dynamic water distribution and mist cooling technology, and the water volume of the secondary cooling zone is 14m 3 / h, one roller water volume is 11m 3 / h, the water volume of the two rollers is 18m 3 / h, three-roller water volume is 6m 3 / h, and the continuous casting speed is controlled at 2.6m / min.

[0072] P4. A walking-beam heating furnace is used to heat the continuous casting billet in three stages. The first stage heating temperature is 930°C, and the holding time is 43 minutes; the second stage heating temperature is 1185°C, and the holding time is 46 minutes; the third stage heating temperature is 1250°C, and the heating time is 32 minutes.

[0073] Comparative Example 3

[0074] A rare earth modified seawater corrosion resistant steel bar is composed of the following components in percentage by mass: C: 0.16%, Si: 0.58%, Mn: 1.36%, Cr: 1.25%, P: 0.035%, S: 0.035%, rare earth alloy: 0.006%, and the balance is Fe and unavoidable impurities; wherein the rare earth alloy is composed of the following elements in percentage by mass: 55% Ce, 30% La, and the balance is Fe.

[0075] The method for preparing the rare earth modified seawater corrosion resistant steel bar comprises the following steps:

[0076] T1. Use an electric furnace to smelt, mix the raw materials according to the mass percentage, add 50% of the molten iron, and the rest is scrap steel. During the smelting process, the raw materials are melted by electric heating, and decarburization is achieved by strengthening the oxygen supply. In this process, a slag-making agent with lime and light-burned dolomite as the main components is added to remove phosphorus and other harmful impurities in the steel. When there is no slag at the eccentric furnace bottom, the steel is tapped, and then alloying treatment is carried out in the ladle. At the beginning of tapping, before the alloy is added, a composite deoxidizer (silicon-calcium alloy, Ca content is 24%, Si content is 58%, and the balance is Fe) is added. When the tapping reaches 1 / 5 of the total mass of the molten steel, FeSi alloy begins to be added, and when the tapping reaches 2 / 3 of the total mass of the molten steel, all FeSi alloys are added. The composition of the molten steel during tapping is controlled to have a C content of 0.72wt%, a P content of ≤0.030wt% (for example, 0.030wt%), and the temperature of the molten steel is controlled to be 1690°C.

[0077] T2. Use LF (Ladle Furnace) furnace refining to refine the reducing slag and implement alloying operations. The binary basicity CaO / SiO2 ratio of the slag is 4.0, and the T.Fe (total iron content) in the slag is ≤0.5% (for example, 0.5%). The LF furnace is subjected to arc heating treatment, and alloy raw materials are added 7 minutes before the end of LF. The order of addition is Si, Mn and rare earth alloy. After adding the alloy, argon is blown into the bottom of the LF refining furnace. The argon flow rate is controlled at 20NL / min, and the argon blowing time is 12 minutes. The LF furnace tapping temperature is 1685°C, the S content in the steel is controlled to be 0.004%, and the O content is controlled to be 0.003%.

[0078] T3, using arc-shaped billet continuous casting machine, the pouring superheat is controlled at 16℃, argon sealing protection pouring technology is adopted, and slag retaining wall is set in the tundish; at the same time, the argon gas flow rate is controlled at 22NL / min in conjunction with the argon gas blowing process into the tundish. The temperature of the continuous casting furnace is 1610℃; electromagnetic stirring and automatic control technology of the crystallizer liquid level are adopted, and the crystallizer water distribution control is 145m 3 / h; the secondary cooling zone uses dynamic water distribution and mist cooling technology, and the water volume of the secondary cooling zone is 14m 3 / h, one roller water volume is 10m 3 / h, the water volume of the two rollers is 18m 3 / h, three-roller water volume is 6m 3 / h, and the continuous casting speed is controlled at 2.6m / min.

[0079] T4. A walking beam heating furnace is used to heat the continuous casting billet in three stages. The first stage heating temperature is 930°C, and the holding time is 43 minutes; the second stage heating temperature is 1185°C, and the holding time is 46 minutes; the third stage heating temperature is 1250°C, and the heating time is 32 minutes.

[0080] Steel bar performance test

[0081] The steel bars of Examples 1 to 3 and Comparative Examples 1 to 3 were sampled and tested for mechanical properties in accordance with the provisions of the national standard GB / T228.4-2019 "Tensile Test of Metal Materials Part 4: Liquid Helium Test Method", and the results are shown in Table 1.

[0082] Table 1 Test results of steel bar performance with different components

[0083]

[0084] As can be seen from Table 1, Examples 1 to 3 and Comparative Examples 1 to 3 obviously meet the requirements of 400MPa grade steel bars in terms of mechanical properties, and have a yield strength of >420MPa, a tensile strength of >540MPa, an elongation after fracture of >18%, and a maximum total elongation of >7.5%. Compared with the steel bars in Comparative Examples 1 to 3, the maximum total elongation of the steel bars in Examples 1 to 3 is significantly improved.

[0085] The steel bars in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to immersion corrosion tests, salt spray corrosion tests and electrochemical corrosion tests according to established procedures. The test results are shown in Table 2.

[0086] The method of the circumferential immersion corrosion test is as follows: Place the ultrasonically cleaned sample in a circumferential immersion test chamber, and conduct a circumferential immersion corrosion test in a chloride ion environment according to the provisions of YB / T4367-2014 "Test Method for Corrosion of Steel Bars in Chloride Ion Environment". The test solution is 2.0±0.05 (wt%) sodium chloride (NaCl), the pH value of the solution is controlled between 6.4 and 7.1, and the temperature of the solution is maintained at 45℃±2℃. After the circumferential immersion corrosion is completed, the sample must be dried at 70℃±10℃. This process continues until a total of 168 hours is reached to determine the average weight loss corrosion rate during this period. The sample corrosion rate is calculated according to the formula in Section 9.1 of the standard.

[0087] The method of salt spray corrosion test is carried out in accordance with the provisions of GB / T 10125-2021 "Artificial atmosphere corrosion test salt spray test". A neutral salt spray test is used, and the solution is a 5%±1% sodium chloride solution at 35℃±2℃, with a pH of 6.6-7.2 and a solution temperature of 35℃±2℃. Before the test, the sample is cleaned with carbon tetrachloride vapor degreasing, using 3 consecutive 1min treatments, with at least 1min interval between each continuous treatment; the sample is thoroughly cleaned with ultrasonic cleaning and acetone solution. After 168h of the test, a 1:1 (volume ratio) hydrochloric acid solution (ρ 20 =1.18 g / mL), in which 3.5 g / L of hexamethylenetetramine corrosion inhibitor was added, and the sample was immersed to remove the corrosion products, and then the sample was washed with water at room temperature, and then washed with acetone, and weighed after drying. The sample was weighed accurately to 1 mg, and the mass loss (g / m 2 ).

[0088] Table 2 Corrosion test results of steel bars with different compositions

[0089]

[0090] It can be seen from Table 2 that compared with the comparative example, the corrosion resistance of each steel bar sample of the embodiment is better than that of the comparative example. The average corrosion rate of the circumferential immersion test of the embodiment is 0.1 g / m2 ·h or less, while the average corrosion rate of the comparative circumferential immersion test was 2.132~4.133g / m 2 At the same time, the average corrosion rate of the salt spray test of the embodiment is also less than 0.1g / m 2 ·h, while the average corrosion rate of the comparative salt spray test was 1.267~1.758g / m 2 h; It can be seen that the corrosion resistance of the steel bars in the embodiment is significantly better than that in the comparative example.

[0091] At the same time, according to the provisions of GB / T 10561-2023 "Standard Rating Chart Microscopic Inspection Method for Determination of Non-metallic Inclusion Content in Steel" and GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals", the steel bars of Examples 1 to 3 and Comparative Examples 1 to 3 were rated for inclusions. The results show that the ratings of Class A, Class B, Class C, and Class D inclusions of the steel bars of Examples 1 to 3 are all within 0.5 to 1, while the ratings of Class A, Class B, Class C, and Class D inclusions of the steel bars of Comparative Examples 1 to 3 are all within the range of 1.5 to 2.5. It can be seen that the inclusion distribution of the steel bars in the examples is significantly better than that of the comparative examples.

[0092] The above-described embodiments are only preferred embodiments of the present application and are not intended to limit the scope of protection of the present application. For any person skilled in the art, the present application may have various changes and modifications. Any simple equivalent changes and modifications made based on the scope of protection of the present application and the contents of the specification should be included in the scope of protection of the present application.

Claims

1. A rare earth modified seawater corrosion resistant steel bar, characterized in that: The invention is composed of the following components in percentage by mass: C: 0.08% to 0.15%, Si: 0.30% to 0.45%, Mn: 1.25% to 1.32%, Cr: 0.85% to 0.94%, P≤0.035%, S≤0.035%, rare earth alloy: 0.008% to 0.012%, and the balance is Fe and unavoidable impurities; the rare earth alloy is composed of the following elements in percentage by mass: 45% to 55% Ce, 25% to 30% La, and the balance is Fe.

2. The method for preparing the rare earth modified seawater corrosion resistant steel bar according to claim 1, characterized in that: The following steps are involved: S1. The raw materials are mixed uniformly according to the mass percentage, wherein the molten iron accounts for 10% to 50% of the total mass of the raw materials, and the remaining raw materials are scrap steel; the raw materials are smelted in an electric furnace, and oxygen supply is strengthened and a slag-making agent is added during the smelting process; a composite deoxidizer is added at the beginning of steel tapping and before the alloy is added; steel is tapped when there is no slag at the eccentric furnace bottom, and then alloying treatment is performed in a ladle; when the amount of steel tapped reaches 1 / 5 of the total mass of the molten steel, FeSi alloy is added, and when the amount of steel tapped reaches 2 / 3 of the total mass of the molten steel, all FeSi alloys are added; when tapping, the temperature of the molten steel is controlled to be 1630 to 1650°C, the carbon content in the molten steel is 0.07wt% to 0.10wt%, and the P content in the molten steel is ≤0.030wt%; S2. Refining the reducing slag by LF furnace refining and alloying operation, the slag binary basicity CaO / SiO2 ratio is 3.5-5.0, T.Fe in the slag is ≤0.5%; the LF furnace tapping temperature is 1650℃-1690℃, the S content in the final molten steel is 0.002wt%-0.004wt%, and the O content is 0.003wt%-0.005wt%; S3, produced by arc-shaped billet continuous casting machine; S4. A walking beam heating furnace is used to heat the continuous casting billet in three stages, wherein the heating temperature in the first stage is lower than the heating temperature in the second stage, and the heating temperature in the second stage is lower than the heating temperature in the third stage.

3. The preparation method according to claim 2, characterized in that: The main components of the slag-forming agent are lime and light-burned dolomite; or / and the composite deoxidizer is a silicon-calcium alloy, wherein the Ca content is 24wt% to 30wt%, the Si content is 55wt% to 65wt%, and the balance is Fe.

4. The preparation method according to claim 2, characterized in that: In step S2, alloy raw materials are added after the LF furnace is vacuum degassed, and the order of addition is Si, Mn and rare earth alloy.

5. The preparation method according to claim 2, characterized in that: In step S2, argon gas is blown into the bottom of the LF furnace, the argon gas flow rate is controlled at 12-20 NL / min, and the argon gas blowing time is 10-18 min.

6. The preparation method according to claim 2, characterized in that: In step S3, the superheat degree of the casting process is 16-32°C; or / and the continuous casting speed is controlled to be 2.0-2.6 m / min.

7. The preparation method according to claim 2, characterized in that: In step S3, an argon sealing protection pouring technology is adopted, and a slag retaining wall is provided in the tundish; at the same time, an argon blowing process is carried out in the tundish, and the argon flow rate is controlled at 7-22 NL / min.

8. The preparation method according to claim 2, characterized in that: In step S3, the temperature of the continuous casting furnace is 1570-1620°C; or / and electromagnetic stirring and automatic crystallizer liquid level control technology are used, and the crystallizer water flow rate is controlled to 135-150m 3 / h; or / and adopting secondary cooling dynamic water distribution and aerosol cooling technology, the water volume of the secondary cooling zone is 14-16m 3 / h, water volume per roller is 9.5~11m 3 / h, the water volume of the two rollers is 17.5~19m 3 / h, three-roller water volume is 4~6m 3 / h.

9. The preparation method according to claim 2, characterized in that: In step S4, the first stage heating temperature is 830°C to 930°C, or / and the second stage heating temperature is 1080°C to 1180°C, or / and the third stage heating temperature is 1150°C to 1250°C.

10. The preparation method according to claim 2, characterized in that: In step S4, the first heating period is 45 to 100 minutes, or / and the second heating period is 45 to 100 minutes, or / and the third heating period is 30 to 80 minutes.

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