235MPa long-life nickel-free rare earth super weathering steel and preparation method thereof

Abstract

The invention relates to the technical field of weathering resistant steel, and provides 235MPa long-service-life nickel-free rare earth super weathering resistant steel which is composed of the following components in percentage by mass: 0.08%-0.10% of C, 0.18%-0.22% of Si, 0.25%-0.35% of Mn, less than or equal to 0.09% of P, less than or equal to 0.010% of S, less than or equal to 0.03% of Al, 0.26%-0.32% of Cr, 0.16%-0.19% of Cu, 0.012%-0.030% of Ti, 0.005%-0.011% of La, 0.011%-0.021% of Ce and the balance of Fe and inevitable impurities. The proportional relation of Ti, La and Ce meets the relational expression that (La + Ce) / Ti is larger than or equal to 0.6 and smaller than or equal to 2.6. According to the technical scheme, the problems of insufficient mechanical property and corrosion resistance of nickel-free weathering steel in related technologies are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of weathering steel, in particular to a 235MPa long-life nickel-free rare earth super weathering steel and a preparation method thereof. BACKGROUND

[0002] In the fields of bridges, containers, power transmission towers and marine engineering, steel is easily oxidized and corroded in the corrosive environment of atmosphere, rainwater and salt, which leads to the decline of structural mechanical properties and the shortening of service life, and thus frequent maintenance or replacement is required, which not only increases economic cost, but also may cause safety hazards. Therefore, it has become an urgent need in the field to develop steel with excellent mechanical properties and corrosion resistance.

[0003] At present, the weathering steel commonly used in the industry mainly improves corrosion resistance by adding alloy elements such as Cr, Ni and Cu, among which Ni can effectively enhance the stability of the passivation film on the surface of the steel, thereby significantly improving the corrosion resistance. For example, CN116732429A discloses an 800MPa grade rare earth weathering steel and a production method thereof, wherein RE uses single La element and is only 20-80ppm, which cannot fill grain boundary defects and refine grains; the noble metal elements Cu, Cr and Ni are still relied on to improve the atmospheric corrosion resistance index, and the cost of noble metals is much higher than that of traditional weathering steel and rare earth weathering steel, which is not conducive to the large-scale production of most enterprises.

[0004] Therefore, it has become a research hotspot in the industry to develop a 235MPa grade weathering steel without nickel, with high mechanical properties and excellent corrosion resistance, which is of great significance to reduce engineering cost, improve structural safety and promote the development of weathering steel. SUMMARY

[0005] The present application provides a 235MPa long-life nickel-free rare earth super weathering steel and a preparation method thereof, which solves the problems of insufficient mechanical properties and corrosion resistance of nickel-free weathering steel in the related art.

[0006] The technical scheme of the present application is as follows: The present application provides a 235MPa long-life nickel-free rare earth super weathering steel, which is composed of the following components in mass percentage: C 0.08%-0.10%, Si 0.18%-0.22%, Mn 0.25%-0.35%, P≤0.09%, S≤0.010%, Al≤0.03%, Cr 0.26%-0.32%, Cu 0.16%-0.19%, Ti 0.012%-0.030%, La 0.005%-0.011%, Ce 0.011%-0.021%, and the balance is Fe and inevitable impurities; the ratio relationship of Ti, La and Ce satisfies the relationship formula: 0.6≤(La+Ce) / Ti≤2.6.

[0007] As a further technical solution, the (La+Ce) / Ti=1.2.

[0008] As a further technical solution, the ratio of Ce and La satisfies the relationship: 1.4≤Ce / La≤3.0.

[0009] The weathering steel enhances the synergistic effect of Ce and La in the steel by limiting the ratio of Ce and La, thereby improving the mechanical properties and corrosion resistance of the weathering steel. Ce can fully fix P and S to form spherical harmless compounds, effectively reducing harmful inclusions that can cause stress concentration, and assisting in grain refinement. La further promotes grain refinement and improves the uniformity of inclusions, ensuring the mechanical properties of the steel and promoting the formation of a dense and stable protective rust layer. When the ratio of Ce and La satisfies the relationship: 1.5≤Ce / La≤3.0, the performance of the weathering steel can be further improved. If La is excessive and Ce is insufficient, the excessive La will lead to uneven distribution of rare earth inclusions, and insufficient Ce will not be able to fully fix harmful elements, causing the steel to easily rust and fall off in outdoor corrosion environments. If La is insufficient and Ce is excessive, the excessive Ce will form coarse inclusions, damaging the continuity of the steel matrix and reducing the mechanical properties of the steel. The present application limits the ratio of Ce and La to optimize the cleanliness, microstructure refinement and corrosion resistance of the steel, thereby improving the mechanical properties and corrosion resistance of the nickel-free rare earth super weathering steel.

[0010] As a further technical solution, the Ce / La=2.

[0011] The present application also provides a preparation method of a 235MPa long-life nickel-free rare earth super weathering steel, which is used for preparing the 235MPa long-life nickel-free rare earth super weathering steel and comprises the following steps: S1, proportioning according to the weight percentage of the components, smelting, refining, continuous casting to obtain a casting blank; S2, after the casting blank is subjected to soaking treatment, rough rolling, finish rolling, cooling and coiling, a 235MPa long-life nickel-free rare earth super weathering steel is obtained.

[0012] As a further technical solution, in step S1, the specific process of continuous casting comprises the following steps: after the refined molten steel is injected into a crystallizer and crystallized, it is cooled and solidified to obtain a semi-finished product rough blank; the semi-finished product rough blank is drawn, straightened and flame cut to obtain a casting blank.

[0013] As a further technical solution, the continuous casting process is carried out under argon protection.

[0014] As a further technical scheme, the flow rate of the cooling water is 8.0-9.0 m / s during the crystallization. The specific water quantity of the cooling solidification is 0.8-1.0 L / Kg.

[0015] As a further technical scheme, the temperature of the homogenization treatment is 1200-1240 DEG C, and the time is 1.5-2.5 h in step S2.

[0016] As a further technical scheme, the initial rolling temperature of the rough rolling is 920-940 DEG C, and the final rolling temperature is 875-925 DEG C in step S2.

[0017] As a further technical scheme, the initial rolling temperature of the finish rolling is 850-900 DEG C, and the final rolling temperature is 780-840 DEG C in step S2.

[0018] As a further technical scheme, the cooling in step S2 comprises the following steps: firstly cooling to 700 DEG C at a rate of 15-25 DEG C / s, and then cooling to 570 DEG C at a rate of 10-16 DEG C / s.

[0019] In the super weather-resistant steel, two-stage different cooling rates are adopted, the first stage is cooled to 700 DEG C at a faster rate of 15-25 DEG C / s, which can quickly inhibit the growth of austenite grains in the steel, and reduce the precipitation and aggregation of harmful inclusions such as coarse carbides and sulfides; the second stage is cooled to 570 DEG C at a slower rate of 10-16 DEG C / s, which can provide suitable conditions for the phase transition of austenite to ferrite and pearlite in the steel under the premise of ensuring the grain refinement effect, promote the formation of uniform and fine phase transition structure, and further improve the mechanical properties of the weather-resistant steel through the fine-grain strengthening effect.

[0020] The working principle and beneficial effects of the present application are as follows: The application discloses a 235MPa long-life nickel-free rare earth super weathering steel, and the weathering steel can realize synchronous improvement of mechanical properties and corrosion resistance by limiting the proportion relationship of Ti, La and Ce. Under the proportion relationship, La and Ce can effectively purify the molten steel, refine the grains, and promote the formation of a dense and stable protective rust layer on the surface of the steel; Ti forms fine carbonitride, produces strong precipitation strengthening effect, and significantly improves the mechanical properties of the steel. If the rare earth La and Ce are excessive, coarse rare earth oxides or sulfides are generated, which reduces the mechanical properties and corrosion resistance of the steel; if the Ti content is insufficient, the number of precipitation strengthening particles is reduced, and the requirement of the mechanical properties is difficult to meet; if the Ti content is too high, coarse TiN inclusions are generated, which destroys the continuity of the matrix. The application limits the proportion relationship of Ti, La and Ce, and when 0.6≤(La+Ce) / Ti≤2.6, the optimization effect of La and Ce on the steel and the strengthening effect of Ti can be best coordinated, so that the high mechanical properties and corrosion resistance under the condition of no nickel are realized. BRIEF DESCRIPTION OF DRAWINGS

[0021] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0022] Figure 1 The metallographic structure diagram of the nickel-free rare earth super weathering steel prepared in the application example 2; Figure 2 The metallographic structure diagram of the weathering steel prepared in the application comparative example 1; Figure 3 The metallographic structure diagram of the weathering steel prepared in the application comparative example 2. DETAILED DESCRIPTION

[0023] The technical solutions in the application examples will be clearly and completely described below in combination with the application examples. Obviously, the described examples are only part of the application examples, but not all the examples. Based on the examples in the application, all the other examples obtained by those skilled in the art without creative labor are involved in the protection scope of the application.

[0024] Example 1 A 235MPa long-life nickel-free rare earth super weathering steel is composed of the following components in percentage by mass: C 0.08%, Si 0.18%, Mn 0.25%, P 0.084%, S 0.007%, Al 0.022%, Cr 0.26%, Cu 0.16%, Ti 0.02%, La 0.008%, Ce 0.016%, and the balance of Fe and inevitable impurities; the value of (La+Ce) / Ti is 1.2, and the value of Ce / La is 2. The application discloses a preparation method of a 235MPa long-service-life nickel-free rare earth super weather-resistant steel. S1, proportioning components according to weight percentages, smelting, refining, continuous casting, and obtaining a casting blank; S2, after the casting blank is treated at 1200 DEG C for 2.5h, rough rolling (initial rolling temperature is 920 DEG C, final rolling temperature is 875 DEG C, and total reduction is 65%), finish rolling (initial rolling temperature is 850 DEG C, final rolling temperature is 780 DEG C), and then cooling at a speed of 20 DEG C / s to 570 DEG C for coiling, a 235MPa long-service-life nickel-free rare earth super weather-resistant steel is obtained; The specific process of the continuous casting comprises the following steps: after the refined molten steel is injected into a crystallizer and cooled and crystallized at a water flow rate of 8.0 m / s, and then cooled and solidified by a specific water amount of 0.8 L / Kg, a semi-finished rough blank is obtained; the semi-finished rough blank is drawn, straightened and hot cut to obtain the casting blank.

[0025] Example 2 The 235MPa long-service-life nickel-free rare earth super weather-resistant steel is composed of the following components in percentage by mass: C 0.09%, Si 0.2%, Mn 0.3%, P 0.086%, S 0.009%, Al 0.025%, Cr 0.29%, Cu 0.18%, Ti 0.02%, La 0.008%, Ce 0.016%, and the balance of Fe and inevitable impurities; the value of (La+Ce) / Ti is 1.2, and the value of Ce / La is 2. The application discloses a preparation method of a 235MPa long-service-life nickel-free rare earth super weather-resistant steel. S1, proportioning components according to weight percentages, smelting, refining, continuous casting, and obtaining a casting blank; S2, after the casting blank is treated at 1220 DEG C for 2h, rough rolling (initial rolling temperature is 930 DEG C, final rolling temperature is 895 DEG C, and total reduction is 65%), finish rolling (initial rolling temperature is 870 DEG C, final rolling temperature is 810 DEG C), and then cooling at a speed of 20 DEG C / s to 570 DEG C for coiling, a 235MPa long-service-life nickel-free rare earth super weather-resistant steel is obtained; The specific process of the continuous casting comprises the following steps: after the refined molten steel is injected into a crystallizer and cooled and crystallized at a water flow rate of 8.5 m / s, and then cooled and solidified by a specific water amount of 0.9 L / Kg, a semi-finished rough blank is obtained; the semi-finished rough blank is drawn, straightened and hot cut to obtain the casting blank. Figure 1 The metallographic structure diagram of the nickel-free rare earth super weather-resistant steel prepared in the embodiment.

[0026] Example 3 A 235MPa long-life nickel-free rare earth super weathering steel, consisting of the following components by mass percentage: C 0.1%, Si 0.22%, Mn 0.35%, P 0.09%, S 0.01%, Al 0.03%, Cr 0.32%, Cu 0.19%, Ti 0.02%, La 0.008%, Ce 0.016%, the balance being Fe and inevitable impurities; the value of (La+Ce) / Ti is 1.2, and the value of Ce / La is 2. A preparation method of a 235MPa long-life nickel-free rare earth super weathering steel, comprising the following steps: S1, component allocation by weight percentage, smelting, refining, continuous casting to obtain a casting blank; S2, the casting blank is heated at 1240℃ for 1.5h, rough rolling (initial rolling temperature is 940℃, final rolling temperature is 925℃, total reduction is 65%), finish rolling (initial rolling temperature is 900℃, final rolling temperature is 840℃), and then cooled to 570℃ at a rate of 20℃ / s and coiled to obtain a 235MPa long-life nickel-free rare earth super weathering steel; The specific process of continuous casting includes the following steps: after the molten steel after refining is injected into the crystallizer and cooled and crystallized at a water flow rate of 9.0m / s, and then cooled and solidified by a specific water amount of 1.0L / Kg, a semi-finished rough blank is obtained; the semi-finished rough blank is drawn, straightened and flame cut to obtain a casting blank.

[0027] Example 4 The difference between this embodiment and embodiment 2 is that a 235MPa long-life nickel-free rare earth super weathering steel, consisting of the following components by mass percentage: C 0.09%, Si 0.2%, Mn 0.3%, P 0.086%, S 0.009%, Al 0.025%, Cr 0.29%, Cu 0.18%, Ti 0.0275%, La 0.0055%, Ce 0.011%, the balance being Fe and inevitable impurities; the value of (La+Ce) / Ti is 0.6, and the value of Ce / La is 2.

[0028] Example 5 The difference between this embodiment and embodiment 2 is that a 235MPa long-life nickel-free rare earth super weathering steel, consisting of the following components by mass percentage: C 0.09%, Si 0.2%, Mn 0.3%, P 0.086%, S 0.009%, Al 0.025%, Cr 0.29%, Cu 0.18%, Ti 0.0125%, La 0.0105%, Ce 0.021%, the balance being Fe and inevitable impurities; the value of (La+Ce) / Ti is 2.52, and the value of Ce / La is 2.

[0029] Example 6 The difference between this example and Example 2 is that a 235 MPa long-life nickel-free rare earth super weathering steel consisting of the following components in mass percent: C 0.09%, Si 0.2%, Mn 0.3%, P 0.086%, S 0.009%, Al 0.025%, Cr 0.29%, Cu 0.18%, Ti 0.02%, La 0.006%, Ce 0.018%, the balance being Fe and unavoidable impurities; the value of (La+Ce) / Ti is 1.2, and the value of Ce / La is 3.

[0030] Example 7 The difference between this example and Example 2 is that a 235 MPa long-life nickel-free rare earth super weathering steel consisting of the following components in mass percent: C 0.09%, Si 0.2%, Mn 0.3%, P 0.086%, S 0.009%, Al 0.025%, Cr 0.29%, Cu 0.18%, Ti 0.02%, La 0.01%, Ce 0.014%, the balance being Fe and unavoidable impurities; the value of (La+Ce) / Ti is 1.2, and the value of Ce / La is 1.4.

[0031] Example 8 The difference between this example and Example 1 is that the cooling is divided into two stages, first cooling at a rate of 15°C / s to 700°C, and then cooling at a rate of 10°C / s to 570°C to be coiled.

[0032] Example 9 The difference between this example and Example 1 is that the cooling is divided into two stages, first cooling at a rate of 15°C / s to 700°C, and then cooling at a rate of 10°C / s to 570°C to be coiled.

[0033] Example 10 The difference between this example and Example 1 is that the cooling is divided into two stages, first cooling at a rate of 20°C / s to 700°C, and then cooling at a rate of 13°C / s to 570°C to be coiled.

[0034] Example 11 The difference between this example and Example 1 is that the cooling is divided into two stages, first cooling at a rate of 25°C / s to 700°C, and then cooling at a rate of 16°C / s to 570°C to be coiled.

[0035] Comparative Example 1 The difference between this embodiment and embodiment 2 is only that a 235 MPa long-life nickel-free rare earth super weathering steel is composed of the following components in mass percentage: C 0.12%, Si 0.21%, Mn 0.65%, P 0.025%, S 0.013%, Al 0.026%, Cr 0.42%, Cu 0.30%, Ti 0.032%, Ni 0.09%, and the balance is Fe and inevitable impurities; Figure 2 The metallographic structure diagram of the weathering steel prepared in this comparative example is shown in Figure 1.

[0036] Comparative Example 2 The difference between this embodiment and embodiment 2 is only that a 235 MPa long-life nickel-free rare earth super weathering steel is composed of the following components in mass percentage: C 0.12%, Si 0.21%, Mn 0.65%, P 0.025%, S 0.013%, Al 0.026%, Cr 0.42%, Cu 0.30%, Ti 0.032%, Ni 0.09%, and the balance is Fe and inevitable impurities; Figure 3 The metallographic structure diagram of the weathering steel prepared in this comparative example is shown in Figure 1.

[0037] Experimental Example 1 The weathering steel prepared in embodiments 1-11 and comparative examples 1-2 is tested according to the following method: 1. Tensile strength, yield strength, and elongation after fracture: The tensile strength and yield strength of the sample are tested according to the test method specified in GB / T 228.1-2021 "Metallic Materials - Tensile Test - Part 1: Room Temperature Test Method", and the test results are shown in Tables 1 and 2.

[0038] 2. Low temperature impact energy: The impact energy of the sample at -20°C and -40°C is tested according to the test method specified in GB / T 229-2020 "Metallic Materials Charpy Pendulum Impact Test Method", and the sample is a standard impact test sample: 10x10x55mm. The test results are shown in Table 3.

[0039] 3. Corrosion resistance: According to TB / T 1979-2023 "Special Metal Materials for Rolling Stock - Atmospheric Corrosion Resistant Steel", the periodic immersion corrosion test method for weathering steel for railway is used for 72h of periodic immersion cycle corrosion test. The average corrosion rate is obtained by calculating the corrosion weight loss per unit area of the sample, and then the relative corrosion rate of the steel grade is obtained. The test results are shown in Table 3.

[0040] Table 1 Test results of embodiments 1-7 and comparative examples 1-2

[0041] From the data in Table 1, the yield strength, tensile strength and elongation at break of Examples 1-7 are higher than those of Comparative Examples 1-2, indicating that the yield strength, tensile strength and elongation at break of the weathering steel are improved by limiting the mass percentages of Ti 0.012%-0.030%, La 0.005%-0.011% and Ce 0.011%-0.021%.

[0042] Table 2 Determination results of yield strength of weathering steel

[0043] From the data in Table 2, the yield strength of Examples 9-11 is higher than that of Example 1 and Example 8, indicating that the yield strength of the weathering steel can be further improved when the cooling rate is 15-25 ℃ / s to 700 ℃ and then 10-16 ℃ / s to 570 ℃ after finish rolling.

[0044] Table 3 Performance test results of weathering steel for low temperature environment

[0045] From Table 3, the low temperature impact energy of Examples 2, 4-5 is higher than that of Comparative Examples 1-2, indicating that the 235 MPa long-life nickel-free rare earth super weathering steel prepared by the present application has excellent low temperature resistance.

[0046] Table 4 Weathering steel corrosion resistance test results

[0047] Examples 2, 4-5 are a kind of 235 MPa long-life nickel-free rare earth super weathering steel, and their corrosion resistance is significantly better than that of the traditional weathering steel of Comparative Example 1 and the traditional rare earth weathering steel of Comparative Example 2, indicating that the weathering steel prepared by the present application has excellent corrosion resistance.

[0048] Comparative Example 1 is a traditional weathering steel, with an average service life of more than 35 years in industrial areas, more than 30 years in coastal areas and more than 15 years in high-cold regions; Comparative Example 2 is a traditional rare earth weathering steel, with an average service life of more than 65 years in industrial areas, more than 55 years in coastal areas and more than 30 years in high-cold regions. The examples in the present application are rare earth super weathering steels, with an average service life of more than 85 years in industrial areas, more than 75 years in coastal areas and more than 50 years in high-cold regions.

[0049] The above merely preferred embodiments of the present application are not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A 235 MPa long-life nickel-free rare earth super-weathering steel, characterized in that, The super-weather-resistant steel is composed of the following components in percentage by mass: C 0.08%-0.10%, Si 0.18%-0.22%, Mn 0.25%-0.35%, P≤0.09%, S≤0.010%, Al≤0.03%, Cr 0.26%-0.32%, Cu 0.16%-0.19%, Ti 0.012%-0.030%, La 0.005%-0.011%, Ce 0.011%-0.021%, and the balance of Fe and inevitable impurities; the ratio of the Ti, La and Ce satisfies the relationship formula: 0.6≤(La+Ce) / Ti≤2.

6.

2. The 235 MPa long-life nickel-free rare earth super-weathering steel according to claim 1, characterized in that, The ratio of the Ce and La satisfies the relationship formula: 1.4≤Ce / La≤3.

0.

3. A method for preparing a 235 MPa long-life nickel-free rare earth super-weathering steel according to any one of claims 1-2, characterized in that, The method comprises the following steps: S1, the components are proportioned according to the weight percentage, smelted, refined, and continuously cast to obtain a casting blank; S2, the casting blank is subjected to soaking treatment, rough rolling, finish rolling, cooling and coiling to obtain the 235MPa long-life nickel-free rare earth super-weather-resistant steel.

4. The preparation method of the 235 MPa long-life nickel-free rare earth super-weathering steel according to claim 3, characterized in that, In step S1, the specific process of the continuous casting comprises the following steps: after the refined molten steel is injected into a crystallizer and crystallized, it is cooled and solidified to obtain a semi-finished product rough blank; the semi-finished product rough blank is drawn, straightened and flame cut to obtain a casting blank.

5. The method for preparing a 235MPa long-life nickel-free rare-earth super weathering steel according to claim 4, characterized in that, The continuous casting process is carried out under argon protection.

6. The method for preparing a 235MPa long-life nickel-free rare-earth super weathering steel according to claim 4, characterized in that, During the crystallization, the flow rate of the cooling water is 8.0-9.0m / s; The specific water quantity for the cooling and solidification is 0.8-1.0L / Kg.

7. The method for preparing a 235MPa long-life nickel-free rare-earth super weathering steel according to claim 3, characterized in that, In step S2, the temperature of the soaking treatment is 1200-1240℃, and the time is 1.5-2.5h.

8. The method of producing a 235 MPa long-life nickel-free rare earth super-weathering steel according to claim 3, characterized by, In step S2, the initial rolling temperature of the rough rolling is 920-940℃, and the final rolling temperature is 875-925℃.

9. The method of producing a 235 MPa long-life nickel-free rare earth super-weathering steel according to claim 3, characterized by, In step S2, the initial rolling temperature of the finish rolling is 850-900℃, and the final rolling temperature is 780-840℃.

10. The method of producing a 235 MPa long-life nickel-free rare earth super-weathering steel according to claim 3, characterized by, In step S2, the cooling comprises the following steps: first cooling to 700℃ at a rate of 15-25℃ / s, and then cooling to 570℃ at a rate of 10-16℃ / s.

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