Low-copper rare earth weathering steel and preparation method thereof

Abstract

The invention provides low-copper rare earth weathering steel and a preparation method thereof. The low-copper rare earth weathering steel comprises the following chemical components in percentage by weight: less than or equal to 0.20% of C, 0.30%-0.50% of Si, 0.60%-0.80% of Mn, less than or equal to 0.075% of P, less than or equal to 0.021% of S, 0.55%-0.75% of Cr, 0.40%-0.60% of Ni, 0.05%-0.10% of Cu, 0.00015%-0.00025% of La and the balance of Fe. And the balance of Fe and inevitable impurities. A trace amount of rare earth element La is added, the microalloying effect of the rare earth element for purifying molten steel and improving the strength and toughness of steel is fully exerted, various mechanical properties of the steel are obviously superior to those of common weathering steel through chemical component control and controlled rolling and controlled cooling process regulation and control design, and the V-shaped notch impact energy at 0 DEG C is larger than or equal to 125 J.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a low-copper rare earth weathering steel and its preparation method. Background Technology

[0002] In industries such as transportation and construction, hot-dip galvanizing is a widely used method for preventing atmospheric corrosion of steel. However, the hot-dip galvanizing process generates large amounts of irritating gases such as NH3 and HCl, as well as dense NH4Cl fumes; the high-temperature zinc bath surface comes into contact with air, and the resulting zinc oxide dust continuously enters the surrounding environment; in addition to air pollution, the hot-dip galvanizing process also produces a large amount of zinc ash and zinc slag, accounting for 20-60% of the total zinc consumption. The disadvantages of the galvanizing process are very obvious: high energy consumption, significant raw material waste, and serious environmental pollution. Adding alloying elements such as Cr, Ni, Mo, and Cu to ordinary carbon steel can improve its corrosion resistance in atmospheric environments by 2 to 8 times compared to ordinary carbon steel, and the longer the service life, the more obvious the corrosion resistance effect. This type of steel is called weathering steel. However, elements such as Cr, Ni, Mo, and Cu are relatively expensive, and there are still some obstacles to large-scale application. my country, on the other hand, has abundant rare earth resources, and adding rare earth elements to steel can significantly improve the mechanical properties and corrosion resistance of steel, while saving on alloy usage and reducing production costs, thus showing broad prospects for widespread application.

[0003] Therefore, it is necessary to study a low-copper rare-earth weathering steel and its preparation method to address the shortcomings of existing technologies and solve or mitigate one or more of the above-mentioned problems. Summary of the Invention

[0004] In view of this, the present invention provides a low-copper rare earth weathering steel and its preparation method. By adding trace amounts of rare earth element La, the microalloying effect of rare earth elements in purifying molten steel and improving the strength and toughness of steel is fully utilized. Through chemical composition control and controlled rolling and cooling process design, a multiphase microstructure of ferrite, polygonal ferrite and pearlite is obtained. Its various mechanical properties are significantly better than those of ordinary weathering steel, with a yield strength ≥520MPa, tensile strength ≥660MPa, and V-notch impact energy ≥125J at 0°C. It has the characteristics of high strength, high corrosion resistance and low cost, and can meet the comprehensive requirements of various industries for atmospheric corrosion resistance, steel mechanical properties and low cost, and has broad prospects for promotion and application.

[0005] On the one hand, a low-copper rare-earth weathering steel has a chemical composition by weight percentage including C≤0.20%, Si: 0.30%~0.50%, Mn: 0.60%~0.80%, P≤0.075%, S≤0.021%, Cr: 0.55~0.75%, Ni: 0.40~0.60%, Cu: 0.05~0.10%, La: 0.00015%~0.00025%; the remainder is Fe and unavoidable impurities.

[0006] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the effective content of Cu+Ni in the low-copper rare earth weathering steel is ≥0.45%.

[0007] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the microstructure of the low-copper rare-earth weathering steel comprises a composite phase microstructure of acicular ferrite, polygonal ferrite, and martensite.

[0008] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the volume fraction of ferrite in the low copper rare earth weathering steel is 15-20%, the volume fraction of pearlite is 30-40%, and the volume fraction of martensite is 55-65%.

[0009] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the low-copper rare-earth weathering steel has a yield strength ≥520MPa, a tensile strength ≥660MPa, an atmospheric corrosion resistance index ≥6.65, and a V-notch impact energy ≥125J at 0°C.

[0010] In accordance with the aspects and any possible implementations described above, a method for preparing low-copper rare-earth weathering steel is further provided, the method comprising: S1: Smelt the raw materials into steel billets according to the preset chemical composition and proportion; S2: The steel billet is rolled through five passes in sequence to obtain rolled steel plate; S3: The finished product is obtained after the controlled cooling process of the rolled steel plate.

[0011] In addition to the aspects described above and any possible implementation, a further implementation is provided, wherein the preset chemical composition ratio and proportion in S1 are: C≤0.20%, Si: 0.30%~0.50%, Mn: 0.60%~0.80%, P≤0.075%, S≤0.021%, Cr: 0.55~0.75%, Ni: 0.40~0.60%, Cu: 0.05~0.10%, La: 0.00015%~0.00025%; the remainder being Fe and unavoidable impurities.

[0012] In addition to the aspects described above and any possible implementation, a further implementation is provided in which the billet is heated to 1100-1200°C and held for 1-2 hours during the S2 five-pass rolling process.

[0013] In addition to the aspects described above and any possible implementation, a further implementation is provided in which the initial rolling temperature of the roughing rolling process in the S2 five-pass rolling process is 850-900°C, the reduction amounts are 30%, 25%, 30%, 25%, and 20% respectively, and the final rolling temperature is 720-770°C.

[0014] In addition to the aspects and any possible implementations described above, a further implementation is provided in which, in the S2 controlled cooling process, after rolling is completed, water is sprayed to cool to a final cooling temperature of 450-490°C, and after final cooling, a slow cooling method is used to bring the temperature to room temperature.

[0015] Compared with the prior art, the present invention can achieve the following technical effects: The low-copper rare-earth weathering steel provided by this invention, in addition to the necessary corrosion-resistant elements, also fully utilizes the micro-alloying effect of rare earth elements in purifying molten steel and improving the strength and toughness of the steel by adding trace amounts of rare earth element La. Its various mechanical properties are significantly better than those of ordinary weathering steel, with a yield strength ≥520MPa, tensile strength ≥660MPa, and V-notch impact energy ≥125J at 0°C. It has the characteristics of high strength, high corrosion resistance, and low cost, and can meet the comprehensive requirements of various industries for atmospheric corrosion resistance, steel mechanical properties, and low cost. It has broad prospects for promotion and application.

[0016] Of course, any product implementing this invention does not necessarily need to achieve all of the technical effects described above at the same time. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating a method for preparing low-copper rare-earth weathering steel according to an embodiment of the present invention. Detailed Implementation

[0019] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0020] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0022] The present invention provides a low-copper rare-earth weathering steel, the chemical composition of which, by weight percentage, includes C≤0.20%, Si: 0.30%~0.50%, Mn: 0.60%~0.80%, P≤0.075%, S≤0.021%, Cr: 0.55~0.75%, Ni: 0.40~0.60%, Cu: 0.35~0.50%, La: 0.00015%~0.00025%; the remainder is Fe and unavoidable impurities. The microstructure of the weathering steel includes acicular ferrite, polygonal ferrite and martensite. It has a yield strength ≥520MPa, tensile strength ≥660MPa, atmospheric corrosion resistance index ≥6.65; and V-notch impact energy ≥125J at 0°C.

[0023] In the chemical composition of this invention, carbon (C) is one of the effective elements for solid solution strengthening in steel. However, an increase in carbon content in steel will worsen the corrosion resistance of the steel and also have a significant adverse effect on its weldability. Therefore, the carbon content should be controlled to be below 0.20% in general.

[0024] In the chemical composition of this invention, silicon (Si) is a commonly used beneficial element in steel, used as a deoxidizer during the smelting process. The deoxidation products are also non-metallic inclusions that dissolve in ferrite. Therefore, the Si content is controlled at 0.30%~0.50%.

[0025] In the chemical composition of this invention, Mn is also a beneficial element, often playing a role in deoxidation and desulfurization during the smelting process. Because it can combine with sulfur to form MnS, it can eliminate most of the adverse effects of S on the properties of steel. Mn deoxidation products can also form inclusions. Furthermore, a high Mn content will reduce the corrosion resistance of the steel; therefore, the Mn content is controlled at 0.60%~0.80%.

[0026] In the chemical composition of this invention, sulfur (S) is a harmful element in steel, which can cause hot brittleness. Therefore, the content of sulfur is controlled to be S ≤ 0.021%.

[0027] In the chemical composition of this invention, the increase of Cr element is beneficial to improving the corrosion resistance of steel and also to improving the strength of steel. However, excessive Cr content will reduce the elongation and reduction of area of ​​steel. The Cr content is controlled at 0.55~0.75%.

[0028] In the chemical composition of this invention, increasing the Ni content in the steel slightly increases the martensite content in the microstructure and results in a more uniform grain size. The yield strength, tensile strength, and elongation of the steel all gradually increase with the increase of Ni content. However, Ni increases the brittleness and overheating sensitivity of the steel, and as a relatively scarce resource, it also increases production costs. Therefore, the Ni content is controlled at 0.40~0.60%.

[0029] In the chemical composition of this invention, Cu plays a prominent role in improving the corrosion resistance of steel, and Cu also has a strong protective effect on rust layers. However, excessively high Cu content can cause copper embrittlement in the steel during hot working. Therefore, considering all factors, the Cu content is controlled at 0.05~0.10%.

[0030] In the chemical composition of this invention, the rare earth element La, as a trace element used in steel, plays a role in purifying molten steel, removing inclusions, and microalloying. It also influences the basic microstructure of the steel, improving its strength, toughness, and corrosion resistance. Increased purity of molten steel effectively improves the overall performance of the steel. Rare earth elements are also effective elements for solid solution strengthening; La dissolved in steel improves the morphology of inclusions, thus affecting the steel's properties. Therefore, the La content is controlled at 0.00015%~0.00025%.

[0031] like Figure 1 As shown, the present invention also provides a method for preparing the above-mentioned low-copper rare earth weathering steel. The specific production method includes smelting the raw material into steel billets according to the chemical composition and proportion of the above-mentioned low-copper rare earth weathering steel, and then obtaining the finished product after passing through five rolling and controlled cooling processes.

[0032] In the heating process, the billet is heated to 1100-1200°C and held for 1-2 hours.

[0033] In the five rolling processes, the initial rolling temperature is 850–900°C, the reduction is 30%, 25%, 30%, 25%, and 20% respectively, and the final rolling temperature is 720–770°C.

[0034] In the controlled cooling process, after rolling, water is sprayed to cool to the final cooling temperature of 450-490°C, and then slow cooling is used to bring it to room temperature.

[0035] Example 1 The low-copper rare-earth weathering steel has the following chemical composition by weight percentage: C 0.17%, Si 0.46%, Mn 0.63%, S 0.015%, P 0.062%, Cr 0.66%, Ni 0.52%, Cu 0.05%, La 0.00021%; the remainder is Fe and unavoidable impurities. The raw materials are smelted into steel billets according to the above chemical composition and proportions; then heated to 1160°C and held for 90 minutes. The initial rolling temperature is 880°C, with reductions of 30%, 25%, 30%, 25%, and 20% respectively, and the final rolling temperature is 762°C. The 60mm thick billets are rolled into steel plates ≤12mm thick. After rolling, the plates are water-cooled to 465°C and then slowly cooled to room temperature. The performance indicators of the finished weathering steel were tested, and its yield strength was 535 MPa, tensile strength was 672 MPa, atmospheric corrosion resistance index was 7.89, and V-notch impact energy at 0°C was 136 J.

[0036] Example 2 The low-copper rare-earth weathering steel has the following chemical composition by weight percentage: C 0.18%, Si 0.42%, Mn 0.68%, S 0.012%, P 0.069%, Cr 0.71%, Ni 0.55%, Cu 0.1%, La 0.00024%; the remainder is Fe and unavoidable impurities. The raw materials are smelted into steel billets according to the above chemical composition and proportions; then heated to 1186°C and held for 102 minutes. The initial rolling temperature is 863°C, with reductions of 30%, 25%, 30%, 25%, and 20% respectively, and the final rolling temperature is 755°C. The 60mm thick billets are rolled into steel plates ≤12mm thick. After rolling, the plates are water-cooled to 472°C and then slowly cooled to room temperature. The performance indicators of the finished weathering steel were tested, and its yield strength was 546 MPa, tensile strength was 679 MPa, atmospheric corrosion resistance index was 7.87, and V-notch impact energy at 0°C was 141 J.

[0037] Example 3 The low-copper rare-earth weathering steel has the following chemical composition by weight percentage: C 0.16%, Si 0.40%, Mn 0.72%, S 0.011%, P 0.055%, Cr 0.63%, Ni 0.49%, Cu 0.08%, La 0.00019%; the remainder is Fe and unavoidable impurities. The raw materials are smelted into steel billets according to the above chemical composition and proportions; then heated to 1156°C and held for 82 minutes. The initial rolling temperature is 860°C, with reductions of 30%, 25%, 30%, 25%, and 20% respectively, and the final rolling temperature is 732°C. The 60mm thick billets are rolled into steel plates ≤12mm thick. After rolling, the plates are water-cooled to 460°C and then slowly cooled to room temperature. The performance indicators of the finished weathering steel were tested, and its yield strength was 540 MPa, tensile strength was 680 MPa, atmospheric corrosion resistance index was 6.94, and V-notch impact energy at 0°C was 146 J.

[0038] As can be seen from the above embodiments, the low-copper rare earth weathering steel prepared by the present invention has good yield strength, tensile strength and atmospheric corrosion resistance, and the V-notch impact energy at 0°C is ≥125J, exhibiting good mechanical properties and comprehensive performance.

[0039] The foregoing has provided a detailed description of a low-copper rare-earth weathering steel and its preparation method according to embodiments of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of this application; furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

[0040] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0041] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0042] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0043] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A low-copper rare-earth weathering steel, characterized in that: The chemical composition, by weight percentage, includes C ≤ 0.20%, Si: 0.30%~0.50%, Mn: 0.60%~0.80%, P ≤ 0.075%, S ≤ 0.021%, Cr: 0.55~0.75%, Ni: 0.40~0.60%, Cu: 0.05~0.10%, La: 0.00015%~0.00025%; the remainder is Fe and unavoidable impurities.

2. The low-copper rare-earth weathering steel according to claim 1, characterized in that: The effective content of Cu+Ni in the low-copper rare earth weathering steel is ≥0.45%.

3. The low-copper rare-earth weathering steel according to claim 1, characterized in that: The microstructure of the low-copper rare-earth weathering steel includes a composite phase of acicular ferrite, polygonal ferrite, and martensite.

4. The low-copper rare-earth weathering steel according to claim 1, characterized in that: The low-copper rare earth weathering steel has a ferrite volume fraction of 15-20%, a pearlite volume fraction of 30-40%, and a martensite volume fraction of 55-65%.

5. The low-copper rare-earth weathering steel according to claim 1, characterized in that: The low-copper rare-earth weathering steel has a yield strength ≥520MPa, a tensile strength ≥660MPa, an atmospheric corrosion resistance index ≥6.65, and a V-notch impact energy ≥125J at 0°C.

6. A method for preparing low-copper rare-earth weathering steel, used to prepare the low-copper rare-earth weathering steel according to any one of claims 1-5, characterized in that, The preparation method includes: S1: Smelt the raw materials into steel billets according to the preset chemical composition and proportion; S2: The steel billet is rolled through five passes in sequence to obtain rolled steel plate; S3: The finished product is obtained after the controlled cooling process of the rolled steel plate.

7. The preparation method according to claim 6, characterized in that: The preset chemical composition ratio and proportion in S1 are: C≤0.20%, Si: 0.30%~0.50%, Mn: 0.60%~0.80%, P≤0.075%, S≤0.021%, Cr: 0.55~0.75%, Ni: 0.40~0.60%, Cu: 0.05~0.10%, La: 0.00015%~0.00025%; the remainder is Fe and unavoidable impurities.

8. The preparation method according to claim 6, characterized in that: In the S2 five-pass rolling process, the billet is heated to 1100-1200°C and held for 1-2 hours.

9. The preparation method according to claim 6, characterized in that: In the S2 five-pass rolling process, the initial rolling temperature of the rough rolling is 850-900°C, the reduction is 30%, 25%, 30%, 25%, and 20% respectively, and the final rolling temperature is 720-770°C.

10. The preparation method according to claim 6, characterized in that: In the S2 controlled cooling process, after rolling, water is sprayed to cool to a final cooling temperature of 450-490°C, and after final cooling, a slow cooling method is used to bring it to room temperature.

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