Pipeline steel L360M and preparation method thereof

Abstract

The invention belongs to the field of ferrous metallurgy, and discloses pipeline steel L360M and a preparation method thereof. The preparation method sequentially comprises the steps of steel grade component preparation, top-bottom combined blown converter smelting, deoxidation alloying, LF furnace refining, slab continuous casting, charging and heating, primary dephosphorization, secondary dephosphorization, vertical roll rolling, reversible rolling, intermediate rolling, hot coil box sending treatment, flying shear, tertiary dephosphorization, finish rolling and continuous rolling, laminar cooling and coiling. In the top-bottom combined blown converter smelting process, the molten iron consumption is larger than or equal to 950 kg / ton; the laminar cooling rate is less than or equal to 8.5 DEG C / s. By controlling precipitation of large-particle TiN, bainite, free cementite and other abnormal structures are reduced, and the impact performance of the pipeline steel L360M steel strip is improved.

Description

Technical Field

[0001] The present invention belongs to the field of iron and steel metallurgy, and more specifically, relates to a pipeline steel L360M and a preparation method thereof. Background Art

[0002] Pipeline steel is widely used in the oil and gas transportation industry, and generally requires high strength, high toughness, low temperature resistance and good welding performance. Research institutes and pipe factories in the oil industry and steel mills and research units in the metallurgical industry jointly carry out project research and conduct in-depth research on the key technologies of high-grade pipeline steel and steel pipes. They have successfully developed pipeline steels of grades such as L290M, L360M, L415M, L485M, and L550M. While improving the quality of spiral submerged arc welded pipes, they have realized the development and production and supply of straight seam submerged arc welded pipes. The product quality and performance have reached the international advanced level, and the comprehensive localization and large-scale application of pipeline steel and steel pipes have been realized. In recent years, with the increasing competition in the steel market, pipeline steel products have developed in the direction of "low cost, high strength, and lightweight", and titanium microalloying technology has been gradually adopted to produce low-cost pipeline steel. As a typical grade of pipeline steel, L360M is mainly used in oil and gas branch network pipelines, requiring an impact energy of ≥80J at -10℃, and a certain amount of surplus. Moreover, the pipeline steel L360M standard requires C≤0.24%, Mn≤1.40%, Si≤0.45%, S≤0.015%, P≤0.025%, CEV≤0.43, and the sum of niobium, vanadium and titanium shall not exceed 0.15%.

[0003] Pipeline steel L360M is produced by top and bottom combined blowing converter smelting, LF furnace white slag making, double-strand slab continuous casting, thermomechanical rolling and other processes. However, there are shortcomings in the production method of pipeline steel L360M, which causes pipeline steel L360M to be affected by abnormal structures such as large particles of TiN and bainite, resulting in an impact energy <80J, which cannot meet the requirements of GB / T 14164-2013 standard.

[0004] Therefore, it is urgent to propose a new preparation method of pipeline steel L360M. Summary of the invention

[0005] The purpose of the present invention is to provide a pipeline steel L360M and a preparation method thereof in view of the deficiencies of the prior art. The present invention improves the impact performance of the pipeline steel L360M steel strip by controlling the precipitation of large TiN particles and reducing abnormal structures such as bainite and free cementite.

[0006] In order to achieve the above object, the present invention provides a method for preparing pipeline steel L360M, which comprises the following steps in sequence:

[0007] Preparation of steel composition, top and bottom combined blowing converter smelting, deoxidation alloying, LF furnace refining, slab continuous casting, furnace charging and heating, primary dephosphorization, secondary dephosphorization, vertical roller rolling, reversible rolling, intermediate rolling, hot coil box treatment, flying shear, tertiary dephosphorization, finishing rolling, laminar cooling and coiling;

[0008] During the top and bottom combined blowing converter smelting process, the molten iron consumption is ≥950kg / ton;

[0009] The laminar cooling rate is ≤8.5°C / s.

[0010] According to the present invention, preferably, the consumption of the molten iron satisfies that the nitrogen content in the molten steel obtained by smelting in the top and bottom combined blowing converter is not higher than 45 ppm.

[0011] According to the present invention, preferably, based on the total weight of the slag-making material refined in the LF furnace, the slag-making material refined in the LF furnace comprises CaO 53%-55%, SiO 28%-10%, Al 2 O 3 23%-26%, and (FeO+MnO)≤0.7%.

[0012] According to the present invention, preferably, the slag material refined in the LF furnace is used to reduce the mass content of sulfur in the molten steel refined in the LF furnace to below 0.005%.

[0013] In the present invention, the higher the effective titanium content in the pipeline steel L360M steel, the higher the strength of the steel and the lower the cost, but the Ti element is very easy to react with N and S to generate compounds such as TiN, Ti4C2S2, and Ti(CN), resulting in a decrease in the effective titanium content. In order to ensure product performance, it is necessary to passively increase the Ti content of the raw material to ensure the effective titanium content in the steel. After the Ti content increases, the probability of TiN precipitation increases, resulting in a decrease in impact energy. Therefore, the converter of the present invention increases the consumption of molten iron to more than 950kg / t, controls the N content in the steel to be no more than 45ppm, reduces the initial nitrogen content in the steel, and promotes the carbon-oxygen reaction rate to avoid nitrogen increase caused by negative pressure inside the converter; the LF furnace improves the desulfurization effect, reduces the S content in the steel to less than 0.005%, reduces the amount of Ti4C2S2 generated, and increases the effective titanium content in the steel that plays a strengthening role; the present invention controls the N and S contents of the reactants in the steel to increase the effective titanium content, thereby reducing the amount of TiN, Ti4C2S2, Ti(CN), etc. generated.

[0014] According to the present invention, preferably, the secondary cooling zone of the slab continuous casting is 1-11 sections, and the secondary cooling water ratio coefficient of the secondary cooling zone is 0.90-0.95.

[0015] In the present invention, water is sprayed on the surface of the ingot during the steelmaking continuous casting process to cool the ingot, so as to promote the transformation of the molten steel from liquid to solid. When the ingot is cooled to a temperature range of 1450-1500°C, it enters the TiN liquid precipitation temperature range, and TiN begins to precipitate. The present invention accelerates the cooling process by increasing the secondary cooling water ratio of the 1-11 sections of the continuous casting process, prompting the ingot temperature to be rapidly reduced to below 1450°C, reducing the residence time of the TiN liquid precipitation temperature range, and effectively inhibiting the precipitation of large particles of TiN above 10μm, thereby controlling the precipitation amount and size of TiN.

[0016] According to the present invention, preferably, the finishing mill group of the finishing rolling and continuous rolling comprises a total of 7 finishing mill stands F0-F6 which are arranged in sequence.

[0017] In the present invention, the laminar cooling rate is reduced to ≤8.5°C / s by adjusting the final rolling temperature and rolling speed of the steel rolling. According to the present invention, preferably, the final rolling temperature of the finishing rolling is 850-900°C;

[0018] The rolling speed of the finishing mill F6 is 2.5-7.0m / s.

[0019] In the present invention, as a preferred solution, the speeds of the seven finishing stands are in a follow-up mode, that is, the computer system automatically calculates the speeds of the remaining six finishing stands according to the speed of the final finishing stand F6 and the reduction rate of each stand.

[0020] In the present invention, the laminar cooling rate of the steel rolling process is reduced from the traditional 9.3°C / s to below 8.5°C / s, which can avoid the precipitation of abnormal structures such as bainite and free cementite.

[0021] Another aspect of the present invention provides pipeline steel L360M prepared by the preparation method of pipeline steel L360M.

[0022] According to the present invention, preferably, the width of the pipeline steel L360M is 500mm-800mm, and the thickness is 2.5mm-14mm.

[0023] According to the present invention, preferably, the impact energy of the pipeline steel L360M at -10°C is ≥180J.

[0024] The beneficial effects of the technical solution of the present invention are as follows:

[0025] The present invention is applied in the iron and steel metallurgical industry, and improves the impact performance of pipeline steel L360M steel strip by controlling the precipitation of large particles of TiN and reducing abnormal structures such as bainite and free cementite, thereby solving the problem that the impact energy of pipeline steel L360M is lower than the standard requirement. (GB / T 14164-2013 stipulates that the impact energy at -10°C is ≥80J).

[0026] The converter of the present invention increases the molten iron consumption to more than 950 kg / t, reduces the N content in the pipeline steel L360M, reduces the Ti element consumption caused by forming TiN with N, and reduces the production cost of the pipeline steel L360M by 5.8 yuan / ton.

[0027] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings.

[0029] Figure 1 The metallographic structure photograph of pipeline steel L360M prepared by the preparation method of pipeline steel L360M provided in Example 1 of the present invention is shown. (X100)

[0030] Figure 2 The metallographic structure photo of pipeline steel L360M prepared by the preparation method of pipeline steel L360M provided in Comparative Example 1 of the present invention is shown. (X500) DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0032] Example 1

[0033] This embodiment provides a method for preparing pipeline steel L360M, the preparation method comprising the following steps in sequence:

[0034] Preparation of steel composition, top and bottom combined blowing converter smelting, deoxidation alloying, LF furnace refining, slab continuous casting, furnace charging and heating, primary dephosphorization, secondary dephosphorization, E1 vertical roller rolling, R1 reversible rolling, R2 intermediate rolling, hot coil box treatment, flying shear, tertiary dephosphorization, F0-F6 finishing rolling, laminar cooling and coiling;

[0035] During the top and bottom combined blowing converter smelting process, the molten iron consumption is 950 kg / ton, and the molten iron consumption satisfies that the nitrogen content in the molten steel obtained by the top and bottom combined blowing converter smelting is not higher than 45 ppm.

[0036] Based on the total weight of the slag material refined in the LF furnace, the slag material refined in the LF furnace includes 53.8% CaO, 8.7% SiO2, 25.2% Al2O3, and 0.65% (FeO+MnO); the slag material refined in the LF furnace is used to reduce the mass content of sulfur in the molten steel obtained by refining in the LF furnace to less than 0.005%.

[0037] The laminar cooling rate is ≤8.5°C / s.

[0038] The secondary cooling zone of the slab continuous casting is 11 sections, and the secondary cooling water ratio coefficient of the secondary cooling zone is 0.92.

[0039] The final rolling temperature of the finishing rolling is 872° C.; the rolling speed of the finishing rolling final stand F6 is 4.2 m / s.

[0040] The width of the pipeline steel L360M is 705 mm and the thickness is 6.5 mm. The impact energy of the pipeline steel L360M at -10°C is 195 J, which meets the requirements of GB / T 14164-2013 standard.

[0041] Comparative Example 1

[0042] The difference between this comparative example and Example 1 is:

[0043] The consumption of molten iron is 870kg / ton, which makes the nitrogen content in the molten steel obtained by top-bottom combined blowing converter smelting high. Nitrogen reacts with Ti in steel to form large particles of TiN, which is prone to stress concentration and cracks, affecting the impact work.

[0044] Calculated by the total weight of the slag material refined in the LF furnace, the slag material refined in the LF furnace includes CaO51.6%, SiO29.2%, Al2O327.8%, and (FeO+MnO)1.2%, which leads to a higher S content in the molten steel obtained by LF furnace refining. S and Ti element generate Ti4C2S2, which affects the effective titanium content.

[0045] The secondary cooling water ratio coefficient in the secondary cooling zone is 0.75, which aggravates the precipitation of large TiN particles;

[0046] The laminar cooling rate is 9.3℃ / s. Due to the high cooling rate, bainite and free cementite structures appear in the steel strip.

[0047] The width of the pipeline steel L360M is 710 mm and the thickness is 6.3 mm. The impact energy of the pipeline steel L360M at -10°C is 78 J, which cannot meet the requirements of GB / T 14164-2013 standard.

[0048] like Figure 1 , 2As shown, they are metallographic structure photos of L360M produced in Example 1 and Comparative Example 1, respectively. Figure 1 , 2 It can be seen that the method of the present invention controls the precipitation of large-particle TiN, bainite and free cementite structures, and plays an important role in improving the impact energy of pipeline steel L360M.

[0049] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing pipeline steel L360M, characterized in that: The preparation method comprises the following steps in sequence: Preparation of steel composition, top and bottom combined blowing converter smelting, deoxidation alloying, LF furnace refining, slab continuous casting, furnace charging and heating, primary dephosphorization, secondary dephosphorization, vertical roller rolling, reversible rolling, intermediate rolling, hot coil box treatment, flying shear, tertiary dephosphorization, finishing rolling, laminar cooling and coiling; During the top and bottom combined blowing converter smelting process, the molten iron consumption is ≥950kg / ton; The laminar cooling rate is ≤8.5°C / s.

2. The method for preparing pipeline steel L360M according to claim 1, wherein: The consumption of the molten iron satisfies that the nitrogen content in the molten steel obtained by smelting in the top and bottom combined blowing converter is not higher than 45 ppm.

3. The method for preparing pipeline steel L360M according to claim 1, wherein: Based on the total weight of the slag-making material refined in the LF furnace, the slag-making material refined in the LF furnace includes CaO 53%-55%, SiO 28%-10%, Al 2 O 3 23%-26%, and (FeO+MnO)≤0.7%.

4. The method for preparing pipeline steel L360M according to claim 3, wherein: The slag material refined in the LF furnace is used to reduce the mass content of sulfur in the molten steel refined in the LF furnace to below 0.005%.

5. The method for preparing pipeline steel L360M according to claim 1, wherein: The secondary cooling zone of the slab continuous casting is sections 1-11, and the secondary cooling water ratio coefficient of the secondary cooling zone is 0.90-0.

95.

6. The method for preparing pipeline steel L360M according to claim 1, wherein: The finishing rolling unit of the finishing rolling series includes 7 finishing rolling stands F0-F6 which are arranged in sequence.

7. The method for preparing pipeline steel L360M according to claim 6, wherein: The final rolling temperature of the finishing rolling is 850-900°C; The rolling speed of the finishing mill F6 is 2.5-7.0 m / s.

8. Pipeline steel L360M prepared by the method for preparing pipeline steel L360M according to any one of claims 1 to 7.

9. The pipeline steel L360M according to claim 8, wherein: The width of the pipeline steel L360M is 500mm-800mm and the thickness is 2.5mm-14mm.

10. The pipeline steel L360M according to claim 8 or 9, wherein: The impact energy of the pipeline steel L360M at -10°C is ≥180J.

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