A production method of a 420mpa grade structural steel plate without niobium nickel having an extremely low yield ratio and high ductility

Abstract

This invention discloses a method for producing 420MPa grade structural steel plates with extremely low yield strength ratio and high plasticity, free of niobium and nickel. The method includes smelting, continuous casting, heating, rolling, and tempering processes. First, the smelting process ensures control over alloy composition and impurity element content. Following vacuum treatment, a calcium treatment is performed to control the morphology and type of inclusions. Second, a dynamic light-reduction, electromagnetic stirring casting process is employed to improve the internal quality of the cast billet. Then, a two-stage rolling and controlled cooling process, along with tempering, is used. In the controlled cooling stage, a weak cooling method is employed to obtain more soft phase microstructure. Finally, high-temperature tempering is used. The structural steel plates obtained by this invention contain ferrite, pearlite, and bainite microstructures, with a yield strength >420MPa and plasticity A. 50 >29%, and yield strength ratio <0.75.

Description

Technical Field

[0001] This invention relates to a method for producing steel plates, specifically a method for producing 420MPa grade structural steel plates that are free of niobium and nickel and have extremely low yield strength ratio and high plasticity. Background Technology

[0002] 420MPa grade structural steel plate is mainly used in engineering machinery and building structures.

[0003] The overall development trend of structural steel is characterized by high strength and toughness, high plasticity, low yield strength ratio, and easy welding.

[0004] 420MPa grade structural steel plates, which have extremely low yield strength ratio and high plasticity, have many advantages in application, including good low-temperature toughness, excellent plasticity, good weldability, and economy.

[0005] By developing a 420MPa grade structural steel plate that is free of niobium and nickel, has an extremely low yield strength ratio and high plasticity, a complete steelmaking, rolling, cooling and tempering process was formed, which reduced production costs, made the process easy to operate, and ensured stable product performance. This process is extremely technically challenging.

[0006] For example, patent CN102776443A discloses a 420MPa-level low alloy high strength extra-thick steel plate and its manufacturing method, in which 0.032-0.042% niobium and 1.36-1.55% manganese are added to the composition, and normalizing process is required for production.

[0007] For example, patent CN111235472B discloses a 420MPa grade low alloy corrosion-resistant steel and its preparation method and application. The composition includes 0.001-0.01% magnesium, 0.2-4.0% nickel, and 1.0-2.1% manganese. The addition of magnesium alloy makes the smelting process more complicated, and the addition of a higher nickel content makes the production cost higher.

[0008] For example, patent CN113802054A discloses a hot-rolled steel plate with a yield strength of 420MPa and its manufacturing method. The plate contains 0.035–0.045% niobium and 0.05–0.07% carbon, producing a 2–3mm thick hot-rolled steel coil. The addition of niobium and the relatively low carbon content increase the smelting cost and production difficulty of the steel, and also result in a thinner steel plate.

[0009] For example, patent CN115637371A discloses a method for producing titanium-reinforced 420MPa grade low-alloy high-strength medium-thick plates, in which 0.040-0.050% titanium is added to the composition, and after rolling and cooling, the plates are kept in an insulated box and stacked for slow cooling. The addition of a relatively large amount of titanium, and the need for insulated box and slow cooling in stacking, increases the production cost and difficulty of the steel.

[0010] For example, patent CN115161555A discloses a rare earth hot-rolled steel plate and manufacturing method for double-sided enamel steel of 410MPa grade. The steel plate contains 0.055–0.077% antimony, 0.0015–0.0029% rare earth element (RE), and 0.78–0.98% chromium. After rolling, it is fired using a double-sided enamel steel plate. This steel grade requires the addition of rare earth elements (antimony and RE) and a relatively high content of chromium. Furthermore, the double-sided enamel steel plate firing process increases the production cost, production steps, and production difficulty. Summary of the Invention

[0011] Objective of the Invention: This invention aims to provide a method for producing 420MPa grade structural steel plates without niobium and nickel, exhibiting extremely low yield strength ratio and high plasticity. The resulting steel plates have a yield strength > 420MPa and an elongation A 50 ≥29%, yield strength ratio <0.75.

[0012] Technical solution: The production method of the 420MPa grade structural steel plate with extremely low yield strength ratio and high plasticity without niobium and nickel as described in this invention includes smelting process, continuous casting process, heating process, rolling and tempering process, etc.

[0013] First, the smelting process ensures control over the alloy composition and impurity element content, while calcium treatment is implemented after vacuum treatment to control the morphology and type of inclusions. Second, the casting process using dynamic light pressure and electromagnetic stirring improves the internal quality of the billet, effectively reducing the level of macro and micro segregation in the center of the billet and increasing the uniformity of composition and structure in the thickness direction of the steel plate.

[0014] A two-stage rolling and controlled cooling process, along with a tempering process, is employed. In the controlled cooling stage, a weak cooling method is used to obtain more soft phase microstructure.

[0015] Finally, high-temperature tempering is applied. The steel plate after high-temperature tempering possesses good comprehensive mechanical properties of strength, plasticity, and toughness, and is widely used in various important structural components manufactured from medium-carbon structural steel.

[0016] The process specifically includes the following steps:

[0017] Smelting: The smelting process involves pre-desulfurization of molten iron, converter blowing, LF refining to adjust the alloy composition, RH vacuum treatment to improve the purity of molten steel, and calcium treatment after soft stirring to ensure that high-purity molten steel with qualified composition is obtained.

[0018] Continuous casting: Dynamic light pressure and electromagnetic stirring technology are used to achieve excellent internal quality of the billet.

[0019] Heating: The 150mm thick billet enters the heating furnace. The heating temperature of the billet is 1180-1220℃, the time in the furnace is 135-225 minutes, and the temperature when it exits the furnace is 1180-1220℃.

[0020] Rolling: Two-stage rolling is adopted, with roughing temperature of 950-1100℃, finishing rolling initial temperature of 820-870℃, and finishing rolling final temperature of 770-820℃; followed by laminar cooling, with a reddening temperature of 600-650℃.

[0021] Furthermore, the cooling rate is 1–20°C / s. The thickness of the finished steel plate is 32–50 mm.

[0022] Tempering process: Tempering temperature is 550~650℃, and tempering time is 100~250min.

[0023] The steel plate of this invention has the following composition by weight percentage: C: 0.12-0.17%, Si: 0.20-0.50%, Mn: 0.7-0.85%, P: ≤0.013%, S: ≤0.003%, Ti: 0.010-0.020%, V: 0.025-0.045%, Cr: 0.45-0.55%, Mo: 0.12-0.20%, Alt: 0.015-0.050%, with the balance being Fe and impurities.

[0024] Preferably, the steel plate has the following composition by weight percentage: C: 0.15-0.17%, Si: 0.36-0.38%, Mn: 0.82-0.85%, P: ≤0.013%, S: ≤0.003%, Ti: 0.013-0.015%, V: 0.037-0.042%, Cr: 0.48-0.53%, Mo: 0.16-0.17%, Alt: 0.032-0.034%, with the balance being Fe and impurities.

[0025] The structural steel plates produced using the above production method contain ferrite, pearlite, and bainite structures, which are beneficial for maintaining strength and excellent toughness.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0027] (1) The steel plate produced by the manufacturing method described above has stable properties, with a yield strength > 420 MPa and an elongation A 50 ≥29%, yield strength ratio <0.75;

[0028] (2) The production method adopts a smelting process that ensures the alloy composition and impurity element content while calcium treatment, combined with dynamic light pressure and electromagnetic stirring casting process to improve the internal quality of the billet and ensure the plasticity and toughness of the steel plate.

[0029] (3) The manufacturing method is simple and low-cost. It uses 150mm thick billet and produces 420MPa grade steel plate with niobium-nickel-free material, extremely low yield strength ratio and high plasticity through controlled rolling, controlled cooling and tempering process. Attached Figure Description

[0030] Figure 1 The image shows a typical microstructure of a 50mm thick structural steel plate obtained after tempering treatment in Example 1 under a metallographic microscope.

[0031] Figure 2 This is a typical microstructure image of a 50mm thick structural steel plate obtained after tempering treatment in Example 2, shown under a metallographic microscope. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0033] Example 1

[0034] A 420MPa grade structural steel plate with niobium-nickel-free structure, extremely low yield strength ratio and high plasticity has the following composition by weight percentage as shown in Table 1.

[0035] The production method for the aforementioned 420MPa grade structural steel plates, which are free of niobium and nickel and have extremely low yield strength ratio and high plasticity, specifically includes the following steps:

[0036] The smelting process involves pre-desulfurization of molten iron, converter blowing, LF refining to adjust alloy composition, RH vacuum treatment to improve the purity of molten steel, and calcium treatment after soft stirring to ensure that high-purity molten steel with qualified composition is obtained.

[0037] Dynamic light reduction and electromagnetic stirring technology are used in continuous casting to achieve excellent internal quality of the billet;

[0038] The process employs a two-stage controlled rolling and cooling (TMCP) process. A 150mm thick cast billet enters the heating furnace, where it is heated to 1196℃ for 180 minutes, exiting at 1184℃. The roughing temperature is 1025℃, the initial finishing temperature is 845℃, and the final finishing temperature is 820℃. Subsequent laminar flow cooling occurs, with a reheat temperature of 642℃. The cooling rate is 8℃ / s. The finished steel plate thickness is 32-50mm.

[0039] The tempering temperature was controlled at 600℃ and the tempering time was 150 min.

[0040] Example 2

[0041] A 420MPa grade structural steel plate with niobium-nickel-free structure, extremely low yield strength ratio and high plasticity has the following composition by weight percentage as shown in Table 1.

[0042] The production method for the aforementioned 420MPa grade structural steel plates, which are free of niobium and nickel and have extremely low yield strength ratio and high plasticity, specifically includes the following steps:

[0043] The smelting process involves pre-desulfurization of molten iron, converter blowing, LF refining to adjust alloy composition, RH vacuum treatment to improve the purity of molten steel, and calcium treatment after soft stirring to ensure that high-purity molten steel with qualified composition is obtained.

[0044] Dynamic light reduction and electromagnetic stirring technology are used in continuous casting to achieve excellent internal quality of the billet;

[0045] The process employs a two-stage controlled rolling and cooling (TMCP) process. A 150mm thick cast billet enters the heating furnace, where it is heated to 1194℃ for 176 minutes, exiting at 1183℃. The roughing rolling temperature is 1033℃, the initial finishing rolling temperature is 833℃, and the final finishing rolling temperature is 818℃. Subsequent laminar flow cooling is used, with a reheat temperature of 650℃. The cooling rate is 8.5℃ / s. The finished steel plate thickness ranges from 32-50mm.

[0046] The tempering temperature was controlled at 600℃ and the tempering time was 150 min.

[0047] Figure 1 , 2 These are typical microstructure images of 420MPa grade structural steel plates obtained after tempering treatment in the examples, shown under a metallographic microscope. Careful observation is required. Figure 1 , 2 The microstructure can be observed to be ferrite, pearlite, and bainite. This ferrite-pearlite-bainite microstructure is beneficial for maintaining strength, excellent toughness, and good plasticity. 50 >29%, and yield strength ratio <0.75.

[0048] The properties of the finished steel plates are shown in Table 2-3 below.

[0049] Table 1 Chemical composition (wt%) of embodiments of the present invention

[0050] Example C Si Mn P S Alt V Ti Cr Mo margin Example 1 0.15 0.38 0.85 0.013 0.004 0.034 0.042 0.013 0.53 0.16 Fe and impurities Example 2 0.17 0.36 0.82 0.012 0.003 0.032 0.037 0.015 0.48 0.17 Fe and impurities

[0051] Table 2 Tensile Properties

[0052]

[0053] Table 3 series of temperature shock properties

[0054]

[0055] It can be seen that the mechanical properties of Examples 1 and 2 both meet the requirements for 420MPa grade quenched and tempered high-strength steel plates. Specifically, the steel plates achieve the following performance levels: yield strength > 420MPa, plasticity A...50 >29%, and yield strength ratio <0.75.

Claims

1. A method for producing a 420MPa grade structural steel plate with extremely low yield strength ratio and high plasticity, free of niobium and nickel, characterized in that, This includes smelting processes, continuous casting processes, heating processes, rolling and tempering processes, among which... Smelting process: The smelting process involves pre-desulfurization of molten iron, converter blowing, LF refining to adjust alloy composition, RH vacuum treatment to improve the purity of molten steel, and calcium treatment after soft stirring to ensure that high-purity molten steel with qualified composition is obtained. Continuous casting process: Dynamic light reduction and electromagnetic stirring technology are used to achieve excellent internal quality of the cast billet; Heating process: A 150mm thick billet enters the heating furnace, the heating temperature of the billet is 1180-1220℃, the time in the furnace is 135-225min, and the temperature when it exits the furnace is 1180-1220℃. Rolling process: Two-stage rolling followed by laminar flow cooling, with a reddening temperature of 600-650℃ and a cooling rate of 1-20℃ / s; Tempering process: Tempering temperature is 550~650℃, tempering time is 100~250min; The structural steel plate has the following composition by weight percentage: C: 0.12-0.17%, Si: 0.20-0.50%, Mn: 0.7-0.85%, P: ≤0.013%, S: ≤0.003%, Ti: 0.010-0.020%, V: 0.025-0.045%, Cr: 0.45-0.55%, Mo: 0.12-0.20%, Alt: 0.015-0.050%, with the balance being Fe and impurities; The structural steel plate contains ferrite, pearlite and bainite.

2. The method for producing 420MPa grade structural steel plates with extremely low yield strength ratio and high plasticity without niobium and nickel according to claim 1, characterized in that, In the rolling process, the roughing temperature is 950-1100℃, the finishing rolling start temperature is 820-870℃, and the finishing rolling finish temperature is 770-820℃.

3. The method for producing 420MPa grade structural steel plates with extremely low yield strength ratio and high plasticity without niobium and nickel according to claim 1, characterized in that, The structural steel plate has the following composition by weight percentage: C: 0.15-0.17%, Si: 0.36-0.38%, Mn: 0.82-0.85%, P: ≤0.013%, S: ≤0.003%, Ti: 0.013-0.015%, V: 0.037-0.042%, Cr: 0.48-0.53%, Mo: 0.16-0.17%, Alt: 0.032-0.034%, with the balance being Fe and impurities.

4. The method for producing 420MPa grade structural steel plates with extremely low yield strength ratio and high plasticity without niobium and nickel according to claim 1, characterized in that, The thickness of the finished steel plate is 32-50mm.

5. The method for producing 420MPa grade structural steel plates with extremely low yield strength ratio and high plasticity without niobium and nickel according to claim 1, characterized in that, The yield strength of the structural steel plate is >420MPa, and its plasticity is A. 50 >29%, yield strength ratio <0.75.

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