Hot continuous rolling ultrahigh-strength steel plate and preparation method thereof

Abstract

The invention provides a hot continuous rolling ultrahigh-strength steel plate and a preparation method thereof, and the hot continuous rolling ultrahigh-strength steel plate comprises the following components in percentage by mass: 0.10-0.20% of C, 0.15-0.30% of Si, 4.5-5.5% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.20-0.42% of V, 0.30-0.50% of Mo and the balance of Fe. By adding V and Mo in the steel plate with the Mn content of 4.5-5.5%, nano precipitation of second-phase particles is regulated and controlled, and the material strength is improved; and martensite is converted into austenite through inverse phase change cover annealing, the deformation induced plasticity effect is achieved in the plastic deformation process, and the ductility, the yield strength and the tensile strength of the steel are effectively improved. The yield strength of the steel plate ranges from 1025 MPa to 1060 MPa, the tensile strength ranges from 1200 MPa to 1332 MPa, the ductility ranges from 15.0% to 18.0%, and the Akv at the temperature of 0 DEG C ranges from 60 J to 90 J.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot-rolled reverse phase transformation type ultra-high strength plate and strip production, and in particular relates to a hot-rolled ultra-high strength steel plate and a preparation method thereof. Background Art

[0002] Safety and lightweight are important development directions for automobiles. Lightweighting of commercial vehicles is even more urgent due to the need to reduce weight and the implementation of emission policies. With the continuous rise in fuel prices and the unprecedented increase in the country's efforts to control pollution, commercial vehicles are trying to reduce the weight of their bodies as much as possible while ensuring safety, so as to achieve economical vehicle operation, reduce fuel consumption and reduce exhaust emissions.

[0003] GB1589-2016 "External dimensions, axle loads and mass limits for automobiles, trailers and automobile trains" clearly stipulates that the total weight of a 6-axle train is limited to 49 tons, while a 6-axle train consisting of 6×2 traction will be limited to 46 tons. The commercial vehicle beam is an important load-bearing and safety component, which directly affects the service life and driving safety of the entire vehicle. Based on the considerations of reducing vehicle weight and improving safety, the material used to make the beam should not only ensure sufficient strength, but also good cold formability and fatigue resistance. Based on the batch use of 500MPa, 600MPa, 700MPa and 800MPa, well-known domestic commercial vehicle companies have successively proposed the development of higher-strength automotive beam steel materials to achieve the goals of lighter body, larger effective load, lower fuel consumption and emissions.

[0004] At present, the main technical means to improve the strength and toughness of steel is microstructure refinement. However, simple microstructure refinement will reduce the uniform plasticity of steel and increase the yield strength ratio while improving the strength and toughness, making it difficult to fully meet the service safety requirements under high strengthening conditions. On the other hand, when the microstructure is refined to a certain extent (effective grain size is about 5 microns), the difficulty of further refinement increases significantly, and the requirements for process conditions become more and more stringent, such as cyclic phase transformation, low temperature and large reduction deformation, etc., which are difficult to achieve for some steels with larger specifications and sizes. Therefore, it is necessary to explore other microstructure regulation principles and process means to improve the strength and toughness of steel in addition to microstructure refinement. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a hot-rolled ultra-high strength steel plate and a preparation method thereof. The steel plate adopts a low-carbon-medium manganese component design to improve the stability of austenite, effectively combines V-Ti nano-precipitation with organizational regulation, and combines high-temperature annealing treatment after rolling. During the annealing process, nano-scale microalloy carbides are precipitated and martensite → austenite reverse transformation occurs simultaneously, so that a nanoparticle-reinforced martensite / austenite structure can be obtained, thereby greatly improving the strength and toughness and plasticity of the material.

[0006] The present invention provides a hot-rolled ultra-high strength steel plate, which comprises the following components by mass fraction:

[0007] C: 0.10%~0.20%, Si: 0.15~0.30%, Mn: 4.5%~5.5%, P≤0.020%, S≤0.010%, V: 0.20%~0.42%, Mo: 0.30~0.50%, balance Fe.

[0008] Preferably, the C: 0.14-0.16%, Si: 0.18-0.22%, Mn: 4.8-5.2%, V: 0.38-0.42%, Mo: 0.36-0.42%, and P≤0.015%.

[0009] Preferably, the microstructure of the hot-rolled ultra-high strength steel plate consists of martensite and austenite of the lath;

[0010] The austenite content is 10-15 vol%.

[0011] Preferably, the yield strength of the hot-rolled ultra-high strength steel plate is 1025-1060 MPa, the tensile strength is 1200-1332 MPa, the elongation is 15.0-18.0% and the 0°C A kv It is 60~90J.

[0012] The present invention provides a method for preparing the hot-rolled ultra-high strength steel plate according to the above technical solution, comprising the following steps:

[0013] According to the chemical composition of the hot-rolled ultra-high strength steel plate, smelting and casting are performed to obtain a slab;

[0014] The slab is heated to 1230±20° C., kept warm for 3.5 to 4.5 hours, subjected to multiple rough rolling and multiple finish rolling to remove the iron oxide scale, and then coiled;

[0015] Hood annealing and cooling are adopted to obtain hot-rolled ultra-high strength steel plates.

[0016] Preferably, the bell-type annealing is performed by heating the temperature to 600-620° C. at a heating rate of 4-7° C. / min and keeping the temperature for 18-20 hours.

[0017] Preferably, the rough rolling is performed 4 to 6 times, and the reduction rate of each pass is greater than or equal to 15%.

[0018] Preferably, the start rolling temperature of the finish rolling is greater than or equal to 1030°C, the number of passes of the finish rolling is 6 to 8 times, and the final rolling temperature is 900 to 950°C.

[0019] Preferably, the coiling temperature is 600-650°C.

[0020] The present invention provides a hot-rolled ultra-high-strength steel plate, which includes the following components by mass fraction: C: 0.10% to 0.20%, Si: 0.15 to 0.30%, Mn: 4.5% to 5.5%, P≤0.020%, S≤0.010%, V: 0.20% to 0.42%, Mo: 0.30 to 0.50%, and the balance is Fe. The present invention improves the material strength by regulating the nano-precipitation of second-phase particles by V and Mo in a steel plate with a Mn content of 4.5% to 5.5%; realizes the transformation of martensite to austenite by reverse phase transformation hood annealing, exerts deformation-induced plasticity in the process of plastic deformation, and effectively improves the elongation, yield strength and tensile strength of the product. The yield strength of the hot-rolled ultra-high-strength steel plate described in the present invention is 1025 to 1060 MPa, the tensile strength is 1200 to 1332 MPa, the elongation is 15.0 to 18.0% and 0°C A kv It is 60~90J. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a SEM image of the hot-rolled ultra-high strength steel plate prepared in Example 2 of the present invention;

[0022] Figure 2 EBSD image of the hot-rolled ultra-high strength steel plate prepared in Example 2 of the present invention;

[0023] Figure 3 TEM image of the hot-rolled ultra-high strength steel plate prepared in Example 2 of the present invention;

[0024] Figure 4 This is a carbon film replica photo of the hot-rolled ultra-high strength steel plate prepared in Example 2 of the present invention;

[0025] Figure 5 XRD diagrams of the hot-rolled ultra-high strength steel plates prepared in Example 1 (620°C) and Example 2 (600°C) of the present invention. DETAILED DESCRIPTION

[0026] The present invention provides a hot-rolled ultra-high strength steel plate, which comprises the following components by mass fraction:

[0027] C: 0.10%~0.20%, Si: 0.15~0.30%, Mn: 4.5%~5.5%, P≤0.020%, S≤0.010%, V: 0.20%~0.42%, Mo: 0.30~0.50%, balance Fe.

[0028] The hot-rolled ultra-high strength steel plate provided by the present invention includes carbon C: 0.10% to 0.20%; specifically 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, or 0.20%. Carbon is an important austenite element in the steel plate and can stabilize the austenite structure. Carbon can react with V in the steel to generate nano-scale carbide VC, produce precipitation strengthening, and improve the strength of the steel. If the carbon content is too low, the austenite structure of the steel will be unstable, the amount of carbide precipitation in the steel will be reduced, and the strength and toughness will be reduced. However, if the carbon content is too high, it will promote the formation of coarse cementite at the austenite grain boundary and reduce the elongation. Therefore, the carbon content in the present invention is 0.10 to 0.20%, preferably 0.14 to 0.16%.

[0029] The hot-rolled ultra-high strength steel plate provided by the present invention comprises Si: 0.15-0.30%; specifically 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, or 0.30%. The silicon element described in the present invention can be dissolved in ferrite and austenite to improve the strength of steel, and its effect is second only to C and P, and is stronger than elements such as Mn, Cr, Ti and Ni; the silicon element can make the dissolved C atoms fully enriched in austenite, thereby improving its stability. It is difficult to obtain residual austenite at room temperature if the Si content is too low. When the Si content is too high, the surface iron oxide scale formed by Si in the heating furnace is difficult to remove, which increases the difficulty of dephosphorization; therefore, the Si content of the present invention is 0.14-0.30%, preferably 0.18-0.22%.

[0030] The hot-rolled ultra-high strength steel plate provided by the present invention includes Mn: 4.5% to 5.5%; specifically 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, or 5.5%. In the present invention, manganese is an austenitizing element. Adding the Mn element can expand the austenite phase region and increase the austenite content, increase the stacking fault energy of the steel, inhibit the martensitic phase transformation, generate dense twins during the deformation process, and effectively improve the elongation of the steel. The manganese content is preferably 4.8 to 5.2%.

[0031] The hot-rolled ultra-high strength steel plate provided by the present invention includes V: 0.20% to 0.42%; specifically 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.40%, 0.41%, or 0.42%;. V is a strong carbide-forming element that can refine grains and improve the strength and toughness of steel. During hot rolling, V carbide precipitation is rare, mainly during hood annealing. The VC precipitation phase particle size is ≤30nm, providing a large precipitation strengthening contribution to compensate for the strength drop caused by dislocation recovery after tempering of medium Mn steel. The V content is preferably 0.38-0.42%; in a specific embodiment, the V content is 0.38% or 0.40%.

[0032] The hot-rolled ultra-high strength steel plate provided by the present invention comprises Mo: 0.30-0.50%; specifically 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.40%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.46%, 0.47%, 0.48%, 0.49% or 0.50%; preferably 0.36-0.42%. In the present invention, the molybdenum element can improve the stability of carbides, play a beneficial role in improving the ductility and toughness of steel, and the molybdenum element can inhibit the growth of second phase particles and improve the precipitation strengthening effect of V-containing second phase particles.

[0033] The hot-rolled ultra-high strength steel plate provided by the present invention comprises P≤0.020% and S≤0.010%.

[0034] In a specific embodiment, the hot-rolled ultra-high strength steel plate comprises the following components by mass fraction:

[0035] C: 0.160%, Si: 0.19%, Mn: 4.74%, P: 0.015%, S: 0.008%, V: 0.38%, Mo: 0.36%, balance Fe;

[0036] Or C: 0.155%, Si: 0.20%, Mn: 4.79%, P: 0.010%, S: 0.005%, V: 0.40%, Mo: 0.41%, and the balance Fe.

[0037] The microstructure of the hot-rolled ultra-high strength steel plate provided by the present invention consists of martensite and austenite of the strip; the content of the austenite is 10-15 vol%.

[0038] The hot-rolled ultra-high strength steel plate provided by the present invention has a yield strength of 1025-1060 MPa, a tensile strength of 1200-1332 MPa, an elongation of 15.0-18.0% and a 0°C A kv It is 60~90J.

[0039] The present invention provides a method for preparing the hot-rolled ultra-high strength steel plate according to the above technical solution, comprising the following steps:

[0040] According to the chemical composition of the hot-rolled ultra-high strength steel plate, smelting and casting are performed to obtain a slab;

[0041] The slab is heated to 1230±20° C., kept warm for 3.5 to 4.5 hours, subjected to multiple rough rolling and multiple finish rolling to remove the iron oxide scale, and then coiled;

[0042] Hood annealing and cooling are adopted to obtain hot-rolled ultra-high strength steel plates.

[0043] The present invention performs smelting according to the chemical composition of the hot-rolled ultra-high-strength steel plate and obtains the slab through casting.

[0044] After obtaining the slab, the present invention heats the slab to 1230±20°C, keeps the temperature for 3.5-4.5 hours, removes the iron oxide scale, performs multiple rough rolling, multiple finish rolling, and coils. The rough rolling in the present invention is performed 4-6 times, and the reduction rate of each pass is greater than or equal to 15%.

[0045] The start rolling temperature of the finishing rolling in the present invention is greater than or equal to 1030° C., the number of finishing rolling passes is 6 to 8 times, and the final rolling temperature is 900 to 950° C. After the finishing rolling, the cooling is controlled and the coiling is performed, and the coiling temperature is 600 to 650° C.

[0046] After coiling, the present invention adopts bell annealing and cooling to obtain hot-rolled ultra-high strength steel plate. The bell annealing in the present invention is to increase the temperature to 600-620°C at a heating rate of 4-7°C / min and keep the temperature for 18-20h.

[0047] The PTT curve of the hot-rolled ultra-high strength steel plate prepared by the method provided by the present invention shows a C-type, and the precipitation from the tempered martensite has the fastest precipitation temperature of about 620°C, which is conducive to obtaining a greater precipitation strengthening effect; hood annealing at the above temperature can obtain a certain amount of reverse transformation austenite, which is conducive to improving the toughness and plasticity of the steel; V microalloying in the hood annealing greatly improves the yield strength of the annealed steel, providing a strengthening increment of about 400MPa.

[0048] In order to further illustrate the present invention, a hot-rolled ultra-high strength steel plate and a preparation method thereof provided by the present invention are described in detail below in combination with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0049] Embodiment 1-2

[0050] The chemical composition of the prepared vanadium-molybdenum microalloyed hot-rolled ultra-high strength steel is shown in Table 1;

[0051] Table 1 Chemical composition of vanadium-molybdenum microalloyed ultra-high strength steel (wt.%)

[0052] serial number C Si Mn P S V Mo margin Example 1 0.160 0.19 4.74 0.015 0.008 0.38 0.36 Fe Example 2 0.155 0.20 4.79 0.010 0.005 0.40 0.41 Fe

[0053] The specific process of the preparation method of the above-mentioned vanadium-molybdenum microalloyed ultra-high strength steel plate is as follows:

[0054] A. Smelting process: After the smelting process, an ultra-high strength steel slab having the chemical composition shown in Table 1 is prepared;

[0055] B. Hot rolling process: The slab is heated, hot rolled and hot coiled. The specific hot rolling process parameters are shown in Table 2;

[0056] Table 2 Main process parameters of hot rolling of vanadium-molybdenum microalloyed ultra-high strength steel

[0057] serial number Heating temperature ℃ Final rolling temperature / ℃ Coiling temperature / ℃ Example 1 1233 907 615 Example 2 1236 919 626

[0058] C. Reverse phase change annealing: Use a bell-type annealing furnace to slowly heat the strip to the target temperature, keep it warm for a period of time, and then cool it with a cooling hood. The parameters are shown in Table 3:

[0059] Table 3 Main process parameters of vanadium-molybdenum microalloyed ultra-high strength steel cover annealing

[0060] serial number Heating speed ℃ / min Hood annealing temperature / ℃ Insulation time / h Example 1 5.0 620 20.0 Example 2 5.0 600 20.0

[0061] The microstructure of the vanadium-molybdenum microalloyed ultra-high strength steel prepared by the process of Example 2 is as follows: Figures 1 to 4 As shown;

[0062] The present invention tests the performance of the above-mentioned vanadium-molybdenum microalloyed ultra-high strength steel according to GB / T228-2010 "Room Temperature Tensile Test Method for Metallic Materials", and its mechanical properties are shown in Table 4 below:

[0063] Table 4 Mechanical properties of vanadium-molybdenum microalloyed ultra-high strength steel

[0064] serial number Yield strength / MPa Tensile strength / MPa Elongation / % 0℃Akv / J Example 1 1021 1225 16.5 73 Example 2 1052 1264 16.0 70

[0065] It can be seen from the above embodiments that the present invention provides a hot-rolled ultra-high strength steel plate, which includes the following components by mass fraction: C: 0.10% to 0.20%, Si: 0.15 to 0.30%, Mn: 4.5% to 5.5%, P≤0.020%, S≤0.010%, V: 0.20% to 0.42%, Mo: 0.30 to 0.50%, and the balance is Fe. The present invention improves the material strength by regulating the nano-precipitation of second-phase particles by V and Mo in a steel plate with a Mn content of 4.5% to 5.5%; realizes the transformation of martensite to austenite by reverse phase transformation hood annealing, exerts deformation-induced plasticity in the process of plastic deformation, and effectively improves the elongation rate, yield strength and tensile strength of the product. The experimental results show that the yield strength of the hot-rolled ultra-high strength steel plate is 1021-1052MPa, the tensile strength is 1225-1264MPa, the elongation is 16.0-16.5% and the 0℃A kv It is 70~73J.

[0066] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A hot-rolled ultra-high strength steel plate, comprising the following components by mass fraction: C: 0.10~0.20%, Si: 0.15~0.30%, Mn: 4.5~5.5%, P≤0.020%, S≤0.010%, V: 0.20~0.42%, Mo: 0.30~0.50%, balance Fe.

2. The hot-rolled ultra-high strength steel plate according to claim 1, characterized in that: The C: 0.14-0.16%, Si: 0.18-0.22%, Mn: 4.8-5.2%, V: 0.38-0.42%, Mo: 0.36-0.42%, and P≤0.015%.

3. The hot-rolled ultra-high strength steel plate according to claim 1, characterized in that: The microstructure of the hot-rolled ultra-high strength steel plate consists of martensite and austenite in the lath; The austenite content is 10-15 vol%.

4. The hot-rolled ultra-high strength steel plate according to claim 1, characterized in that: The hot-rolled ultra-high strength steel plate has a yield strength of 1025-1060 MPa, a tensile strength of 1200-1332 MPa, an elongation of 15.0-18.0% and a 0°C A kv It is 60~90J.

5. A method for preparing the hot rolled ultra-high strength steel plate according to any one of claims 1 to 4, comprising the following steps: According to the chemical composition of hot-rolled ultra-high strength steel plates, they are smelted and cast into slabs; The slab is heated to 1230±20° C., kept warm for 3.5 to 4.5 hours, subjected to multiple rough rolling and multiple finish rolling to remove the iron oxide scale, and then coiled; Hood annealing and cooling are adopted to obtain hot-rolled ultra-high strength steel plates.

6. The preparation method according to claim 5, characterized in that: The bell-type annealing is to increase the temperature to 600-620° C. at a heating rate of 4-7° C. / min and keep the temperature for 18-20 hours.

7. The preparation method according to claim 5, characterized in that: The rough rolling is performed 4 to 6 times, and the reduction rate of each pass is greater than or equal to 15%.

8. The preparation method according to claim 5, characterized in that: The start rolling temperature of the finishing rolling is greater than or equal to 1030°C, the number of passes of the finishing rolling is 6 to 8 times, and the final rolling temperature is 900 to 950°C.

9. The preparation method according to claim 5, characterized in that: The coiling temperature is 600-650°C.

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