A high-strength, high-ductility steel with a yield strength of 1100 MPa and its manufacturing method

Abstract

This invention discloses an ultra-high strength and ductility steel with a yield strength of 1100 MPa. Its chemical composition by mass percentage is: C: 0.03%-0.08%, Si: 0.2%-0.60%, Mn: 1.0%-2.0%, Al: 0.01-0.05%; P: ≤0.001%, S: ≤0.002%, Cr: 1.5%-3.5%, Mo: 0.5-1.5%; Nb: 0.05%-0.10%; Ti: 0.02-0.06%; V: 0.10%-0.30%, with the remainder being Fe. The invention also discloses its preparation method. This invention breaks the paradox of the incompatibility between strength and ductility, meeting the requirements for high strength, high ductility, and excellent weldability of steel plates. Employing solution treatment and aging treatment processes, the steel plate meets the following technical requirements: yield strength ≥1100 MPa, elongation ≥15%, and reduction of area ≥55%.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgical materials technology, and in particular to an ultra-high strength ductile steel with a yield strength of 1100MPa and its manufacturing method, which can be used in heavy machinery equipment, pipelines, marine vessels, bridges, containers and other fields. Background Technology

[0002] With the rapid development of society and industry, human demand for the comprehensive performance of steel materials is increasing, requiring steel plates to have high strength, high plasticity, and excellent weldability. For traditional high-strength steel, the main methods are to increase the C and Mn content and add alloying elements such as Cu, Cr, and Ni to improve hardenability, thereby obtaining a martensitic or mixed martensitic and bainitic microstructure. This is achieved through a combination of solid solution strengthening and microstructure strengthening mechanisms to achieve high strength. However, high C and Mn content increases the carbon equivalent, which seriously affects weldability.

[0003] Currently, most ultra-high strength steels with a strength of 1100MPa or higher adopt a low-carbon microalloying design route. The high C content leads to poor plasticity, toughness, and weldability, which is not ideal in practical engineering applications. Some researchers have also proposed high Ni content alloy systems, which can significantly improve weldability, but the high Ni content leads to high production costs. Summary of the Invention

[0004] The purpose of this invention is to provide an ultra-high strength ductile steel with a yield strength of 1100MPa and its manufacturing method, breaking the paradox of the incompatibility between strength and ductility, and meeting the requirements of high strength, high ductility and excellent weldability of steel plates. By adopting solution treatment and aging treatment processes, the steel plate meets the following technical requirements: yield strength ≥1100MPa, elongation ≥15%, and reduction of area ≥55%.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses an ultra-high strength ductile steel with a yield strength of 1100 MPa, whose chemical composition by mass percentage is as follows: C: 0.03%-0.08%, Si: 0.2%-0.60%, Mn: 1.0%-2.0%, Al: 0.01-0.05%; P: ≤0.001%, S: ≤0.002%, Cr: 1.5%-3.5%, Mo: 0.5-1.5%; Nb: 0.05%-0.10%; Ti: 0.02-0.06%; V: 0.10%-0.30%, with the remainder being Fe and unavoidable inclusions.

[0007] Furthermore, the chemical composition by mass percentage is as follows: C: 0.072%, Si: 0.481%, Mn: 1.47%, Al: 0.030%; P: 0.00088%, S: 0.0016%, Cr: 2.43%, Mo: 0.772%; Nb: 0.067%; Ti: 0.041%; V: 0.21%, with the remainder being Fe and unavoidable inclusions.

[0008] Furthermore, the chemical composition by mass percentage is as follows: C: 0.067%, Si: 0.482%, Mn: 1.48%, Al: 0.030%; P: 0.00092%, S: 0.0016%, Cr: 2.42%, Mo: 0.780%; Nb: 0.070%; Ti: 0.045%; V: 0.19%, with the remainder being Fe and unavoidable inclusions.

[0009] A method for preparing ultra-high strength and ductility steel with a yield strength of 1100 MPa includes the following steps:

[0010] ① Smelting

[0011] The process involves blast furnace hot metal pretreatment, converter top and bottom blowing smelting, aluminum deoxidation, refining in ladle furnace, adding alloys, adjusting the composition to the target composition, and then transferring to RH vacuum degassing.

[0012] ② Continuous casting

[0013] Electromagnetic stirring and light reduction technology are used for continuous casting of slabs, which are then stacked and cooled slowly after casting.

[0014] ③ Rolling

[0015] The billet is heated to 1200±20℃ and held for 2-5 hours. High-pressure water is used for descaling before rough rolling and during rolling. The rough rolling temperature is 1100-1160℃, the finishing rolling temperature is 980-1060℃, and the final rolling temperature is >920℃. The billet is rolled into 8-20mm thick steel plates.

[0016] ④ Heat treatment

[0017] The steel plate is held at 900℃ for 30-60 minutes and then water-quenched to room temperature; subsequently, it is tempered at 500-640℃ for 30-120 minutes and then air-cooled to room temperature.

[0018] Furthermore, the quenched structure is lath martensite, and the tempered structure is tempered sorbite.

[0019] Furthermore, the ultra-high strength ductile steel meets the following technical requirements: yield strength ≥1100MPa, elongation ≥15%, and reduction of area ≥55%.

[0020] Ingredient design basis:

[0021] C: Carbon is a solid solution strengthening element that significantly improves strength. Traditional high-strength steels generally use carbon solid solution strengthening to achieve high strength, but high carbon content not only reduces weldability but also forms coarse cementite during tempering, severely affecting plasticity. This invention adopts an ultra-low carbon design, with a carbon content designed to be 0.03%-0.08%.

[0022] Mn: Manganese is a solid solution strengthening element that significantly affects strength and also refines grain size. However, excessive manganese content can easily cause component segregation in the cast billet, resulting in severe banded structures and reduced toughness. The manganese content in this invention is designed to be 1.0-2.0%.

[0023] Cr: Chromium is a weather-resistant element that can increase the corrosion resistance of steel, while also effectively improving hardenability and tempering stability. The chromium content in this invention is designed to be 1.5%-3.5%.

[0024] Mo: Molybdenum can increase the hardenability and thermal stability of steel, and combine with carbon to form nano-carbides, thereby increasing strength. The molybdenum content in this invention is designed to be 0.5-1.5% Mo.

[0025] Nb, Ti, and V: Niobium, titanium, and vanadium combine with carbon to form carbides, which pin grain boundaries, refine grains, and simultaneously form nano-carbides to improve strength. In this invention, the contents of niobium, titanium, and vanadium are designed to be 0.05%-0.10%, 0.02-0.06%, and 0.1-0.30%, respectively.

[0026] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0027] This invention relates to an ultra-high strength and ductility steel with a yield strength of 1100 MPa, exhibiting excellent strength-ductility balance. This steel is an ultra-low carbon steel with low C content, resulting in excellent weldability. Simultaneously, its low alloy element content leads to low production costs. The high strength and ductility significantly improve the stability of large structures, ensuring safety. Its excellent weldability, low sensitivity to cold cracking, and wide range of preheating and post-heating temperatures, or even the elimination of preheating altogether, greatly reduce manufacturing costs.

[0028] The method for preparing ultra-high strength ductile steel with a yield strength of 1100MPa of the present invention is simple, requires low equipment, and has good controllability in smelting, rolling and heat treatment processes, making it easy to achieve industrial production.

[0029] The ultra-high strength and ductility steel of the present invention, with a yield strength of 1100MPa, achieves excellent tensile properties by controlling heat treatment processes such as rolling, solution treatment, and aging treatment, which allow alloying elements to fully play their role in refining grains and improving hardenability, effectively refining the martensitic lath structure, and obtaining steel plates that meet the following technical requirements: yield strength ≥1100MPa, elongation ≥15%, and reduction of area ≥55%. Attached Figure Description

[0030] The present invention will be further described below with reference to the accompanying drawings.

[0031] Figure 1 The tempered microstructure of Example 1 is shown below;

[0032] Figure 2 The fracture morphology of room temperature tensile test is shown in Example 1. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments. The embodiments are merely descriptions of the best implementation of the present invention and do not limit the scope of the present invention in any way.

[0034] The present invention discloses an ultra-high strength ductile steel with a yield strength of 1100 MPa and its preparation method. The composition of the ultra-high strength ductile steel is as follows: by mass percentage, C: 0.03%-0.08%, Si: 0.2%-0.60%, Mn: 1.0%-2.0%, Al: 0.01-0.05%, P: ≤0.001%, S≤0.002%, O: ≤0.0080%, Cr: 1.5%-3.5%, Mo: 0.5-1.5%, Nb: 0.05%-0.10%, Ti: 0.02-0.06%, V: 0.10%-0.30%, with the remainder being Fe and unavoidable inclusions.

[0035] The composition design principle of this 1100MPa grade ultra-high strength and ductility steel is as follows:

[0036] The design concept of this invention is to use low C content and alloying elements to reduce the carbon equivalent and obtain excellent welding performance. Reducing the C content significantly decreases the strength of the steel plate. To meet strength requirements, new strengthening mechanisms are proposed: firstly, solid solution strengthening through alloying elements; secondly, adding microalloying elements Nb, Ti, and V to pin grain boundaries and refine grains, achieving a fine-grain strengthening mechanism; thirdly, the precipitation strengthening mechanism achieved by nano-precipitates MC (M representing Nb, Ti, and V) or M2C (M representing Mo) precipitated during tempering; and fourthly, the high density of dislocations in lath martensite, achieving a dislocation strengthening mechanism.

[0037] The method for preparing ultra-high strength and ductility steel with a yield strength of 1100 MPa as described in this invention includes the following steps:

[0038] Smelting: Hot metal pretreatment—converter top and bottom blowing smelting—LF ladle refining—RH vacuum degassing—slab continuous casting (electromagnetic stirring, light reduction)—stacking and slow cooling;

[0039] Rolling: Slab heating—descaling—rough rolling—finish rolling—ACC cooling—quality inspection—sampling inspection—finished product warehousing.

[0040] The chemical composition (mass percentage) of each embodiment of the present invention is shown in Table 1 and the process parameters are shown in Table 2.

[0041] Table 1

[0042]

[0043] The above embodiments employ blast furnace molten iron pretreatment, converter top and bottom re-blowing smelting, aluminum deoxidation, transfer to ladle furnace for refining, adjustment of composition to target composition, and then transfer to RH vacuum degassing; slab continuous casting is carried out using electromagnetic stirring and light reduction technology, and the slabs are stacked and slowly cooled after continuous casting.

[0044] The billet is heated to 1200±20℃ and held for 2-5 hours. High-pressure water is used for descaling before rough rolling and during rolling. The rough rolling temperature is 1100-1160℃, the finishing rolling temperature is 980-1060℃, and the final rolling temperature is >920℃. The billet is rolled into 8-20mm thick steel plates.

[0045] The steel plate is held at 900℃ for 30-60 minutes and then water-quenched to room temperature; subsequently, it is tempered at 500-640℃ for 30-120 minutes and then air-cooled to room temperature.

[0046] Table 2

[0047]

[0048] After rolling and quenching and tempering heat treatment, steel plates were sampled transversely and processed into φ5 bars for room temperature tensile testing. The tensile performance results are shown in Table 3.

[0049] Table 3 Tensile properties of the examples

[0050]

[0051] As shown in Table 3, the ultra-high strength and ductility steel with a yield strength of 1100MPa and its manufacturing method provided by the present invention produce steel plates with a yield strength >1100MPa, elongation >15%, reduction of area >55%, and good matching of strength and ductility.

[0052] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A high-strength, high-ductility steel with a yield strength of 1100 MPa, characterized in that, The chemical composition by mass percentage is as follows: C: 0.03%-0.08%, Si: 0.2%-0.60%, Mn: 1.0%-2.0%, Al: 0.01-0.05%; P: ≤0.001%, S: ≤0.002%, Cr: 1.5%-3.5%, Mo: 0.5-1.5%; Nb: 0.05%-0.10%. Ti: 0.02-0.06%; V: 0.10%-0.30%, the remainder being Fe and unavoidable inclusions; Its preparation method is characterized by comprising the following steps: ① Smelting The process involves blast furnace hot metal pretreatment, converter top and bottom blowing smelting, aluminum deoxidation, refining in ladle furnace, adding alloys, adjusting the composition to the target composition, and then transferring to RH vacuum degassing. ② Continuous casting Electromagnetic stirring and light reduction technology are used for continuous casting of slabs, which are then stacked and cooled slowly after casting. ③ Rolling The billet is heated to 1200±20℃ and held for 2-5 hours. High-pressure water is used for descaling before rough rolling and during rolling. The rough rolling temperature is 1100-1160℃, the finishing rolling temperature is 980-1060℃, and the final rolling temperature is >920℃. The billet is rolled into 8-20mm thick steel plates. ④ Heat treatment The steel plate is held at 900℃ for 30-60 minutes and then water-quenched to room temperature; subsequently, it is tempered at 500-640℃ for 30-120 minutes and then air-cooled to room temperature.

2. The ultra-high strength and ductility steel with a yield strength of 1100 MPa according to claim 1, characterized in that, The chemical composition by mass percentage is: C: 0.072%, Si: 0.481%, Mn: 1.47%, Al: 0.030%; P: 0.00088%, S: 0.0016%, Cr: 2.43%, Mo: 0.772%; Nb: 0.067%; Ti: 0.041%; V: 0.21%, the remainder being Fe and unavoidable inclusions.

3. The ultra-high strength and ductility steel with a yield strength of 1100 MPa according to claim 1, characterized in that, The chemical composition by mass percentage is: C: 0.067%, Si: 0.482%, Mn: 1.48%, Al: 0.030%; P: 0.00092%, S: 0.0016%, Cr: 2.42%, Mo: 0.780%; Nb: 0.070%; Ti: 0.045%; V: 0.19%, the remainder being Fe and unavoidable inclusions.

4. The ultra-high strength and ductility steel with a yield strength of 1100 MPa according to claim 1, characterized in that, The quenched structure is lath martensite, and the tempered structure is tempered sorbite.

5. The ultra-high strength and ductility steel with a yield strength of 1100 MPa according to claim 1, characterized in that, The ultra-high strength ductile steel meets the following technical requirements: yield strength ≥1100MPa, elongation ≥15%, and reduction of area ≥55%.

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