CN115354237A - Hot-rolled ultrahigh-strength steel plate with tensile strength of 1000MPa and preparation method thereof - Google Patents

Abstract

A hot-rolled ultrahigh-strength steel plate with 1000 MPa-level tensile strength and a preparation method thereof belong to the technical field of metallurgy. The hot-rolled ultrahigh-strength steel plate with the tensile strength of 1000MPa comprises the following components in percentage by mass: c:0.06 to 0.12 percent; mn:1.0 to 2.0 percent; si:0.08 to 0.2 percent; ti:0.05 to 0.13 percent; cr:0.7 to 1.5 percent; p is less than or equal to 0.02 percent; s is less than or equal to 0.01 percent; the balance of Fe and inevitable impurities. The preparation method comprises the following steps: 1) Smelting the mixture into a casting blank according to the chemical component proportion of the hot rolled steel plate; 2) And (3) preserving the heat of the casting blank, carrying out hot rolling, cooling to a proper temperature at a certain cooling rate, and then raising the temperature on line to coil. The obtained hot-rolled ultrahigh-strength steel plate with the tensile strength of 1000MPa mainly comprises bainite, residual austenite and nano-scale carbide, wherein the carbide is dispersed and distributed on a bainite matrix, the yield strength is not less than 750MPa, the tensile strength is not less than 1000MPa, and the elongation A is not less than 15%.

Description

Tensile strength 1000MPa class hot-rolled ultra-high strength steel plate and preparation method thereof

technical field

The invention relates to the technical field of metallurgy, in particular to a hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa and a preparation method thereof.

Background technique

In order to achieve the goals of energy saving, emission reduction and safety, the steel industry has been committed to the development of high-strength steel, requiring the materials used to further increase the strength, so as to reduce the amount of steel used and achieve the purpose of light weight.

The data shows that every 10% reduction in the total vehicle weight will increase the fuel economy by about 4.9% on average. However, every 100kg reduction in vehicle weight will increase the safety risk by 3% to 4.5%. Therefore, while reducing weight, it is also necessary to consider the issue of collision safety, not only high strength, but also good plasticity.

With the rapid development of large-scale construction machinery, weight reduction, and automobile lightweight, the demand for hot-rolled ultra-high-strength steel with a tensile strength of 1000 MPa is increasing. It is not only used in automotive structural components and skeleton components, but also in chassis components and track Frame components, components for construction machinery, etc. are also widely used and have broad application prospects.

At present, there are few ultra-high-strength steels with a tensile strength of 1000MPa at home and abroad, and according to existing research, to obtain high strength, it is necessary to add hardenable elements such as C, Mn, Mo, etc., and online/quenching+tempering is mostly used Process production has problems such as high alloy content, high production cost, low coiling temperature, difficult control, long process flow, and low plasticity.

The invention patent with the notification number CN101008066B discloses a hot-rolled martensitic steel plate with a tensile strength higher than 1000 MPa. The chemical composition mass percentage of the steel plate is: C: 0.08～0.20; Si≤0.8; Mn: 0.5～2.0; Al: 0.010～0.060; N≤0.008; P≤0.020; S≤0.005; ≤0.10 and Nb: one or more of 0.01-0.05; others are composed of Fe and unavoidable impurities. The structure of the steel plate produced by this method is mainly martensite, and the low coiling temperature is low (150 ° C ~ Ms), the strength is high but the plasticity is low (low elongation ≤ 9%), and the high content of Si element is easy to produce Quenching cracks tend to accumulate on the surface of the steel plate and form fayalite (Fe ₂ SiO ₄ ) on the surface, which affects the surface quality and becomes the starting point of cracks during bending.

The invention patent with the notification number CN109023111B discloses a 1000MPa grade hot-rolled automobile frame steel and its manufacturing method. The chemical composition mass percentage of the steel plate is: C 0.10-0.20%; Si≤0.10%; Mn: 1.5-1.7%; S≤0.005%; P≤0.015%; Nb: 0.045～0.055%; Ti: 0.08～0.10%; N≤40ppm; Als: 0.025～0.060%; H≤0.002%; the balance is Fe. The structure of the steel plate produced by this method is martensite + a small amount of ferrite, which has relatively high strength, but the elongation is low at 10-11.5%. The two-stage controlled cooling process is adopted, and the intermediate temperature is first cooled to 600-650 ° C. Then it is rapidly cooled to 200-300°C for coiling, the coiling temperature is low, the production process control is difficult, and the carbon content is high, which is easy to reduce the weldability, and the high content of Nb element will also increase the cost.

The invention patent with publication number CN109735775A discloses a 1000MPa grade ultra-high-strength hot-rolled steel strip and its production method. The chemical composition mass percentage of the hot-rolled steel strip is: C: 0.08-0.15%; Mn: 2.30-2.83%; Si≤ 0.80%; Als: 0.025～0.052%; S≤0.020%; P≤0.030%; Cr: 0.50～0.70%; Ti: 0.01～0.05%; Mo: 0.15～0.30%; the balance is Fe and unavoidable impurities . The microstructure of the steel plate produced by the method is ferrite+bainite+martensite structure, has relatively high strength, and the plasticity is 9-14%. However, this method uses a high content of Si and Mn elements, which will increase the difficulty of controlling the surface of the steel plate, and become the starting point of cracks during bending; if the Mn content exceeds 2.0%, it is easy to segregate and cause problems such as banded structure, which affects the formability. Elements increase production costs.

The invention patent with the publication number CN110331326A discloses a 1000MPa grade thin-gauge hot-rolled high-strength dual-phase steel plate and its preparation method. The chemical composition of the steel plate is: C: 0.10-0.20%; Si: 0.80-1.20%; : 1.20～2.0%; P: ≤0.020%; S: ≤0.010%; Ti: 0.010～0.040%; Cr: 0.20～0.60%; Als: 0.020～0.060%; the balance is Fe and unavoidable inclusions. The microstructure of the hot-rolled steel plate produced by this invention is ferrite + martensite, the yield strength of the product is ≥550MPa, the tensile strength is ≥1000MPa, and the yield ratio is ≤0.60. Low and high content of Si element makes it more difficult to control the surface of the steel plate. At the same time, the three-stage controlled cooling process is adopted, the coiling temperature is low, and the precise control of the process is difficult.

The invention patent with publication number CN105925896A discloses a 1000MPa grade high-strength and high-plasticity hot-rolled steel plate and its manufacturing method. The mass percentage of the chemical composition of the steel plate is: C 0.15-0.3%; Mn 5-6%; N 0.05-0.12%; Si<0.2%; S<0.01%; P<0.01%; Al 0.002-0.04%; For Fe. The invention is prepared through the steps of smelting, casting, hot rolling, and reverse phase transformation annealing. The microstructure is lath-shaped austenite and tempered martensite, which has high strength and high elongation. However, due to the addition of high content of C, Mn and N elements lead to poor weldability, and problems such as banded structures caused by segregation of Mn elements affect formability.

The invention patent with publication number CN109207849A discloses a high-strength and high-plasticity 1000MPa grade hot-rolled steel plate and a preparation method. The mass percentage of the chemical composition of the steel plate is: C: 0.05-0.40%; Mn: 1.00-5.00%; Si: 0.70-1.60%; Al: 0.1-1.00%; Nb: 0.01-0.10%; V: 0.01-0.10% ; N: 0.002-0.005%; the balance is Fe and unavoidable impurities. By adding Nb and V microalloying elements combined with C and N to form nanoscale cluster precipitates to strengthen the matrix structure and reduce the strength difference between the two matrix structures (ferrite and martensite), the steel plate has high strength and high plasticity, but the The yield strength of the steel plate produced by the method is low, and at the same time, the high content of Si element makes it difficult to control the surface of the steel plate, and the band structure caused by the segregation of Mn element affects the formability, and the more Nb element increases the production cost.

Through the above analysis of the existing technology of 1000MPa grade hot-rolled ultra-high strength steel, it can be seen that the current existing technology has the following characteristics: (1) In order to obtain high strength, a large amount of C, Mn, Si and other elements are added, which makes it difficult to control the surface of the steel plate and forms a band. Shaped structure affects formability, etc., or adding one or more expensive microalloying elements Ti, Nb, V, Mo, etc. increases the cost of steel; (2) The cooling process is complicated or the coiling temperature is low, which makes it difficult to precisely control the process ; (3) The structure of the steel plate is mostly ferrite + martensite or full martensite, etc., with high strength but low plasticity.

With the development of nanotechnology, nanomaterials and nanotechnology are introduced into iron and steel materials, and the use of precipitation strengthening and grain refinement of nanoscale precipitates has become one of the most promising ways of strengthening and toughening metal materials, and it is also a new type of ultra-high strength steel. The most important strengthening mechanism. At present, due to the limited precipitation strengthening effect of a single titanium-containing microalloyed steel, the strength level of the steel plate is not high. Therefore, the development of titanium-containing composite microalloyed steel has received more and more attention.

Published techniques for titanium-containing composite microalloyed steels include:

The invention patent with the publication number CN107287519A discloses a vanadium-containing hot-rolled coil for automobile structure and a production method. The chemical composition mass percentage of the steel plate is: C: 0.05-0.15%; Mn: 1.2-2.0%; Si≤0.50 %; Nb+V+Ti: 0.08-0.20%; P≤0.035%; S≤0.025%; Als: 0.01-0.06%; the balance is Fe and unavoidable impurities. More Nb, V, Ti microalloying elements are added, and the tensile strength of the steel plate produced is 800MPa.

The invention patent with the publication number CN107043890A discloses a hot-rolled automobile steel with a thickness of 1.5-3.0 mm and a yield strength greater than 700 MPa and its manufacturing method. The chemical composition and mass percentage of it are: C: 0.02-0.06%; Mn: 1.20～2.00%; Al: 0.010～0.050%; P≤0.01%; S≤0.05%; Nb: 0.01～0.05%; Ti: 0.05～0.12%; V: 0.05～0.20%; The balance is Fe and unavoidable impurities; the yield strength of the produced steel plate is 700-760MPa, the tensile strength is 760-870MPa, and the elongation A is 18-21%.

The invention patent with the publication number CN104264052A discloses a steel plate for construction machinery and its production method. The chemical composition of the steel plate is: C: 0.05-0.09%; Si: 0.05-0.30%; Mn: 1.5-2.0%; P≤0.025%; S≤0.005%; Nb: 0～0.07%; Ti: 0.08～0.15%; Mo: 0.10～0.30%; Als: 0.015～0.06%; Ca: 0.0010～0.0030%; N≤0.006%; The balance is Fe. The thickness of the steel plate is 3.0-8.5mm, the yield strength of the product is ≥700MPa, the tensile strength is ≥785MPa, and the elongation after fracture is ≥15%.

The invention patent with the publication number CN106319389A discloses low-cost, high-machinability steel for engineering machinery and its manufacturing method. The mass percentage of its composition is: C: 0.06-0.10%; Si: 0.30-0.60%; 1.60%; P: ≤0.015%; S: ≤0.0030%; Ni: 0.20～0.60%; Cr: 0.50～0.80%; Mo: 0.25～0.55%; V: 0.025～0.065%; Ti: 0.008-0.018%; Al: 0.030-0.070%; N: ≤0.0050%; Ca: 0.0010-0.0040%; the balance is Fe and unavoidable impurities. The yield strength of the steel plate produced by the method is ≥630MPa, and the tensile strength is ≥700MPa.

In the above patents on titanium-containing composite microalloy strengthening steel, three or more of the Nb-V-Ti-Mo microalloying elements are added, which leads to an increase in the cost of the steel, and the strength of the produced hot-rolled steel plate is lower than 1000MPa, which is difficult to obtain. To meet the current market demand for steel product reduction.

To sum up, the existing hot-rolled steel sheets with a tensile strength of 1000MPa are mainly composed of martensite in their microstructure. Although the tensile strength can reach 1000MPa, they have low plasticity and low yield strength. Ultra-high-strength steel plate with low alloy cost, simple rolling process, higher strength and good plasticity.

Contents of the invention

Aiming at the problems in the above-mentioned prior art, the present invention provides a hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa and its preparation method, which adopts the method of rapid cooling to the bainite region after rolling, and then immediately conducts on-line heat treatment, Especially through low-cost Ti and Cr microalloying composition design and rolling and cooling process control, the precipitation strengthening of Ti-Cr composite microalloying steel can be realized, and the effects of fine grain strengthening, phase transformation strengthening and precipitation strengthening can be fully exerted. Production Hot-rolled bainite ultra-high-strength steel, the tensile strength of 1000MPa grade hot-rolled ultra-high-strength steel plate, its yield strength is more than 750MPa, the tensile strength is more than 1000MPa, and the elongation after fracture is more than 15%, while ensuring high tensile strength. , with high yield strength and high elongation after fracture, can meet the synchronous improvement of strength and plasticity, and can realize the improvement of the comprehensive performance of steel.

In order to realize the above-mentioned purpose of the invention, the present invention adopts following technical scheme:

The first aspect of the present invention is to provide a hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa. The chemical components of the raw materials and the mass percentages of each chemical component of the raw materials are: C: 0.06-0.12%; Mn: 1.0-2.0 %; Si: 0.08-0.2%; Ti: 0.05-0.13%; Cr: 0.7-1.5%; P≤0.02%; S≤0.01%; the balance is Fe and unavoidable impurities.

The hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa has a microstructure of bainite, retained austenite and nanoscale carbides, and the nanoscale carbides are dispersedly distributed on the bainite matrix.

Further, the sum of volume percentages of bainite, retained austenite and nano-scale carbides is ≥95%, and the size of nano-scale carbides is mainly 3-20 nm.

The hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa has a yield strength of more than 750 MPa, a tensile strength of more than 1000 MPa, and an elongation after fracture of more than 15%.

The thickness of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa is 2-4 mm.

In the present invention, the selection of chemical composition in the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa grade is determined as follows:

C element is used to improve the strength of the material and is the cheapest element to improve the strength.

Mn element is used to significantly reduce the Ar ₁ temperature of steel and the decomposition rate of austenite. Mn is a solid solution strengthening element, which can be infinitely solid-soluted with Fe and can increase the strength of steel.

As an effective element to increase the strength of the steel plate without reducing the ductility, the Si element is dissolved in ferrite and austenite to increase the strength of the steel. Si can reduce the diffusion rate of carbon in ferrite, so that the precipitated carbides are not easy to coarsen.

Ti and C elements form high-temperature-resistant TiC particles, which play a role in precipitation strengthening, and are pinned to the original austenite grain boundary to prevent the growth of austenite grains and improve welding performance.

Cr is a carbide-forming element with a medium affinity with C. Cr carbides are evenly distributed in the iron matrix, and the strength of the steel is improved through precipitation strengthening. It has the effect of hindering grain growth under short-term heating and can refine the structure. , to enhance the strength and toughness of steel. At the same time, in the present invention, Cr and Ti form composite carbides, which is beneficial to refine the size of precipitates, increase the volume fraction of precipitates, and improve the strength and hardness of the steel plate.

P and S are harmful impurity elements in steel. P elements in steel are easy to segregate at grain boundaries, and the starting point of grain boundary cracks during processing reduces the toughness and bending workability of steel. S exists in the form of inclusions such as MnS in steel. Therefore, when the steel plate is bent, the interface between the matrix and the inclusion becomes the starting point of pores, resulting in a decrease in the bending workability of the steel plate. Therefore, the lower the content of P and S, the better.

Therefore, by optimizing the design of the alloy composition and reasonably avoiding precious components, the ratio of each element is reasonable to realize the precipitation strengthening of Ti-Cr composite microalloy steel, increase the volume fraction of nano-precipitates to the greatest extent, and increase the strength of the steel plate.

The invention provides a method for preparing a hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa, comprising the following steps:

Step 1, smelting billet:

According to the chemical composition of the raw materials contained in the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa and the mass percentage of each chemical composition of the raw materials, the raw materials are weighed, smelted and cast to prepare an ingot; the ingot is prepared into a slab; wherein, the tensile strength is 1000MPa Grade hot-rolled ultra-high-strength steel plate, the chemical composition of raw materials and the mass percentage of each chemical composition of raw materials are: C: 0.06-0.12%; Mn: 1.0-2.0%; Si: 0.08-0.2%; Ti: 0.05-0.13%; Cr: 0.7～1.5%; P≤0.02%; S≤0.01%; the balance is Fe and unavoidable impurities;

Step 2, hot rolling:

(1) Heat the slab at 1225±25°C for 2 to 3 hours to obtain the slab after heat preservation;

(2) Hot-rolling the heat-preserved slab, the starting rolling temperature is 1000-1100°C, the finishing rolling temperature is 830-900°C, and the cumulative reduction rate is 90%-95%, to obtain a hot-rolled plate; : Before hot rolling, the thickness of the slab is 40mm, and after hot rolling, the thickness of the slab is 2-4mm;

(3) Cool the hot-rolled sheet to 450-550°C at a cooling rate of 80-150°C/s, then heat it online to 600±10°C and coil it, and then keep it in a heat treatment furnace at 600±10°C for 1 hour The furnace was cooled to room temperature to obtain a hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa.

In the above step 1, the ingot is prepared into a slab. The procedure is to heat the ingot to 1225±25°C for 3 hours, then forge it at 1150°C to form a 40mm thick slab, and then air cool it to room temperature. The total reduction 60%.

In said step 2, during the heat preservation process of the slab, the high heat preservation temperature and appropriate heat preservation time can ensure the complete solid solution of alloy elements such as Ti, Cr and their carbonitrides, and prevent the formation of large particle precipitates, which will damage the properties of the steel. .

In the step 2, in the hot rolling process, a large cumulative rolling reduction rate of 90% to 95% is used to deform the material in the austenite recrystallization zone and the non-recrystallization zone, and refine the austenite grain grains, increasing the dislocations in the deformed austenite, thus refining the structure after phase transformation.

In the step 2, after hot rolling, the steel plate is rapidly cooled to 450-550°C at a cooling rate of 80-150°C/s, and then heated online to 600±10°C for coiling. Through the control of cooling conditions and heating temperature, the precipitation and growth of precipitates during the cooling process are inhibited, and a large number of Ti-Cr composite microalloy nano-scale precipitates are precipitated during the online heat treatment and isothermal process, which enhances the precipitation strengthening effect and improves the strength of the steel plate.

The beneficial effects of the present invention are as follows:

(1) The present invention adopts Ti and Cr microalloying methods, which have better precipitation strengthening and fine-grain strengthening effects in steel, and do not contain precious metals such as Ni and Mo, and the alloy cost is relatively low;

(2) The technical process adopted in the present invention is simple, has the advantages of mass production, economical ease, etc., and can meet the needs of industrialization;

(3) The yield strength of the steel plate provided by the invention is greater than 750MPa, the tensile strength is greater than 1000MPa, the elongation after fracture is greater than 15%, and has high strong plasticity;

(4) The present invention also has the characteristics of stable mechanical properties and strong adaptability, and the mechanical properties of the product meet the needs of the market for light weight.

Description of drawings

Fig. 1 is the microstructure morphology of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa grade prepared in Example 1 of the present invention;

Fig. 2 is a dark field image of the center of the precipitate phase under TEM of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa grade prepared in Example 1 of the present invention.

Detailed ways

In the following examples, the melting furnace is an 80 kg vacuum induction melting furnace.

In the following examples, the hot rolling mill used is a Ф450 mm reversing hot rolling mill.

The technical solutions in the embodiments of the present invention will be described below with reference to the drawings in the embodiments of the present invention. However, the described embodiments represent some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that, in the case of no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but not as a limitation of the present invention.

Example 1

A hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa, the chemical composition and mass percentage of raw materials contained in it are C: 0.12%; Mn: 1.8%; Si: 0.08%; Ti: 0.13%; Cr: 0.7%; P : 0.004%; S: 0.006%; the balance is Fe and unavoidable impurities.

In this embodiment, the preparation method of the prepared hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa comprises the following steps:

(1) According to the raw material chemical composition of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa, the raw material is smelted and cast into an ingot. The chemical composition is C: 0.12%; Mn: 1.8%; Si: 0.1 %; Ti: 0.13%; Cr: 0.7%; P: 0.004%; The 40mm thick slab is then air cooled to room temperature with a total reduction of 60%.

(2) The slab after forging enters the heating furnace for heating and heat preservation, the heat preservation temperature is 1250° C., and the heat preservation time is 2.5 hours to obtain the slab after heat preservation;

(3) Continuously hot-rolling the slab after heat preservation, the starting rolling temperature is 1100°C, the finishing rolling temperature is 900°C, the rolling cumulative reduction rate is 90%, and the thickness of the steel plate after rolling is 4mm;

(4) Cool the hot-rolled steel plate to 450°C at a cooling rate of 80°C/s, then heat it online to 610°C for coiling, and then hold it in a heat treatment furnace at 600°C for 1 hour and cool it to room temperature to obtain the Hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa.

The mechanical properties of the 1000MPa-grade hot-rolled ultra-high-strength steel plate prepared in this example were tested, and the yield strength was 756MPa, the tensile strength was 1079MPa, and the elongation after fracture was 16.8%.

The metallographic structure of the 1000MPa grade hot-rolled ultra-high-strength steel plate prepared in this example is shown in Figure 1. The sum of the volume percentages of solid and nanoscale carbides is 95%. The dark field image of the precipitate center under the transmission electron microscope is shown in Figure 2. It can be seen that nanoscale carbides are diffusely distributed on the bainite matrix, and the size of nanoscale carbides is The range is mainly 3-20nm.

Example 2

A hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa, the chemical composition of its raw materials and the chemical composition of each raw material are C: 0.1%; Mn: 1.5%; Si: 0.12%; Ti: 0.05%; Cr: 1.5% ; P: 0.005%; S: 0.005%; the balance is Fe and unavoidable impurities.

In this embodiment, the preparation method of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa includes the following steps:

(1) According to the chemical composition of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa, the raw materials are selected and melted into ingots. The chemical composition is C: 0.1%; Mn: 1.5%; Si: 0.12%; Ti: 0.05%; Cr: 1.5%; P: 0.005%; S: 0.005%; the balance is Fe and unavoidable impurities; heat the ingot to 1225±25°C for 3 hours, and then forge it into a 40mm thick slab at 1150°C , and then air cooled to room temperature with a total reduction of 60%.

(2) The slab after forging is heated in a heating furnace, the heating temperature is 1200° C., and the heating time is 2 hours to obtain the slab after heat preservation;

(3) Continuously hot rolling the slab after heating and isothermal, the starting rolling temperature is 1000°C, the finishing rolling temperature is 830°C, the rolling cumulative reduction rate is 92.5%, and the thickness of the steel plate after rolling is 3mm;

(4) Cool the hot-rolled steel plate to 500°C at a cooling rate of 90°C/s, then heat it online to 600°C for coiling, and then hold it in a heat treatment furnace at 600°C for 1 hour and cool it to room temperature to obtain Hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa.

The hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa grade prepared in this embodiment has a yield strength of 768 MPa, a tensile strength of 1090 MPa, and an elongation after fracture of 16.2%.

The microstructure of the 1000MPa hot-rolled ultra-high-strength steel plate prepared in this example is granular bainite, retained austenite and nano-scale carbides, and the size range of nano-scale carbides is mainly 5-15 nm.

Example 3

A hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa, the chemical composition of its raw materials is C: 0.06%; Mn: 1.9%; Si: 0.1%; Ti: 0.1%; Cr: 1.0%; P: 0.004% ; S: 0.005%; the balance is Fe and unavoidable impurities.

The preparation method of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa in this embodiment comprises the following steps:

(1) According to the raw material chemical composition of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa, the raw material is smelted into an ingot, and its chemical composition is C: 0.06%; Mn: 1.9%; Si: 0.1%; Ti: 0.1%; Cr: 1.0%; P: 0.004%; S: 0.005%; the balance is Fe and unavoidable impurities; the ingot is heated to 1225±25°C for 3h, and then forged at 1150°C to a thickness of 40mm The slab was then air cooled to room temperature with a total reduction of 60%.

(2) The slab after forging is heated in a heating furnace, the heating temperature is 1225° C., and the heating time is 3 hours to obtain the slab after heat preservation;

(3) Continuously hot rolling the slab after heating isothermal, the rolling start temperature is 1050°C, the finish rolling temperature is 880°C, the rolling cumulative reduction rate is 95%, and the thickness of the steel plate after rolling is 2mm;

(4) Cool the hot-rolled steel plate to 550°C at a cooling rate of 150°C/s, then heat it online to 590°C for coiling, and then hold it in a heat treatment furnace at 600°C for 1 hour and cool it to room temperature to obtain Hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa.

The hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa grade prepared in this example has a yield strength of 800 MPa, a tensile strength of 1147 MPa, and an elongation after fracture of 15.4%.

The 1000MPa hot-rolled ultra-high-strength steel plate prepared in this example has a microstructure of granular bainite, retained austenite and nanoscale carbides, and the size range of nanoscale carbides is mainly 4-16nm.

Example 4

A hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa, the chemical composition of the raw materials is C: 0.08%; Mn: 1.8%; Si: 0.19%; Ti: 0.08%; Cr: 1.0%; P: 0.006% ; S: 0.005%; the balance is Fe and unavoidable impurities.

In this embodiment, the preparation method of the above-mentioned hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa includes the following steps:

(1) According to the raw material chemical composition of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa, the raw material is smelted into an ingot, and its chemical composition is C: 0.08%; Mn: 1.8%; Si: 0.19%; Ti: 0.08%; Cr: 1.0%; P: 0.006%; S: 0.005%; the balance is Fe and unavoidable impurities; the ingot is heated to 1225±25°C for 3 hours, and then forged at 1150°C to a thickness of 40mm The slab was then air cooled to room temperature with a total reduction of 60%.

(2) The slab after forging is heated in a heating furnace, the heating temperature is 1220° C., and the heating time is 3 hours to obtain a slab after heat preservation;

(3) Continuously hot rolling the slab after heating isothermal, the rolling start temperature is 1040°C, the finish rolling temperature is 890°C, the rolling cumulative reduction rate is 95%, and the thickness of the steel plate after rolling is 2mm;

(4) Cool the hot-rolled steel plate to 550°C at a cooling rate of 150°C/s, then heat it online to 600°C for coiling, and then hold it in a heat treatment furnace at 600°C for 1 hour and cool it to room temperature to obtain Hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa.

The 1000MPa hot-rolled ultra-high-strength steel plate prepared in this example has a yield strength of 800MPa, a tensile strength of 1147MPa, and an elongation after fracture of 15.9%.

The microstructure of the 1000 MPa grade hot-rolled ultra-high-strength steel plate prepared in this example is granular bainite, retained austenite and nano-scale carbides, and the size range of nano-scale carbides is mainly 6-10 nm.

Comparative example 1

A kind of steel plate, with embodiment 1, difference is:

In step (2), the holding temperature of the slab is 1150°C, and the holding time is 2.5h. Because the holding temperature of the slab is too low, the alloying elements and their carbides are not completely dissolved, forming large-grain precipitates, and reducing the The volume fraction of nanoscale carbides in the subsequent isothermal process impairs the properties of the steel plate.

Comparative example 2

A kind of steel plate, with embodiment 1, difference is:

In step (2), the holding temperature of the slab is 1280° C., and the holding time is 2 hours. Because the holding temperature of the slab is too high, the austenite grains are coarse, resulting in a coarse final structure, which damages the performance of the steel plate.

Comparative example 3

A kind of steel plate, with embodiment 1, difference is:

In step (3), the rolling start temperature is 960°C, the finish rolling temperature is 798°C, and the cumulative reduction rate is 90%. Since the start rolling temperature and finish rolling temperature are too low during the hot rolling process, the austenite will Insufficient grain refinement and uneven grain size during the crystallization process affect the final structure and impair the performance of the steel plate.

Comparative example 4

A kind of steel plate, with embodiment 1, difference is:

In step (3), the cumulative reduction rate is 80%. Since the cumulative reduction rate is low in the hot rolling process, the austenite is not deformed sufficiently in the recrystallized zone and the non-recrystallized zone, and the austenite grains The refinement is not significant, and the final structure is coarse, resulting in a decrease in the performance of the steel plate.

Comparative example 5

A kind of steel plate, with embodiment 1, difference is:

In step (4), rapidly cool to 550°C at a cooling rate of 60°C/s, and then heat online to 650°C for coiling. Since the cooling process control after hot rolling is very critical to phase transformation, if the cooling rate is low, then The driving force of the phase transformation is insufficient, and the bainite lath is thicker after the phase transformation, which reduces the performance of the steel plate. If the coiling temperature is too high, the size of the carbide precipitated during the coiling process of the steel plate is large, which seriously damages the performance of the steel plate.

However, in the present invention, after hot rolling, it is rapidly cooled to the bainite region, and then heated to 600°C isothermally so that the Ti-Cr composite microalloy is precipitated during the isothermal process to enhance the precipitation strengthening effect and increase the strength of the steel plate.

Comparative example 6

A kind of steel plate, with embodiment 1, difference is:

In step (4), rapidly cool to 400°C at a cooling rate of 60°C/s, and then heat online to 600°C for coiling. Since the cooling rate and final cooling temperature are too low, it is easy to form a martensite structure, and the structure is coarse , impairs the performance of the steel plate.

Comparative example 7

A kind of steel plate, with embodiment 1, difference is:

Si content is 0.7%, and Mn content is 2.0%, then its high content Si element causes steel plate surface to control difficulty big, the problems such as band structure that Mn element segregation causes, yield strength is low, and the present invention passes Si, Mn content Control and adjustment can achieve high yield strength while having high tensile strength and high plasticity.

Comparative example 8

A kind of steel plate, with embodiment 1, difference is:

Without Ti element, the austenite grains are easy to become coarse during the slab reheating process, which deteriorates the performance of the steel plate, and is not conducive to the precipitation of carbides in the subsequent isothermal process, reducing the precipitation strengthening effect.

Comparative example 9

A kind of steel plate, with embodiment 1, difference is:

Without Cr element, only Ti-containing carbides are precipitated in the isothermal process, the number of carbides is reduced, and the size of carbides is larger, which reduces the precipitation strengthening effect.

The above are only part of the embodiments of the present invention, and are not intended to limit the implementation and protection scope of the present invention. For those skilled in the art, they should be able to realize that all equivalent replacements made by using the description and illustrations of the present invention The solutions obtained with obvious changes shall all be included in the protection scope of the present invention.

Claims (7)

1. A hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa grade, characterized in that, the raw material chemical composition contained in the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa grade and the mass percentage of each raw material chemical composition are: C: 0.06 ~0.12%; Mn: 1.0~2.0%; Si: 0.08~0.2%; Ti: 0.05~0.13%; Cr: 0.7~1.5%; P≤0.02%; S≤0.01%; the balance is Fe and unavoidable Impurities. 2. The hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa according to claim 1, wherein the microstructure of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa is bainite and retained austenite And nano-scale carbides, nano-scale carbides are dispersed on the bainite matrix. 3. The hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa according to claim 2, characterized in that the sum of the volume percentages of bainite, retained austenite, and nanoscale carbides is greater than or equal to 95%, and nanoscale carbides The particle size is mainly 3-20nm. 4. The hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa according to claim 1, wherein the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa has a yield strength of 750 MPa or more and a tensile strength of 1000 MPa or more. The elongation after breaking is more than 15%. 5. The hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa according to claim 1, wherein the thickness of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa is 2-4 mm. 6. The preparation method of the 1000MPa grade hot-rolled ultra-high-strength steel plate with a tensile strength of any one of claims 1-5, characterized in that it comprises the steps of: Step 1, smelting billet: According to the chemical composition of the raw materials contained in the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa and the mass percentage of each chemical composition of the raw materials, the raw materials are weighed, smelted and cast to prepare an ingot; the ingot is prepared into a slab; wherein, the tensile strength is 1000MPa Grade hot-rolled ultra-high-strength steel plate, the chemical composition of raw materials and the mass percentage of each chemical composition of raw materials are: C: 0.06-0.12%; Mn: 1.0-2.0%; Si: 0.08-0.2%; Ti: 0.05-0.13%; Cr: 0.7～1.5%; P≤0.02%; S≤0.01%; the balance is Fe and unavoidable impurities; Step 2, hot rolling: (1) Heat the slab at 1225±25°C for 2 to 3 hours to obtain the slab after heat preservation; (2) Hot-rolling the heat-preserved slab, the starting rolling temperature is 1000-1100°C, the finishing rolling temperature is 830-900°C, and the cumulative reduction rate is 90%-95%, to obtain a hot-rolled plate; : Before hot rolling, the thickness of the slab is 40mm, and after hot rolling, the thickness of the slab is 2-4mm; (3) Cool the hot-rolled sheet to 450-550°C at a cooling rate of 80-150°C/s, then heat it online to 600±10°C and coil it, and then keep it in a heat treatment furnace at 600±10°C for 1 hour The furnace was cooled to room temperature to obtain a hot-rolled ultra-high-strength steel plate with a tensile strength of 1000 MPa. 7. The method for preparing hot-rolled ultra-high-strength steel plates with a tensile strength of 1000 MPa according to claim 6, characterized in that, in the step 1, the ingot is prepared into a slab, and the procedure is to heat the ingot to Hold at 1225±25°C for 3 hours, then forge at 1150°C to form a 40mm thick slab, and then air cool to room temperature with a total reduction of 60%.

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