CN115354237B - Hot-rolled ultrahigh-strength steel plate with tensile strength of 1000MPa and preparation method thereof - Google Patents

Abstract

A hot rolled ultra-high 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: 0.06-0.12%; 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%; the balance being Fe and unavoidable impurities. The preparation method comprises the following steps: 1) Smelting into a casting blank according to the chemical composition ratio 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 heating to coiling on line. The obtained hot-rolled ultra-high 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 more than or equal to 750MPa, the tensile strength is more than or equal to 1000MPa, and the elongation A is more than or equal to 15%.

Description

Hot-rolled ultra-high-strength steel plate with tensile strength of 1000MPa and preparation method thereof

Technical field

The invention relates to the field of metallurgical technology, and specifically relates 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 energy conservation, emission reduction and safety goals, the steel industry has been committed to developing high-strength steel, requiring the materials used to further increase the strength, in order to reduce the use of steel and achieve lightweight purposes.

Data show that for every 10% reduction in vehicle total weight, fuel economy increases by about 4.9% on average. However, every 100kg reduction in vehicle weight results in an increase in safety risks of 3% to 4.5%. Therefore, while reducing weight, it is also necessary to consider the issue of collision safety, which not only requires high strength, but also maintains good plasticity.

With the rapid development of upsizing and downsizing of engineering machinery and lightweighting of automobiles, the demand for hot-rolled ultra-high-strength steel with a tensile strength of 1000MPa is increasing day by day. It is not only used in automobile structural components and frame components, but also in chassis components and crawler tracks. Frame components, construction machinery components, etc. are also widely used and have broad application prospects.

At present, there are few ultra-high-strength steels that can produce tensile strength of 1000MPa at home and abroad. According to existing research, to obtain high strength, hardenable elements such as C, Mn, and Mo need to be added, 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 announcement number CN101008066B discloses a hot-rolled martensitic steel plate with a tensile strength higher than 1000MPa. 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; Ti: 0.01～0.03, V ≤0.10 and Nb: one or more of 0.01 to 0.05; the others are composed of Fe and unavoidable impurities. The structure of the steel plate produced by this method is mainly martensite. It adopts low coiling temperature (150℃~Ms), high strength but low plasticity (low elongation ≤9%). At the same time, higher 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 processing.

The invention patent with announcement number CN109023111B discloses a 1000MPa grade hot-rolled automobile girder 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. It has high strength, but the elongation is low at 10-11.5%. It adopts a two-stage controlled cooling process and is first cooled to an intermediate temperature of 600-650°C. Then it is quickly cooled to 200-300°C for coiling. The coiling temperature is low and the production process control is difficult. The carbon content is high, which easily reduces the weldability. The high content of Nb element will also increase the cost.

The invention patent with publication number CN109735775A discloses a 1000MPa 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 inevitable impurities . The microstructure of the steel plate produced by this method is ferrite + bainite + martensite, with high strength and a plasticity of 9 to 14%. However, this method uses 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 structures, which affects the formability. At the same time, high content of Mo elements increase production costs.

The invention patent with publication number CN110331326A discloses a 1000MPa thin specification hot-rolled high-strength dual-phase steel plate and its preparation method. The chemical composition mass percentage of the steel plate is: C: 0.10~0.20%; Si: 0.80~1.20%; Mn : 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 inevitable 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-to-strength ratio is ≤0.60. It has high tensile strength, but the yield strength is biased. The low and high content of Si element makes it more difficult to control the surface of the steel plate. At the same time, a three-stage controlled cooling process is adopted, the coiling temperature is low, and it is difficult to accurately control the process.

The invention patent with publication number CN105925896A discloses a 1000MPa high-strength and high-plasticity hot-rolled steel plate and its manufacturing method. The chemical composition mass percentage 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%; remainder for Fe. The invention is prepared through smelting, casting, hot rolling, reverse transformation annealing and other steps. The microstructure is lath-like austenite and tempered martensite. It 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 the segregation of Mn elements, which affect the molding performance.

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 chemical composition mass percentage 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 inevitable impurities. By adding Nb and V microalloying elements combined with C and N to form nanoscale cluster precipitates, the matrix structure is strengthened and the strength difference between the two matrix structures (ferrite and martensite) is reduced. The steel plate has high strength and high plasticity, but the The yield strength of the steel plate produced by this method is low. At the same time, the high content of Si element makes it difficult to control the surface of the steel plate. The segregation of Mn element causes problems such as banded structure, which affects the formability. More Nb elements increase 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 bands. The shape structure affects the forming performance, etc., or the addition of one or more expensive micro-alloying elements Ti, Nb, V, Mo, etc. increases the cost of steel; (2) The cooling process is complex or the coiling temperature is low, making it difficult to accurately control the process. ; (3) The structure of steel plates 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 steel materials. The use of precipitation strengthening and grain refinement of nanoscale precipitated phases has become one of the most promising ways to strengthen and toughen metal materials, and it is also a new type of ultra-high-strength steel. The most important reinforcement mechanism. At present, due to the limited precipitation strengthening effect of a single titanium-containing microalloyed steel and the low strength level of the steel plate, the development of titanium-containing composite microalloyed steel has received more and more attention.

The disclosed technologies for titanium-containing composite microalloyed steel include:

The invention patent with publication number CN107287519A discloses a vanadium-containing hot-rolled coil plate for automobile structures 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 inevitable impurities. More Nb, V, and Ti micro-alloying elements are added, and the tensile strength of the produced steel plate is 800MPa.

The invention patent with publication number CN107043890A discloses a hot-rolled automobile steel with a thickness of 1.5 to 3.0 mm and a yield strength of greater than 700 MPa and a manufacturing method thereof. Its chemical composition and mass percentage are: C: 0.02 to 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%; Mo: 0.12～0.20%; 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 publication number CN104264052A discloses a steel plate for engineering machinery and its production method. The chemical composition of the steel plate in mass percentage 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 product yield strength is ≥700MPa, the tensile strength is ≥785MPa, and the elongation after fracture is ≥15%.

The invention patent with publication number CN106319389A discloses low-cost, high-machinability steel for engineering machinery and its manufacturing method. Its composition mass percentage is: C: 0.06-0.10%; Si: 0.30~0.60%; Mn: 1.00~ 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%; B: 0.0008～0.0020%; Ti: 0.008～0.018%; Al: 0.030～0.070%; N: ≤0.0050%; Ca: 0.0010～0.0040%; the balance is Fe and inevitable impurities. The steel plate produced by this method has a yield strength of ≥630MPa and a tensile strength of ≥700MPa.

The above patents on titanium-containing composite microalloy strengthened steel add three or more of the Nb-V-Ti-Mo microalloy elements, which leads to an increase in the cost of the steel, and the strength of the hot-rolled steel plate produced is less than 1000MPa, making it difficult to Meet the current market demand for steel product reduction.

To sum up, the microstructure of existing hot-rolled steel plates with tensile strength reaching 1000MPa is mainly martensite. Although the tensile strength can reach 1000MPa, its plasticity is low and the yield strength is low. A kind of steel plate with high tensile strength is needed. Ultra-high strength steel plate with low alloy cost, simple rolling process, higher strength and good plasticity.

Contents of the invention

In view of the problems existing in the above-mentioned prior art, the present invention provides a hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa and a preparation method thereof, which adopts a method of rapidly cooling to the bainite zone after rolling, and then immediately performing online heat treatment. In particular, through the composition design of low-cost Ti and Cr microalloying and the control of rolling and cooling processes, the precipitation strengthening of Ti-Cr composite microalloyed steel can be achieved, and the effects of fine grain strengthening, phase transformation strengthening and precipitation strengthening can be fully utilized to produce Hot-rolled bainite ultra-high-strength steel is produced. This hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa has a yield strength of more than 750MPa, a tensile strength of more than 1000MPa, and an elongation after fracture of more than 15%. It ensures high tensile strength at the same time. , has high yield strength and high elongation after fracture, can meet the simultaneous improvement of strength and plasticity, and can achieve the improvement of the comprehensive performance of steel.

In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

The first aspect of the present invention is to provide a hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa. The chemical composition of the raw materials and the mass percentage of each chemical composition 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 inevitable impurities.

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

Furthermore, the sum of the volume percentages of bainite, retained austenite, and nanoscale carbides is ≥95%, and the size of nanoscale carbides is mainly 3 to 20 nm.

The hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa has a yield strength of more than 750MPa, a tensile strength of more than 1000MPa, 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 1000MPa is 2 to 4 mm.

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

The C element is used to increase the strength of materials and is the cheapest element to increase 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 is infinitely solid solution with Fe and can improve the strength of steel.

Si element is an effective element that improves the strength of steel plates without reducing ductility. It is solid dissolved in ferrite and austenite and can improve the strength of steel. Si can reduce the diffusion rate of carbon in ferrite, making the precipitated carbides less likely to coarsen.

Ti and C elements form high-temperature-resistant TiC particles, which play a precipitation strengthening role and are pinned to the original austenite grain boundaries to prevent austenite grains from growing, which can improve welding performance.

Cr is a carbide-forming element with a medium affinity to the C element. Cr carbide is relatively evenly distributed in the iron matrix. It improves the strength of steel through precipitation strengthening. It has the effect of hindering the growth of grains under short-term heating and can refine the structure. , 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 refining the size of precipitates, increasing the volume fraction of precipitates, and improving the strength and hardness of the steel plate.

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

Therefore, by optimizing the design of alloy components and reasonably avoiding valuable components, and rationalizing the ratio of each element, precipitation strengthening of Ti-Cr composite microalloy steel can be achieved, maximizing the volume fraction of nano-precipitated phases, and increasing 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 1000MPa, which includes the following steps:

Step 1, smelting and billet making:

Weigh the raw materials 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, smelt and cast to prepare an ingot; prepare the ingot into a slab; among them, the tensile strength is 1000MPa Grade hot-rolled ultra-high-strength steel plate, the raw material chemical composition 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 inevitable impurities;

Step 2, hot rolling:

(1) Insulate the slab at 1225±25°C for 2 to 3 hours to obtain the slab after insulation;

(2) Hot-roll the heat-insulated slab with an opening rolling temperature of 1000-1100°C, a final rolling temperature of 830-900°C, and a cumulative reduction rate of 90%-95% to obtain a hot-rolled plate; wherein : Before hot rolling, the slab thickness is 40mm, after hot rolling, the slab thickness is 2~4mm;

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

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

In the described step 2, during the slab insulation process, high insulation temperature and appropriate insulation time can ensure that Ti, Cr and other alloying elements and their carbonitrides are completely dissolved, preventing the formation of large particle precipitation phases and damaging the performance of the steel. .

In the described step 2, during 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 non-recrystallization zone and refine the austenite grain. grains, increasing dislocations in deformed austenite, thereby refining the structure after phase transformation.

In step 2, the hot-rolled 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 cooling conditions and heating temperature control, the precipitation and growth of precipitates during the cooling process are suppressed, and a large amount of Ti-Cr composite microalloy nanoscale precipitates are precipitated during online heat treatment and isothermal processes, 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 micro-alloying method to achieve better precipitation strengthening and fine-grain strengthening effects in steel. It does not contain precious metals such as Ni and Mo, and the alloy cost is low;

(2) The process used in the present invention is simple, has the advantages of mass production, economy and ease of implementation, 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 it has high strong plasticity;

(4) The invention also has the characteristics of stable mechanical properties and strong adaptability, and the mechanical properties of the product meet the market demand for lightweighting.

Description of the drawings

Figure 1 shows the metallographic structure of a hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa prepared in Example 1 of the present invention;

Figure 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 prepared in Example 1 of the present invention.

Detailed ways

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

In the following examples, the hot rolling mill used is a Ф450mm reversible hot rolling mill.

The technical solutions in the embodiments of the present invention will be described below with reference to the accompanying drawings in the embodiments of the present invention. However, the described embodiments represent only some, but 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 any creative work shall fall within the scope of protection of the present invention.

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

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

Example 1

A hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa. The chemical composition of the raw materials and their mass percentages 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 inevitable impurities.

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

(1) After selecting the raw materials according to the chemical composition of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa, they are smelted and cast into an ingot. The chemical composition in mass percentage is C: 0.12%; Mn: 1.8%; Si: 0.1 %; Ti: 0.13%; Cr: 0.7%; P: 0.004%; S: 0.006%; the balance is Fe and inevitable impurities; heat the ingot to 1225±25℃ and keep it for 3h, and then forge it at 1150℃ The 40mm thick slab is then air cooled to room temperature with a total reduction of 60%.

(2) The forged slab enters the heating furnace for heating and insulation. The insulation temperature is 1250°C and the insulation time is 2.5 hours to obtain the insulation slab;

(3) Continuous hot rolling is performed on the heat-insulated slab. The opening rolling temperature is 1100°C, the final rolling temperature is 900°C, the cumulative rolling reduction rate is 90%, and the thickness of the steel plate after rolling is 4mm;

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

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

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

Example 2

A hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa. The chemical composition of the raw materials and the chemical composition of each raw material in mass percentage 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 inevitable impurities.

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

(1) After selecting the raw materials according to the chemical composition of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa, it is smelted into an ingot. Its chemical composition in mass percentage 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 inevitable impurities; heat the ingot to 1225±25℃ and keep it for 3 hours, and then forge it into a 40mm thick slab at 1150℃ , and then air-cooled to room temperature, with a total reduction of 60%.

(2) The forged slab is heated in a heating furnace at a heating temperature of 1200°C and a heating time of 2 hours to obtain a heat-insulated slab;

(3) Continuous hot rolling is performed on the isothermally heated slab. The opening rolling temperature is 1000°C, the final rolling temperature is 830°C, the cumulative rolling reduction rate is 92.5%, and the thickness of the steel plate after rolling is 3mm;

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

The hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa prepared in this example has a yield strength of 768MPa, a tensile strength of 1090MPa, 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 nanoscale carbides. The size range of nanoscale carbides is mainly 5 to 15nm.

Example 3

A hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa. The chemical composition of the raw materials in mass percentage 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 inevitable impurities.

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

(1) After selecting the raw materials according to the chemical composition of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa, the raw materials are smelted into an ingot. The chemical composition in mass percentage 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 inevitable impurities; heat the ingot to 1225±25℃ and keep it for 3 hours, and then forge it to 40mm thick at 1150℃ The slab was then air cooled to room temperature with a total reduction of 60%.

(2) The forged slab is heated in a heating furnace at a heating temperature of 1225°C and a heating time of 3 hours to obtain a heat-insulated slab;

(3) Continuous hot rolling is performed on the isothermally heated slab. The opening rolling temperature is 1050°C, the final rolling temperature is 880°C, the cumulative rolling reduction rate is 95%, and the thickness of the steel plate after rolling is 2mm;

(4) The hot-rolled steel plate is cooled to 550°C at a cooling rate of 150°C/s, then heated online to 590°C for coiling, and then isothermally cooled to room temperature in a 600°C heat treatment furnace for 1 hour 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 1000MPa prepared in this example has a yield strength of 800MPa, a tensile strength of 1147MPa, and an elongation after fracture of 15.4%.

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

Example 4

A hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa. The chemical composition of the raw materials in mass percentage 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 inevitable impurities.

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

(1) After selecting the raw materials according to the chemical composition of the hot-rolled ultra-high-strength steel plate with a tensile strength of 1000MPa, the raw materials are smelted into an ingot. The chemical composition in mass percentage 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 inevitable impurities; heat the ingot to 1225±25℃ and keep it for 3 hours, and then forge it to 40mm thick at 1150℃ The slab was then air cooled to room temperature with a total reduction of 60%.

(2) The forged slab is heated in a heating furnace at a heating temperature of 1220°C and a heating time of 3 hours to obtain a heat-insulated slab;

(3) Continuous hot rolling is performed on the isothermally heated slab. The opening rolling temperature is 1040°C, the final rolling temperature is 890°C, the cumulative rolling reduction rate is 95%, and the thickness of the steel plate after rolling is 2mm;

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

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

Comparative example 1

A steel plate, the same as Embodiment 1, except that:

In step (2), the slab holding temperature is 1150°C and the holding time is 2.5 hours. Because the slab holding temperature is too low, the alloy elements and their carbides are not completely dissolved, forming large particle precipitates and reducing the The volume fraction of nanoscale carbides in the subsequent isothermal process damages the performance of the steel plate.

Comparative example 2

A steel plate, the same as Embodiment 1, except that:

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

Comparative example 3

A steel plate, the same as Embodiment 1, except that:

In step (3), the opening rolling temperature is 960°C, the final rolling temperature is 798°C, and the cumulative reduction rate is 90%. Since the opening rolling temperature and the final rolling temperature are too low during the hot rolling process, the austenite will be regenerated. During the crystallization process, the grain refinement is insufficient and the grain size is uneven, which affects the final structure and damages the performance of the steel plate.

Comparative example 4

A steel plate, the same as Embodiment 1, except that:

In step (3), the cumulative reduction rate is 80%. Since the cumulative reduction rate is low during the hot rolling process, the austenite is not fully deformed 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 reduction in the performance of the steel plate.

Comparative example 5

A steel plate, the same as Embodiment 1, except that:

In step (4), it is rapidly cooled to 550°C at a cooling rate of 60°C/s, and then heated online to 650°C for coiling. Since the cooling process control after hot rolling is very critical to the phase transformation, if the cooling rate is low, then If the phase transformation driving force is insufficient, the bainite laths after phase transformation will be thicker, which reduces the performance of the steel plate. If the coiling temperature is too high, the carbides precipitated during the coiling process will be larger in size, seriously damaging the performance of the steel plate.

In the present invention, after hot rolling, it is quickly cooled to the bainite zone, and then heated to 600°C isothermally, allowing the Ti-Cr composite microalloy to precipitate during the isothermal process to enhance the precipitation strengthening effect and improve the strength of the steel plate.

Comparative example 6

A steel plate, the same as Embodiment 1, except that:

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, a martensite structure is easily formed and the structure is coarse. , damaging the performance of the steel plate.

Comparative example 7

A steel plate, the same as Embodiment 1, except that:

The Si content is 0.7% and the Mn content is 2.0%. The high content of Si element leads to difficulty in controlling the surface of the steel plate, problems such as banded structure caused by the segregation of Mn element, and low yield strength. However, the present invention controls the Si and Mn contents. Control and adjustment can achieve high tensile strength and plasticity as well as high yield strength.

Comparative example 8

A steel plate, the same as Embodiment 1, except that:

Without Ti element, the austenite grains will easily become coarse during the reheating process of the slab, which will deteriorate the performance of the steel plate. At the same time, it is not conducive to the precipitation of carbides in the subsequent isothermal process and reduces the precipitation strengthening effect.

Comparative example 9

A steel plate, the same as Embodiment 1, except that:

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

The above are only some embodiments of the present invention, and are not intended to limit the implementation and protection scope of the present invention. Those skilled in the art should be able to realize that equivalent substitutions can be made by using the description and illustrations of the present invention. Any solutions resulting from obvious changes shall be included in the protection scope of the present invention.

Claims (4)

1. The hot-rolled ultrahigh-strength steel plate with the tensile strength of 1000MPa is characterized by comprising the following raw material chemical components in percentage by mass: c: 0.06-0.12%; 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%; the balance of Fe and unavoidable impurities;

the preparation method of the hot-rolled ultrahigh-strength steel plate with the tensile strength of 1000MPa comprises the following steps:

step 1, smelting and blanking:

weighing raw materials according to the raw material chemical components and the mass percentages of the raw material chemical components contained in the hot-rolled ultrahigh-strength steel plate with the tensile strength of 1000MPa, and smelting and casting to prepare an ingot; preparing an ingot into a slab;

step 2, hot rolling:

(1) The slab is insulated for 2 to 3 hours at the temperature of 1225 plus or minus 25 ℃ to obtain the insulated slab;

(2) Hot rolling the heat-preserving slab, wherein the initial rolling temperature is 1000-1100 ℃, the final rolling temperature is 830-900 ℃, and the accumulated rolling reduction is 90-95%, so as to prepare a hot rolled plate; wherein: the thickness of the slab is 40mm before hot rolling, and the thickness of the slab is 2-4 mm after hot rolling;

(3) Cooling the hot rolled plate to 450-550 ℃ at a cooling rate of 80-150 ℃/s, then heating to 600+/-10 ℃ on line, coiling, then preserving heat in a heat treatment furnace at 600+/-10 ℃ for 1h, and cooling to room temperature to obtain a hot rolled ultrahigh-strength steel plate with 1000MPa level of tensile strength;

in the step (1), an ingot is prepared into a slab, the procedures are that the ingot is heated to 1225+/-25 ℃ and is preserved for 3 hours, then the ingot is forged into a slab with the thickness of 40mm at 1150 ℃, and then the slab is air-cooled to room temperature, wherein the total rolling reduction is 60%;

the microstructure of the hot rolled ultra-high strength steel plate with the tensile strength of 1000MPa is bainite, retained austenite and nanoscale carbide, and the nanoscale carbide is dispersed and distributed on a bainite matrix.

2. The hot rolled ultra-high strength steel plate with the tensile strength of 1000MPa according to claim 1, wherein the sum of the volume percentages of the bainite, the retained austenite and the nano-scale carbide is more than or equal to 95%, and the nano-scale carbide is mainly 3-20 nm in size.

3. The hot-rolled ultra-high strength steel sheet with a tensile strength of 1000MPa according to claim 1, wherein the hot-rolled ultra-high strength steel sheet with a tensile strength of 1000MPa has a yield strength of 750MPa or more, a tensile strength of 1000MPa or more, and a post-fracture elongation of 15% or more.

4. The hot-rolled ultra-high-strength steel sheet with a tensile strength of 1000MPa according to claim 1, wherein the thickness of the hot-rolled ultra-high-strength steel sheet with a tensile strength of 1000MPa is 2-4 mm.