CN115044830B - Lightweight TWIP steel based on twinning induced plasticity and ordered strengthening and preparation method thereof - Google Patents

Abstract

The invention provides a lightweight TWIP steel based on twinning induced plasticity and ordered strengthening, which comprises the following components in percentage by mass: the preparation method of the light TWIP steel comprises the following steps of weighing a proper amount of pure Fe, pure Mn, pure Al, pure Si and pure C with purity not lower than 99.9% as raw materials, obtaining a finished product ingot through vacuum induction smelting, coating an decarburization inhibitor on the finished product ingot, drying the finished product ingot, carrying out high-temperature homogenization treatment, carrying out hot forging processing on the treated ingot after heat penetration, cutting a hot forged thick slab to obtain a strip, carrying out hot rolling on the obtained strip after heat penetration, carrying out water quenching to room temperature after the completion of hot rolling, carrying out multi-pass cold rolling on a hot rolled plate, and carrying out solution treatment on the obtained cold rolled plate under the protection of argon to complete the preparation of the light TWIP steel.

Description

A lightweight TWIP steel based on twin-induced plasticity and ordered strengthening and its preparation method

Technical field

The invention belongs to the technical field of TWIP steel, and specifically relates to a preparation method of lightweight TWIP steel based on twin-induced plasticity and orderly strengthening.

Background technique

As issues such as energy crisis, environmental pollution, and resource shortages become increasingly prominent, the transportation industry has put forward urgent needs for energy conservation, emission reduction, and cost reduction. Therefore, it is imperative to develop lightweight vehicles. In order to achieve lightweight while ensuring sufficient safety, the structural steel of the new generation of vehicles needs to have both higher strength and plasticity and low density. Traditional high aluminum content FeMnAlC austenitic lightweight steel has excellent properties such as high strength 300~1200MPa and low density <7.2g/cm3. ^It is widely used in aircraft landing gear, missile casings, automobile body-in-white, liquefied petroleum gas ships and offshore engineering. It has wide application prospects in lifting equipment and other aspects.

The low density is directly related to the addition of high content of the light element Al. In addition, the addition of high contents of Al 8 to 10 wt.% and C ≥ 1 wt.% is conducive to the formation of different degrees of chemically ordered structures inside the alloy, such as chemical short-range ordering, chemical long-range ordering clusters, etc. Since dislocations cut through this type of chemically ordered structure will produce anti-phase boundaries and increase the energy of the system, the existence of this type of ordered structure will increase the yield strength. This strengthening method is called order strengthening. Among them, the energy of the anti-phase boundary depends on the degree of chemical order. The higher the energy of the anti-phase boundary, the more significant the strengthening effect. It is worth noting that the increase in Al and C content will increase the stacking fault energy of steel, but high Al and high C are necessary conditions for the formation of chemical ordering in austenitic lightweight steel, and chemical ordering will also increase the layering fault energy of steel. Error energy, so the introduction of chemical ordering inevitably leads to high-level error energy. A large number of previous studies have shown that stacking fault energy is closely related to the deformation mechanism of austenitic steel: in the case of high-level stacking fault energy, dislocation slip is the only deformation mechanism, and the plasticity is often low at this time; when the stacking fault energy is reduced To a certain extent, deformation twins will form and lead to the twin-induced plasticity (TWIP) effect, thereby significantly improving plasticity; when the stacking fault energy is less than or equal to 20mJ/ ^m2 , stress-induced martensite will form and lead to phase transformation-induced plasticity ( TRIP) effect will also significantly improve plasticity. Obviously, while the introduction of chemical ordering brings about an increase in strength, it often results in a decrease in plasticity due to an increase in stacking fault energy.

Research in recent years has shown that Si can reduce the stacking fault energy in austenitic steel and promote the TWIP effect; in addition, Si can also enhance the degree of chemical ordering in austenitic lightweight steel. Considering the adjustment of the Si and Al content, it is expected to retain strong chemical ordering in austenitic lightweight steel while reducing the stacking fault energy to introduce the TWIP effect, achieving high strength and high plasticity without significantly increasing the steel density;

Based on this, a preparation method of lightweight TWIP steel based on twin-induced plasticity and ordered strengthening is proposed.

Contents of the invention

The technical problem to be solved by the present invention is to provide a preparation method of lightweight TWIP steel based on twin-induced plasticity and orderly strengthening in view of the above-mentioned shortcomings of the existing technology. Based on the adjustment of the Al and Si element content, the development of a method with both chemical properties and Lightweight TWIP steel with sequential strengthening and twinning-induced plasticity solves the current problem of incompatibility between high strength and high plasticity of lightweight steel.

In order to solve the above technical problems, the technical solution adopted by the present invention is:

The first aspect is a lightweight TWIP steel based on twin-induced plasticity and orderly strengthening. The mass percentage of the constituent elements of the lightweight TWIP steel is: 20% to 24% Mn, 5% to 7% Al, 0.8 to 1.2 %C, 0~4% Si, the balance is Fe and inevitable impurity elements.

Further, the sum of the mass percentages of Mn and Al in the lightweight TWIP steel is not less than 25% to ensure that the lightweight TWIP steel obtains 100% austenite phase after solution quenching;

The mass percentage ratio of Al and C in the lightweight TWIP steel is not less than 4.2 to ensure that the lightweight TWIP steel forms chemical order after solution quenching;

The mass percentage ratio of Al and Si in the lightweight TWIP steel is not higher than 4 to ensure that the lightweight TWIP steel has medium and low stacking fault energy and generates deformation twins during the plastic deformation stage.

In the second aspect, a method for preparing lightweight TWIP steel based on twin-induced plasticity and ordered strengthening includes the following steps:

S1. Weigh an appropriate amount of pure Fe, pure Mn, pure Al, pure Si, and pure C with a purity of not less than 99.9% as raw materials, and obtain the finished ingot through vacuum induction melting;

S2. Coat the finished ingot with a layer of anti-decarburization agent and dry it at room temperature, followed by high-temperature homogenization treatment;

S3. Heat the ingot processed in S2 and then perform hot forging processing, and then cut the hot forged thick slab to obtain long strips;

S4. The obtained long strip is first heated through and then hot-rolled. After the hot-rolling is completed, the water is quenched to room temperature, and then the hot-rolled plate is cold-rolled in multiple passes;

S5. Place the obtained cold-rolled plate under argon protection for solution treatment to complete the preparation of lightweight TWIP steel.

Furthermore, in S2, the high-temperature homogenization treatment is a treatment of more than 3 hours at 1100°C, and is water-cooled and quenched after the treatment.

Further, in S3, the ingot processed in S2 is first kept at 1050°C for more than 40 minutes and heated through, and then hot forged. The total deformation is 80%, and then the wire EDM machine is used for hot forging. Cut long strips from thick slabs.

Further, in S4, the obtained strip is first heated at 1050°C for more than 40 minutes, and then hot-rolled in multiple passes using a double-roller plate and strip rolling mill. The deformation amount in each pass is not higher than 25%, and the total deformation is The amount is 85%. After hot rolling is completed, the water is quenched to room temperature.

Further, after the hot rolling is completed in S4 and water quenched to room temperature, a double-roller plate and strip rolling mill is used to cold-roll the hot-rolled plate in multiple passes. The deformation amount in each pass is not more than 5%, and the total deformation amount is 50%.

Further, in S5, the cold-rolled plate is placed under argon protection for solution treatment at 1050°C, and then quenched after heat preservation to complete the treatment.

Further, the time of solid solution treatment and heat preservation shall be based on obtaining equiaxed austenite grains with a grain size of 70.0±2.1 μm.

Compared with the prior art, the present invention has the following advantages:

The high-strength, high-plastic, lightweight TWIP steel prepared in the present invention based on twin-induced plasticity and ordered strengthening has low cost, low density, and is easy to process. It also has medium and low stacking fault energy and a high degree of chemical order, making the alloy It has high yield strength, tensile strength, uniform elongation and total elongation. Under the optimal ingredient ratio and optimal solution treatment, the yield strength and tensile strength reach ~434MPa and ~845MPa respectively, and the uniform elongation is And the total elongation reaches 78% and 98%. The lightweight TWIP steel in the present invention has low preparation cost and has the advantages of high strength, high plasticity, low density, etc., and is widely used in aircraft landing gear, missile casings, and automobile body-in-white. , liquefied petroleum gas ships and offshore lifting equipment have broad application prospects.

Description of the drawings

Figure 1 is an electron backscattered diffraction EBSD pattern of the lightweight TWIP steel prepared in Examples 1 to 3 of the present invention.

Figure 2 is a transmission electron microscope TEM analysis result of the initial microstructure of the lightweight TWIP steel prepared in Examples 1 to 3 of the present invention.

Figure 3 is a diagram showing the change of stacking fault energy with Si content of the lightweight TWIP steel prepared in Examples 1 to 3 of the present invention.

Figure 4 shows the room temperature tensile engineering stress-strain curve of the lightweight TWIP steel prepared in Examples 1 to 3 of the present invention and the transmission electron microscope TEM analysis results of the microstructure near some fractures.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Embodiment 1, the present invention provides a technical solution: the main constituent elements and mass percentages of a lightweight TWIP steel based on twin-induced plasticity and orderly strengthening are: 71% Fe, 22% Mn, 6% Al, 1% C, 0%Si.

The stacking fault energy of this TWIP steel is 60mJ/m ² and the density is 7.16g/cm ³ .

The preparation method of lightweight TWIP steel based on twin-induced plasticity and ordered strengthening includes the following steps:

S1. Use pure Fe, pure Mn, pure Al, pure Si, pure C with a purity of not less than 99.9% as raw materials, and obtain the finished ingot through vacuum induction melting.

S2. Coat the obtained finished ingot with a layer of anti-decarburization agent and place it in a room temperature environment to dry, then homogenize it at 1100°C for more than 3 hours and then quench it.

S3. The homogenized ingot is kept at 1050°C for more than 40 minutes and then hot forged. The total deformation is 80%. , and then use a wire EDM machine to cut long strips from the hot forged thick slab.

S4. After the obtained strip is heated at 1050°C for more than 40 minutes, it is hot-rolled in multiple passes using a double-roller plate and strip rolling mill. The deformation in each pass is not higher than 25%, and the total deformation is 85%. Hot rolling After completion, the water is quenched to room temperature, and then a double-roller plate and strip rolling machine is used to cold-roll the hot-rolled plate in multiple passes. The deformation in each pass is not more than 5%, and the total deformation is 50%.

S5. Place the cold-rolled plate under argon protection for solution treatment at 1050°C, hold it for a certain period of time and then quench. The holding time is set based on obtaining equiaxed austenite grains with a grain size of 70.0±2.1μm. Quench after completion of heat preservation.

The initial structure of the steel prepared in this example was characterized by EBSD and TEM, as shown in Figures 1 and 2. It can be seen from the figure that the initial structure of the alloy prepared in this example is an equiaxed single-phase austenite structure, without the formation of ferrite or cementite, and a certain volume fraction of chemical compounds is formed on the matrix. order, its size is about 1nm.

It can be seen from Figure 4 that deformation twins exist near the fracture of the steel prepared in this example.

The mechanical properties of the steel prepared in this example were measured according to GB/T 228.1-2010 "Tensile Test of Metal Materials Part 1: Room Temperature Test Method". The results are shown in Figure 4. The yield strength and tensile strength are respectively Reached 308MPa and 633MPa, and the uniform elongation and total elongation reached 47% and 68% respectively.

Example 2, the main constituent elements and mass percentages of a lightweight TWIP steel based on twin-induced plasticity and orderly strengthening are: 69.5% Fe, 22% Mn, 6% Al, 1% C, 1.5% Si. The stacking fault energy of this TWIP steel is 56mJ/m ² and the density is 7.05g/cm ³ .

The preparation method of lightweight TWIP steel based on twin-induced plasticity and ordered strengthening includes the following steps:

S1. Use pure Fe, pure Mn, pure Al, pure Si, pure C with a purity of not less than 99.9% as raw materials, and obtain the finished ingot through vacuum induction melting.

S2. Coat the ingot obtained in the previous step with a layer of anti-decarburization agent and dry it at room temperature, then homogenize it at 1100°C for more than 3 hours and then quench it.

S3. The ingot homogenized in S2 is kept at 1050°C for more than 40 minutes and then hot forged. The total deformation is 80%, and then a wire EDM machine is used to cut long pieces from the hot forged thick slab. strip.

S4. After the obtained strip is heated at 1050°C for more than 40 minutes, it is hot-rolled in multiple passes using a double-roller plate and strip rolling mill. The deformation in each pass is not higher than 25%, and the total deformation is 85%. Hot rolling After completion, the water is quenched to room temperature, and then a double-roller plate and strip rolling machine is used to cold-roll the hot-rolled plate in multiple passes. The deformation in each pass is not more than 5%, and the total deformation is 50%.

S5. Place the cold-rolled plate under argon protection for solution treatment at 1050°C, hold it for a certain period of time and then quench. The holding time is set based on obtaining equiaxed austenite grains with a grain size of 70.0±2.1μm. Quench after completion of heat preservation.

The initial structure of the steel prepared in this example was characterized by EBSD and TEM, as shown in Figures 1 and 2. It can be seen from the figure that the initial structure of the alloy prepared in this example is an equiaxed single-phase austenite structure, without the formation of ferrite or cementite, and a certain volume fraction of chemical compounds is formed on the matrix. order, its size is about 1nm.

The mechanical properties of the steel prepared in this example were measured according to GB/T 228.1-2010 "Tensile Test of Metal Materials Part 1: Room Temperature Test Method". The results are shown in Figure 4. The yield strength and tensile strength are respectively reached 344MPa and 736MPa, and the uniform elongation and total elongation reached 63% and 85% respectively.

Example 3, the main constituent elements and mass percentages of a lightweight TWIP steel based on twin-induced plasticity and orderly strengthening are: 68% Fe, 22% Mn, 6% Al, 1% C, 3% Si. The stacking fault energy of this TWIP steel is 51mJ/m ² and the density is 6.96g/cm ³ .

The preparation method of lightweight TWIP steel based on twin-induced plasticity and ordered strengthening includes the following steps:

S1. Use pure Fe, pure Mn, pure Al, pure Si, pure C with a purity of not less than 99.9% as raw materials, and obtain the finished ingot through vacuum induction melting.

S2. Coat the obtained ingot with a layer of anti-decarburization agent and dry it at room temperature, then homogenize it at 1100°C for more than 3 hours and then quench it.

S3. The homogenized ingot is kept at 1050°C for more than 40 minutes and then hot forged. The total deformation is 80%, and then a wire EDM machine is used to cut long strips from the hot forged thick slab.

S4. After the obtained strip is heated at 1050°C for more than 40 minutes, it is hot-rolled in multiple passes using a double-roller plate and strip rolling mill. The deformation in each pass is not more than 25%, and the total deformation is 85%. Hot rolling After completion, the water is quenched to room temperature, and then a double-roller plate and strip rolling machine is used to cold-roll the hot-rolled plate in multiple passes. The deformation in each pass is not more than 5%, and the total deformation is 50%.

S5. Place the cold-rolled plate under argon protection for solution treatment at 1050°C, hold it for a certain period of time and then quench. The holding time is set based on obtaining equiaxed austenite grains with a grain size of 70.0±2.1μm. Quench after completion of heat preservation.

The initial structure of the steel prepared in this example was characterized by EBSD and TEM, as shown in Figures 1 and 2. It can be seen from the figure that the initial structure of the alloy prepared in this example is an equiaxed single-phase austenite structure, without the formation of ferrite or cementite, and a certain volume fraction of chemical compounds is formed on the matrix. order, its size is about 1nm.

It can be seen from Figure 4 that deformation twins exist near the fracture of the steel prepared in this example.

The mechanical properties of the steel prepared in this example were measured according to GB/T 228.1-2010 "Tensile Test of Metal Materials Part 1: Room Temperature Test Method". The results are shown in Figure 4. The yield strength and tensile strength are respectively Reached 440MPa and 845MPa, and the uniform elongation and total elongation reached 78% and 98% respectively.

It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that these entities or operations are mutually exclusive. any such actual relationship or sequence exists between them. Furthermore, the terms "comprises," "comprises," or any other variation thereof are intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but also those not expressly listed other elements, or elements inherent to the process, method, article or equipment.

Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art will understand that various changes, modifications, and substitutions can be made to these embodiments without departing from the principles and spirit of the invention. and modifications, the scope of the invention is defined by the appended claims and their equivalents.

Claims (7)

1. A lightweight TWIP steel based on twin-induced plasticity and orderly strengthening, characterized in that: the mass percentage of the constituent elements of the lightweight TWIP steel is: 20%~24%Mn, 5%~7%Al, 0.8 ~1.2%C, 3~4%Si, the balance is Fe and inevitable impurity elements; The sum of the mass percentages of Mn and Al in the lightweight TWIP steel is not less than 25% to ensure that the lightweight TWIP steel obtains 100% austenite phase after solution quenching; The mass percentage ratio of Al and C in the lightweight TWIP steel is not less than 4.2 to ensure that the lightweight TWIP steel forms chemical order after solution quenching; The mass percentage ratio of Al and Si in the lightweight TWIP steel is not higher than 4 to ensure that the lightweight TWIP steel has medium and low stacking fault energy and generates deformation twins during the plastic deformation stage; The preparation method of lightweight TWIP steel based on twin-induced plasticity and orderly strengthening includes the following steps: S1. Weigh an appropriate amount of pure Fe, pure Mn, pure Al, pure Si, and pure C with a purity of not less than 99.9% as raw materials, and obtain the finished ingot through vacuum induction melting; S2. Coat the finished ingot with a layer of anti-decarburization agent and dry it at room temperature, followed by high-temperature homogenization treatment; S3. Heat the ingot processed in S2 and then perform hot forging processing, and then cut the hot forged thick slab to obtain long strips; S4. The obtained long strip is first heated through and then hot-rolled. After the hot-rolling is completed, the water is quenched to room temperature, and then the hot-rolled plate is cold-rolled in multiple passes; S5. Place the obtained cold-rolled plate under argon protection for solution treatment to complete the preparation of lightweight TWIP steel; the solution treatment temperature is 1050°C, and the solution treatment heat preservation time is to obtain a grain size of 70.0 Equiaxed austenite grains of ±2.1μm shall prevail. 2. A method for preparing lightweight TWIP steel based on twin-induced plasticity and orderly strengthening according to claim 1, characterized in that it includes the following steps: S1. Weigh an appropriate amount of pure Fe, pure Mn, pure Al, pure Si, and pure C with a purity of not less than 99.9% as raw materials, and obtain the finished ingot through vacuum induction melting; S2. Coat the finished ingot with a layer of anti-decarburization agent and dry it at room temperature, followed by high-temperature homogenization treatment; S3. Heat the ingot processed in S2 and then perform hot forging processing, and then cut the hot forged thick slab to obtain long strips; S4. The obtained long strip is first heated through and then hot-rolled. After the hot-rolling is completed, the water is quenched to room temperature, and then the hot-rolled plate is cold-rolled in multiple passes; S5. Place the obtained cold-rolled plate under argon protection for solution treatment to complete the preparation of lightweight TWIP steel. 3. A method for preparing lightweight TWIP steel based on twin-induced plasticity and orderly strengthening according to claim 2, characterized in that in S2, the high-temperature homogenization treatment is a treatment of more than 3 hours at 1100°C. , water cooling and quenching after treatment. 4. A method for preparing lightweight TWIP steel based on twin-induced plasticity and orderly strengthening according to claim 2, characterized in that in S3, the ingot processed in S2 is first placed at 1050°C. The heat is kept for more than 40 minutes and heated through, and then hot forged. The total deformation is 80%, and then a wire EDM machine is used to cut long strips from the hot forged thick slab. 5. A method for preparing lightweight TWIP steel based on twin-induced plasticity and orderly strengthening according to claim 2, characterized in that in S4, the obtained strip is first heated at 1050°C for more than 40 minutes. Finally, a double-roller plate and strip rolling mill is used to perform multi-pass hot rolling. The deformation amount in each pass is no more than 25%, and the total deformation amount is 85%. After the hot rolling is completed, the water is quenched to room temperature. 6. A method for preparing lightweight TWIP steel based on twin-induced plasticity and orderly strengthening according to claim 5, characterized in that after hot rolling is completed in S4 and water quenched to room temperature, a double-roller plate and strip mill is used. , the hot-rolled plate is cold rolled in multiple passes, the deformation in each pass is no more than 5%, and the total deformation is 50%. 7. A method for preparing lightweight TWIP steel based on twin-induced plasticity and orderly strengthening according to claim 2, characterized in that in S5, the cold-rolled plate is placed under argon gas protection for solidification at 1050°C. Solvent treatment, heat preservation and then quenching to complete the treatment.