CN117626136A - High-strength high-plasticity hot-rolled high-manganese NPR steel and preparation method thereof - Google Patents

Abstract

The invention provides a high-strength, high-plasticity hot-rolled high-manganese NPR steel and a preparation method thereof, and belongs to the technical field of high-manganese steel preparation. The chemical composition of the high manganese steel of the present invention is calculated in mass percentage: C: 0.3~0.6%, Mn: 20~25%, Nb: 0.02~0.05%, S≤0.005%, P≤0.005%, and the rest is Fe and inevitable impurity elements. The preparation method includes the following steps: using vacuum smelting technology to pour into a slab; heating and insulating the slab; subjecting the insulated slab to high-temperature continuous rolling; and water quenching to room temperature after the final rolling. The present invention controls the comprehensive properties of the material by adjusting the volume fraction of austenite and ε martensite in the material. The yield strength of the high manganese NPR steel prepared according to the above steps is 300-400Mpa, the tensile strength is 1000-1200Mpa, and the work hardening The index is ≥0.85, the elongation after fracture is 85-95%, and the strong plastic volume is ≥96Gpa·%.

Description

A high-strength and high-plasticity hot-rolled high-manganese NPR steel and its preparation method

Technical field

The invention belongs to the technical field of high manganese steel preparation, and specifically relates to a high-strength, high-plasticity hot-rolled high-manganese NPR steel and a preparation method thereof.

Background technique

With the increase in energy demand, the depth and scale of resource extraction continue to increase. The geological environment of deep rock is complex and often has characteristics such as high ground stress and large deformation. The rock mass exhibits a large deformation mechanical state. Due to the characteristics of low tensile strength, poor elongation performance, and uneven deformation, traditional support materials are prone to local deformation, causing necking and fracture failure. They are difficult to meet the support needs of deep rock formations and can easily lead to engineering disasters. Negative Poisson’s ratio (NPR) anchor steel has high strength and toughness, no yield platform and super energy absorption, which can effectively solve this problem.

The design composition of NPR anchor steel is high manganese steel. At normal temperature, the structure of high manganese steel is usually single-phase austenite or austenite + martensite. Among them, austenite has a face-centered cubic structure, with many lattice slip systems, and the slip is easy to activate, ensuring the material has good plasticity, while the presence of martensite ensures the material's high strength and hardness. In addition, during the deformation process, the γ austenite with the fcc structure gradually transforms into the ε martensite with the hcp structure. At the same time, there is also a transformation from ε martensite to the α' martensite with the bcc structure. During the structural transformation process, there is usually It causes significant work hardening behavior and triggers the transformation-induced plasticity (TRIP) effect, which improves the strength and plasticity of the material at the same time. In addition, the addition of Nb element can refine the grains. The combination of C and Nb elements in the alloy produces fine NbC precipitates to refine the martensite flakes formed by austenite transformation, which can make the alloy have high performance. Plasticity while ensuring high tensile strength.

The invention patent "NPR Non-magnetic Anchor Steel Material and Production Method" (publication number: CN108754305A) discloses a mass percentage of: C: 0.4-0.7%, Mn: 15-20%, Cr: 1-18% , Si: 0.3-3%, Ca: 0.05-0.15%, Cu: ≤ 0.03%, Ni: ≤ 0.02%, S: ≤ 0.001%, P: ≤ 0.001% all-austenitic non-magnetic anchor steel material, Cr in the material can increase the stacking fault energy of Fe-Mn alloy, reducing the stacking fault probability and the driving force of martensitic phase transformation, which reduces the elongation. Si element can improve the strength and hardness of steel, but it can also reduce the plasticity of the material.

The invention patent "Production Method of NPR Anchor Steel Materials" (publication number: CN108754339B) discloses that the mass percentages are: C: 0.4-0.7%, Mn: 15-20%, Si: ≤0.1%, Cr: ≤0.01% , Cu: ≤ 0.03%, Ni: ≤ 0.02%, S: ≤ 0.001%, P: ≤ 0.001%, and the rest are Fe and inevitable impurity elements. The content of Mn in this invention is low, and the transformation of austenite to ε martensite and ε martensite to α' martensite cannot occur simultaneously during the tensile deformation process. The work hardening rate is low and sufficient transformation cannot occur. TRIP effect, making its elongation less than 80%.

For this reason, it is still necessary to develop technology to improve the comprehensive performance of high manganese NPR steel to solve application problems.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method to achieve high machining by controlling the average grain size, regulating the austenite volume fraction and stability through reasonable component ratio and optimizing the amount of deformation, and effective TRIP effect. Hardening rate, improve the comprehensive performance of high manganese NPR steel, while reducing alloying costs.

One aspect to achieve the above purpose is to provide a high-strength and high-plasticity hot-rolled high-manganese NPR steel, whose components and mass percentages are: C: 0.3~0.6%, Mn: 20~25%, Nb: 0.02~0.05% , S≤0.005%, P≤0.005%, and the rest are Fe and inevitable impurity elements.

Furthermore, the components and mass percentages of high-strength and high-plasticity hot-rolled high-manganese NPR steel are: C: 0.35~0.55%, Mn: 20.3~24.7%, Nb: 0.021~0.045%, S≤0.005%, P≤ 0.005%, the rest is Fe and inevitable impurity elements.

Further, the high-strength and high-plasticity hot-rolled high-manganese NPR steel has a yield strength of 300-400Mpa, a tensile strength of 1000-1200Mpa, a work hardening index ≥ 0.85, an elongation after fracture of 85-95%, and a strong plastic area ≥ 96Gpa·%.

Another aspect to achieve the above purpose is to provide a production method of high-strength and high-plasticity hot-rolled high-manganese NPR steel, which includes the following steps:

(1) According to the chemical composition of a high-strength and high-plasticity hot-rolled high-manganese NPR steel, proportioned by mass percentage, vacuum smelting technology is used to cast the billet;

(2) Heating the slab before rolling, the heating temperature is controlled at 1100~1200℃, and kept at this temperature for 120~180min;

(3) The heat-insulated slab is subjected to high-temperature continuous rolling at 900 to 1150°C, with a total reduction rate of not less than 80 to 90%. After the final rolling is completed, the water is quenched to room temperature to obtain high-strength and high-plasticity hot-rolled steel. Manganese NPR steel.

The chemical composition of the high-strength and high-plasticity hot-rolled high-manganese NPR steel, in terms of mass percentage, is C: 0.3-0.6%, Mn: 20-25%, Nb: 0.02-0.05%, S≤0.005%, P≤0.005 %, the rest is Fe and inevitable impurity elements.

The yield strength of the high-strength and high-plasticity hot-rolled high manganese NPR steel is 300-400Mpa, the tensile strength is 1000-1200Mpa, the work hardening index is ≥0.85, the elongation after fracture is 85-95%, and the strong plastic volume is ≥96Gpa ·%.

Further, in the heating described in step (2), the temperature is controlled at 1140-1170°C, and the holding time is 120 minutes.

Further, the opening rolling temperature of the high-temperature continuous rolling described in step (3) is 1080-1100°C, and the final rolling temperature is 950-970°C.

Further, the number of passes of high-temperature continuous rolling described in step (3) is 7 to 8 times, the reduction rate of a single pass is 20 to 22%, and the total reduction rate is 84 to 87%.

Further, the microstructure of the high-strength and high-plasticity hot-rolled high-manganese NPR steel produced in step (3) is austenite and ε martensite, wherein the volume percentage of austenite is 50 to 60%; The austenite and ε martensite structures present a uniform layered alternating distribution.

The functions and mechanisms of various raw materials and main processes of the present invention:

C: C element is mainly concentrated in retained austenite, increasing the amount of retained austenite and improving austenite stability; it also plays the role of solid solution strengthening and improves the tensile strength of steel. It is the most economical and effective element in steel. Strengthening elements. If the C content in the design is low, good solid solution strengthening effect cannot be obtained; but if the C content is high, excessive carbide precipitation will occur, resulting in reduced plasticity of the steel. Therefore, from the perspective of economy and comprehensive performance, the C content in the present invention is controlled at 0.3-0.6%, and preferably the C content is 0.35-0.55%.

Mn: Mn element is the main alloy element in high manganese steel, which has the function of expanding the austenite phase area and stabilizing the austenite structure. Mn element affects the deformation mechanism of steel by affecting the stacking fault energy in austenite. As the Mn content gradually increases, the structural transformation mechanism in high manganese steel changes from austenite to α' martensite, and develops as Austenite → ε martensite → α' martensite transformation, and further develops into austenite → ε martensite transformation. In addition, as the Mn content increases, the ε martensite content in the alloy gradually increases, the martensite laths become smaller, and the intersections between the laths become denser, which can improve the strength and hardness of the steel. However, too high Mn will promote the formation of network carbides in the as-cast structure, hinder rolling and deformation, and worsen low-temperature toughness. Therefore, the Mn content range is controlled at 20-25%, and preferably the Mn content is 20.3-24.7%.

Nb: The carbide NbC formed by the combination of Nb element and C in the structure can prevent the growth of grains and refine the grains. It can effectively improve the strength of steel and reduce the temper brittleness of steel; but the Plasticity and toughness as well as elongation will be affected. Therefore, the Nb content range is controlled between 0.02% and 0.05%, and preferably the Nb content ranges between 0.021% and 0.045%.

S: The S element is usually a harmful element in steel. It not only affects the strength and welding performance of the material, but also easily forms sulfide inclusions, deteriorating the plasticity and toughness of the material; however, S can improve the cutting performance of steel. Therefore, the range of S content should be ≤0.005%.

P: P element is usually a harmful element in steel. Since steel contains a large amount of Mn element, it will increase the segregation of P at the grain boundaries and weaken the grain boundaries, so the P content should be reduced as much as possible. Therefore, the range of P content should be ≤0.005%.

The reason why the present invention heats the slab before rolling, and controls the heating temperature to 1100-1200°C, and keeps it at this temperature for 120-180 minutes, is because according to the alloy composition, heating to 1100-1200°C can soften the material and improve the quality of the rolling mill. The deformation ability enables hot rolling with large reduction. The heat preservation time is 120 to 180 minutes. In order to ensure that the core temperature of the slab sample reaches above 1080°C, the heat preservation time should not be too long. Too long a time can easily lead to coarse grains.

The reason why the present invention opens the furnace for high-temperature continuous rolling at 900-1150°C, and the total reduction rate is not less than 80-90%, is because only at this temperature can single-pass large deformation rolling be achieved, which is not low. The total reduction rate of 80 to 90% can effectively refine the grains.

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

1. The composition design of the present invention is simple, requiring only C, Mn and trace Nb elements, simple material production and preparation, low alloying cost, and wide application range; the present invention adopts high-temperature continuous rolling, the rolling process is simple, high feasibility, and shortened production line, reducing the production cycle, reducing production costs and resource consumption.

2. The present invention controls the volume fraction, shape and shape of austenite and ε martensite in the structure by designing the alloy composition, holding time during processing, reduction amount during rolling and cooling method after rolling. Distribution state, the yield strength of the prepared high manganese NPR steel is 300~500Mpa, and the tensile strength is 1000~1200Mpa. The effective TRIP effect improves the work hardening rate of the steel, and the work hardening index is ≥0.85, making the steel during the stretching process The local necking is delayed, and the total elongation after fracture is 80-95%, and the strong plastic product is ≥96.9Gpa·%, which greatly improves the overall performance of the material.

Description of drawings

Figure 1 is a Kikuchi zone contrast diagram of high-strength, high-plasticity hot-rolled high-manganese NPR steel in Example 1 of the present invention;

Figure 2 is the stress-strain curve of high-strength, high-plasticity hot-rolled high-manganese NPR steel in Example 1 of the present invention;

Figure 3 shows the work hardening rate and true stress-true strain curve of high-strength, high-plasticity hot-rolled high-manganese NPR steel in Example 1 of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention and are not intended to limit the present invention.

Example 1

A kind of high-strength and high-plasticity hot-rolled high-manganese NPR steel. The chemical composition of the high-manganese steel in mass percentage is: C: 0.46%, Mn: 20.1%, Nb: 0.022%, S≤0.005%, P≤0.005 %, the rest is Fe and inevitable impurity elements.

The production method of the above-mentioned high-strength and high-plasticity hot-rolled high-manganese NPR steel includes the following steps:

(1) According to the chemical composition of high manganese NPR steel, proportion it by mass percentage, use vacuum smelting technology, and pour it into a billet;

(2) Before rolling, the air-cooled slab is heated, the heating temperature is controlled at 1140°C, and kept at this temperature for 120 minutes;

(3) The heat-insulated slab is subjected to high-temperature continuous rolling, with the starting rolling temperature being 1090°C and the final rolling temperature being 960°C. The slab needs to go through 8 passes of hot rolling, with a total reduction rate of 84.9%, and a thickness of the rolled plate of 11.3mm. After rolling, the slab is water-cooled to room temperature. The Kikuchi zone contrast diagram of the hot-rolled plate is shown in Figure 1.

The microstructure of the high-strength and high-plasticity hot-rolled high-manganese NPR steel prepared by the present invention is a two-phase structure of austenite and ε martensite, in which the volume percentage of austenite is 57.5%; the austenite and ε martensite The martensite structure presents a uniform layered alternating distribution.

After the high-strength and high-plasticity hot-rolled high-manganese NPR steel prepared by the present invention is uniaxially stretched, the TRIP effect of austenite and ε martensite in its structure fully occurs, its tensile strength is 1104.1Mpa, and its elongation is 88.1 %, the strong plastic product is 97.3Gpa%, the yield strength is 320.3Mpa, and its stress-strain curve is shown in Figure 2. The effective TRIP effect increases the work hardening rate of the steel, and the work hardening index reaches 0.92, which delays the local necking of the steel during the stretching process. The work hardening rate and true stress-true strain curve are shown in Figure 3.

Example 2

A kind of high-strength and high-plasticity hot-rolled high-manganese NPR steel. The chemical composition of the high-manganese steel in mass percentage is: C: 0.47%, Mn: 22.8%, Nb: 0.025%, S≤0.005%, P≤0.005 %, the rest is Fe and inevitable impurity elements.

The production method of the above-mentioned high-strength and high-plasticity hot-rolled high-manganese NPR steel includes the following steps:

(1) According to the chemical composition of high manganese NPR steel, proportion it by mass percentage, use vacuum smelting technology, and pour it into a billet;

(2) Heat the air-cooled slab before rolling. The heating temperature is controlled at 1150°C and kept at this temperature for 120 minutes;

(3) The heat-insulated slab is subjected to high-temperature continuous rolling, with the starting rolling temperature being 1100°C and the final rolling temperature being 970°C. The slab needs to go through 8 passes of hot rolling with a total reduction rate of 85.6%. After rolling, it is water-cooled to room temperature.

The microstructure of the high-strength and high-plasticity hot-rolled high-manganese NPR steel prepared by the present invention is a two-phase structure of austenite and ε martensite, in which the volume percentage of austenite is 56.3%; the austenite and ε The martensite structure presents a uniform layered alternating distribution.

After the high-strength and high-plasticity hot-rolled high-manganese NPR steel prepared by the present invention is uniaxially stretched, the TRIP effect fully occurs in austenite and ε martensite in its structure, and its tensile strength is 1112.3Mpa, and the effective TRIP effect is improved The work hardening rate and work hardening index of the steel reaches 0.90, which delays the local necking of the steel during the stretching process. The elongation rate is 86.5%, the strong plastic product is 96.2Gpa%, and the yield strength is 331.5Mpa.

Example 3

A kind of high-strength and high-plasticity hot-rolled high-manganese NPR steel. The chemical composition of the high-manganese steel in mass percentage is: C: 0.35%, Mn: 23.2%, Nb: 0.043%, S≤0.005%, P≤0.005 %, the rest is Fe and inevitable impurity elements.

The production method of the above-mentioned high-strength and high-plasticity hot-rolled high-manganese NPR steel includes the following steps:

(1) According to the chemical composition of high manganese NPR steel, proportion it by mass percentage, use vacuum smelting technology, and pour it into a billet;

(2) Before rolling, the air-cooled slab is heated, the heating temperature is controlled at 1160°C, and kept at this temperature for 120 minutes;

(3) The heat-insulated slab is subjected to high-temperature continuous rolling, with the starting rolling temperature being 1120°C and the final rolling temperature being 980°C. The slab needs to go through 8 passes of hot rolling with a total reduction rate of 86.14%. After rolling, it is water-cooled to room temperature.

The microstructure of the high-strength and high-plasticity hot-rolled high-manganese NPR steel prepared by the present invention is a two-phase structure of austenite and ε martensite, in which the volume percentage of austenite is 55.9%; the austenite and ε The martensite structure presents a uniform layered alternating distribution.

After the high-strength and high-plasticity hot-rolled high-manganese NPR steel prepared by the present invention is uniaxially stretched, the TRIP effect fully occurs in austenite and ε martensite in its structure, and its tensile strength is 1096.5Mpa, and the effective TRIP effect is improved The work hardening rate and work hardening index of the steel reached 0.94, which delayed the local necking of the steel during the stretching process. The elongation rate was 88.7%, the strong plastic product was 97.3Gpa%, and the yield strength was 313.9Mpa.

Example 4

A kind of high-strength and high-plasticity hot-rolled high-manganese NPR steel. The chemical composition of the high-manganese steel in mass percentage is: C: 0.55%, Mn: 24.7%, Nb: 0.03%, S≤0.005%, P≤0.005 %, the rest is Fe and inevitable impurity elements.

The production method of the above-mentioned high-strength and high-plasticity hot-rolled high-manganese NPR steel includes the following steps:

(1) According to the chemical composition of high manganese NPR steel, proportion it by mass percentage, use vacuum smelting technology, and pour it into a billet;

(2) Heat the air-cooled slab before rolling. The heating temperature is controlled at 1150°C and kept at this temperature for 120 minutes;

(3) The heat-insulated slab is subjected to high-temperature continuous rolling, with the starting rolling temperature being 1110°C and the final rolling temperature being 970°C. The slab needs to go through 8 passes of hot rolling with a total reduction rate of 84.29%. After rolling, it is water-cooled to room temperature.

The microstructure of the high-strength and high-plasticity hot-rolled high-manganese NPR steel prepared by the present invention is a two-phase structure of austenite and ε martensite, in which the volume percentage of austenite is 54.81%; the austenite and ε The martensite structure presents a uniform layered alternating distribution.

After the high-strength and high-plasticity hot-rolled high-manganese NPR steel prepared by the present invention is uniaxially stretched, the austenite and ε martensite in its structure fully undergo the TRIP effect, and its tensile strength is 1241.4Mpa, and the effective TRIP effect is improved The work hardening rate and work hardening index of the steel reached 0.88, which delayed the local necking of the steel during the stretching process. The elongation rate was 77.6%, the strong plastic product was 96.3Gpa%, and the yield strength was 352.8Mpa.

Claims (8)

1. The high-strength high-plasticity hot-rolled high-manganese NPR steel is characterized by comprising the following components in percentage by mass: c:0.3 to 0.6 percent, mn: 20-25%, nb: 0.02-0.05%, S is less than or equal to 0.005%, P is less than or equal to 0.005%, and the balance is Fe and unavoidable impurity elements.

2. The high strength high plasticity hot rolled high manganese NPR steel according to claim 1, wherein the high manganese NPR steel comprises the following components in percentage by mass: c:0.35 to 0.55 percent, mn:20.3 to 24.7 percent, nb: 0.021-0.045%, S is less than or equal to 0.005%, P is less than or equal to 0.005%, and the balance is Fe and unavoidable impurity elements.

3. The high strength high plasticity hot rolled high manganese NPR steel according to claim 1, wherein the yield strength of the high manganese NPR steel is 300-400 Mpa, the tensile strength is 1000-1200 Mpa, the work hardening index is not less than 0.85, the elongation after break is 85-95%, and the product of strength and elongation is not less than 96 Gpa.

4. The preparation method of the high-strength high-plasticity hot-rolled high-manganese NPR steel is characterized by comprising the following steps of:

(1) According to the chemical components of the high-strength high-plasticity hot-rolled high-manganese NPR steel, the high-strength high-plasticity hot-rolled high-manganese NPR steel is poured into blanks by adopting a vacuum smelting technology;

(2) Heating the plate blank before rolling, controlling the heating temperature to 1100-1200 ℃, and preserving heat for 120-180 min at the heating temperature;

(3) Continuously rolling the heat-preserving plate blank at 900-1150 ℃ at a total rolling reduction of not less than 80-90%, and quenching the plate blank to room temperature after finishing rolling to obtain high-strength high-plasticity hot-rolled high-manganese NPR steel;

the high-strength high-plasticity hot-rolled high-manganese NPR steel comprises the following chemical components in percentage by mass: 0.3 to 0.6 percent, mn: 20-25%, nb: 0.02-0.05%, S is less than or equal to 0.005%, P is less than or equal to 0.005%, and the balance is Fe and unavoidable impurity elements;

the yield strength of the prepared high-strength high-plasticity hot-rolled high-manganese NPR steel is 300-400 Mpa, the tensile strength is 1000-1200 Mpa, the work hardening index is more than or equal to 0.85, the elongation after fracture is 85-95%, and the strong plastic product is more than or equal to 96 Gpa.

5. The method for producing high strength, high plasticity hot rolled high manganese NPR steel according to claim 4, wherein the heating in step (2) is performed at 1140-1170 ℃ for 120min.

6. The method for producing high strength, high plasticity hot rolled high manganese NPR steel according to claim 4, wherein the high temperature continuous rolling in step (3) has a start rolling temperature of 1080 to 1100 ℃ and a finish rolling temperature of 950 to 970 ℃.

7. The method for producing high strength and high plasticity hot rolled high manganese NPR steel according to claim 4 or 6, wherein the high temperature continuous rolling in step (3) is performed for 7 to 8 times, the single pass rolling reduction is 20 to 22%, and the total rolling reduction is 84 to 87%.

8. The method for producing high strength, high plasticity, hot rolled high manganese NPR steel according to claim 4, wherein the microstructure of the high strength, high plasticity, hot rolled high manganese NPR steel produced in step (3) is austenite and epsilon martensite, wherein the volume percentage of austenite is 50-60%; the austenite and epsilon martensite structures exhibit a uniform layered alternating distribution.