WO2021128837A1 - Super-tough steel material and manufacturing method therefor - Google Patents

Abstract

A super-tough steel material and a manufacturing method therefor, which belong to the field of steel materials and the processing and preparation thereof, and specifically relate to a super-tough steel material used for a low-temperature condition and a manufacturing method therefor. The steel material comprises the following chemical elements in percentage by weight: 0.10 to 0.15% of C, 29.5 to 31.5% of Mn, with the balance being Fe and inevitable impurities. The manufacturing method comprises the following steps: A1, smelting under protection of argon, and performing remelting treatment on electro slag; A2, hot rolling or hot forging; A3, annealing at 900°C to 1100°C for 1 hour, and quenching; and A4, cold rolling, annealing a cold rolled plate at 700°C to 1200°C for 1 hour, and then quenching. The steel material has simple composition elements, does not contain a noble metal, has an average grain size of less than 30 microns, has a completely face-centered cubic structure, and is non-magnetic; and the steel material has especially prominent performance at a low-temperature condition, and the impact energy thereof at a low temperature exceeds all metal materials currently known.

Description

Super tough steel material and manufacturing method thereof Technical field

The invention belongs to the field of steel materials and their processing and preparation, and in particular relates to a super tough steel material used under low temperature conditions and a manufacturing method thereof.

Background technique

Working equipment under low temperature conditions, such as outer space (approximately 4K) for collecting space debris satellite outer panels, and cryogenic superconducting field cooling devices (2K-4K), have extremely demanding material requirements.

In addition, conventional applications on the ground, such as liquefied natural gas storage tanks (liquefaction temperature -163°C), polar icebreakers, etc., also have extremely high requirements on the toughness and impact resistance of the materials.

Under the above-mentioned environment, common metal materials have the problems of brittle fracture and poor impact toughness.

The current research, the structural materials supporting superconducting magnets is a main direction.

In various superconductor technologies such as nuclear fusion power generation, particle accelerators, and superconducting energy storage, superconducting magnets are used because a large amount of current is required to generate a strong magnetic field. Since superconducting magnets generate a lot of electromagnetic force and are usually cooled by liquid helium to a low temperature of 2-4k, the structural materials supporting the superconducting magnets need to be high-strength and can withstand the huge electromagnetic force at low temperatures. In addition, the influence of structural materials on the magnetic field must be minimized.

Existing materials as structural materials supporting superconducting magnets may include austenitic stainless steel, high Mn steel, aluminum alloys, titanium alloys, and fiber reinforced plastics.

The strength and toughness of ordinary austenitic stainless steels at low temperatures are insufficient, while the stability of the austenite phase in nitrogen-containing low-carbon stainless steels is insufficient. Part of the austenite phase transforms into a ferromagnetic martensite phase after low-temperature deformation. Toughness decreases.

Austenitic stainless steel with a further increase in nickel content, as a structural material for low temperature, has problems such as increased cost and high thermal expansion coefficient. Compared with austenitic stainless steel, fiber-reinforced plastic has the advantages of non-magnetic, easy to handle, low specific gravity, low thermal expansion coefficient, and low unit section strength. In addition, although titanium alloys have low specific gravity and high strength, they involve a problem that they have low toughness at low temperatures and are expensive.

Aluminum alloy is widely used at low temperature due to its light weight, high strength, and extremely low magnetic permeability. However, the strength of aluminum alloy is insufficient, and it also involves weldability problems.

There are currently two types of low temperature metals. The first type is low temperature steel represented by 9% Ni steel. The process of manufacturing 9% Ni steel is very complicated, requiring two quenching + dual phase zone quenching + tempering (RLT) , Quenching + dual phase zone quenching + tempering (QLT), quenching + tempering (QT) and other complex heat treatments, the manufacturing cost is very high, and because it contains a large amount of precious metal Ni, the alloy cost is very high. The main structure of the steel is a body-centered cubic martensite structure, so it is magnetic, and the low-temperature impact value is less than 150J. For 9% Ni steel, as the temperature decreases, both the strength and plasticity increase, while the low-temperature impact toughness decreases.

The second type of technology is high-entropy and medium-entropy alloys. High-entropy alloys can obtain nearly 400J of impact energy at low temperatures. However, because high-entropy and medium-entropy alloys contain a large amount of precious metals Co, Ni and V, their alloy costs are very high. Moreover, ultra-pure smelting is required, and the smelting cost is very high. At present, high-entropy alloys are still in the laboratory stage, and there are no reports of large-scale production.

There are many applications of high manganese steel under low temperature conditions, such as JP63259022A, JPH0215151A, JPS6227557A, JPS58107477A, JPS61143563A, JPH02205631A, US6761780B2 and so on. The high manganese steel disclosed in the above documents basically contains elements such as cadmium, nickel, niobium, and erbium.

Current research on low-temperature impact toughness:

1. High-entropy alloy

[1]Xia,S.Q.,Gao,M.C.,Zhang,Y..(2017).Abnormal temperature dependence of impact toughness inal x cocrfeni system high entropy alloys.Materials Chemistry andPhysics,S0254058417304637.

It is disclosed that the CoCrFeNi high-entropy alloy has an impact energy of 397.87J at 77K, which is the highest value among metal materials currently known, and it reverses the temperature effect. The lower the temperature, the higher the impact value.

The article concludes that the ability to form nano twins and the fracture of small dimples are the keys to improving impact toughness.

[2]Li,D.Y.,&Zhang,Y..(2016).The ultrahigh charpy impact toughness of forged alxcocrfeni high entropy alloys at room and cryogenic temperatures.Intermetallics,70,24-28.

The following were disclosed:

Al0.1CoCrFeNi: 289J/77K, 420J/RT, σy: 412MPa/77K, σy: 250MPa/298K

Al0.3CoCrFeNi: 328J/77K, 413J/RT, σy: 515MPa/77K, σy: 220MPa/298K

For the above two materials, the temperature decreases and the strength and plasticity increase at the same time, but the impact does not show the anti-temperature effect, and the temperature decreases the impact energy.

[3] Bernd Gludovatz, Anton Hohenwarter, Dhiraj Catoor, Edwin H. Chang, Easo P. George, Robert O. Ritchie. A Fracture-resistant high-entropy alloy for cryogenic applications. Science. 2014, v 345: 1153-1158.

It is disclosed that the tensile properties of CrMnFeCoNi have an inverse temperature effect. When the temperature is reduced, the strength and plasticity increase at the same time, the plane slip of the dislocation is activated at room temperature, and the deformation twins are activated after the temperature is reduced, resulting in stable work hardening ability. But it does not show the anti-temperature effect of impact toughness, and the value is relatively stable at low temperatures:

Jk: 293K～250kJ/m2, 200K～260kJ/m2, 77K～255kJ/m2;

KJIC: 293K～217MPa·m1/2, 200K～221MPa·m1/2, 77K～219MPa·m1/2.

2. TWIP steel

Generally speaking, TWIP steel has a high Mn content (12-30%) and a small amount of C (<1%), Si (<3%) or Al (<3%). Its structure at room temperature is a single austenite structure and a small amount of annealing twin structure.

[4]Seok Su Sohn, Seokmin Hong, Junghoon Lee, Byeong-Chan Suh, Sung-Kyu Kim, Byeong-Joo Lee, Nack J. Kim, Sunghak Lee. Effects of Mn and Al contents Charon impactogenic-temperature tense and properties in four austenitic high-Mn steels. 2015 Acta Materialia, 100, 39-52.

The article discloses that the four steels, Fe-19Mn, Fe-19Mn-2Al, Fe-22Mn, and Fe-22Mn-2Al, have a large increase in yield strength at low temperatures, but the plasticity has not increased simultaneously, and the impact toughness has no anti-temperature effect. The toughness value is very low:

Charpy impact energy(J)

Fe-19Mn: 83.4±1.6(RT) 10.3±0.2(-196℃)

Fe-19Mn-2Al: 87.6±3.2(RT) 16.8±0.9(-196℃)

Fe-22Mn: 84.2±1.6(RT) 36.6±0.4(-196℃)

Fe-22Mn-2Al: 90.7±1.1(RT) 42.0±0.2(-196℃)

[5]Kim,H.,Ha,Y.,Kwon,KH,Kang,M.,Kim,NJ,&Lee,S..(2015).Interpretation of cryogenic-temperature charpy impact toughness by microstructural evolution of dynamically compressed specimens in austenitic 0.4C-(22-26)Mn steels.ActaMaterialia,87,332-343.

The article discloses that the yield strength is adjusted at low temperature, but the plasticity is not significantly improved, and there is no anti-temperature effect on low-temperature impact, and the impact energy decreases at low temperature (-196°C).

Under low temperature conditions, the stacking fault energy is reduced by -30% compared to room temperature. It is believed that 0.4C-22Mn is due to the occurrence of a large amount of ε-martensite, which causes the TRIP mechanism. At the same time, TWIP is also working, so it is better than 0.4C-24Mn and 0.4C-26Mn. Improved impact power.

[6]Yu,L.,Yufei,L.,Wei,L.,Mahmoud,K.,Huibin,L.,&Xuejun,J..(2018).Hierarchical microstructure design of a bimodal grained twinning-induced plasticity steel with excellent cryogenic mechanical properties. Acta Materialia,158,79-94.

The article discloses: Fe-0.45C-24Mn-0.05Si-2Al-0.1Nb steel, as the temperature decreases, the strength and elongation increase simultaneously, but the low-temperature impact toughness decreases as the temperature decreases, and there is no anti-temperature effect.

The relevant materials are summarized in the following table:

Table 1: Material summary table

Continued Table 1: Material Summary Table

Summary of the invention

The purpose of the present invention is to solve the problems of brittle fracture and poor impact toughness of metal materials under low temperature conditions. The metal materials have super toughness under low temperature conditions, and the impact energy is greater than 420J.

In this application, the low temperature refers to the temperature of liquid nitrogen (-196°C).

In order to achieve the above objective, the present invention proposes a super tough steel material, which includes the following chemical elements in weight percentage: 0.10～0.15% C, 29.5-1.5% Mn, and the rest is Fe and unavoidable impurities.

At the same time, the present invention also proposes the following manufacturing methods:

A1. The weight percentage of 0.10～0.15% of C, 29.5% to 31.5% of Mn, the rest is Fe and inevitable impurities are smelted under argon gas protection, and electroslag remelting treatment;

A2. Hot rolling or hot forging: billet heating temperature 1150℃～1250℃, blooming temperature or initial forging temperature≧800℃, final rolling temperature or final forging temperature≧600℃, air cooling after hot rolling or hot forging, into 20mm ～40mm hot-rolled plate or hot-forged plate;

A3. The hot-rolled plate or hot-forged plate is annealed at 900℃～1100℃ for 1 hour, and then quenched;

A4. The quenched steel sheet is cold rolled, with a cold rolling deformation of 50% to 75%, and cold rolled into a cold rolled plate with a thickness of about 10mm; the cold rolled plate is annealed at 700°C to 1200°C for 1 hour, and then quenched.

The limitation of each element in the present invention:

C: Carbon is an interstitial solute element, and the strength of steel can be effectively improved by solid solution strengthening. In order to obtain the required yield stress at low temperatures, the content of carbon must be controlled to 0.05% or higher. On the other hand, when the carbon content exceeds 0.18%, the austenite phase is unstable, and carbides of the hard phase are easily precipitated during the annealing process. The lower magnetic permeability can no longer be maintained at low temperatures, and the weldability and workability are reduced. The preferable range of carbon is 0.10 to 0.15%.

Mn: Manganese helps stabilize the austenite phase at low temperatures and obtain extremely low magnetic permeability. For this reason, the manganese content must reach 29.0% or more. On the other hand, if the manganese content is too large, the toughness, weldability, and workability will all decrease, so the preferable range of manganese is 29.5% to 31.5%.

Others are iron and unavoidable impurities. Obviously, the lower the content of the inevitable impurities, the better, but from the perspective of industrial economy, Si≦0.01, S≦0.008, and P≦0.008 are acceptable.

If the Si content is too large, the low-temperature impact toughness will be reduced. Therefore, the upper limit is preferably controlled to 0.01% by weight.

Both S and P impair the hot workability of steel, and cracks occur during welding. Therefore, in the present invention, it is preferable that S is controlled to 0.008% by weight or less, and P is controlled to be 0.008% by weight or less.

Description of the process steps of the present invention:

In step A1, in order to prevent the volatilization of Mn during the smelting process, argon gas is used for protection. After the smelting is completed, electroslag remelting is performed.

In step A2, the effects of hot forging and hot rolling in the present invention are basically the same, as long as the temperature requirements are ensured.

Step A4, the fine layer structure is obtained by cold rolling, and the sample after the cold rolling is annealed to obtain fine grains; the lower the annealing temperature, the smaller the grain size is obtained, but when the annealing temperature is lower than 700 degrees, there are The partially recrystallized structure and the partially recrystallized structure are a hard phase, which is detrimental to low-temperature impact performance. Therefore, in the present invention, the annealing temperature after cold rolling is controlled at 700°C to 1200°C.

The deformation mechanism of Fe-Mn-C austenitic steel is directly related to temperature and stacking fault energy. When the stacking fault energy is lower than 18mJ/m ² ε-martensitic transformation easily occurs, and the stacking fault energy is 12～35mJ/m2 At this time, twin deformation is the main deformation method. The calculation of stacking fault energy in an ideal state can be calculated according to formula (1-1):

Γ=2ρΔG ^γ→ε +2σ (1-1)

Where Γ is the stacking fault energy; ρ is the molar surface density along the {111} plane; ΔG ^γ→ε is the molar Gibbs free energy when γ-->ε; σ is the interface energy of γ/ε.

Ρ in formula (1-1) can be expressed by formula (1-2):

In the formula, a——lattice constant;

N-Avogadro's constant.

The molar Gibbs free energy ΔGγ→ε when γ→ε in the formula (1-1) is calculated in the Fe-Mn-C three-series alloy can be expressed by the formula (1-3):

Where χ _i is the mole percentage of element i;

Molar free energy required for element i when γ-->ε transition occurs;

Molar free energy required for ij element interaction when γ-->ε transition occurs;

Since the stacking fault energy is also related to the grain size, the expression of the stacking fault energy with the addition of the grain size excess term is Formula 1-4:

Γ=2ρ△G ^γ→ε +2σ ^γ/ε +2ρ△G _ex (1-4)

Where ΔG _ex is

ΔG _ex ＝170.06exp(-d/18.55) (1-5)

The above studies have shown that the reduction of stacking fault energy due to temperature reduction is prone to martensite transformation, while grain refinement can effectively offset the reduction in stacking fault energy caused by temperature reduction, and can partially inhibit martensite transformation. Increasing the Mn content also has a positive effect on inhibiting martensite. Therefore, the present invention proposes a combination of a Mn content of about 30% and grain refinement to inhibit martensite transformation at low temperatures.

Beneficial effects: using the technical solution provided by the present invention, the steel has simple constituent elements and does not contain precious metals; through alloying design and structure control, a steel with a stable austenite structure and an average grain size of less than 30 microns is obtained. It has a completely face-centered cubic structure and is non-magnetic. At room temperature, the tensile strength is greater than or equal to 220 MPa, the highest is 230 MPa, the tensile strength is 520 MPa, the highest is 531 MPa, the uniform elongation is 50%, the total elongation is 65%, and the impact energy is higher than 310 J. Up to 340J; under low temperature conditions, the yield strength during stretching can reach 360MPa, the tensile strength is higher than 750MPa, and the highest can reach 860MPa. The uniform elongation is about 80%, the total elongation is higher than 84%, and the impact energy is higher than 400J. , Up to 458J. The performance is particularly outstanding under low temperature conditions, and the low temperature impact energy exceeds all currently known metal materials.

Description of the drawings

Figure 1 shows the fine-grained Fe-30Mn-0.11C steel with an average grain size of 5.6 microns;

Figure 2 is a histogram of the grain size distribution of fine-grained Fe-30Mn-0.11C steel with an average grain size of 5.6 microns;

Figure 3 shows the stress-strain curves of Fe-30Mn-0.11C steel with different grain sizes when it is stretched at room temperature (RT) and liquid nitrogen temperature (LNT);

Figure 4 shows the EBSD microstructure analysis of Fe-30Mn-0.11C steel with an average grain size of 5.6 microns after breaking at room temperature;

Figure 5 shows the EBSD structure analysis of Fe-30Mn-0.11C steel with an average grain size of 6 microns after liquid nitrogen temperature breaking;

Figure 6 shows the EBSD phase analysis of Fe-30Mn-0.11C steel with an average grain size of 5.6 microns after liquid nitrogen temperature breaking;

Figure 7 is a 3D reconstruction photo of Fe-30Mn-0.11C steel liquid nitrogen impact fracture with an average grain size of 5.6 microns;

Figure 8 is the SEM photo of the Fe-30Mn-0.11C steel liquid nitrogen impact fracture with an average grain size of 5.6 microns;

Figure 9 shows the low-temperature impact energy comparison between Fe-30Mn-0.11C steel with an average grain size of 5.6 microns and steel with different Mn content;

Figure 10 shows the comparison of Fe-30Mn-0.11C steel with an average grain size of 5.6 microns and different low-temperature metal materials;

Figure 11 is a photo of a sample of Fe-30Mn-0.11C steel with an average grain size of 5.6 microns and an average grain size of 47.0 microns after being impacted at liquid nitrogen temperature and room temperature.

In Figure 11, the fine-grained Fe-30Mn-0.11C steel with an average grain size of 5.6 microns was obtained by 50% cold rolling + annealing at 700°C for 1 hour; the average grain size is Fe with a grain size of 47.0 microns -30Mn-0.11C steel is obtained without cold rolling.

Detailed ways

Comparative example 1: 0.05% C, 30.4% Mn, the rest is Fe and unavoidable impurities, Si≦0.01, S≦0.008, P≦0.008. Hot rolling after smelting.

After 50% cold rolling and annealing at 650°C for 2 hours, Fe-30.4%Mn-0.05%C steel with an average grain size of 1.3 microns is obtained. The yield strength can reach 430MPa, the tensile strength 699MPa, and the uniform elongation at room temperature. The rate reaches 40.3%, the total elongation rate can reach 51.7%, the average impact energy is 278J; the average low temperature impact energy is 172J.

Comparative example 2: 0.05% C, 30.4% Mn, the rest is Fe and unavoidable impurities, Si≦0.01, S≦0.008, P≦0.008. Hot forging treatment after smelting.

After 50% cold rolling and annealing at 1100°C for 1 hour, Fe-30.4%Mn-0.05%C steel with an average grain size of 20 microns is obtained. The yield strength when stretched at room temperature can reach 204MPa, the tensile strength is 525MPa, and it is stretched uniformly. The rate reaches 39.4%, the total elongation rate can reach 51.4%, the average impact energy is 329.6J; the average low temperature impact energy is 325J.

Table 2. Performance parameters of Comparative Examples 1 and 2

In Comparative Example 1, the average grain size obtained by the lower annealing temperature after cold rolling is smaller, and all indexes at room temperature are better than Comparative Example 2, but the impact energy index is not as good as Comparative Example 2. In the above-mentioned comparative example, the impact energy at low temperature is lower than that at room temperature, and there is no anti-temperature effect.

The following examples are the characteristics of steel materials with different chemical element compositions defined in the present invention.

Example 1: Fe-29.5%Mn-0.10%C, annealed at 700°C for 1 hour after passing 50% cold rolling.

Example 2: Fe-30%Mn-0.11%C, passed through 50% cold rolling and then annealed at 700°C for 1 hour.

Example 3: Fe-31.5%Mn-0.15%C, annealed at 700°C for 1 hour after passing 50% cold rolling.

Table 3. Room temperature and liquid nitrogen temperature impact energy of steel samples with different compositions

In the above examples, three samples were made in each case. It can be seen that, compared with the comparative example, the impact energy is greatly improved under low temperature conditions, and an inverse temperature effect occurs. Among them, the performance index of Example 2 is the best.

The following examples and comparative examples obtain the characteristics of Fe-30%Mn-0.11%C steel materials for different processes.

Example 2: 0.11% C, 30% Mn, the rest is Fe and unavoidable impurities. After hot forging and annealing, 50% cold rolling, rolling speed of 4.2m/s, pass deformation of 1mm/pass; after cold rolling, annealing at 700℃ for 1 hour, Fe-30 with an average grain size of 5.6 microns is obtained ％Mn-0.11％C steel, the yield strength can reach 230MPa when stretched at room temperature, the tensile strength is 531MPa, the uniform elongation can reach 50%, the total elongation can reach 65%, and the average impact energy is 334J; it yields when stretched at low temperature. The strength can reach 360MPa, the tensile strength is 860MPa, the uniform elongation can reach 70%, the total elongation can reach 84%, and the average impact energy is 453J.

Figures 1 and 2 are the metallographic structure diagram and the grain size distribution histogram of the steel obtained in Example 2. It can be seen that the average grain size is 5.6 microns.

Comparative Example 3: After hot forging, annealed at 1000°C for 1 hour, Fe-30%Mn-0.11%C steel with an average grain size of 47 microns is obtained. The yield strength can reach 180MPa and the tensile strength 495MPa at room temperature, uniform. The elongation rate reaches 53%, the total elongation rate can reach 66%, and the average impact energy is 372J; the yield strength can reach 320MPa, the tensile strength 732MPa, the uniform elongation rate can reach 80%, and the total elongation rate can reach 87%. , The average impact energy is 269J.

Table 4. Room temperature and liquid nitrogen temperature tensile properties of Fe-30Mn-0.11C steel samples obtained by different treatments

Table 5. Room temperature and liquid nitrogen temperature impact energy of Fe-30Mn-0.11C steel samples obtained by different treatments

Comparative Example 3 did not undergo the process of cold rolling and maintained a larger grain size. It can be seen that, compared to Example 2 and Comparative Example 3, the cold-rolled sample has a smaller crystal grain size, and the overall performance, especially the performance at the temperature of liquid nitrogen, is more prominent.

The stress-strain curves of Example 2 and Comparative Example 3 during stretching at room temperature (RT) and liquid nitrogen temperature (LNT) are shown in FIG. 3.

Example 4: 0.11% C, 30% Mn, the rest is Fe and unavoidable impurities. Hot forging annealing 50% cold rolling, rolling speed is 4.2m/s, pass deformation is 1mm/pass; after cold rolling, annealing at 1200℃ for 1 hour, an average grain size of 26 microns of Fe-30% is obtained Mn-0.11%C steel, the yield strength can reach 220MPa when tensile at room temperature, the tensile strength is 520MPa, the uniform elongation can reach 54%, the total elongation can reach 65%, and the average impact energy is 315J; the yield strength at low temperature tensile It can reach 280MPa, the tensile strength is 777MPa, the uniform elongation can reach 82%, the total elongation can reach 86%, and the average impact energy value of liquid nitrogen temperature is 423J.

Example 5: 0.11% C, 30% Mn, the rest is Fe and unavoidable impurities. Hot forging annealing 50% cold rolling, rolling speed 4.2m/s, pass deformation 1mm/pass; after cold rolling, annealing at 900°C for 1 hour, an average grain size of 10.7 microns of Fe-30% is obtained Mn-0.11%C steel, tensile strength at room temperature can reach 225MPa, tensile strength 524MPa, uniform elongation can reach 55%, total elongation can reach 66%, average impact energy is 320J; yield strength at low temperature tensile It can reach 285MPa, the tensile strength is 818MPa, the uniform elongation can reach 83%, the total elongation can reach 85%, and the average impact energy value of liquid nitrogen temperature is 421J.

Table 6. Room temperature and liquid nitrogen temperature tensile properties of Fe-30Mn-0.11C steel samples obtained by different heat treatments after cold rolling

Table 7. Room temperature and liquid nitrogen temperature impact energy of Fe-30Mn-0.11C steel samples obtained by different heat treatments after cold rolling

In the above embodiments, other process conditions are basically the same, and the difference is that the annealing temperature after cold rolling is different. The annealing temperature is low, the average grain size obtained is small, and the annealing temperature is high, the average grain size obtained is large. The liquid nitrogen temperature impact energy index of steel with a small average grain size is the highest.

The figure shows the characteristics of the fine-grained Fe-30Mn-0.11C steel with an average grain size of 5.6 microns with the best low-temperature performance.

It can be seen from Fig. 4 that the microstructure of the parallel ends after breaking is dominated by dislocation deformation after room temperature stretching.

It can be seen from Figure 5 that the deformation after stretching at liquid nitrogen temperature is dominated by dislocations and twins.

It can be seen from Figure 6 that there is no martensitic transformation after the liquid nitrogen temperature is broken.

It can be seen from Figure 7 that there is a large diameter reduction near the impact fracture. In addition to the main crack, there are 2 cracks in other directions. Even under the impact of liquid nitrogen temperature, the sample did not break into two sections.

It can be seen from Figure 8 that the impact fracture morphology is sub-micron dimples.

It can be seen from Fig. 9 that compared with other high manganese steels, the steel disclosed in the present invention has super low temperature toughness and an impact energy value greater than 450J.

It can be seen from Figure 10 that the steel disclosed in the present invention with an average inch size of 5.6 microns has super low temperature toughness, liquid nitrogen temperature impact energy value is greater than 450J, and its room temperature yield strength is not low compared with other metal materials.

In Figure 11:

a Photograph of Fe-30Mn-0.11C steel with a grain size of 5.6 microns after the impact of liquid nitrogen temperature;

b Sample photos of Fe-30Mn-0.11C steel with a grain size of 5.6 microns after impact at room temperature;

c A sample photo of Fe-30Mn-0.11C steel with a grain size of 47.0 microns after the impact of liquid nitrogen temperature;

d Photograph of Fe-30Mn-0.11C steel with a grain size of 47.0 microns after impact at room temperature.

It can be seen that the impact of the two samples at room temperature and liquid nitrogen temperature did not cause the samples to disconnect.

The invention obtains a stable austenite structure through alloying design, and obtains a steel with an average grain size of a microstructure less than 30 microns through structure control, and the steel has a complete face-centered cubic structure and is non-magnetic. The fine-grained structure of this composition does not produce brittle martensite at low temperature when it is stretched and impacted at room temperature and low temperature. A large number of coordinated twin deformations are generated during the deformation process, and the impact fracture is a large number of small sub-micron toughness. The large diameter shrinkage occurs near the impact fracture and absorbs a large amount of impact energy.

The steel plate prepared by the invention has an impact energy that exceeds all currently known metal materials under low temperature conditions, and has broad prospects for application under low temperature conditions.

Claims (5)

1. A super tough steel material characterized by including the following chemical elements in weight percentage: 0.10～0.15% C, 29.5-1.5% Mn, the rest being Fe and unavoidable impurities;

   The manufacturing method of the super tough steel material includes the following steps:

   A1. The weight percentage of 0.10～0.15% of C, 29.5% to 31.5% of Mn, the rest is Fe and inevitable impurities are smelted under argon gas protection, and electroslag remelting treatment;

   A2. Hot rolling or hot forging: billet heating temperature 1150℃～1250℃, blooming temperature or initial forging temperature≧800℃, final rolling temperature or final forging temperature≧600℃, air cooling after hot rolling or hot forging, into 20mm ～40mm hot-rolled plate or hot-forged plate;

   A3. The hot-rolled plate or hot-forged plate is annealed at 900℃～1100℃ for 1 hour, and then quenched;

   A4. The quenched steel sheet is cold rolled, with a cold rolling deformation of 50% to 75%, and cold rolled into a cold rolled plate with a thickness of about 10mm; the cold rolled plate is annealed at 700°C to 1200°C for 1 hour, and then quenched.
2. The steel material according to claim 1, wherein the weight percentage of the C element is 0.11%, the weight percentage of the Mn element is 30%, and the rest is Fe and unavoidable impurities.
3. The steel material of claim 1 or 2, wherein the average grain size of the microstructure is less than 30 microns.
4. The steel material of claim 3, wherein the average grain size of the microstructure is 5.6 microns.
5. The iron and steel material according to claim 1, wherein the average value of the impact energy at low temperature (liquid nitrogen temperature) of the iron and steel material is greater than 420J.

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