Steel for 500MPa-grade low-temperature-resistant high-manganese non-magnetic reinforcing steel bar and production method

Abstract

The invention provides steel for 500MPa-grade low-temperature-resistant high-manganese non-magnetic steel bars and a production method. The steel comprises the following components: 0.25 to 0.45 percent of C, 0.15 to 0.35 percent of Si, 20 to 30 percent of Mn, less than or equal to 0.025 percent of P, less than or equal to 0.025 percent of S, 0.05 to 0.15 percent of V, 0.01 to 0.03 percent of Nb, 2.0 to 4.0 percent of Al, 0.01 to 0.03 percent of N and the balance of Fe and inevitable impurity elements. And 4.6 < = L = 1.5 * [C] + 0.20 * [Mn] + 10.0 * [N] < = 6.5. Compared with the prior art, the components are smelted, the normal-temperature mechanical property of the product meets the requirement by adopting the production method, and the product has good toughness and plasticity and notch sensitivity resistance in a low-temperature environment of-165 DEG C. The production cost of the steel bar is low, the production process is feasible, and the market prospect is good.

Description

Technical Field

[0001] The invention belongs to the field of non-magnetic steel bar production, and specifically relates to a 500MPa-grade low-temperature-resistant high-manganese non-magnetic steel bar and a production method. Background Art

[0002] Non-magnetic steel has a wide range of uses, involving many fields such as electricity, rail transit, machinery, national defense and military industry, and construction. Among them, the generator guard ring used in the power industry has high stress, so non-magnetic steel is needed to reduce the leakage magnetic flux at the end of the motor rotor; the guide mechanism of the magnetic levitation train of rail transit, superconducting power generation, transmission and energy storage equipment, and large-scale nuclear fusion devices, etc., in order to reduce the impact of the magnetic field on the material, also require a large amount of non-magnetic steel; in the field of national defense and military industry, non-magnetic steel is used to manufacture the hull of minesweepers and non-magnetic engines, structural materials for concealed submarines, etc.; the magnetic shelters in the construction industry use non-magnetic steel to avoid the influence of magnetic fields. In addition, non-magnetic bearings, oil drill collars, non-magnetic molds, etc. also require non-magnetic steel materials.

[0003] Therefore, the development of low-cost, high-performance non-magnetic steel materials is of great significance to my country's civil and national defense military construction.

[0004] The patent with publication number CN 117512308 A published on February 6, 2024 discloses a non-magnetic steel bar and a preparation method thereof, and the set chemical composition includes: C, Si, Mn, P, S, Cr, V, O, N and Fe; wherein, by mass fraction, the C content is 0.55-0.65%, the Si content is 0.45-0.55%, the Mn content is 18.0-18.5%, the P content is ≤0.010%, the S content is ≤0.010%, the Cr content is 3.0-3.5%, the V content is 1.70-1.73%, the O content is 0-0.0010%, and the N content is 0.0140-0.0150%. The production method comprises: heating a cast billet with a set chemical composition; rolling the heated cast billet and controlling the rolling process parameters to obtain hot-rolled steel; cooling the hot-rolled steel and controlling the terminal temperature of the cooling to obtain non-magnetic steel bars.

[0005] However, in the above prior art, the added C and V content is too high, which easily leads to brittle steel bars and affects low temperature performance. Therefore, it is very necessary to provide a non-magnetic steel bar with good strength and low temperature performance. Summary of the invention

[0006] The purpose of the present invention is to provide a 500MPa grade low temperature resistant high manganese non-magnetic steel for steel bars and a production method thereof, wherein an austenite structure is formed at room temperature by adding Mn, Al, and N and combining steelmaking and rolling processes to meet the requirement of magnetic permeability ≤ 1.05, and Nb and V are added to improve the mechanical properties of the steel bars by utilizing their precipitation strengthening effect, and the room temperature performance reaches R eL ≥500MPa, R m ≥630MPa, A≥30%, and have good low temperature resistance, no notch specimen R under -165℃ low temperature environment eL ≥575MPa, A gt ≥3%, notched specimen A gt ≥1%, notch sensitivity index NSR ≥1.0 (NSR = R of notched specimen m / R of unnotched specimen eL ), which can meet the technical requirements of non-magnetic steel bar mechanical properties in severe winter areas. The production process of the present invention is not complicated and is suitable for large-scale industrial production and promotion and application.

[0007] The specific technical solutions of the present invention are as follows:

[0008] A 500MPa grade low temperature resistant high manganese non-magnetic steel for steel bars, comprising the following components in percentage by mass:

[0009] C 0.25-0.45%, Si 0.15-0.35%, Mn 20-30%, P≤0.025%, S≤0.025%, V0.05-0.15%, Nb 0.01-0.03%, Al 2.0-4.0%, N 0.01-0.03%, and the rest are Fe and unavoidable impurity elements.

[0010] The composition of the 500MPa grade low temperature resistant high manganese non-magnetic steel bar also satisfies: 4.6≤L=1.5×

[0011] [C]+0.20×[Mn]+10.0×[N]≤6.5. To improve the strength and non-magnetic properties of steel.

[0012] In the formula, each symbol represents the corresponding chemical component content × 100%.

[0013] The room temperature structure of the 500MPa grade low temperature resistant high manganese non-magnetic steel bar is austenite.

[0014] The magnetic permeability of the 500MPa grade low temperature resistant high manganese non-magnetic steel bar is ≤1.05; the room temperature performance R eL ≥500MPa, R m ≥630MPa, A≥30%; R for unnotched specimens at -165℃ low temperature eL ≥575MPa, Agt ≥3%; Notched specimen A gt ≥1%; Notch sensitivity index NSR ≥1.0 (NSR = R of notched specimen m / R of unnotched specimen eL ).

[0015] Preferably, R eL ≥530MPa, R m ≥690MPa, A≥42%; R for unnotched specimens at -165℃ low temperature eL ≥575MPa, A gt ≥5%; Notched specimen A gt ≥3%; notch sensitivity index NSR ≥1.3.

[0016] The present invention provides a method for producing 500MPa-grade low-temperature-resistant high-manganese non-magnetic steel for reinforcement, comprising the following process flow:

[0017] Smelting → LF furnace refining → RH vacuum treatment → continuous casting → rolling.

[0018] The smelting includes an electric furnace or a converter, first adding scrap steel + ferromanganese alloy, and then adding molten iron, wherein molten iron accounts for 30-50%, and scrap steel + ferromanganese alloy accounts for 70-50%. Turn on the electrode and start the oxygen gun to heat up, and the end point requirements are: P≤0.010%, S≤0.010%, and the temperature is 1560-1610℃; slag blocking and steel tapping, adding aluminum iron and slag when about 1 / 4 of the molten steel is tapped, and adding aluminum cakes when about 3 / 4 of the steel is tapped. After the tapping is completed, an appropriate amount of aluminum particles are evenly thrown onto the slag surface according to the amount of slag.

[0019] The LF furnace refining: argon is blown from the bottom of the ladle throughout the whole process, and the argon flow rate is based on the molten steel not splashing out of the ladle; 0.83-1.65kg / t of pre-melted refining slag and 6.67-8.33kg / t of lime are added, TFe+MnO in the slag is ≤1.0%, and alloys are added before, during and after LF furnace refining to adjust the content of Si, Mn, V and Al elements according to the component analysis results before entering the LF furnace, wherein Al is added by feeding aluminum wire, and other alloys are added in blocks through the feeding system. The temperature out of the LF furnace is 1565-1585℃.

[0020] The RH vacuum degassing: the temperature of the molten steel entering the RH vacuum furnace is 1525-1545°C; in the early stage of vacuum, the vacuum holding time is ≥12 minutes, and the composition is adjusted in the middle stage of vacuum according to the composition analysis results in the early stage of vacuum, and the vacuum holding time is guaranteed to be ≥8 minutes after adjustment. The temperature out of the RH vacuum furnace is 1485-1505°C.

[0021] The continuous casting is to carry out continuous casting of 150 square billets, adopt full-process protection casting, the pouring temperature is 1450-1470°C, the crystallizer cooling water flow is 3000 liters / minute, and the secondary cooling water volume is 0.8-1.2 liters / kilogram to ensure the surface quality of the square billets.

[0022] The rolling is carried out by a bar rolling mill: the heating temperature is controlled at 1150-1250°C, the steel tapping temperature is controlled at 980-1080°C, three-stage water cooling is adopted after finish rolling, the temperature drops by 150-250°C, and the upper cooling bed temperature is controlled at 800-900°C.

[0023] The functions of alloying elements in the present invention are as follows:

[0024] C: An element that is conducive to forming a single-phase austenite structure, and has a good solid solution strengthening effect, which is effective in improving the strength of steel. However, as the C content increases, a single austenite structure can be obtained under water quenching or air cooling, but too high a C content will reduce the plasticity of the steel and increase the tendency of austenite grain growth, thereby increasing the magnetic permeability. The C content of the present invention is controlled at 0.25-0.45%.

[0025] Si: Its main function in steel is deoxidation. Since the atomic radius of Si is much smaller than that of austenite, its solid solution strengthening effect is obvious. However, Si is a non-carbide forming element and can reduce the solubility of C in austenite, thereby causing carbides in steel to precipitate, which is not conducive to the stability of austenite structure. The Si content of the present invention is controlled at 0.15-0.35%.

[0026] Mn: It is a strong austenite forming element, which can expand the austenite region, stabilize the austenite structure, and improve the toughness and plasticity in low temperature environment. Most of the Mn in the steel can be dissolved in the austenite to form a substitution solid solution, and as the Mn content increases, the temperature of the austenite to martensite transformation is further reduced, increasing the stability of the austenite. The Mn content of the present invention is controlled at 20-30%.

[0027] V: is an element that strongly forms carbonitrides. The fine dispersed precipitates of VC, VN and V(CN) formed inhibit the growth of austenite grains. At the same time, the fine dispersed precipitates of VC, VN and V(CN) are beneficial to the nucleation of austenite and improve the strength of steel through coherent distortion and dispersion strengthening. The V content of the present invention is controlled at 0.05-0.15%.

[0028] Nb: is an element that strongly forms carbonitrides. The fine dispersed precipitates of NbC, NbN and Nb(CN) formed inhibit the growth of austenite grains. At the same time, the fine dispersed precipitates of NbC, NbN and Nb(CN) are beneficial to the nucleation of austenite and improve the strength of steel through coherent distortion and dispersion strengthening. The Nb content of the present invention is controlled at 0.01-0.03%.

[0029] Al: It can increase the stacking fault energy of austenite, strongly inhibit martensitic transformation, stabilize austenitic structure, and is one of the key elements of austenitic steel. However, the upper limit of Al content depends on whether high-temperature delta ferrite appears, and the lower limit depends on whether the transformation of low-temperature austenite to martensite can be avoided. The Al content of the present invention is controlled at 2.0-4.0%.

[0030] N: is a strong austenite forming element and an interstitial solid solution element, which forms VN and V(CN) compounds with V, greatly improving the strength of steel. The N content of the present invention is controlled at 0.01-0.03%.

[0031] P and S are harmful impurity elements, which are not conducive to ensuring the strong plasticity and low magnetic properties of steel. The content of P and S in the present invention is controlled to be ≤0.025%.

[0032] The key to the present invention is to achieve non-magnetic properties, adopt a high C-high Mn component system, and add a certain amount of Al to expand the austenite phase region, so as to obtain a single-phase austenite structure, which greatly reduces the magnetic permeability of the steel and improves the toughness and plasticity in a low-temperature environment. At the same time, V-Nb composite microalloying is adopted to utilize its precipitation strengthening effect to improve the mechanical properties of the steel bar.

[0033] The non-magnetic property and mechanical property of the steel bar of the present invention are achieved by utilizing the combined effect of the above elements rather than the individual effect of each element.

[0034] Compared with the prior art, the present invention can produce non-magnetic steel bars with excellent performance by smelting according to the above composition, using electric furnace or converter smelting, LF furnace refining, RH vacuum degassing, 150 square billet continuous casting, and bar rolling mill rolling. Its room temperature mechanical properties reach: yield strength R eL ≥500MPa, tensile strength R m ≥630MPa, elongation after fracture A≥30%; mechanical properties at -165℃ low temperature environment: R for unnotched specimen eL ≥575MPa, A gt ≥3%, notched specimen A gt ≥1%; notch sensitivity index NSR ≥1.0; evaluated by the measurement method of GJB 937-90 weak magnetic material magnetic permeability, its relative magnetic permeability ≤1.05. In summary, the room temperature mechanical properties of the product of the present invention meet the requirements of HRB500E steel bars in GB 1499.2, and have good toughness and plasticity and notch sensitivity under a low temperature environment of -165°C, which can meet the needs of non-magnetic field buildings in my country's severely cold winter regions. In addition, the production cost of the steel bars of the present invention is low, the production process is feasible, and it has good market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1This is the room temperature structure of a typical 500MPa low-temperature-resistant high-manganese non-magnetic steel bar of the present invention (magnification 100). DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Example 1-Example 2

[0038] A 500MPa grade low temperature resistant high manganese non-magnetic steel for steel bars, comprising the following components in percentage by mass:

[0039] As shown in Table 1, the remainder not shown in Table 1 is Fe and inevitable impurity elements.

[0040] Comparative Example

[0041] A high manganese non-magnetic steel for reinforcing bars comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurity elements.

[0042] Table 1 Melting chemical composition of examples and comparative examples (%)

[0043] Case C Si Mn P S V Nb Al N L value Example 1 0.43 0.32 20.2 0.011 0.009 0.135 0.015 3.5 0.025 4.94 Example 2 0.40 0.33 21.3 0.012 0.007 0.124 0.016 2.9 0.022 5.08 Comparative Example 0.25 0.30 20 0.013 0.01 0.12 0.012 3.5 0.012 4.50

[0044] The production method of the 500MPa grade low temperature resistant high manganese non-magnetic steel bar described in Example 1 comprises the following steps:

[0045] (1) Electric furnace smelting (120 tons): First add scrap steel + ferromanganese alloy, then add molten iron, of which molten iron accounts for 40% and scrap steel + ferromanganese alloy accounts for 60%. Turn on the electrode and start the oxygen gun to heat up. The end point is: 0.010% P, 0.009% S, and the temperature is 1595℃. Slag blocking is used for tapping. When about 1 / 4 of the molten steel is tapped, aluminum iron and slag are added. When about 3 / 4 of the steel is tapped, aluminum cakes are added. After the tapping is completed, an appropriate amount of aluminum particles are evenly sprinkled on the slag surface according to the amount of slag.

[0046] (2) LF furnace refining: argon is blown from the bottom of the ladle throughout the whole process, and the argon flow rate is based on the molten steel not splashing out of the ladle; 155kg of pre-melted refining slag and 910kg of lime are added, and the slag contains 1.0% TFe+MnO. According to the component analysis results before entering the LF furnace, alloys are added before, during and after LF furnace refining to adjust the content of Si, Mn, V and Al elements. Among them, Al is added by feeding aluminum wire, and other alloys are added in bulk through the feeding system. The temperature out of the LF furnace is 1580℃.

[0047] (3) RH vacuum degassing: The temperature of the molten steel entering the RH vacuum furnace from the ladle is 1530°C, the vacuum holding time in the early stage of vacuum is 13 minutes, the vacuum holding time after the composition adjustment in the middle stage of vacuum is 8.5 minutes, and the temperature out of the RH vacuum furnace is 1495°C.

[0048] (4) Billet continuous casting: pouring temperature 1460°C, mold cooling water flow 3000 L / min, secondary cooling water volume 1.0 L / kg.

[0049] (5) Bar mill rolling: heating temperature, steel tapping temperature control, and upper cooling bed temperature are shown in Table 2.

[0050] The production method of the 500MPa grade low temperature resistant high manganese non-magnetic steel bar described in Example 2 comprises the following steps:

[0051] (1) Electric furnace smelting (120 tons): First add scrap steel + ferromanganese alloy, then add molten iron, of which molten iron accounts for 31% and scrap steel + ferromanganese alloy accounts for 69%. Turn on the electrode and start the oxygen gun to heat up the temperature. The end point is 0.008% P, 0.006% S, and the temperature is 1560℃. Slag blocking is used for tapping. When about 1 / 4 of the molten steel is tapped, aluminum iron and slag are added. When about 3 / 4 of the steel is tapped, aluminum cakes are added. After the tapping is completed, an appropriate amount of aluminum particles are evenly sprinkled on the slag surface according to the amount of slag.

[0052] (2) LF furnace refining: argon is blown from the bottom of the ladle throughout the whole process, and the argon flow rate is based on the molten steel not splashing out of the ladle; 120kg of pre-melted refining slag and 815kg of lime are added, and the slag contains 0.81% TFe+MnO. According to the component analysis results before entering the LF furnace, alloys are added before, during and after LF furnace refining to adjust the content of Si, Mn, V and Al elements. Among them, Al is added by feeding aluminum wire, and other alloys are added in blocks through the feeding system. The temperature out of the LF furnace is 1568℃.

[0053] (3) RH vacuum degassing: The temperature of the molten steel entering the RH vacuum furnace from the ladle is 1525°C; the vacuum holding time in the early stage of vacuum is 13.5 minutes. According to the composition analysis results in the early stage of vacuum, the vacuum holding time is 10 minutes after the composition is adjusted in the middle stage of vacuum. The temperature out of the RH vacuum furnace is 1490°C.

[0054] (4) 150 square billet continuous casting: pouring temperature 1450℃, mold cooling water flow 3000L / min, secondary cooling water volume 0.8L / kg.

[0055] (5) Bar mill rolling: heating temperature, steel tapping temperature control, and upper cooling bed temperature are shown in Table 2.

[0056] The production method of the high manganese non-magnetic steel bar of the comparative example comprises the following steps:

[0057] (1) Electric furnace smelting: first add scrap steel + ferromanganese alloy, then add molten iron, molten iron accounts for 45%, scrap steel + ferromanganese alloy accounts for 55%. Turn on the electrode and start the oxygen gun to heat up. The end point requirements are: 0.012％P , 0.010% S, temperature 1605℃. Slag blocking tapping, add aluminum iron and slag when tapping about 1 / 4 of the molten steel, add aluminum cake when tapping about 3 / 4 of the molten steel, and after tapping, evenly sprinkle appropriate amount of aluminum particles on the slag surface according to the amount of slag.

[0058] (2) LF furnace refining: argon is blown from the bottom of the ladle throughout the entire process, and the argon flow rate is based on the molten steel not splashing out of the ladle; pre-melted refining slag is added 220kg , 1000kg lime, 0.7% TFe+MnO in slag, according to the analysis results before entering LF furnace, alloys are added before, during and after LF furnace refining to adjust the content of Si, Mn, V and Al elements, among which Al is added by feeding aluminum wire, and other alloys are added in block form through the feeding system. The temperature out of LF furnace is 1585℃.

[0059] (3) RH vacuum degassing: The temperature of the molten steel when the ladle enters the RH vacuum furnace 1550℃ ; The vacuum holding time in the early stage of vacuum is 15 minutes. According to the analysis results of the components in the early stage of vacuum, the vacuum holding time in the middle stage of vacuum is adjusted to ensure 12.5 minutes of vacuum holding time. The RH vacuum furnace temperature is 1510℃ .

[0060] (4) Billet continuous casting: pouring temperature 1470℃, mold cooling water flow 3000L / min, secondary cooling water volume 1.15L / kg to ensure billet surface quality.

[0061] (5) Bar mill rolling: heating temperature, steel tapping temperature control, and upper cooling bed temperature are shown in Table 2.

[0062] Table 2 Rolling parameters of various embodiments and comparative examples

[0063] Case Heating temperature(℃) Steel tapping temperature (℃) Upper cooling bed temperature (℃) Example 1 1180 1020 840 Example 2 1220 1060 860 Comparative Example 1185 1021 860

[0064] The mechanical properties, metallographic structures and relative magnetic permeabilities of the embodiments of the present invention and the comparative examples at room temperature and -165°C low temperature are shown in Table 4. eL is the yield strength; R m is the tensile strength; A is the elongation after fracture under 5d gauge length (d is the nominal diameter of the steel bar), NSR = R of the notched specimen m / R of unnotched specimen eL .

[0065] Table 3 Mechanical properties of examples and comparative examples at room temperature and low temperature

[0066]

[0067] The underlined data above do not meet the requirements of the present invention.

[0068] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A 500MPa grade low temperature resistant high manganese non-magnetic steel for steel bars, characterized in that: The 500MPa grade low temperature resistant high manganese non-magnetic steel bar steel comprises the following components in mass percentage: C 0.25-0.45%, Si 0.15-0.35%, Mn 20-30%, P≤0.025%, S≤0.025%, V0.05-0.15%, Nb 0.01-0.03%, Al 2.0-4.0%, N 0.01-0.03%, and the rest are Fe and unavoidable impurity elements.

2. The 500MPa grade low temperature resistant high manganese non-magnetic steel for steel bars according to claim 1, characterized in that: The composition of the 500MPa grade low temperature resistant high manganese non-magnetic steel bar also satisfies: 4.6≤L=1.5×[C]+0.20×[Mn]+10.0×[N]≤6.

5.

3. The 500MPa grade low temperature resistant high manganese non-magnetic steel for reinforcement according to claim 1 or 2, characterized in that: The room temperature structure of the 500MPa grade low temperature resistant high manganese non-magnetic steel bar is austenite.

4. The 500MPa low temperature resistant high manganese non-magnetic steel for reinforcement according to claim 1 or 2, characterized in that: The magnetic permeability of the 500MPa grade low temperature resistant high manganese non-magnetic steel bar is ≤1.05; the room temperature performance R eL ≥500MPa, R m ≥630MPa, A≥30%; R for unnotched specimens at -165℃ low temperature eL ≥575MPa, A gt ≥3%; Notched specimen A gt ≥1%; notch sensitivity index NSR ≥1.

0.

5. A method for producing the 500MPa grade low temperature resistant high manganese non-magnetic steel for steel bars according to any one of claims 1 to 4, characterized in that: The production method comprises the following process flow: smelting→LF furnace refining→RH vacuum treatment→continuous casting→rolling.

6. The production method according to claim 5, characterized in that The smelting includes an electric furnace or a converter, first adding scrap steel + ferromanganese alloy, and then adding molten iron, wherein the molten iron accounts for 30-50%, and the scrap steel + ferromanganese alloy accounts for 70-50%; the end point requirements are: P≤0.010%, S≤0.010%, and the temperature is 1560-1610℃.

7. The production method according to claim 5, characterized in that: The LF furnace refining: adding pre-melted refining slag 0.83-1.65 kg / t, lime 6.67-8.33 kg / t, TFe+MnO in the slag ≤1.0%, the temperature out of the LF furnace is 1565-1585°C.

8. The production method according to claim 5, characterized in that: The RH vacuum degassing: the temperature of the molten steel entering the RH vacuum furnace is 1525-1545°C; in the early stage of vacuum, the vacuum holding time is ≥12 minutes, and the composition is adjusted in the middle stage of vacuum, and the vacuum holding time is guaranteed to be ≥8 minutes after adjustment; the temperature out of the RH vacuum furnace is 1485-1505°C.

9. The production method according to claim 5, characterized in that: The continuous casting is to carry out continuous casting of 150 square billets, adopt full-process protection casting, the pouring temperature is 1450-1470°C, the crystallizer cooling water flow rate is 3000 liters / minute, and the secondary cooling water volume is 0.8-1.2 liters / kilogram.

10. The production method according to claim 5, characterized in that: In the rolling, the heating temperature is controlled at 1150-1250°C, the steel tapping temperature is controlled at 980-1080°C, three-stage water cooling is adopted after finish rolling, the temperature drops by 150-250°C, and the upper cooling bed temperature is controlled at 800-900°C.

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