Steel for magnesium smelting tank, production method of steel, 1280 DEG C high-temperature deformation-resistant magnesium smelting tank and manufacturing method of 1280 DEG C high-temperature deformation-resistant magnesium smelting tank

Abstract

The invention provides steel for a magnesium smelting tank, a production method of the steel, the magnesium smelting tank capable of resisting 1280 DEG C high-temperature deformation and a manufacturing method of the magnesium smelting tank. The steel comprises the following components: 0.40%-0.50% of C, 0.05%-0.20% of Si, 1.70%-2.00% of Mn, 8.50%-9.50% of Cr, 0.40%-0.60% of W, 0.010%-0.025% of Al, 0.20%-0.50% of V, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.040%-0.070% of N, less than or equal to 0.0040% of O and the balance of Fe and other inevitable impurities. Compared with the prior art, the 1280 DEG C high-temperature deformation resistant steel for the magnesium smelting tank is obtained through a component system which is moderate in Cr content and does not contain Ni through component design; and the manufacturing requirement of the high-capacity magnesium smelting tank with the diameter larger than or equal to 900 mm is met, and the service life exceeds 2200 hours.

Description

Technical Field

[0001] The present invention belongs to the field of high alloy steel, and specifically relates to a steel for magnesium smelting pots, its production method, a magnesium smelting pot resistant to high temperature deformation at 1280 °C, and its manufacturing method. Background Art

[0002] At present, 80% of the world's primary magnesium is produced by the thermal reduction method, and more than 90% of it is produced by the Pidgeon process in the thermal reduction method. The thermal reduction method requires a high-temperature negative pressure environment. Generally, the temperature is below 1230 °C. In recent years, to improve the magnesium smelting efficiency, the reduction temperature has been gradually increased, reaching a maximum of 1280 °C. At 1280 °C, the high-temperature strength of the magnesium smelting pot is insufficient, and deformation and fracture failure frequently occur, affecting the magnesium smelting efficiency.

[0003] The patent with the publication number CN101805833A, published on August 18, 2010, discloses a magnesium smelting reduction pot and its preparation method. The disclosed magnesium smelting reduction pot includes a pot body and an outer coating layer. The composition of the pot body by weight percentage is: C: 0.2% - 0.4%, Mn: 1.0% - 2.0%, Si: 0.6% - 2.0%, Cr: 24.0% - 26.0%, Ni: 6.0% - 8.0%, Ti: 0.015% - 0.05%, Re: 0.03% - 0.10%, and the balance is iron. This patent uses 24 - 26% Cr and 6% - 8% Ni as the main raw materials, and through rare earth treatment, it is cast into a magnesium reduction pot. This patent uses high alloy steel, and the manufacturing process is still casting. Although it can improve the service life, the outer diameter of the smelting pot is 370 mm, and the service temperature is about 1200 °C. However, the low service temperature is not conducive to efficient magnesium smelting. Summary of the Invention

[0004] The purpose of the present invention is to provide a steel for magnesium smelting pots and its production method. Through composition design, under the conditions of no Ni and low Cr, a steel for magnesium smelting pots resistant to high temperature deformation at 1280 °C can be obtained. And it can be used to produce magnesium smelting pots with a diameter ≥ 900 mm.

[0005] Another purpose of the present invention is to provide a magnesium smelting pot resistant to high temperature deformation at 1280 °C and its manufacturing method, which is manufactured by using the above-mentioned steel for magnesium smelting pots in combination with a heat treatment process. The high-temperature yield strength of the product at 1280 °C ≥ 33 MPa. The anti-collapse deformation ability at 1280 °C is greater than 25 MPa, meeting the manufacturing requirements of large-capacity (diameter ≥ 900 mm) magnesium smelting pots. The service life of the manufactured large-capacity magnesium smelting pots exceeds 2200 hours.

[0006] The specific technical solution of the present invention is as follows:

[0007] A steel for magnesium smelting pots, including the following components by mass percentage:

[0008] C 0.40% - 0.50%, Si 0.05% - 0.20%, Mn 1.70% - 2.00%, Cr 8.50% - 9.50%, W 0.40% - 0.60%, Al 0.010% - 0.025%, V 0.20% - 0.50%, P ≤ 0.020%, S ≤ 0.010%, N 0.040 - 0.070%, O ≤ 0.0040%, the balance being Fe and other unavoidable impurities.

[0009] The composition of the steel for magnesium smelting ladle satisfies: 99.25% ≤ 12×%C + 5×%Mn - 4×%Si + 9×%Cr + 8.5×%W + 2×%V + 85×%N ≤ 107.45%.

[0010] The composition of the steel for magnesium smelting ladle also satisfies: 4.80% ≤ (%C + 6×%N) / 9 - (8×%Si + 3×%Mn) / 7 + (2×%Cr + 4×%W + 11×%V) / 4.

[0011] A production method of steel for magnesium smelting ladle provided by the present invention includes the following technological processes:

[0012] Smelting in electric arc furnace or converter → Refining in LF furnace → Vacuum degassing in RH or VD → Continuous casting of round billet.

[0013] For the continuous casting of round billet, round billets with a diameter of Φ380mm - Φ1200mm are produced; preferably, round billets with a diameter of Φ900mm - Φ1200mm are produced; the superheat is 30°C - 70°C. The diameter R of the continuous casting billet and the drawing speed v should comply with R 2 ×

[0014] v = 98000, where the unit of the diameter R of the continuous casting billet is mm and the unit of the drawing speed v is m / min; the frequency f of the final electromagnetic stirring and the diameter R of the continuous casting billet should comply with R / f = 180, where the unit of the frequency f of the final electromagnetic stirring is Hz and the unit of the diameter R of the continuous casting billet is mm.

[0015] A manufacturing method of a magnesium smelting ladle resistant to high-temperature deformation at 1280°C provided by the present invention includes heat treatment, and the heat treatment method includes normalizing and tempering.

[0016] For the normalizing, normalizing: the heating temperature T is 1100 - 1200°C, the holding time t1 is determined by the wall thickness S of the steel pipe, t1 = 3.5×S, and air cooling. Wherein, the unit of the holding time t1 is min and the unit of the wall thickness S of the steel pipe is mm.

[0017] For the tempering, tempering: the tempering temperature is 600 - 700°C, the holding time t2 is determined by the wall thickness S of the steel pipe, t2 = 4×S, and air cooling. Wherein, the unit of the holding time t2 is min and the unit of the wall thickness S of the steel pipe is mm.

[0018] A magnesium smelting pot resistant to high-temperature deformation at 1280°C provided by the present invention is manufactured by the above method. For the magnesium smelting pot resistant to high-temperature deformation at 1280°C, the crystal grain size of the 1 / 2 wall thickness of the steel pipe is 85 - 95μm; the high-temperature yield strength of the 1 / 2 wall thickness of the steel pipe at 1280°C is ≥33MPa, and the tensile strength is ≥38MPa; the anti-collapse deformation ability at 1280°C is greater than 25MPa, meeting the manufacturing requirements of the magnesium smelting pot at 1280°C. The service life of the large-capacity magnesium smelting pot made of this steel exceeds 2200 hours.

[0019] The design concept of the present invention is as follows:

[0020] C: C is the cheapest strengthening element in steel. At room temperature, for every 0.1% increase in solid solution C, the strength can be increased by about 450MPa. In addition, C forms precipitation phases with alloying elements in steel, playing a role in precipitation strengthening. However, too high carbon content is prone to the tendency of graphitization, so C is controlled at 0.40% - 0.50%.

[0021] Si: Si is an effective solid solution strengthening element in steel, improving the strength and hardness of steel. Si can play a deoxidizing role during steelmaking and is a commonly used deoxidizer. However, Si is prone to instability at high temperatures, so the content of Si in high-temperature steel should not be too high. Therefore, the content of Si is controlled at 0.05% - 0.20%.

[0022] Mn: Mn can play a role in solid solution strengthening. For every 0.1% increase in Mn, the high-temperature strength can be increased by 2.5MPa. Mn combined with S can prevent the hot brittleness caused by S. However, excessive Mn will reduce the plasticity of steel. Therefore, the content of Mn is controlled at 1.70% - 2.00%.

[0023] Cr: Cr is a carbide-forming element. Cr can improve both the hardenability and strength of steel. Cr can improve the oxidation resistance of steel and increase corrosion resistance. Cr is the main element to improve the high-temperature strength of steel, usually with a content of 5% - 25%. However, Cr has a high cost, and excessive addition cannot significantly improve the strength but increase the cost. On the other hand, too high Cr content will lead to an increase in the viscosity of steel during production, which is not conducive to casting. The content of Cr should be controlled at 8.50% - 9.50%.

[0024] W: W mainly improves the heat resistance of steel. W dissolved in the matrix can keep the structure of steel relatively stable during the tempering process. Usually, adding 0.1% of Mo can increase the high-temperature strength by 0.8MPa. Therefore, Mo is controlled at 0.40% - 0.60%.

[0025] V: V is a strong C, N compound forming element. V(C, N) is fine and dispersed, and maintains a coherent relationship with the matrix, which can play a role in strengthening and refining the structure. The strengthening of the matrix can increase the resistance to the initiation and propagation of fatigue cracks, thereby improving the fatigue strength. The V content is controlled at 0.20% - 0.50% of V.

[0026] Al: Al is the main deoxidizer in steelmaking. Al combines with N to form fine and dispersed AlN, and maintains a coherent relationship with the matrix, which can play a role in strengthening and refining the structure, and can increase the resistance to the initiation and propagation of fatigue cracks, thereby improving the creep strength of the steel. The Al content is controlled at 0.010% - 0.025%.

[0027] N: N is an inexpensive strengthening element. The solution strengthening effect of N is the same as that of C. At room temperature, for every 0.1% increase in N, the strength is increased by 450 MPa. At high temperatures, for every 0.1% increase in N, the strength can be increased by 15 MPa. However, if the N content in the steel is too high, it is easy to cause bubbles. And increasing nitrogen in the steel requires high pressure and is not easy to operate. Therefore, the nitrogen content is controlled at 0.04% - 0.07%.

[0028] The steel for magnesium smelting ladles requires high strength. Generally, materials with high room temperature strength also have high high temperature strength. However, through research, it is found that this rule is not completely followed at a temperature of 1280°C. Refining grain elements cannot improve the high temperature strength of the steel at high temperatures. Solution strengthening and dispersion strengthening are the main means to improve high strength. Through research, it is determined that in a high temperature environment, C can effectively improve the high temperature strength, and the contribution coefficient to high strength is 12; N also has a solution strengthening effect, but the high temperature solution effect of N is stronger, and the high temperature strength contribution coefficient is 85; W improves the high temperature strength by improving the tempering stability and solution strengthening effect, and the contribution coefficient to high temperature strength is 8.5; Mn improves the strength by expanding the high temperature phase region during the phase transformation process, and the contribution coefficient to high temperature strength is 5; Cr has an atomic size similar to that of Fe, can achieve substitutional solid solution, and Cr can improve the high temperature oxidation effect, making a greater contribution to high strength, and the contribution coefficient is 9; Si is a non-metallic element and also the main solution strengthening element in the steel. However, in a high temperature environment, Si is not beneficial to high temperature strength, so the contribution coefficient is -4; V can provide the high temperature strength of the steel through both solution and dispersion methods. However, V has a pinning effect on the grain boundary when combined with N, which is not conducive to high temperature strength. Therefore, the contribution coefficient to high temperature strength is 2. To ensure the high temperature strength and toughness of the steel, it is not possible to only ensure the high temperature strength of the steel. Therefore, let the high temperature strengthening factor in the steel be represented by the A value, then 99.25% ≤ A value ≤ 107.45%,

[0029] A value = 12 × %C + 5 × %Mn - 4 × %Si + 9 × %Cr + 8.5 × %W + 2 × %V + 85 × %N.

[0030] Magnesium smelting pots require excellent high-temperature creep resistance during service. The high-temperature creep resistance is related to the strength of the steel on the one hand, and also related to the grain boundary stability, precipitation, and solid solution stability of the steel. Therefore, it is necessary to limit the ratio of C, Si, Mn, Cr, W, N, and V. Since the atomic scales of C and N are small, they can only exist in the form of interstitial atoms during strengthening and will slip under high-temperature stress, so their influence on high-temperature creep is relatively small. Si and Mn contribute greatly to the room-temperature strength of the steel, but they are not conducive to the homogenization of the steel and are prone to unstable deviation at high temperatures, so they are not conducive to high-temperature creep performance. Cr, W, and V can form second phases with C and N in the steel, and the second phases can effectively pin dislocations and stacking faults in the steel, thereby slowing down the creep rate. Let the high-temperature creep factor in the steel be represented by Y. According to the different effects of alloying elements, the coefficient obtained through inductive analysis is 4.80% ≤ Y value, and Y value = (%C + 6 × %N) / 9 -

[0031] (8 × %Si + 3 × %Mn) / 7 + (2 × %Cr + 4 × %W + 11 × %V) / 4.

[0032] Compared with the prior art, through composition design, the present invention obtains a steel for magnesium smelting pots with a moderate Cr content and no Ni-containing composition system, which can withstand high-temperature deformation at 1280°C; the seamless steel pipe manufacturing process is adopted to improve the high-temperature strength and deformation resistance of the magnesium smelting pot, and the service life of the magnesium smelting pot at 1280°C is increased. Moreover, it meets the manufacturing requirements of large-capacity (diameter ≥ 900 mm) magnesium smelting pots, and the service life of the manufactured large-capacity magnesium smelting pots exceeds 2200 hours. Specific embodiments

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] Examples 1 - 4

[0035] A steel for magnesium smelting pots includes the mass percentage components shown in Table 1: The balance not shown in Table 1 is Fe and unavoidable impurities.

[0036] Comparative examples 1 - 4

[0037] A steel for magnesium smelting pots includes the mass percentage components shown in Table 1: The balance not shown in Table 1 is Fe and unavoidable impurities.

[0038] Table 1 Chemical Compositions (wt%) of Embodiments and Comparative Examples of the Present Invention

[0039]

[0040] The production methods of the steel for magnesium smelting pots in the above embodiments and comparative examples have the following process flow:

[0041] Converter smelting → LF furnace refining → RH vacuum degassing → Continuous casting of Φ1000mm round billets.

[0042] Converter smelting: Determine the oxygen content before tapping. During the tapping process, the operation of leaving steel is adopted to avoid slagging down;

[0043] LF furnace refining: Adjust elements such as C, Si, Mn, Cr, W, V, etc. to the target values;

[0044] RH vacuum degassing: The pure degassing time is ≥15 minutes to ensure that the [H] content after vacuum treatment is ≤1.5 ppm, avoid the appearance of white spots in the steel and cause hydrogen embrittlement phenomenon. Nitrogen is used as the lifting gas;

[0045] Continuous casting: Produce continuous casting billets with a diameter of 1000mm, with a superheat of 50°C, a casting speed of 0.098m / min, and an end electromagnetic stirring of 5.56Hz.

[0046] The manufacturing process of the magnesium smelting pots using the above embodiments and comparative examples is as follows: Round billet continuous casting → Punching → Round billet heating → Pipe piercing → Sizing → Heat treatment → Machining → Flaw detection → Packaging and warehousing. The key heat treatment process is as follows:

[0047] Normalizing: The heating temperature (T, °C) is 1100 - 1200°C, and the holding time (t1, min) is determined by the wall thickness (S, mm) of the steel pipe, t1 = 3.5×S, air cooling.

[0048] Tempering: The tempering temperature is 600 - 700°C, and the holding time (t2, min) is determined by the wall thickness (S, mm) of the steel pipe, t2 = 4×S, air cooling.

[0049] The heat treatment process parameters of the above embodiments and comparative examples are shown in Table 2.

[0050] Table 2 List of Heat Treatment Process Conditions of Embodiments and Comparative Examples of the Present Invention

[0051]

[0052] The performance detection methods are as follows:

[0053] Microstructure: Samples are taken at the 1 / 2 radius of the steel pipe for metallographic and grain size analysis.

[0054] Performance: Tensile, impact, and collapse resistance specimens are taken at the 1 / 2 radius of the steel pipe, and mechanical property tests are carried out with reference to GB / T228, GB / T229, and GB / T38822. The mechanical properties are shown in Table 3.

[0055] Table 3 List of Performance Detection of Examples and Comparative Examples of the Present Invention

[0056]

[0057] For Examples 1-4, the chemical composition and production method of the steel are properly controlled. Its chemical composition meets the requirements, and the strength and high-temperature creep performance of the steel are both good. The chemical composition of Comparative Example 1 meets the requirements of the present invention, but the A value is relatively high. Even after heat treatment according to the process of the present invention, the high-temperature performance at 1280°C of the product is relatively low, the collapse resistance at 1280°C is also reduced, and the service life is shortened. The chemical composition of Comparative Example 2 meets the requirements of the present invention, but the Y value is relatively low. Even after heat treatment according to the process of the present invention, the high-temperature performance at 1280°C of the product is relatively low, the collapse resistance at 1280°C is also reduced, and the service life is shortened. The chemical composition of Comparative Example 3 meets the requirements of the present invention, but the A value does not meet the requirements of the present invention, and it is not produced according to the heat treatment process of the present invention. The grain size of the product is relatively small, and the high-temperature performance also decreases. The chemical composition of Comparative Example 4 is properly controlled, but the heat treatment process is improper, resulting in a relatively large grain size and unsatisfactory overall performance.

[0058] The underlined data above do not meet the requirements of the present invention.

[0059] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. 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 labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A magnesium smelting tank steel, characterized in that: The magnesium smelting tank steel comprises the following components in mass percentage: C 0.40%~0.50%, Si 0.05%~0.20%, Mn 1.70%~2.00%, Cr 8.50%~9.50%, W0.40%~0.60%, Al 0.010%~0.025%, V 0.20%~0.50%, P≤0.020%, S≤0.010%, N0.040~0.070%, O≤0.0040%, and the rest are Fe and other unavoidable impurities.

2. The magnesium smelting tank steel according to claim 1, characterized in that: The composition of the magnesium smelting tank steel meets the following requirements: 99.25%≤12×%C+5×%Mn-4×%Si+9×%Cr+8.5×%W+2×%V+85×%N≤107.45%.

3. The magnesium smelting tank steel according to claim 1 or 2, characterized in that: The composition of the magnesium smelting tank steel also satisfies: 4.80%≤(%C+6×%N) / 9-(8×%Si+3×%Mn) / 7+(2×%Cr+4×%W+11×%V) / 4.

4. A method for producing magnesium smelting tank steel according to any one of claims 1 to 3, characterized in that: The production method comprises the following process flow: Electric arc furnace or converter smelting → LF furnace refining → RH or VD vacuum degassing → round billet continuous casting.

5. The production method according to claim 4, characterized in that: For round billet continuous casting, the billet diameter R and the casting speed v should meet the following conditions: 2 ×v=98000, where the unit of continuous casting billet diameter R is mm and the unit of casting speed v is m / min.

6. The production method according to claim 4 or 5, characterized in that: The terminal electromagnetic stirring frequency f and the continuous casting billet diameter R should meet the requirement of R / f=180, wherein the terminal electromagnetic stirring frequency f is in Hz and the continuous casting billet diameter R is in mm.

7. A method for manufacturing a 1280°C high temperature resistant deformable magnesium smelting tank, characterized in that: The magnesium smelting tank is manufactured using the steel for magnesium smelting tank according to any one of claims 1 to 3, wherein the manufacturing method includes heat treatment, and the heat treatment method includes normalizing and tempering.

8. The manufacturing method according to claim 7, characterized in that: The normalizing, normalizing: heating temperature T is 1100-1200°C, holding time t1 is determined by the steel pipe wall thickness S, t1=3.5×S, air cooling; wherein, the holding time t1 is in min, and the steel pipe wall thickness S is in mm.

9. The manufacturing method according to claim 7, characterized in that: The tempering, tempering: tempering temperature 600 ~ 700 ℃, holding time t2 is determined by the steel pipe wall thickness S, t2 = 4 × S, air cooling; wherein, the holding time t2 unit min, steel pipe wall thickness S unit mm.

10. A 1280°C high temperature resistant deformable magnesium smelting tank, characterized in that: The 1280°C high temperature deformable magnesium smelting tank is manufactured by the manufacturing method according to any one of claims 7 to 9, and the grain size of the steel pipe 1 / 2 wall thickness is 85-95μm; the high temperature yield strength of the steel pipe 1 / 2 wall thickness at 1280°C is ≥33MPa, and the tensile strength is ≥38MPa; The anti-collapse deformation capacity at 1280℃ is greater than 25MPa; the service life exceeds 2200 hours.

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