Heat-resistant steel for metal smelting equipment and preparation method thereof

Abstract

The invention relates to the technical field of metal smelting, and discloses a heat-resistant steel for metal smelting equipment and a preparation method thereof. The chemical composition of the heat-resistant steel for metal smelting equipment is as follows by mass percentage: C: 0.35-0.45%, Mn: 1.5-2.3%, Si: ≤0.15%, P: ≤0.025%, S: ≤0.015%, Cr: 8.5-10.0%, Mo: 0.4-1.0%, N: 0.040-0.080%, Ni: ≤0.40%, Nb: 0.04-0.08%, Al: ≤ 0.005%, Cu: ≤0.25%, Ti: ≤0.01%, Zr: ≤0.01%, the balance is Fe and unavoidable impurity elements. By controlling the range of alloying elements such as Cr, Mo, Nb, N and strictly controlling the upper limits of Cu, Al, Ti and Zr, good room temperature mechanical properties, high temperature tensile properties and long-lasting creep properties of heat-resistant steel for metal smelting equipment are guaranteed; at the same time, through tube billet smelting, steel tube rolling and heat treatment processes, the comprehensive performance of metal smelting equipment is improved, its service life is extended and its manufacturing cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of metal smelting, and discloses heat-resistant steel for metal smelting equipment and a preparation method thereof. Background Art

[0002] Metal smelting equipment has relatively stringent requirements on its own materials. Magnesium metal is a lightweight metal structural material with good metallic properties. It can be combined with a variety of metals to produce lightweight and high-strength alloy materials. It is widely used in aviation, aerospace, metallurgy, transportation and other departments. With the increase in demand for magnesium metal, higher requirements are also put forward for magnesium smelting equipment. In the existing technology, the main production processes for preparing magnesium are silicon thermal method and electrolysis method. In the process equipment of silicon thermal method magnesium smelting technology, the reduction tank is an important equipment unit. At present, the steel used for magnesium smelting reduction tank is mainly made of ZG35Cr24Ni7SiN, and the reduction tank is made of centrifugal casting tube. Since the reduction tank of this material contains a large amount of precious elements such as nickel and molybdenum, the furnace charge is expensive, so the production cost remains high. Due to the poor working conditions of the reduction tank, it is easy to cause severe oxidation corrosion and strength reduction under high temperature conditions. The tank is unstable at high temperature. The tank body is prone to creep, deformation and cracks, which makes it fail prematurely and the service life is only 60 to 70 days. The short life and high price of reduction tanks are a major problem in the magnesium smelting industry. Improving the comprehensive performance of reduction tanks, extending the service life of reduction tanks, and reducing the manufacturing cost of reduction tanks have become important issues in the magnesium smelting industry. Summary of the invention

[0003] The object of the present invention is to provide a heat-resistant steel for metal smelting equipment and a preparation method thereof, so as to improve the comprehensive performance of the metal smelting equipment, extend its service life and reduce its manufacturing cost.

[0004] In order to solve the above technical problems, the present invention provides a technical solution for heat-resistant steel for metal smelting equipment, as follows:

[0005] A heat-resistant steel for metal smelting equipment, the chemical composition of the heat-resistant steel for metal smelting equipment is as follows by mass percentage: C: 0.35-0.45%, Mn: 1.5-2.3%, Si: ≤ 0.15%, P: ≤ 0.025%, S: ≤ 0.015%, Cr: 8.5-10.0%, Mo: 0.4-1.0%, N: 0.040-0.080%, Ni: ≤ 0.40%, Nb: 0.04-0.08%, Al: ≤ 0.005%, Cu: ≤ 0.25%, Ti: ≤ 0.01%, Zr: ≤ 0.01%, and the balance is Fe and unavoidable impurity elements.

[0006] Furthermore, the room temperature yield strength Rp0.2 of the heat-resistant steel for metal smelting equipment is ≥ 700MPa, the tensile strength Rm is ≥ 850MPa, and the elongation A is ≥ 12%.

[0007] Furthermore, the heat-resistant steel for metal smelting equipment has a yield strength Rp0.2 ≥ 12MPa, a tensile strength Rm ≥ 20MPa, and an elongation A ≥ 40% at 1250°C.

[0008] Furthermore, the heat-resistant steel used for the metal smelting equipment has a lasting strength of not less than 3000 hours at 1250°C and 12Mpa continuous strength.

[0009] The present invention also provides a method for preparing heat-resistant steel for metal smelting equipment, comprising the following steps:

[0010] The above-mentioned heat-resistant steel raw materials for metal smelting equipment are smelted by using the smelting process of EAF electric furnace or BOF converter plus LF refining plus RH vacuum treatment, and the chemical composition range is precisely controlled, and the round tube billet is continuously cast;

[0011] Annealing the round tube billet, and after annealing, manufacturing a seamless steel tube by using a tube making method of oblique rolling, piercing or hot extrusion;

[0012] The rough pipe after sizing is normalized and tempered by using a car bottom type LPG heat treatment furnace.

[0013] Furthermore, after the heat treatment, the inner and outer surfaces of the steel pipe are roughened to a degree of 12.5 to 50 μm.

[0014] Furthermore, the round tube billet is annealed by adopting an annealing process of 870°C ±10°C furnace cooling.

[0015] Furthermore, the seamless steel pipe is manufactured by the pipe manufacturing method using oblique rolling, piercing or hot extrusion, comprising:

[0016] The round tube blank is heated in an annular heating furnace at a temperature of 1120° C. to 1180° C.

[0017] The round tube billet is perforated by a tapered roller perforator to form a rough tube. During the perforation, the temperature of the steel tube is controlled at 1150℃~1180℃.

[0018] The rough tube is subjected to uniform wall and diameter expansion rolling by a two-roller leveling machine to obtain a rough tube, and the temperature of the steel tube is controlled at 1020° C. to 1150° C. during the tube rolling;

[0019] Use a five-stand sizing machine to sizing the rough pipe after rolling.

[0020] Furthermore, the process of using a car bottom type LPG heat treatment furnace to perform normalizing and tempering heat treatment on the sized rough pipe comprises:

[0021] The rough pipe after sizing is subjected to normalizing and tempering heat treatment by using a car bottom type LPG heat treatment furnace. The normalizing heat treatment temperature is controlled at 1020℃~1050℃, the holding time is 1~1.5 minutes per 1mm wall thickness, and the total holding time is not less than 30 minutes. After the holding is completed, the pipe is taken out of the furnace and blown to be quickly cooled to below 93℃;

[0022] The tempering heat treatment temperature is controlled at 690℃~710℃, the holding time is 3~4 minutes per 1mm wall thickness, and the total holding time is not less than 90 minutes. After the holding is completed, it is taken out of the furnace and air-cooled to below 600℃, and straightened with heat.

[0023] Compared with the prior art, the heat-resistant steel for metal smelting equipment and the preparation method provided by the present invention ensure good room temperature mechanical properties, high temperature tensile properties and long-lasting creep properties of the heat-resistant steel for metal smelting equipment by selecting and controlling the range of steel chemical composition, controlling the range of alloy elements such as Cr, Mo, Nb, N and strictly controlling the upper limits of Cu, Al, Ti and Zr. Compared with the heat-resistant steel for magnesium smelting reduction tank in the prior art, the content of precious metals Cr and Ni in the material is reduced, and the production cost of the heat-resistant steel for magnesium smelting reduction tank is effectively reduced; at the same time, through tube billet smelting, steel tube rolling and heat treatment processes, the comprehensive performance of the metal smelting equipment is improved, its service life is extended, and its manufacturing cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a metallographic diagram of a heat-resistant steel for metal smelting equipment in one embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present invention clearer, the following will be described in detail with reference to the accompanying drawings. However, it will be appreciated by those skilled in the art that in the various embodiments of the present invention, many technical details are provided in order to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical scheme claimed for protection in the claims of the present application can be implemented.

[0026] The invention provides a heat-resistant steel for metal smelting equipment. The chemical composition of the heat-resistant steel for metal smelting equipment is as follows by mass percentage: C: 0.35-0.45%, Mn: 1.5-2.3%, Si: ≤ 0.15%, P: ≤ 0.025%, S: ≤ 0.015%, Cr: 8.5-10.0%, Mo: 0.4-1.0%, N: 0.040-0.080%, Ni: ≤ 0.40%, Nb: 0.04-0.08%, Al: ≤ 0.005%, Cu: ≤ 0.25%, Ti: ≤ 0.01%, Zr: ≤ 0.01%, and the balance is Fe and unavoidable impurity elements.

[0027] The heat-resistant steel for metal smelting equipment provided in the present invention ensures good room temperature mechanical properties of the heat-resistant steel for metal smelting equipment by controlling the chemical composition range of the heat-resistant steel, and obtains good high temperature tensile properties and long-lasting creep properties under 1250°C. After experimental verification, the room temperature yield strength Rp0.2 ≥ 700MPa, tensile strength Rm ≥ 850MPa, and elongation A ≥ 12% of the heat-resistant steel for metal smelting equipment provided in the present invention; at 1250°C, the yield strength Rp0.2 ≥ 12MPa, the tensile strength Rm ≥ 20MPa, and the elongation A ≥ 40%; the heat-resistant steel for metal smelting equipment has a long-lasting strength of not less than 3000 hours at 1250°C and 12Mpa pressure.

[0028] The mechanism for selecting the range of chemical composition content of heat-resistant steel for metal smelting equipment in the present invention application is as follows: by controlling the range of alloying elements such as Cr, Mo, Nb, and N, the precipitation strengthening effect of C and N compounds is strengthened, and the high-temperature creep ability is improved; and the residual content of microalloys such as Cu, Ti, Al, and Zr is strictly controlled. These elements are easy to form compounds with C and N, affecting the precipitation strengthening effect of Nb with C and N, and will form TiN compounds at the same time. Due to the high melting temperature of TiN, it cannot be dissolved back and precipitated secondary by heat treatment, and it is difficult to control its size. In order to avoid the formation of precipitates such as TiN, the content of Ti and Zr is reduced; Al and N have a strong tendency to combine, which has an adverse effect on the role of N elements in steel. Therefore, the Al content is controlled and the Al content is reduced as much as possible, so that the proportion of martensitic lath structure is higher, ensuring the high-temperature toughness and long-lasting creep performance of steel, while being able to meet the use temperature and efficiency requirements of magnesium smelting reduction tanks.

[0029] The present invention also provides a method for preparing heat-resistant steel for metal smelting equipment, comprising the following steps:

[0030] Billet smelting: adopt the smelting process of EAF electric furnace or BOF converter plus LF refining plus RH vacuum treatment, smelt the heat-resistant steel raw material for metal smelting equipment, accurately control its chemical composition range, and continuously cast it into round billets; other suitable process flows for smelting and casting can also be adopted; the round billets are annealed, and the annealing process is 870℃±10℃ furnace cooling.

[0031] Steel pipe rolling: After the round tube billet is annealed, the seamless steel pipe is made by oblique rolling, piercing or hot extrusion;

[0032] The round tube billet is heated in an annular heating furnace, and the heating temperature is controlled at 1120°C to 1180°C; preferably, the heating temperature is 1160°C to 1180°C.

[0033] The round tube billet is perforated by a tapered roller perforator to form a rough tube. During the perforation, the temperature of the steel tube is controlled at 1150℃~1180℃.

[0034] The rough pipe is rolled with a two-roller leveling machine to achieve uniform wall and diameter expansion. The temperature of the steel pipe is controlled at 1020℃~1150℃ during the rolling process to obtain the rough pipe.

[0035] A five-stand sizing mill is used to sizing the rough pipe after rolling; the leveling rolling has a large contact area and uniform deformation, which can eliminate the spiral lines on the inner and outer surfaces caused by the oblique rolling expansion to the greatest extent, improve the uniformity of the wall thickness of the steel pipe, and obtain steel pipes with excellent size and performance.

[0036] Heat treatment: The rough pipe after sizing is subjected to normalizing and tempering heat treatment in a car-bottomed LPG heat treatment furnace. The normalizing heat treatment temperature is controlled at 1020℃~1050℃, the holding time is 1~1.5 minutes for every 1mm wall thickness, and the total holding time is not less than 30 minutes. After the holding is completed, the pipe is taken out of the furnace and blown to be quickly cooled to below 93℃, and then tempered; the tempering heat treatment temperature is controlled at 690℃~710℃, the holding time is 3~4 minutes for every 1mm wall thickness, and the total holding time is not less than 90 minutes. After the holding is completed, the pipe is taken out of the furnace and air-cooled to below 600℃, and then straightened with temperature.

[0037] Preferably, in order to improve the laser cladding performance of the steel pipe, the inner and outer surfaces of the heat-treated steel pipe are roughened by grinding the surface of the steel pipe with a grinding wheel to a roughness of 12.5 to 50 μm, which is beneficial to increase the bonding strength of the cladding layer.

[0038] In an exemplary embodiment, a round tube billet is continuously cast through a smelting process of an EAF electric furnace, LF refining, and RH vacuum treatment. During the EAF electric furnace, LF refining, and RH vacuum treatment and continuous casting process, the operation specifications are strictly followed to make the chemical composition and grain structure of the steel uniform and the steel pure to ensure the performance of the steel pipe. The obtained tube billets are sampled and numbered to obtain tube billets with serial numbers 1 to 3. The chemical composition of the tube billets with serial numbers 1 to 3, excluding Fe and unavoidable impurity elements, is shown in Table 1:

[0039] Table 1 Chemical composition test record of No. 1-3 tube blank (unit: wt%)

[0040] Serial number C Mn Si P S Cr Mo N Ni Nb Al Cu Ti Zr 1 0.42 1.83 0.05 0.012 0.002 8.88 0.48 0.050 0.05 0.05 0.005 0.02 0.001 0.010 2 0.38 2.23 0.09 0.011 0.002 9.50 0.43 0.060 0.05 0.05 0.002 0.02 0.001 0.003 3 0.40 1.50 0.15 0.012 0.003 10.0 0 1.00 0.080 0.35 0.08 0.005 0.20 0.001 0.003

[0041] The chemical compositions of the tube blanks No. 1-3 are all within the range selected for the chemical composition of the heat-resistant steel for metal smelting equipment in the present invention.

[0042] The tube billets No. 1-3 are rolled and heat treated. During the steel tube rolling process, various process parameters such as tube billet heating temperature, piercing temperature, leveling final rolling temperature and sizing are controlled to meet the index requirements of steel tube process size and performance. The round tube billet is pierced by a tapered roller piercing machine to form a rough tube. The temperature of the steel tube is controlled at 1150℃~1180℃ during piercing. The rough tube is rolled with a two-roller leveling machine to expand the wall. The temperature of the steel tube is controlled at 1020℃~1150℃ during tube rolling to obtain a rough tube.

[0043] A five-stand sizing mill is used to sizing the rough pipe after rolling; the leveling rolling has a large contact area and uniform deformation, which can eliminate the spiral lines on the inner and outer surfaces caused by the oblique rolling expansion to the greatest extent, improve the uniformity of the wall thickness of the steel pipe, and obtain steel pipes with excellent size and performance.

[0044] A car-bottom LPG heat treatment furnace is used to normalize and temper the rough pipe after sizing. The normalizing heat treatment temperature is controlled at 1020℃~1050℃, the holding time is 1~1.5 minutes for every 1mm wall thickness, and the total holding time is not less than 30 minutes. After the holding is completed, the pipe is taken out of the furnace and blown to be quickly cooled to below 93℃, and then tempered; the tempering heat treatment temperature is controlled at 690℃~710℃, the holding time is 3~4 minutes for every 1mm wall thickness, and the total holding time is not less than 90 minutes. After the holding is completed, the pipe is taken out of the furnace and air-cooled to below 600℃, and then straightened with temperature.

[0045] After rolling and heat treatment, the pipe billets No. 1-3 are made into heat-resistant steel for metal smelting equipment, and their performance is tested. The test results are shown in Table 2.

[0046] Table 2 Performance test record of heat-resistant steel for metal smelting equipment made from tube billets No. 1-3

[0047] Serial number temperature Yield StrengthMpa Tensile strengthMpa Elongation% High temperature Yield StrengthMpa Tensile strengthMpa Elongation% 1 Room temperature 775 950 15 1250℃ 14 20 42 2 Room temperature 790 995 16 1250℃ 16 24 45 3 Room temperature 815 1025 13 1250℃ 14 21 42

[0048] It can be seen from Table 1 and Table 2 that the heat-resistant steel seamless steel pipe for metal alloy equipment provided by the present invention has uniform chemical composition, stable performance and good comprehensive performance. Under room temperature conditions, the yield strength Rp0.2 of the heat-resistant steel for metal smelting equipment is ≥ 700MPa, the tensile strength Rm ≥ 850MPa, and the elongation A ≥ 12%; under 1250°C conditions, the yield strength Rp0.2 of the heat-resistant steel for metal smelting equipment is ≥ 12MPa, the tensile strength Rm ≥ 20MPa, and the elongation A ≥ 40% at 1250°C; the sample No. 2 was selected for a 1250°C, 12Mpa continuous strength test, and the lasting strength exceeded 3000 hours. The present invention adopts the above-mentioned method for preparing heat-resistant steel for metal smelting equipment and controls the chemical composition of heat-resistant steel for metal smelting equipment, so that the upper limit of the use temperature of ferrite heat-resistant steel reaches 1250°C, which can meet the equipment requirements of metal smelting equipment, such as being used for metal smelting reduction tanks and related pipelines. In particular, compared with the material of magnesium smelting reduction tanks in the prior art, the high-temperature performance is more excellent and the service life is extended. At the same time, the use of precious metals Cr and Ni is reduced, and the manufacturing cost of the magnesium smelting reduction tank is reduced.

[0049] Those skilled in the art will appreciate that the above-mentioned embodiments are specific examples for implementing the present invention, and in actual applications, various changes may be made thereto in form and detail without departing from the spirit and scope of the present invention.

Claims

1. A heat-resistant steel for metal smelting equipment, characterized in that: The chemical composition of the heat-resistant steel for metal smelting equipment is as follows by mass percentage: C: 0.35~0.45%, Mn: 1.5~2.3%, Si: ≤0.15%, P: ≤0.025%, S: ≤0.015%, Cr: 8.5~10.0%, Mo: 0.4~1.0%, N: 0.040~0.080%, Ni: ≤0.40%, Nb: 0.04~0.08%, Al: ≤0.005%, Cu: ≤0.25%, Ti: ≤0.01%, Zr: ≤0.01%, and the balance is Fe and unavoidable impurity elements; the heat-resistant steel for metal smelting equipment has a yield strength Rp0.2 ≥12MPa, a tensile strength Rm ≥20MPa, and an elongation A ≥ 40%; the room temperature yield strength Rp0.2 of the heat-resistant steel for metal smelting equipment is ≥700MPa, the tensile strength Rm ≥ 850MPa, and the elongation A ≥ 12%.

2. The heat-resistant steel for metal smelting equipment according to claim 1, characterized in that: The heat-resistant steel used for the metal smelting equipment has a lasting strength of not less than 3000 hours at 1250° C. and 12 MPa continuous strength.

3. A method for preparing heat-resistant steel for metal smelting equipment, characterized in that: The steps include: The raw material of the heat-resistant steel for metal smelting equipment according to any one of claims 1 to 2 is smelted by adopting a smelting process of an EAF electric furnace or a BOF converter plus LF refining plus RH vacuum treatment, and its chemical composition range is precisely controlled, and the raw material is continuously cast into a round tube billet; Annealing the round tube billet, and after annealing, manufacturing a seamless steel tube by using a tube making method of oblique rolling, piercing or hot extrusion; The rough pipe after sizing is normalized and tempered by using a car bottom type LPG heat treatment furnace.

4. The method for preparing heat-resistant steel for metal smelting equipment according to claim 3, characterized in that: After heat treatment, the steel pipe is subjected to inner and outer surface roughness processing, with a roughness of 12.5-50 μm.

5. The method for preparing heat-resistant steel for metal smelting equipment according to claim 3, characterized in that: The round tube billet annealing process adopts 870°C ±10°C furnace cooling.

6. The method for preparing heat-resistant steel for metal smelting equipment according to claim 3, characterized in that: The round tube blank is annealed, and after annealing, a seamless steel tube is manufactured by a tube manufacturing method of oblique rolling and perforation, including: Before the round tube billet is annealed, the round tube billet is heated to 1120° C. to 1180° C. in an annular heating furnace; After the round tube billet is annealed, a tapered roller piercing machine is used to pierce the round tube billet at 1150℃~1180℃ to form a rough tube; The rough tube is subjected to uniform wall and diameter expansion rolling at 1020° C. to 1150° C. using a two-roller leveling machine to obtain a rough tube; Use a five-stand sizing machine to sizing the rough pipe after rolling.

7. The method for preparing heat-resistant steel for metal smelting equipment according to claim 3, characterized in that: The method of using a car bottom type LPG heat treatment furnace to perform normalizing and tempering heat treatment on the sized rough pipe comprises: The rough pipe after sizing is subjected to normalizing and tempering heat treatment by using a car bottom type LPG heat treatment furnace. The normalizing heat treatment temperature is controlled at 1020℃~1050℃, the holding time is 1~1.5 minutes per 1mm wall thickness, and the total holding time is not less than 30 minutes. After the holding is completed, the pipe is taken out of the furnace and blown to be quickly cooled to below 93℃; The tempering heat treatment temperature is controlled at 690℃~710℃, the holding time is 3~4 minutes per 1mm wall thickness, and the total holding time is not less than 90 minutes. After the holding is completed, it is taken out of the furnace and air-cooled to below 600℃, and straightened with heat.

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