LU501948B1 - Alloy-reinforced high-carbon steel casting material and manufacturing method thereof - Google Patents

Abstract

The present invention discloses an alloy-reinforced high-carbon steel casting material. The high-carbon steel casting material is manufactured by subjecting a high-carbon steel, a micro-grain silicon carbide-doped high-nickel austenitic stainless steel pretreatment material, large-grain silicon carbide, and manganese metal to high-temperature smelting. The casting has excellent low-temperature toughness performance and compressive strength at 0°C to -26°C (especially about -20°C), and is especially suitable for the manufacture of cryogenic valve body castings for fluid pipelines.

Description

ALLOY-REINFORCED HIGH-CARBON STEEL CASTING MATERIAL AND LU501948

MANUFACTURING METHOD THEREOF Technical Field

[0001] The present invention belongs to the field of casting materials, and in particular, relates to an alloy-reinforced high-carbon steel valve body casting material that can be used in a mild low-temperature environment, and a manufacturing method thereof. Background

[0002] In the field of valve body casting, with the rapid development of petrochemical enterprises, there has been a large market demand for valve bodies that can be used in mild low-temperature environments (0°C to -46°C, especially -20°C). In particular, in fluid-like (such as oil, gas, water, and chemical solutions) pipeline systems, valve bodies often involve high-speed flow and shut-off, which requires high strength and toughness of materials. Due to the limitation of fluid properties, such fluid-like valve bodies are commonly used in low-temperature (about -20°C) environments.

[0003] At present, stainless steel such as austenitic stainless steel is usually used as the main valve body material in the ultra-low-temperature environment (such as no higher than -100°C) in the market. However, considering factors such as mechanical strength and production cost, low-carbon steel is usually used as the main material for valve body castings at general low temperatures such as 0°C to -46°C. For example, LCB and LCC are ferritic steels commonly used for low-temperature valves in a temperature range of 0°C to -46°C, which can meet the specification requirements of ASTM A352/A352M.

[0004] For this temperature range, medium and high-carbon steels are usually not used in the prior art (such carbon steels have a C content usually of no less than 0.3%, or even as high as 1%); and even if steels with high carbon contents are used, corresponding treatment to reduce a carbon content is also required in subsequent processing.

[0005] This is because low-carbon steels can overcome the embrittlement problem to some extent at a low temperature due to excellent plasticity and toughness. While high-carbon steels (with a C content usually of no less than 0.3%) have prominent mechanical strength such as hardness, sufficient plasticity and toughness cannot ensured at a low temperature, which affects parameters such as elongation and low-temperature impact energy of valve body materials. When this type of materials are directly used to produce castings, it is prone to material defects, especially the tensile strength and low-temperature impact energy are not qualified, which cannot meet the use standard requirements.

[0006] However, in an operating environment of about -20°C, the use of low-carbon steels has 1 the following disadvantages: When a low-carbon steel is used as a raw material on large scaleU501948 the cost is relatively high, or the carbon reduction treatment is required subsequently, which increases the procedures and cost. In addition, when a low-carbon steel with a C content usually of no more than 0.3% such as LCB/LCC steel is used, such a hypoeutectoid steel has metallographic structures of pearlite and ferrite after heat treatment, and due to a low C content in the raw material, a proportion of pearlite in the structure after heat treatment is small, such that the plasticity is prominent, but the strength is low.

[0007] In the prior art, CN105385802A discloses a casting process for a low-temperature high-toughness ductile iron butterfly valve body, which involves cumbersome process steps, and adopts large-grain silicon carbide and various inoculants and nodularizers to achieve the mechanical properties. In the patent application 202010741430, a high-cost low-carbon steel material is used and too many alloy additive components are added, which results in a too-high cost, a complicated manufacturing process, and serious excess performance in an environment of about -20°C.

[0008] Therefore, it is one of the difficult problems to be solved in the prior art to avoid or reduce the brittleness of high-carbon steel casting materials at mild low temperatures (0°C to -26°C, especially about -20°C), such that the material can ensure adequate plasticity and toughness for valve body castings without the carbon reduction treatment and without the addition of excessive alloying components. Summary

[0009] In order to achieve the above objective of the present invention, the present invention provides an alloy-reinforced high-carbon steel casting material and a manufacturing method thereof. The casting has excellent plasticity and toughness and high low-temperature impact performance at 0°C to -26°C (especially -20 + 5°C), which is especially suitable for the manufacture of cryogenic valve body castings for fluid pipelines.

[0010] The high-carbon steel casting material is manufactured based on a specific alloy-doped carbon steel raw material, and the overall performance of a casting is adjusted by doping an alloy and a modifying component such as silicon carbide and manganese and adopting a specific heat treatment process, and components such as ferrite and content distribution proportions thereof in the structure are controlled to improve the low-temperature impact performance, which optimizes the plasticity and toughness and achieves the purpose of grain refinement (due to the high C content of the high-carbon steel raw material, the material has a relatively high strength, and thus it is generally not necessary to optimize the hardness).

[0011] In a first aspect, the present invention provides an alloy-reinforced high-carbon steel casting material. The high-carbon steel casting material is manufactured by subjecting a high-carbon steel, a micro-grain SiC-doped high-nickel austenitic stainless steel pretreatment 2 material, large-grain silicon carbide, and manganese metal to high-temperature smelting BE501948 1,400°C or higher.

[0012] Preferably, a ratio of a weight of the high-carbon steel to a total weight of the raw materials is preferably no less than 90 wt%.

[0013] Further preferably, based on a mass of the high-carbon steel raw material, proportions of the other components are as follows: the micro-grain SiC-doped high-nickel austenitic stainless steel pretreatment material: 3% to 10% and preferably 5% to 10% (namely, 5 wt% to 10 wt% of the high-carbon steel raw material), large-grain silicon carbide: 0.1% to 0.2%, and the manganese metal: 0.1% to 0.3% (preferably 0.2% to 0.3%).

[0014] The high-carbon steel has a carbon content of 0.3% to 0.9% and preferably 0.3% to

0.7%; and more preferably, in mass percentage, the high-carbon steel includes: 0.30% < C <

0.60%, 0.10% =< Si < 0.50%, 0.50% < Mn = 1.0%, S < 0.05%, P = 0.05%, Ni =< 0.50%, Cr < 0.50%, Mo < 0.20% (a total content of Ni, Cr, and Mo is less than 1%), and the remaining of Fe.

[0015] In mass percentage, the high-nickel austenitic stainless steel raw material includes no more than 0.1% of carbon (C); preferably, in mass percentage, the high-nickel austenitic stainless steel raw material includes: C < 0.05%, Cr: 15% to 18%, Ni: 12% to 15%, Mo: 2% to 3%, Si: 0.5% to 1%, and the remaining of iron (Fe) and inevitable impurities; and the impurities include P < 0.03%, S < 0.03%, and Sn + As + Pb < 0.03%.

[0016] The large-grain silicon carbide has a particle size of 100 um to 500 um and preferably 100 um to 300 um; and the micro-grain silicon carbide has a particle size of 5 um to 50 um and preferably 10 um to 30 um.

[0017] The micro-grain SiC-doped high-nickel austenitic stainless steel pretreatment material is prepared through the following steps (namely, a stainless steel pretreatment method of doping micro-grain SiC):

[0018] 1) in a vacuum smelting furnace equipped with a stirring device, placing 100 parts of an austenitic stainless steel alloy at a furnace bottom and placing 10 to 30 parts (preferably 10 to 20 parts) of a micro-grain silicon carbide powder in an upper feeding bin, sealing, and vacuumizing;

[0019] 2) heating to allow the austenitic stainless steel alloy to be completely melted, and starting to stir a molten alloy for 3 min to 10 min at a stirring rate of 200 rpm to 300 rpm; raising a temperature of a furnace body appropriately (preferably raising by 100°C to 150°C) and slowly feeding the micro-grain silicon carbide powder in batches, where a feeding speed and a feeding area are controlled such that the feeding is as uniform as possible (the feeding is preferably conducted by fully covering a melt area); and after the feeding is completed, maintaining the temperature of the furnace body and further stirring for 15 min to 30 min; and

[0020] 3) reducing the temperature appropriately (preferably reducing by 50°C to 100°C) and reducing the stirring rate to 100 r/min to 150 r/min to conduct low-speed stirring for 10 min to 15 min; stopping the stirring and holding the temperature for 15 min to 30 min; introducing an inert 3 gas such as argon to allow a pressure in the furnace to rise to and stabilize at atmospheri¢/501948 pressure, taking a product out from the furnace, and pouring the product into a mold; air-cooling the product to 500°C to 600°C, holding the temperature for 4 h to 6 h, and further air-cooling the product to about 100°C; and quickly cooling the product to about room temperature through water quenching, and mechanically pulverizing an obtained alloy ingot into particles for later use, which preferably have a particle size of 0.5 mm to 10 mm.

[0021] In a second aspect, the present invention also provides a manufacturing method of the alloy-modified high-carbon steel casting, including the following steps:

[0022] 1) raw material smelting:

[0023] S1: weighing the following materials according to predetermined mass proportions: the high-carbon steel, the micro-grain SiC-doped high-nickel austenitic stainless steel pretreatment material, the large-grain silicon carbide, and the manganese metal (where the main raw material (high-carbon steel) is pretreated by rust removal or surface polishing to remove surface impurities);

[0024] S2: in a nitrogen atmosphere, heating the high-carbon steel to 1,400°C or higher in an electric furnace for melting, and successively adding the micro-grain SiC-doped high-nickel austenitic stainless steel pretreatment material, the large-grain silicon carbide, and the manganese metal powder in batches under stirring; after the feeding is completed, heating to 1,500°C or higher (preferably 1,550°C to 1,580°C), and further stirring for 10 min to 15 min; and stopping the stirring, and allowing a resulting melt to stand for 5 min to15 min to obtain a molten alloy raw material;

[0025] where based on the mass of the high-carbon steel raw material, proportions of the other components are as follows: the micro-grain SiC-doped high-nickel austenitic stainless steel pretreatment material: 5% to 10% (namely, 5 wt% to 10 wt% of the high-carbon steel raw material), the large-grain silicon carbide: 0.1% to 0.2%, and the manganese metal: 0.2% to

0.3%;

[0026] in this step, since the smelting is conducted in an inert gas atmosphere, a deoxidation procedure may not be required; and optionally, other tempering treatments such as desulfurization or slag-forming is conducted if necessary;

[0027] in this step, component and impurity contents of the high-nickel austenitic stainless steel and high-carbon steel raw materials are controlled to meet the aforementioned requirements of the present invention; when necessary, a high-carbon steel raw material melt in which contents of particular components do not meet standards is subjected to tempering treatments such as slag-forming or desulfurization to make an impurity content meet the requirements; and various tempering treatment technologies for adjusting impurities are known in the art and will not be repeated here;

[0028] through strict control of raw materials, the tempering treatment required in subsequent 4 treatment steps can be reduced or avoided, thereby greatly simplifying the casting procedurés/501948 and improving the manufacturing efficiency;

[0029] 2) pouring: cooling the molten alloy to 1,450°C to 1,480°C, pouring, and cooling to 500°C or lower (preferably 400°C to 500°C); and separating a resulting casting, removing a casting riser, and smoothing a surface of the casting to obtain a molded blank;

[0030] 3) heat-treatment tempering: conducting the double heat treatment of specific S1 and S2 below in a heat treatment furnace:

[0031] S1: gradient heating-tempering treatment:

[0032] placing the molded blank in an electric heat treatment furnace, heating to 650°C to 700°C at a heating rate of 90°C/h to 100°C/h, and holding the temperature for 0.5 h to 1 h; heating to 820°C to 870°C at a heating rate of 120°C/h to 150°C/h, holding the temperature for 2 h to 3 h, and stopping the heating; naturally cooling the blank to 600°C to 620°C in the furnace, and air-cooling the blank to 100°C to 150°C outside the furnace; and heating to 700°C + 10°C at a constant heating rate of 60°C/h to 90°C/h, holding the temperature for 1 h to 2 h, and air-cooling the blank to room temperature outside the furnace;

[0033] S2: secondary tempering:

[0034] heating the above tempered blank to 700°C to 750°C at a heating rate of 100°C/h to 120°C/h, holding the temperature for 1 h to 2 h, and quenching with water to 100°C to 200°C; heating to 700°C + 10°C at a heating rate of 100°C/h to 120°C/h, holding the temperature for 2 h to 3 h, and stopping the heating; and after a temperature in the furnace naturally drops to 500°C + 20°C, taking the blank out from the furnace, and naturally cooling the blank to room temperature to obtain a molded product.

[0035] In a third aspect, the present invention also provides a casting product manufactured by the above method, especially a valve body casting.

[0036] In a fourth aspect, the present invention also provides use of the above alloy-modified high carbon steel casting in the manufacture of a valve body casting for a low-temperature environment, where the low-temperature environment is preferably at 0°C to -26°C.

[0037] The present invention has the following beneficial technical effects.

[0038] 1) The valve body casting made from a high-carbon steel material according to the present invention has excellent plasticity and toughness, which is suitable for mild low-temperature environments at 0°C to -26°C (with excellent low-temperature impact toughness especially at about -20°C) and is especially suitable for the manufacture of valve body castings for fluid pipelines.

[0039] 2) By reinforcing a low-cost, high-strength, and high-carbon steel raw material with an alloy, adaptively determining a specific heat treatment method, and controlling components such as ferrite and content distribution thereof in a structure, the present invention achieves the purpose of plasticity and toughness optimization and grain refinement, avoids the unstable low-temperature impact toughness of the high-carbon steel, and improves the quality of l4/501948 low-temperature valve casting, which has an average tensile strength = 600 MPa, an elongation = 20%, and an average impact index (Ak value) = 50 J at 26°C, and can be used to meet the large demand of enterprises and markets in fields including petrochemicals and pharmaceutical chemicals for mild low-temperature valves.

[0040] 3) In the present invention, there is no need to add a variety of alloys, and a silicon carbide-doped stainless steel is adopted as the main modification material. Since less components are added, the segregation of various alloying elements added in the steel structure can be effectively reduced, making the organizational structure more delicate and uniform. In addition, the manufacturing process in an oxygen-free atmosphere is simple, avoids tedious tempering procedures such as slag removal and deoxidation, and thus is suitable for mass production.

[0041] 4) In the manufacturing process of the present invention, the large-grain silicon carbide powder is fed in batches through multi-coverage, which avoids the accumulation, agglomeration, or gas entrapment of the powder on a melt, effectively avoids the generation of bubbles, and improves the quality of a casting. In addition, the stainless steel alloy is modified by micro-grain silicon carbide at other parts, such that the added silicon carbide is distributed uniformly, the influence of the agglomeration or surface gas caused by the addition of silicon carbide on melt properties is further reduced, and the bubble effect caused by the addition of the micro-grain powder is effectively removed to achieve the purpose of uniform dispersion without high-speed stirring. Moreover, shapes of large and small particles correspond to smelting of raw materials with different sizes and properties, with uniform quality. Detailed Description of the Embodiments

[0042] The following specific examples are only used to illustrate the present invention, and do not constitute any limitation to the protection scope.

[0043] Preparation Example 1

[0044] Preparation of a micro-grain SiC-doped high-nickel austenitic stainless steel pretreatment material

[0045] 1) In a vacuum smelting furnace equipped with a stirring device, 65 kg of an austenitic stainless steel (in mass percentage, the austenitic stainless steel included: C: 0.03%, Cr: 16.2%, Ni: 14.5%, Mo: 2.3%, Si: 0.6%, and the remaining of iron and inevitable impurities; and the impurities included: P < 0.03%, S < 0.03%, and Sn + As + Pb < 0.03%) alloy was placed at a furnace bottom and 13 kg of a micro-grain silicon carbide powder (which had an average particle size of 30 um and a silicon content of 60% to 65%) was placed in an upper feeding bin, and the furnace was sealed and vacuumized.

6

[0046] 2) The austenitic stainless steel alloy was heated to about 1,580°C such that tHé/501948 austenitic stainless steel alloy was completely melted, and a molten alloy was stirred for 5 min at a stirring rate of 260 rpm; a temperature of a furnace body was raised appropriately (raised by about 50°C) and the micro-grain silicon carbide powder was slowly fed in batches, where the micro-grain silicon carbide powder was uniformly fed by fully covering a melt area; and after the feeding was completed, the temperature of the furnace body was maintained and a resulting mixture was further stirred for 15 min.

[0047] 3) The temperature was reduced to 1,530°C and the stirring rate was reduced to 120 r/min to conduct low-speed stirring for 10 min; the stirring was stopped and the temperature was held for 15 min; argon was introduced to allow a pressure in the furnace to rise to and stabilize at atmospheric pressure, and a product was taken out from the furnace, poured into a mold, air-cooled to 500°C to 550°C and kept at the temperature for 4 h, further air-cooled to about 100°C, and quickly cooled to room temperature through water quenching; and an obtained alloy ingot was mechanically pulverized into particles of 1 mm to 5 mm for later use.

[0048] Example 1

[0049] A manufacturing method of the alloy-modified high-carbon steel casting was provided, including the following steps.

[0050] 1) Raw material smelting:

[0051] S1: The following materials were weighed according to predetermined mass proportions: about 0.8 t of a commercially-available dry high-carbon steel subjected to surface cleaning treatment (in mass percentage, the high-carbon steel included about: C: 0.6%, Si: 0.40%, Mn:

0.8%, S < 0.05%, P < 0.05%, Ni: 0.35%, Cr: 0.3%, Mo: 0.16%, and the remaining of Fe and inevitable impurities), 62 kg of the micro-grain SiC-doped high-nickel austenitic stainless steel pretreatment material prepared in Preparation Example 1, 1.5 kg of large-grain silicon carbide (with an average particle size of about 0.2 mm), and 2 kg of manganese.

[0052] S2: Air in an electric furnace was replaced with nitrogen, the high-carbon steel was heated to 1,400°C or higher in the electric furnace for melting, and the micro-grain SiC-doped high-nickel austenitic stainless steel pretreatment material, the large-grain silicon carbide, and the manganese metal powder (with a particle size of about 0.5 mm to 1 mm) were successively added in batches (4 to 5 batches) under stirring (that is, the stainless steel pretreatment material was first added and then the manganese powder was added); after the feeding was completed, a resulting mixture was heated to 1,560°C and further stirred for 10 min; and the stirring was stopped, and a resulting melt was allowed to stand for 5 min to obtain a molten alloy raw material.

[0053] 2) Pouring: The molten alloy was cooled to 1,460°C, poured, and cooled to 450°C to 500°C; and a resulting casting was separated, a casting riser was removed, and a surface of the casting was smoothed to obtain a molded blank.

7

[0054] 3) Heat-treatment tempering: The following double heat treatment was conducted inl&/501948 heat treatment furnace.

[0055] S1: Gradient heating-tempering treatment:

[0056] The molded blank was placed in an electric heat treatment furnace, heated to 680°C at a heating rate of 90°C/h and kept at the temperature for 0.5 h, and heated to 850°C at a heating rate of 120°C/h and kept at the temperature for 2 h, and then the heating was stopped; and the blank was naturally cooled to 600°C in the furnace, air-cooled to 100°C outside the furnace, heated to 700°C + 10°C at a constant heating rate of 60°C/h and kept at the temperature for 2 h, and air-cooled to room temperature outside the furnace.

[0057] S2: Secondary tempering:

[0058] The above tempered blank was heated to 700°C at a heating rate of 120°C/h and kept at the temperature for 1 h, quenched with water to about 120°C, and heated to 700°C + 10°C at a heating rate of 120°C/h and kept at the temperature for 3 h, and the heating was stopped; and after a temperature in the furnace naturally dropped to about 500°C, the blank was taken out from the furnace and naturally cooled to room temperature to obtain a molded product.

[0059] Example 2

[0060] 1) Raw material smelting:

[0061] S1: The following materials were weighed according to predetermined mass proportions: about 0.8 t of a commercially-available dry high-carbon steel subjected to surface cleaning treatment (with a composition the same as above), 80 kg of the micro-grain SiC-doped high-nickel austenitic stainless steel pretreatment material prepared in Preparation Example 1,

1.6 kg of large-grain silicon carbide, and 2.3 kg of manganese.

[0062] S2: Air in an electric furnace was replaced with nitrogen, the high-carbon steel was heated in the electric furnace for melting, and the micro-grain SiC-doped high-nickel austenitic stainless steel pretreatment material, the large-grain silicon carbide, and the manganese metal powder were successively added in batches (5 batches) under stirring; after the feeding was completed, a resulting mixture was heated to 1,550°C and further stirred for 10 min; and the stirring was stopped, and a resulting melt was allowed to stand for 5 min to obtain a molten alloy raw material.

[0063] 2) Pouring: The molten alloy was cooled to 1,480°C, poured, and cooled to 450°C to 500°C; and a resulting casting was separated, a casting riser was removed, and a surface of the casting was smoothed to obtain a molded blank.

[0064] 3) Heat-treatment tempering: The following double heat treatment was conducted in a heat treatment furnace.

[0065] S1: Gradient heating-tempering treatment:

[0066] The molded blank was placed in an electric heat treatment furnace, heated to 700°C at a heating rate of 96°C/h and kept at the temperature for 1 h, and heated to 870°C at a heating rate 8 of 150°C/h and kept at the temperature for 3 h, and then the heating was stopped; and the blahk/501948 was naturally cooled to 600°C in the furnace, air-cooled to about 150°C outside the furnace, heated to 700°C + 5°C at a constant heating rate of 90°C/h and kept at the temperature for 2 h, and air-cooled to room temperature outside the furnace.

[0067] S2: Secondary tempering:

[0068] The above tempered blank was heated to 750°C at a heating rate of 120°C/h and kept at the temperature for 1 h to 2 h, quenched with water to about 100°C to 150°C, and heated to 700°C + 5°C at a heating rate of 120°C/h and kept at the temperature for 3 h, and the heating was stopped; and after a temperature in the furnace naturally dropped to about 500°C, the blank was taken out from the furnace and naturally cooled to room temperature to obtain a molded product.

[0069] Comparative Example 1

[0070] Manufacturing steps in this comparative example were the same as that in Example 1, except that, in step 1), an equal amount of a high-nickel austenitic stainless steel raw material without any treatment was used instead of the micro-grain SiC-doped stainless steel pretreatment material in this comparative example, and no additional large-grain silicon carbide was added.

[0071] Comparative Example 2

[0072] Manufacturing steps 1) and 2) were the same as that in Example 1, except that the heat-treatment tempering in step 3) did not adopt the secondary tempering, but only adopted $1, namely, gradient heating-tempering treatment.

[0073] Effect Example:

[0074] The low-temperature toughness performance test method (ASTMA370) in the patent application 202010741430 was adopted to conduct a low-temperature toughness test, which was specifically as follows.

[0075] The high-carbon steel raw material in Example 1 was adopted as a basic control sample, and the steel was melted and casted into a sample blank (the rest sample blanks had the same specifications). Except for the basic control sample, sample blanks of the rest test groups were treated by a heat-treatment step in a corresponding example, and 5 samples were taken from each group (the optimal value, the worst value, and the average value were taken for comparison) (except for the basic control sample, the samples of the example and comparative example groups had an average tensile strength exceeding 600 MPa (which meets the requirement that a valve body casting should have a strength greater than 450 MPa) and an elongation exceeding 20%, and thus met the requirements of valve body casting materials, which will not be compared here).

[0076] A low-temperature toughness performance test was conducted for the examples according to the standard ASTM A370, and a low-temperature impact toughness value (Ak value, 9

J-cm?) was measured at -26°C on an impact tester. Results were shown in the table below. LU501948

[0077] Table 1 Low-temperature toughness performance of casting samples

[0078] Worst Ak value Average Ak value Optimal Ak value

[0079] In summary, the high-carbon steel castings of the example group of the present invention involve specific raw material compositions, manufacturing processes, and suitable heat-treatment processes, and with excellent strength and mechanical properties, the high-carbon steel castings have significantly-improved low-temperature impact toughness values at -26°C and are suitable for the manufacture of valve body castings for fluid pipelines in an environment of about -20°C.

[0080] The above examples are merely preferred examples of the present invention, and do not limit the present invention in any form. Any simple modifications and equivalent changes and modifications made to the above examples according to the technical essence of the present invention by any person skilled in the art without departing from the content of the technical solutions of the present invention shall fall within the scope of the present invention.

Claims (8)

Claims LU501948

1. An alloy-reinforced high-carbon steel casting material, characterized in that the high-carbon steel casting material is manufactured by subjecting a high-carbon steel, a micro-grain silicon carbide-doped high-nickel austenitic stainless steel pretreatment material, large-grain silicon carbide, and manganese metal to high-temperature smelting at 1,400°C or higher; and preferably, based on a mass of the high-carbon steel raw material, mass percentages of the other components are as follows: the micro-grain silicon carbide-doped high-nickel austenitic stainless steel pretreatment material: 5% to 10%, the large-grain silicon carbide: 0.1% to 0.2%, and the manganese metal: 0.2% to 0.3%.

2. The high-carbon steel casting material according to claim 1, characterized in that the high-carbon steel has a carbon content of 0.3% to 0.9%, and preferably 0.3% to 0.7%; and more preferably, in mass percentage, the high-carbon steel comprises: 0.30% <= C < 0.60%, 0.10% = Si < 0.50%, 0.50% < Mn < 1.0%, S < 0.05%, P < 0.05%, Ni < 0.50%, Cr < 0.50%, Mo < 0.20%, and the remaining of Fe, wherein a total content of Ni, Cr, and Mo is less than 1%.

3. The high-carbon steel casting material according to claim 1, characterized in that in mass percentage, the high-nickel austenitic stainless steel raw material comprises no more than 0.1% of carbon; preferably, in mass percentage, the high-nickel austenitic stainless steel raw material comprises: C < 0.05%, Cr: 15% to 18%, Ni: 12% to 15%, Mo: 2% to 3%, Si: 0.5% to 1%, and the remaining of iron and inevitable impurities; and the impurities comprise P < 0.03% and S =

0.03%.

4. The high-carbon steel casting material according to claim 1, characterized in that the large-grain silicon carbide has a particle size of 100 um to 300 um, and the micro-grain silicon carbide has a particle size of 5 um to 50 um.

5. The high-carbon steel casting material according to claim 1, characterized in that the micro-grain silicon carbide-doped high-nickel austenitic stainless steel pretreatment material is prepared through the following steps: 1) in a vacuum smelting furnace equipped with a stirring device, placing 100 parts of an austenitic stainless steel alloy at a bottom of the vacuum smelting furnace, and placing 10 to 30 parts of a micro-grain silicon carbide powder in an upper feeding bin, followed by sealing and vacuumizing; 11

2) heating to allow the austenitic stainless steel alloy to be completely melted to obtainla/501948 molten alloy, and starting to stir the molten alloy for 3 min to 10 min at a stirring rate of 200 rpm to 300 rpm; raising a temperature of a furnace body appropriately and slowly feeding the micro-grain silicon carbide powder in batches, wherein a feeding speed and a feeding area are controlled to achieve uniform feeding, and after the feeding is completed, maintaining the temperature of the furnace body and further stirring for 15 min to 30 min; and 3) reducing the temperature by 50°C to 100°C and reducing the stirring rate to 100 r/min to 150 r/min to conduct low-speed stirring for 10 min to 15 min; stopping the stirring and holding the temperature for 15 min to 30 min; introducing an inert gas to allow a pressure in the furnace to rise to and stabilize at atmospheric pressure, taking a product out from the furnace, and pouring the product into a mold; air-cooling the product to 500°C to 600°C, holding the temperature for 4 h to 6 h, and further air-cooling the product to about 100°C; and quickly cooling the product to about room temperature through water quenching to obtain an alloy ingot, and mechanically pulverizing the alloy ingot into particles for later use.

6. A method for manufacturing a casting based on the high-carbon steel casting material according to any one of claims 1 to 5, characterized by comprising the following steps: 1) smelting raw materials: S1: weighing the following materials according to predetermined mass proportions: the high-carbon steel, the micro-grain silicon carbide-doped high-nickel austenitic stainless steel pretreatment material, the large-grain silicon carbide, and the manganese metal, wherein based on the mass of the high-carbon steel raw material, proportions of the other components are as follows: the micro-grain silicon carbide-doped high-nickel austenitic stainless steel pretreatment material: 5% to 10%, the large-grain silicon carbide: 0.1% to 0.2%, and the manganese metal:

0.2% to 0.3%; S2: in a nitrogen atmosphere, heating the high-carbon steel as a main raw material to 1,400°C or higher in an electric furnace for melting, and successively adding the micro-grain silicon carbide-doped high-nickel austenitic stainless steel pretreatment material, the large-grain silicon carbide, and the manganese metal powder in batches under stirring; after the adding is completed, heating to 1,500°C or higher, and further stirring for 10 min to 15 min; and stopping the stirring, and allowing a resulting melt to stand for 5 min to15 min to obtain a molten alloy raw material; 2) pouring: cooling the molten alloy raw material to 1,450°C to 1,480°C for pouring, and after the pouring, cooling a resulting casting to 500°C or lower, and separating the resulting casting, 12 removing a casting riser, and smoothing a surface of the casting to obtain a molded blank; ~~ LU501948 3) heat-treatment tempering: conducting the following double heat treatment in a heat treatment furnace: S1: gradient heating-tempering treatment: placing the molded blank in an electric heat treatment furnace, heating to 650°C to 700°C at a heating rate of 90°C/h to 100°C/h, and holding the temperature for 0.5 h to 1 h; then heating to 820°C to 870°C at a heating rate of 120°C/h to 150°C/h, holding the temperature for 2 h to 3 h, and then stopping the heating; naturally cooling the blank to 600°C to 620°C in the furnace, and then air-cooling the blank to 100°C to 150°C outside the furnace; and then heating to 700°C + 10°C at a constant heating rate of 60°C/h to 90°C/h, holding the temperature for 1 h to 2 h, and air-cooling the blank to room temperature outside the furnace; S2: secondary tempering: heating the above tempered blank to 700°C to 750°C at a heating rate of 100°C/h to 120°C/h, holding the temperature for 1 h to 2 h, and quenching with water to 100°C to 200°C; then heating to 700°C + 10°C at a heating rate of 100°C/h to 120°C/h, holding the temperature for 2 h to 3 h, and then stopping the heating; and after a temperature in the furnace naturally drops to 500°C + 20°C, taking the blank out from the furnace, and naturally cooling the blank to room temperature to obtain a finished casting.

7. A finished casting manufactured by the method according to claim 6.

8. The casting according to claim 7, characterized in that the casting is a valve body casting for a low-temperature environment of 0°C to -26°C.

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