Method for producing high-pressure fuel common rail 304 stainless steel for engine

Abstract

The application discloses a production method of engine high-pressure fuel common rail 304 stainless steel. The smelting method of the engine high-pressure fuel common rail 304 stainless steel comprises electric arc furnace smelting, argon-oxygen converter blowing, ladle refining and continuous casting, and the chemical components are as follows in percentage by mass: 0.02% <= C <= 0.07%, 0.4% <= Si <= 0.6%, 0.1% <= Mn <= 2.0%, 0.025% <= P <= 0.04%, 0.015% <= S <= 0.03%, 18% <= Cr <= 19%, 8% <= Ni <= 8.5%, and the balance is iron and inevitable impurities. The electric arc furnace smelting, argon-oxygen converter blowing, ladle refining and continuous casting process is adopted, the machining tool life of the 304 stainless steel is effectively improved by accurately controlling the S and P contents, and the steel is prevented from forming large-size inclusions due to the overlong extension of inclusions in the steel, so that the anti-leakage performance is achieved.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel technology, and in particular relates to a production method of 304 stainless steel suitable for high-pressure fuel common rail in engines. Background Technology

[0002] In recent years, gasoline-powered vehicles have faced intense competition from new energy vehicles. Furthermore, due to changing trends in domestic and international trade, many foreign-invested, joint-venture, and domestically-owned automobile companies in China are experiencing pressure regarding raw material supply. There is a gradual shift from importing auto parts to producing them domestically and using locally sourced raw materials. Stainless steel materials for automotive engine common rails are one such example. High-pressure common rails are primarily used to connect fuel lines and cylinders, and are designed to withstand high-pressure environments.

[0003] Currently, a large proportion of common fuel rails in engines are made by brazing machined parts. To ensure quality and keep production costs low, stainless steel with good machinability and corrosion resistance is typically used in the manufacture of common fuel rails, primarily in automotive engine manufacturing and other fields.

[0004] In existing technologies, 304 stainless steel produced through smelting methods fails the high-pressure (450 atm) helium gas testing process when used to manufacture common rail fuel systems. The leakage rate exceeds 10%, rendering the system unusable. Manufacturing such systems as finished fuel rails results in significant cost losses, and the installation of these products on vehicles could lead to fuel leaks. Furthermore, 304 stainless steel produced through conventional smelting methods often has uncontrolled sulfur content, resulting in low levels that cause difficulties in chip removal and rapid tool wear during machining. Summary of the Invention

[0005] To at least partially solve the technical problems existing in the prior art, the present invention provides a production method for 304 stainless steel suitable for high-pressure fuel common rail in engines.

[0006] The present invention relates to a production method for 304 stainless steel suitable for common rail fuel in engines, characterized in that the smelting method for 304 stainless steel suitable for common rail fuel in engines includes: electric arc furnace smelting - argon-oxygen furnace blowing - ladle refining - continuous casting - rolling, wherein the chemical composition by mass percentage is: 0.02%≤C≤0.07%, 0.4%≤Si≤0.6%, 0.1%≤Mn≤2.0%, 0.025%≤P≤0.04%, 0.015%≤S≤0.03%, 18%≤Cr≤19%, 8%≤Ni≤8.5%, with the balance being iron and unavoidable impurities;

[0007] Electric arc furnace smelting: Smelting stainless steel in an electric arc furnace;

[0008] Argon-oxygen furnace blowing: After adjusting the composition of stainless steel smelted in electric arc furnace to the required range for 304 stainless steel except for sulfur, silicon is added to 0.4-0.6% for preliminary deoxidation, carbon is controlled at 0.03-0.07%, sulfur is removed to below 0.005%, and slag is skimmed off when tapping the steel until the slag surface thickness is below 50mm.

[0009] Steel ladle refining: After argon-oxygen furnace blowing, the slag basicity of the molten steel is adjusted to 2.0-2.5. 1-2 kg / ton of steel-aluminum agent is added to adjust the slag to be grayish-white or white. 0.2-0.3 kg / ton of calcium wire or calcium silicate wire is fed in. Iron sulfide is added to adjust the sulfur content to 0.015-0.03%, and iron phosphate is added to adjust the phosphorus content to 0.025-0.04%. Bottom blowing and stirring are carried out during the feeding process, and the steel is allowed to stand before leaving the station.

[0010] Continuous casting: Molten steel that has been left to stand is continuously cast into steel billets under electromagnetic stirring, with a billet casting speed ≤400kg / min;

[0011] Rolling: The billet is heated to a temperature above 1250℃ and the final rolling temperature is above 1100℃. The rolling specification is Φ15~40mm to avoid excessive elongation of inclusions during the rolling process.

[0012] Furthermore, in the above-mentioned production method for 304 stainless steel suitable for high-pressure fuel common rail in engines, during the ladle refining process, a strong stirring mode is adopted, and the stirring time is 10 to 15 minutes, so that the sulfur element is evenly distributed in the molten steel and the resulting manganese sulfide is finely dispersed.

[0013] Furthermore, in the above-mentioned production method for 304 stainless steel suitable for common rail fuel in engines, during the ladle refining process, the bottom-blown gas is argon, with an argon flow rate of 200-300 L / min.

[0014] Furthermore, in the above-mentioned production method for 304 stainless steel suitable for common rail fuel in engines, the settling time during the ladle refining process is ≥20 min.

[0015] Furthermore, in the above-mentioned production method of 304 stainless steel for common rail fuel in engines, a heat replenishment technique is used during the rolling process.

[0016] The method of the present invention for producing 304 stainless steel for common rail fuel in engines has the following advantages and beneficial effects:

[0017] By controlling the sulfur and phosphorus content, machinability was improved. The sulfur and phosphorus content levels and cutting performance are comparable to imported materials and superior to ordinary 304 stainless steel, extending cutting tool life by more than three times, significantly improving machining efficiency and reducing costs. Furthermore, a special smelting process was employed, with the refining process ensuring uniform and fine distribution of inclusions in the steel, allowing sufficient time for the removal of large inclusions. This prevents helium leaks caused by excessively large inclusions, effectively reducing the helium leak rate to below 0.02%, which is superior to the typical helium leak rate of 0.02-0.80% for domestic and international oil rail steel. The content of various precious alloying elements was controlled at low levels, omitting the addition of some imported precious metals such as Cu and Mo, ensuring excellent performance at a low cost. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for further understanding of the embodiments of the present invention and constitute a part of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0019] Figure 1 It is an inclusion in free-machining, leak-resistant 304 stainless steel. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0021] The present invention relates to a production method for 304 stainless steel suitable for common rail fuel in engines. The method for smelting the 304 stainless steel for common rail fuel in engines comprises: electric arc furnace smelting – argon-oxygen furnace blowing – ladle refining – continuous casting – rolling. Its chemical composition by mass percentage is: 0.02% ≤ C ≤ 0.07%, 0.4% ≤ Si ≤ 0.6%, 0.1% ≤ Mn ≤ 2.0%, 0.025% ≤ P ≤ 0.04%, 0.015% ≤ S ≤ 0.03%, 18% ≤ Cr ≤ 19%, 8% ≤ Ni ≤ 8.5%, with the balance being iron and unavoidable impurities. The addition of sulfur and phosphorus elements improves the machinability of the 304 stainless steel.

[0022] Electric arc furnace smelting: Smelting stainless steel in an electric arc furnace;

[0023] Argon-oxygen furnace blowing: After adjusting the composition of stainless steel smelted in electric arc furnace to the required range for 304 stainless steel except for sulfur, silicon is added to 0.4-0.6% for preliminary deoxidation, carbon is controlled at 0.03-0.07%, sulfur is removed to below 0.005%, and slag is skimmed off during tapping until the slag surface thickness is below 50mm, so as to avoid affecting the purity of molten steel.

[0024] Steel ladle refining: After argon-oxygen furnace blowing, the slag basicity of the molten steel is adjusted to 2.0-2.5. 1-2 kg / ton of steel-aluminum additive is added to adjust the slag to a grayish-white or white color. 0.2-0.3 kg / ton of calcium wire or calcium silicate wire is fed in to reduce oxides in the molten steel. Ferrosulfur is added to adjust the sulfur content to 0.015-0.03%, and ferrophosphorus is added to adjust the phosphorus content to 0.025-0.04%. Bottom blowing and stirring are performed during the feeding process to ensure uniform distribution of sulfur in the molten steel, resulting in finely dispersed manganese sulfide. Figure 1 As shown, to avoid the formation of large-sized impurities, the A-class impurity rating is ≤2.5. Before leaving the station, the B, C, and D-class inclusions are formed by standing for a period of time, which are ≤2.5. The oxide inclusions are removed by the "Si-Al-Ca" deoxidation technology, combined with strong stirring and long-term standing to remove the oxide inclusions of the steel grade.

[0025] Continuous casting: Molten steel that has been left to stand is continuously cast into steel billets under electromagnetic stirring, with a billet casting speed ≤400kg / min;

[0026] Rolling: The billet is heated to a temperature above 1250℃ and the final rolling temperature is above 1100℃. This reduces the high-temperature strength of the billet matrix, thereby reducing the extrusion pressure on inclusions during rolling and minimizing the deformation of inclusions along the rolling direction during hot rolling, thus lowering the inclusion rating. Ensure the inclusion size is smaller than the blind hole size of the component, with rolling specifications of Φ15~40mm, to avoid excessive elongation of inclusions during rolling.

[0027] Furthermore, in the production method of 304 stainless steel for common rail fuel of the present invention, during the ladle refining process, a strong stirring mode is adopted and the stirring time is 10 to 15 minutes, so that the sulfur element is evenly distributed in the molten steel and the manganese sulfide formed is finely dispersed.

[0028] Furthermore, in the production method of 304 stainless steel for common rail fuel of the present invention, during the ladle refining process, the bottom blowing gas is argon, and the argon flow rate is 200-300 L / min.

[0029] Furthermore, in the production method of 304 stainless steel for common rail fuel of the present invention, the settling time during the ladle refining process is ≥20 min.

[0030] Furthermore, in the production method of 304 stainless steel for common rail fuel of the present invention, a heat replenishment technique is used during the rolling process.

[0031] Example 1

[0032] In this embodiment, 304 stainless steel suitable for high-pressure fuel common rail of the engine is smelted.

[0033] Electric arc furnace smelting: Smelting stainless steel in an electric arc furnace;

[0034] Argon-oxygen furnace blowing: After adjusting the composition of stainless steel smelted in electric arc furnace to the required range for 304 stainless steel except for sulfur, silicon is added to 0.4% for preliminary deoxidation, carbon is controlled at 0.03%, sulfur is deoxidized to below 0.005%, and slag is skimmed off when tapping the steel until the slag surface thickness is below 50mm.

[0035] Steel ladle refining: After the argon-oxygen furnace blowing, the slag basicity of the molten steel is adjusted to 2.1, 1 kg / ton of steel-aluminum agent is added, 0.2 kg / ton of calcium wire is fed in, ferrosulfite is added to adjust the sulfur content to 0.022%, and ferrophosphorus is added to adjust the phosphorus content to 0.028%. During the feeding process, strong stirring mode is used for 10 minutes, and the bottom blowing argon flow rate is 200 L / min. Before leaving the station, the steel is allowed to stand for 21 minutes.

[0036] Continuous casting: Molten steel that has been allowed to stand is continuously cast into steel billets under electromagnetic stirring. The billet casting speed is 350 kg / min.

[0037] Rolling: The billet is heated to 1250℃ and the final rolling temperature is 1120℃. The rolling specifications are Φ15~40mm to avoid excessive elongation of inclusions during the rolling process.

[0038] The chemical composition of the finished product is as follows:

[0039] 0.05 0.42 1.20 0.028 0.022 18.2 8.2

[0040] The inclusion rating results according to GB / T 10561 are shown in the table below. No leakage was found during the high-pressure helium test.

[0041] 0 1.0 0 1.0 0 0.5 0 0.5

[0042] The tool life is 3.3 times longer than that of ordinary 304 stainless steel (S: 0.003%, P: 0.02%).

[0043] Example 2

[0044] In this embodiment, 304 stainless steel suitable for high-pressure fuel common rail of the engine is smelted.

[0045] Electric arc furnace smelting: Smelting stainless steel in an electric arc furnace;

[0046] Argon-oxygen furnace blowing: After adjusting the composition of stainless steel smelted in electric arc furnace to the required range for 304 stainless steel except for sulfur, silicon is added to 0.5% for preliminary deoxidation, carbon is controlled at 0.05%, sulfur is deoxidized to below 0.005%, and slag is skimmed off when tapping the steel until the slag surface thickness is below 50mm.

[0047] Steel ladle refining: After argon-oxygen furnace blowing, the slag basicity of the molten steel is adjusted to 2.3, 1.5 kg / ton of steel-aluminum agent is added, 0.25 kg / ton of calcium wire is fed in, ferrosulfite is added to adjust the sulfur content to 0.023%, and ferrophosphorus is added to adjust the phosphorus content to 0.031%. During the feeding process, strong stirring mode is used for 12 minutes, and the bottom blowing argon flow rate is 230 L / min. Before leaving the station, the temperature is adjusted to 1530℃ and allowed to stand for 24 minutes.

[0048] Continuous casting: Molten steel that has been allowed to stand is continuously cast into steel billets under electromagnetic stirring at a casting speed of 380 kg / min.

[0049] Rolling: The billet is heated to 1260℃ and the final rolling temperature is 1130℃. The rolling specifications are Φ15~40mm to avoid excessive elongation of inclusions during the rolling process.

[0050] The chemical composition of the finished product is as follows:

[0051] 0.03 0.26 1.34 0.031 0.023 18.1 8.3

[0052] The inclusion rating results according to GB / T 10561 are shown in the table below. No leakage was found during the high-pressure helium test.

[0053] 0 1.5 0 0.5 0 1.0 0 0.5

[0054] The tool life is 3.5 times longer than that of ordinary 304 stainless steel (S: 0.003%, P: 0.02%).

[0055] Example 3

[0056] In this embodiment, 304 stainless steel suitable for high-pressure fuel common rail of the engine is smelted.

[0057] Electric arc furnace smelting: Smelting stainless steel in an electric arc furnace;

[0058] Argon-oxygen furnace blowing: After adjusting the composition of stainless steel smelted in electric arc furnace to the required range for 304 stainless steel except for sulfur, silicon is added to 0.6% for preliminary deoxidation, carbon is controlled at 0.07%, sulfur is removed to below 0.005%, and slag is skimmed off during tapping until the slag surface thickness is below 50mm.

[0059] Steel ladle refining: After argon-oxygen furnace blowing, adjust the slag basicity of the molten steel to 2.5, add 2 kg / ton steel-aluminum agent, feed 0.3 kg / ton calcium wire, add ferrosulfite to adjust the sulfur content to 0.028%, add ferrophosphorus to adjust the phosphorus content to 0.037%, use strong stirring mode during the feeding process, stirring time is 15 min, bottom blowing argon flow rate is 300 L / min, adjust the temperature to 1520℃ before leaving the station and let it stand for 28 min;

[0060] Continuous casting: Molten steel that has been left to stand is continuously cast into steel billets under electromagnetic stirring, with a billet casting speed of 400 kg / min;

[0061] Rolling: The billet is heated to 1270℃ and the final rolling temperature is 1130℃. The rolling specifications are Φ15~40mm to avoid excessive elongation of inclusions during the rolling process.

[0062] The chemical composition of the finished product is as follows:

[0063] 0.035 0.38 1.59 0.037 0.028 18.3 8.2

[0064] The inclusion rating results according to GB / T 10561 are shown in the table below. No leakage was found during the high-pressure helium test.

[0065] 0 2.0 0 1.5 0 1.0 0 0.5

[0066] The tool life is 3.8 times longer than that of ordinary 304 stainless steel (S: 0.003%, P: 0.02%).

[0067] In summary, compared with the prior art, the production method of the present invention for 304 stainless steel suitable for high-pressure fuel common rail systems in engines has the following advantages and beneficial effects:

[0068] By controlling the sulfur and phosphorus content, the machinability of 304 stainless steel was improved, extending cutting tool life by more than three times and significantly reducing machining costs per ton of steel. Furthermore, a special smelting process was employed to prevent inclusions in the steel from growing and causing helium leaks, effectively reducing the helium leak rate to below 0.02%.

[0069] It should be noted that, unless otherwise expressly specified and limited, the term "connection" or its synonyms should be interpreted broadly in this document. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. Furthermore, expressions such as "first" and "second" are merely used to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Meanwhile, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. In addition, the terms "front," "rear," "left," "right," "upper," and "lower" in this document refer to the placement states shown in the accompanying drawings.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing 304 stainless steel for high-pressure fuel common rail systems in engines, characterized in that, The smelting method for the 304 stainless steel suitable for common rail fuel in engines includes: electric arc furnace smelting - argon-oxygen furnace blowing - ladle refining - continuous casting - rolling. Its chemical composition by mass percentage is: 0.02%≤C≤0.07%, 0.4%≤Si≤0.6%, 0.1%≤Mn≤2.0%, 0.025%≤P≤0.04%, 0.015%≤S≤0.03%, 18%≤Cr≤19%, 8%≤Ni≤8.5%, with the balance being iron and unavoidable impurities. Electric arc furnace smelting: Smelting stainless steel in an electric arc furnace; Argon-oxygen furnace blowing: After adjusting the composition of stainless steel smelted in electric arc furnace to the required range for 304 stainless steel except for sulfur, silicon is added to 0.4-0.6% for preliminary deoxidation, carbon is controlled at 0.03-0.07%, sulfur is removed to below 0.005%, and slag is skimmed off during tapping until the slag surface thickness is below 50mm to avoid affecting the purity of the molten steel. Steel ladle refining: After argon-oxygen furnace blowing, the slag basicity of the molten steel is adjusted to 2.0-2.

5. 1-2 kg / ton of steel-aluminum additive is added to adjust the slag to a grayish-white or white color. 0.2-0.3 kg / ton of calcium wire or calcium silicate wire is fed in to reduce oxides in the molten steel. Ferrosulfur is added to adjust the sulfur content to 0.015-0.03%, and ferrophosphorus is added to adjust the phosphorus content to 0.025-0.04%. Bottom blowing and stirring are performed during the feeding process. The steel is allowed to settle before leaving the station. Strong stirring is used, with a stirring time of 10-20 minutes. For 15 minutes, the bottom-blowing gas is argon, with a flow rate of 200-300 L / min, to ensure uniform distribution of sulfur in the molten steel. This results in finely dispersed manganese sulfide, preventing the formation of large-sized impurities and achieving a Class A impurity rating of ≤2.

5. Before leaving the station, the steel is allowed to stand, resulting in Class B, C, and D inclusions of ≤2.

5. Oxide inclusions are removed using the "Si-Al-Ca" deoxidation technology, combined with strong stirring and prolonged standing to remove steel oxide inclusions. The standing time is ≥20 minutes. Continuous casting: Molten steel that has been left to stand is continuously cast into steel billets under electromagnetic stirring, with a billet casting speed ≤400kg / min; Rolling: The billet is heated to a temperature above 1250℃ and the final rolling temperature is above 1100℃. The rolling specifications are Φ15~40mm. To avoid excessive elongation of inclusions during the rolling process, heat compensation technology is used during rolling.

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