A method for manufacturing a high-strength cast steel alloy and applications thereof

Abstract

The application discloses a manufacturing method and application of a high-strength cast steel alloy, and the method comprises the following steps: increasing the molten iron to a first temperature above 1700 DEG C to remove carbon, phosphorus and sulfur, so that the content of carbon, phosphorus and sulfur is within a target value; reducing the molten iron to a second temperature of 1650-1700 DEG C, adding silicon, molybdenum and copper into the molten iron, and blowing inert gas at the same time, and pouring to form a semi-finished steel ingot; increasing the temperature of the semi-finished steel ingot to a third temperature of 1650-1700 DEG C to melt and treat to obtain a melt, reducing the melt to a fourth temperature of 1550-1600 DEG C, adding MnFe, CrFe, BFe, VFe, Nb, Ni and rare earth elements to stir and melt, adding pure Al to remove oxygen and slag to obtain a target melt; and pouring the target melt to form the high-strength cast steel alloy. The high-strength cast steel alloy is prepared by using the manufacturing method, and a casting is prepared by using the high-strength cast steel alloy as a raw material, and the casting can reach a higher tensile strength and yield strength without heat treatment.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of alloy casting preparation, and in particular to a high-strength cast steel alloy manufacturing method and application. BACKGROUND

[0002] Global automobile technology is developing in the depth of "low carbonization, informatization and intelligentization", and multiple technical routes are developing in parallel. The technology as a whole presents a development trend of platformization, integration, light weight and high pressure. Component integration has become an industry trend.

[0003] The prior art CN107841691B discloses a 750MPa-grade ultra-high-strength Fe-Mn-Al-C light cast steel and a preparation method thereof. The light steel has a tensile strength of not less than 750MPa and a yield strength of not less than 700MPa by setting a high C content (0.60-1.50%) and a reasonable Si content (0.50-1.50%), and has a very good combination of strength, density and plasticity, and is very suitable for manufacturing automobile complex structure castings and can effectively reduce the weight of the automobile.

[0004] However, in the above prior art, the high C content can improve the tensile strength and yield strength, but as the carbon content increases, the pearlite volume will gradually increase, which improves the strength, but reduces the toughness of the steel, raises the brittle transition temperature and deteriorates the welding performance. In addition, the manufacturing process also needs to go through a heat treatment process, and the increase of the heat treatment process will increase the smelting cost and energy consumption.

[0005] Therefore, it is urgent to provide a high-strength cast steel alloy manufacturing method and application to solve the above technical problems. SUMMARY

[0006] The application provides a high-strength cast steel alloy manufacturing method and application. The manufacturing method can minimize the carbon content and add trace amounts of alloying elements to prepare a cast steel alloy with high tensile strength and high yield strength. The cast steel alloy is used as a raw material to prepare a casting. The casting obtained does not need to be heat treated and can achieve a mechanical property of a tensile strength of not less than 960MPa and a yield strength of not less than 710MPa, and can be used for manufacturing automobile complex structure castings with high mechanical strength requirements.

[0007] According to some embodiments, a method for manufacturing a high-strength cast steel alloy is provided, comprising the following steps: manufacturing a semi-finished steel ingot; raising the molten iron to a first temperature of 1700 DEG C or above for decarburization, dephosphorization, and desulfurization treatment to achieve the carbon, phosphorus, and sulfur content within the target value; lowering the molten iron to a second temperature of 1650-1700 DEG C, then adding a certain amount of silicon, molybdenum, and copper into the molten iron while passing inert gas to pour the semi-finished steel ingot; smelting the semi-finished steel ingot; raising the temperature of the semi-finished steel ingot to a third temperature of 1650-1700 DEG C for melting treatment to obtain a melt, lowering the melt to a fourth temperature of 1550-1600 DEG C, adding a certain amount of MnFe, CrFe, BFe, VFe, Nb powder, Ni powder, and rare earth elements for stirring and melting, and adding pure Al for oxygen and slag removal to obtain a target melt; pouring; pouring the target melt to manufacture a high-strength cast steel alloy.

[0008] Preferably, the content of the carbon is 0.3%-0.4% by weight.

[0009] The target value of the carbon is set to 0.3%-0.4%.

[0010] The target value of the phosphorus is set to 0.03%-0.04%.

[0011] The target value of the sulfur is set to ≤0.02%.

[0012] Preferably, the content of the silicon is 0.25%-0.50% by weight.

[0013] The added content of the silicon is set to 0.25%-0.50%, such as 0.3%, 0.35%, 0.4%, 0.45%.

[0014] The added content of the molybdenum is set to 0.35%-0.45%, such as 0.38%, 0.40%, 0.42%, 0.44%.

[0015] The added content of the copper is set to 0.04%-0.08%, such as 0.05%, 0.06%, 0.07%.

[0016] Preferably, the content of the silicon is 0.25%-0.50% by weight.

[0017] The added content of the MnFe is set to 1.0%-1.5%, such as 1.1%, 1.2%, 1.3%, 1.4%.

[0018] The added content of the CrFe is set to 1.5%-3.5%, such as 1.8%, 2.0%, 2.5%, 2.8%, 3.2%.

[0019] The added content of the BFe is set to 0.025%-0.035%, such as 0.028%, 0.030%, 0.032%.

[0020] The adding content of the VFe is set to 0.1%-0.2%, such as 0.12%, 0.14%, 0.16%, 0.18%;

[0021] The adding content of the Nb powder is set to 0.02%-0.05%, such as 0.025%, 0.03%, 0.035%, 0.04%;

[0022] The adding content of the Ni powder is set to 0.8%-1.5%, such as 1.0%, 1.2%, 1.4%;

[0023] The adding content of the rare earth element is set to 0.02%-0.04%, such as 0.025%, 0.028%, 0.030%, 0.035%.

[0024] Preferably, the smelting semi-finished steel ingot is melted in a vacuum environment with a vacuum degree of ≤200mbar.

[0025] Preferably, before the molten iron is poured into a semi-finished steel ingot, the method further comprises:

[0026] GaF2 is added to the molten iron to remove oxygen and slag;

[0027] and / or,

[0028] GaF2 is added to the molten iron to remove oxygen and slag during the melting process of the semi-finished steel ingot to obtain a melt.

[0029] According to some embodiments, the application further provides a high-strength cast steel alloy, which is made according to the above method and comprises the following raw materials in mass fraction: 0.3%≤carbon≤0.4%, 0.03%≤phosphorus≤0.04%, sulfur≤0.02%, 0.02%≤nitrogen≤0.04%, 0.025%≤boron≤0.035%, 1.5%≤chromium≤3.5%, 0.1%≤vanadium≤0.2%, 0.02%≤niobium≤0.05%, 0.35%≤molybdenum≤0.45%, 0.25%≤silicon≤0.50%, 1.0%≤manganese≤1.5%, 0.3%≤aluminum≤0.4%, 0.8%≤nickel≤1.5%, 0.04%≤copper≤0.08%, 0.02%≤rare earth element≤0.04%, and iron.

[0030] Preferably, the high-strength cast steel alloy has a tensile strength of 960MPa or more, such as 964MPa, 965MPa, 970MPa, 975MPa, a yield strength of 710MPa or more, such as 713MPa, 718MPa, 721MPa, and an elongation at break of 9% or more.

[0031] According to some embodiments, the application further provides a vehicle body thin-walled part made of the high-strength cast steel alloy.

[0032] According to some embodiments, the application further provides a vehicle comprising the vehicle body thin-walled part.

[0033] Advantages:

[0034] The application provides a manufacturing method and application of a high-strength cast steel alloy. Compared with the castings made of steel alloys in the prior art which need to be heat treated to achieve high tensile strength and yield strength, the application optimizes the alloy composition of the steel alloy and combines with the corresponding preparation process to prepare a high-strength cast steel alloy different from that in the prior art. The high-strength cast steel alloy has high tensile strength and yield strength. Then, the high-strength cast steel alloy is used as a raw material to prepare a casting. The casting can be prepared under the condition of no heat treatment to obtain a large-scale integrated cast steel thin-walled casting with high mechanical properties. The steel tensile strength of the casting at the key stress position reaches 960 MPa, the yield strength reaches 710 MPa, and the elongation rate is more than 9%. Since the casting is not heat treated, the thin-walled part prepared from the casting will not deform, has excellent stability, and will effectively ensure the size of the thin-walled vehicle body part, meet the market demand for large-scale integrated cast steel thin-walled castings, and reduce the smelting cost and energy consumption without heat treatment.

[0035] For the high-strength cast steel alloy, since it has appropriate contents of manganese, chromium, boron, vanadium, and niobium, and other elements are controlled at appropriate contents and combined with them, and the high-strength cast steel alloy is prepared by the manufacturing method of the application, the casting made of the high-strength cast steel alloy does not need to be heat treated in subsequent processes to achieve high tensile strength and yield strength. Mainly, the carbonitride compounds formed by chromium, vanadium, and nickel reacting with carbon and nitrogen, the phosphorus compounds formed by chromium, vanadium, and nickel reacting with phosphorus, and the molybdenum silicon nitride compounds form intergranular solid solution. The NiAl compound formed by the Ni element and the deoxidizing agent Al element can effectively strengthen the matrix strength, and the NiAl nucleates and precipitates quickly. In this precipitation process, Mo is enriched intergranularly and forms a cluster structure. The multiple precipitation organizations and the matrix synergistically deform to maintain the continuity of the microstructure deformation, avoiding the initiation of microcracks. The addition of the Cu element will diffuse with Fe at the grain boundary to form a ring-shaped distribution, form a pinning effect on the grain boundary, effectively inhibit grain growth, refine the bainite structure, and strengthen the matrix strength. The addition of rare earth elements can effectively improve the morphology and size of inclusions, and the periphery is enriched with MnCrFeP solid solution, which converts impurities into secondary strengthening phases, thereby obtaining high yield and tensile strength.

[0036] For the production method, in order to ensure the alloying composition of the high-strength cast steel alloy, the application selects a step-by-step process, that is, a semi-finished steel ingot is first produced, and then manganese, chromium, boron, vanadium, niobium, nickel, and rare earth elements are added based on the semi-finished steel ingot to finally obtain a finished steel ingot containing the target composition. In the production process of the semi-finished steel ingot, nitrogen gas is passed while adding silicon and molybdenum to the molten iron, which can form a large amount of molybdenum silicon nitride compound. Then, adding MnFe, CrFe, BFe, VFe, Nb, and other elements in the semi-finished steel ingot melting can effectively reduce the formation and segregation of chromium, vanadium, and niobium nitrides, thereby obtaining better performance. Using this production process and combining the addition content of various alloying elements, a high-strength cast steel alloy different from the prior art can be prepared. The castings prepared from the high-strength cast steel alloy as a raw material can achieve high tensile strength and yield strength without heat treatment. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort based on these drawings.

[0038] Figure 1 To prepare a high-strength cast steel product from the target values selected from the alloying composition range of the present embodiment 2, sample 1, sample 2, and sample 3 are selected to make a force extensometer curve graph. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the embodiments of the present application will be described in detail below with reference to the drawings. However, those skilled in the art can understand that in the embodiments of the present application, many technical details are proposed in order to make the readers better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed by the present application can be implemented. The following embodiments are classified for convenience of description, and should not constitute any limitation on the specific implementation of the present application. The embodiments can be combined with each other and mutually referenced without contradiction.

[0040] The castings made of steel alloy in the prior art need to be heat treated to achieve high tensile strength, yield strength, and elongation. On the one hand, the heat treatment process increases the smelting cost and energy consumption. On the other hand, for thin-walled parts of the vehicle body, which are sensitive to temperature, the thin-walled parts after heat treatment will deform, thereby failing to guarantee the size of the thin-walled vehicle body parts.

[0041] Therefore, the embodiment of the present application provides a manufacturing method and application of high-strength cast steel alloy. By controlling the content of each alloying element in each step within the target value, a high-strength cast steel alloy different from the prior art can be prepared, which has high yield and high tensile strength. The castings made of the high-strength cast steel alloy as a raw material do not need to be heat treated, i.e. omit the heating process, and can also achieve high yield and high tensile strength, while heat treatment-free effectively ensures the size of the thin-walled body part, and also can reduce the alloy production cost and energy consumption.

[0042] Embodiment 1

[0043] The manufacturing method of a high-strength cast steel alloy provided in the embodiment 1 will be described in detail below with reference to the accompanying drawings. The manufacturing method comprises the following steps:

[0044] Step 1: manufacturing a semi-finished steel ingot; preparing raw materials according to the set composition of the semi-finished steel ingot, and then melting and pouring the raw materials to form a semi-finished steel ingot;

[0045] Specifically, first, the molten iron is raised to a first temperature of 1700°C or higher for decarburization, dephosphorization, and desulfurization treatment, so that the target value of carbon is 0.3%-0.4%, the target value of phosphorus is 0.03%-0.04%, and the target value of sulfur is ≤0.02%. In this operation, harmful substances or impurities can be removed at high temperature by raising the molten iron to 1700°C or higher. The content of carbon, phosphorus and sulfur elements is detected to determine whether to continue heating. If the content is higher than the target value, continue heating until the content of carbon, phosphorus and sulfur elements is reduced to or below the target value range.

[0046] Then, the temperature of the molten iron is lowered to a second temperature of 1650-1700°C, and then 0.25%-0.50% silicon, 0.35%-0.45% molybdenum and 0.04%-0.08% copper are added to the molten iron, and at the same time, inert gas such as nitrogen is passed, and then molten steel is obtained. In this operation, by lowering the temperature, it can be ensured that the added elements are fully fused, but it cannot be too low, which cannot effectively fuse, but also cannot be set too high, which will have heat loss. Therefore, in this embodiment, the second temperature is set to 1650-1700°C.

[0047] Then, GaF2 is added to the molten steel at 2 kg / ton for slag removal and preliminary oxygen removal. The metal components in the molten steel react with oxygen to form slag, and the slag combines with GaF2 to remove oxygen and slag.

[0048] Finally, the middle 3 / 4 molten liquid in the smelting furnace is taken to cast the semi-finished steel ingot. Since the impurity density is smaller, the impurities formed will float in the upper half of the molten liquid, so the middle 3 / 4 molten liquid has less impurities. In this preparation process, a semi-finished steel ingot is first made, which can not only ensure the alloy composition but also facilitate transportation to the place where smelting is needed.

[0049] Step 2: Smelting semi-finished steel ingot; after melting the semi-finished steel ingot prepared above, the corresponding target melt is obtained;

[0050] Specifically, the semi-finished steel ingot is remelted in a vacuum environment with a vacuum degree ≤200 mbar. First, the semi-finished steel ingot prepared above is heated to a third temperature of 1650-1700°C for melting treatment to obtain a melt, and GaF2 is added at 2 kg / ton for slag removal and preliminary oxygen removal. Then, the melt is lowered to a fourth temperature of 1550-1600°C, and 1.0%-1.5% MnFe, 1.5%-3.5% CrFe, 0.025%-0.035% BFe, 0.1%-0.2% VFe, 0.02%-0.05% Nb powder, 0.8%-1.5% Ni powder and 0.02%-0.04% rare earth elements are added for stirring and melting to obtain the corresponding target melt. Finally, 0.3%-0.4% pure aluminum and oxygen are added at 0.3 kg / ton to the target melt for reaction for oxygen removal and slag removal. In this operation, by lowering the fourth temperature to 1550-1600°C, and then adding MnFe, CrFe, BFe, VFe, Nb powder, Ni powder and rare earth elements, more metal elements can be retained. The rare earth elements can be one or more of La, Ce, Y, etc., which can be freely selected. In addition, in the process of making high-strength cast steel alloy, smelting is needed in a vacuum environment with a vacuum degree ≤200 mbar to ensure that the oxygen content in the high-strength cast steel alloy is A lower oxygen content can effectively reduce FeO, MnO and other inclusions in the high-strength cast steel alloy.

[0051] Step 3: Pouring; the target melt prepared above is poured to form a high-strength cast steel alloy.

[0052] In the present application, by optimizing the alloy composition of the steel alloy and combining with the corresponding preparation process, a high-strength cast steel alloy different from the prior art can be prepared, and then a casting is prepared by taking the high-strength cast steel alloy as a raw material, and the casting can achieve high tensile strength and yield strength without heat treatment in subsequent processes, thereby realizing the preparation of a large-scale integrated cast steel thin-wall casting with high mechanical properties, and since the key heat treatment process is omitted, the thin-wall part will not deform, thereby effectively ensuring the size of the thin-wall body part, meeting the market demand for large-scale integrated cast steel thin-wall castings, and the heat treatment-free process also does not increase the smelting cost, thereby achieving the purpose of reducing energy consumption.

[0053] Carbon: The main role of carbon is to act as a gap solid solution element to improve the strength of the cast steel. However, too high carbon will reduce the plasticity and toughness, especially the plasticity; and too low carbon will need to increase the strength elements such as manganese and molybdenum. From the matching of performance and cost, the present application selects to control the carbon content to be 0.3% to 0.4% (here, the content of each element described below refers to the weight content).

[0054] Silicon: The main role of silicon is to act as a reducing agent and deoxidizing agent during steelmaking. However, too high silicon will cause solid solution strengthening of austenite and ferrite, resulting in reduced toughness, therefore, the present application selects to control the silicon content to be 0.25% to 0.50%.

[0055] Manganese: Manganese is an effective element for improving the strength of the alloy cast steel, which can effectively improve the low-temperature impact toughness of the cast steel and also improve the low-temperature toughness of the weld. In addition, in the present application, the addition of manganese can promote the solubility of nitrogen in the steel, and is also conducive to the combined addition of aluminum and niobium to form aluminum nitride, niobium carbonitride, etc. However, when the manganese exceeds 1.5%, it will increase the chemical composition segregation during casting, resulting in reduced plasticity and toughness, but too low manganese will result in insufficient strength. Therefore, the present application selects to control the manganese content to be 1.0% to 1.5%.

[0056] Phosphorus and sulfur: In the present alloy cast steel, phosphorus and sulfur are harmful elements that affect the purity of the steel, and too high phosphorus and sulfur will reduce the impact toughness, especially the low-temperature toughness. However, too low control will increase the production cost. Considering the above factors, the present application selects to control the content of phosphorus and sulfur to be 0.03% to 0.04% for phosphorus and ≤0.02% for sulfur.

[0057] Molybdenum: Molybdenum is an effective element for improving the strength of the alloy cast steel, and molybdenum is also a key element for improving plasticity. However, too high molybdenum will reduce the toughness, and too low molybdenum will not guarantee the ability of the cast steel part to obtain tempered sorbite. Therefore, the present application selects to control the molybdenum content to be 0.35% to 0.45%.

[0058] Chromium: Chromium is an effective element to improve the strength of the alloy cast steel, and the combination of chromium, manganese and molybdenum further enhances the hardenability and strength of the steel. Too high chromium addition will lead to the increase of carbon equivalent, and too low chromium will not achieve the appropriate strength. Therefore, the chromium content is controlled to be 1.5% to 3.5% in the present application.

[0059] Aluminum and niobium are used to refine the grain, especially the austenite grain refinement, and nitrogen is mainly used to cooperate with aluminum and niobium to form a certain amount of nitride. The nitride can promote the grain refinement of the cast steel during the casting process and high temperature normalizing. In addition, aluminum can also be an effective deoxidizer, but too high aluminum will increase the non-metallic inclusion defects and cracking tendency, and too low aluminum will not refine the grain. Therefore, the aluminum content is controlled to be 0.3% to 0.4% in the present application.

[0060] The addition of niobium can also reduce the existence of austenite mixed crystal, but too high niobium will seriously reduce the low temperature impact toughness, and too low niobium will not be combined with aluminum. Therefore, the niobium content is controlled to be 0.02% to 0.05% in the present application.

[0061] In summary, the cast steel formed by the cast steel material with the above composition has suitable contents of carbon, manganese, molybdenum and chromium, thus improving the strength of the cast steel; meanwhile, the high-strength cast steel alloy in the embodiment is prepared by controlling other elements at suitable contents and cooperating with them and using the manufacturing method of the present application. The high-strength cast steel alloy is mainly prepared in the process of manufacturing the semi-finished steel ingot. Nitrogen is passed while silicon and molybdenum are added to the molten iron, so that a large amount of molybdenum silicon nitride compounds are formed. Then, MnFe, CrFe, BFe, VFe, Nb, Ni and rare earth elements are added in the process of remelting the semi-finished steel ingot. Chromium, vanadium and nickel respectively react with carbon and nitrogen to form carbonitride compounds, chromium, vanadium and nickel respectively react with phosphorus to form phosphide compounds, and the molybdenum silicon nitride compounds together form an intergranular solid solution. The NiAl compound formed by the Ni element and the deoxidizing agent Al element can effectively strengthen the matrix strength, and the NiAl nucleates and precipitates quickly. In this precipitation process, Mo is enriched intergranularly and forms a cluster structure. The various precipitation organizations and the matrix synergistically deform to maintain the continuity of the microstructure deformation, avoiding the initiation of microcracks. The addition of Cu element will diffuse with Fe at the grain boundary to form a ring-shaped distribution, forming a pinning effect on the grain boundary, effectively inhibiting grain growth, refining the bainite structure and strengthening the matrix strength. The addition of rare earth elements can effectively improve the morphology and size of inclusions, and the periphery is enriched with MnCrFeP solid solution, which converts impurities into secondary strengthening phase to obtain higher yield and tensile strength. The steel tensile strength of the high-strength cast steel alloy reaches 960 MPa or more, the yield strength reaches 710 MPa or more, and the elongation reaches 9% or more. The high-strength cast steel alloy in the embodiment is used as a raw material to manufacture a casting, and the casting obtained without heat treatment also has high tensile strength and yield strength. Compared with the casting manufactured by the conventional steel alloy in the prior art which needs to be heat treated, the heat treatment-free method in the embodiment effectively ensures the size of the thin-walled body part, meets the market demand for large-scale integrated cast steel thin-walled castings, and also does not increase the smelting cost, achieving the purpose of reducing energy consumption.

[0062] Embodiment 2

[0063] Example 2 provides a high-strength cast steel alloy, which is prepared according to the preparation method of Example 1 above, and includes, in percentage by weight: 0.3%≤carbon≤0.4%, 0.03%≤phosphorus≤0.04%, sulfur≤0.02%, 0.02%≤nitrogen≤0.04%, 0.025%≤boron≤0.035%, 1.5%≤chromium≤3.5%, 0.1%≤vanadium≤0.2%, 0.02%≤niobium≤0.05%, 0.35%≤molybdenum≤0.45%, 0.25%≤silicon≤0.50%, 1.0%≤manganese≤1.5%, 0.3%≤aluminum≤0.4%, 0.8%≤nickel≤1.5%, 0.04%≤copper≤0.08%, 0.02%≤rare earth elements≤0.04%, and iron and other inevitable elements.

[0064] The cast steel alloy has a tensile strength of 960 MPa or more, a yield strength of 710 MPa or more, and a fracture elongation of 9% or more.

[0065] Example 3

[0066] Example 3 provides a vehicle body thin-wall part formed of the high-strength cast steel alloy of Example 2 above.

[0067] Example 4

[0068] Example 4 provides a vehicle including the vehicle body thin-wall part of Example 3 above.

[0069] The disclosure of Example 1 is further illustrated in detail below by way of Preparation Examples 1-3 and Comparative Examples 1-7. The raw materials used in the preparation examples can be obtained by commercial channels.

[0070] Preparation Example 1

[0071] A high-strength cast steel alloy prepared in this Preparation Example 1 has the following chemical components: 0.3% carbon, 0.25% silicon, 0.35% molybdenum, 1.0% manganese, 0.03% phosphorus, 0.001% sulfur, 1.5% chromium, 0.025% boron, 0.1% vanadium, 0.02% niobium, 0.3% aluminum, 0.02% nitrogen, 0.8% nickel, 0.04% copper, and 0.02% rare earth elements, wherein the rare earth elements are one or more of La, Ce, Y, and the like.

[0072] The preparation method of the high-strength cast steel alloy of this Preparation Example 1 includes the following steps:

[0073] 1) Making semi-finished steel ingot: the molten iron is raised to a first temperature above 1700°C for proper decarburization, dephosphorization, desulfurization treatment, to reach the target value of carbon content of 0.3%; the target value of phosphorus content of 0.03%; the target value of sulfur content of 0.001%; then the molten iron is lowered to a second temperature of 1650°C, 0.25% silicon, 0.35% molybdenum and 0.04% copper are added to the molten iron, and nitrogen gas is blown at the same time; then 2kg / ton of GaF2 is added for slag removal and preliminary oxygen removal; finally, the middle 3 / 4 molten liquid in the smelting furnace is taken for casting to make semi-finished steel ingot.

[0074] 2) Melting semi-finished steel ingot: the semi-finished steel ingot is remelted in a vacuum environment with a vacuum degree of ≤200mbar, first the semi-finished steel ingot is heated to a third temperature of 1650°C, 2kg / ton of GaF2 is added for slag removal and preliminary oxygen removal to obtain a melt, the melt is lowered to a fourth temperature of 1550°C, then 1.0%MnFe, 1.5%CrFe, 0.025%BFe, 0.1%VFe, 0.02%Nb powder, 0.8%Ni powder and 0.02% rare earth elements are added for sufficient stirring and melting to obtain a target melt.

[0075] 3) Casting; 0.3kg / ton of 0.3% pure Al is added to the target melt for oxygen and slag removal, then the target melt is poured into a mold to make a cast steel alloy.

[0076] Preparation Examples 2-3, Comparative Examples 1-7

[0077] Among them, the preparation methods of Preparation Examples 2-3 and Comparative Examples 1-2 are the same as that of Preparation Example 1, and the specific differences in alloy components and contents are shown in Table 1:

[0078] Table 1 (mass percentage, %)

[0079]

[0080] Comparative Example 1 and the preparation method in this preparation example 1 are the same, the difference is the difference in alloy component content, set part of the alloy component content to be lower than the range interval of the alloy component content in this preparation example 1.

[0081] Comparative Example 2 and the preparation method in this preparation example 3 are the same, the difference is the difference in alloy component content, set part of the alloy component content to be higher than the range interval of the alloy component content in this preparation example 3.

[0082] Comparative Example 3 and the alloy component content in this preparation example 1 are the same, the difference is that the conventional process is used to make cast steel alloy, the specific steps are as follows:

[0083] First, iron and the target alloy components are added to the melting furnace and heated to a temperature of over 1700℃ for smelting and decarburization, dephosphorization, and desulfurization. After the carbon, phosphorus, and sulfur meet the component requirements, GaF2 is added to the molten steel at a rate of 2 kg / ton for slag removal and preliminary deoxygenation. Finally, the molten steel is cast into steel ingots.

[0084] Comparative Example 4 has the same alloy composition as Example 2, except that it uses a conventional process to produce the cast steel alloy.

[0085] Comparative Example 5 has the same alloy composition as Example 3, except that it uses a conventional process to produce the cast steel alloy.

[0086] Comparative Example 6 has the same alloy composition as Comparative Example 1, the difference being that it uses a conventional process to produce the cast steel alloy.

[0087] Comparative Example 7 and Comparative Example 2 have the same alloy composition, the difference being that the cast steel alloy is produced using conventional processes.

[0088] The testing methods for various indicators of the finished cast steel parts produced in the following embodiments are as follows:

[0089] Tensile strength: The tensile strength of the finished cast steel parts obtained in each embodiment and the comparative product were tested in accordance with GB / T228.

[0090] Yield strength: The yield strength of the finished cast steel parts obtained in each embodiment and the comparative product were tested in accordance with GB / T228.

[0091] like Figure 1 As shown, the force-extensometer curves are obtained from samples 1, 2, and 3 of the high-strength cast steel parts prepared by taking any target value from the alloy composition range of this Example 2. The force-extensometer curves show that within the alloy composition range, the tensile strength, yield strength, and elongation at break can all meet the performance requirements of this Example 2. Table 2 below shows the performance analysis results of the high-strength cast steel parts prepared using the preparation examples 1, 2, and 3 of this invention and comparative examples 1-7.

[0092] Table 2

[0093]

[0094] A comparison of the experimental data from Preparation Examples 1-3 and Comparative Examples 1-7 in Table 2 reveals that:

[0095] From the experimental data comparison of Preparation Example 1-Preparation Example 3, it can be found that when the content of various alloy components is selected within the alloy component interval of the present application and combined with the manufacturing method of the present application, the tensile strength, yield strength and elongation after fracture all meet the requirements of the present application, and the test state is normal.

[0096] From the experimental data comparison of Preparation Example 1 and Comparative Example 1, it can be found that when the content of part of the key alloy components in Comparative Example 1 is lower than the alloy component interval of the present application and combined with the manufacturing method of the present application, the tensile strength, yield strength and elongation after fracture all do not meet the requirements of the present application, and the test state is abnormal.

[0097] From the experimental data comparison of Preparation Example 3 and Comparative Example 2, it can be found that when the content of part of the key alloy components in Comparative Example 2 is higher than the alloy component interval of the present application and combined with the manufacturing method of the present application, the tensile strength, yield strength and elongation after fracture all do not meet the requirements of the present application, and the test state is abnormal.

[0098] From the experimental data comparison of Preparation Example 1 and Comparative Example 3, Preparation Example 2 and Comparative Example 4, Preparation Example 3 and Comparative Example 5, it can be found that when the content of various alloy components is within the alloy component interval of the present application and combined with the conventional manufacturing method, the tensile strength, yield strength and elongation after fracture all do not meet the requirements of the present application, and the test state is abnormal.

[0099] From the experimental data comparison of Comparative Example 1 and Comparative Example 6, it can be found that when the content of part of the key alloy components is set to be lower than the alloy component interval of the present application and combined with the conventional manufacturing method, the tensile strength, yield strength and elongation after fracture all do not meet the requirements of the present application, and the test state is abnormal.

[0100] From the experimental data comparison of Comparative Example 2 and Comparative Example 7, it can be found that when the content of part of the key alloy components is set to be higher than the alloy component interval of the present application and combined with the conventional manufacturing method, the tensile strength, yield strength and elongation after fracture all do not meet the requirements of the present application, and the test state is abnormal.

[0101] In summary, only when the content interval of various alloy components in the embodiments of the present application is combined with the manufacturing method of the present application, can a high-strength cast steel alloy with high tensile strength and high yield strength be prepared.

[0102] It should be understood that the foregoing detailed description of the application, rather than limiting the application, is intended to explain and describe the current application to those skilled in the art. Accordingly, any modification, equivalent replacement, improvement, etc. made without departing from the spirit and scope of the application shall be included in the protection scope of the application. In addition, the claims of the present application are intended to cover all variations and modifications falling within the scope and boundary of the appended claims or the equivalent form of such scope and boundary.

Claims

1. A method for manufacturing a high-strength cast steel alloy, characterized in that, Includes the following steps: Semi-finished steel ingots are produced; the molten iron is raised to a first temperature of over 1700℃ for decarburization, dephosphorization, and desulfurization treatment to ensure that the carbon, phosphorus, and sulfur content is within the target value; the molten iron is lowered to a second temperature of 1650-1700℃, and then a certain amount of silicon, molybdenum, and copper are added to the molten iron while inert gas is introduced, and then cast to produce semi-finished steel ingots. Semi-finished steel ingots are smelted; the temperature of the semi-finished steel ingots is raised to a third temperature of 1650-1700℃ to obtain a melt; the melt is lowered to a fourth temperature of 1550-1600℃; a certain amount of MnFe, CrFe, BFe, VFe, Nb powder, Ni powder and rare earth elements are added and stirred to melt; pure Al is added to remove oxygen and slag to obtain the target melt. Casting; casting the target melt into a high-strength cast steel alloy.

2. The manufacturing method according to claim 1, characterized in that, By weight percentage, The target value for carbon is set at 0.3% to 0.4%; The target value for phosphorus is set at 0.03% to 0.04%; The target value for sulfur is set to ≤0.02%.

3. The manufacturing method according to claim 2, characterized in that, By weight percentage, The silicon content is set to 0.25% to 0.50%; The molybdenum content is set to 0.35%–0.45%; The copper content is set to 0.04% to 0.08%.

4. The manufacturing method according to claim 3, characterized in that, By weight percentage, The added MnFe content is set to 1.0% to 1.5%; The CrFe content is set to 1.5%–3.5%; The content of added BFe is set to 0.025% to 0.035%; The content of VFe added is set to 0.1% to 0.2%; The content of Nb powder added is set to 0.02% to 0.05%; The content of Ni powder added is set to 0.8% to 1.5%; The content of the rare earth elements is set to be 0.02% to 0.04%.

5. The manufacturing method according to claim 1, characterized in that, The semi-finished steel ingots are melted in a vacuum environment with a vacuum degree of ≤200mbar.

6. The manufacturing method according to claim 1, characterized in that, Before pouring molten iron to form semi-finished steel ingots, the process also includes: GaF2 is added to the molten iron to remove oxygen and slag; And / or, In the process of melting the semi-finished steel ingot to obtain the melt, GaF2 is also added for deoxygenation and slag removal.

7. A high-strength cast steel alloy, characterized in that, The high-strength cast steel alloy is manufactured according to any one of claims 1-6, and comprises the following raw materials in the following mass fractions: 0.3%≤carbon≤0.4%, 0.03%≤phosphorus≤0.04%, sulfur≤0.02%, 0.02%≤nitrogen≤0.04%, 0.025%≤boron≤0.035%, 1.5%≤chromium≤3.5%, 0.1%≤vanadium≤0.2%, 0.02%≤niobium≤0.05%, 0.35%≤molybdenum≤0.45%, 0.25%≤silicon≤0.50%, 1.0%≤manganese≤1.5%, 0.3%≤aluminum≤0.4%, 0.8%≤nickel≤1.5%, 0.04%≤copper≤0.08%, 0.02%≤rare earth elements≤0.04%, and iron.

8. The high-strength cast steel alloy according to claim 7, characterized in that, The high-strength cast steel alloy has a tensile strength of 960 MPa or higher, a yield strength of 710 MPa or higher, and an elongation at break of 9% or higher.

9. A thin-walled component for a car body, characterized in that, Made of the high-strength cast steel alloy as described in claim 7 or 8.

10. A vehicle, characterized in that, Including the thin-walled body component as described in claim 9.

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