Manufacturing method and application of cast steel alloy

Abstract

The invention discloses a manufacturing method and application of a cast steel alloy, and the method comprises the following steps: heating molten iron to a first temperature higher than 1700 DEG C for decarburization, dephosphorization and desulfurization treatment, so that the contents of carbon, phosphorus and sulfur are within target values; cooling the molten iron to a second temperature of 1650-1700 DEG C, adding a certain amount of silicon and molybdenum into the molten iron, introducing inert gas at the same time, and casting to prepare a 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, reducing the melt to a fourth temperature of 1550-1600 DEG C, adding a certain amount of MnFe, CrFe, BFe, VFe and Nb powder, stirring and melting to obtain a target melt; and casting the target melt to prepare the cast steel alloy. The cast steel alloy is prepared through the manufacturing method, the cast steel alloy serves as a raw material to prepare a casting, the obtained casting can have high tensile strength, yield strength and ductility under the heat-treatment-free condition, and then the large integrated cast steel thin-wall casting which is excellent in size stability and meets the market requirement is prepared.

Description

Technical Field

[0001] The present application relates to the technical field of alloy casting preparation, and in particular to a method for preparing a cast steel alloy and its application. Background Art

[0002] The global automotive technology is deeply integrated and developed with "low-carbonization, informatization, and intelligence", and multiple technical routes are developing in parallel. The overall technology shows a trend of platformization, integration, lightweight, and high pressure. The integration of components has become an industry trend.

[0003] Compared with integrated cast aluminum, integrated cast steel has obvious advantages, such as mechanical properties 2 to 3 times higher than cast aluminum, simple connection method, direct connection by welding, simple parts repair, cost advantage, and the price of steel is much lower than that of aluminum alloy. Therefore, castings made of integrated cast steel can be used for thin-walled parts of vehicle bodies, but castings made of integrated cast steel in the prior art often need to undergo a heat treatment process before they can achieve higher tensile strength, yield strength, and elongation, and adding a heat treatment process will increase smelting costs and increase energy consumption.

[0004] Therefore, it is urgent to provide a method for preparing a cast steel alloy and its application to solve the above technical problems. Summary of the invention

[0005] The present application provides a method for preparing a cast steel alloy and its application. The cast steel alloy is prepared by the preparation method, and then the cast steel alloy is used as a raw material to prepare a casting. The obtained casting does not need to be subjected to heat treatment and can achieve high tensile strength, yield strength, and elongation, and can be used for thin-walled parts of vehicle bodies.

[0006] According to some embodiments, a method for preparing a cast steel alloy is provided, comprising the following steps:

[0007] Making semi-finished steel ingots; raising the molten iron to a first temperature greater than 1700°C for decarburization, dephosphorization and desulfurization to achieve target contents of carbon, phosphorus and sulfur; lowering the molten iron to a second temperature of 1650-1700°C, then adding a certain amount of silicon and molybdenum to the molten iron while passing inert gas, and finally casting to make semi-finished steel ingots;

[0008] Melting the semi-finished steel ingot; raising the temperature of the semi-finished steel ingot to a third temperature of 1650-1700° C. for melting treatment to obtain a melt, lowering the melt to a fourth temperature of 1550-1600° C., and adding a certain amount of MnFe, CrFe, BFe, VFe and Nb powder for stirring and melting to obtain a target melt;

[0009] Pouring; pouring the target melt to form a cast steel alloy.

[0010] Preferably, in terms of weight percentage, the target value of carbon is set to ≤0.25%; the target value of phosphorus is set to 0.02% to 0.035%; and the target value of sulfur is set to ≤0.035%.

[0011] Preferably, in terms of weight percentage, the added content of silicon is set to 0.25% to 0.50%; the added content of molybdenum is set to ≤0.45%, and further, the added content of molybdenum is set to 0.20% to 0.35%, such as 0.20%, 0.25%, 0.30%, 0.35%; the added content of MnFe is set to 0.6% to 0.9%, such as 0.6%, 0.75%, 0.80%, 0.9%; the added content of CrFe is set to 1.2% to 1.5%, such as 1.2% , 1.35%, 1.40%, 1.5%; the added content of BFe is set to 0.08% ~ 0.1% such as 0.08%, 0.085%, 0.09%, 0.1%; the added content of VFe is set to 0.1% ~ 0.15% such as 0.1%, 0.12%, 0.125%, 0.13%, 0.14%, 0.15%; the added content of Nb powder is set to 0.02% ~ 0.05% such as 0.02%, 0.03%, 0.035%, 0.04%, 0.05%.

[0012] Preferably, the following alloy raw materials are further added to the smelting semi-finished steel ingot in the step: Ni powder and pure aluminum, and the semi-finished steel ingot is melted in a vacuum environment with a vacuum degree of ≤200 mbar.

[0013] Preferably, in terms of weight percentage, the target value of carbon is set to 0.25% to 0.35%; the target value of phosphorus is set to ≤0.035%; and the target value of sulfur is set to ≤0.035%.

[0014] Preferably, in terms of weight percentage, the added content of silicon is set to 0.2% to 0.35%, such as 0.25%, 0.27%, 0.30%, and 0.32%; the added content of molybdenum is set to 0.35% to 0.45%, such as 0.37%, 0.40%, and 0.42%; the added content of MnFe is set to 0.6% to 0.9%, such as 0.65%, 0.70%, 0.75%, 0.80%, and 0.85%; the added content of CrFe is set to 1.2% to 1.5%, such as 1.25%, 1.3%, 1.35%, 1.4%, and 1.45%; the added content of BFe The addition content of is set to 0.025% ~ 0.035% such as 0.030%, 0.032%, 0.034%; the addition content of VFe is set to 0.1% ~ 0.15%; such as 0.12%, 0.13%, 0.14%; the addition content of Nb powder is set to 0.02% ~ 0.05% such as 0.03%, 0.04%; the addition content of Ni powder is set to 0.8% ~ 1.5% such as 0.9%, 1.0%, 1.2%, 1.4%; the addition content of pure aluminum is set to 0.3% ~ 0.4% such as 0.32%, 0.34%, 0.36%, 0.38%.

[0015] Preferably, the following alloy raw materials are further added to the smelting of the semi-finished steel ingot in the step: TiFe, cobalt and rare earth elements, and the semi-finished steel ingot is melted in a vacuum environment with a vacuum degree of ≤150 mbar.

[0016] Preferably, in terms of weight percentage, the target value of carbon is set to 0.3% to 0.4%; the target value of phosphorus is set to 0.03% to 0.04%; and the target value of sulfur is set to ≤0.02%.

[0017] Preferably, in terms of weight percentage, the added content of silicon is set to 0.25% to 0.50%, such as 0.30%, 0.35%, 0.40%, and 0.45%; the added content of molybdenum is set to 0.35% to 0.45%, such as 0.38%, 0.40%, and 0.42%; the added content of MnFe is set to 1% to 1.5%, such as 1.2%, 1.3%, and 1.4%; the added content of CrFe is set to 1.5% to 3.5%, such as 2.0%, 2.5%, 3.0%, and 3.4%; the added content of BFe is set to 0.025% to 0.035%, such as 0.030%, 0.032%, and 0.034%; the added content of VFe is set to 0.1% to 0.2%, such as 0.12%, 0. 14%, 0.16%, 0.18%; the added content of the Nb powder is set to 0.02%~0.05% such as 0.03%, 0.04%; the added content of the Ni powder is set to 2%~3.5% such as 2.4%, 2.8%, 3.0%, 3.2%; the added content of the pure aluminum is set to 0.3%~0.4% such as 0.32%, 0.34%, 0.36%, 0.38%; the added content of the TiFe is set to 0.8%~1.2% such as 0.9%, 1.0%, 1.1%; the added content of the cobalt is set to 1.5%~2.5% such as 1.7%, 1.9%, 2.1%, 2.2%; the added content of the rare earth element is set to 0.1%~0.15% such as 0.12%, 0.13%, 0.14%.

[0018] According to some embodiments, the present application also provides a cast steel alloy, which is produced according to the production method, and the cast steel alloy includes the following raw materials in mass fraction: carbon ≤ 0.25%, 0.02% ≤ phosphorus ≤ 0.035%, sulfur ≤ 0.035%, 0.02% ≤ nitrogen ≤ 0.04%, 0.08% ≤ boron ≤ 0.1%, 1.2% ≤ chromium ≤ 1.5%, 0.1% ≤ vanadium ≤ 0.15%, 0.02% ≤ niobium ≤ 0.05%, 0.20% ≤ molybdenum ≤ 0.35%, 0.25% ≤ silicon ≤ 0.50%, 0.6% ≤ manganese ≤ 0.9%, 0.04% ≤ aluminum ≤ 0.45% and iron.

[0019] According to some embodiments, the present application also provides a cast steel alloy, which is produced according to the production method, and the cast steel alloy includes the following raw materials in mass fraction: 0.25% ≤ carbon ≤ 0.35%, phosphorus ≤ 0.035%, sulfur ≤ 0.035%, 0.02% ≤ nitrogen ≤ 0.04%, 0.025% ≤ boron ≤ 0.035%, 1.2% ≤ chromium ≤ 1.5%, 0.1% ≤ vanadium ≤ 0.15%, 0.02% ≤ niobium ≤ 0.05%, 0.35% ≤ molybdenum ≤ 0.45%, 0.2% ≤ silicon ≤ 0.35%, 0.6% ≤ manganese ≤ 0.9%, 0.3% ≤ aluminum ≤ 0.4%, 0.8% ≤ nickel ≤ 1.5% and iron.

[0020] According to some embodiments, the present application also provides a cast steel alloy, which is manufactured according to the manufacturing method, and the cast steel alloy includes 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% ≤ manganese ≤ 1.5%, 0.3% ≤ aluminum ≤ 0.4%, 2% ≤ nickel ≤ 3.5%, 1.5% ≤ cobalt ≤ 2.5%, 0.8% ≤ titanium ≤ 1.2%, 0.1% ≤ rare earth elements ≤ 0.15% and iron.

[0021] According to some embodiments, the present application also provides a thin-walled vehicle body part, which is made of the cast steel alloy.

[0022] According to some embodiments, the present application also provides a vehicle, comprising the thin-walled vehicle body part.

[0023] Beneficial effects:

[0024] The present application provides a method for preparing a cast steel alloy and its application. Compared with the prior art in which castings made of steel alloys need to undergo a heat treatment process before they can achieve higher tensile strength, yield strength and elongation, the present application optimizes the alloy composition of the steel alloy and combines it with a corresponding preparation process to prepare a cast steel alloy that is different from the prior art. The cast steel alloy has higher tensile strength, yield strength and elongation. Then, the cast steel alloy is used as a raw material to prepare a casting. The obtained casting can prepare a large-scale integrated cast steel thin-walled casting with higher mechanical properties under the condition of no heat treatment. The casting has a steel tensile strength of 620Mpa, a yield strength of 470Mpa and an elongation at break of more than 16.5% at a key stress-bearing part. Since the casting is not subjected to heat treatment, the thin-walled part prepared by the casting has less deformation and good dimensional stability, which will effectively ensure the size of the thin-walled body parts and meet the market demand for large-scale integrated cast steel thin-walled castings. At the same time, no heat treatment can also save manufacturing costs and reduce energy consumption.

[0025] For the cast steel alloy, since it has appropriate contents of manganese, chromium, boron, vanadium and niobium, and other elements are controlled to cooperate with them at appropriate contents, and the cast steel alloy is prepared by the preparation method of the present application, the castings made by the cast steel alloy do not need to undergo heat treatment in subsequent processes, and can achieve high tensile strength, yield strength, and elongation; mainly by utilizing carbonitrides formed by the reaction of chromium, vanadium, and niobium with carbon and nitrogen, respectively, phosphorus compounds formed by the reaction of chromium, vanadium, and niobium with phosphorus, and molybdenum silicon nitrogen compounds to form intergranular solid solutions, so that the internal organizational structure is arranged more regularly and the intergranular gap is smaller, which can improve the organizational morphology and transform the organizational morphology from needle-shaped to blocky and granular, and the formed solid solution disperses and refines the alloy microstructure, which can then improve the comprehensive mechanical properties of the alloy.

[0026] As for the production method, in order to ensure the composition of the alloy in the cast steel alloy, the present application chooses to proceed step by step. It is necessary to first produce a semi-finished steel ingot, and then add manganese, chromium, boron, vanadium and niobium based on the semi-finished steel ingot, and finally obtain a finished steel ingot containing the target composition. In the production process of the semi-finished steel ingot, nitrogen is passed while adding the elements silicon and molybdenum to the molten iron. A large amount of molybdenum silicon nitrogen compounds can be formed while forming a protective gas. Then, MnFe, CrFe, BFe, VFe, Nb and other elements are added to the melted semi-finished steel ingot to effectively reduce the formation and segregation of nitrides such as chromium, vanadium and niobium, thereby obtaining better performance. This production process and the addition content of various alloy components can be used to prepare a cast steel alloy that is different from the prior art. Then, a casting is prepared using the cast steel alloy as a raw material. The obtained casting does not require heat treatment and can achieve higher tensile strength, yield strength and elongation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 This is an enlarged schematic diagram of the metallographic structure showing block and granular shapes of the internal structure of the cast steel alloy in the embodiment of the present application;

[0029] Figure 2 Force-extensometer curves of sample 1, sample 2 and sample 3 selected from the cast steel alloy products prepared by taking any target value within the alloy composition range of Example 4 of the present application;

[0030] Figure 3 Force-extensometer curves of sample 1, sample 2 and sample 3 selected from the cast steel alloy products prepared by taking any target value within the alloy composition range of Example 5 of the present application;

[0031] Figure 4 Force-extensometer curves of Samples 1, 2 and 3 selected from the cast steel alloy products prepared by taking any target value within the alloy composition range of Example 6 of the present application. DETAILED DESCRIPTION

[0032] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the embodiments of the present application will be described in detail below in conjunction with the accompanying drawings. However, it will be appreciated by those skilled in the art that in the embodiments of the present application, many technical details are proposed in order to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical scheme claimed in the present application can also be implemented. The division of the following embodiments is for the convenience of description, and the specific implementation of the present application should not be construed as any limitation, and the various embodiments can be combined with each other and quoted from each other without contradiction.

[0033] In the prior art, castings made of steel alloys need to undergo heat treatment before they can achieve high tensile strength, yield strength, and elongation. On the one hand, adding a heat treatment step will increase costs and increase energy consumption; on the other hand, for thin-walled car body parts, the size of the parts is sensitive to temperature. After heat treatment, the thin-walled parts will undergo severe deformation, and then the size and stability of the thin-walled car body parts cannot be guaranteed.

[0034] Therefore, the embodiments of the present application provide a method for preparing a cast steel alloy and an application thereof. By controlling the content of each alloy component within the target value in each step, a cast steel alloy different from the prior art can be prepared, and the cast steel alloy has higher tensile strength, yield strength, elongation and other properties. The cast steel alloy is used as a raw material to make castings, and the obtained castings do not need to undergo heat treatment, that is, the heat treatment process is omitted, and higher tensile strength, yield strength and elongation can be achieved. At the same time, the heat treatment-free process will effectively ensure the dimensional accuracy of thin-walled body parts, and can also reduce the alloy production cost and energy consumption.

[0035] Example 1

[0036] The following is a detailed description of a method for preparing a cast steel alloy provided in this embodiment 1 in conjunction with the accompanying drawings. The method comprises the following steps:

[0037] Step 1: Making 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 make the semi-finished steel ingot;

[0038] Specifically, the process includes: firstly, heating the molten iron to a first temperature above 1700°C for decarburization, dephosphorization and desulfurization to achieve target values ​​of carbon ≤ 0.25%, phosphorus 0.02% to 0.035%, and sulfur ≤ 0.035%. In this operation, harmful substances or impurities can be removed at high temperature by heating the molten iron to above 1700°C. Whether to continue heating is determined by detecting the content of carbon, phosphorus and sulfur elements. If the content is higher than the target value, heating is continued until the content of carbon, phosphorus and sulfur elements is removed to below the target value.

[0039] The temperature of the molten iron is then lowered to a second temperature of 1650-1700°C, and then 0.25%-0.50% silicon and 0.20%-0.35% molybdenum are added to the molten iron, and at the same time, an inert gas such as nitrogen is passed through, and then molten steel is obtained. In this operation, the temperature can be lowered to ensure that the added elements are fully integrated. At the same time, the temperature cannot be lowered too low to effectively integrate, but it cannot be set too high to cause heat loss. Therefore, in this embodiment, the second temperature is set at 1650-1700°C.

[0040] Then, GaF2 is added to the molten steel at a rate of 2 kg / ton for slag removal and preliminary deoxidation. The metal components in the molten steel react with oxygen to form slag, which then combines with GaF2 to deoxidize and remove slag.

[0041] Finally, the molten steel is poured into semi-finished steel ingots.

[0042] In the preparation process, a semi-finished steel ingot is first produced, which can ensure the alloy composition and can be easily transported to a place where smelting is required for smelting.

[0043] Step 2: Melting the semi-finished steel ingot; melting the semi-finished steel ingot prepared above to obtain a corresponding target melt;

[0044] Specifically, the process includes: firstly, raising the temperature of the semi-finished steel ingot prepared above to a third temperature of 1650-1700°C for melting treatment to obtain a melt, and adding GaF2 at 2 kg / ton for slag removal and preliminary deoxidation; then lowering the melt to a fourth temperature of 1550-1600°C, and then adding 0.6%-0.9% MnFe, 1.2%-1.5% CrFe, 0.08%-0.1% BFe, 0.1%-0.15% VFe, and 0.02%-0.05% Nb powder for stirring and melting to obtain a corresponding target melt; and finally, adding 0.04%-0.45% pure aluminum and oxygen at 0.3 kg / ton to the target melt for reaction to deoxidize and remove slag. In this operation, more metal elements can be retained by lowering the fourth temperature to 1550-1600°C and then adding MnFe, CrFe, BFe, VFe, and Nb powder.

[0045] Step 3: pouring: pouring the target melt prepared above to make a cast steel alloy.

[0046] In the present application, by optimizing the alloy composition of the steel alloy and combining it with the corresponding preparation process, a cast steel alloy different from the prior art can be prepared, and then a casting is prepared using the cast steel alloy as the raw material. The obtained casting can achieve high tensile strength, yield strength, and elongation without undergoing heat treatment in subsequent processes, thereby achieving the preparation of large-scale integrated cast steel thin-walled castings with high mechanical properties. Moreover, since the key heat treatment process is omitted, the thin-walled parts will not be deformed, and the size of the thin-walled body parts will be effectively guaranteed, meeting the market demand for large-scale integrated cast steel thin-walled castings. At the same time, the heat treatment is waived and the smelting cost does not need to be increased, thereby achieving the purpose of reducing energy consumption.

[0047] Carbon: The main function of carbon is to act as an interstitial solid solution element to improve the strength of cast steel. However, too high carbon will reduce plasticity and toughness, especially plasticity; while too low carbon requires the addition of strength elements such as manganese and molybdenum. From the perspective of performance and cost matching, this application chooses to control the carbon content to be less than or equal to 0.25% (the content here and the content of each element below are all weight content).

[0048] Silicon: Silicon is mainly used as a reducing agent and deoxidizer in the steelmaking process. However, too much silicon will strengthen the austenite and ferrite solid solution, resulting in reduced toughness. Therefore, the present application selects to control the silicon content to 0.25% to 0.50%.

[0049] Manganese: Manganese is an effective element for improving the strength of alloy cast steel. It can effectively improve the low-temperature impact toughness of cast steel and also improve the low-temperature toughness of welds. In addition, in the present application, the addition of manganese can promote the solubility of nitrogen in steel, and is also beneficial to the composite addition of aluminum and niobium to form aluminum nitride, niobium carbonitride, etc. However, when manganese exceeds 1.5%, it will increase the segregation of chemical composition during the casting process, resulting in reduced plasticity and toughness, but too low manganese will lead to insufficient strength. For this reason, the present application chooses to control the manganese content to 0.6% to 0.9%.

[0050] Phosphorus and sulfur: In this alloy cast steel, phosphorus and sulfur are harmful elements that affect the purity of the steel. Too high phosphorus and sulfur will reduce impact toughness, especially low-temperature toughness. However, if the content is too low, it will increase the production cost. Based on the above factors, this application chooses to control the content of phosphorus and sulfur to 0.02% to 0.035% for phosphorus and ≤0.035% for sulfur.

[0051] Molybdenum: Molybdenum is an effective element to improve the strength of alloy cast steel, and it is also a key element to improve plasticity. However, too high a molybdenum content will reduce toughness, and too low a molybdenum content will not guarantee the ability of the cast steel to obtain tempered sorbite. For this reason, this application chooses to control the molybdenum content to ≤0.45%. In order to reasonably control material costs, the molybdenum content can be further optimized to 0.20% to 0.35%.

[0052] Chromium: Chromium is an effective element to improve the strength of alloy cast steel, and the combined effect of chromium, manganese and molybdenum further enhances the hardenability and strength of steel. Too much chromium addition will lead to an increase in carbon equivalent, while too little chromium will not achieve the appropriate strength. For this reason, this application chooses to control the chromium content to 1.2% to 1.5%.

[0053] Aluminum and niobium are used together to refine grains, especially austenite grains. Nitrogen is mainly used to form a certain amount of nitrides with aluminum and niobium. Nitrides can promote grain refinement of cast steel during the casting process and high-temperature normalizing. In addition, aluminum can also be used as an effective deoxidizer. However, too much aluminum will increase non-metallic inclusion defects and cracking tendency, and too little aluminum will not be able to refine grains. For this reason, this application chooses to control the aluminum content to 0.04% to 0.45%. The addition of niobium can also reduce the presence of austenite mixed crystals, but too much niobium will seriously reduce low-temperature impact toughness, and too little niobium cannot be compounded with aluminum. For this reason, this application chooses to control the niobium content to 0.02% to 0.05%.

[0054] In summary, the cast steel formed by the cast steel material having the above composition has a suitable content of carbon, manganese, molybdenum and chromium, so the strength of the cast steel is improved; at the same time, the cast steel alloy in the present embodiment is prepared by controlling the other elements to be matched with them at a suitable content and adopting the preparation method of the present application. The cast steel alloy is mainly formed by using carbonitride compounds formed by the reaction of chromium, vanadium, and niobium with carbon and nitrogen, phosphorus compounds formed by the reaction of chromium, vanadium, and niobium with phosphorus, and molybdenum silicon nitrogen compounds to form an intergranular solid solution, so that the internal organizational structure is arranged more regularly, the intergranular gap is smaller, the organizational morphology can be improved, and the organizational morphology is transformed from needle-shaped to blocky and granular (such as Figure 1 As shown), and the formed solid solution disperses and refines the alloy microstructure, which can then improve the comprehensive mechanical properties of the cast steel alloy. The steel tensile strength of the cast steel alloy reaches 620Mpa, the yield strength reaches 470Mpa, and the elongation reaches more than 16.5%; the cast steel alloy in this embodiment is used as a raw material to make castings, and the obtained castings do not need to undergo heat treatment to achieve high tensile strength, yield strength and elongation. Compared with the castings made of conventional steel alloys in the prior art that need to undergo a heat treatment process, the heat-free treatment in this embodiment will effectively ensure the size of thin-walled body parts, and can also reduce the alloy production cost and energy consumption.

[0055] Example 2

[0056] The difference between step 1 of Example 2 and step 1 of Example 1 is that the target value of carbon is set to 0.25% to 0.35%, the target value of phosphorus is set to ≤0.035%, the target value of sulfur is set to ≤0.035%, the added content of silicon is set to 0.2% to 0.35%, and the added content of molybdenum is set to 0.35% to 0.45%.

[0057] The difference between step 2 of embodiment 2 and step 2 of embodiment 1 is that the semi-finished steel ingot is remelted in a vacuum environment with a vacuum degree of ≤200 mbar, and the addition content of MnFe is set to 0.6%~0.9%, the addition content of CrFe is set to 1.2%~1.5%, the addition content of BFe is set to 0.025%~0.035%, the addition content of VFe is set to 0.1%~0.15%, the addition content of Al is set to 0.3%~0.4%, the addition content of Nb powder is set to 0.02%~0.05%, and the addition content of Ni powder is set to 0.8%~1.5%.

[0058] In this embodiment 2, the alloy composition of the steel alloy is optimized, and the corresponding preparation process is combined to prepare a cast steel alloy different from the prior art. In the process of preparing the cast steel alloy, smelting in a vacuum environment with a vacuum degree of ≤200mbar can ensure that the oxygen content in the cast steel alloy is less than 8*10-6 , the lower oxygen content can effectively reduce FeO, MnO and other inclusions in the cast steel alloy. Specifically, in the production process of semi-finished steel ingots, when adding Si and Mo to Fe water and passing nitrogen, a large amount of molybdenum silicon nitrogen compounds can be formed, and then MnFe, CrFe, BFe, VFe, Nb, Ni and other elements are added to the smelted semi-finished steel ingots. Carbon and nitrogen compounds formed by Cr, V, and Ni, phosphorus compounds formed by Cr, V, and Ni, and molybdenum silicon nitrogen compounds together form intergranular solid solutions. Ni elements and deoxidizer Al elements form NiAl compounds, which can effectively enhance the strength of the matrix, and NiAl nucleation and precipitation are relatively fast. In this precipitation process, Mo will be enriched between grains and form a cluster structure. The synergistic deformation of various precipitation structures and the matrix maintains the continuity of microstructural deformation and avoids the initiation of microcracks, which improves yield and tensile strength. The strength is ensured while the elongation is guaranteed, so as to obtain a cast steel alloy with good comprehensive mechanical properties. The tensile strength of the cast steel alloy reaches 870Mpa, the yield strength reaches 650Mpa, and the elongation reaches more than 12%. The cast steel alloy is then used as a raw material to prepare a casting, and the obtained casting can achieve high comprehensive mechanical properties of tensile strength, yield strength and elongation without heat treatment in subsequent processes, thereby realizing the preparation of large-scale integrated cast steel thin-walled castings with high mechanical properties. Moreover, since the key heat treatment process is omitted, the thin-walled parts will not be deformed, and then the size of the thin-walled body parts will be effectively guaranteed, meeting the market demand for large-scale integrated cast steel thin-walled castings. At the same time, the heat treatment is not required and the smelting cost does not need to be increased, thereby achieving the purpose of reducing energy consumption.

[0059] Example 3

[0060] The difference between step 1 of Example 3 and step 1 of Example 1 is that the target value of carbon is set to 0.3%~0.4%, the target value of phosphorus is set to 0.03%~0.04%, the target value of sulfur is set to ≤0.02%, the added content of silicon is set to 0.25%~0.50%, and the added content of molybdenum is set to 0.35%~0.45%.

[0061] The difference between step 2 of embodiment 3 and step 2 of embodiment 1 is that the semi-finished steel ingot is remelted in a vacuum environment with a vacuum degree of ≤150 mbar, and the content of MnFe is set to 1% to 1.5%, the content of CrFe is set to 1.5% to 3.5%, the content of BFe is set to 0.025% to 0.035%, the content of VFe is set to 0.1% to 0.2%, the added content of Al is set to 0.3% to 0.4%, the content of Nb powder is set to 0.02% to 0.05%, the content of Ni powder is set to 2% to 3.5%, the content of Co is set to 1.5% to 2.5%, the content of TiFe is set to 0.8% to 1.2%, the content of rare earth elements is set to 0.1% to 0.15%, and the rare earth elements are one or more of La, Ce, Y and other elements, and the categories can be freely selected.

[0062] In this embodiment 3, the alloy composition of the steel alloy is optimized, and a cast steel alloy different from the prior art can be prepared by combining the corresponding preparation process. The lower 3 / 4 of the molten liquid is taken from the smelting furnace to make a semi-finished steel ingot. Mn, Ni, Cr, B, V, Nb, Co, and Ti are added to the semi-finished steel ingot as a basis to finally obtain a cast steel alloy with a target composition. In the process of making the cast steel alloy, the smelting is carried out in a vacuum environment with a vacuum degree of ≤150 mbar to ensure that the oxygen content in the cast steel alloy is less than 6*10 -6, the lower oxygen content can effectively reduce FeO, MnO and other inclusions in the cast steel alloy. Rare earth elements are added to the melting furnace before pouring to make a cast steel alloy with the target composition. Specifically, in the process of making semi-finished steel ingots, nitrogen is passed while adding Si and Mo to Fe water, which can form a large amount of molybdenum silicon nitrogen compounds. Then, MnFe, CrFe, BFe, VFe, Nb, Ni and other elements are added to the smelted semi-finished steel ingots. Carbon and nitrogen compounds formed by Cr, V, and Ni, phosphorus compounds formed by Cr, V, and Ni, and molybdenum silicon nitrogen compounds jointly form intergranular solid solutions. Ni elements and deoxidizer Al elements form NiAl compounds, which can effectively enhance the strength of the matrix, and NiAl nucleation and precipitation are relatively fast. In this precipitation process, Mo will be enriched in the intergranular space and form a cluster structure. The synergistic deformation of various precipitation structures and the matrix maintains the continuity of microstructural deformation and avoids the initiation of microcracks. Co can promote the uniform nucleation and dispersion precipitation of nano-scale MoTiNi and other compounds, and the formation of martensite These nano-scale dispersed secondary strengthening intermetallic compounds Mo-Co-CN, Ti-Co-CN, and Ni-Co-CN can further improve the strength to obtain an ultra-high strength cast steel alloy. The tensile strength of the cast steel alloy reaches 1217Mpa, the yield strength reaches 969Mpa, and the elongation reaches more than 4%. The cast steel alloy is then used as the raw material to prepare castings, and the obtained castings can achieve ultra-high tensile strength and yield strength without heat treatment in subsequent processes, thereby realizing the preparation of large-scale integrated cast steel thin-walled castings with ultra-high mechanical properties. Moreover, since the key heat treatment process is omitted, the thin-walled parts will not be deformed, which will effectively ensure the size of the thin-walled body parts and meet the market demand for large-scale integrated cast steel thin-walled castings. At the same time, the absence of heat treatment does not increase the smelting cost, thereby achieving the purpose of reducing energy consumption.

[0063] Example 4

[0064] Embodiment 4 provides a cast steel alloy, which is manufactured according to the manufacturing method of the above-mentioned embodiment 1. The cast steel alloy includes, by weight percentage: carbon ≤0.25%, silicon 0.25%~0.50%, phosphorus 0.02%~0.035%, sulfur ≤0.035%, molybdenum 0.20%~0.35%, manganese 0.6%~0.9%, chromium 1.2%~1.5%, boron 0.08%~0.1%, vanadium 0.1%~0.15%, niobium 0.02%~0.05%; aluminum 0.04%~0.45%, nitrogen 0.02%~0.04%, and the balance is iron and other inevitable elements.

[0065] The cast steel alloy has a tensile strength of 615-656 MPa, such as 620 MPa, 643 MPa, 645 MPa, and 656 MPa, a yield strength of 468-485 MPa, such as 468 MPa, 470 MPa, 472 MPa, and 485 MPa, and a fracture elongation of more than 16.5.

[0066] Example 5

[0067] Embodiment 5 provides a cast steel alloy, which is manufactured according to the manufacturing method of the above-mentioned embodiment 2. The cast steel alloy includes, by weight percentage: 0.25%≤carbon≤0.35%, phosphorus≤0.035%, sulfur≤0.035%, 0.02%≤nitrogen≤0.04%, 0.025%≤boron≤0.035%, 1.2%≤chromium≤1.5%, 0.1%≤vanadium≤0.15%, 0.02%≤niobium≤0.05%, 0.35%≤molybdenum≤0.45%, 0.2%≤silicon≤0.35%, 0.6%≤manganese≤0.9%, 0.3%≤aluminum≤0.4%, 0.8%≤nickel≤1.5%, and the remainder is iron and other inevitable elements.

[0068] The cast steel alloy has a tensile strength of 850-900 MPa, such as 860 MPa, 870 MPa, 874 MPa, 879 MPa, 882 MPa, and 890 MPa; a yield strength of 620-700 MPa, such as 630 MPa, 650 MPa, 656 MPa, 661 MPa, and 665 MPa; and a breaking elongation of more than 12%.

[0069] Example 6

[0070] Embodiment 6 provides a cast steel alloy, which is manufactured according to the manufacturing method of the above-mentioned embodiment 3. The cast steel alloy includes, by weight percentage: 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% ≤ manganese ≤ 1.5%, 0.3% ≤ aluminum ≤ 0.4%, 2% ≤ nickel ≤ 3.5%, 1.5% ≤ cobalt ≤ 2.5%, 0.8% ≤ titanium ≤ 1.2%, 0.1% ≤ rare earth elements ≤ 0.15%, and the balance is iron and other inevitable elements.

[0071] The cast steel alloy has a tensile strength of 1200-1220 MPa, such as 1208 MPa, 1209 MPa, and 1217 MPa; a yield strength of 950-980 MPa, such as 962 MPa, 969 MPa, and 971 MPa; and a fracture elongation of more than 4%.

[0072] Example 7

[0073] Example 7 provides a thin-walled vehicle body part, which is formed by the cast steel alloy of Example 4 or the cast steel alloy of Example 5 or the cast steel alloy of Example 6.

[0074] Example 8

[0075] Embodiment 8 provides a vehicle, which includes the thin-walled vehicle body part of embodiment 7 above.

[0076] The disclosure of Example 1 is further described in detail below through Preparation Examples 1-3 and Comparative Examples 1-7. The raw materials used in the Preparation Examples can all be obtained through commercial channels.

[0077] Preparation Example 1

[0078] A cast steel alloy prepared in this Preparation Example 1 has the chemical composition of 0.1% carbon, 0.25% silicon, 0.20% molybdenum, 0.6% manganese, 0.020% phosphorus, 0.001% sulfur, 1.2% chromium, 0.08% boron, 0.1% vanadium, 0.02% niobium, 0.04% aluminum, 0.02% nitrogen, other impurity elements and the balance iron.

[0079] The method for preparing a cast steel alloy in Preparation Example 1 comprises the following steps:

[0080] 1) Making semi-finished steel ingots: raising the molten iron to a first temperature of above 1700°C for proper decarburization, dephosphorization and desulfurization to reach a target carbon content of 0.1%; a target phosphorus content of 0.02%; and a target sulfur content of 0.001%; ​​then lowering the molten iron to a second temperature of 1650°C, adding 0.25% silicon and 0.20% molybdenum to the molten iron, and passing nitrogen at the same time; then adding GaF2 at 2 kg / ton for slag removal and preliminary deoxidation; finally, pouring the molten steel to make semi-finished steel ingots.

[0081] 2) Melting semi-finished steel ingots: heat the semi-finished steel ingots to a third temperature of 1650°C, add GaF2 at 2 kg / ton to remove slag and preliminarily deoxidize to obtain a melt, cool the melt to a fourth temperature of 1550°C, then add 0.6% MnFe, 1.2% CrFe, 0.08% BFe, 0.1% VFe, and 0.02% Nb powders to fully stir and melt to obtain a target melt.

[0082] 3) Pouring; adding 0.04% pure Al to the target melt at 0.3 kg / ton for deoxidation and deslagging, and then pouring the target melt into a mold to form a cast steel alloy.

[0083] Preparation Examples 2 to 3, Comparative Examples 1 to 7

[0084] The preparation methods of Preparation Examples 2 to 3 and Comparative Examples 1-2 are the same as those of Preparation Example 1. The differences in specific alloy components and contents are shown in Table 1:

[0085] Table 1 (mass percentage, %)

[0086]

[0087] The processes of the preparation methods in Comparative Example 1 and Preparation Example 1 are the same, except that the content of the alloy components is different, and the content of the components of some alloys is set to a range lower than the content of the alloy components in Preparation Example 1.

[0088] The manufacturing process of Comparative Example 2 is the same as that of Preparation Example 3, except that the content of the alloy components is different, and the content of the components of some alloys is set to a range higher than that of the alloy components in Preparation Example 3.

[0089] Comparative Example 3 has the same alloy component content as that in Preparation Example 1, except that a conventional process is used to prepare the cast steel alloy. The specific steps are as follows:

[0090] First, add iron and target alloy components into the melting furnace, raise the temperature to above 1700℃ for smelting and decarburization, dephosphorization and desulfurization treatment. After the carbon, phosphorus and sulfur meet the composition requirements, add GaF2 into the molten steel at 2kg / ton for slag removal and preliminary deoxidation. Finally, the molten steel is poured into ingots.

[0091] Comparative Example 4 has the same alloy component content as that in Preparation Example 2, except that conventional processes are used to prepare the cast steel alloy.

[0092] Comparative Example 5 has the same alloy component content as that in Preparation Example 3, except that the cast steel alloy is prepared using conventional processes.

[0093] The alloy components in Comparative Example 6 are the same as those in Comparative Example 1, except that the cast steel alloy is prepared using conventional processes.

[0094] The alloy components in Comparative Example 7 are the same as those in Comparative Example 2, except that the cast steel alloy is prepared using conventional processes.

[0095] The test methods for various indicators of the finished steel castings produced in the following examples are as follows:

[0096] Tensile strength: The tensile strength of the finished steel castings obtained in each embodiment and the comparative example products were tested in accordance with GB / T228.

[0097] Yield strength: Yield strength test was performed on the finished steel castings obtained in each embodiment and the comparative example products according to GB / T228.

[0098] like Figure 2 As shown in the figure, it is a force-extensometer curve of sample 1, sample 2 and sample 3 selected from the cast steel alloy finished products prepared by taking any target value within the alloy composition range of this embodiment 4. From the force-extensometer curve, it can be shown that within the alloy composition range, the tensile strength, yield strength and elongation at break can all meet the performance requirements of the cast steel alloy in this embodiment 4; the following Table 2 shows the performance analysis results of the finished steel castings prepared by Preparation Example 1, Preparation Example 2, Preparation Example 3 and Comparative Examples 1-7 of the present invention.

[0099] Table 2

[0100]

[0101]

[0102] From the comparison of the experimental data of Preparation Examples 1-3 and Comparative Examples 1-7 in Table 2, it can be found that:

[0103] From the comparison of the experimental data of Preparation Example 1 to Preparation Example 3, it can be found that when the content of various alloy components is selected within the alloy component range of this application and combined with the production method of this application, the tensile strength, yield strength and elongation after fracture of the cast steel alloy all meet the requirements of this application, and the test state is normal.

[0104] From the comparison of the experimental data of Preparation Example 1 and Comparative Example 1, it can be found that when the content of some key alloy components in Comparative Example 1 is lower than the alloy component range of the present application and combined with the production method of the present application, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of the present application, and the test state is abnormal.

[0105] From the comparison of the experimental data of Preparation Example 3 and Comparative Example 2, it can be found that when the content of some key alloy components in Comparative Example 2 is higher than the alloy component range of the present application and combined with the production method of the present application, the tensile strength and yield strength of the cast steel alloy are higher than the tensile strength and yield strength in Example 3 of the present embodiment, but the elongation after fracture is still lower than the elongation after fracture in Example 3 of the present embodiment, and the test state is abnormal.

[0106] From the comparison of the experimental data of Preparation Example 1 and Comparative Example 3, Preparation Example 2 and Comparative Example 4, and Preparation Example 3 and Comparative Example 5, it can be found that when the contents of various alloy components are within the alloy component range of this application and combined with the conventional production method, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of this application, and the test state is abnormal.

[0107] From the comparison of the experimental data of Comparative Example 1 and Comparative Example 6, it can be found that when the component content of some key alloys is set to be lower than the alloy component range of this application and combined with the conventional production method, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of this application, and the test status is abnormal.

[0108] From the comparison of the experimental data of Comparative Example 2 and Comparative Example 7, it can be found that when the component content of some key alloys is set to be higher than the alloy component range of this application and combined with the conventional production method, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of this application, and the test status is abnormal.

[0109] The disclosure of Example 2 is further described in detail below through Preparation Examples 4 to 6 and Comparative Examples 8 to 14. The raw materials used in the Preparation Examples can all be obtained through commercial channels.

[0110] Preparation Example 4

[0111] A cast steel alloy prepared in this Preparation Example 4 has the chemical composition of: 0.25% carbon, 0.2% silicon, 0.35% molybdenum, 0.6% manganese, 0.001% phosphorus, 0.001% sulfur, 1.2% chromium, 0.025% boron, 0.1% vanadium, 0.02% niobium, 0.3% aluminum, 0.02% nitrogen, 0.8 nickel, other impurity elements and the balance iron.

[0112] The method for preparing a cast steel alloy in Preparation Example 4 comprises the following steps:

[0113] 1) Making semi-finished steel ingots: raising the molten iron to a first temperature of above 1700°C for proper decarburization, dephosphorization and desulfurization to reach a target carbon content of 0.25%; a target phosphorus content of 0.001%; ​​and a target sulfur content of 0.001%; ​​then lowering the molten iron to a second temperature of 1650°C, adding 0.2% silicon and 0.35% molybdenum to the molten iron, and passing nitrogen at the same time; then adding GaF2 at 2 kg / ton for slag removal and preliminary deoxidation; finally, pouring the molten steel to make semi-finished steel ingots.

[0114] 2) Melting semi-finished steel ingots: remelt the semi-finished steel ingots in a vacuum environment with a vacuum degree of ≤200mbar, first heat the semi-finished steel ingots to a third temperature of 1650°C, add GaF2 at 2Kg / ton to remove slag and preliminarily deoxidize to obtain a melt, cool the melt to a fourth temperature of 1550°C, then add 0.6% MnFe, 1.2% CrFe, 0.025% BFe, 0.1% VFe, 0.02% Nb powder, and 0.8% Ni powder to fully stir and melt to obtain a target melt.

[0115] 3) Pouring; adding 0.3% pure Al to the target melt at 0.3 kg / ton for deoxidation and deslagging, and then pouring the target melt into a mold to form a cast steel alloy.

[0116] Preparation Examples 5 to 6, Comparative Examples 8 to 14

[0117] The preparation methods of Preparation Examples 5-6 and Comparative Examples 8-9 are the same as those of Preparation Example 4. The differences in specific alloy components and contents are shown in Table 3:

[0118] Table 3 (mass percentage, %)

[0119]

[0120] The process of the comparative example 8 is the same as that of the preparation method in the present preparation example 4, except that the content of the alloy components is different, and the content of the components of some alloys is set to a range lower than the content of the alloy components in the present preparation example 4.

[0121] The process of the preparation method in Comparative Example 9 is the same as that in Preparation Example 4, except that the content of the alloy components is different, and the content of the components of some alloys is set to a range higher than the content of the alloy components in Preparation Example 4.

[0122] Comparative Example 10 has the same alloy component content as that in Preparation Example 4, except that a conventional process is used to prepare the cast steel alloy, and the specific steps are as follows:

[0123] First, add iron and target alloy components into the melting furnace, raise the temperature to above 1700℃ for smelting and decarburization, dephosphorization and desulfurization treatment. After the carbon, phosphorus and sulfur meet the composition requirements, add GaF2 into the molten steel at 2kg / ton for slag removal and preliminary deoxidation. Finally, the molten steel is poured into ingots.

[0124] Comparative Example 11 has the same alloy component content as that in Preparation Example 5, except that conventional processes are used to prepare the cast steel alloy.

[0125] Comparative Example 12 has the same alloy component content as that in Preparation Example 6, except that conventional processes are used to prepare the cast steel alloy.

[0126] The alloy components in Comparative Example 13 are the same as those in Comparative Example 8, except that the cast steel alloy is prepared using conventional processes.

[0127] The alloy components in Comparative Example 14 are the same as those in Comparative Example 9, except that the cast steel alloy is prepared using conventional processes.

[0128] The test methods for various indicators of the finished steel castings produced in the following examples are as follows:

[0129] Tensile strength: The tensile strength of the finished steel castings obtained in each embodiment and the comparative example products were tested in accordance with GB / T228.

[0130] Yield strength: Yield strength test was performed on the finished steel castings obtained in each embodiment and the comparative example products according to GB / T228.

[0131] like Figure 3 As shown in the figure, it is a force-extensometer curve of sample 1, sample 2 and sample 3 selected from the cast steel alloy finished products prepared by taking any target value within the alloy composition range of this embodiment 5. From the force-extensometer curve, it can be shown that within the alloy composition range, the tensile strength, yield strength and elongation at break can all meet the performance requirements of the cast steel alloy in this embodiment 5; the following Table 4 shows the performance analysis results of the finished steel castings prepared by Preparation Example 4, Preparation Example 5, Preparation Example 6 and Comparative Examples 8-14 of the present invention.

[0132] Table 4

[0133]

[0134]

[0135] From the comparison of the experimental data of Preparation Examples 4-6 and Comparative Examples 8-14 in Table 4, it can be found that:

[0136] From the comparison of the experimental data of Preparation Example 4 to Preparation Example 6, it can be found that when the content of various alloy components is selected within the alloy component range of this application and combined with the production method of this application, the tensile strength, yield strength and elongation after fracture of the cast steel alloy all meet the requirements of this application, and the test state is normal.

[0137] From the comparison of the experimental data of Preparation Example 4 and Comparative Example 8, it can be found that when the content of some key alloy components in Comparative Example 8 is lower than the alloy component range of the present application and combined with the production method of the present application, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of the present application, and the test state is abnormal.

[0138] From the comparison of the experimental data of Preparation Example 5 and Comparative Example 9, it can be found that when the content of some key alloy components in Comparative Example 9 is higher than the alloy component range of the present application and combined with the production method of the present application, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of the present application, and the test state is abnormal.

[0139] From the comparison of the experimental data of Preparation Example 4 and Comparative Example 10, Preparation Example 5 and Comparative Example 11, and Preparation Example 6 and Comparative Example 12, it can be found that when the contents of various alloy components are within the alloy component range of this application and combined with the conventional production method, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of this application, and the test state is abnormal.

[0140] From the comparison of the experimental data of Comparative Example 8 and Comparative Example 13, it can be found that when the component content of some key alloys is set to be lower than the alloy component range of this application and combined with the conventional production method, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of this application, and the test state is abnormal.

[0141] From the comparison of the experimental data of Comparative Example 9 and Comparative Example 14, it can be found that when the component content of some key alloys is set to be higher than the alloy component range of this application and combined with the conventional production method, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of this application, and the test status is abnormal.

[0142] The disclosure of Example 3 is further described in detail below through Preparation Examples 7 to 9 and Comparative Examples 15 to 21. The raw materials used in the Preparation Examples can all be obtained through commercial channels.

[0143] Preparation Example 7

[0144] A cast steel alloy prepared in this Preparation Example 7 has the chemical composition of: 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, 2.0% nickel, 0.8% titanium, 1.5% Co, 0.1% rare earth elements, other impurity elements and the balance iron.

[0145] The method for preparing a cast steel alloy in Preparation Example 7 comprises the following steps:

[0146] 1) Making semi-finished steel ingots: raising the molten iron to a first temperature of above 1700°C for proper decarburization, dephosphorization and desulfurization to reach a target carbon content of 0.3%; a target phosphorus content of 0.03%; and a target sulfur content of 0.001%; ​​then lowering the molten iron to a second temperature of 1650°C, adding 0.25% silicon and 0.35% molybdenum to the molten iron, and passing nitrogen at the same time; then adding GaF2 at 2 kg / ton for slag removal and preliminary deoxidation; finally, pouring the molten steel to make semi-finished steel ingots.

[0147] 2) Melting semi-finished steel ingots: remelt the semi-finished steel ingots in a vacuum environment with a vacuum degree of ≤150mbar, first heat the semi-finished steel ingots to a third temperature of 1650°C, add GaF2 at 2Kg / ton to remove slag and preliminarily deoxidize to obtain a melt, cool the melt to a fourth temperature of 1550°C, then add 1.0% MnFe, 1.5% CrFe, 0.025% BFe, 0.1% VFe, 0.02% Nb powder, 2.0% Ni powder, 0.8% TiFe, 1.5% Co and 0.1% rare earth elements and stir and melt them thoroughly to obtain a target melt.

[0148] 3) Pouring; adding 0.3% pure Al to the target melt at 0.3 kg / ton for deoxidation and deslagging, and then pouring the target melt into a mold to form a cast steel alloy.

[0149] Preparation Examples 8-9, Comparative Examples 15-21

[0150] The preparation methods of Preparation Examples 8 to 9 and Comparative Examples 15 to 21 are the same as those of Preparation Example 7. The differences in specific alloy components and contents are shown in Table 5:

[0151] Table 5

[0152]

[0153]

[0154] The process of the comparative example 15 is the same as that of the preparation method in the present preparation example 7, except that the content of the alloy components is different, and the content of the components of some alloys is set to a range lower than the content of the alloy components in the present preparation example 7.

[0155] The process of the comparative example 16 is the same as that of the preparation method in the present preparation example 9, except that the content of the alloy components is different, and the content of the components of some alloys is set to a range higher than the content of the alloy components in the present preparation example 9.

[0156] Comparative Example 17 has the same alloy component content as that in Preparation Example 7, except that a conventional process is used to prepare the cast steel alloy, and the specific steps are as follows:

[0157] First, add iron and target alloy components into the melting furnace, raise the temperature to above 1700℃ for smelting and decarburization, dephosphorization and desulfurization treatment. After the carbon, phosphorus and sulfur meet the composition requirements, add GaF2 into the molten steel at 2kg / ton for slag removal and preliminary deoxidation. Finally, the molten steel is poured into ingots.

[0158] The alloy component contents in Comparative Example 18 are the same as those in Preparation Example 8, except that conventional processes are used to prepare the cast steel alloy.

[0159] Comparative Example 19 has the same alloy component content as that in Preparation Example 9, except that conventional processes are used to prepare the cast steel alloy.

[0160] The alloy components in Comparative Example 20 are the same as those in Comparative Example 15, except that the cast steel alloy is prepared using conventional processes.

[0161] The alloy components in Comparative Example 21 are the same as those in Comparative Example 16, except that the conventional process is used to produce the cast steel alloy.

[0162] The test methods for various indicators of the finished steel castings produced in the following examples are as follows:

[0163] Tensile strength: The tensile strength of the finished steel castings obtained in each embodiment and the comparative example products were tested in accordance with GB / T228.

[0164] Yield strength: Yield strength test was performed on the finished steel castings obtained in each embodiment and the comparative example products according to GB / T228.

[0165] like Figure 4 As shown in the figure, it is a force-extensometer curve of sample 1, sample 2 and sample 3 selected from the cast steel alloy finished products prepared by taking any target value within the alloy composition range of this embodiment 6. From the force-extensometer curve, it can be shown that within the alloy composition range, the tensile strength, yield strength and elongation at break can all meet the performance requirements of the cast steel alloy in this embodiment 6; the following Table 6 shows the performance analysis results of the finished steel castings prepared by Preparation Example 7, Preparation Example 8, Preparation Example 9 and Comparative Examples 15-21 of the present invention.

[0166] Table 6

[0167]

[0168]

[0169] From the comparison of the experimental data of Preparation Examples 7-9 and Comparative Examples 15-21 in Table 6, it can be found that:

[0170] From the comparison of the experimental data of Preparation Examples 7 to 9, it can be found that when the contents of various alloy components are selected within the alloy component range of this application and combined with the production method of this application, the tensile strength, yield strength and elongation after fracture of the cast steel alloy all meet the requirements of this application, and the test state is normal.

[0171] From the comparison of the experimental data of Preparation Example 7 and Comparative Example 15, it can be found that when the content of some key alloy components in Comparative Example 15 is lower than the alloy component range of the present application and combined with the production method of the present application, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of the present application, and the test state is abnormal.

[0172] From the comparison of the experimental data of Preparation Example 9 and Comparative Example 16, it can be found that when the content of some key alloy components in Comparative Example 16 is higher than the alloy component range of the present application and combined with the production method of the present application, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of the present application, and the test state is abnormal.

[0173] From the comparison of the experimental data of Preparation Example 7 and Comparative Example 17, Preparation Example 8 and Comparative Example 18, and Preparation Example 9 and Comparative Example 19, it can be found that when the contents of various alloy components are within the alloy component range of this application and combined with the conventional production method, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of this application, and the test state is abnormal.

[0174] From the comparison of the experimental data of Comparative Example 15 and Comparative Example 20, it can be found that when the component content of some key alloys is set to be lower than the alloy component range of this application and combined with the conventional production method, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of this application, and the test status is abnormal.

[0175] From the comparison of the experimental data of Comparative Example 16 and Comparative Example 21, it can be found that when the component content of some key alloys is set to be higher than the alloy component range of this application and combined with the conventional production method, the tensile strength, yield strength and elongation after fracture of the cast steel alloy do not meet the requirements of this application, and the test state is abnormal.

[0176] It should be understood that the above specific embodiments of the present application are only used to illustrate or explain the principles of the present application, and do not constitute a limitation to the present application. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present application should be included in the protection scope of the present application. In addition, the claims attached to the present application are intended to cover all changes and modifications that fall within the scope and boundaries of the attached claims or the equivalent forms of such scope and boundaries.

Claims

1. A method for producing a cast steel alloy, characterized in that: The steps include: Making semi-finished steel ingots; raising the molten iron to a first temperature greater than 1700°C for decarburization, dephosphorization and desulfurization to achieve target contents of carbon, phosphorus and sulfur; lowering the molten iron to a second temperature of 1650-1700°C, then adding a certain amount of silicon and molybdenum to the molten iron while passing inert gas, and finally casting to make semi-finished steel ingots; Melting the semi-finished steel ingot; raising the temperature of the semi-finished steel ingot to a third temperature of 1650-1700° C. for melting treatment to obtain a melt, lowering the melt to a fourth temperature of 1550-1600° C., and adding a certain amount of MnFe, CrFe, BFe, VFe and Nb powder for stirring and melting to obtain a target melt; Pouring; pouring the target melt to form a cast steel alloy.

2. The method according to claim 1, characterized in that: In terms of weight percentage, The target value of carbon is set to ≤ 0.25%; The target value of phosphorus is set to 0.02% to 0.035%; The target value for sulfur is set to ≤ 0.035%.

3. The method according to claim 2, characterized in that: In terms of weight percentage, The added content of silicon is set to 0.25% to 0.50%; The added content of molybdenum is set to ≤0.45%; The added content of MnFe is set to 0.6% to 0.9%; The added content of CrFe is set to 1.2% to 1.5%; The added content of BFe is set to 0.08% to 0.1%; The added content of VFe is set to 0.1% to 0.15%; The added content of the Nb powder is set to 0.02% to 0.05%.

4. The method according to claim 1, characterized in that: The following alloy raw materials are further added to the smelting semi-finished steel ingot in the step: Ni powder and pure aluminum, and the semi-finished steel ingot is melted in a vacuum environment with a vacuum degree of ≤200mbar.

5. The method according to claim 4, characterized in that: In terms of weight percentage, The target value of carbon is set to 0.25% to 0.35%; The target value of phosphorus is set to ≤ 0.035%; The target value for sulfur is set to ≤ 0.035%.

6. The method according to claim 5, characterized in that: In terms of weight percentage, The added content of silicon is set to 0.2% to 0.35%; The added content of molybdenum is set to 0.35% to 0.45%; The added content of MnFe is set to 0.6% to 0.9%; The added content of CrFe is set to 1.2% to 1.5%; The added content of BFe is set to 0.025% to 0.035%; The added content of VFe is set to 0.1% to 0.15%; The added content of the Nb powder is set to 0.02% to 0.05%; The added content of the Ni powder is set to 0.8% to 1.5%; The added content of pure aluminum is set to 0.3% to 0.4%.

7. The method according to claim 4, characterized in that: The following alloy raw materials are further added to the smelting semi-finished steel ingot in the step: TiFe, cobalt and rare earth elements, and the semi-finished steel ingot is melted in a vacuum environment with a vacuum degree of ≤150mbar.

8. The method according to claim 7, characterized in that: In terms of weight percentage, The target value of carbon is set to 0.3% to 0.4%; The target value of phosphorus is set to 0.03% to 0.04%; The target value for sulfur is set to ≤ 0.02%.

9. The manufacturing method according to claim 8, characterized in that: In terms of weight percentage, The added content of silicon is set to 0.25% to 0.50%; The added content of molybdenum is set to 0.35% to 0.45%; The added content of MnFe is set to 1% to 1.5%; The added content of CrFe is set to 1.5% to 3.5%; The added content of BFe is set to 0.025% to 0.035%; The added content of VFe is set to 0.1% to 0.2%; The added content of the Nb powder is set to 0.02% to 0.05%; The added content of the Ni powder is set to 2% to 3.5%; The added content of pure aluminum is set to 0.3% to 0.4%; The added content of TiFe is set to 0.8% to 1.2%; The added content of cobalt is set to 1.5% to 2.5%; The added content of the rare earth element is set to 0.1% to 0.15%.

10. A cast steel alloy, characterized in that The cast steel alloy is manufactured according to the manufacturing method according to any one of claims 1 to 3, wherein the cast steel alloy comprises the following raw materials by mass fraction: carbon ≤ 0.25%, 0.02% ≤ phosphorus ≤ 0.035%, sulfur ≤ 0.035%, 0.02% ≤ nitrogen ≤ 0.04%, 0.08% ≤ boron ≤ 0.1%, 1.2% ≤ chromium ≤ 1.5%, 0.1% ≤ vanadium ≤ 0.15%, 0.02% ≤ niobium ≤ 0.05%, 0.20% ≤ molybdenum ≤ 0.35%, 0.25% ≤ silicon ≤ 0.50%, 0.6% ≤ manganese ≤ 0.9%, 0.04% ≤ aluminum ≤ 0.45% and iron; Alternatively, the cast steel alloy is produced according to the production method according to any one of claims 4 to 6, wherein the cast steel alloy comprises the following raw materials by mass fraction: 0.25%≤carbon≤0.35%, phosphorus≤0.035%, sulfur≤0.035%, 0.02%≤nitrogen≤0.04%, 0.025%≤boron≤0.035%, 1.2%≤chromium≤1.5%, 0.1%≤vanadium≤0.15%, 0.02%≤niobium≤0.05%, 0.35%≤molybdenum≤0.45%, 0.2%≤silicon≤0.35%, 0.6%≤manganese≤0.9%, 0.3%≤aluminum≤0.4%, 0.8%≤nickel≤1.5% and iron; Alternatively, the cast steel alloy is produced according to the production method according to any one of claims 7 to 9, wherein the cast steel alloy includes 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% ≤ manganese ≤ 1.5%, 0.3% ≤ aluminum ≤ 0.4%, 2% ≤ nickel ≤ 3.5%, 1.5% ≤ cobalt ≤ 2.5%, 0.8% ≤ titanium ≤ 1.2%, 0.1% ≤ rare earth elements ≤ 0.15% and iron.

11. A thin-walled vehicle body part, characterized in that: Prepared from the cast steel alloy as claimed in claim 10.

12. A vehicle, characterized in that: It comprises the thin-walled vehicle body part as claimed in claim 11.

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