Method for producing a cast steel alloy and use thereof

Abstract

The application discloses a manufacturing method and application of cast steel alloy, and the method comprises the following steps: increasing the molten iron to a first temperature above 1700 DEG C for decarburization, dephosphorization and desulfurization treatment, so as to achieve the content of carbon, phosphorus and sulfur within the target value; reducing the molten iron to a second temperature of 1650-1700 DEG C, adding a certain amount of silicon and molybdenum into the molten iron while passing inert gas, 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 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 for stirring and melting to obtain a target melt; and pouring the target melt to form the cast steel alloy. The cast steel alloy is prepared by the manufacturing method, and a cast piece is prepared by taking the cast steel alloy as a raw material; the cast piece can achieve higher tensile strength, yield strength and elongation without heat treatment, and then a large integrated cast steel thin-wall cast piece with excellent dimensional stability and meeting market demand is prepared.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of alloy casting preparation, and in particular to a 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 developed 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] Compared with integrated cast aluminum, integrated cast steel has obvious advantages, such as mechanical performance being 2-3 times higher than that of cast aluminum, simple connection mode, simple part repair, cost advantage, and the price of steel being much lower than that of aluminum alloy. Therefore, the castings made of integrated cast steel can be used for vehicle body thin-wall parts. However, the castings made of integrated cast steel in the prior art often need to be subjected to a heat treatment process to achieve high tensile strength, yield strength and elongation. The heat treatment process increases smelting cost and energy consumption.

[0004] Therefore, there is an urgent need to provide a cast steel alloy manufacturing method and application to solve the above technical problems. SUMMARY

[0005] The application provides a cast steel alloy manufacturing method and application. The cast steel alloy is prepared by using the manufacturing method, and the castings are prepared by using the cast steel alloy as raw material. The obtained castings do not need to be subjected to a heat treatment process and can achieve high tensile strength, yield strength and elongation, and can be used for vehicle body thin-wall parts.

[0006] According to some embodiments, a cast steel alloy manufacturing method is provided, which comprises the following steps:

[0007] A semi-finished steel ingot is prepared. Molten iron is raised to a first temperature of 1700 DEG C or higher for decarburization, dephosphorization and desulfurization treatment to achieve the composition content of carbon, phosphorus and sulfur within the target value. The molten iron is lowered to a second temperature of 1650-1700 DEG C, a certain amount of silicon and molybdenum is added to the molten iron, inert gas is blown, and finally the semi-finished steel ingot is prepared by pouring.

[0008] The semi-finished steel ingot is smelted. The temperature of the semi-finished steel ingot is raised to a third temperature of 1650-1700 DEG C for melting treatment to obtain a melt. The melt is lowered to a fourth temperature of 1550-1600 DEG C, and a certain amount of MnFe, CrFe, BFe, VFe and Nb powder is added for stirring and melting to obtain a target melt.

[0009] Pouring; the target melt is poured to prepare a cast steel alloy.

[0010] As preferred, the target value of the carbon is set to be ≤0.25%; the target value of the phosphor is set to be 0.02%-0.035%; the target value of the sulfur is set to be ≤0.035% in terms of weight percentage.

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

[0012] As preferred, the following alloy raw materials are also added in the smelting semi-product steel ingot step: Ni powder and pure aluminum, and the semi-product steel ingot is melted under a vacuum environment with a vacuum degree ≤200mbar.

[0013] As preferred, the target value of the carbon is set to be 0.25%-0.35%; the target value of the phosphor is set to be ≤0.035%; the target value of the sulfur is set to be ≤0.035% in terms of weight percentage.

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

[0015] As preferred, the following alloy raw materials are also added in the smelting semi-product ingot step: TiFe, cobalt and rare earth elements, and the semi-product ingot is melted in a vacuum environment with a vacuum degree ≤150mbar.

[0016] As preferred, the target value of the carbon is set to 0.3%~0.4% by weight percentage; the target value of the phosphorus is set to 0.03%~0.04%; the target value of the sulfur is set to ≤0.02%.

[0017] As preferred, the added content of the silicon is set to 0.25%~0.50% such as 0.30%, 0.35%, 0.40%, 0.45% by weight; the added content of the molybdenum is set to 0.35%~0.45% such as 0.38%, 0.40%, 0.42%; the added content of the MnFe is set to 1%~1.5% such as 1.2%, 1.3%, 1.4%; the added content of the CrFe is set to 1.5%~3.5% such as 2.0%, 2.5%, 3.0%, 3.4%; the added content of the BFe is set to 0.025%~0.035% such as 0.030%, 0.032%, 0.034%; the added content of the VFe is set to 0.1%~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 application further provides a cast steel alloy prepared according to the preparation method, the cast steel alloy comprising raw materials in the following mass fractions: 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 application further provides a cast steel alloy prepared by the method, the cast steel alloy comprising raw materials in the following mass fractions: 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 application further provides a cast steel alloy prepared by the method, the cast steel alloy comprising 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%≤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 application further provides a vehicle body thin-wall part prepared from the cast steel alloy.

[0022] According to some embodiments, the application further provides a vehicle comprising the vehicle body thin-wall part.

[0023] Beneficial effects:

[0024] The application provides a manufacturing method and application of cast steel alloy. Compared with the castings manufactured by the steel alloy in the prior art, the castings manufactured by the cast steel alloy in the application can reach higher tensile strength, yield strength and elongation without heat treatment. The cast steel alloy is prepared by optimizing the alloy composition of the steel alloy and combining with the corresponding preparation process. The cast steel alloy has higher tensile strength, yield strength and elongation. Then, the castings are prepared by using the cast steel alloy as raw material. The castings can be prepared into large integrated cast steel thin-wall castings with high mechanical properties under the condition of heat treatment free. The castings have a steel tensile strength of 620 Mpa, a yield strength of 470 Mpa and a fracture elongation of more than 16.5% at the key stress position. Since the castings do not need heat treatment, the thin-wall parts prepared from the castings have small deformation and good dimensional stability, thereby effectively ensuring the size of the thin-wall body parts, meeting the market demand for large integrated cast steel thin-wall castings, and saving the manufacturing cost and reducing the energy consumption.

[0025] For the cast steel alloy, the cast steel alloy has suitable contents of manganese, chromium, boron, vanadium and niobium, and other elements are controlled at suitable contents. The cast steel alloy is prepared by the manufacturing method. The castings manufactured by the cast steel alloy do not need heat treatment in subsequent processes and can reach higher tensile strength, yield strength and elongation. The carbonitrides formed by chromium, vanadium and niobium reacting with carbon and nitrogen, the phosphides formed by chromium, vanadium and niobium reacting with phosphorus and the molybdenum silicon nitride compound jointly form intergranular solid solution, the internal organizational structure is more regular, the intergranular gap is smaller, the organizational form is improved, the organizational form is changed from acicular to blocky and granular, the formed solid solution disperses and refines the alloy microstructure, and the comprehensive mechanical properties of the alloy are improved.

[0026] For the manufacturing method, in order to ensure the composition of the alloy in the cast steel alloy, the application is selected in steps. The semi-finished steel ingot is prepared first, and then manganese, chromium, boron, vanadium and niobium are added based on the semi-finished steel ingot to obtain the finished steel ingot containing target components. In the process of preparing the semi-finished steel ingot, nitrogen gas is passed while adding silicon and molybdenum to the molten iron to form a protective gas and a large amount of molybdenum silicon nitride compound. Then, MnFe, CrFe, BFe, VFe and Nb are added in the melting of the semi-finished steel ingot to effectively reduce the formation and segregation of chromium, vanadium and niobium nitrides, thereby obtaining better performance. The manufacturing process and the addition of various alloy components can prepare the cast steel alloy different from the prior art. The castings are prepared by using the cast steel alloy as raw material. The castings can reach higher tensile strength, yield strength and elongation without heat treatment. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed in the embodiments will be briefly introduced as follows. Obviously, the accompanying drawings in the following description only need to be some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0028] Figure 1 It is a magnified schematic diagram of the blocky and granular metallographic structure of the internal organizational structure of the cast steel alloy in the embodiments of the present application;

[0029] Figure 2 It is a force-extensometer curve diagram of sample 1, sample 2 and sample 3 selected from the finished cast steel alloy prepared by taking target values at random within the alloy composition range of the embodiment 4 of the present application;

[0030] Figure 3 It is a force-extensometer curve diagram of sample 1, sample 2 and sample 3 selected from the finished cast steel alloy prepared by taking target values at random within the alloy composition range of the embodiment 5 of the present application;

[0031] Figure 4 It is a force-extensometer curve diagram of sample 1, sample 2 and sample 3 selected from the finished cast steel alloy prepared by taking target values at random within the alloy composition range of the embodiment 6 of the present application. DETAILED DESCRIPTION

[0032] 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 accompanying 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 realized. The following embodiments are classified for the 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.

[0033] The castings made of steel alloy in the prior art need to be heat treated to achieve higher tensile strength, yield strength and elongation. On the one hand, the heat treatment process increases the cost and energy consumption. On the other hand, for thin-walled parts of the vehicle body, the size of the parts is sensitive to temperature. The thin-walled parts after heat treatment will be severely deformed, which cannot guarantee the size and stability of the thin-walled parts of the vehicle body.

[0034] Therefore, the embodiment of the present application provides a manufacturing method and application of a cast steel alloy. By controlling the content of each alloying element in each step within a target value, a cast steel alloy different from the prior art can be prepared. The cast steel alloy has high tensile strength, yield strength, elongation and other properties. The castings made of the cast steel alloy as a raw material do not need to be heat treated, i.e., the heat treatment process is omitted, and can also achieve high tensile strength, yield strength and elongation. Meanwhile, the heat treatment-free process effectively ensures the dimensional accuracy of the thin-walled body parts, and can also reduce the production cost of the alloy and energy consumption.

[0035] Embodiment 1

[0036] The manufacturing method of the cast steel alloy provided in the embodiment 1 will be described in detail below with reference to the accompanying drawings. The manufacturing method includes the following steps:

[0037] 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;

[0038] Specifically, first, the molten iron is raised to a first temperature of 1700°C or higher for decarburization, dephosphorization and desulfurization treatment to achieve a target value of carbon ≤0.25%, phosphorus 0.02%-0.035% and sulfur ≤0.035%. 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, heating is continued until the content of carbon, phosphorus and sulfur elements is removed to below the target value.

[0039] Then, the temperature of the molten iron is 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, inert gas such as nitrogen is passed through, and then molten steel is obtained. In this operation, by lowering the temperature, it can be ensured that the added elements are fully fused. However, it cannot be lowered too much, which cannot effectively fuse, but it also cannot be set too high, which will have heat loss. Therefore, in the embodiment, the second temperature is set to 1650-1700°C.

[0040] 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.

[0041] Finally, the molten steel is poured to form a semi-finished steel ingot.

[0042] In the preparation process, a semi-finished steel ingot is first prepared, which can not only ensure the alloying elements but also facilitate transportation to a place where melting is needed.

[0043] Step 2: smelting semi-finished steel ingot; after the semi-finished steel ingot prepared above is melted, a corresponding target melt is obtained;

[0044] Specifically, first, the semi-finished steel ingot prepared above is raised to a third temperature of 1650-1700℃ 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℃, and 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 are added for stirring and melting to obtain a corresponding target melt; finally, 0.04%-0.45% 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, more metal elements can be retained by lowering the fourth temperature to 1550-1600℃, and then adding MnFe, CrFe, BFe, VFe, and Nb powder.

[0045] Step 3: pouring; the target melt prepared above is poured to form a cast steel alloy.

[0046] In the present application, by optimizing the alloy components of the steel alloy and combining with the corresponding preparation process, a cast steel alloy different from the prior art can be prepared, and then a casting is prepared from the cast steel alloy as a raw material, and the casting obtained can achieve high tensile strength, yield strength, and elongation without heat treatment in subsequent processes, thereby realizing the preparation of a large-scale integrated cast steel thin-walled casting with high mechanical properties, and since the key heat treatment process is omitted, the thin-walled part will not deform, thereby effectively ensuring the size of the thin-walled body part, meeting the market demand for large-scale integrated cast steel thin-walled castings, and at the same time, heat treatment is not required, which does not increase the smelting cost, achieving the purpose of reducing energy consumption.

[0047] Carbon: The main role of carbon is as a gap solid solution element to improve the strength of the cast steel. However, too high carbon will reduce plasticity and toughness, especially plasticity; and too low carbon will require the addition of strength elements such as manganese and molybdenum. From the perspective of performance and cost matching, the present application selects to control the carbon content to be less than or equal to 0.25% (here and below, the content of each element refers to the weight content).

[0048] Silicon: The main role of silicon is to be used as a reducing agent and deoxidizer in the steelmaking process. 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%-0.50%.

[0049] Manganese: Manganese is an effective element to improve the strength of the alloy cast steel, which can effectively improve the low temperature impact toughness of the cast steel and also can 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 at the same time is beneficial to the combined addition of aluminum and niobium to form aluminum nitride, niobium carbonitride and the like. However, when the manganese exceeds 1.5%, it will increase the chemical composition segregation during casting, resulting in a decrease in plasticity and toughness, but too low manganese will result in insufficient strength. Therefore, the present application selects to control the content of manganese to be 0.6% to 0.9%.

[0050] Phosphorus and sulfur: In the present alloy cast steel, phosphorus and sulfur are harmful elements, which 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 phosphorus 0.02% to 0.035%, and sulfur ≤0.035%.

[0051] Molybdenum: Molybdenum is an effective element to improve the strength of the alloy cast steel, and molybdenum is also a key element to improve the 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 content of molybdenum to be ≤0.45%. In order to reasonably control the material cost, the content of molybdenum can be further optimized to be 0.20% to 0.35%.

[0052] 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 result in an increase in carbon equivalent, and too low chromium will not achieve the appropriate strength. Therefore, the present application selects to control the content of chromium to be 1.2% to 1.5%.

[0053] Aluminum and niobium are used to refine the grains, especially the austenite grain refinement, and nitrogen is mainly used to cooperate with aluminum and niobium to form a certain amount of nitride, which can promote the grain refinement of the cast steel during the casting process and high temperature normalizing. In addition, aluminum can also be used as an effective deoxidizer. However, too high aluminum will increase the non-metallic inclusion defects and cracking tendency, and too low aluminum will not refine the grains. Therefore, the present application selects to control the content of aluminum to be 0.04% to 0.45%. The addition of niobium can also reduce the existence of austenite mixed grains, but too high niobium will seriously reduce the low temperature impact toughness, and too low niobium will not be combined with aluminum. Therefore, the present application selects to control the content of niobium to be 0.02% to 0.05%.

[0054] In summary, the cast steel formed from the above-described cast steel material, due to its suitable content of carbon, manganese, molybdenum, and chromium, has improved strength. Simultaneously, by controlling the appropriate content of other elements and combining them with the alloy using the manufacturing method of this application, the cast steel alloy of this embodiment is prepared. This cast steel alloy mainly utilizes carbonitriding 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 intergranular solid solutions. This results in a more regular internal microstructure, smaller intergranular gaps, and improved microstructure morphology, transforming the microstructure from acicular to blocky and granular (e.g., Figure 1 As shown in the figure, the solid solution formed disperses and refines the alloy microstructure, thereby improving the comprehensive mechanical properties of the cast steel alloy. The tensile strength of the cast steel alloy reaches 620 MPa, the yield strength reaches 470 MPa, and the elongation reaches over 16.5%. Using the cast steel alloy in this embodiment as raw material to make castings, the resulting castings do not require heat treatment and can achieve high tensile strength, yield strength, and elongation. Compared with the conventional steel alloy castings in the prior art that require heat treatment, this heat-free method in this embodiment can effectively ensure the dimensions of thin-walled body parts and also reduce alloy production costs 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 Example 2 and step 2 of Example 1 is that the semi-finished steel ingot is remelted in a vacuum environment with a vacuum degree ≤200mbar, 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, by optimizing the alloy composition of the steel alloy and combining it with the corresponding preparation process, a cast steel alloy that differs from existing technologies can be prepared. During the production of the cast steel alloy, melting in a vacuum environment with a vacuum degree ≤200 mbar ensures that the oxygen content in the cast steel alloy is <8*10.-6 The lower oxygen content can effectively reduce FeO, MnO and other inclusions in the cast steel alloy. Specifically, in the process of manufacturing the semi-finished steel ingot, nitrogen is passed while Si and Mo are added to the Fe water, which can form a large amount of molybdenum silicon nitride compounds. Then, MnFe, CrFe, BFe, VFe, Nb, Ni and other elements are added in the smelting of the semi-finished steel ingot. The carbonitride compounds formed by Cr, V and Ni, the phosphide compounds formed by Cr, V and Ni, 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, avoid the initiation of microcracks, improve the yield and tensile strength while ensuring the elongation, and obtain a cast steel alloy with good comprehensive mechanical properties. The tensile strength of the cast steel alloy reaches 870 MPa, the yield strength reaches 650 MPa, and the elongation is more than 12%. The cast steel alloy is used as a raw material to prepare a casting, and the casting can achieve high tensile strength, yield strength and elongation in subsequent processes without heat treatment, thereby realizing the preparation of a large-scale integrated cast steel thin-walled casting with high mechanical properties. Since the key heat treatment process is omitted, the thin-walled part will not deform, thereby effectively ensuring the size of the thin-walled body part, meeting the market demand for large-scale integrated cast steel thin-walled castings, and also eliminating the need for heat treatment to improve smelting costs, achieving the purpose of reducing energy consumption.

[0059] Example 3

[0060] Step 1 of Example 3 is different from Step 1 of Example 1 in 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 Example 3 and step 2 of Example 1 is that the semi-finished steel ingot is remelted in a vacuum environment with a vacuum degree ≤150mbar, and the content of MnFe is set to 1%~1.5%, the content of CrFe is set to 1.5%~3.5%, the content of BFe is set to 0.025%~0.035%, the content of VFe is set to 0.1%~0.2%, the content of Al is set to 0.3%~0.4%, the content of Nb powder is set to 0.02%~0.05%, the content of Ni powder is set to 2%~3.5%, the content of Co is set to 1.5%~2.5%, the content of TiFe is set to 0.8%~1.2%, and the content of rare earth elements is set to 0.1%~0.15%. The rare earth elements are one or more of La, Ce, Y, etc., and the types can be freely selected.

[0062] In this embodiment 3, by optimizing the alloy composition of the steel alloy and combining it with the corresponding preparation process, a cast steel alloy different from the existing technology can be prepared. The lower 3 / 4 of the molten liquid in the melting furnace is taken to form a semi-finished steel ingot. Based on this semi-finished steel ingot, Mn, Ni, Cr, B, V, Nb, Co, and Ti are added to finally obtain the cast steel alloy with the target composition. Melting in a vacuum environment with a vacuum degree ≤150 mbar during the production of the cast steel alloy ensures the oxygen content in the cast steel alloy. The lower oxygen content can effectively reduce FeO, MnO and other inclusions in the cast steel alloy, and the rare earth elements are added into the melting furnace before pouring to produce the cast steel alloy with the target composition. Specifically, in the process of producing the semi-finished steel ingot, nitrogen gas is passed while Si and Mo are added to the Fe water, which can form a large amount of molybdenum silicon nitride compound, and then MnFe, CrFe, BFe, VFe, Nb, Ni and other elements are added in the smelting of the semi-finished steel ingot. The carbonitride compounds formed by Cr, V and Ni, the phosphorus compounds formed by Cr, V and Ni, and the molybdenum silicon nitride compound 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 structures and the matrix synergistically deform to maintain the continuity of the microstructure deformation, avoiding the initiation of microcracks. Co can promote the uniform nucleation and dispersion precipitation of nanoscale MoTiNi compounds. The nanoscale dispersed secondary strengthening intermetallic compounds Mo-Co-C-N, Ti-Co-C-N and Ni-Co-C-N formed in the martensite can further enhance the strength, and an ultra-high strength cast steel alloy is obtained. The tensile strength of the cast steel alloy reaches 1217 MPa, the yield strength reaches 969 MPa, and the elongation is more than 4%. The cast steel alloy is used as a raw material to prepare a casting, and the casting can achieve ultra-high tensile strength and yield strength without heat treatment in subsequent processes, thereby realizing the preparation of a large-scale integrated cast steel thin-walled casting with ultra-high mechanical properties. Since the key heat treatment process is omitted, the thin-walled part will not deform, thereby effectively ensuring the size of the thin-walled body part, meeting the market demand for large-scale integrated cast steel thin-walled castings, and eliminating the need for heat treatment without increasing the smelting cost, thereby achieving the purpose of reducing energy consumption.

[0063] Embodiment 4

[0064] Embodiment 4 provides a cast steel alloy prepared according to the preparation method of Embodiment 1. The cast steel alloy includes, in terms of 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 being iron and other unavoidable elements.

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

[0066] Example 5

[0067] Example 5 provides a cast steel alloy made according to the method of Example 2 above, the cast steel alloy comprising, in weight percent: 0.25%≤ C ≤ 0.35%, P ≤ 0.035%, S ≤ 0.035%, 0.02%≤ N ≤ 0.04%, 0.025%≤ B ≤ 0.035%, 1.2%≤ Cr ≤ 1.5%, 0.1%≤ V ≤ 0.15%, 0.02%≤ Nb ≤ 0.05%, 0.35%≤ Mo ≤ 0.45%, 0.2%≤ Si ≤ 0.35%, 0.6%≤ Mn ≤ 0.9%, 0.3%≤ Al ≤ 0.4%, 0.8%≤ Ni ≤ 1.5%, and the balance being Fe and other unavoidable 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, 890 MPa; a yield strength of 620-700 MPa, such as 630 MPa, 650 MPa, 656 MPa, 661 MPa, 665 MPa; and an elongation at fracture of 12% or more.

[0069] Example 6

[0070] Example 6 provides a cast steel alloy made according to the method of Example 3 above, the cast steel alloy comprising, in weight percent: 0.3%≤ C ≤ 0.4%, 0.03%≤ P ≤ 0.04%, S ≤ 0.02%, 0.02%≤ N ≤ 0.04%, 0.025%≤ B ≤ 0.035%, 1.5%≤ Cr ≤ 3.5%, 0.1%≤ V ≤ 0.2%, 0.02%≤ Nb ≤ 0.05%, 0.35%≤ Mo ≤ 0.45%, 0.25%≤ Si ≤ 0.50%, 1%≤ Mn ≤ 1.5%, 0.3%≤ Al ≤ 0.4%, 2%≤ Ni ≤ 3.5%, 1.5%≤ Co ≤ 2.5%, 0.8%≤ Ti ≤ 1.2%, 0.1%≤ RE ≤ 0.15%, and the balance being Fe and other unavoidable elements.

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

[0072] Example 7

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

[0074] Example 8

[0075] Example 8 provides a vehicle comprising the vehicle body thin-walled part of Example 7 above.

[0076] 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 are all commercially available.

[0077] Preparation Example 1

[0078] A cast steel alloy prepared by the present Preparation Example 1 has the following chemical composition: 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 of iron.

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

[0080] 1) Preparation of semi-finished steel ingot: raise the molten iron to a first temperature of 1700°C or higher for proper decarburization, dephosphorization, and desulfurization treatment, so that the target content of carbon is 0.1%, the target content of phosphorus is 0.02%, and the target content of sulfur is 0.001%; then lower the molten iron to a second temperature of 1650°C, add 0.25% silicon and 0.20% molybdenum to the molten iron while simultaneously passing nitrogen gas; then add GaF2 at 2 kg / ton for slag removal and preliminary deoxidation; and finally pour the molten steel to prepare a semi-finished steel ingot.

[0081] 2) Melting of semi-finished steel ingot: heat the semi-finished steel ingot to a third temperature of 1650°C, add GaF2 at 2 kg / ton for slag removal and preliminary deoxidation to obtain a melt, lower 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 powder for thorough stirring and melting to obtain a target melt.

[0082] 3) Pouring: add 0.04% pure Al at 0.3 kg / ton to the target melt for deoxidation and slag removal, and then pour the target melt into a mold to prepare a cast steel alloy.

[0083] Preparation Examples 2-3 and Comparative Examples 1-7

[0084] The preparation examples 2-3, comparative examples 1-2 and the preparation method of preparation example 1 are the same, and the specific differences in alloy components and contents are shown in Table 1:

[0085] Table 1 (mass percentage, %)

[0086]

[0087] The preparation method of comparative example 1 and the present preparation example 1 is the same, except that the difference is in the content of the alloy components, and the content of part of the alloy components is set to be lower than the range interval of the alloy component content in the present preparation example 1.

[0088] The preparation method of comparative example 2 and the present preparation example 3 is the same, except that the difference is in the content of the alloy components, and the content of part of the alloy components is set to be higher than the range interval of the alloy component content in the present preparation example 3.

[0089] Comparative example 3 and the present preparation example 1 have the same alloy component content, except that the conventional process is used to make the cast steel alloy, and the specific steps are as follows:

[0090] First, iron and target alloy components are added to the melting furnace, and the temperature is raised to above 1700℃ for melting and decarburization, dephosphorization, and desulfurization treatment. After the carbon, phosphorus, and sulfur meet the component requirements, GaF2 is added to the molten steel at 2kg / ton for slag removal and preliminary oxygen removal. Finally, the molten steel is poured into a steel ingot.

[0091] Comparative example 4 and the present preparation example 2 have the same alloy component content, except that the conventional process is used to make the cast steel alloy.

[0092] Comparative example 5 and the present preparation example 3 have the same alloy component content, except that the conventional process is used to make the cast steel alloy.

[0093] Comparative example 6 and comparative example 1 have the same alloy component content, except that the conventional process is used to make the cast steel alloy.

[0094] Comparative example 7 and comparative example 2 have the same alloy component content, except that the conventional process is used to make the cast steel alloy.

[0095] The test methods of each index of the finished cast steel product produced in the following examples are as follows:

[0096] Tensile strength: The tensile strength of the finished cast steel product of each example and the comparative product is tested according to GB / T228.

[0097] Yield strength: The yield strength of the finished cast steel product of each example and the comparative product is tested according to GB / T228.

[0098] As Figure 2 shown, the force-extensometer curve of the sample 1, sample 2 and sample 3 selected from the cast steel alloy finished product prepared by taking the target value from the alloy composition range of the present embodiment 4 can show that within the alloy composition range, the tensile strength, yield strength and elongation at break can all reach the performance required by the cast steel alloy in the present embodiment 4; Table 2 below gives the performance analysis results of the cast steel finished product prepared by the preparation example 1, preparation example 2, preparation example 3 and comparative examples 1-7 of the present application.

[0099] Table 2

[0100]

[0101] From the experimental data comparison of the preparation examples 1-3 and comparative examples 1-7 in Table 2, it can be found that:

[0102] From the experimental data comparison of the preparation examples 1-3, it can be found that when the content of various alloy components is selected within the alloy composition interval of the present application and combined with the manufacturing method of the present application, the tensile strength, yield strength and elongation at break of the cast steel alloy all meet the requirements of the present application, and the test state is normal.

[0103] From the experimental data comparison of the 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 composition interval of the present application and combined with the manufacturing method of the present application, the tensile strength, yield strength and elongation at break of the cast steel alloy all do not meet the requirements of the present application, and the test state is abnormal.

[0104] From the experimental data comparison of the 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 composition interval of the present application and combined with the manufacturing method of the present application, the tensile strength and yield strength of the cast steel alloy are higher than those in the present embodiment 3, but the elongation at break is still lower than that in the present embodiment 3, and the test state is abnormal.

[0105] From the experimental data comparison of the preparation example 1 and comparative example 3, the preparation example 2 and comparative example 4, and the preparation example 3 and comparative example 5, it can be found that when the content of various alloy components is within the alloy composition interval of the present application and combined with the conventional manufacturing method, the tensile strength, yield strength and elongation at break of the cast steel alloy all do not meet the requirements of the present application, and the test state is abnormal.

[0106] 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 composition interval of the present application and combined with the conventional manufacturing method, the tensile strength, yield strength and elongation at break of the cast steel alloy all do not meet the requirements of the present application, and the test state is abnormal.

[0107] 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 part of the key alloy is set to be higher than the alloy component interval of the present application and the conventional manufacturing method is used, the tensile strength, yield strength and elongation after fracture of the cast steel alloy cannot meet the requirements of the present application, and the test state is abnormal.

[0108] The disclosure of Embodiment 2 is further illustrated in detail below by Preparation Examples 4-6 and Comparative Examples 8-14. The raw materials used in the preparation examples can be obtained by commercial channels.

[0109] Preparation Example 4

[0110] A cast steel alloy prepared in the present preparation example 4 has the following chemical components: 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 of iron.

[0111] The manufacturing method of the cast steel alloy of the present preparation example 4 includes the following steps:

[0112] 1) Manufacturing semi-finished steel ingot: raising the molten iron to a first temperature of 1700°C or higher for proper decarburization, dephosphorization and desulfurization treatment, so as to achieve a target content of 0.25% carbon, 0.001% phosphorus and 0.001% sulfur; then lowering the molten iron to a second temperature of 1650°C, adding 0.2% silicon and 0.35% molybdenum into the molten iron while blowing nitrogen gas; then adding GaF2 at 2 kg / ton for deslagging and preliminary deoxidation; finally pouring the molten steel to manufacture a semi-finished steel ingot.

[0113] 2) Remelting the semi-finished steel ingot: remelting the semi-finished steel ingot in a vacuum environment with a vacuum degree of ≤200 mbar, first heating the semi-finished steel ingot to a third temperature of 1650°C, adding GaF2 at 2 kg / ton for deslagging and preliminary deoxidation to obtain a melt, lowering the melt to a fourth temperature of 1550°C, then adding 0.6% MnFe, 1.2% CrFe, 0.025% BFe, 0.1% VFe, 0.02% Nb powder and 0.8% Ni powder for fully stirring and dissolving to obtain a target melt.

[0114] 3) Pouring: adding 0.3% pure Al at 0.3 kg / ton into the target melt for deoxidation and deslagging, then pouring the target melt into a mold to manufacture a cast steel alloy.

[0115] Preparation Examples 5-6 and Comparative Examples 8-14

[0116] The preparation examples 5-6, the comparative examples 8-9 and the preparation example 4 have the same production process, and the difference between the alloy components and the content is shown in Table 3:

[0117] Table 3 (mass percentage, %)

[0118]

[0119] The comparative example 8 and the preparation example 4 have the same production process, and the difference is that the content of the alloy components is set to be lower than the range interval of the alloy components in the preparation example 4.

[0120] The comparative example 9 and the preparation example 4 have the same production process, and the difference is that the content of the alloy components is set to be higher than the range interval of the alloy components in the preparation example 4.

[0121] The comparative example 10 has the same alloy component content as the preparation example 4, and the difference is that a conventional process is used to produce the cast steel alloy, and the specific steps are as follows:

[0122] First, iron and target alloy components are added to a melting furnace, and the temperature is raised to above 1700°C for melting and decarburization, dephosphorization and desulfurization treatment. After the carbon, phosphorus and sulfur meet the component requirements, GaF2 is added to the molten steel at 2 kg / ton for slag removal and preliminary oxygen removal. Finally, the molten steel is poured into a steel ingot.

[0123] The comparative example 11 has the same alloy component content as the preparation example 5, and the difference is that a conventional process is used to produce the cast steel alloy.

[0124] The comparative example 12 has the same alloy component content as the preparation example 6, and the difference is that a conventional process is used to produce the cast steel alloy.

[0125] The comparative example 13 has the same alloy component content as the comparative example 8, and the difference is that a conventional process is used to produce the cast steel alloy.

[0126] The comparative example 14 has the same alloy component content as the comparative example 9, and the difference is that a conventional process is used to produce the cast steel alloy.

[0127] The test methods of each index of the finished cast steel products produced in the following examples are as follows:

[0128] Tensile strength: The tensile strength of the finished cast steel products of each example and the comparative example products is tested according to GB / T228.

[0129] Yield strength: The yield strength of the finished cast steel products of each example and the comparative example products is tested according to GB / T228.

[0130] AsFigure 3 As shown in the force-extensometer curve diagram of the sample 1, the sample 2 and the sample 3 selected from the finished cast steel alloy prepared by taking the target value from the alloy composition range of the present embodiment 5, it can be shown from the force-extensometer curve diagram that within the alloy composition range, the tensile strength, the yield strength and the elongation at break can all reach the performance required by the cast steel alloy in the present embodiment 5; the following Table 4 gives the performance analysis results of the finished cast steel prepared by the preparation example 4, the preparation example 5, the preparation example 6 and the comparative examples 8-14 of the present application.

[0131] Table 4

[0132]

[0133] From the experimental data comparison of the preparation examples 4-6 and the comparative examples 8-14 in Table 4, it can be found that:

[0134] From the experimental data comparison of the preparation examples 4-6, it can be found that when the content of various alloy components is selected within the alloy composition interval of the present application and combined with the manufacturing method of the present application, the tensile strength, the yield strength and the elongation at break of the cast steel alloy all meet the requirements of the present application, and the test state is normal.

[0135] From the experimental data comparison of the preparation example 4 and the comparative example 8, it can be found that when the content of part of the key alloy components in the comparative example 8 is lower than the alloy composition interval of the present application and combined with the manufacturing method of the present application, the tensile strength, the yield strength and the elongation at break of the cast steel alloy all do not meet the requirements of the present application, and the test state is abnormal.

[0136] From the experimental data comparison of the preparation example 5 and the comparative example 9, it can be found that when the content of part of the key alloy components in the comparative example 9 is higher than the alloy composition interval of the present application and combined with the manufacturing method of the present application, the tensile strength, the yield strength and the elongation at break of the cast steel alloy all do not meet the requirements of the present application, and the test state is abnormal.

[0137] From the experimental data comparison of the preparation example 4 and the comparative example 10, the preparation example 5 and the comparative example 11, the preparation example 6 and the comparative example 12, it can be found that when the content of various alloy components is within the alloy composition interval of the present application and combined with the conventional manufacturing method, the tensile strength, the yield strength and the elongation at break of the cast steel alloy all do not meet the requirements of the present application, and the test state is abnormal.

[0138] From the experimental data comparison of the comparative example 8 and the comparative example 13, it can be found that when the content of part of the key alloy components is set to be lower than the alloy composition interval of the present application and combined with the conventional manufacturing method, the tensile strength, the yield strength and the elongation at break of the cast steel alloy all do not meet the requirements of the present application, and the test state is abnormal.

[0139] From the experimental data comparison of Comparative Example 9 and Comparative Example 14, it can be found that when the composition content of part of the key alloy is set to be higher than the alloy composition interval of the present application and combined with the conventional production method, the tensile strength, yield strength and elongation after fracture of the cast steel alloy cannot meet the requirements of the present application, and the test state is abnormal.

[0140] The disclosure of Embodiment 3 is further illustrated in detail below by Preparation Examples 7-9 and Comparative Examples 15-21. The raw materials used in the preparation examples can be obtained by commercial channels.

[0141] Preparation Example 7

[0142] A cast steel alloy prepared in the present preparation example 7 has the following chemical composition: 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 of iron.

[0143] The production method of the cast steel alloy of the present preparation example 7 includes the following steps:

[0144] 1) Production of semi-finished steel ingot: the molten iron is raised to a first temperature of 1700°C or higher for proper decarburization, dephosphorization and desulfurization treatment, so that the target content of carbon is 0.3%, the target content of phosphorus is 0.03%, and the target content of sulfur is 0.001%; then the molten iron is lowered to a second temperature of 1650°C, 0.25% silicon and 0.35% molybdenum are added to the molten iron, and nitrogen gas is blown at the same time; then GaF2 is added at 2 kg / ton for deslagging and preliminary deoxidation; finally, the molten steel is poured to produce a semi-finished steel ingot.

[0145] 2) Remelting of semi-finished steel ingot: the semi-finished steel ingot is remelted in a vacuum environment with a vacuum degree of ≤150 mbar, the semi-finished steel ingot is first heated to a third temperature of 1650°C, GaF2 is added at 2 kg / ton for deslagging and preliminary deoxidation 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, 2.0% Ni powder, 0.8% TiFe, 1.5% Co and 0.1% rare earth elements are added for sufficient stirring and melting to obtain a target melt.

[0146] 3) Pouring: 0.3% pure Al is added to the target melt at 0.3 kg / ton for deoxidation and deslagging, and then the target melt is poured into a mold to produce a cast steel alloy.

[0147] Preparation Examples 8-9 and Comparative Examples 15-21

[0148] The preparation examples 8-9, the comparative examples 15-21 and the preparation method of the preparation example 7 are the same, and the specific differences in alloy components and contents are shown in Table 5:

[0149] Table 5

[0150]

[0151] The preparation method of the comparative example 15 and the preparation example 7 is the same, and the difference is the difference in the content of the alloy components, and the content of part of the alloy components is set to be lower than the range interval of the content of the alloy components in the preparation example 7.

[0152] The preparation method of the comparative example 16 and the preparation example 9 is the same, and the difference is the difference in the content of the alloy components, and the content of part of the alloy components is set to be higher than the range interval of the content of the alloy components in the preparation example 9.

[0153] The comparative example 17 and the alloy component content in the preparation example 7 are the same, and the difference is that a conventional process is used to make a cast steel alloy, and the specific steps are as follows:

[0154] First, iron and target alloy components are added to a melting furnace, and the temperature is raised to above 1700 DEG C for melting and decarburization, dephosphorization, and desulfurization treatment. After the carbon, phosphorus, and sulfur meet the component requirements, GaF2 is added to the molten steel at 2 kg / ton for slag removal and preliminary oxygen removal. Finally, the molten steel is poured into a steel ingot.

[0155] The comparative example 18 and the alloy component content in the preparation example 8 are the same, and the difference is that a conventional process is used to make a cast steel alloy.

[0156] The comparative example 19 and the alloy component content in the preparation example 9 are the same, and the difference is that a conventional process is used to make a cast steel alloy.

[0157] The comparative example 20 and the comparative example 15 have the same alloy component content, and the difference is that a conventional process is used to make a cast steel alloy.

[0158] The comparative example 21 and the comparative example 16 have the same alloy component content, and the difference is that a conventional process is used to make a cast steel alloy.

[0159] The test methods of each index of the finished cast steel product made in the following examples are as follows:

[0160] Tensile strength: The tensile strength of the cast steel product obtained in each example and the comparative product is tested according to GB / T228.

[0161] Yield strength: The yield strength of the cast steel product obtained in each example and the comparative product is tested according to GB / T228.

[0162] As Figure 4 shown, the force-extensometer curve of the sample 1, sample 2 and sample 3 selected from the finished cast steel alloy prepared by taking the target value from the alloy composition range of the present embodiment 6 can show that within the alloy composition range, the tensile strength, yield strength and elongation at break can all reach the performance requirements of the cast steel alloy in the present embodiment 6; Table 6 below gives the performance analysis results of the finished cast steel prepared by the preparation example 7, preparation example 8, preparation example 9 and comparative examples 15-21 of the present application.

[0163] Table 6

[0164]

[0165] From the experimental data comparison of the preparation examples 7-9 and comparative examples 15-21 in Table 6, it can be found that:

[0166] From the experimental data comparison of the preparation examples 7-9, it can be found that when the content of various alloy components is selected within the alloy composition interval of the present application and combined with the manufacturing method of the present application, the tensile strength, yield strength and elongation at break of the cast steel alloy all meet the requirements of the present application, and the test state is normal.

[0167] From the experimental data comparison of the preparation example 7 and comparative example 15, it can be found that when the content of part of the key alloy components in comparative example 15 is lower than the alloy composition interval of the present application and combined with the manufacturing method of the present application, the tensile strength, yield strength and elongation at break of the cast steel alloy all do not meet the requirements of the present application, and the test state is abnormal.

[0168] From the experimental data comparison of the preparation example 9 and comparative example 16, it can be found that when the content of part of the key alloy components in comparative example 16 is higher than the alloy composition interval of the present application and combined with the manufacturing method of the present application, the tensile strength, yield strength and elongation at break of the cast steel alloy all do not meet the requirements of the present application, and the test state is abnormal.

[0169] From the experimental data comparison of the preparation example 7 and comparative example 17, the preparation example 8 and comparative example 18, and the preparation example 9 and comparative example 19, it can be found that when the content of various alloy components is within the alloy composition interval of the present application and combined with the conventional manufacturing method, the tensile strength, yield strength and elongation at break of the cast steel alloy all do not meet the requirements of the present application, and the test state is abnormal.

[0170] From the experimental data comparison of comparative example 15 and comparative example 20, it can be found that when the content of part of the key alloy components is set to be lower than the alloy composition interval of the present application and combined with the conventional manufacturing method, the tensile strength, yield strength and elongation at break of the cast steel alloy all do not meet the requirements of the present application, and the test state is abnormal.

[0171] From the comparison of the experimental data of Comparative Example 16 and Comparative Example 21, it can be found that when the composition content of part of the key alloy is set to be higher than the alloy composition interval of the present application and the conventional manufacturing method is used, the tensile strength, yield strength and elongation after fracture of the cast steel alloy cannot meet the requirements of the present application, and the test state is abnormal.

[0172] It should be understood that the above specific embodiments of the present application are only used for illustrative or explanatory purposes of the principles of the present application, and do not constitute a limitation on the present application. Therefore, any modification, equivalent replacement, improvement, etc. made without departing from the spirit and scope of the present application shall be included in the protection scope of the present application. In addition, the appended 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 forms of such scope and boundary.

Claims

1. A method of making a cast steel alloy, characterized by, The method comprises the following steps: manufacturing a semi-finished steel ingot; raising the molten iron to a first temperature of 1700℃ or above for decarburization, dephosphorization and desulfurization treatment to achieve the target values of carbon, phosphorus and sulfur content; lowering the molten iron to a second temperature of 1650-1700℃, then adding a certain amount of silicon and molybdenum into the molten iron while passing inert gas, and finally pouring to manufacture the semi-finished steel ingot; melting the semi-finished steel ingot; raising the temperature of the semi-finished steel ingot to a third temperature of 1650-1700℃ for melting treatment to obtain a melt, lowering the melt to a fourth temperature of 1550-1600℃, 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 manufacture a cast steel alloy.

2. The manufacturing method according to claim 1, wherein the target values of the carbon, phosphorus and sulfur are set as follows in terms of weight percentage: the target value of the carbon is set to be ≤0.25%; the target value of the phosphorus is set to be 0.02%-0.035%; and the target value of the sulfur is set to be ≤0.035%.

3. The manufacturing method according to claim 2, wherein the added contents of the silicon, molybdenum, MnFe, CrFe, BFe, VFe and Nb powder are set as follows in terms of weight percentage: the added content of the silicon is set to be 0.25%-0.50%; the added content of the molybdenum is set to be ≤0.45%; the added content of the MnFe is set to be 0.6%-0.9%; the added content of the CrFe is set to be 1.2%-1.5%; the added content of the BFe is set to be 0.08%-0.1%; the added content of the VFe is set to be 0.1%-0.15%; and the added content of the Nb powder is set to be 0.02%-0.05%.

4. The manufacturing method according to claim 1, wherein the following alloy raw materials are further added in the step of melting the semi-finished steel ingot: 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 manufacturing method according to claim 4, wherein the target values of the carbon, phosphorus and sulfur are set as follows in terms of weight percentage: the target value of the carbon is set to be 0.25%-0.35%; the target value of the phosphorus is set to be ≤0.035%; and the target value of the sulfur is set to be ≤0.035%.

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

7. The manufacturing method according to claim 4, wherein ​ ​ ​ ​ ​ In the smelting semi-finished steel ingot step, TiFe, cobalt and rare earth elements are also added, and the semi-finished steel ingot is melted in a vacuum environment with a vacuum degree of ≤150 mbar.

8. The manufacturing method of claim 7, wherein, in terms of weight percentage, the target value of the carbon is set to 0.3%-0.4%; the target value of the phosphorus is set to 0.03%-0.04%; the target value of the sulfur is set to ≤0.02%.

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

10. A cast steel alloy characterized in that, The cast steel alloy is prepared by the manufacturing method of any one of claims 1-3, and includes raw materials with the following mass fractions: 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; or, the cast steel alloy is prepared by the manufacturing method of any one of claims 4-6, and includes raw materials with the following mass fractions: 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. or made according to the manufacturing method of any one of claims 7-9, said cast steel alloy comprising 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%≤ 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 body part of a vehicle, characterized in that made from the cast steel alloy of claim 10.

12. A vehicle characterized by comprising: a vehicle body thin-walled part comprising the cast steel alloy of claim 11.

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