Manufacturing method and application of high-strength cast steel alloy

Abstract

The invention discloses a manufacturing method and application of a high-strength cast steel alloy. The method comprises the steps that molten iron is heated to the first temperature higher than 1700 DEG C to be decarbonized, dephosphorized and desulfurized, so that the content of carbon, phosphorus and sulfur is within target values; cooling the molten iron to a second temperature of 1650-1700 DEG C, adding silicon, molybdenum and copper 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 MnFe, CrFe, BFe, VFe, Nb, Ni and rare earth elements for stirring and melting, and adding pure Al for deoxidizing and deslagging to obtain a target melt; and casting the target melt to prepare the high-strength cast steel alloy. The high-strength cast steel alloy is prepared through the manufacturing method, a casting is prepared from the high-strength cast steel alloy as a raw material, and the obtained casting can achieve high tensile strength and yield strength without heat treatment.

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 high-strength 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] Prior art CN107841691B discloses a 750MPa grade ultra-high strength Fe-Mn-Al-C lightweight cast steel and a preparation method thereof. This lightweight steel has a composition setting of a relatively high C content (0.60-1.50%) and a reasonable Si content (0.50-1.50%), and its tensile strength is ≥750MPa, and its yield strength is ≥700MPa. It has a very good combination of strength, density and plasticity, and is very suitable for manufacturing complex structural castings for automobiles and can effectively reduce the weight of the automobile.

[0004] However, in the above-mentioned prior art, the tensile strength and yield strength can be improved by a higher C content. However, as the carbon content increases, the amount of pearlite will gradually increase. Although this improves the strength, it reduces the toughness of the steel, increases the brittle transition temperature and deteriorates the welding performance. In addition, a heat treatment process is required during the production process, and adding a heat treatment process will increase the smelting cost and increase energy consumption.

[0005] Therefore, there is an urgent need to provide a method for preparing a high-strength cast steel alloy and its application to solve the above-mentioned technical problems. Summary of the invention

[0006] The present application provides a method for preparing a high-strength cast steel alloy and its application. The method can reduce the carbon content as much as possible and simultaneously add trace amounts of alloying elements to prepare a cast steel alloy with high tensile strength and high yield strength. The cast steel alloy is then used as a raw material to prepare castings. The obtained castings do not need to be subjected to heat treatment and can achieve mechanical properties of a tensile strength of more than 960 MPa and a yield strength of more than 710 MPa. The castings can be used for manufacturing complex structural castings for automobiles with high mechanical strength requirements.

[0007] According to some embodiments, a method for making a high-strength cast steel alloy is provided, comprising the following steps: making a semi-finished steel ingot; raising the temperature of 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, molybdenum and copper to the molten iron while passing an inert gas, and casting to form a semi-finished steel ingot; smelting the semi-finished steel ingot; raising the temperature of the semi-finished steel ingot to a third temperature of 1650-1700°C for melting to obtain a melt, lowering the melt to a fourth temperature of 1550-1600°C, adding a certain amount of MnFe, CrFe, BFe, VFe, Nb powder, Ni powder and rare earth elements for stirring and melting, and adding pure Al for deoxidation and slag removal to obtain a target melt; casting; casting the target melt to form a high-strength cast steel alloy.

[0008] A preferred solution is, by weight percentage,

[0009] The target value of carbon is set to 0.3% to 0.4%;

[0010] The target value of phosphorus is set to 0.03% to 0.04%;

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

[0012] A preferred solution is, by weight percentage,

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

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

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

[0016] A preferred solution is, by weight percentage,

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

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

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

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

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

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

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

[0024] A preferred solution is that the smelted semi-finished steel ingot is melted in a vacuum environment with a vacuum degree of ≤200 mbar.

[0025] A preferred solution is that before pouring molten iron into semi-finished steel ingots, the process further includes:

[0026] Add GaF to the molten iron 2 Deoxidize and remove slag;

[0027] and / or,

[0028] In the process of melting the semi-finished steel ingot to obtain a melt, GaF 2 Deoxidize and remove slag.

[0029] According to some embodiments, the present application also provides a high-strength cast steel alloy, which is manufactured according to the manufacturing method, and the high-strength 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%, 1.0% ≤ manganese ≤ 1.5%, 0.3% ≤ aluminum ≤ 0.4%, 0.8% ≤ nickel ≤ 1.5%, 0.04% ≤ copper ≤ 0.08%, 0.02% ≤ rare earth elements ≤ 0.04% and iron.

[0030] A preferred solution is that the tensile strength of the high-strength cast steel alloy is above 960 MPa, such as 964 MPa, 965 MPa, 970 MPa, 975 MPa, the yield strength is above 710 MPa, such as 713 MPa, 718 MPa, 721 MPa, and the elongation at break is above 9%.

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

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

[0033] Beneficial effects:

[0034] The present application provides a method for preparing a high-strength 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 a high tensile strength and yield strength, the present application optimizes the alloy composition of the steel alloy and combines it with a corresponding preparation process to prepare a high-strength cast steel alloy that is different from the prior art. The high-strength cast steel alloy has high tensile strength and yield strength. Then, the high-strength cast steel alloy is used as a raw material to prepare a casting. The obtained casting can prepare a large-scale integrated cast steel thin-walled casting with high mechanical properties under the condition of no heat treatment. The steel tensile strength of the casting at the key stress-bearing part reaches 960Mpa, the yield strength reaches 710Mpa, and the elongation reaches more than 9%. Since the casting is not subjected to heat treatment, the thin-walled parts prepared by the casting will not deform and have excellent 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 is required without increasing the smelting cost and reducing energy consumption.

[0035] For high-strength cast steel alloys, since they have appropriate manganese, chromium, boron, vanadium and niobium contents, and other elements are controlled to cooperate with them at appropriate contents, and the high-strength cast steel alloy is prepared by the preparation method of the present application, the castings made by the high-strength cast steel alloy do not need to undergo heat treatment in subsequent processes, and can achieve higher tensile strength and yield strength; mainly by utilizing carbonitrides formed by the reaction of chromium, vanadium, and nickel with carbon and nitrogen, respectively, phosphorus compounds formed by the reaction of chromium, vanadium, and nickel with phosphorus, and molybdenum silicon nitrogen compounds to form intergranular solid solutions; NiAl compounds formed by Ni element and deoxidizer Al element can The matrix strength is effectively enhanced, and the NiAl nucleation and precipitation are faster. 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 microstructure deformation and avoids the initiation of microcracks. The addition of Cu elements will diffuse with Fe at the grain boundaries to form a ring distribution, forming a pinning effect on the grain boundaries, effectively inhibiting grain growth, refining bainite structure, and strengthening matrix strength. The addition of rare earth elements can effectively improve the morphology and size of inclusions, enrich MnCrFeP solid solution around them, transform impurities into secondary strengthening phases, and then obtain higher yield and tensile strengths.

[0036] As for the production method, in order to ensure the composition of the alloy in the high-strength 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, niobium, nickel, rare earth elements, etc. 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, which can form a large amount of molybdenum silicon nitrogen compounds. Then, adding MnFe, CrFe, BFe, VFe, Nb and other elements to the melted semi-finished steel ingot can 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 high-strength cast steel alloy that is different from the prior art. Then, a casting is prepared using the high-strength cast steel alloy as a raw material. The obtained casting does not need to be heat treated and can achieve higher tensile strength and yield strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] 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.

[0038] Figure 1 The force-extensometer curves of the samples 1, 2 and 3 are selected from the high-strength steel casting products obtained by taking any target value within the alloy composition range of Example 2. DETAILED DESCRIPTION

[0039] 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.

[0040] In the prior art, castings made of steel alloys need to undergo heat treatment before they can achieve higher tensile strength, yield strength, and elongation. On the one hand, adding the heat treatment process will increase the smelting cost and increase energy consumption; on the other hand, for thin-walled car body parts, they are sensitive to temperature, and the thin-walled parts that have been heat treated will deform, and then the size of the thin-walled car body parts cannot be guaranteed.

[0041] Therefore, the embodiments of the present application provide a method for preparing a high-strength cast steel alloy and an application thereof. By controlling the content of each alloy component within the target value in each step, a high-strength cast steel alloy different from the prior art can be prepared, and the high-strength cast steel alloy has properties such as high yield and high tensile strength. The high-strength 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 heating process is omitted, and high yield and high tensile strength can be achieved. At the same time, the heat-free treatment will effectively ensure the size of thin-walled body parts, and can also reduce the alloy production cost and energy consumption.

[0042] Example 1

[0043] The following is a detailed description of a method for preparing a high-strength cast steel alloy provided in this embodiment 1 in conjunction with the accompanying drawings. The method comprises the following steps:

[0044] 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;

[0045] Specifically, the process includes: firstly, heating the molten iron to a first temperature above 1700°C for decarburization, dephosphorization and desulfurization treatment to achieve a target carbon value of 0.3% to 0.4%, a target phosphorus value of 0.03% to 0.04% and a target sulfur value of ≤0.02%. 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 and reduced to within the target value range or below.

[0046] The temperature of the molten iron is then lowered to a second temperature of 1650-1700°C, and then 0.25%-0.50% silicon, 0.35%-0.45% molybdenum and 0.04%-0.08% copper are added to the molten iron, and at the same time, 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.

[0047] Then add GaF into the molten steel at 2 kg / ton. 2 The slag is removed and the initial deoxidation is carried out. The metal components in the molten steel react with oxygen to form slag, which is then reacted with GaF 2 Combined to remove oxygen and slag.

[0048] Finally, the middle 3 / 4 of the molten liquid is taken from the smelting furnace for pouring to form a semi-finished steel ingot. Since the impurity density is smaller, the impurities formed will float in the upper part of the molten liquid. Therefore, the middle 3 / 4 of the molten liquid has fewer impurities. In this preparation process, a semi-finished steel ingot is first made, which can ensure the alloy composition and can be easily transported to a place where smelting is required for smelting.

[0049] Step 2: Melting the semi-finished steel ingot; melting the semi-finished steel ingot prepared above to obtain a corresponding target melt;

[0050] Specifically, the semi-finished steel ingot is remelted in a vacuum environment with a vacuum degree of ≤200mbar, the temperature of the semi-finished steel ingot prepared above is first raised to a third temperature of 1650-1700°C for melting to obtain a melt, and GaF is added at a rate of 2 kg / ton. 2 Carry out slag removal and preliminary deoxidation; then cool the melt to a fourth temperature of 1550-1600°C, and then add 1.0%-1.5% MnFe, 1.5%-3.5% CrFe, 0.025%-0.035% BFe, 0.1%-0.2% VFe, 0.02%-0.05% Nb powder, 0.8%-1.5% Ni powder and 0.02%-0.04% rare earth elements for stirring and melting to obtain a corresponding target melt; finally, add 0.3%-0.4% pure aluminum and oxygen at 0.3Kg / ton to the target melt for reaction to carry out deoxidation and slag removal. In this operation, by lowering the fourth temperature to 1550-1600°C, and then adding MnFe, CrFe, BFe, VFe, Nb powder, Ni powder and rare earth elements, more metal elements can be retained, wherein the rare earth elements can be one or more of La, Ce, Y and other elements, and the category can be freely selected; in addition, in the process of making high-strength cast steel alloy, it is necessary to melt in a vacuum environment with a vacuum degree of ≤200mbar to ensure that the oxygen content in the high-strength cast steel alloy is less than 8*10 -6 , lower oxygen content can effectively reduce FeO, MnO and other inclusions in high-strength cast steel alloys.

[0051] Step 3: pouring: pouring the target melt prepared above to make a high-strength cast steel alloy.

[0052] In the present application, by optimizing the alloy composition of the steel alloy and combining it with the corresponding preparation process, a high-strength cast steel alloy different from the prior art can be prepared, and then a casting is prepared using the high-strength cast steel alloy as the raw material. The obtained casting can achieve 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 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.

[0053] 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 0.3% to 0.4% (the content here and the content of each element below are all weight content).

[0054] 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%.

[0055] 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 1.0% to 1.5%.

[0056] 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 0.03% to 0.04% phosphorus and ≤0.02% sulfur.

[0057] 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, while too low a molybdenum content will not guarantee the ability of the cast steel to obtain tempered troostite. For this reason, the present application selects to control the molybdenum content to 0.35% to 0.45%.

[0058] 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, the present application chooses to control the chromium content to 1.5% to 3.5%.

[0059] 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, but 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 0.3% to 0.4%.

[0060] The addition of niobium can also reduce the presence of austenite mixed crystals, but too much niobium will seriously reduce the low-temperature impact toughness, and too little niobium cannot be composited with aluminum. For this reason, the present application chooses to control the niobium content to 0.02% to 0.05%.

[0061] In summary, the cast steel formed by the cast steel material with 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 high-strength cast steel alloy in the present embodiment is prepared by controlling other elements in suitable contents and cooperating with them and adopting the preparation method of the present application. The high-strength cast steel alloy is mainly prepared in the process of preparing the semi-finished steel ingot. When adding silicon and molybdenum to the molten iron, nitrogen is passed through, and a large amount of molybdenum-silicon-nitrogen compounds can be formed. Then, in the process of remelting the semi-finished steel ingot, MnFe, CrFe, BFe, VFe, Nb, Ni and rare earth elements are added, chromium, vanadium and nickel react with carbon and nitrogen to form carbon and nitrogen compounds, chromium, vanadium and nickel react with phosphorus to form phosphorus compounds and molybdenum-silicon-nitrogen compounds to form intergranular solid solutions, and the Ni element reacts with the deoxidizer Al element. The formed NiAl compound can effectively enhance the strength of the matrix, and the NiAl nucleation and precipitation are relatively fast. In this precipitation process, Mo will be enriched between crystals and form a cluster structure. The coordinated deformation of various precipitation structures and the matrix maintains the continuity of microstructure deformation and avoids the initiation of microcracks. The addition of Cu element will diffuse with Fe at the grain boundary to form a ring distribution, forming a pinning effect on the grain boundary, effectively inhibiting grain growth, refining bainite structure, and strengthening matrix strength. The addition of rare earth elements can effectively improve the shape and size of inclusions, enrich MnCrFeP solid solution at the periphery, transform impurities into secondary strengthening phases, and obtain higher yield and tensile strength. The tensile strength of the high-strength cast steel alloy reaches more than 960Mpa, the yield strength reaches more than 710Mpa, and the elongation reaches more than 9%. The high-strength cast steel alloy in this embodiment is used as the raw material to make castings. The obtained castings do not need to undergo heat treatment and can achieve high tensile strength and yield strength. 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 meet the market demand for large-scale integrated cast steel thin-walled castings. At the same time, the heat-free treatment does not increase the smelting cost, thereby achieving the purpose of reducing energy consumption.

[0062] Example 2

[0063] Embodiment 2 provides a high-strength cast steel alloy, which is manufactured according to the manufacturing method of the above-mentioned embodiment 1. The high-strength 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%, 1.0%≤manganese≤1.5%, 0.3%≤aluminum≤0.4%, 0.8%≤nickel≤1.5%, 0.04%≤copper≤0.08%, 0.02%≤rare earth elements≤0.04% and iron and other inevitable elements.

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

[0065] Example 3

[0066] Embodiment 3 provides a thin-walled vehicle body part, which is formed by using the high-strength cast steel alloy in the above-mentioned embodiment 2.

[0067] Example 4

[0068] Embodiment 4 provides a vehicle, which includes the thin-walled vehicle body part of embodiment 3 above.

[0069] 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.

[0070] Preparation Example 1

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

[0072] The method for preparing a high-strength cast steel alloy in Preparation Example 1 comprises the following steps:

[0073] 1) Making semi-finished steel ingots: raising the molten iron to a first temperature of 1700°C or above for proper decarburization, dephosphorization and desulfurization to 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, 0.35% molybdenum and 0.04% copper to the molten iron, and passing nitrogen at the same time; then adding GaF at a rate of 2 kg / ton 2 Carry out slag removal and preliminary deoxidation; finally, take 3 / 4 of the molten liquid in the middle of the smelting furnace for pouring to form a semi-finished steel ingot.

[0074] 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 the third temperature of 1650°C, and add GaF at a rate of 2 kg / ton. 2 The slag removal and preliminary deoxidation are performed to obtain a melt, which is then cooled to a fourth temperature of 1550°C, and then 1.0% MnFe, 1.5% CrFe, 0.025% BFe, 0.1% VFe, 0.02% Nb powder, 0.8% Ni powder and 0.02% rare earth elements are added and fully stirred and melted to obtain a target melt.

[0075] 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.

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

[0077] 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:

[0078] Table 1 (mass percentage, %)

[0079]

[0080] 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.

[0081] 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.

[0082] 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:

[0083] First, iron and target alloy components are added to the melting furnace, and the temperature is raised to above 1700℃ for smelting and decarburization, dephosphorization and desulfurization. After the carbon, phosphorus and sulfur meet the composition requirements, GaF2 is added to the molten steel at 2kg / ton for slag removal and preliminary deoxidation. Finally, the molten steel is poured into ingots.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] The test methods for various indicators of the finished steel castings produced in the following examples are as follows:

[0089] 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.

[0090] 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.

[0091] like Figure 1 As shown in the figure, it is a force-extensometer curve of sample 1, sample 2 and sample 3 selected from the high-strength steel casting finished products prepared by taking any target value within the alloy composition range of this embodiment 2. 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 reach the performance required in this embodiment 2; the following Table 2 shows the performance analysis results of the high-strength steel casting finished products prepared by Preparation Example 1, Preparation Example 2, Preparation Example 3 of the present invention and Comparative Examples 1-7.

[0092] Table 2

[0093]

[0094] 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:

[0095] 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 all meet the requirements of this application, and the test state is normal.

[0096] 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 all fail to meet the requirements of the present application, and the test status is abnormal.

[0097] 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, yield strength and elongation after fracture all fail to meet the requirements of the present application, and the test status is abnormal.

[0098] 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 content of various alloy components is within the alloy component range of this application and combined with the conventional production method, the tensile strength, yield strength and elongation after fracture do not meet the requirements of this application, and the test state is abnormal.

[0099] 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 all fail to meet the requirements of this application, and the test status is abnormal.

[0100] 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 all fail to meet the requirements of this application, and the test status is abnormal.

[0101] In summary, only by adopting the content range of each alloy component in the embodiment of the present application and combining it with the production method of the present application, can a high-strength cast steel alloy with high tensile strength and high yield strength be prepared.

[0102] It should be understood that the 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 high-strength 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, molybdenum and copper to the molten iron while passing inert gas, and 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., adding a certain amount of MnFe, CrFe, BFe, VFe, Nb powder, Ni powder and rare earth elements for stirring and melting, and adding pure Al for deoxidation and deslagging to obtain a target melt; Pouring; pouring the target melt to form a high-strength 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 0.3% 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%.

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 0.35% to 0.45%; The added content of copper is set to 0.04% to 0.08%.

4. The method according to claim 3, characterized in that: In terms of weight percentage, The added content of MnFe is set to 1.0% 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 0.8% to 1.5%; The added content of the rare earth element is set to 0.02% to 0.04%.

5. The method according to claim 1, characterized in that: The smelting semi-finished steel ingot is melted in a vacuum environment with a vacuum degree of ≤200mbar.

6. The method according to claim 1, characterized in that: Before the molten iron is poured into semi-finished steel ingots, it also includes: Adding GaF2 into the molten iron to remove oxygen and slag; and / or, In the process of melting the semi-finished steel ingot to obtain a melt, GaF2 is added to remove oxygen and slag.

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

8. The high strength cast steel alloy according to claim 7, characterized in that: The high-strength cast steel alloy has a tensile strength of more than 960 MPa, a yield strength of more than 710 MPa, and a fracture elongation of more than 9%.

9. A thin-walled car body part, characterized in that: Made of the high-strength cast steel alloy as claimed in claim 7 or 8.

10. A vehicle, characterized in that: It comprises the thin-walled vehicle body part as claimed in claim 9.

Images