30crmov9 alloy steel billet and method for manufacturing the same

Abstract

The present application relates to a kind of 30CrMoV9 alloy steel billet and its preparation method, preparation method includes the raw material of molten iron and scrap steel is put into electric furnace and is smelted, oxygen blowing treatment is carried out in smelting process to adjust the content of carbon in molten iron, and lime is added in smelting process to adjust the content of phosphorus in molten iron;10% of molten steel is retained, and the remaining molten steel is tapped into ladle refining furnace and is refined, and the content of each element in molten steel is adjusted in refining process;The obtained molten steel is into vacuum degassing refining furnace and is vacuum treated, and first molten steel is obtained;After breaking vacuum, first molten steel is used for pouring, to obtain 30CrMoV9 alloy steel billet.30CrMoV9 alloy steel billet prepared by the preparation method of the present application meets the stringent requirements of low Ti, high purity, high strength, high toughness for crankshaft material.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking technology, specifically relating to a 30CrMoV9 alloy steel billet and its preparation method. Background Technology

[0002] One application of 30CrMoV9 alloy steel is in the manufacture of crankshafts for exported diesel engines. The crankshaft is one of the key moving parts of a diesel engine, and its reliability directly affects the normal operation of the entire diesel engine.

[0003] Due to the large number of alloying elements and high alloy content, controlling the oxygen and inclusion content during the smelting process of 30CrMoV9 alloy steel is very difficult, easily leading to excessive Ti content and TiN non-metallic inclusion content. Conventional smelting raw materials and steelmaking processes cannot meet the compositional requirements of 30CrMoV9 alloy steel for low Ti content (Ti≤0.0035%), oxygen content [O]≤20ppm in molten steel, and purity requirements for TiN non-metallic inclusions ≤1.5 grade.

[0004] TiN, a non-metallic inclusion in steel, is a brittle and hard inclusion that can severely impair the fatigue life of crankshafts made of 30CrMoV9 alloy steel. Furthermore, the higher the Ti or N content in the steel, the larger the size of the TiN inclusions, and the greater the negative impact on the fatigue life of crankshafts made of 30CrMoV9 alloy steel. Therefore, controlling the Ti and N content in molten steel is of paramount importance. Summary of the Invention

[0005] In order to solve all or part of the above problems, the present invention aims to provide a 30CrMoV9 alloy steel billet and its preparation method.

[0006] According to one aspect of the present invention, a method for preparing a 30CrMoV9 alloy steel billet is provided, comprising:

[0007] The raw materials, consisting of molten iron and scrap steel, are fed into an electric furnace for smelting. During the smelting process, oxygen is blown to adjust the carbon content of the molten steel, and lime is added to adjust the phosphorus content of the molten steel.

[0008] 10% of the molten steel is retained, and the remaining molten steel is tapped into the ladle refining furnace for refining, and the content of each element in the molten steel is adjusted during the refining process;

[0009] The obtained molten steel is fed into a vacuum degassing refining furnace for vacuum treatment to obtain the first molten steel.

[0010] After the vacuum is broken, the first molten steel is used for casting to obtain a 30CrMoV9 alloy steel billet. The 30CrMoV9 alloy steel billet, by mass percentage, comprises the following components: C = 0.31%, Si = 0.31%, Mn = 0.67%, P = 0.008%, S = 0.001%, Cr = 2.62%, Mo = 0.21%, Ni = 0.19%, V = 0.19%, Ti = 0.0035%, Cu = 0.01%, [H] = 0.88 × 10⁻⁶. -4 %, [O]=0.0018%, [N]=0.0045%.

[0011] Furthermore, the process of feeding the raw materials composed of molten iron and scrap steel into an electric furnace for smelting, performing oxygen blowing during the smelting process to adjust the carbon content of the molten steel, and adding lime during the smelting process to adjust the phosphorus content of the molten steel specifically involves:

[0012] The ratio of molten steel to scrap steel in the raw materials is controlled to be greater than 70%. The raw materials are fed into an electric furnace for smelting. During the smelting process, oxygen blowing is performed to adjust the carbon content in the molten steel, and lime is added during the smelting process to adjust the phosphorus content in the molten steel.

[0013] Furthermore, after the raw materials consisting of molten iron and scrap steel are fed into an electric furnace for smelting, oxygen blowing is performed during the smelting process to adjust the carbon content in the molten steel, and lime is added during the smelting process to adjust the phosphorus content in the molten steel, the method further includes: sampling and analyzing the chemical composition of the molten steel in the electric furnace, and adjusting the amount of oxygen blowing and lime added according to the analysis results to obtain a second molten steel with a C content of 0.08% and a P content of 0.006%.

[0014] The specific steps of retaining 10% of the molten steel and refining the remaining molten steel in a ladle refining furnace, and adjusting the content of each element in the molten steel during the refining process, are as follows: After obtaining the second molten steel, retain 10% of the second molten steel and refining the remaining molten steel in a ladle refining furnace, and adjusting the content of each element in the second molten steel during the refining process.

[0015] Furthermore, the step of retaining 10% of the second molten steel after obtaining it, and tapping the remaining molten steel into a ladle refining furnace for refining, and adjusting the content of each element in the second molten steel during the refining process, further includes:

[0016] After obtaining the second molten steel, 10% of the second molten steel is retained, and the remaining second molten steel is tapped into a ladle refining furnace for refining. Refining slag for deoxidation and desulfurization is added with the steel stream entering the ladle refining furnace to control the oxygen and sulfur content in the second molten steel. Argon gas is blown and stirred during the refining process to control the nitrogen content in the second molten steel. Metal elements are added with the steel stream entering the ladle refining furnace to adjust the content of metal elements in the second molten steel.

[0017] Furthermore, the specific steps of adding metallic elements along with the steel stream entering the ladle refining furnace to adjust the content of metallic elements in the second molten steel are as follows:

[0018] Along with the steel stream entering the ladle refining furnace, carbon ferromanganese (77% Mn, 7% C, 0.02% Ti), carbon ferrosilicon (75% Si, 0.06% C, 0.015% Ti), carbon ferrochrome (60% Cr, 0.06% C, <0.01% Ti), aluminum, ferronickel, ferromolybdenum, and ferrovanadium are added to adjust the content of metallic elements in the second molten steel.

[0019] Furthermore, the addition of refining slag for deoxidation and desulfurization along with the steel stream entering the ladle refining furnace to control the oxygen and sulfur content in the second molten steel specifically involves:

[0020] A mixture of lime containing 94% CaO and 0.003% TiO2 is added along with the steel stream entering the ladle refining furnace, as well as a synthetic slag consisting of 45%-55% CaO, 26%-36% Al2O3 and less than 7% SiO2.

[0021] Furthermore, after reserving 10% of the molten steel and refining the remaining molten steel in a ladle refining furnace, and adjusting the content of each element in the molten steel during the refining process, the method further includes: sampling and analyzing the chemical composition of the molten steel in the ladle refining furnace, and adjusting the content of each element in the second molten steel according to the analysis results to obtain a third molten steel comprising the following contents by mass percentage: C = 0.29%, Si = 0.31%, Mn = 0.69%, P = 0.010%, S = 0.001%, Ni = 0.20%, Cr = 2.5%, Cu = 0.02%, Al = 0.047%, Mo = 0.21%, V = 0.19%, Ti = 0.0025%.

[0022] Furthermore, the obtained molten steel is put into a vacuum degassing refining furnace for vacuum treatment to obtain the first molten steel. Specifically, the obtained molten steel is put into a vacuum degassing refining furnace for vacuum treatment, the vacuum degree of the vacuum treatment is adjusted to 60 Pa, the molten steel is controlled to be held at this vacuum degree for 16-22 minutes, and after the vacuum is broken, it is stirred for 16-20 minutes to obtain the first molten steel.

[0023] Furthermore, the process of casting the first molten steel after vacuum breaking to obtain the 30CrMoV9 alloy steel billet specifically involves: controlling the casting superheat to 50-55℃ after vacuum breaking, the ingot casting speed to 0.05-0.06t / min, the riser casting speed to 0.06-0.08t / min, and using argon sealing protection to cast the first molten steel to obtain the 30CrMoV9 alloy steel billet.

[0024] The present invention also provides a 30CrMoV9 alloy steel billet, which is prepared by any one of the methods described above.

[0025] As can be seen from the above technical solution, the 30CrMoV9 alloy steel billet and its preparation method provided by the present invention have the following beneficial effects:

[0026] The 30CrMoV9 alloy steel billet prepared by the method of this invention meets the stringent requirements of low Ti content, high purity, high strength, and high toughness for crankshaft materials.

[0027] This invention improves the impact toughness KU2 of alloy steel billet by 60 J by adding 0.13-0.20% V.

[0028] This invention implements low Ti control throughout the entire process to achieve the component requirement of low Ti content of ≤0.0035%.

[0029] In this invention, argon is used throughout the refining process in the ladle refining furnace; during the vacuum degassing refining furnace process, the flow rate of nitrogen or argon for soft stirring is controlled according to the change in the [N] content of the molten steel to achieve [N] ≤ 0.0060%.

[0030] The present invention employs a low superheat rapid casting solidification technology, controlling the casting superheat to 50-55℃, the ingot casting speed to 0.05-0.06t / min, and the riser casting speed to 0.06-0.08t / min. This facilitates the floating of non-metallic inclusions in the molten steel, ensuring that the non-metallic inclusions TiN in the steel are ≤1.5 grade. Attached Figure Description

[0031] Figure 1 This is a flowchart illustrating a method for preparing a 30CrMoV9 alloy steel billet according to an embodiment of the present invention. Detailed Implementation

[0032] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0033] When a range of values ​​is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0034] The present invention mainly addresses the high purity requirements of 30CrMoV9 alloy steel crankshafts for diesel engines, which have low Ti content and low TiN non-metallic inclusion content, thereby providing 30CrMoV9 alloy steel crankshafts for diesel engines with high overall strength and toughness.

[0035] The preparation method of this invention includes electric furnace smelting, LF (ladle refining furnace) refining, VD (vacuum degassing furnace) vacuum degassing treatment, and die casting.

[0036] Specifically, such as Figure 1 As shown, this invention illustrates a method for preparing a 30CrMoV9 alloy steel billet, comprising the following steps:

[0037] Step S001: The raw materials consisting of molten iron and scrap steel are put into an electric furnace for smelting. During the smelting process, oxygen blowing is carried out to adjust the carbon content of the molten steel, and lime is added during the smelting process to adjust the phosphorus content of the molten steel.

[0038] The specific steps are as follows: control the ratio of molten steel and the sum of molten steel and scrap steel in the raw materials to be greater than 70%, put the raw materials into the electric furnace for smelting, perform oxygen blowing treatment during the smelting process to adjust the carbon content of the molten steel, and add lime during the smelting process to adjust the phosphorus content of the molten steel.

[0039] The raw materials for smelting include molten steel and scrap steel, with the ratio of molten steel to the sum of both exceeding 70%. The content of sulfur (S), phosphorus (P), and other harmful elements in the raw materials must be strictly controlled. The raw materials also need to be thoroughly baked before smelting.

[0040] The purpose of blowing oxygen during electric arc furnace smelting is to convert carbon into CO and / or CO2 gas through oxidation reaction and then release it, thereby reducing the carbon content of the molten steel. The purpose of adding lime during smelting is to use lime to form slag and remove corresponding harmful elements, such as phosphorus. Thus, the purpose of reducing carbon and phosphorus is achieved through electric arc furnace smelting.

[0041] In step S001, the raw materials consisting of molten iron and scrap steel are fed into an electric furnace for smelting. During the smelting process, oxygen blowing is performed to adjust the carbon content in the molten steel, and lime is added during the smelting process to adjust the phosphorus content in the molten steel. The preparation method of this embodiment of the invention further includes: sampling and analyzing the chemical composition of the molten steel in the electric furnace, and adjusting the amount of oxygen blowing and lime added according to the analysis results to obtain a second molten steel with a C content of 0.08% and a P content of 0.006%.

[0042] Step S002: Retain 10% of the molten steel, and tap the remaining molten steel into the ladle refining furnace for refining, while adjusting the content of each element in the molten steel during the refining process.

[0043] Step S002, which retains 10% of the molten steel and taps the remaining steel into the ladle refining furnace, aims to prevent the final ladle refining process from involving slag. Oxidized slag not only has a high oxygen content but also produces numerous oxidation products. If electric arc furnace oxidized slag enters the molten steel, it will increase the oxygen content and total amount of inclusions in the subsequent refining process. The temperature of the molten steel entering the ladle refining furnace is 1523℃.

[0044] Since step S001 yields a second molten steel with corresponding carbon and phosphorus content, step S002 retains 10% of the molten steel. The remaining molten steel is tapped into a ladle refining furnace for refining, and the content of each element in the molten steel is adjusted during the refining process. Specifically, after obtaining the second molten steel, 10% of the second molten steel is retained, and the remaining second molten steel is tapped into a ladle refining furnace for refining, and the content of each element in the second molten steel is adjusted during the refining process.

[0045] After obtaining the second molten steel, 10% of the second molten steel is retained, and the remaining second molten steel is tapped into a ladle refining furnace for refining. The refining process further includes adjusting the content of various elements in the second molten steel, including: retaining 10% of the second molten steel after obtaining it, and tapping the remaining second molten steel into a ladle refining furnace for refining; adding refining slag for deoxidation and desulfurization along with the steel stream entering the ladle refining furnace to control the oxygen and sulfur content in the second molten steel; blowing argon gas to stir during the refining process to control the nitrogen content in the second molten steel; and adding metallic elements along with the steel stream entering the ladle refining furnace to adjust the content of metallic elements in the second molten steel.

[0046] Specifically, the addition of refining slag for deoxidation and desulfurization to the steel stream entering the ladle refining furnace to control the oxygen and sulfur content in the second molten steel involves adding a lime mixture containing 94% CaO and 0.003% TiO2, as well as a synthetic slag containing 45%-55% CaO, 26%-36% Al2O3, and less than 7% SiO2.

[0047] In this embodiment, the purpose of adding lime mixture and synthetic slag during the refining process in the ladle refining furnace is to control the oxygen and sulfur content in the molten steel. After adding the above raw materials, this application also includes controlling the basicity (CaO / SiO2 ratio) of the steel slag above the molten steel in the ladle refining furnace to be 6-7. The oxygen content [O] in the steel refined by the ladle refining furnace is ≤0.0018%, and the sulfur content [S] is ≤0.002%.

[0048] The purpose of stirring with argon gas during the refining process is to control the nitrogen content in the second molten steel, with the target being [N] ≤ 0.0060%.

[0049] The metal elements added along with the steel stream entering the ladle refining furnace to adjust the metal element content of the second molten steel are as follows: carbon ferromanganese with Mn=77%, C=7%, and Ti=0.02% is added; carbon ferrosilicon with Si=75%, C=0.06%, and Ti=0.015% is added; carbon ferrochrome with Cr=60%, C=0.06%, and Ti<0.01% is added; and metallic aluminum, ferronickel, ferromolybdenum, and ferrovanadium are added to adjust the metal element content of the second molten steel.

[0050] In step S002, 10% of the molten steel is retained, and the remaining molten steel is tapped into a ladle refining furnace for refining. After adjusting the content of each element in the molten steel during the refining process, the preparation method of this embodiment further includes: sampling and analyzing the chemical composition of the molten steel in the ladle refining furnace, and adjusting the content of each element in the second molten steel according to the analysis results to obtain a third molten steel containing the following contents by mass percentage: C = 0.29%, Si = 0.31%, Mn = 0.69%, P = 0.010%, S = 0.001%, Ni = 0.20%, Cr = 2.5%, Cu = 0.02%, Al = 0.047%, Mo = 0.21%, V = 0.19%, Ti = 0.0025%.

[0051] In step S002, the third molten steel is obtained and the temperature of the molten steel reaches 1675°C. After the steel is tapped, it is subjected to vacuum treatment in a vacuum degassing refining furnace. The temperature of the molten steel entering the vacuum degassing refining furnace is 1659°C.

[0052] Step S003: The obtained molten steel enters a vacuum degassing refining furnace for vacuum treatment to obtain the first molten steel.

[0053] The specific steps are as follows: control the molten steel from the ladle refining furnace to enter the vacuum degassing refining furnace for vacuum treatment, adjust the vacuum degree of the vacuum treatment to 60Pa, control the molten steel to be kept at this vacuum degree for 16-22 minutes, and stir for 16-20 minutes after breaking the vacuum to obtain the first molten steel.

[0054] For vacuum treatment before entering the vacuum degassing refining furnace, the holding time of molten steel under high vacuum is 16-22 minutes, and the soft stirring time is 16-20 minutes. The soft stirring effect is ideally achieved when the slag surface shows obvious creeping and the molten steel is not exposed. After vacuum treatment, the [H] in the molten steel should be less than or equal to 0.88 × 10⁻⁶. -4 %.

[0055] Step S004: After breaking the vacuum, the first batch of molten steel is used for casting to obtain a 30CrMoV9 alloy steel billet. The obtained 30CrMoV9 alloy steel billet, by mass percentage, includes the following components: C = 0.31%, Si = 0.31%, Mn = 0.67%, P = 0.008%, S = 0.001%, Cr = 2.62%, Mo = 0.21%, Ni = 0.19%, V = 0.19%, Ti = 0.0035%, Cu = 0.01%, [H] = 0.88 × 10⁻⁶. -4 %, [O]=0.0018%, [N]=0.0045%.

[0056] The specific steps are as follows: After breaking the vacuum, control the casting superheat to 50-55℃, the ingot casting speed to 0.05-0.06 t / min, the riser casting speed to 0.06-0.08 t / min, and use argon sealing protection to cast using the first batch of molten steel to obtain a 30CrMoV9 alloy steel billet. The 30CrMoV9 alloy steel billet, by mass percentage, includes the following components: C = 0.31%, Si = 0.31%, Mn = 0.67%, P = 0.008%, S = 0.001%, Cr = 2.62%, Mo = 0.21%, Ni = 0.19%, V = 0.19%, Ti = 0.0035%, Cu = 0.01%, [H] = 0.88 × 10⁻⁶. -4 %, [O]=0.0018%, [N]=0.0045%.

[0057] For the casting process, a low superheat fast casting solidification technology is adopted, controlling the casting superheat to 50-55℃, the ingot casting speed to 0.05-0.06t / min, and the riser casting speed to 0.06-0.08t / min. This is conducive to the floating of non-metallic inclusions in the molten steel, achieving a TiN level of ≤1.5 in the steel.

[0058] In this embodiment of the invention, the impact toughness KU2 of the alloy steel billet was increased by 60 J by adding 0.13-0.20% V.

[0059] In this embodiment of the invention, the raw materials used are first-grade lime, carbon silicon ferrophosphate, and carbon chromium ferrophosphate. Low Ti control is carried out throughout the entire process to achieve the component requirement of low Ti content of ≤0.0035%.

[0060] In this embodiment of the invention, argon is used throughout the refining process in the ladle refining furnace; during the vacuum degassing refining furnace process, the flow rate of nitrogen or argon for soft stirring is controlled according to the change in the [N] content of the molten steel to achieve [N] ≤ 0.0060%.

[0061] The casting adopts a low superheat fast casting solidification technology, controlling the casting superheat to 50-55℃, the ingot casting speed to 0.05-0.06t / min, and the riser casting speed to 0.06-0.08t / min. This is conducive to the floating of non-metallic inclusions in the molten steel, achieving a non-metallic inclusion TiN ≤ 1.5 grade in the steel.

[0062] This invention also provides a 30CrMoV9 alloy steel billet, which is prepared using the method of any of the above embodiments.

[0063] The 30CrMoV9 alloy steel billet prepared by the preparation method of this invention meets the stringent requirements of low Ti content, high purity, high strength, and high toughness for crankshaft materials.

[0064] Specifically, the chemical composition of the 30CrMoV9 alloy steel billet prepared by the method of this invention is as follows: C = 0.31%, Si = 0.31%, Mn = 0.67%, P = 0.008%, S = 0.001%, Cr = 2.62%, Mo = 0.21%, Ni = 0.19%, V = 0.19%, Ti = 0.0035%, Cu = 0.01%, [H] = 0.88 × 10⁻⁶. -4 %, [O]=0.0018%, [N]=0.0045%.

[0065] Experiments were conducted on the 30CrMoV9 alloy steel billet prepared using the preparation method described in this invention. The low-magnification microstructure grades were: general porosity 0.5 grade, central porosity 0.5 grade, ingot segregation 0 grade, and point segregation 0 grade. The inclusion grades were: Class A fine series 0 grade, coarse series 0 grade; Class B fine series 0.5 grade, coarse series 0 grade; Class C fine series 0 grade, coarse series 0 grade; Class D fine series 0.5 grade, coarse series 0.5 grade; Class DS 0 grade; TiN = 0 grade. The mechanical properties were: yield strength RP0.2 = 1042 MPa, tensile strength Rm = 1141 MPa, elongation A = 17%, reduction of area Z = 64%, room temperature U-shaped impact KU2 = 138 J, and room temperature V-shaped impact KV2 = 82 J.

[0066] To understand the preparation method of the embodiments of the present invention, the present invention will be described below through specific embodiments:

[0067] At 14:38, the electric furnace was charged. The raw materials charged included 15.3 tons of scrap steel and 69.90 tons of molten iron, for a total weight of 85.2 tons.

[0068] Oxygen was blown and lime was added at 15:02, with a total oxygen blowing volume of 4511 Nm³. 3 The oxygen blowing rate is 52.95 Nm³ per ton of raw material. 3 The total amount of lime added was 4352 kg, which is 51.08 kg of lime per ton of raw material.

[0069] At 15:50 (time), the chemical composition of the molten steel was analyzed as follows: C = 0.08%, Si = 0.03%, Mn = 0.06%, P = 0.006%, S = 0.020%, Ni = 0.007%, Cr = 0.04%, Mo = 0.002%, Cu = 0.008%, Ti = 0.0003%.

[0070] At 15:51, the electric furnace tapped steel at a temperature of 1650℃. 398 kg of grade 1 lime (CaO = 94%, TiO2 = 0.003%), 398 kg of synthetic slag (CaO = 45%-55%, Al2O3 = 26%-36%, SiO2 < 7%), 83 kg of carbon ferrosilicon, 512 kg of carbon ferromanganese, 1010 kg of carbon ferrochrome, and 210 kg of aluminum shot were added with the tapped steel.

[0071] At 16:05, the steel entered the LF station with a temperature of 1523℃.

[0072] Power was supplied at 16:07 (time) for slag removal.

[0073] At 16:25, a sample of the molten steel was taken for analysis. The composition of the molten steel was as follows: C = 0.25%, Si = 0.16%, Mn = 0.50%, P = 0.008%, S = 0.003%, Cr = 0.72%, Cu = 0.01%, Al = 0.060%, Ni = 0.02%, Mo = 0.037%, V = 0.02%, Ti = 0.0009%.

[0074] Then, the composition of the molten steel was adjusted by adding 450 kg of grade 1 lime, 236 kg of carbon manganese ferromanganese (Mn = 77%, C = 7%, Ti = 0.02%), 75 kg of carbon silicon ferromanganese (Si = 75%, C = 0.06%, Ti = 0.015%), 2843 kg of carbon chromium ferromanganese (Cr = 60%, C = 0.06%, Ti < 0.01%), 100 kg of aluminum wire, 573 kg of nickel ferromanganese, 182 kg of molybdenum ferromanganese, and 220 kg of vanadium ferromanganese.

[0075] At 16:36, the composition of the molten steel was analyzed. The composition of the molten steel was: C = 0.27%, Si = 0.24%, Mn = 0.60%, P = 0.009%, S = 0.001%, Ni = 0.09%, Cr = 1.61%, Cu = 0.02%, Al = 0.045%, Mo = 0.18%, V = 0.14%, Ti = 0.0020%.

[0076] At 16:51, the composition of the molten steel was analyzed. The composition of the molten steel was: C = 0.31%, Si = 0.31%, Mn = 0.67%, P = 0.008%, S = 0.001%, Cr = 2.62%, Mo = 0.21%, Ni = 0.19%, V = 0.19%, Ti = 0.0035%, Cu = 0.01%.

[0077] At 17:00 (time), the LF station was opened, and the temperature of the molten steel was 1675℃.

[0078] At 17:05, the steel entered the VD station with a temperature of 1659℃.

[0079] The vacuuming process began at 17:12 and reached the ultimate vacuum level of 60 Pa at 17:20.

[0080] It broke through the sky at 17:37, with a temperature of 1598℃ and H = 0.5 × 10⁻⁶. -4 %.

[0081] Argon gas soft stirring was performed at 17:45.

[0082] Soft stirring was stopped at 18:05 (time), molten steel temperature: 1567℃. A covering agent was added to the ladle before it left the station. The composition of the VD molten steel leaving the station was: C = 0.30%, Si = 0.32%, Mn = 0.68%, P = 0.009%, S = 0.001%, Ni = 0.19%, Cr = 2.61%, Cu = 0.02%, Al = 0.030%, Mo = 0.21%, V = 0.18%, Ti = 0.0030%. The composition of the molten steel was the same as that of the first molten steel.

[0083] At 18:10, the steel entered the casting station at a temperature of 1557℃.

[0084] Argon sealing protection was used for casting at 18:30. 1.3t of steel was poured before casting, and 2.1t remained after casting. Ingot type: 8.4t steel ingot. Casting speed: First batch of 6 ingots: ingot body 15 minutes 24 seconds, cap 9 minutes 26 seconds; Second batch of 4 ingots: ingot body 12 minutes 13 seconds, cap 7 minutes.

[0085] The steel ingot was delivered at 20:05 (time).

[0086] The 30CrMoV9 alloy steel billet prepared by the preparation method of this invention meets the stringent requirements of low Ti content, high purity, high strength, and high toughness for crankshaft materials.

[0087] The present invention has been disclosed above with reference to preferred embodiments. However, those skilled in the art should understand that these embodiments are merely illustrative of the invention and should not be construed as limiting its scope. It should be noted that any variations and substitutions equivalent to these embodiments should be considered to be covered within the scope of the claims. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a 30CrMoV9 alloy steel billet, characterized in that, include: The raw materials, consisting of molten iron and scrap steel, are fed into an electric furnace for smelting. During the smelting process, oxygen is blown to adjust the carbon content of the molten steel, and lime is added to adjust the phosphorus content of the molten steel. 10% of the molten steel is retained, and the remaining molten steel is tapped into the ladle refining furnace for refining, and the content of each element in the molten steel is adjusted during the refining process; The obtained molten steel is fed into a vacuum degassing refining furnace for vacuum treatment to obtain the first molten steel. After the vacuum is broken, the first molten steel is used for casting to obtain a 30CrMoV9 alloy steel billet. The 30CrMoV9 alloy steel billet, by mass percentage, comprises the following components: C=0.31%, Si=0.31%, Mn=0.67%, P=0.008%, S=0.001%, Cr=2.62%, Mo=0.21%, Ni=0.19%, V=0.19%, Ti=0.0035%, Cu=0.01%, [H]=0.88×10⁻⁶. -4 %, [O]=0.0018%, [N]=0.0045%.

2. The method according to claim 1, characterized in that, The process of smelting raw materials consisting of molten iron and scrap steel in an electric furnace, performing oxygen blowing during smelting to adjust the carbon content of the molten steel, and adding lime during smelting to adjust the phosphorus content of the molten steel are specifically as follows: The mass ratio of molten iron and the sum of molten iron and scrap steel in the raw materials is controlled to be greater than 70%. The raw materials are put into an electric furnace for smelting. During the smelting process, oxygen blowing is carried out to adjust the carbon content of the molten steel, and lime is added during the smelting process to adjust the phosphorus content of the molten steel.

3. The method according to claim 1, characterized in that, After the raw materials consisting of molten iron and scrap steel are fed into an electric furnace for smelting, oxygen blowing is performed during the smelting process to adjust the carbon content of the molten steel, and lime is added during the smelting process to adjust the phosphorus content of the molten steel, the method further includes: sampling and analyzing the chemical composition of the molten steel in the electric furnace, and adjusting the amount of oxygen blowing and lime added according to the analysis results to obtain a second molten steel with a C content of 0.08% and a P content of 0.006%. The specific steps of retaining 10% of the molten steel and refining the remaining molten steel in a ladle refining furnace, and adjusting the content of each element in the molten steel during the refining process, are as follows: After obtaining the second molten steel, retain 10% of the second molten steel and refining the remaining molten steel in a ladle refining furnace, and adjusting the content of each element in the second molten steel during the refining process.

4. The method according to claim 3, characterized in that, After obtaining the second molten steel, retaining 10% of the second molten steel and tapping the remaining second molten steel into a ladle refining furnace for refining, and adjusting the content of each element in the second molten steel during the refining process, further includes: After obtaining the second molten steel, 10% of the second molten steel is retained, and the remaining second molten steel is tapped into a ladle refining furnace for refining. Refining slag for deoxidation and desulfurization is added with the steel stream entering the ladle refining furnace to control the oxygen and sulfur content in the second molten steel. Argon gas is blown and stirred during the refining process to control the nitrogen content in the second molten steel. Metal elements are added with the steel stream entering the ladle refining furnace to adjust the content of metal elements in the second molten steel.

5. The method according to claim 4, characterized in that, The specific steps for adding metallic elements to the steel stream entering the ladle refining furnace to adjust the content of metallic elements in the second molten steel are as follows: Along with the steel stream entering the ladle refining furnace, carbon ferromanganese (77% Mn, 7% C, 0.02% Ti), carbon ferrosilicon (75% Si, 0.06% C, 0.015% Ti), carbon ferrochrome (60% Cr, 0.06% C, <0.01% Ti), aluminum, ferronickel, ferromolybdenum, and ferrovanadium are added to adjust the content of metallic elements in the second molten steel.

6. The method according to claim 4, characterized in that, The addition of refining slag for deoxidation and desulfurization along with the steel stream entering the ladle refining furnace to control the oxygen and sulfur content in the second molten steel specifically involves: A mixture of lime containing 94% CaO and 0.003% TiO2 is added along with the steel stream entering the ladle refining furnace, as well as a synthetic slag consisting of 45%-55% CaO, 26%-36% Al2O3 and less than 7% SiO2.

7. The method according to claim 1, characterized in that, After refining the remaining molten steel (10%) into a ladle refining furnace and adjusting the content of each element in the molten steel during the refining process), the method further includes: sampling and analyzing the chemical composition of the molten steel in the ladle refining furnace, and adjusting the content of each element in the second molten steel according to the analysis results to obtain a third molten steel containing the following contents by mass percentage: C=0.29%, Si=0.31%, Mn=0.69%, P=0.010%, S=0.001%, Ni=0.20%, Cr=2.5%, Cu=0.02%, Al=0.047%, Mo=0.21%, V=0.19%, Ti=0.0025%.

8. The method according to claim 1, characterized in that, The obtained molten steel is fed into a vacuum degassing refining furnace for vacuum treatment to obtain the first molten steel. Specifically, the molten steel is fed into a vacuum degassing refining furnace for vacuum treatment. The vacuum degree of the vacuum treatment is adjusted to 60 Pa. The molten steel is kept at this vacuum degree for 16-22 minutes, and after the vacuum is broken, it is stirred for 16-20 minutes to obtain the first molten steel.

9. The method according to claim 1, characterized in that, The process of pouring the first molten steel after breaking the vacuum to obtain the 30CrMoV9 alloy steel billet specifically involves: controlling the pouring superheat to 50-55℃ after breaking the vacuum, the ingot pouring speed to 0.05-0.06t / min, the riser pouring speed to 0.06-0.08t / min, and using argon sealing protection to pour the first molten steel to obtain the 30CrMoV9 alloy steel billet.

10. A 30CrMoV9 alloy steel billet, characterized in that, It is prepared using the method described in any one of claims 1-9.

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