Production process of 40CrH steel for automobile steering knuckle smelted by adopting electric furnace

Abstract

The invention relates to the technical field of steel production, in particular to a production process of 40CrH steel smelted by an electric furnace and used for automobile steering knuckles, and the steel comprises the following chemical components in percentage by weight: 0.385%-0.410% of C, 0.20%-0.32% of Si, 0.73%-0.77% of Mn, less than or equal to 0.022% of P, less than or equal to 0.020% of S, 1.02%-1.06% of Cr, 0.020%-0.040% of Alt, less than or equal to 0.04% of Mo, less than or equal to 0.0004% of B, less than or equal to 0.08% of Cu and the balance of Fe and impurities. The production process route comprises ecological electric furnace smelting, LF refining, RH vacuum degassing, continuous casting, heating and rolling. According to the method, the finished steel has narrow hardenability and good comprehensive performance by accurately controlling the chemical components of the steel and combining the technological means of electric furnace end point control, crystallizer and solidification end electromagnetic stirring, rolling temperature optimization and the like.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to a production process of large-size 40CrH steel for automobile steering knuckles smelted by an electric furnace. Background Art

[0002] 40CrH is a kind of structural steel with guaranteed hardenability. After quenching and tempering, it is used to manufacture mechanical parts that bear medium loads and medium speeds, such as steering knuckles, rear axles and other parts of automobiles. Since such parts are mainly subjected to bending and impact loads, they are one of the vulnerable parts on automobiles. Therefore, this type of steel is required to have sufficient strength, narrow hardenability bandwidth and excellent bending fatigue performance. In order to meet the requirements of automobile manufacturers for the performance of 40CrH steel products, the chemical composition of the steel needs to be reasonably designed during production and precisely controlled to ensure that the hardenability of the steel fluctuates within a narrow range; at the same time, it is also necessary to focus on controlling the mechanical properties, non-metallic inclusions, banded structure grade, grain size grade and other indicators of the steel. In addition, the larger the specifications of the steel, the more difficult it is to control its composition and organizational uniformity, and the harderenability is more likely to fluctuate greatly, which will seriously affect the processing accuracy of the workpiece and reduce its service life.

[0003] The Chinese patent application with application number 201910431061.6 discloses "a method for producing steel for automobile steering knuckles". The process route adopted is converter + LF furnace + VD furnace or RH furnace. The chemical composition of the steel is C=0.37%~0.39%, Si=0.20%~0.30%, Mn=0.75%~0.80%, P≤0.020%, S≤0.015%, Cr=1.05%~1.10%, Ni≤0.30%, Al≤0.0015%~0.0040%, the total of Cu, Ni, V, Sn≤0.8%, H≤0.0002%, O≤0.0020%, and the rest is Fe and unavoidable impurities. It adopts a medium-carbon high-alloy composition design system, LF+VD composite refining technology, strictly controls the purity of molten steel, and adopts a new technology of high-temperature, high-pressure rolling and slow cooling to develop 40CrH steel for automotive steering knuckles, which has a fatigue bench test of 1 million times without damage. The steel produced by this method has good indicators, low gas content and non-metallic inclusion content, and can well meet the use requirements of ultra-high hardenability and fatigue life of automotive steering knuckles. However, it adopts the converter smelting process path, and the finished product specifications after rolling are only ø50~ø100mm, which is not suitable for the production of steering knuckle steel with specifications above ø100mm. Summary of the invention

[0004] The present invention provides a production process of 40CrH steel for automobile steering knuckles smelted in an electric furnace, which is suitable for the production of large-size automobile steering knuckles with a maximum diameter of ø150mm. Through reasonable design and precise control of the chemical composition of the steel, combined with process means such as electric furnace endpoint control, electromagnetic stirring of the crystallizer and solidification end, and optimization of rolling temperature, the finished steel has narrow hardenability and good comprehensive performance, meeting the user's requirements.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A production process of 40CrH steel for automobile steering knuckles smelted by electric furnace, the chemical composition of 40CrH steel is C: 0.385%-0.410%, Si: 0.20%-0.32%, Mn: 0.73%-0.77%, P≤0.022%, S≤0.020%, Cr: 1.02%-1.06%, Alt: 0.020%-0.040%, Mo≤0.04%, B≤0.0004%, Cu≤0.08%, the balance is Fe and unavoidable impurities; the finished steel specification is ø120-ø150mm; the production process route is ecological electric furnace smelting, LF refining, RH vacuum degassing, continuous casting, heating and rolling, wherein the process control is as follows: 1) Ecological electric furnace smelting: The ecological electric furnace uses all scrap steel for smelting. By weight percentage, the endpoint C content is controlled to be 0.05%-0.10%, and the endpoint P content is ≤0.012%; the tapping temperature is 1600-1620℃, and the tapping time is controlled to be 5-6min; when the tapping volume reaches 15-20t, the following alloys are added in sequence: 1.3-1.5kg / t steel of aluminum ingots for remelting, 5.5-6.5kg / t steel of high carbon ferromanganese, 14.0-16.0kg / t steel of high carbon ferrochrome, 4.0-5.0kg / t steel of silicon manganese alloy, and 600kg / furnace of lime and 500kg / furnace of synthetic slag are added to the ladle; 2) LF refining: After the ladle is in place, turn on the argon gas, and the argon gas flow rate is 300-500NL / min; add 3.5-4.5kg / t of lime, and thin slag is formed when the power is supplied for 3-5 minutes. At this time, adjust the argon gas flow rate to 150-250NL / min; add 180-230kg / furnace of silicon carbide for diffusion deoxidation; close the furnace door and supply power for 20 minutes, dip the slag, and measure the temperature and take a sample after confirming that the slag is white; perform alloying treatment according to the first full analysis composition, including adding 0.3-1.0kg / t of ferrosilicon, 0.5-1.5kg / t of high carbon ferromanganese, 2.0-3.0kg / t of high carbon ferrochrome, and 1.0-3.0kg / t of alumina balls; after the second full analysis composition is adjusted, adjust the argon gas flow rate to 100-200NL / min; 3) RH vacuum degassing: After the ladle seat is on the ladle car, argon gas is blown, and the argon gas flow rate is 300-450NL / min; after the ladle enters the working position, the lifting operation is started, the immersion tube insertion depth is greater than 400mm, the argon gas is turned off, the vacuum degree is less than 100Pa, and the duration is ≥15min; after breaking the air, calcium treatment is carried out, and 150-250m / furnace of silicon calcium wire is fed; before static blowing and stirring, 0.7-1.0kg / t steel of covering agent is added, the static blowing and stirring time is ≥20min, and the static blowing argon gas flow rate is 10-60NL / min; 4) Continuous casting: Control the billet drawing speed to prevent large slag from falling; electromagnetic stirring is used in the crystallizer and at the end of solidification; 5) Rolling: The starting rolling temperature is 1000℃~1200℃, and the final rolling temperature is 800℃~1100℃.

[0006] During the ecological electric furnace smelting process, the added alloy is pre-baked at a temperature of 600-800°C.

[0007] During the continuous casting process, medium carbon steel mold protection slag is used as the continuous casting protection slag.

[0008] During the continuous casting process, the relationship between the superheat of molten steel and the continuous casting speed is as follows: When the superheat is less than 20℃, the pulling speed is controlled at 0.44~0.46m / min; When the temperature is 20℃≤superheat<35℃, the pulling speed is controlled at 0.41~0.43m / min; When the temperature is 35℃≤superheat<45℃, the pulling speed is controlled at 0.39~0.41m / min; When the superheat is ≥45℃, the pulling speed is controlled at 0.34~0.36m / min.

[0009] The continuous casting adopts a large square billet continuous casting machine; the electromagnetic stirring parameters of the crystallizer are: current 380~420A, frequency 1.5~2.5Hz; the electromagnetic stirring parameters at the end of continuous casting are: current 400~440A, frequency 6~8Hz; the electromagnetic stirring mode of the crystallizer and the end of continuous casting is alternating forward and reverse stirring.

[0010] High-pressure water is used for descaling before rolling, and the descaling pressure is 28 to 30 MPa.

[0011] The hardness value of the finished steel at 9mm from the end face is J9: 46~51HRC; the banded structure grade is ≤5, the grain size grade is ≥5; the non-metallic inclusion grade: Class A coarse series ≤3.0, Class A fine series ≤3.0, Class B coarse series ≤2.0, Class B fine series ≤2.0, Class C coarse series ≤1.0, Class C fine series ≤1.0, Class D coarse series ≤1.0, Class D fine series ≤1.0, Class Ds ≤1.0.

[0012] The mechanical properties of the finished steel are: yield strength ≥785MPa, tensile strength ≥980MPa, section shrinkage ≥45%, elongation after fracture ≥9%, and room temperature impact toughness KU2 ≥48J.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1) Through reasonable design and precise control of the chemical composition of steel, combined with the process means such as electric furnace endpoint control, electromagnetic stirring of the crystallizer and solidification end, and optimization of rolling temperature, the finished steel has narrow hardenability and good comprehensive performance to meet the user's requirements.

[0014] 2) Suitable for the production of large-sized automobile steering knuckles with a maximum diameter of ø150mm. DETAILED DESCRIPTION

[0015] The present invention discloses a production process of 40CrH steel for automobile steering knuckles smelted by electric furnace. The chemical composition of the 40CrH steel is C: 0.385%-0.410%, Si: 0.20%-0.32%, Mn: 0.73%-0.77%, P≤0.022%, S≤0.020%, Cr: 1.02%-1.06%, Alt: 0.020%-0.040%, Mo≤0.04%, B≤0.0004%, Cu≤0.08%, and the balance is Fe and unavoidable impurities; the finished steel material specification is ø120-ø150mm; the production process route is ecological electric furnace smelting, LF refining, RH vacuum degassing, continuous casting, heating and rolling, wherein the following process is controlled: 1) Ecological electric furnace smelting: The ecological electric furnace uses all scrap steel for smelting. By weight percentage, the endpoint C content is controlled to be 0.05%-0.10%, and the endpoint P content is ≤0.012%; the tapping temperature is 1600-1620℃, and the tapping time is controlled to be 5-6min; when the tapping volume reaches 15-20t, the following alloys are added in sequence: 1.3-1.5kg / t steel of aluminum ingots for remelting, 5.5-6.5kg / t steel of high carbon ferromanganese, 14.0-16.0kg / t steel of high carbon ferrochrome, 4.0-5.0kg / t steel of silicon manganese alloy, and 600kg / furnace of lime and 500kg / furnace of synthetic slag are added to the ladle; 2) LF refining: After the ladle is in place, turn on the argon gas, and the argon gas flow rate is 300-500NL / min; add 3.5-4.5kg / t of lime, and thin slag is formed when the power is supplied for 3-5 minutes. At this time, adjust the argon gas flow rate to 150-250NL / min; add 180-230kg / furnace of silicon carbide for diffusion deoxidation; close the furnace door and supply power for 20 minutes, dip the slag, and measure the temperature and take a sample after confirming that the slag is white; perform alloying treatment according to the first full analysis composition, including adding 0.3-1.0kg / t of ferrosilicon, 0.5-1.5kg / t of high carbon ferromanganese, 2.0-3.0kg / t of high carbon ferrochrome, and 1.0-3.0kg / t of alumina balls; after the second full analysis composition is adjusted, adjust the argon gas flow rate to 100-200NL / min; 3) RH vacuum degassing: After the ladle seat is on the ladle car, argon gas is blown, and the argon gas flow rate is 300-450NL / min; after the ladle enters the working position, the lifting operation is started, the immersion tube insertion depth is greater than 400mm, the argon gas is turned off, the vacuum degree is less than 100Pa, and the duration is ≥15min; after breaking the air, calcium treatment is carried out, and 150-250m / furnace of silicon calcium wire is fed; before static blowing and stirring, 0.7-1.0kg / t steel of covering agent is added, the static blowing and stirring time is ≥20min, and the static blowing argon gas flow rate is 10-60NL / min; 4) Continuous casting: Control the billet drawing speed to prevent large slag from falling; electromagnetic stirring is used in the crystallizer and at the end of solidification; 5) Rolling: The starting rolling temperature is 1000℃~1200℃, and the final rolling temperature is 800℃~1100℃.

[0016] During the ecological electric furnace smelting process, the added alloy is pre-baked at a temperature of 600-800°C.

[0017] During the continuous casting process, medium carbon steel mold protection slag is used as the continuous casting protection slag.

[0018] During the continuous casting process, the relationship between the superheat of molten steel and the continuous casting speed is as follows: When the superheat is less than 20℃, the pulling speed is controlled at 0.44~0.46m / min; When the temperature is 20℃≤superheat<35℃, the pulling speed is controlled at 0.41~0.43m / min; When the temperature is 35℃≤superheat<45℃, the pulling speed is controlled at 0.39~0.41m / min; When the superheat is ≥45℃, the pulling speed is controlled at 0.34~0.36m / min.

[0019] The continuous casting adopts a large square billet continuous casting machine; the electromagnetic stirring parameters of the crystallizer are: current 380~420A, frequency 1.5~2.5Hz; the electromagnetic stirring parameters at the end of continuous casting are: current 400~440A, frequency 6~8Hz; the electromagnetic stirring mode of the crystallizer and the end of continuous casting is alternating forward and reverse stirring.

[0020] High-pressure water is used for descaling before rolling, and the descaling pressure is 28 to 30 MPa.

[0021] The hardness value of the finished steel at 9mm from the end face is J9: 46~51HRC; the banded structure grade is ≤5, the grain size grade is ≥5; the non-metallic inclusion grade: Class A coarse series ≤3.0, Class A fine series ≤3.0, Class B coarse series ≤2.0, Class B fine series ≤2.0, Class C coarse series ≤1.0, Class C fine series ≤1.0, Class D coarse series ≤1.0, Class D fine series ≤1.0, Class Ds ≤1.0.

[0022] The mechanical properties of the finished steel are: yield strength ≥785MPa, tensile strength ≥980MPa, section shrinkage ≥45%, elongation after fracture ≥9%, and room temperature impact toughness KU2 ≥48J.

[0023] The reasons for designing the chemical components and content (weight percentage) ranges of the 40CrH steel for automobile steering knuckle smelted by electric furnace described in the present invention are as follows: Carbon is the most important component that determines the hardness of martensite obtained after quenching of steel. As the carbon content increases, the martensite hardness increases, and the corresponding hardenability of the steel also increases. However, as the carbon content increases, the yield strength and tensile strength of the steel increase, while the plasticity and impact toughness decrease. Therefore, the hardenability of steel cannot be improved blindly by increasing the carbon content. In order to ensure that the hardenability fluctuation range is within 4HRC, the present invention adopts a narrow composition design and controls the C content range to 0.385% to 0.410%.

[0024] Silicon can improve the hardenability of hypoeutectoid steel, and it is cheap and effective. Silicon can also improve the hardness, strength, yield strength and yield strength ratio of ferrite and austenite. Its effect is stronger than that of manganese, nickel, chromium, tungsten, aluminum, vanadium, etc., and it helps to improve the fatigue strength of steel. However, too high silicon content can easily lead to a decrease in the cold working performance of steel; therefore, the present invention controls the Si content range to 0.20% to 0.32%.

[0025] Manganese can significantly improve the hardenability and hot working properties of steel, but when the manganese content is too high, it will coarsen the grains of the steel to a certain extent and increase the supercooling ability of austenite, resulting in cold cracks in the steel; therefore, the present invention controls the Mn content to be in the range of 0.73% to 0.77%.

[0026] Phosphorus can be dissolved in austenite to increase the hardenability of steel, but phosphorus is prone to segregation in steel and reduce the plasticity and toughness of steel. In order to reduce the influence of P element on the mechanical properties of steel, the present invention controls the P content to ≤0.022%.

[0027] Sulfur combines with manganese to form MnS, which weakens the strengthening effect of manganese and causes the hardenability of steel to decrease. Sulfur also easily causes hot brittleness of steel and reduces the ductility and toughness of steel. Therefore, the present invention controls the S content to ≤0.020%.

[0028] Chromium is an element that improves the hardenability of steel and can make the steel have better toughness and plasticity. In order to ensure that the hardenability of the steel fluctuates within a set range, the present invention controls the Cr content range to be 1.02% to 1.06%.

[0029] Aluminum is mainly added to steel as a deoxidizer. In addition to reducing the dissolved oxygen in molten steel, the dispersed fine aluminum nitride particles formed by Al and N can refine the grains; however, when the Al content increases, brittle inclusions such as Al2O3 are easily formed during the molten steel smelting process, reducing the purity of the molten steel. Therefore, the present invention controls the total Al content in the steel to be 0.020% to 0.040%.

[0030] Molybdenum, boron and copper are residual elements in 40CrH steel, and the lower the content, the better. Taking equipment capacity and production cost into consideration, the present invention controls the Mo content to ≤0.04%, the B content to ≤0.0004%, and the Cu content to ≤0.08%.

[0031] The production process of 40CrH steel for automobile steering knuckle smelted by electric furnace described in the present invention, the design reasons of each process and process parameters are as follows: 1. Ecological electric furnace smelting; The ecological electric furnace uses all scrap steel for smelting, and controls the end point C0.05%~0.10%, and the end point P≤0.012% (both are weight percentages) to reduce the initial oxygen content in the steel and prevent slag rephosphorization; steel tapping begins when the molten steel temperature reaches 1600~1620℃, and the tapping time is controlled at 5~6min; when the tapping volume reaches 15~20t, in order to reduce the temperature drop in the steel tapping process and shorten the LF refining power-on time, the baked alloys (baking temperature is 600~800℃) are added in sequence, including 1.3~1.5kg / t steel of aluminum ingots for remelting, 5.5~6.5kg / t steel of high carbon ferromanganese, 14.0~16.0kg / t steel of high carbon ferrochrome, and 4.0~5.0kg / t steel of silicon manganese alloy; in addition, 600kg / furnace of lime and 500kg / furnace of synthetic slag are added to the ladle.

[0032] 2. LF refining; After the ladle is in place, turn on the argon gas, and the argon flow rate is 300-500NL / min. After the ladle enters the smelting station, add 3.5-4.5kg / t of lime, supply power for 3-5 minutes, and after the thin slag is formed, adjust the argon flow rate to 150-250NL / min; add 180-230kg / furnace of silicon carbide for diffusion deoxidation, and do not allow large argon stirring to heat up. After closing the furnace door and supplying power for 20 minutes, dip the slag, confirm that the slag is white, measure the temperature and take a sample. Perform alloying treatment according to the first full analysis composition, including adding 0.3-1.0kg / t of ferrosilicon, 0.5-1.5kg / t of high carbon ferromanganese, 2.0-3.0kg / t of high carbon ferrochrome, and 1.0-3.0kg / t of alumina balls; after the second full analysis composition is adjusted, adjust the argon flow rate to 100-200NL / min.

[0033] 3. RH vacuum degassing; After the ladle seat is on the ladle car, argon gas is blown, and the argon gas flow rate is 300-450NL / min; after the ladle enters the working position, the lifting operation is started, the immersion tube is inserted to a depth greater than 400mm, the argon gas is turned off, the vacuum degree is <100Pa, and the duration is ≥15min to remove the gas in the steel; after breaking the air, calcium treatment is carried out, and 150-250m / furnace of silicon-calcium wire is fed; before static blowing and stirring, 0.7-1.0kg / t of covering agent is added to prevent the steel liquid surface from being exposed to air inhalation and oxidation. The static blowing stirring time is ≥20min, and the static blowing argon gas flow rate is 10-60NL / min to promote the floating removal of inclusions in the steel; static blowing is preferably performed with slight movement of the slag surface and no exposure of the molten steel.

[0034] 4. Continuous casting; The molten steel after vacuum degassing is hoisted to the casting position, and the continuous casting billet drawing speed is controlled according to Table 1. The continuous casting ladle adopts a continuous slag detection device to prevent the ladle from slagging. The continuous casting electromagnetic stirring parameters are shown in Table 2, and the continuous casting protection slag adopts medium carbon steel crystallizer protection slag.

[0035] Table 1: Continuous casting superheat control range

[0036] Table 2: Continuous casting electromagnetic stirring parameters

[0037] 5. Rolling; High-pressure water descaling is used before rolling, and the descaling pressure is 28~30MPa; the starting rolling temperature is 1000℃~1200℃, the final rolling temperature is 800℃~1100℃, and the finished product specification is ø120~ø150mm.

[0038] In order to more intuitively embody the present invention, the embodiments of the present invention are further described in conjunction with examples. The following examples are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technical solution that can be obviously obtained by a person skilled in the art within the technical scope disclosed in the present invention, including simple changes or equivalent replacements, is within the protection scope of the present invention.

[0039] Example:

[0040] The chemical composition of the steel of each embodiment is shown in Table 1, the electric furnace smelting parameters of each embodiment are shown in Table 2, the LF refining process parameters of each embodiment are shown in Table 3, the RH vacuum degassing process parameters of each embodiment are shown in Table 4, the continuous casting process parameters of each embodiment are shown in Table 5, and the rolling process parameters of each embodiment are shown in Table 6; the macrostructure inspection results of the finished steel of each embodiment are shown in Table 7, the mechanical properties of the finished steel of each embodiment are shown in Table 8, the end hardenability, banded structure and grain size grade of the finished steel of each embodiment are shown in Table 9, and the classification and grading results of non-metallic inclusions in the finished steel of each embodiment are shown in Table 10.

[0041] Table 1: Chemical composition of steel (wt%)

[0042] Table 2: Ecological electric furnace smelting process parameters

[0043] Table 3: LF refining process parameters

[0044] Table 4: RH vacuum degassing process parameters

[0045] Table 5: Continuous casting process parameters

[0046] Table 6: Rolling process parameters

[0047] Table 7: Macrostructure test results of finished steel products (grade)

[0048] Table 8: Mechanical properties of finished steel

[0049] Table 9: End hardenability, banded structure and grain size of finished steel

[0050] In the table, J9 refers to the hardness value at 9 mm from the end face.

[0051] Table 10: Classification and grading results of non-metallic inclusions in finished steel products

[0052] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. The production process of 40CrH steel for automobile steering knuckles smelted by electric furnace is characterized by: The chemical composition of 40CrH steel is C: 0.385% ~ 0.410%, Si: 0.20% ~ 0.32%, Mn: 0.73% ~ 0.77%, P ≤ 0.022%, S ≤ 0.020%, Cr: 1.02% ~ 1.06%, Alt: 0.020% ~ 0.040%, Mo ≤ 0.04%, B ≤ 0.0004%, Cu ≤ 0.08%, the balance is Fe and unavoidable impurities; the finished steel specification is ø 120 ~ ø 150mm; the production process route is ecological electric furnace smelting, LF refining, RH vacuum degassing, continuous casting, heating and rolling, and the process control is as follows: 1) Ecological electric furnace smelting: The ecological electric furnace uses all scrap steel for smelting. By weight percentage, the endpoint C content is controlled to be 0.05%-0.10%, and the endpoint P content is ≤0.012%; the tapping temperature is 1600-1620℃, and the tapping time is controlled to be 5-6min; when the tapping volume reaches 15-20t, the following alloys are added in sequence: 1.3-1.5kg / t steel of aluminum ingots for remelting, 5.5-6.5kg / t steel of high carbon ferromanganese, 14.0-16.0kg / t steel of high carbon ferrochrome, 4.0-5.0kg / t steel of silicon manganese alloy, and 600kg / furnace of lime and 500kg / furnace of synthetic slag are added to the ladle; 2) LF refining: After the ladle is in place, turn on the argon gas, and the argon gas flow rate is 300-500NL / min; add 3.5-4.5kg / t of lime, and thin slag is formed when the power is supplied for 3-5 minutes. At this time, adjust the argon gas flow rate to 150-250NL / min; add 180-230kg / furnace of silicon carbide for diffusion deoxidation; close the furnace door and supply power for 20 minutes, dip the slag, and measure the temperature and take a sample after confirming that the slag is white; perform alloying treatment according to the first full analysis composition, including adding 0.3-1.0kg / t of ferrosilicon, 0.5-1.5kg / t of high carbon ferromanganese, 2.0-3.0kg / t of high carbon ferrochrome, and 1.0-3.0kg / t of alumina balls; after the second full analysis composition is adjusted, adjust the argon gas flow rate to 100-200NL / min; 3) RH vacuum degassing: After the ladle seat is on the ladle car, argon gas is blown, and the argon gas flow rate is 300-450NL / min; after the ladle enters the working position, the lifting operation is started, the immersion tube insertion depth is greater than 400mm, the argon gas is turned off, the vacuum degree is less than 100Pa, and the duration is ≥15min; after breaking the air, calcium treatment is carried out, and 150-250m / furnace of silicon calcium wire is fed; before static blowing and stirring, 0.7-1.0kg / t steel of covering agent is added, the static blowing and stirring time is ≥20min, and the static blowing argon gas flow rate is 10-60NL / min; 4) Continuous casting: Control the billet drawing speed to prevent large slag from falling; electromagnetic stirring is used in the crystallizer and at the end of solidification; 5) Rolling: The starting rolling temperature is 1000℃~1200℃, and the final rolling temperature is 800℃~1100℃.

2. The production process of 40CrH steel for automobile steering knuckle using electric furnace smelting according to claim 1 is characterized in that: During the ecological electric furnace smelting process, the added alloy is pre-baked at a temperature of 600-800°C.

3. The production process of 40CrH steel for automobile steering knuckle by electric furnace smelting according to claim 1, characterized in that: During the continuous casting process, medium carbon steel mold protection slag is used as the continuous casting protection slag.

4. The production process of 40CrH steel for automobile steering knuckle using electric furnace smelting according to claim 1 is characterized in that: During the continuous casting process, the relationship between the superheat of molten steel and the continuous casting speed is as follows: When the superheat is less than 20℃, the pulling speed is controlled at 0.44~0.46m / min; When the temperature is 20℃≤superheat<35℃, the pulling speed is controlled at 0.41~0.43m / min; When the temperature is 35℃≤superheat<45℃, the pulling speed is controlled at 0.39~0.41m / min; When the superheat is ≥45℃, the pulling speed is controlled at 0.34~0.36m / min.

5. The production process of 40CrH steel for automobile steering knuckle by electric furnace smelting according to claim 1, characterized in that: The continuous casting adopts a large square billet continuous casting machine; the electromagnetic stirring parameters of the crystallizer are: current 380~420A, frequency 1.5~2.5Hz; the electromagnetic stirring parameters at the end of continuous casting are: current 400~440A, frequency 6~8Hz; the electromagnetic stirring mode of the crystallizer and the end of continuous casting is alternating forward and reverse stirring.

6. The production process of 40CrH steel for automobile steering knuckle by electric furnace smelting according to claim 1, characterized in that: High-pressure water is used for descaling before rolling, and the descaling pressure is 28 to 30 MPa.

7. The production process of 40CrH steel for automobile steering knuckle by electric furnace smelting according to claim 1, characterized in that: The hardness value of the finished steel at 9mm from the end face is J9: 46~51HRC; the banded structure grade is ≤5, the grain size grade is ≥5; the non-metallic inclusion grade: Class A coarse series ≤3.0, Class A fine series ≤3.0, Class B coarse series ≤2.0, Class B fine series ≤2.0, Class C coarse series ≤1.0, Class C fine series ≤1.0, Class D coarse series ≤1.0, Class D fine series ≤1.0, Class Ds ≤1.

0.

8. The production process of 40CrH steel for automobile steering knuckle by electric furnace smelting according to claim 1, characterized in that: The mechanical properties of the finished steel are: yield strength ≥785MPa, tensile strength ≥980MPa, section shrinkage ≥45%, elongation after fracture ≥9%, and room temperature impact toughness KU2 ≥48J.

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