A method for producing aluminum-containing free-cutting gear steel

Abstract

The present invention discloses a method for producing aluminum-containing free-cutting gear steel, and belongs to the field of metallurgical technology. The method includes converter smelting, refining process, continuous casting process, heating and rolling process; in the converter process, the S content of the molten iron entering the furnace is ≤0.045%, and the terminal [S] content is controlled to be ≤0.040%; in the refining process, no Al products are added during the LF refining process, the refining slag adopts low basicity operation, the binary basicity of the final slag is controlled at 1.4-1.6, the molten steel is not desulfurized, and the aluminum wire is used for deoxidation before leaving the station; the RH vacuum refining limit vacuum degree is ≤30Pa, and the total exhaust time is ≥30min; the continuous casting process is fully protected casting, and the plug rod argon blowing process is adopted, and the pulling speed is 1.0-1.2m / min. The whole process of the present invention does not carry out sulfur feeding, and the sulfur in the molten iron is used to meet the requirements of the easy cutting property of the gear steel.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for producing aluminum-containing free-cutting gear steel. Background Art

[0002] The rapid development of the automotive industry has put forward higher requirements for aluminum-sulfur free-cutting steel, that is, good cutting performance and mechanical properties. During the continuous casting and solidification process, the sulfur element in aluminum-containing free-cutting gear steel combines with manganese to form manganese sulfide precipitation phase (i.e., type A inclusions), which can cut off the continuity of the matrix and increase the cutting performance of the steel, thereby improving the surface quality and performance of the product.

[0003] As the degree of machining automation increases, the requirements for the machinability of materials will increase accordingly. The cost of machining accounts for about 40% of the cost of parts. It is an urgent need for steel material users to reduce the cost of machining, make free-cutting steel adapt to automatic machining production lines, and improve labor productivity. Therefore, the development of low-sulfur and multi-element free-cutting steel with controlled sulfide morphology is an important development direction in the future.

[0004] According to the information currently available, the industry's research on free-cutting gear steel is mainly focused on the control measures for sulfides during the continuous casting process. To produce sulfur-containing free-cutting steel, the process of first desulfurization and then sulfurization is adopted. During the sulfurization process, the degree of segregation of the S element is unstable, resulting in the early precipitation of MnS in the molten steel, which increases the difficulty of controlling Class A inclusions. For example, Patent Publication No. CN102011062 B discloses a free-cutting gear steel and its smelting method. This method ensures the sulfur content of the free-cutting gear steel by adding a sulfur-containing alloy after desulfurization. In actual production, it is found that this method has unstable control over sulfides. For example, Patent Publication No. CN 102703817 B discloses a free-cutting gear steel and its production process. The sulfur content of the molten steel is controlled by feeding a sulfur line into a VD furnace. In actual production, the sulfide control of the gear steel produced according to this method is not stable.

[0005] In summary, some research has been carried out in China on the control of sulfides in free-cutting gear steel. Although these studies have achieved certain results in the control of sulfides, overall the sulfide control is not stable enough. Summary of the invention

[0006] The present invention provides a method for producing aluminum-containing free-cutting gear steel. The method can stably control the level of Class A inclusions in the free-cutting gear steel to below level 2.0 through reasonable control of chemical composition and production process.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for producing aluminum-containing free-cutting gear steel, the method comprising converter smelting, refining process, continuous casting process, heating and rolling process;

[0008] In the converter process, the S content of the molten iron entering the furnace is ≤0.045%, and the end point [S] content is controlled to be ≤0.040%;

[0009] The refining process includes LF refining and RH vacuum refining; the LF refining process does not add Al products, the refining slag adopts low basicity operation, the binary basicity of the final slag is controlled at 1.4-1.6, the molten steel is not desulfurized, and the aluminum wire is used for deoxidation before leaving the station; the RH vacuum refining limit vacuum degree is ≤30Pa, and the total exhaust time is ≥30min;

[0010] The continuous casting process is performed with full protection casting, adopts a stopper rod argon blowing process, and requires stable drawing speed control, with a drawing speed of 1.0-1.2 m / min.

[0011] In the converter process of the present invention, the addition of Al products and slag washing materials is prohibited, the oxygen content of the molten steel is ≥100ppm, the high oxidizability of the molten steel is ensured, the residual steel operation is performed during the tapping process, and slag addition is prohibited.

[0012] In the refining process of the present invention, the amount of lime added in the LF refining process is 500-600kg, and the fluorite is 80-100kg. The aluminum wire is deoxidized before leaving the station, and the Als target composition is adjusted to 0.030-0.035%.

[0013] In the refining process of the present invention, the RH refining exhaust time is ≥30 minutes, no calcium treatment is performed during the whole process, and no soft blowing is performed before leaving the station.

[0014] The continuous casting process of the present invention obtains the chemical composition and mass percentage of the continuous casting billet: C: 0.18-0.20wt%, Si: 0.20-0.25wt%, Mn: 0.90-0.95wt%, P≤0.015wt%, S: 0.015-0.025wt%, Als: 0.015-0.030wt%, Cr: 1.08-1.13wt%, Ti: 0.05-0.07wt%, Ca≤0.0010wt%; the total oxygen content is ≤15ppm, and the balance is Fe and unavoidable impurities.

[0015] In the heating process of the present invention, the heating temperature of the ingot in the heating furnace is 1150-1180°C, the heating time is 150-180min, and the ingot is descaled by 15-18Mpa high-pressure water after being taken out of the furnace.

[0016] According to the rolling process of the present invention, the heated ingot is subjected to rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling in sequence to obtain hot-rolled gear steel bars, which are subjected to controlled rolling and controlled cooling, and the steel-out rhythm is controlled to be 110-115s to ensure that the finishing rolling temperature is 920-950°C.

[0017] The gear steel of the present invention has Class A inclusions ≤ Grade 2.0, a grain size ≥ Grade 8.0, and a banded structure ≤ Grade 1.0.

[0018] The diameter specification of the gear steel of the present invention is 20-90 mm.

[0019] The gear steel of the present invention has a yield strength of 850-1350 MPa, a tensile strength of 1080-1500 MPa, an elongation after fracture of ≥12%, and a cross-sectional shrinkage of ≥50%.

[0020] Theoretical analysis of each process parameter of the present invention is as follows:

[0021] No Al products are added for deoxidation during steel tapping from the converter to ensure high oxidation of the molten steel. By optimizing the LF refining slag system and making Ca-Si low-basicity slag, the molten steel is not desulfurized. Al wire is added before the LF exits the station to ensure the Al content requirements of the steel grade. The inherent sulfur in the molten iron is used to meet the machinability requirements of the gear steel, avoiding the partial sulfur content of the molten steel caused by adding sulfur-containing alloys or adding sulfur wires. The inherent sulfur in the molten iron is used to ensure uniform sulfur elements in the molten steel, which are dispersed and precipitated in small amounts during the continuous casting process to reduce the level of Class A inclusions.

[0022] The method for producing aluminum-containing free-cutting gear steel of the present invention does not require sulfuring throughout the entire process, utilizes sulfur in molten iron to meet the free-cutting property requirements of the gear steel, and can effectively control the segregation of the S element, thereby achieving a gear steel Class A inclusion level of ≤2.0.

[0023] The beneficial effects of the above technical solution are: 1. The present invention effectively utilizes the sulfur content in the molten iron, and does not desulfurize in the refining process. It is forbidden to add Al products for deoxidation during the converter steel-making process to ensure the high oxidation of the molten steel. The molten steel is not deoxidized during the converter steel-making process; LF refining produces low-basicity refining slag, and does not feed S wire throughout the process. The sulfur in the molten iron is used to meet the easy-to-cut requirements of gear steel, and at the same time, the segregation of sulfur elements in gear steel is controlled to ensure that MnS is finely dispersed and precipitated during the solidification process, and the level of Class A inclusions is reduced. 2. The tool life of the gear steel of the present invention is increased by 2.5-3 times during cutting, and the cutting process is easier to break chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the morphology of sulfides in the finished gear steel bar product of Example 1;

[0025] Figure 2 This is the morphology of sulfides in the finished gear steel bar product of Example 2;

[0026] Figure 3 This is the morphology of sulfides in the finished gear steel bar product of Example 3;

[0027] Figure 4 This is the morphology of sulfides in the finished gear steel bar product of Example 4;

[0028] Figure 5 This is the morphology of sulfides in the finished gear steel bar of Example 5. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below in conjunction with specific embodiments. Example 1

[0030] A method for producing aluminum-containing free-cutting gear steel includes converter smelting, refining process, R10 arc continuous casting, heating and rolling process, and the specific control is as follows:

[0031] 1) In the converter process, the S content of the molten iron entering the furnace is 0.031%, and the final [S] content is controlled to be 0.029%. During the steel-making process, it is forbidden to add Al products and slag washing materials. The oxygen content of the molten steel is 100ppm to ensure the high oxidation property of the molten steel. The amount of slag is strictly controlled during the steel-making process.

[0032] 2) Refining process, including LF refining and RH vacuum refining; No Al products are added in the LF refining process, the refining slag adopts low alkalinity operation, the amount of lime added is 500kg, fluorite is 100kg, and the binary alkalinity of the final slag is controlled at 1.4 to ensure that there is no desulfurization in the LF refining process. 200m of aluminum wire is used for deoxidation before leaving the station, and the Als target composition is adjusted to 0.032%; the RH vacuum refining limit vacuum degree is 20Pa, the total exhaust time is 30min, no calcium treatment is performed throughout the process, and soft blowing is prohibited before leaving the station.

[0033] 3) Continuous casting process: The casting is protected throughout the process, and the plug rod argon blowing process is adopted. The casting speed is required to be stably controlled at 1.1m / min. After the billet is off the line, it is put into the pit for slow cooling;

[0034] 4) Heating process: the ingot is heated to 1180℃ in a heating furnace for 160min, and then descaled by 18Mpa high-pressure water after being taken out of the furnace.

[0035] 5) Rolling process: the heated ingot is subjected to rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling to obtain hot-rolled gear steel bars, which are subjected to controlled rolling and cooling, and the steel-out rhythm is controlled to 115s to ensure that the finishing rolling temperature is controlled at 920℃. The bars are sheared, collected, packaged and stacked for slow cooling after passing through the cooling bed.

[0036] The gear steel hot-rolled bar obtained in this embodiment has a specification of φ90 mm, a Class A inclusion level of 1.0, chemical composition and mass percentage are shown in Table 1, and properties are shown in Table 2.

[0037] The tool life of the hot-rolled gear steel bar obtained in this embodiment is increased by 2.5 times during cutting, and the cutting process is easier to break chips.

[0038] The aluminum-containing free-cutting gear steel bar in this embodiment successfully utilizes the sulfur in the molten iron to meet the free-cutting requirements of the gear steel. After inspection, the grain size is 9.0 and the banded structure is 1.0; Figure 1 It shows that the sulfides in the finished rods are evenly dispersed; the tool life of gear cutting used after processing by downstream users is increased by 2.5 times, and the cutting process is easier to break chips. Example 2

[0039] A method for producing aluminum-containing free-cutting gear steel includes converter smelting, refining process, R10 arc continuous casting, heating and rolling process, and the specific control is as follows:

[0040] 1) In the converter process, the S content of the molten iron entering the furnace is 0.029%, and the final [S] content is controlled to be 0.025%. In the steel-making process, it is forbidden to add Al products and slag washing materials. The oxygen content of the molten steel is 105ppm to ensure the high oxidation property of the molten steel. The amount of slag is strictly controlled in the steel-making process.

[0041] 2) Refining process, including LF refining and RH vacuum refining; No Al products are added in the LF refining process, the refining slag adopts low alkalinity operation, the amount of lime added is 520kg, fluorite is 80kg, and the binary alkalinity of the final slag is controlled at 1.42 to ensure that there is no desulfurization in the LF refining process. 200m of aluminum wire is used for deoxidation before leaving the station, and the Als target composition is adjusted to 0.034%; the RH vacuum refining limit vacuum degree is 18Pa, the total exhaust time is 30min, no calcium treatment is carried out in the whole process, and soft blowing is prohibited before leaving the station.

[0042] 3) Continuous casting process: The casting is protected throughout the process, and the plug rod argon blowing process is adopted. The casting speed is required to be stably controlled at 1.0m / min. After the billet is off the line, it is put into the pit for slow cooling;

[0043] 4) Heating process: the ingot is heated to 1180℃ in a heating furnace for 150min, and then descaled by 18Mpa high-pressure water after being taken out of the furnace.

[0044] 5) Rolling process: the heated ingot is subjected to rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling to obtain hot-rolled gear steel bars, which are subjected to controlled rolling and cooling, and the steel-out rhythm is controlled for 110s to ensure that the finishing rolling temperature is controlled at 920℃. The bars are sheared, collected, packaged and stacked for slow cooling after passing through the cooling bed.

[0045] The gear steel hot-rolled bar obtained in this embodiment has a specification of φ40 mm, a Class A inclusion level of 0.5, chemical composition and mass percentage are shown in Table 1, and properties are shown in Table 2.

[0046] The tool life of the hot-rolled gear steel bar obtained in this embodiment is increased by 2.5 times during cutting, and the cutting process is easier to break chips.

[0047] The aluminum-containing free-cutting gear steel bar in this embodiment successfully utilizes the sulfur in the molten iron to meet the free-cutting requirements of the gear steel. After inspection, the grain size is 9.5 and the banded structure is 1.0; Figure 2 It shows that the sulfides in the finished rods are evenly dispersed; the tool life of gear cutting used after processing by downstream users is increased by 2.5 times, and the cutting process is easier to break chips. Example 3

[0048] A method for producing aluminum-containing free-cutting gear steel includes converter smelting, refining process, R10 arc continuous casting, heating and rolling process, and the specific control is as follows:

[0049] 1) In the converter process, the S content of the molten iron entering the furnace is 0.025%, and the final [S] content is controlled to be 0.021%. During the steel-making process, it is forbidden to add Al products and slag washing materials. The oxygen content of the molten steel is 110ppm to ensure the high oxidation property of the molten steel. The amount of slag is strictly controlled during the steel-making process.

[0050] 2) Refining process, including LF refining and RH vacuum refining; No Al products are added in the LF refining process, the refining slag adopts low alkalinity operation, the amount of lime added is 580kg, fluorite is 90kg, and the binary alkalinity of the final slag is controlled at 1.55 to ensure that there is no desulfurization in the LF refining process. 200m of aluminum wire is used for deoxidation before leaving the station, and the Als target composition is adjusted to 0.031%; the RH vacuum refining limit vacuum degree is 18Pa, the total exhaust time is 32min, no calcium treatment is carried out in the whole process, and soft blowing is prohibited before leaving the station.

[0051] 3) Continuous casting process: The casting was protected throughout the whole process, and the plug rod argon blowing process was adopted. The pulling speed was required to be stably controlled at 1.2m / min. The ingot was slowly cooled in the pit after it came off the line. The chemical composition and mass percentage of the obtained continuous casting ingot are shown in Table 1.

[0052] 4) Heating process: the ingot is heated to 1170℃ in a heating furnace for 170min, and then descaled by 18Mpa high-pressure water after being taken out of the furnace.

[0053] 5) Rolling process: the heated ingot is subjected to rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling to obtain hot-rolled gear steel bars, which are subjected to controlled rolling and controlled cooling, and the steel-out rhythm is controlled to 115s to ensure that the finishing rolling temperature is controlled at 930℃. The bars are sheared, collected, packaged and stacked for slow cooling after passing through the cooling bed.

[0054] The gear steel hot-rolled bar obtained in this embodiment has a specification of φ20 mm, a Class A inclusion level of 0.5, chemical composition and mass percentage are shown in Table 1, and properties are shown in Table 2.

[0055] The tool life of the hot-rolled gear steel bar obtained in this embodiment is increased by 2.5 times during cutting, and the cutting process is easier to break chips.

[0056] The aluminum-containing free-cutting gear steel bar in this embodiment successfully utilizes the sulfur in the molten iron to meet the free-cutting requirements of the gear steel. After inspection, the grain size is 9.5 and the banded structure is 0.5; Figure 3 It shows that the sulfides in the finished rods are evenly dispersed; the tool life of gear cutting used after processing by downstream users is increased by 2.5 times, and the cutting process is easier to break chips. Example 4

[0057] A method for producing aluminum-containing free-cutting gear steel includes converter smelting, refining process, R10 arc continuous casting, heating and rolling process, and the specific control is as follows:

[0058] 1) In the converter process, the S content of the molten iron entering the furnace is 0.030%, and the final [S] content is controlled to be 0.027%. During the steel-making process, it is forbidden to add Al products and slag washing materials. The oxygen content of the molten steel is 124ppm to ensure the high oxidation property of the molten steel. The amount of slag is strictly controlled during the steel-making process.

[0059] 2) Refining process, including LF refining and RH vacuum refining; No Al products are added in the LF refining process, the refining slag adopts low alkalinity operation, the amount of lime added is 550kg, fluorite is 95kg, and the binary alkalinity of the final slag is controlled at 1.50 to ensure that there is no desulfurization in the LF refining process. 250m of aluminum wire is used for deoxidation before leaving the station, and the Als target composition is adjusted to 0.033%; The ultimate vacuum degree of RH vacuum refining is 15Pa, the total exhaust time is 31min, no calcium treatment is performed throughout the process, and soft blowing is prohibited before leaving the station.

[0060] 3) Continuous casting process: The casting is protected throughout the process, and the plug rod argon blowing process is adopted. The casting speed is required to be stably controlled at 1.1m / min. After the billet is off the line, it is put into the pit for slow cooling;

[0061] 4) Heating process: the ingot is heated to 1160℃ in a heating furnace for 150min, and then descaled by 16Mpa high-pressure water after being taken out of the furnace.

[0062] 5) Rolling process: the heated ingot is subjected to rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling to obtain hot-rolled gear steel bars, which are subjected to controlled rolling and controlled cooling, and the steel-out rhythm is controlled to 112s to ensure that the finishing rolling temperature is controlled at 950℃. The bars are sheared, collected, packaged and stacked for slow cooling after passing through the cooling bed.

[0063] The gear steel hot-rolled bar obtained in this embodiment has a specification of φ70 mm, a Class A inclusion level of 1.0, chemical composition and mass percentage are shown in Table 1, and properties are shown in Table 2.

[0064] The tool life of the hot-rolled gear steel bar obtained in this embodiment is increased by 3 times during cutting, and the cutting process is easier to break chips.

[0065] The aluminum-containing free-cutting gear steel bar in this embodiment successfully utilizes the sulfur in the molten iron to meet the free-cutting requirements of the gear steel. After inspection, the grain size is 9.0 and the banded structure is 1.0; Figure 4 It shows that the sulfides in the finished rods are evenly dispersed; the tool life of gear cutting used after processing by downstream users is increased by 3 times, and the cutting process is easier to break chips. Example 5

[0066] A method for producing aluminum-containing free-cutting gear steel includes converter smelting, refining process, R10 arc continuous casting, heating and rolling process, and the specific control is as follows:

[0067] 1) In the converter process, the S content of the molten iron entering the furnace is 0.045%, and the final [S] content is controlled to be 0.040%; during the steel-making process, it is prohibited to add Al products and slag washing materials. The oxygen content of the molten steel is 137ppm to ensure the high oxidation property of the molten steel. The amount of slag is strictly controlled during the steel-making process.

[0068] 2) Refining process, including LF refining and RH vacuum refining; No Al products are added in the LF refining process, the refining slag adopts low alkalinity operation, the amount of lime added is 600kg, fluorite is 100kg, and the binary alkalinity of the final slag is controlled at 1.60 to ensure that there is no desulfurization in the LF refining process. 200m of aluminum wire is used for deoxidation before leaving the station, and the Als target composition is adjusted to 0.035%; the RH vacuum refining limit vacuum degree is 30Pa, the total exhaust time is 35min, no calcium treatment is carried out in the whole process, and soft blowing is prohibited before leaving the station.

[0069] 3) Continuous casting process: The casting is protected throughout the process, and the plug rod argon blowing process is adopted. The casting speed is required to be stably controlled at 1.1m / min. After the billet is off the line, it is put into the pit for slow cooling;

[0070] 4) Heating process: the ingot is heated to 1150℃ in a heating furnace for 180min, and then descaled by 15Mpa high-pressure water after being taken out of the furnace.

[0071] 5) Rolling process: the heated ingot is subjected to rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling to obtain hot-rolled gear steel bars, which are subjected to controlled rolling and controlled cooling, and the steel-out rhythm is controlled to 115s to ensure that the finishing rolling temperature is controlled at 930℃. The bars are sheared, collected, packaged and stacked for slow cooling after passing through the cooling bed.

[0072] The gear steel hot-rolled bar obtained in this embodiment has a specification of φ32 mm, a Class A inclusion level of 0.5, chemical composition and mass percentage are shown in Table 1, and properties are shown in Table 2.

[0073] The tool life of the hot-rolled gear steel bar obtained in this embodiment is increased by 3 times during cutting, and the cutting process is easier to break chips.

[0074] The aluminum-containing free-cutting gear steel bar in this embodiment successfully utilizes the sulfur in the molten iron to meet the free-cutting requirements of the gear steel. After inspection, the grain size is 9.5 and the banded structure is 0.5; Figure 5 It shows that the sulfides in the finished rods are evenly dispersed; the tool life of gear cutting used after processing by downstream users is increased by 3 times, and the cutting process is easier to break chips.

[0075] Table 1 Chemical composition and mass percentage (wt%) of gear steel of Examples 1-5

[0076]

[0077] The balance of the components in Table 1 is Fe and unavoidable impurities.

[0078] Table 2 Mechanical properties of gear steels in Examples 1-5

[0079]

[0080] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for producing aluminum-containing free-cutting gear steel, characterized in that: The method includes converter smelting, refining process, continuous casting process, heating and rolling process; In the converter process, the S mass percentage of the molten iron entering the furnace is ≤0.045%, and the end point [S] mass percentage is controlled to be ≤0.040%; The refining process includes LF refining and RH vacuum refining; the LF refining process does not add Al products, the refining slag adopts low basicity operation, the binary basicity of the final slag is controlled at 1.4-1.6, the molten steel is not desulfurized, and the aluminum wire is used for deoxidation before leaving the station; the RH vacuum refining limit vacuum degree is ≤30Pa, and the total exhaust time is ≥30min; The continuous casting process is fully protected, adopts a stopper rod argon blowing process, and has a casting speed of 1.0-1.2 m / min.

2. The method for producing aluminum-containing free-cutting gear steel according to claim 1, characterized in that: It is prohibited to add Al products and slag washing materials during the steel-making process of the converter step, and the oxygen content of the molten steel is ≥100ppm, measured in mass units.

3. The method for producing aluminum-containing free-cutting gear steel according to claim 1, characterized in that: In the refining process, the amount of lime added in the LF refining process is 500-600kg, and the amount of fluorite added is 80-100kg. The aluminum wire is deoxidized before leaving the station, and the mass percentage of the Als target component is adjusted to 0.030-0.035%.

4. The method for producing aluminum-containing free-cutting gear steel according to claim 1, characterized in that: In the refining process, the RH refining exhaust time is ≥30 minutes, no calcium treatment is performed during the whole process, and no soft blowing is performed before leaving the station.

5. The method for producing aluminum-containing free-cutting gear steel according to claim 1, characterized in that: The chemical composition and mass percentage of the continuous casting billet obtained in the continuous casting process are as follows: C: 0.18-0.20wt%, Si: 0.20-0.25wt%, Mn: 0.90-0.95wt%, P≤0.015wt%, S: 0.015-0.025wt%, Als: 0.015-0.030wt%, Cr: 1.08-1.13wt%, Ti: 0.05-0.07wt%, Ca≤0.0010wt%; the total oxygen content is ≤15ppm, and the balance is Fe and unavoidable impurities.

6. A method for producing aluminum-containing free-cutting gear steel according to any one of claims 1 to 5, characterized in that: In the heating process, the heating temperature of the ingot into the heating furnace is 1150-1180°C, the heating time is 150-180min, and the ingot is descaled by 15-18MPa high-pressure water after being taken out of the furnace.

7. A method for producing aluminum-containing free-cutting gear steel according to any one of claims 1 to 5, characterized in that: In the rolling process, the heated ingot is subjected to rough rolling, intermediate rolling, pre-finishing rolling and finishing rolling in sequence to obtain hot-rolled gear steel bars, which are subjected to controlled rolling and controlled cooling, and the steel-out rhythm is controlled to be 110-115s to ensure that the finishing rolling temperature is 920-950°C.

8. A method for producing aluminum-containing free-cutting gear steel according to any one of claims 1 to 5, characterized in that: The gear steel has Class A inclusions ≤ Grade 2.0, a grain size ≥ Grade 8.0, and a banded structure ≤ Grade 1.

0.

9. A method for producing aluminum-containing free-cutting gear steel according to any one of claims 1 to 5, characterized in that: The gear steel has a diameter specification of 20-90 mm.

10. A method for producing aluminum-containing free-cutting gear steel according to any one of claims 1 to 5, characterized in that: The gear steel has a yield strength of 850-1350 MPa, a tensile strength of 1080-1500 MPa, an elongation after fracture of ≥12%, and a cross-sectional shrinkage of ≥50%.

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