Manufacturing method of microalloyed steel ring-cast iron composite brake drum

Abstract

The invention discloses a manufacturing method of a microalloyed steel ring-cast iron composite brake drum. The manufacturing method comprises the following steps that S1, a steel plate with the thickness of 15.9-16.1 mm for a brake drum shell is subjected to laser cutting blanking; s2, the round cake is manufactured into a brake drum shell steel ring through the following processes of center hole and bolt hole punching in the middle, primary spinning forming, secondary spinning forming, outer diameter roll forming, end punch forming and burr cutting, and the thickness of the steel ring ranges from 5.95 mm to 6.05 mm; s3, weighing the raw materials; s4, heating is conducted; and S5, the microalloyed steel ring-cast iron composite brake drum blank manufactured in the step S4 is subjected to machine addition and sizing. The forming process of the shell in the bimetal composite brake drum and matching of chemical components and hardness of the two sides are explained for the first time, a manufacturing chain is more perfect, and the service life of the microalloyed steel ring-cast iron composite brake drum is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of brake drum manufacturing technology, and particularly relates to a method for manufacturing a micro-alloyed steel ring-cast iron composite brake drum. Background Technology

[0002] Brake drums are one of the core components of the braking system. As a safety component for automobile movement, wheel brake drums require steel with excellent strength, plasticity, toughness, and good stamping formability, weldability, fatigue resistance, and corrosion resistance. "High speed, high load, lightweight, and high efficiency" are gradually becoming the mainstream development trend for commercial vehicles, meeting energy conservation and environmental protection requirements. However, during braking, the brake drum generates a large amount of heat through close friction with the brake shoes, converting the vehicle's kinetic energy into thermal energy, thereby slowing down or stopping the vehicle. As the friction pair of a drum brake, the brake drum, in addition to possessing the strength and static stiffness required of a component, should also have the highest possible and most stable coefficient of friction, as well as high wear resistance, heat resistance, heat dissipation, and heat capacity.

[0003] Because brake drums are used under high-speed, heavy-load, and frequent braking conditions, many performance problems have gradually emerged in the products of domestic brake drum manufacturers during use. Bimetallic brake drums are made from different metals or alloys through specific processes, resulting in brake drums with good wear resistance, good thermal conductivity, sufficient strength, and toughness, which to some extent meets the needs of vehicles during braking. Gray cast iron / steel bimetallic brake drums are a typical type and are currently widely used in medium and heavy-duty vehicles. Bimetallic composite drums use high-strength, high-elongation materials such as steel for the outer shell and gray cast iron or similar materials as friction materials internally. While this can solve the problem of brake drum cracking and failure, in actual use, bimetallic composite drums suffer from large braking deformation and insufficient braking force.

[0004] Meanwhile, the new composite brake drum is made by spinning steel and then producing steel-iron composite brake drums by centrifugal casting. Because the manufacturing process of this composite brake drum involves thinning and spinning with large deformation, cracks often occur during the use and processing of steel, causing unnecessary economic losses to composite brake drum manufacturers.

[0005] As automobiles continue to evolve towards higher speeds and heavier loads, the demands on braking systems are increasing. Medium and heavy-duty trucks operating in high-altitude or mountainous regions often require continuous and emergency braking. During braking, the contact surface between the brake drum and brake shoes experiences a rapid temperature rise due to friction, while the outer surface of the brake drum heats up more slowly. This continuous braking and cooling process leads to cyclical thermal stress, causing thermal fatigue cracks in the brake drum. Furthermore, truck drivers often use water cooling to rapidly cool the brake drums to ensure timely braking. However, extreme high and low temperatures cause phase changes within the brake drum, reducing its lifespan.

[0006] Chinese patents CN 116292686 A and CN 113458363 A disclose a micro-alloyed bimetallic composite brake drum and its manufacturing method; CN 117167416 A discloses a textured reinforced steel rim-gray cast iron bimetallic composite brake drum and its manufacturing method; and CN 117167416 A discloses a textured reinforced steel rim-gray cast iron bimetallic composite brake drum. These patents focus on the composition and forming process of the gray cast iron lining of the bimetallic composite brake drum, but do not address the composition, properties, hardness, or microstructure of the outer steel rim. The forming process of the composite brake drum shell is complex, with a cumulative thinning deformation rate of approximately 62.5%. Improper grain size control can easily lead to cracking, reducing the yield of the composite brake drum.

[0007] In summary, the aforementioned patents have not formed a complete set of methods for manufacturing microalloyed steel ring-cast iron composite brake drums. Therefore, further research is needed on how to improve the matching of the formability, microstructure, and performance of bimetallic composite brake drums, thereby improving their long-term performance. Summary of the Invention

[0008] The purpose of this invention is to provide a manufacturing method for a microalloyed steel ring-cast iron composite brake drum. This invention is the first to explain the forming process of the outer shell of the bimetallic composite brake drum, as well as the matching of the chemical composition and hardness on both sides, making the manufacturing chain more complete and improving the service life of the microalloyed steel ring-cast iron composite brake drum.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] This invention discloses a method for manufacturing a micro-alloyed steel ring-cast iron composite brake drum, comprising the following steps:

[0011] S1: The brake drum shell with a thickness of 15.9-16.1mm is cut into blanks using a steel plate by laser cutting. The laser cutting machine has a power of 3000-6000W and a cutting speed of 0.8-1.2m / min. The edge of the round blank is cut by 1.5-2.5mm using a machine tool to remove the heat-affected zone of the laser cutting.

[0012] S2: The disc is made into the brake drum outer shell steel ring using the following process: punching the center hole and bolt hole in the middle - first spinning forming - second spinning forming - outer diameter roll forming - end stamping forming - trimming the burrs. Steel ring thickness: 5.95-6.05mm;

[0013] S3: Weigh the following raw materials by weight percentage: C: 3.00-3.35%, Si: 1.80-1.95%, Mn: 0.90-1.15%, S: 0.09-0.12%, P: 0.12-0.16%, Cu: 0.10-0.15%, Nb: 0.05-0.10%, Mo: 0.20-0.35%, La+Ce: 0.04-0.10%, with the remainder being Fe and unavoidable trace impurities;

[0014] S4: The brake drum outer shell steel ring is heated by a high-frequency induction heating device at a temperature of 800-900℃ for 10-20 seconds. The molten gray cast iron from step S3 is then poured into the inner wall of the steel ring outer shell in step S2 using a centrifugal forming composite casting process. After casting, the water-cooled iron sleeve device located on the outer wall of the steel ring outer shell is activated to cool the microalloyed steel ring-cast iron composite brake drum blank. The casting temperature of the molten cast iron is 1340-1450℃.

[0015] S5: The micro-alloyed steel ring-cast iron composite brake drum blank prepared in step S4 is machine-processed to a fixed length.

[0016] The steel plate for the outer casing comprises the following components by weight percentage:

[0017] C: 0.05-0.10%, Si: 0.10-0.25%, Mn: 0.45-0.75%, P: ≤0.015%, S: ≤0.009%, Alt: 0.015-0.045%, Nb: 0.005-0.015%, Ti: 0.010-0.025%, N: 0.0015-0.0050%, La+Ce: 0.0010-0.0040%, with the balance being Fe and unavoidable impurities.

[0018] Furthermore, when the temperature of the molten gray cast iron is 1340-1450℃, the molten metal inside is in full contact with the steel outer shell during pouring, avoiding various defects such as shrinkage cavities and porosity, ensuring a good bond between the two, and improving the overall performance of gray cast iron.

[0019] Furthermore, the steel plate for the outer casing comprises the following components by weight percentage: C: 0.05%, Si: 0.22%, Mn: 0.75%, P: 0.012%, S: 0.005%, Alt: 0.040%, Nb: 0.10%, Ti: 0.022%, N: 0.0016%, La+Ce: 0.0032%, with the balance being Fe and unavoidable impurities.

[0020] Furthermore, the room temperature microstructure of the steel plate base material for the outer shell is ferrite + pearlite, wherein the pearlite content is 1%, the ferrite grain size grade is 11.0, the elongation after fracture A50 in both the transverse and longitudinal directions is ≥48%, and the surface Brinell hardness HBW is 112.

[0021] Furthermore, the laser cutting machine has a power of 3000W and a cutting speed of 0.8m / min. The machine tool is used to cut the edge of the round disc by 1.5mm to remove the heat-affected zone of the laser cutting.

[0022] Furthermore, the gray cast iron liquid comprises the following components by weight percentage: C: 3.0%, Si: 1.90%, Mn: 1.25%, S: 0.12%, P: 0.17%, Cu: 0.25%, Nb: 0.08%, Mo: 0.34%, La+Ce: 0.05%, with the remainder being Fe and unavoidable trace impurities.

[0023] Furthermore, a high-frequency induction heating device is used to heat the steel ring of the brake drum shell at a temperature of 854°C for 16 seconds. The molten gray cast iron liquid of the composition in step S4 is then poured into the inner wall of the steel ring shell described in step S3 using a centrifugal forming composite casting process. During centrifugal casting, the shell rotation speed is 540 r / min, the pouring temperature is 1448°C, the pouring time is 6 seconds, and the thickness of the inner gray cast iron layer is set to 4.5 mm.

[0024] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0025] This invention provides a microalloyed steel ring-cast iron composite brake drum. Compared with ordinary low-carbon steel / gray cast iron bimetallic brake drums, to ensure the formability of the microalloyed steel ring and reduce the deformation and cracking rate, the steel used for the brake drum shell adopts an Nb-Ti-La+Ce microalloyed composition design. Simultaneously, the heating and rolling processes are precisely controlled, resulting in fine ferrite grains. The pearlite content, which is detrimental to formability, is controlled to ≤3% in area fraction. Furthermore, the pearlite content in the cast iron of the composite brake drum liner is not less than 94%, with smaller pearlite interlayer spacing and denser precipitated flake graphite. This not only refines the microstructure of the matrix and flake graphite but also improves the strength, toughness, and thermal conductivity of the gray cast iron in the brake drum liner, laying a solid foundation for extending the service life of the brake drum. Specifically, this is reflected in:

[0026] 1. Composition of gray cast iron lining: The gray cast iron structure of the composite metal brake drum incorporates microalloying elements such as Cu, Nb, Mo, La, and Ce to promote microstructure refinement and improve high-temperature friction performance. Cu can inhibit ferrite formation, promote the formation of fine pearlite, and improve cross-sectional sensitivity; Nb can refine the macro and microstructure of gray cast iron, improving its wear resistance and thermal stability; Mo strengthens pearlite, provides the decomposition temperature of pearlite, improves high-temperature creep resistance, and helps to extend the service life of the brake drum; trace amounts of La and Ce rare earth elements can purify grain boundaries and reduce inclusions. At the same time, La and Ce effectively adsorb / segregate to hinder graphite coarsening and promote the formation of slender micro and nano graphite. The microalloying elements such as Cu, Nb, Mo, La, and Ce refine the graphite structure.

[0027] In terms of casting process: When the temperature of the molten gray cast iron is 1340-1450℃, the molten metal inside is in full contact with the steel outer shell during casting, avoiding various defects such as shrinkage cavities and porosity, ensuring good bonding between the two and improving the overall performance of gray cast iron.

[0028] In summary, the synergistic effect of the fine flake graphite in the lining of the microalloyed steel ring-cast iron composite brake drum and the highly ductile matrix in this invention can improve the formability, thermal conductivity, wear resistance, and high-temperature creep resistance of the bimetallic brake drum, extend the service life and cycle life of the brake drum, and has good socio-economic benefits. It can provide research ideas for further development of bimetallic brake drums that can reliably serve in complex road conditions. Attached Figure Description

[0029] The present invention will be further described below with reference to the accompanying drawings.

[0030] Figure 1 The microstructure of the steel coil base material for the microalloyed brake drum shell. Detailed Implementation

[0031] To enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments given are not intended to limit the present invention. A microalloyed steel ring-cast iron composite brake drum and its manufacturing method specifically include:

[0032] (1) Hot-rolled coils with a thickness of 15.9-16.1 mm for brake drum housings are produced using a 2250 mm hot continuous rolling line. The chemical composition of these coils is as follows: C: 0.05-0.10%, Si: 0.10-0.25%, Mn: 0.45-0.75%, P: ≤0.015%, S: ≤0.009%, Alt: 0.015-0.045%, Nb: 0.005-0.015%, Ti: 0.010-0.025%, N: 0.0015-0.0050%, La+Ce: 0.0010-0.0040%, with the balance being Fe and unavoidable impurities. The room temperature microstructure of the base material is ferrite + pearlite, with pearlite content ≤3%, ferrite grain size grade: 9.0-11.0, elongation at break A50 ≥45% in both transverse and longitudinal directions, and surface Brinell hardness HBW: 110-135.

[0033] (2) The brake drum shell is processed into a round disc shape by hot-rolled coil using laser cutting. The power of the laser cutting machine is 3000-6000W and the cutting speed is 0.8-1.2m / min. The edge of the disc is cut by 1.5-2.5mm using a machine tool to remove the heat-affected zone of laser cutting.

[0034] (3) The disc-shaped base material is made into a brake drum outer shell steel ring using the following process: punching the center hole and bolt hole in the middle - first spinning forming - second spinning forming - outer diameter roll forming - end stamping forming - trimming the burrs. Steel ring thickness: 5.95-6.05mm.

[0035] (4) Weigh the following raw materials by weight percentage: C: 3.00-3.35%, Si: 1.80-1.95%, Mn: 0.90-1.15%, S: 0.09-0.12%, P: 0.12-0.16%, Cu: 0.10-0.15%, Nb: 0.05-0.10%, Mo: 0.20-0.35%, La+Ce: 0.04-0.10%, with the remainder being Fe and unavoidable trace impurities.

[0036] (5) The brake drum outer shell steel ring is heated by a high frequency induction heating device. The heating temperature is 800-900℃ and the time is 10-20s. The molten gray cast iron liquid of step (4) is poured into the inner wall of the steel ring outer shell of step (3) through a centrifugal forming composite casting process. The rotation speed of the outer shell during centrifugal casting is 500-900r / min, the pouring temperature is 1340-1450℃, the pouring time is 2-5s, and the thickness of the inner gray cast iron layer is set to 2.5-10mm.

[0037] (6) After the casting is completed, start the water-cooled iron sleeve device located on the outer wall of the steel ring shell to cool the micro-alloyed steel ring-cast iron composite brake drum blank.

[0038] (7) The microalloyed steel ring-cast iron composite brake drum blank is machined to length, and the pearlite content in the cast iron is ≥94%, the sum of graphite, ferrite and carbide content is ≤6%, the graphite in the graphite phase is curved and slender graphite, and the Brinell hardness of the inner gray cast iron surface is HBW: 240-270.

[0039] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0040] Example 1:

[0041] (1) A microalloyed steel ring-cast iron composite brake drum and its manufacturing method, wherein a 16.1 mm thick hot-rolled coil for brake drum shell is produced by a 2250 mm hot continuous rolling production line. Its chemical composition is: C: 0.05%, Si: 0.22%, Mn: 0.75%, P: 0.012%, S: 0.005%, Alt: 0.040%, Nb: 0.10%, Ti: 0.022%, N: 0.0016%, La+Ce: 0.0032%, with the balance being Fe and unavoidable impurities. The room temperature microstructure of its base material is ferrite + pearlite, wherein the pearlite content is 1%, the ferrite grain size grade is 11.0, the elongation after fracture in the transverse and longitudinal directions is A50 ≥ 48%, and the surface Brinell hardness HBW is 112.

[0042] (2) The brake drum shell is processed into a round disc shape by hot-rolled coil using laser cutting. The power of the laser cutting machine is 3000W and the cutting speed is 0.8m / min. The edge of the disc is cut by 1.5mm using a machine tool to remove the heat-affected zone of laser cutting.

[0043] (3) The disc-shaped base material is made into a brake drum outer shell steel ring using the following process: punching the center hole and bolt hole in the middle - first spinning forming - second spinning forming - outer diameter roll forming - end stamping forming - trimming the burrs. Steel ring thickness: 6.05mm.

[0044] (4) Weigh the following raw materials by weight percentage: C: 3.0%, Si: 1.90%, Mn: 1.25%, S: 0.12%, P: 0.17%, Cu: 0.25%, Nb: 0.08%, Mo: 0.34%, La+Ce: 0.05%, with the remainder being Fe and unavoidable trace impurities.

[0045] (5) The brake drum outer shell steel ring is heated by a high frequency induction heating device. The heating temperature is 854℃ and the time is 16s. The molten gray cast iron liquid of step (4) is poured into the inner wall of the steel ring outer shell of step (3) through centrifugal forming composite casting process. The rotation speed of the outer shell during centrifugal casting is 540r / min, the pouring temperature is 1448℃, the pouring time is 6s, and the thickness of the inner gray cast iron is set to 4.5mm.

[0046] (6) After the casting is completed, start the water-cooled iron sleeve device located on the outer wall of the steel ring shell to cool the micro-alloyed steel ring-cast iron composite brake drum blank.

[0047] (7) The micro-alloyed steel ring-cast iron composite brake drum blank is machined to length, and the pearlite content in the cast iron is 96%, the sum of graphite, ferrite and carbide content is 4%, the graphite in the graphite phase is curved and slender graphite, and the Brinell hardness of the inner gray cast iron surface is HBW: 248.

[0048] Example 2:

[0049] (1) A microalloyed steel ring-cast iron composite brake drum and its manufacturing method, wherein a 2250mm hot continuous rolling production line is used to produce a 16.1mm thick hot rolled coil for the brake drum shell, the chemical composition of which is: C:0.08%, Si:0.15%, Mn:0.65%, P:0.010%, S:0.007%, Alt:0.032%, Nb:0.008%, Ti:0.012%, N:0.0045%, La+Ce:0.0012%, with the balance being Fe and unavoidable impurities. The room temperature microstructure of the base material is ferrite + pearlite, wherein the pearlite content is 2%, the ferrite grain size grade is 10.0, the elongation after fracture in the transverse and longitudinal directions is A50≥49%, and the surface Brinell hardness HBW is 121.

[0050] (2) The brake drum shell is processed into a round disc shape by hot-rolled coil using laser cutting. The power of the laser cutting machine is 4000W and the cutting speed is 1.0m / min. The edge of the disc is cut by 2.0mm using a machine tool to remove the heat-affected zone of laser cutting.

[0051] (3) The disc-shaped base material is made into a brake drum outer shell steel ring using the following process: punching the center hole and bolt hole in the middle - first spinning forming - second spinning forming - outer diameter roll forming - end stamping forming - trimming the burrs. Steel ring thickness: 6.0mm.

[0052] (4) Weigh the following raw materials by weight percentage: C: 3.00%, Si: 1.85%, Mn: 0.95%, S: 0.10%, P: 0.13%, Cu: 0.13%, Nb: 0.05%, Mo: 0.35%, La+Ce: 0.07%, with the remainder being Fe and unavoidable trace impurities.

[0053] (5) The brake drum outer shell steel ring is heated by a high frequency induction heating device. The heating temperature is 800℃ and the time is 10s. The molten gray cast iron liquid of step (4) is poured into the inner wall of the steel ring outer shell of step (3) through centrifugal forming composite casting process. The rotation speed of the outer shell during centrifugal casting is 820r / min, the pouring temperature is 1490℃, the pouring time is 4s, and the thickness of the inner gray cast iron is set to 6mm.

[0054] (6) After the casting is completed, start the water-cooled iron sleeve device located on the outer wall of the steel ring shell to cool the micro-alloyed steel ring-cast iron composite brake drum blank.

[0055] (7) The micro-alloyed steel ring-cast iron composite brake drum blank is machined to length, and the pearlite content in the cast iron is 97%, the sum of graphite, ferrite and carbide content is 3%, the graphite in the graphite phase is curved and slender graphite, and the Brinell hardness of the inner gray cast iron surface is HBW: 268.

[0056] Example 3:

[0057] (1) A microalloyed steel ring-cast iron composite brake drum and its manufacturing method, specifically including: using a 2250mm hot continuous rolling production line to produce a 15.9mm thick hot rolled coil for the brake drum shell, the chemical composition of which is: C:0.10%, Si:0.12%, Mn:0.50%, P:0.015%, S:0.003%, Alt:0.020%, Nb:0.005%, Ti:0.015%, N:0.0030%, La+Ce:0.0015%, with the balance being Fe and unavoidable impurities, the room temperature microstructure of the base material is ferrite + pearlite, wherein the pearlite content is 3%, the ferrite grain size grade is 11.0, the elongation after fracture in the transverse and longitudinal directions is A50≥50%, and the surface Brinell hardness HBW is 134.

[0058] (2) The brake drum shell is processed into a round disc shape by hot-rolled coil using laser cutting. The power of the laser cutting machine is 6000W and the cutting speed is 1.2m / min. The edge of the disc is cut by 2.5mm using a machine tool to remove the heat-affected zone of laser cutting.

[0059] (3) The disc-shaped base material is made into a brake drum outer shell steel ring using the following process: punching the center hole and bolt hole in the middle - first spinning forming - second spinning forming - outer diameter roll forming - end stamping forming - trimming the burrs. Steel ring thickness: 5.95mm.

[0060] (4) Weigh the following raw materials by weight percentage: C: 3.35%, Si: 1.90%, Mn: 0.92%, S: 0.11%, P: 0.13%, Cu: 0.15%, Nb: 0.06%, Mo: 0.21%, La+Ce: 0.10%, with the remainder being Fe and unavoidable trace impurities.

[0061] (5) The brake drum outer shell steel ring is heated by a high frequency induction heating device. The heating temperature is 900℃ and the time is 11s. The molten gray cast iron liquid of step (4) is poured into the inner wall of the steel ring outer shell of step (3) through centrifugal forming composite casting process. The rotation speed of the outer shell during centrifugal casting is 400r / min, the pouring temperature is 1342℃, the pouring time is 2s, and the thickness of the inner gray cast iron is set to 2.5mm.

[0062] (6) After the casting is completed, start the water-cooled iron sleeve device located on the outer wall of the steel ring shell to cool the micro-alloyed steel ring-cast iron composite brake drum blank.

[0063] (7) The micro-alloyed steel ring-cast iron composite brake drum blank is machined to length, and the pearlite content in the cast iron is 98%, the sum of graphite, ferrite and carbide content is 2%, the graphite in the graphite phase is curved and slender graphite, and the Brinell hardness of the inner gray cast iron surface is HBW: 268.

[0064] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for manufacturing a micro-alloyed steel ring-cast iron composite brake drum, characterized in that, Includes the following steps: S1: The brake drum shell with a thickness of 15.9-16.1mm is cut into blanks using a steel plate by laser cutting. The laser cutting machine has a power of 3000-6000W and a cutting speed of 0.8-1.2m / min. The edge of the round blank is cut by 1.5-2.5mm using a machine tool to remove the heat-affected zone of the laser cutting. S2: The disc is made into the brake drum outer shell steel ring using the following process: punching the center hole and bolt hole in the middle - first spinning forming - second spinning forming - outer diameter roll forming - end stamping forming - trimming the burrs. Steel ring thickness: 5.95-6.05mm; S3: Weigh the following raw materials by weight percentage: C: 3.00-3.35%, Si: 1.80-1.95%, Mn: 0.90-1.15%, S: 0.09-0.12%, P: 0.12-0.16%, Cu: 0.10-0.15%, Nb: 0.05-0.10%, Mo: 0.20-0.35%, La+Ce: 0.04-0.10%, with the remainder being Fe and unavoidable trace impurities; S4: The brake drum outer shell steel ring is heated by a high-frequency induction heating device at a temperature of 800-900℃ for 10-20 seconds. The molten gray cast iron from step S3 is then poured into the inner wall of the steel ring outer shell in step S2 using a centrifugal forming composite casting process. After casting, the water-cooled iron sleeve device located on the outer wall of the steel ring outer shell is activated to cool the micro-alloyed steel ring-cast iron composite brake drum blank. The casting temperature of the molten cast iron is 1340-1450℃. S5: The micro-alloyed steel ring-cast iron composite brake drum blank prepared in step S4 is machine-processed to a fixed length; The steel plate for the outer casing comprises the following components by weight percentage: C: 0.05-0.10%, Si: 0.10-0.25%, Mn: 0.45-0.75%, P: ≤0.015%, S: ≤0.009%, Alt: 0.015-0.045%, Nb: 0.005-0.015%, Ti: 0.010-0.025%, N: 0.0015-0.0050%, La+Ce: 0.0010-0.0040%, with the balance being Fe and unavoidable impurities.

2. The manufacturing method of the microalloyed steel ring-cast iron composite brake drum according to claim 1, characterized in that, When the temperature of the molten gray cast iron is 1340-1450℃, the molten metal inside is in full contact with the steel outer shell during the pouring process, which avoids shrinkage cavities and porosity defects, ensures good bonding between the two, and improves the overall performance of gray cast iron.

3. The manufacturing method of the microalloyed steel ring-cast iron composite brake drum according to claim 1, characterized in that, The steel plate for the outer casing comprises the following components by weight percentage: C: 0.05%, Si: 0.22%, Mn: 0.75%, P: 0.012%, S: 0.005%, Alt: 0.040%, Nb: 0.10%, Ti: 0.022%, N: 0.0016%, La+Ce: 0.0032%, with the balance being Fe and unavoidable impurities.

4. The manufacturing method of the microalloyed steel ring-cast iron composite brake drum according to claim 3, characterized in that, The steel plate base material for the outer shell has a room temperature microstructure of ferrite + pearlite, wherein the pearlite content is 1%, the ferrite grain size grade is 11.0, the elongation after fracture A50 in both the transverse and longitudinal directions is ≥48%, and the surface Brinell hardness HBW is 112.

5. The manufacturing method of the microalloyed steel ring-cast iron composite brake drum according to claim 4, characterized in that, The laser cutting machine has a power of 3000W and a cutting speed of 0.8m / min. The machine tool cuts the edge of the round disc by 1.5mm to remove the heat-affected zone of the laser cutting.

6. The method for manufacturing the microalloyed steel ring-cast iron composite brake drum according to claim 1, characterized in that, The gray cast iron liquid comprises the following components by weight percentage: C: 3.0%, Si: 1.90%, Mn: 1.25%, S: 0.12%, P: 0.17%, Cu: 0.25%, Nb: 0.08%, Mo: 0.34%, La+Ce: 0.05%, with the remainder being Fe and unavoidable trace impurities.

7. The method for manufacturing the microalloyed steel ring-cast iron composite brake drum according to claim 1, characterized in that, A high-frequency induction heating device is used to heat the steel ring of the brake drum shell to a temperature of 854℃ for 16 seconds. The molten gray cast iron liquid of the composition in step S4 is then poured into the inner wall of the steel ring shell described in step S3 through a centrifugal casting composite casting process. During centrifugal casting, the shell rotation speed is 540 r / min, the pouring temperature is 1448℃, and the pouring time is 6 seconds. The thickness of the inner gray cast iron layer is set to 4.5 mm.

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