Method for improving surface hardness uniformity of brake disc

Abstract

The invention provides a method for improving the surface hardness uniformity of a brake disc, and relates to the technical field of cast iron. The invention discloses a method for improving surface hardness uniformity of a brake disc. The method comprises the following steps: smelting furnace charge to obtain molten iron; molten iron is discharged in batches through a transfer ladle, meanwhile, a silicon-barium inoculant is added for first-time stream inoculation, and inoculated molten iron is obtained; and pouring the molten iron subjected to inoculation treatment and carrying out pouring stream inoculation by using a silicon-antimony inoculant at the same time, so as to obtain the brake disc with uniform surface hardness. The brake disc obtained through the method for improving the surface hardness uniformity of the brake disc has a uniform and fine matrix structure, the hardness difference of the brake surface of the brake disc is reduced, and the purpose of improving the surface hardness uniformity of the brake disc is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of cast iron, and particularly to a method for improving the surface hardness uniformity of a brake disc. Background Art

[0002] The brake disc is made of gray cast iron, which has good thermal conductivity, wear resistance and high cost performance. However, the brake disc has the problem of uneven surface hardness. For a brake disc with uneven surface hardness, the surface wear of the brake disc is uneven during the braking process, which easily leads to brake judder and affects the driving experience of the driver. In order to solve the problem of uneven surface hardness of the brake disc, the brake disc should have a uniform matrix structure. Summary of the Invention

[0003] Based on the technical problems existing in the background art, the present invention proposes a method for improving the surface hardness uniformity of a brake disc.

[0004] A method for improving the surface hardness uniformity of a brake disc proposed by the present invention includes the following steps: melting the furnace charge to obtain molten iron; discharging the molten iron in batches through a transfer ladle, and adding a silicon-barium inoculant for primary in-stream inoculation at the same time to obtain the inoculated molten iron; pouring the inoculated molten iron and using a silicon-antimony inoculant for in-pouring in-stream inoculation at the same time, and a brake disc with uniform surface hardness can be obtained.

[0005] Preferably, the furnace charge includes one or more of pig iron, scrap steel, carburizer, ferromanganese, and ferrochrome.

[0006] More preferably, the pig iron, by mass fraction, includes: C: 4.4±0.1%; Si: 0.6-1.0%; Mn≤0.2%; P≤0.06%; S≤0.02%; Cr≤0.02%; Al≤0.05%; Ti≤0.05%; Pb≤0.0005%; As≤0.0008%; other trace elements<0.01%, and the balance is Fe.

[0007] More preferably, the scrap steel, by mass fraction, includes: C<0.5%; Si<0.3%; Mn<0.65%; P<0.045%; S<0.03%; Cr<0.05%; Al<0.5%; Ti<0.05%; Pb<0.0008%; As<0.0008%; other trace elements<0.01%, and the balance is Fe.

[0008] More preferably, the carburizer, by mass fraction, includes: C≥98%; S≤0.05%; N≤250PPM; volatile matter≤0.5%; H2O≤0.5%.

[0009] More preferably, the ferromanganese, by mass fraction, comprises: Mn: 65 - 66%; C: 6.6 - 7.2%; Si: 2.5 - 3.0%; P < 0.15%; S < 0.02%; the balance being Fe.

[0010] More preferably, the ferrochrome, by mass fraction, comprises: Cr: 58.0 - 62.0%; C < 6.0%; Si < 3.0%; P < 0.03%; S < 0.04%; the balance being Fe.

[0011] Preferably, the mass percentages of the chemical components of the hot metal comprise: C: 3.70 - 3.90%; Si: 1.60 - 2.10%; Mn: 0.4 - 0.8%; P ≤ 0.10%; S ≤ 0.10%; Cr: 0.10 - 0.20%; the balance being Fe and other inevitable impurities.

[0012] Preferably, the smelting temperature is 1500 - 1520 °C.

[0013] Preferably, the silicon-barium inoculant, by mass fraction, comprises: Si: 70 - 75%, Ba: 3 - 4%, the balance being Fe.

[0014] The present invention uses a silicon-barium inoculant in the in-stream inoculation during the first water discharge. The barium-containing (Ba) inoculant has a strong anti-decay ability, can extend the decay time of the inoculant, refine the matrix structure of the cast iron, increase the number of eutectic cells, and has a better inoculation effect.

[0015] Preferably, the particle size of the silicon-barium inoculant is 3 - 10 mm.

[0016] The present invention adopts the principle of large particles in large quantities, so that the hot metal can still ensure a better inoculation effect for a long time and extend the inoculation decay time.

[0017] More preferably, the particles of the silicon-barium inoculant with a particle size < 3 mm and > 10 mm do not exceed 10%.

[0018] Preferably, the mass of the silicon-barium inoculant is 0.2 - 0.4% of the mass of the hot metal.

[0019] Preferably, slag skimming treatment is carried out after the inoculation treatment.

[0020] Preferably, the pouring temperature is 1370 - 1450 °C.

[0021] Controlling the pouring temperature within a certain range in the present invention helps to improve the inoculation effect and the surface hardness uniformity of the brake disc.

[0022] Preferably, the silicon-antimony inoculant, by mass fraction, comprises: Si: 70 - 75%, Sb: 1.5 - 2.0%, the balance being Fe.

[0023] The present invention uses an inoculant containing a trace amount of antimony (Sb) element for in-stream inoculation treatment, increasing the pearlite content in the matrix structure, refining the pearlite lamellar spacing, reducing the hardness difference on the braking surface of the brake disc, and improving the hardness uniformity of the brake disc surface.

[0024] Preferably, the mass of the silicon-antimony inoculant is 0.05 - 0.15% of the mass of the molten iron after inoculation treatment.

[0025] Preferably, the particle size of the silicon-antimony inoculant is 0.2 - 1.0 mm.

[0026] During in-stream pouring, an inoculant with a particle size of 0.2 - 1.0 mm is used. Adopting the principle of using fine particles in small amounts can accelerate the melting speed of the inoculant, avoid the defects of slag pores, and achieve the purpose of instantaneous inoculation.

[0027] More preferably, the particles of the silicon-antimony inoculant with a particle size < 0.2 mm and > 1.0 mm do not exceed 10%.

[0028] The beneficial effects of the present invention are as follows:

[0029] In the present invention, a silicon-barium inoculant is used in the first in-stream inoculation during the tapping process. The inoculant containing barium (Ba) has a strong anti-decay ability, can extend the decay time of the inoculant, refine the matrix structure of cast iron, and increase the number of eutectic cells. The present invention adopts the principle of using large particles in large amounts, enabling the molten iron to still ensure a better inoculation effect for a long time and extending the inoculation decay time. The present invention uses an inoculant containing a trace amount of antimony (Sb) element for in-stream inoculation treatment, increasing the pearlite content in the matrix structure, refining the pearlite lamellar spacing, reducing the hardness difference on the braking surface of the brake disc, and improving the hardness uniformity of the brake disc surface. During in-stream pouring, an inoculant with a particle size of 0.2 - 1.0 mm is used. Adopting the principle of using fine particles in small amounts can accelerate the melting speed of the inoculant, avoid the defects of slag pores, and achieve the purpose of instantaneous inoculation. By using an inoculant with a suitable particle size, suitable composition, and suitable addition amount, the present invention eliminates ferrite in the brake disc, refines the pearlite lamellar spacing, enables the brake disc to have a uniform and fine matrix structure, reduces the hardness difference on the braking surface of the brake disc, and achieves the purpose of improving the hardness uniformity of the brake disc surface. Specific Embodiments

[0030] The technical solutions of the present invention are described in detail through specific embodiments.

[0031] The materials, reagents, etc. used in the following examples and comparative examples can be obtained from commercial channels without special instructions.

[0032] Example 1

[0033] A method for improving the surface hardness uniformity of a brake disc, comprising the following steps: melting furnace charge at 1510 °C to obtain molten iron, then discharging the molten iron five times through a transfer ladle. During the process of discharging the molten iron, for the first-time in-stream inoculation of the molten iron, a silico-barium inoculant with a particle size of 3 - 10 mm and an addition amount of 0.2% is used; for the in-stream inoculation during pouring, a silico-antimony inoculant with a particle size of 0.2 - 1.0 mm and an addition amount of 0.1% is used, and the pouring temperature is 1400 °C. Among them, the silico-barium inoculant contains 70 - 75% silicon (Si) and 3 - 4% barium (Ba); the silico-antimony inoculant contains 70 - 75% silicon (Si) and 1.5 - 2.0% antimony (Sb).

[0034] Example 2

[0035] A method for improving the surface hardness uniformity of a brake disc, comprising the following steps: melting furnace charge at 1510 °C to obtain molten iron, then discharging the molten iron five times through a transfer ladle. During the process of discharging the molten iron, for the first-time in-stream inoculation of the molten iron, a silico-barium inoculant with a particle size of 3 - 10 mm and an addition amount of 0.3% is used; for the in-stream inoculation during pouring, a silico-antimony inoculant with a particle size of 0.2 - 1.0 mm and an addition amount of 0.1% is used, and the pouring temperature is 1400 °C. Among them, the silico-barium inoculant contains 70 - 75% silicon (Si) and 3 - 4% barium (Ba); the silico-antimony inoculant contains 70 - 75% silicon (Si) and 1.5 - 2.0% antimony (Sb).

[0036] Example 3

[0037] A method for improving the surface hardness uniformity of a brake disc, comprising the following steps: melting furnace charge at 1510 °C to obtain molten iron, then discharging the molten iron five times through a transfer ladle. During the process of discharging the molten iron, for the first-time in-stream inoculation of the molten iron, a silico-barium inoculant with a particle size of 3 - 10 mm and an addition amount of 0.4% is used; for the in-stream inoculation during pouring, a silico-antimony inoculant with a particle size of 0.2 - 1.0 mm and an addition amount of 0.1% is used, and the pouring temperature is 1400 °C. Among them, the silico-barium inoculant contains 70 - 75% silicon (Si) and 3 - 4% barium (Ba); the silico-antimony inoculant contains 70 - 75% silicon (Si) and 1.5 - 2.0% antimony (Sb).

[0038] Comparative Example 1

[0039] The difference between Comparative Example 1 and Example 1 is only that for the first-time in-stream inoculation, a ferrosilicon inoculant with a particle size of 3 - 10 mm and an addition amount of 0.3% is used, and for the in-stream inoculation during pouring, a ferrosilicon inoculant with a particle size of 0.2 - 1.0 mm and an addition amount of 0.10% is used.

[0040] Test the pearlite content, pearlite lamellar spacing, and hardness of the brake disc with uniform surface hardness prepared by the above method for improving the surface hardness uniformity of the brake disc according to the GB / T 7216 - 2023 Gray Cast Iron Metallographic Inspection Standard. The test results are shown in Table 1.

[0041] Table 1

[0042] Project Example 1 Example 2 Example 3 Comparative Example 1 Pearlite content 95％ 98％ 95％ 90％ Pearlite lamellar spacing 0.57μm 0.35μm 0.69μm 0.82μm Hardness (HB) 155-175 170-180 150-165 150-170 Hardness difference (HB) 15 10 15 20

[0043] In the present invention, the silicon-antimony inoculant refines the pearlite lamellar spacing, and the silicon-barium inoculant prolongs the inoculation decay time. In Example 1, the average value of the pearlite lamellar spacing is about 0.57 μm. However, the amount of the silicon-barium inoculant is small, and there is still a large amount of ferrite. The improvement of the hardness difference is small; in Example 2, the average value of the pearlite lamellar spacing is about 0.35 μm. The content of the inoculant is moderate, the pearlite lamellar spacing is uniformly fine and small, and the hardness difference is small; in Example 3, the average value of the pearlite lamellar spacing is about 0.69 μm. However, due to the excessive amount of the silicon-barium inoculant, over-inoculation occurs, and the high carbon equivalent leads to an increase in ferrite, and the pearlite lamellar spacing continues to grow and become larger. The improvement of the hardness difference is small. In Comparative Example 1, the average value of the pearlite lamellar spacing is about 0.82 μm. The inoculation effect of ordinary 75 ferrosilicon is poor, the inoculation decay is fast, a large amount of ferrite is generated, the pearlite lamellar spacing is large, and the hardness difference is large.

[0044] In summary, the brake disc obtained by the method for improving the surface hardness uniformity of the brake disc provided by the present invention has uniformly fine pearlite lamellar spacing and small hardness difference.

[0045] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for improving the surface hardness uniformity of a brake disc, characterized in that, It includes the following steps: Smelt the furnace charge to obtain molten iron; Discharge the molten iron in portions through a transfer ladle, and at the same time add a silicon-barium inoculant for in-stream inoculation for the first time to obtain the inoculated molten iron; Pour the inoculated molten iron while using a silicon-antimony inoculant for in-stream inoculation during pouring, and a brake disc with uniform surface hardness can be obtained.

2. The method for improving the surface hardness uniformity of a brake disc according to claim 1, characterized in that, The silicon-barium inoculant, by mass fraction, includes: Si: 70-75%, Ba: 3-4%, and the balance is Fe.

3. The method for improving the surface hardness uniformity of a brake disc according to claim 1, characterized in that, The mass of the silicon-barium inoculant is 0.2-0.4% of the mass of the molten iron.

4. The method for improving the surface hardness uniformity of a brake disc according to claim 1, characterized in that, The silicon-antimony inoculant, by mass fraction, includes: Si: 70-75%, Sb: 1.5-2.0%, and the balance is Fe.

5. The method for improving the surface hardness uniformity of a brake disc according to claim 1, characterized in that, The mass of the silicon-antimony inoculant is 0.05-0.15% of the mass of the inoculated molten iron.

6. The method for improving the surface hardness uniformity of a brake disc according to claim 1, characterized in that, The particle size of the silicon-barium inoculant is 3-10 mm.

7. The method for improving the surface hardness uniformity of a brake disc according to claim 1, characterized in that, The particle size of the silicon-antimony inoculant is 0.2-1.0 mm.

8. The method for improving the surface hardness uniformity of a brake disc according to claim 1, characterized in that, The smelting temperature is 1500-1520 °C.

9. The method for improving the surface hardness uniformity of a brake disc according to claim 1, characterized in that The pouring temperature is 1370-1450 °C.