Preparation method of low-cost high-strength high-toughness ADI casting

Abstract

The invention provides a preparation method of a low-cost, high-strength and high-toughness ADI casting, and mainly relates to the field of casting materials and heat treatment. The invention discloses a preparation method of a low-cost high-strength high-toughness ADI casting. The preparation method comprises the following steps: smelting; 60% of low-manganese steel scrap with the manganese content smaller than or equal to 0.5% and 40% of scrap iron are taken and added into a smelting furnace to be smelted, low-temperature smelting is conducted at the temperature of 1460-1480 DEG C, and then high-temperature standing is conducted for 5-10 min within the range of 1490-1510 DEG C; spheroidizing and inoculating; the spheroidizing bag containing the molten iron is hoisted to a wire feeding spheroidizing machine to be subjected to spheroidizing treatment; casting is conducted; the molten iron obtained after spheroidizing inoculation is subjected to casting molding in a mold; heat treatment is conducted, specifically, the cooled casting is heated to 840 + / -10 DEG C, and then isothermal quenching is conducted under the temperature condition of 370 + / -10 DEG C; the method has the beneficial effects that cost can be reduced, efficiency can be improved, and casting products with higher quality can be prepared with lower cost.

Description

Technical Field

[0001] The present invention mainly relates to the field of casting materials and heat treatment, and specifically is a method for preparing low-cost, high-strength and high-toughness ADI castings. Background Art

[0002] Austempered ductile iron (ADI) is a new type of casting engineering material with excellent performance and broad market application prospects. ADI castings are produced by a two-step method of producing castings and heat treating castings, but there are common industry problems such as non-dense and low-quality castings, high production costs and low production efficiency. The specific problems are as follows: During the molten iron smelting and spheroidizing pouring process, the molten iron is impure and has many inclusions, resulting in non-dense castings. Improper production methods and casting processes cause shrinkage / voids inside the castings, resulting in non-dense castings. Due to the limitations of the production methods, under the same carbon equivalent conditions, the graphite ball diameter is large, the number of graphite balls is small, and the spheroidization rate is low, and high-quality castings cannot be obtained. When producing castings, high-purity pig iron and precious metals such as Ni, Mo, and Cu need to be added to increase the production cost of castings. Improper setting of heat treatment parameters increases the heat treatment time, which not only causes energy waste, but also seriously restricts the improvement of production efficiency. Summary of the invention

[0003] In order to solve the deficiencies of the prior art, the present invention provides a method for preparing ADI castings with low cost, high strength and high toughness, which can reduce costs and increase efficiency, and prepare casting products with higher quality at a lower cost.

[0004] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0005] A method for preparing a low-cost, high-strength, and high-toughness ADI casting comprises the following steps:

[0006] S1: smelting; 60 parts of low-manganese scrap steel with a manganese content of less than or equal to 0.5% and 40 parts of iron filings are added to the smelting furnace for smelting, and silicon carbide, high-temperature graphitized carburizer and 75 ferrosilicon are added. Before the start of smelting, they are added to the bottom of the electric furnace together with the first batch of scrap steel and iron filings, and low-temperature smelting is carried out at a temperature of 1460℃-1480℃ for 45±2min, followed by high-temperature standing at 1490-1510℃ for 5-10min to purify the molten iron, and the molten iron is taken out of the furnace after the composition test is qualified;

[0007] S2: Spheroidizing and inoculating; hoist the spheroidizing ladle containing molten iron to the wire feeding spheroidizing machine for spheroidizing treatment, add spheroidizing line 21 meters, spheroidizing line feeding speed 28m / min, inoculating line 10 meters for spheroidizing and inoculating, inoculating line feeding speed 20m / min;

[0008] S3: Mold design; make an iron mold according to the workpiece structure and apply a sand layer inside the iron mold;

[0009] S4: Casting: The molten iron after spheroidization is cast into a mold at a casting temperature of 1420±20℃;

[0010] S5: Heat treatment: heat the cooled casting to 840±10℃ for 40min, then perform isothermal quenching at 370±10℃ for 60min, then cool the casting after it is taken out of the furnace;

[0011] Specifically, in the S1, the manganese content in the low manganese scrap steel is: 0.3%-0.5%.

[0012] Specifically, in S1, 2 parts of silicon carbide with a particle size of 1-10 mm and a purity of 90%, 1 part of high-temperature graphitized carburizer and 0.7 parts of 75 ferrosilicon are added, and they are added to the bottom of the electric furnace together with the first batch of scrap steel and iron filings before smelting begins, and no other alloys are added.

[0013] Specifically, in S3, the thickness of the sand layer inside the iron mold is 5 mm on average.

[0014] Specifically, after the casting is quenched in S5, it enters a 60°C water curtain cleaning machine to clean the residual salt in the casting, and the casting is water-cooled while cleaning the casting. Then the casting is cooled to room temperature in the air.

[0015] Specifically, the casting workpiece in S4 is a commercial vehicle chassis balancing suspension.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] 1. The present invention does not use precious alloys such as Cu, Ni, and Mo, which greatly reduces the cost of ADI castings. This cost reduction alone is about 25%. In order to reduce the problem of low alloy content and poor hardenability of castings in the cast iron of this technology, 0.3-0.5% Mn is added, which improves the hardenability of the castings and reduces the cost of the castings.

[0018] 2. The present invention improves the quality of ADI castings, shortens the heat treatment time, reduces costs and improves efficiency, and is more economical, energy-saving and environmentally friendly.

[0019] 3. The ADI castings provided by this technology have better performance advantages and lower costs, providing a solid material foundation for the lightweight design of OEMs and having obvious social and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Attached Figure 1 This is a metallographic diagram of the shaft head of the bracket in Example 3 of the present invention;

[0021] Attached Figure 2This is a metallographic diagram of the wing part of the bracket in Example 3 of the present invention;

[0022] Attached Figure 3 This is a metallographic diagram of the reinforcing ribs of the bracket in Example 3 of the present invention; DETAILED DESCRIPTION

[0023] The present invention will be further described with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the application.

[0024] Embodiment 1:

[0025] A method for preparing a low-cost, high-strength, and high-toughness ADI casting comprises the following steps:

[0026] Melting: Take 60 parts of low-manganese scrap steel and 40 parts of iron filings and add them into the smelting furnace for smelting, with a total mass of 1000kg. The Mn content is 0.35%, add 2 parts of silicon carbide with a particle size of 1-10mm and a purity of 90%, and add 1 part of high-temperature graphitized carburizer and 0.7 parts of 75 ferrosilicon. Before the start of smelting, add them to the bottom of the electric furnace together with the first batch of scrap steel and iron filings, and carry out low-temperature smelting at a temperature of 1460℃ for 45min. In addition, no other alloys are added. Then stand at a high temperature within the range of 1490℃ to purify the molten iron; then carry out spheroidization inoculation; add 21 meters of spheroidization line, the feeding speed of the spheroidization line is 28m / min, and the inoculation line is 10 meters for spheroidization inoculation, and the feeding speed of the inoculation line is 20m / min.

[0027] Design the mold for casting workpieces; make iron molds according to the workpiece structure, use mold design software for numerical simulation in casting process design, optimize and iterate the casting process multiple times, eliminate defects such as inclusions, shrinkage / pores inside the castings, and improve the intrinsic density of the castings. Add a sand coating layer inside the iron mold, and through production experiments, reduce the thickness of the sand coating layer as much as possible while ensuring the quality of the castings, so that the average thickness of the sand coating layer is 5mm, in order to save materials and reduce production costs.

[0028] Casting; the molten iron after spheroidization is cast in a mold. In this embodiment, the cast workpiece is a commercial vehicle chassis balance suspension, the casting temperature is 1400°C, and the workpiece after casting is air-cooled.

[0029] Heat treatment: The cooled casting is heated to 830℃ for 40 minutes, then isothermally quenched at 360℃ for 60 minutes, and then the casting is cooled after being taken out of the furnace. After the casting is quenched, it is placed in a 60℃ water curtain cleaning machine to clean the residual salt in the casting. The casting is water-cooled while being cleaned, and then cooled to room temperature in the air.

[0030] Under the same process conditions, at least two specimens with a diameter of 8±0.05mm and a length of 15cm were cast in the furnace.

[0031] The tensile test was carried out on the furnace sample of workpiece No. 11 / 12, and the results are as follows:

[0032] The tensile data record table of the furnace sample in Example 1

[0033] Sample diameter do Tensile strength ≥900Rm Elongation after fracture ≥10A Sectional reduction ratio Z (rod) Specified plastic extension strength ≥ 600Rp Test date Remark unit mm MPa % % MPa Sample 11 7.99 1133.1481 13.5000 10.8266 851.7284 2024-11-1916:41:48 Sample 12 7.99 1119.4009 12.8750 9.9995 839.6953 2024-11-1916:55:11

[0034] Embodiment 2:

[0035] A method for preparing a low-cost, high-strength, and high-toughness ADI casting comprises the following steps:

[0036] Melting: Take 60 parts of low-manganese scrap steel and 40 parts of iron filings and add them into the smelting furnace for smelting, with a total mass of 1000kg. The Mn content is 0.35%, add 2 parts of silicon carbide with a particle size of 1-10mm and a purity of 90%, and add 1 part of high-temperature graphitized carburizer and 0.7 parts of 75 ferrosilicon. Before the start of smelting, add them to the bottom of the electric furnace together with the first batch of scrap steel and iron filings, and carry out low-temperature smelting at a temperature of 1480℃ for 45min. In addition, no other alloys are added. Then stand at a high temperature within the range of 1510℃ to purify the molten iron; then carry out spheroidization and inoculation; add 21 meters of spheroidization line, the feeding speed of spheroidization line is 28m / min, and 10 meters of inoculation line are used for spheroidization and inoculation, and the feeding speed of inoculation line is 20m / min.

[0037] Design the mold for casting workpieces; make iron molds according to the workpiece structure, use mold design software for numerical simulation in casting process design, optimize and iterate the casting process multiple times, eliminate defects such as inclusions, shrinkage / pores inside the castings, and improve the intrinsic density of the castings. Add a sand coating layer inside the iron mold, and through production experiments, reduce the thickness of the sand coating layer as much as possible while ensuring the quality of the castings, so that the average thickness of the sand coating layer is 5mm, in order to save materials and reduce production costs.

[0038] Casting; the molten iron after spheroidization is cast in a mold. In this embodiment, the casting workpiece is a commercial vehicle chassis balance suspension, the casting temperature is 1440°C, and the workpiece after casting is air-cooled.

[0039] Heat treatment: The cooled casting is heated to 850℃, kept at this temperature for 40 minutes, and then isothermally quenched at 380℃ for 60 minutes. The casting is then cooled after being taken out of the furnace. After the casting is quenched, it is placed in a 60℃ water curtain cleaning machine to clean the residual salt from the casting. The casting is water-cooled while being cleaned, and then cooled to room temperature in the air.

[0040] Under the same process conditions, at least two specimens with a diameter of 8±0.05mm and a length of 15cm were cast in the furnace.

[0041] The tensile test was carried out on the furnace specimen of workpiece No. 18 / 19, and the results are as follows:

[0042] The tensile data record table of the furnace sample in Example 2

[0043] Sample diameter do Tensile strength ≥900Rm Elongation after fracture ≥10A Sectional reduction ratio Z (rod) Specified plastic extension strength ≥ 600Rp Test date Remark unit mm MPa % % MPa Sample 18 7.98 1106.9395 10.8250 9.2971 840.7563 2024-11-2215:41:48 Sample 19 8.00 1100.7266 11.0000 7.8400 728.8592 2024-11-2215:52:24

[0044] Embodiment 3:

[0045] A method for preparing a low-cost, high-strength, and high-toughness ADI casting comprises the following steps:

[0046] Melting; take 60 parts of low-manganese scrap steel and 40 parts of iron filings and add them into the smelting furnace for smelting, wherein the Mn content is 0.50%, add 2 parts of silicon carbide with a particle size of 1-10mm and a purity of 90%, and add 1 part of high-temperature graphitized carburizer and 0.7 parts of 75 ferrosilicon at the same time, and add them to the bottom of the electric furnace together with the first batch of scrap steel and iron filings before the start of smelting, and carry out low-temperature smelting at a temperature of 1470℃ for 45min, and then stand at a high temperature within the range of 1490℃ to purify the molten iron; then carry out spheroidization inoculation; add 21 meters of spheroidization line, the feeding speed of spheroidization line is 28m / min, and 10 meters of inoculation line are carried out for spheroidization inoculation, and the feeding speed of inoculation line is 20m / min.

[0047] Design the mold for casting workpieces; make iron molds according to the workpiece structure, use mold design software for numerical simulation in casting process design, optimize and iterate the casting process multiple times, eliminate defects such as inclusions, shrinkage / pores inside the castings, and improve the intrinsic density of the castings. Add a sand coating layer inside the iron mold, and through production experiments, reduce the thickness of the sand coating layer as much as possible while ensuring the quality of the castings, so that the average thickness of the sand coating layer is 5mm, in order to save materials and reduce production costs.

[0048] Casting; the molten iron after spheroidization is cast in a mold. In this embodiment, the casting workpiece is a commercial vehicle chassis balance suspension, the casting temperature is 1420°C, and the workpiece is air-cooled after casting.

[0049] Heat treatment: The cooled casting is heated to 840℃ for 40 minutes, then isothermally quenched at 370℃ for 60 minutes, and then the casting is cooled after being taken out of the furnace. After the casting is quenched, it is placed in a 60℃ water curtain cleaning machine to clean the residual salt in the casting. The casting is water-cooled while being cleaned, and then cooled to room temperature in the air.

[0050] Under the same process conditions, at least two specimens with a diameter of 8±0.05mm and a length of 15cm were cast in the furnace.

[0051] The tensile test was carried out on the furnace sample of workpiece No. 21 / 22, and the results are as follows:

[0052] The tensile data record table of the furnace sample in Example 3

[0053] Sample diameter do Tensile strength ≥900Rm Elongation after fracture ≥10A Sectional reduction ratio Z (rod) Specified plastic extension strength ≥ 600Rp Test date Remark unit mm MPa % % MPa Sample 21 8.00 1245.3811 15.4500 11.4049 986.5187 2024-11-25 15:41:29 Furnace sample 1 Sample 22 7.99 1254.3794 15.5000 10.5509 1004.9172 2024-11-25 15:55:43 Furnace sample 2

[0054] In combination with the above embodiments, it can be seen that under the conditions of Embodiment 3, the tensile strength of the workpiece is higher, the elongation after fracture is higher, the plastic extension strength is higher, and its mechanical properties are significantly better than those of Embodiments 1 and 2.

[0055] The fin plate and the two side reinforcement ribs of the workpiece of Example 3 were respectively subjected to tensile tests, and the results are as follows:

[0056] The tensile data record table of the sample cut from the workpiece in Example 3

[0057] Sample diameter do Tensile strength ≥900Rm Elongation after fracture ≥10A Sectional reduction ratio Z (rod) Specified plastic extension strength ≥ 600Rp Test date Remark unit mm MPa % % MPa Sample 1 7.95 1232.6808 13.3750 9.3706 1063.3633 2024-08-28 16:24:28 wing Sample 2 7.94 1220.1583 12.8750 9.8980 1037.2432 2024-08-28 16:37:00 Reinforcement Sample 3 7.95 1214.1826 13.0000 10.2869 1050.4182 2024-08-28 16:58:59 Reinforcement

[0058] The various properties of the workpiece cast under the conditions of Example 3 are slightly different from those of the sample. It can be seen that in terms of tensile strength and elongation after fracture, the performance of the workpiece is lower than that of the sample, but the plastic ductility strength is significantly enhanced compared with the sample. Moreover, at a relatively low cost, the performance of the workpiece under the process conditions of the present invention is still far higher than the standard. Under the premise of saving costs, there is no reduction in strength, which provides a solid material foundation for the lightweight design of the main engine manufacturer.

[0059] Attached Figure 1-3 These are the metallographic images of the workpiece's shaft head, wings, and reinforcement ribs, among which:

[0060] Metallographic inspection of ductile iron of shaft head: spheroidization rate: 84%, grade: 3; number of graphite particles (pieces / square millimeter) = 252; graphite size distribution: grade 6: 56.34%; grade 7: 40.16%; grade 8: 3.50%.

[0061] Metallographic inspection of wing ductile iron shows spheroidization rate: 86%, grade: 3; number of graphite particles (pieces / square millimeter) = 330; graphite size distribution: grade 6: 20.23%; grade 7: 75.07%; grade 8: 4.70%.

[0062] Metallographic inspection of ductile iron for reinforcement bar: spheroidization rate: 87%, grade: grade 3; number of graphite particles (pieces / square millimeter) = 498; graphite size distribution: grade 6: 33.19%; grade 7: 52.48%; grade 8: 14.34%.

[0063] It can be seen from the data that the ductile iron castings under the process conditions of the present invention have a high spheroidization rate, and the number of graphite particles at the reinforcing ribs is large, which makes the reinforcing ribs hard and strong. The distribution of graphite particle size in each part is relatively uniform, which makes the overall performance of the casting consistent and the toughness better. This technology does not add additional expensive alloys, meets the strength requirements of commercial vehicle chassis parts, and is more economical, energy-saving and environmentally friendly.

Claims

1. A method for preparing a low-cost, high-strength, high-toughness ADI casting, characterized in that: The following steps are involved: S1: smelting; 60 parts of low-manganese scrap steel with a manganese content of less than or equal to 0.5% and 40 parts of iron filings are added to the smelting furnace for smelting, and silicon carbide, high-temperature graphitized carburizer and 75 ferrosilicon are added. Before the start of smelting, they are added to the bottom of the electric furnace together with the first batch of scrap steel and iron filings, and low-temperature smelting is carried out at a temperature of 1460℃-1480℃ for 45±2min, followed by high-temperature standing at 1490-1510℃ for 5-10min to purify the molten iron, and the molten iron is taken out of the furnace after the composition test is qualified; S2: Spheroidizing and inoculating; hoist the spheroidizing ladle containing molten iron to the wire feeding spheroidizing machine for spheroidizing treatment, add spheroidizing line 21 meters, spheroidizing line feeding speed 28m / min, inoculating line 10 meters for spheroidizing and inoculating, inoculating line feeding speed 20m / min; S3: Mold design; make an iron mold according to the workpiece structure and apply a sand layer inside the iron mold; S4: Casting: The molten iron after spheroidization is cast into a mold at a casting temperature of 1420±20℃; S5: Heat treatment: Heat the cooled casting to 840±10°C for 40 minutes, then perform isothermal quenching at 370±10°C for 60 minutes, and then cool the casting after it is taken out of the furnace.

2. The method for preparing a low-cost, high-strength, high-toughness ADI casting according to claim 1, characterized in that: In the S1, the manganese content in the low manganese scrap steel is: 0.3%-0.5%.

3. The method for preparing a low-cost, high-strength, high-toughness ADI casting according to claim 1, characterized in that: In the S1, 2 parts of silicon carbide with a particle size of 1-10 mm and a purity of 90%, 1 part of high-temperature graphitized carburizer and 0.7 parts of 75 ferrosilicon are added, and they are added to the bottom of the electric furnace together with the first batch of scrap steel and iron filings before smelting begins, and no other alloys are added.

4. The method for preparing a low-cost, high-strength, high-toughness ADI casting according to claim 1, characterized in that: In S3, the thickness of the sand layer inside the iron mold is 5 mm on average.

5. The method for preparing a low-cost, high-strength, high-toughness ADI casting according to claim 1, characterized in that: After the casting is quenched in S5, it enters a 60°C water curtain cleaning machine to clean the residual salt in the casting. While cleaning the casting, the casting is water-cooled, and then the casting is cooled to room temperature in the air.

6. The method for preparing a low-cost, high-strength, high-toughness ADI casting according to claim 1, characterized in that: The casting workpiece in S4 is a commercial vehicle chassis balancing suspension.

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