A ductile iron, casting and its preparation method

Abstract

The present invention belongs to the technical field of ductile iron preparation, and discloses ductile iron, castings and a preparation method thereof. The ductile iron comprises the following chemical components by weight percentage: C: 3.68 - 3.75%, Si: 2.35 - 2.45%, Mn ≤ 0.10%, P: 0.010 - 0.030%, S: 0.008 - 0.015%, Ti ≤ 0.010%, Sb: 0.0050 - 0.0060%, Sn: 0.050 - 0.060%, La: 0.0065 - 0.0080%, Mg: 0.035 - 0.045%, and the balance is Fe and inremovable impurities; the preparation method of the ductile iron comprises the following steps: Step 1: feeding raw materials into a smelter to obtain molten iron; Step 2: skimming the molten iron and removing impurities; Step 3: pouring the molten iron obtained in Step 2 into an electric furnace, adding silicon carbide accounting for 0.20 - 0.30% of the weight of the molten iron during this process, and then carrying out nodulizing inoculation treatment; Step 4: carrying out casting to obtain ductile iron, and carrying out in-stream inoculation treatment during the casting process. By limiting the composition and dosage of the ductile iron and cooperating with the control of the addition time and dosage of silicon carbide in the preparation process, the pearlite in the ductile iron can be evenly distributed and the pearlite quantity can be stably controlled between 35 - 45%.

Description

Technical Field

[0001] The present invention relates to the technical field of ductile iron preparation, and particularly relates to a ductile iron, a casting and a preparation method thereof. Background Art

[0002] Laser quenching is a quenching technology that uses a laser to heat the surface of a material above the phase transformation point. As the material cools itself, austenite transforms into martensite, thereby hardening the surface of the material.

[0003] Since some castings produced from ductile iron need to meet the requirements of high hardness and high wear resistance, the castings produced from ductile iron can be finely processed by means of laser quenching to improve their surface hardness and wear resistance, and at the same time improve their mechanical properties and surface quality. This treatment method can not only improve the strength and wear resistance of the material, but also retain excellent toughness and plasticity.

[0004] For example, in the prior art 1: Chinese Patent No. 201510413103.5 discloses a finishing process for the connecting arm and steering wheel of QT600 ductile iron. The steps are as follows: stress relief annealing treatment of the casting; rough and fine machining; normalizing treatment; fine machining; overall surface nitriding composite treatment of the workpiece; laser quenching treatment of the parts with rounded corners of the workpiece; deformation measurement; 0.1 mm of fine machining and polishing adjustment; The present invention improves the product stability and repeatability. After the product is nitrided as a whole, the rounded corner positions are laser quenched, so that the surface of the casting obtains high hardness, while ensuring the original hardness, finish and quality of the cast iron, reliable quality, eliminating the internal stress in the casting, reducing the tendency of the product to gradually crack at the rounded corner part, increasing the hardness value of the laser quenching area of the connecting arm and steering seat, and solving the contradiction between hardness and fine machining accuracy. And because the number of parts treated by laser quenching is small, the distortion amount of the casting after laser quenching is almost zero.

[0005] The above technology uses laser quenching technology to improve the hardness of ductile iron. However, since only the rounded corner parts of the product are laser quenched, the demand for hardness improvement after laser quenching is not high. Therefore, the prior art 1 does not conduct in-depth research on the performance improvement of the hardened layer formed by laser quenching.

[0006] It is found that the hardened layer obtained after laser quenching is not only related to the process adopted, but also has a great relationship with the ductile iron itself. For example, the quantity of pearlite and ferrite in the ductile iron, as well as the uniformity of the pearlite distribution in the ductile iron, all have a great influence on the performance of the hardened layer obtained after laser quenching. In order to improve the surface hardness and wear resistance of the castings produced from ductile iron, corresponding ductile iron needs to be developed to maximize the comprehensive performance of the hardened layer obtained after laser quenching. Summary of the Invention

[0007] One of the objectives of the present invention is to provide a ductile iron, which not only has excellent mechanical properties, but also contains pearlite within a specific content range, with uniform distribution of pearlite, and can maximize the comprehensive properties of the hardened layer obtained after laser quenching.

[0008] Another objective of the present invention is to provide a method for preparing a casting, which can finish machining the ductile iron according to customer requirements, and then perform laser quenching treatment on the die surface to obtain a hardened layer with high mechanical properties.

[0009] Meanwhile, the present invention also provides a casting, which is obtained by casting and finishing machining the ductile iron of the present invention in sequence. The hardened layer obtained after laser quenching treatment of this casting has extremely excellent mechanical properties, and due to the uniform distribution of pearlite in the ductile iron, it can make the properties of each position of the hardened layer relatively uniform, and will not generate too large stress difference to cause distortion and failure of the casting.

[0010] To achieve the above objectives, the present invention provides a ductile iron, and the ductile iron includes the following chemical components by weight percentage: C: 3.68 - 3.75%, Si: 2.35 - 2.45%, Mn ≤ 0.10%, P: 0.010 - 0.030%, S: 0.008 - 0.015%, Ti ≤ 0.010%, Sb: 0.0050 - 0.0060%, Sn: 0.050 - 0.060%, La: 0.0065 - 0.0080%, Mg: 0.035 - 0.045%, and the balance is Fe and inremovable impurities;

[0011] The preparation method of the ductile iron includes the following steps:

[0012] Step 1: Put raw materials into melting to obtain molten iron;

[0013] Step 2: Skim the molten iron and remove impurities;

[0014] Step 3: Pour the molten iron obtained in Step 2 into an electric furnace, and add silicon carbide accounting for 0.20 - 0.30% of the weight of the molten iron during this process, and then perform nodulizing and inoculating treatment;

[0015] Step 4: Perform casting to obtain ductile iron, and perform in-stream inoculation treatment during the casting process.

[0016] The present invention limits the components in the ductile iron, mainly including: (1) The amounts of manganese and copper in the ductile iron are controlled very low. Since the metal prices of manganese and copper are relatively high, the technical solution of not adding manganese and copper elements additionally in the present invention can effectively control the uniformity and quantity of pearlite, and reduce production costs; (2) Sb and Sn elements are added to the ductile iron and the amounts are extremely small, but strict control is required.

[0017] At the same time, during the preparation of ductile iron, the present invention is different from the prior art in which silicon carbide is added before or during smelting. In the present invention, a certain amount of silicon carbide is added during the process of transferring the molten iron to the electric furnace.

[0018] The present invention limits the components in ductile iron and delays the addition of silicon carbide. The two work together to ensure that the ductile iron has a high spheroidization rate, a large number of graphite nodules, a pearlite content between 35-45%, and a uniform distribution of pearlite. The ductile iron ensures the performance improvement of the hardened layer obtained after laser quenching, while maximizing the overall performance of the hardened layer and achieving uniform performance improvement throughout the hardened layer.

[0019] More preferably, the raw materials in step 1 are pig iron, recycled materials, scrap steel, recarburizer, and ferrosilicon.

[0020] Further preferably, the raw materials in step 1 are 20-30% pig iron, 20-30% recycled materials, 40-58% scrap steel, 1.22-2.16% recarburizer, and 0.50-1.24% ferrosilicon; and the manganese and titanium contents in the pig iron, recycled materials, and scrap steel must be strictly controlled, i.e., Mn ≤ 0.10%, Ti ≤ 0.010%.

[0021] The amount of pearlite in the ductile iron is 35-45%.

[0022] Preferably, the smelting temperature in step 1 is 1460-1500°C.

[0023] Preferably, the specific operation of step 2 is: cooling the molten iron to 1360-1400°C after deslagging.

[0024] Furthermore, the specific operation of step 3 is: pouring the molten iron cooled in step 2 into an electric furnace, adding 0.20-0.30% silicon carbide by weight of the molten iron during the process, heating to 1440-1460° C. and keeping the temperature for 8 minutes to perform spheroidization inoculation treatment.

[0025] Furthermore, in step 3, before the spheroidizing inoculation treatment, 1.2% of the weight of the molten iron by weight of a spheroidizing agent, 0.4% of the weight of the molten iron by weight of a first special-effect inoculant, 0.0056-0.0066% of the weight of the molten iron by weight of Sb, 0.055-0.065% of Sn and 0.15% of crushed steel particles are added to the molten iron after insulation to cover the molten iron.

[0026] Preferably, the composition of the spheroidizing agent is Mg: 5.52%, Si: 45.5%, La: 0.98%, Ca: 1.75%, Al: 0.44%, and the remainder is Fe; the particle size is 5-25 mm;

[0027] Preferably, the composition of the first special-effect inoculant is Si: 74.3%, Ba: 2.25%, Ce: 1.22%, Al: 0.78%, the balance being Fe, and the particle size is 3 - 8 mm.

[0028] Further, the specific operation of step 4 is: pouring at 1340 - 1350 °C, and adding a second special-effect inoculant accounting for 0.1% of the weight of the molten iron for in-stream inoculation treatment during the pouring process.

[0029] Preferably, the composition of the second special-effect inoculant is Si: 72.1%, Ca: 2.33%, appropriate amount of S, appropriate amount of O, Al: 0.46%, the balance being Fe, and the particle size is 0.2 - 0.7 mm.

[0030] The present invention also discloses a method for preparing a casting, which includes the following steps:

[0031] Step a: Pouring the above-mentioned ductile iron into a furan resin sand mold and cooling to obtain a casting blank;

[0032] Step b: After precision machining the mold surface of the casting blank, performing laser quenching treatment.

[0033] The precision machining is to perform precision milling and other machining methods on the mold surface of the casting blank to meet the dimensional accuracy requirements of customers.

[0034] Preferably, the power of the laser quenching treatment is 3000 - 3200 W, and the scanning speed is 360 - 390 mm / min.

[0035] The present invention also discloses a casting, which is prepared by using the above-mentioned method for preparing a casting. The thickness of the hardened layer obtained by laser quenching of the casting is 0.4 - 0.5 mm, and the hardness is 350 - 400 HBW.

[0036] Beneficial effects

[0037] Compared with the prior art, the present invention has at least the following advantages:

[0038] (1) The present invention discloses a ductile iron. By limiting the composition and dosage of the ductile iron and cooperating with the control of the addition time and dosage of silicon carbide during the preparation process, not only can the pearlite in the ductile iron be evenly distributed and the pearlite quantity be stably controlled between 35% and 45%, but also the number of graphite balls in the ductile iron can be increased to meet the requirements of subsequent further laser quenching treatment;

[0039] (2) For the casting prepared by precision machining the ductile iron of the present invention, after laser quenching of its mold surface, the hardened layer produced by laser quenching has excellent mechanical properties and can meet the requirements of the downstream industry. Description of the drawings

[0040] The present invention will be further described below in conjunction with the accompanying drawings and embodiments;

[0041] Figure 1 It is the spheroidization rate picture of the sample block with a thickness of 300 mm prepared in Example 3 of the present invention;

[0042] Figure 2 It is the pearlite quantity picture of the sample block with a thickness of 300 mm prepared in Example 3 of the present invention;

[0043] Figure 3 It is the spheroidization rate picture of the sample block with a thickness of 300 mm prepared in Comparative Example 1 of the present invention;

[0044] Figure 4 It is the pearlite quantity picture of the sample block with a thickness of 300 mm prepared in Comparative Example 2 of the present invention;

[0045] Figure 5 It is the spheroidization rate picture of the sample block with a thickness of 300 mm prepared in Comparative Example 3 of the present invention;

[0046] Figure 6 It is the pearlite quantity picture of the sample block with a thickness of 300 mm prepared in Comparative Example 5 of the present invention;

[0047] Figure 7 It is the pearlite quantity picture of the sample block with a thickness of 300 mm prepared in Comparative Example 6 of the present invention;

[0048] Figure 8 It is the spheroidization rate picture of the sample block with a thickness of 300 mm prepared in Comparative Example 7 of the present invention;

[0049] Figure 9 It is the front view of the castings in Application Examples 1 and 2 of the present invention;

[0050] Figure 10 It is the bottom view of the castings in Application Examples 1 and 2 of the present invention;

[0051] Figure 11 It is the top view of the castings in Application Examples 1 and 2 of the present invention;

[0052] Figure 12 It is the left view of the castings in Application Examples 1 and 2 of the present invention;

[0053] Figure 13 It is the three-dimensional view of the castings in Application Examples 1 and 2 of the present invention. Detailed implementation manners

[0054] The present invention will be further described below in conjunction with the embodiments, but it does not constitute any limitation to the present invention. Any limited modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0055] To elaborate on the technical content of the present invention in detail, the following further explanations are provided in conjunction with the embodiments.

[0056] In the following examples and comparative examples, the composition of the spheroidizing agent is Mg: 5.52%, Si: 45.5%, La: 0.98%, Ca: 1.75%, Al: 0.44%, the balance being Fe; the particle size is 5 - 25 mm; the composition of the first special-effect inoculant is Si: 74.3%, Ba: 2.25%, Ce: 1.22%, Al: 0.78%, the balance being Fe, and the particle size is 3 - 8 mm; the composition of the second special-effect inoculant is Si: 72.1%, Ca: 2.33%, S in appropriate amount, O in appropriate amount, Al: 0.46%, the balance being Fe, and the particle size is 0.2 - 0.7 mm; the composition of the silicon carbide is SiC: 93% (Si: 65%, C: 28%), Fe2O3: 1.2%, Al2O3: 1.1%, the balance being Fe, and the particle size is 1 - 5 mm; antimony (Sb) is sourced from 99.95% antimony grains crushed to a particle size of 1 - 5 mm, and the absorption rate at 1440 - 1460 °C is 91%; tin (Sn) is sourced from 99.92% tin grains with a particle size of 3 - 10 mm, and the absorption rate at 1440 - 1460 °C is 92%.

[0057] In the following examples and comparative examples, unless otherwise specified, the % is by weight.

[0058] Example 1

[0059] A ductile iron is prepared by the following steps:

[0060] Step 1: Pig iron, return scrap, steel scrap, carburizer, and ferrosilicon are melted at a temperature of 1460 °C to obtain molten iron.

[0061] Step 2: The molten iron is slagged off and then cooled to 1360 °C.

[0062] Step 3: The molten iron cooled in Step 2 is poured into an electric furnace. During this process, 0.20% by weight of the molten iron of silicon carbide is added. After heating to 1450 °C and holding for 8 min, 1.2% by weight of the molten iron of the spheroidizing agent, 0.4% by weight of the molten iron of the first special-effect inoculant, 0.0058% by weight of the molten iron of Sb, 0.062% by weight of the molten iron of Sn, and 0.15% by weight of steel shot are added for covering, and spheroidizing inoculation treatment is carried out.

[0063] Step 4: Pouring is carried out at 1345 °C. During the pouring process, 0.1% by weight of the molten iron of the second special-effect inoculant is added for in-stream inoculation treatment.

[0064] Samples were taken after pouring, and the chemical composition of the ductile iron was obtained as follows: C: 3.68%, Si: 2.42%, Mn: 0.08%, P: 0.018%, S: 0.011%, Ti: 0.007%, Sb: 0.0053%, Sn: 0.057%, La: 0.0071%, Mg: 0.035%, and the balance was Fe and non-removable impurities.

[0065] Example 2

[0066] A kind of ductile iron is prepared by the following steps:

[0067] Step 1: Pig iron, return scrap, steel scrap, carburizer, and ferrosilicon were melted at a temperature of 1460 °C to obtain molten iron;

[0068] Step 2: The molten iron was slagged off and then cooled to 1360 °C;

[0069] Step 3: The molten iron cooled in Step 2 was poured into an electric furnace. During this process, silicon carbide accounting for 0.20% of the weight of the molten iron was added. After heating to 1450 °C and holding for 8 minutes, a nodulizer accounting for 1.2% of the weight of the molten iron, a first special inoculant accounting for 0.4% of the weight of the molten iron, Sb accounting for 0.0061% of the weight of the molten iron, Sn accounting for 0.059% of the weight of the molten iron, and broken steel particles accounting for 0.15% of the weight of the molten iron were added for covering, and nodulizing inoculation treatment was carried out;

[0070] Step 4: Pouring was carried out at 1342 °C, and a second special inoculant accounting for 0.1% of the weight of the molten iron was added during the pouring process for in-stream inoculation treatment;

[0071] Samples were taken after pouring, and the chemical composition of the ductile iron was obtained as follows: C: 3.71%, Si: 2.38%, Mn: 0.07%, P: 0.011%, S: 0.015%, Ti: 0.009%, Sb: 0.0055%, Sn: 0.054%, La: 0.0068%, Mg: 0.036%, and the balance was Fe and non-removable impurities.

[0072] Example 3

[0073] A kind of ductile iron is prepared by the following steps:

[0074] Step 1: Pig iron, return scrap, steel scrap, carburizer, and ferrosilicon were melted at a temperature of 1460 °C to obtain molten iron;

[0075] Step 2: The molten iron was slagged off and then cooled to 1360 °C;

[0076] Step 3: Pour the molten iron after cooling in Step 2 into the electric furnace. During this process, add silicon carbide accounting for 0.30% of the weight of the molten iron, heat it up to 1450°C, keep it warm for 8 minutes, then add a spheroidizing agent accounting for 1.2% of the weight of the molten iron, a first special-effect inoculant accounting for 0.4% of the weight of the molten iron, Sb accounting for 0.0066% of the weight of the molten iron, Sn accounting for 0.062% of the weight of the molten iron, and steel chips accounting for 0.15% of the weight of the molten iron to cover, and conduct spheroidizing and inoculating treatment;

[0077] Step 4: Pour at 1348°C. During the pouring process, add a second special-effect inoculant accounting for 0.1% of the weight of the molten iron for in-stream inoculating treatment;

[0078] After pouring, take a sample. The chemical composition of the ductile iron obtained is: C: 3.75%, Si: 2.44%, Mn: 0.088%, P: 0.028%, S: 0.011%, Ti: 0.010%, Sb: 0.0060%, Sn: 0.057%, La: 0.0065%, Mg: 0.040%, and the balance is Fe and inremovable impurities.

[0079] Example 4

[0080] A kind of ductile iron is prepared by the following steps:

[0081] Step 1: Melting pig iron, return scrap, steel scrap, carburant, and ferrosilicon at a temperature of 1460°C to obtain molten iron;

[0082] Step 2: Skim the molten iron and then cool it down to 1360°C;

[0083] Step 3: Pour the molten iron after cooling in Step 2 into the electric furnace. During this process, add silicon carbide accounting for 0.25% of the weight of the molten iron, heat it up to 1450°C, keep it warm for 8 minutes, then add a spheroidizing agent accounting for 1.2% of the weight of the molten iron, a first special-effect inoculant accounting for 0.4% of the weight of the molten iron, Sb accounting for 0.0065% of the weight of the molten iron, Sn accounting for 0.060% of the weight of the molten iron, and steel chips accounting for 0.15% of the weight of the molten iron to cover, and conduct spheroidizing and inoculating treatment;

[0084] Step 4: Pour at 1350°C. During the pouring process, add a second special-effect inoculant accounting for 0.1% of the weight of the molten iron for in-stream inoculating treatment;

[0085] After pouring, take a sample. The chemical composition of the ductile iron obtained is: C: 3.72%, Si: 2.40%, Mn: 0.076%, P: 0.010%, S: 0.013%, Ti: 0.005%, Sb: 0.0059%, Sn: 0.055%, La: 0.0077%, Mg: 0.041%, and the balance is Fe and inremovable impurities.

[0086] Comparative Example 1

[0087] A ductile iron is prepared by the following steps:

[0088] Step 1: Smelt pig iron, return scrap, steel scrap, recarburizer, and ferrosilicon at a temperature of 1460 °C to obtain molten iron;

[0089] Step 2: Remove slag from the molten iron and then cool it down to 1360 °C;

[0090] Step 3: Pour the molten iron cooled in Step 2 into an electric furnace. During this process, add silicon carbide accounting for 0.20% of the weight of the molten iron, heat it up to 1450 °C, keep it warm for 8 minutes, then add a nodulizer accounting for 1.2% of the weight of the molten iron, a first special-effect inoculant accounting for 0.4% of the weight of the molten iron, Sn accounting for 0.062% of the weight of the molten iron, and steel shot accounting for 0.15% of the weight of the molten iron to cover, and conduct nodulizing inoculation treatment;

[0091] Step 4: Conduct casting at 1344 °C. During the casting process, add a second special-effect inoculant accounting for 0.1% of the weight of the molten iron for in-stream inoculation treatment;

[0092] After casting, take a sample. The chemical composition of the ductile iron obtained is: C: 3.75%, Si: 2.45%, Mn: 0.083%, P: 0.026%, S: 0.013%, Ti: 0.009%, Sn: 0.057%, La: 0.0067%, Mg: 0.038%, and the balance is Fe and inremovable impurities.

[0093] Comparative Example 2

[0094] A ductile iron is prepared by the following steps:

[0095] Step 1: Smelt pig iron, return scrap, steel scrap, recarburizer, and ferrosilicon at a temperature of 1460 °C to obtain molten iron;

[0096] Step 2: Remove slag from the molten iron and then cool it down to 1360 °C;

[0097] Step 3: Pour the molten iron cooled in Step 2 into an electric furnace. During this process, add silicon carbide accounting for 0.20% of the weight of the molten iron, heat it up to 1450 °C, keep it warm for 8 minutes, then add a nodulizer accounting for 1.2% of the weight of the molten iron, a first special-effect inoculant accounting for 0.4% of the weight of the molten iron, Sb accounting for 0.0066% of the weight of the molten iron, and steel shot accounting for 0.15% of the weight of the molten iron to cover, and conduct nodulizing inoculation treatment;

[0098] Step 4: Conduct casting at 1345 °C. During the casting process, add a second special-effect inoculant accounting for 0.1% of the weight of the molten iron for in-stream inoculation treatment;

[0099] Samples were taken after pouring, and the chemical composition of the ductile iron obtained was: C: 3.73%, Si: 2.42%, Mn: 0.079%, P: 0.025%, S: 0.014%, Ti: 0.007%, Sb: 0.0060%, La: 0.0071%, Mg: 0.038%, and the balance was Fe and non-removable impurities.

[0100] Comparative Example 3

[0101] A kind of ductile iron is prepared by the following steps:

[0102] Step 1: Pig iron, return scrap, steel scrap, carburizer, and ferrosilicon were melted at a temperature of 1460 °C to obtain molten iron;

[0103] Step 2: The molten iron was slagged off and then cooled to 1360 °C;

[0104] Step 3: The molten iron cooled in Step 2 was poured into an electric furnace. During this process, silicon carbide accounting for 0.20% of the weight of the molten iron was added, and after heating to 1450 °C and holding for 8 min, a nodulizer accounting for 1.2% of the weight of the molten iron, a first special-effect inoculant accounting for 0.4% of the weight of the molten iron, Sb accounting for 0.0046% of the weight of the molten iron, Sn accounting for 0.062% of the weight of the molten iron, and steel granule fragments accounting for 0.15% of the weight of the molten iron were added for covering, and nodulizing and inoculating treatment was carried out;

[0105] Step 4: Pouring was carried out at 1346 °C, and a second special-effect inoculant accounting for 0.1% of the weight of the molten iron was added during the pouring process for in-stream inoculation treatment;

[0106] Samples were taken after pouring, and the chemical composition of the ductile iron obtained was: C: 3.69%, Si: 2.45%, Mn: 0.086%, P: 0.030%, S: 0.008%, Ti: 0.008%, Sb: 0.0042%, Sn: 0.057%, La: 0.0066%, Mg: 0.042%, and the balance was Fe and non-removable impurities.

[0107] Comparative Example 4

[0108] A kind of ductile iron is prepared by the following steps:

[0109] Step 1: Pig iron, return scrap, steel scrap, carburizer, and ferrosilicon were melted at a temperature of 1460 °C to obtain molten iron;

[0110] Step 2: The molten iron was slagged off and then cooled to 1360 °C;

[0111] Step 3: Pour the molten iron after cooling in Step 2 into an electric furnace. During this process, add silicon carbide accounting for 0.20% of the weight of the molten iron, heat up to 1450 °C, keep it warm for 8 min, then add a nodulizer accounting for 1.2% of the weight of the molten iron, a first special-effect inoculant accounting for 0.4% of the weight of the molten iron, Sb accounting for 0.0070% of the weight of the molten iron, Sn accounting for 0.062% of the weight of the molten iron, and steel chips accounting for 0.15% of the weight of the molten iron to cover, and conduct nodulizing and inoculating treatment;

[0112] Step 4: Carry out casting at 1348 °C. During the casting process, add a second special-effect inoculant accounting for 0.1% of the weight of the molten iron for in-stream inoculating treatment;

[0113] Take a sample after casting. The chemical composition of the ductile iron obtained is: C: 3.70%, Si: 2.37%, Mn: 0.083%, P: 0.024%, S: 0.012%, Ti: 0.010%, Sb: 0.0064%, Sn: 0.057%, La: 0.0074%, Mg: 0.045%, and the balance is Fe and impurities that cannot be removed.

[0114] Comparative Example 5

[0115] A kind of ductile iron is prepared by the following steps:

[0116] Step 1: Smelt pig iron, return scrap, scrap steel, carburant, and ferrosilicon at a temperature of 1460 °C to obtain molten iron;

[0117] Step 2: Skim the molten iron and then cool it down to 1360 °C;

[0118] Step 3: Pour the molten iron after cooling in Step 2 into an electric furnace. During this process, add silicon carbide accounting for 0.20% of the weight of the molten iron, heat up to 1450 °C, keep it warm for 8 min, then add a nodulizer accounting for 1.2% of the weight of the molten iron, a first special-effect inoculant accounting for 0.4% of the weight of the molten iron, Sb accounting for 0.0066% of the weight of the molten iron, Sn accounting for 0.044% of the weight of the molten iron, and steel chips accounting for 0.15% of the weight of the molten iron to cover, and conduct nodulizing and inoculating treatment;

[0119] Step 4: Carry out casting at 1350 °C. During the casting process, add a second special-effect inoculant accounting for 0.1% of the weight of the molten iron for in-stream inoculating treatment;

[0120] Take a sample after casting. The chemical composition of the ductile iron obtained is: C: 3.74%, Si: 2.35%, Mn: 0.080%, P: 0.022%, S: 0.008%, Ti: 0.009%, Sb: 0.0060%, Sn: 0.040%, La: 0.0067%, Mg: 0.044%, and the balance is Fe and impurities that cannot be removed.

[0121] Comparative Example 6

[0122] A ductile iron is prepared by the following steps:

[0123] Step 1: Melting pig iron, return materials, scrap steel, carburizer, and ferrosilicon at a temperature of 1460 °C to obtain molten iron;

[0124] Step 2: Skimming the molten iron and then cooling it to 1360 °C;

[0125] Step 3: Pouring the molten iron cooled in Step 2 into an electric furnace. During this process, add silicon carbide accounting for 0.20% of the weight of the molten iron. After heating to 1450 °C and holding for 8 minutes, add a spheroidizing agent accounting for 1.2% of the weight of the molten iron, a first special-effect inoculant accounting for 0.4% of the weight of the molten iron, Sb accounting for 0.0066% of the weight of the molten iron, Sn accounting for 0.071% of the weight of the molten iron, and steel chips accounting for 0.15% of the weight of the molten iron for covering, and conduct spheroidizing inoculation treatment;

[0126] Step 4: Pouring at 1340 °C. During the pouring process, add a second special-effect inoculant accounting for 0.1% of the weight of the molten iron for in-stream inoculation treatment;

[0127] After pouring, sampling is carried out, and the chemical composition of the ductile iron obtained is: C: 3.71%, Si: 2.45%, Mn: 0.083%, P: 0.029%, S: 0.012%, Ti: 0.007%, Sb: 0.0060%, Sn: 0.065%, La: 0.0069%, Mg: 0.039%, and the balance is Fe and inremovable impurities.

[0128] Comparative Example 7

[0129] A ductile iron is prepared by the following steps:

[0130] Step 1: Melting pig iron, return materials, scrap steel, carburizer, and ferrosilicon at a temperature of 1460 °C to obtain molten iron. During the melting process, add silicon carbide accounting for 0.30% of the total weight of pig iron, return materials, scrap steel, carburizer, and ferrosilicon when at least 50% of the solids are melted into molten iron;

[0131] Step 2: Skimming the molten iron and then cooling it to 1360 °C;

[0132] Step 3: Pouring the molten iron cooled in Step 2 into an electric furnace. After heating to 1450 °C, add a spheroidizing agent accounting for 1.2% of the weight of the molten iron, a first special-effect inoculant accounting for 0.4% of the weight of the molten iron, Sb accounting for 0.0066% of the weight of the molten iron, Sn accounting for 0.062% of the weight of the molten iron, and steel chips accounting for 0.15% of the weight of the molten iron for covering, and conduct spheroidizing inoculation treatment;

[0133] Step 4: Pouring at 1344 °C. During the pouring process, add a second special-effect inoculant accounting for 0.1% of the weight of the molten iron for in-stream inoculation treatment;

[0134] Samples were taken after pouring, and the chemical composition of the ductile iron was obtained as follows: C: 3.73%, Si: 2.42%, Mn: 0.092%, P: 0.029%, S: 0.013%, Ti: 0.009%, Sb: 0.0060%, Sn: 0.057%, La: 0.0074%, Mg: 0.042%, and the balance was Fe and non-removable impurities.

[0135] Comparative Example 8

[0136] A kind of ductile iron is prepared by the following steps:

[0137] Step 1: Pig iron, return scrap, steel scrap, carburizer, ferrosilicon and silicon carbide were melted at a temperature of 1460 °C to obtain molten iron. The addition amount of silicon carbide was 0.3% of the total weight of pig iron, return scrap, steel scrap, carburizer and ferrosilicon.

[0138] Step 2: After slag removal of the molten iron, the temperature was lowered to 1360 °C.

[0139] Step 3: Pour the molten iron cooled in Step 2 into an electric furnace, heat it to 1450 °C, and then add a spheroidizing agent accounting for 1.2% of the weight of the molten iron, a first special inoculant accounting for 0.4% of the weight of the molten iron, Sb accounting for 0.0066% of the weight of the molten iron, Sn accounting for 0.062% of the weight of the molten iron, and steel shot accounting for 0.15% of the weight of the molten iron to cover, and carry out spheroidizing inoculation treatment.

[0140] Step 4: Pouring was carried out at 1349 °C, and a second special inoculant accounting for 0.1% of the weight of the molten iron was added during the pouring process for in-stream inoculation treatment.

[0141] Samples were taken after pouring, and the chemical composition of the ductile iron was obtained as follows: C: 3.73%, Si: 2.42%, Mn: 0.079%, P: 0.014%, S: 0.007%, Ti: 0.006%, Sb: 0.0060%, Sn: 0.057%, La: 0.0071%, Mg: 0.041%, and the balance was Fe and non-removable impurities.

[0142] The ductile iron obtained in Examples 1-4 and Comparative Examples 1-8 was respectively cast into sample blocks with a thickness of 70 mm and 300 mm (both the length and width were 400 mm × 400 mm). The center point was taken for metallographic microscope detection to analyze its metallographic structure, and the spheroidization rate and the amount of pearlite were obtained.

[0143] It was found that the spheroidization rate of the sample blocks with a thickness of 70 mm and 300 mm prepared in Examples 1-4 and the sample blocks with a thickness of 70 mm prepared in Comparative Examples 1-8 was greater than 92%, and the number of graphite balls was greater than 400 per mm 2 and the amount of pearlite was greater than 35%;

[0144] Among them, the spheroidization rate and pearlite quantity obtained from the metallographic structure analysis of the center point of the sample block with a thickness of 300 mm prepared in Example 3 are shown in Figure 1 and Figure 2 .

[0145] The spheroidization rate obtained from the metallographic structure analysis of the center point of the sample block with a thickness of 300 mm prepared in Comparative Example 1 is shown in Figure 3 .

[0146] The pearlite quantity obtained from the metallographic structure analysis of the center point of the sample block with a thickness of 300 mm prepared in Comparative Example 2 is shown in Figure 4 .

[0147] The spheroidization rate obtained from the metallographic structure analysis of the center point of the sample block with a thickness of 300 mm prepared in Comparative Example 3 is shown in Figure 5 .

[0148] The pearlite quantity obtained from the metallographic structure analysis of the center point of the sample block with a thickness of 300 mm prepared in Comparative Example 5 is shown in Figure 6 .

[0149] The pearlite quantity obtained from the metallographic structure analysis of the center point of the sample block with a thickness of 300 mm prepared in Comparative Example 6 is shown in Figure 7 .

[0150] The spheroidization rate obtained from the metallographic structure analysis of the center point of the sample block with a thickness of 300 mm prepared in Comparative Example 7 is shown in Figure 8 .

[0151] However, compared with the sample block with a thickness of 300 mm prepared in Example 3, for the sample blocks with a thickness of 300 mm prepared in Comparative Example 1 and Comparative Example 3, the spheroidization rate is significantly reduced and the number of graphite balls is also significantly reduced; for the sample blocks with a thickness of 300 mm prepared in Comparative Example 2 and Comparative Example 5, the pearlite quantity is significantly reduced; for the sample blocks with a thickness of 300 mm prepared in Comparative Example 4 and Comparative Example 6, their pearlite quantities are both increased, and the pearlite quantity is greater than 45%, but due to the too high content of Sb or Sn, the spheroidization rate is significantly decreased, and the spheroidization rate is lower than 86% and the number of graphite balls is also reduced; for the sample blocks with a thickness of 300 mm prepared in Comparative Example 7 and Comparative Example 8, the change in their pearlite quantity is not significant, but due to the incorrect timing of adding silicon carbide, the spheroidization rate is decreased and is lower than 89%, and the number of graphite balls is reduced more compared with Example 3.

[0152] It can be seen from this that by controlling the components and contents of ductile iron, especially by controlling the contents of antimony and tin, and coordinating the timing and amount of adding silicon carbide during the preparation process, the present invention can prepare castings with high thickness, high spheroidization rate, large number of graphite balls and pearlite quantity maintained at 35-45%.

[0153] In particular, regarding the control of the pearlite quantity, the technical solution of the present invention can achieve a uniform distribution of pearlite in a sample block with a thickness of 300 mm by controlling the contents of antimony and tin in ductile iron, the addition timing and addition amount of silicon carbide during the preparation process;

[0154] Samples with a thickness of 300 mm were prepared in Examples 1-4 and Comparative Examples 1-8, and points were taken at the four corners and the center for metallographic microscope inspection to obtain the pearlite quantity. Specifically, see Table 1, where point 1 is the test point in the upper left corner, point 2 is the test point in the upper right corner, point 3 is the test point in the lower left corner, point 4 is the test point in the lower right corner, and point 5 is the test point in the center;

[0155] Table 1 Test results of the pearlite uniformity of samples with a thickness of 300 mm prepared in Examples 1-4 and Comparative Examples 1-8

[0156]

[0157]

[0158] It can be seen from the results in Table 1 that:

[0159] It can be known from Examples 1-4 that the ductile iron castings obtained by casting according to the present invention have the advantages of high spheroidization rate, uniform pearlite distribution, and the pearlite quantity controlled between 35% and 45%.

[0160] It can be known from the data comparison between Example 3 and Comparative Example 1 and Comparative Example 3 that in Comparative Example 1 and Comparative Example 3, due to the lack of Sb or insufficient Sb content respectively, the spheroidization rate decreased significantly. Although the pearlite quantity did not decrease significantly, the pearlite distribution uniformity at each point decreased.

[0161] It can be known from the data comparison between Example 3 and Comparative Example 2 and Comparative Example 5 that in the case of lack of Sn or too little Sn content, both the pearlite uniformity and quantity will decrease significantly.

[0162] It can be known from the data comparison between Example 3 and Comparative Example 4 and Comparative Example 6 that the present invention can effectively balance and improve the spheroidization rate by controlling the contents of Sb and Sn, ensuring the advantages that the pearlite quantity is between 35% and 45% and is uniformly distributed.

[0163] It can be known from the data comparison between Example 3 and Comparative Example 7 and Comparative Example 8 that the present invention can play a role in instantaneously increasing the nucleation cores of the molten iron and improving the spheroidization rate by controlling the addition timing and addition amount of silicon carbide, and can effectively improve the spheroidization rate of the casting and the distribution uniformity of pearlite.

[0164] Laser quenching process test:

[0165] The sample blocks with a thickness of 300 mm prepared in Example 3 were respectively processed by the following laser quenching processes to obtain Samples 1-6 with a hardened layer on the surface;

[0166] Sample 1: Laser quenching power 3000 W, scanning speed 390 mm / min;

[0167] Sample 2: Laser quenching power 3200 W, scanning speed 360 mm / min;

[0168] Sample 3: Laser quenching power 3200 W, scanning speed 320 mm / min;

[0169] Sample 4: Laser quenching power 3200 W, scanning speed 420 mm / min;

[0170] Sample 5: Laser quenching power 2800 W, scanning speed 360 mm / min;

[0171] Sample 6: Laser quenching power 3500 W, scanning speed 360 mm / min.

[0172] Using the same above test method, the hardness of the surface hardened layer of Samples 1-6 was measured at the four corners and the center, and the results are shown in Table 2:

[0173] Table 2 Hardness results of the hardened layer obtained by different laser quenching processes

[0174]

[0175] According to the results in Table 2, it can be seen that: when the laser quenching power is 3000 - 3200 W and the scanning speed is 360 - 390 mm / min, the hardness of the hardened layer is within 350 - 400 HBW, and the hardness difference is less than 15 HBW; when the laser quenching power is low or the scanning speed is fast, the hardness of the hardened layer is lower than 350 HBW, and the hardness difference is greater than 15 HBW; when the laser quenching power is high or the scanning speed is slow, the hardness of the hardened layer is lower than 400 HBW, and the hardness difference is greater than 15 HBW.

[0176] Using the laser quenching process of Sample 2, the sample blocks with a thickness of 300 mm prepared in Comparative Examples 1-8 were subjected to laser quenching, and then their hardness was measured at the four corners and the center using the above test method, and the results are shown in Table 3;

[0177] Table 3 Hardness results of the laser quenching hardened layer of the sample blocks with a thickness of 300 mm prepared in Comparative Examples 1-8

[0178]

[0179] According to the data in Table 2 of Sample 2 and the data in Table 3, it can be seen that:

[0180] When the Sb content is absent or too low, the spheroidization rate is lower than 92%, the number of graphite nodules is less than 400 per mm 2 and the pearlite content is less than 35%, the hardness of the hardened layer is lower than 350 HBW, and the hardness difference is greater than 15 HBW. Good results cannot be achieved, and customer requirements cannot be met.

[0181] Application Example 1

[0182] A casting is poured into a furan resin sand mold using the steps of Example 3 to obtain Figures 9 - 13 a casting. The material of the casting is QT500-7A, the weight of the casting is 12,880 kg, the external dimensions of the casting are 2,032 mm × 2,021 mm × 1,095 mm, and the wall thickness of the mold surface is 328 mm;

[0183] The mechanical properties of the casting are tested at the four corners and the center using the same testing method as above, and the results are as follows:

[0184] The hardness (HBW) of the mold surface of the casting: Point 1: 185, Point 2: 188, Point 3: 191, Point 4: 188, Point 5: 192, spheroidization rate: 95%, number of graphite nodules: 500 per mm 2 , pearlite content: 42%, ferrite content: the balance;

[0185] The mechanical properties of the sample taken from the casting body (a sample with a diameter of 24 mm and a length of 328 mm is taken from the center part in terms of the mold surface thickness) are: tensile strength R m : 462 MPa, yield strength R P0.2 : 327 MPa, elongation A: 6.0%. These mechanical property results are significantly better than the guiding values in Table C1 of the mechanical properties of the casting body sample in Appendix C of "Ductile Iron Castings" GB / T 1348-2019 for the material grade QT500-7 / C with the casting wall thickness t: when 60 < t ≤ 200, the tensile strength R m (min) 400 MPa, yield strength R P0.2 (min): 260 MPa, elongation A(min): 3%.

[0186] Using a laser quenching power of 3,200 W and a scanning speed of 360 mm / min to perform laser quenching on the mold surface of the casting ( Figure 10 ), a hardened layer with a thickness of 0.46 mm is finally obtained. After testing, the hardness (HBW) of the hardened layer is Point 1: 382, Point 2: 385, Point 3: 380, Point 4: 388, Point 5: 381.

[0187] Application Example 2

[0188] A casting is poured into a furan resin sand mold using the steps of Example 3 to obtain Figures 9 - 13The casting, with the casting material being QT500-7A, casting weight: 15850 kg, casting external dimensions: 2193 mm × 2250 mm × 1245 mm, die surface wall thickness: 372 mm;

[0189] Mechanical property tests were carried out on the casting, and the results are as follows:

[0190] Hardness of the casting die surface (HBW): Point 1: 179, Point 2: 178, Point 3: 183, Point 4: 176, Point 5: 181, spheroidization rate: 93%, number of graphite balls: 400 pieces / mm 2 , pearlite quantity: 40%, ferrite quantity: the balance;

[0191] Mechanical properties of the casting body sample (taking a sample with a diameter of 24 mm and a length of 372 mm from the die surface thickness and the central part): Tensile strength R m : 455 MPa, yield strength R P0.2 : 318 MPa, elongation A: 6.5%. These mechanical property results are significantly better than the mechanical property guiding value table C1 in Appendix C of "Ductile Iron Castings" GB / T 1348-2019 for the material grade QT500-7 / C when the casting wall thickness t: 60 < t ≤ 200, the tensile strength R m (min) 400 MPa, yield strength R P0.2 (min): 260 MPa, elongation A(min): 3% of the guiding values.

[0192] The die surface of the casting ( Figure 10 ) was laser quenched using a laser quenching power of 3200 W and a scanning speed of 360 mm / min, and finally a hardened layer with a thickness of 0.48 mm was obtained. After testing, the hardness (HBW) of the hardened layer is Point 1: 372, Point 2: 370, Point 3: 379, Point 4: 372, Point 5: 369.

[0193] The embodiments presented in this article are only implementation manners selected according to combinations of all possible embodiments. The appended claims should not be limited by the embodiments that illustrate the present invention. Some numerical ranges used in the claims include sub-ranges within them, and variations within these ranges should also be covered by the appended claims.

Claims

1. A ductile iron, characterized in that, The ductile iron comprises the following chemical components in weight percentage: C: 3.68-3.75%, Si: 2.35-2.45%, Mn≤0.10%, P: 0.010-0.030%, S: 0.008-0.015%, Ti≤0.010%, Sb: 0.0050-0.0060%, Sn: 0.050-0.060%, La: 0.0065-0.0080%, Mg: 0.035-0.045%, and the balance is Fe and non-removable impurities; The preparation method of the ductile iron comprises the following steps: Step 1: Smelting the raw materials to obtain molten iron; Step 2: Deslagging the molten iron and removing impurities; Step 3: Pour the molten iron obtained in step 2 into an electric furnace, add 0.20-0.30% of the weight of the molten iron into silicon carbide, and then perform spheroidization inoculation treatment; Step 4: Casting is performed to obtain ductile iron, and inoculation treatment is performed during the pouring process; The amount of pearlite in the ductile iron is 35-45%.

2. The ductile cast iron according to claim 1, wherein The smelting temperature in step 1 is 1460-1500°C.

3. The ductile cast iron according to claim 1, characterized in that, The specific operation of step 2 is: slagging the molten iron and then cooling it to 1360-1400°C.

4. The ductile iron according to claim 1, characterized in that The specific operation of step 3 is: pouring the molten iron cooled in step 2 into the electric furnace, adding 0.20-0.30% of the weight of the molten iron with silicon carbide during the process, heating to 1440-1460° C. and then keeping the temperature for 8 minutes to perform spheroidization inoculation treatment.

5. The ductile cast iron according to claim 4, characterized in that, In step 3, before the spheroidizing inoculation treatment, 1.2% of the weight of the molten iron by weight of a spheroidizing agent, 0.4% of the weight of the molten iron by weight of a first special-effect inoculant, 0.0056-0.0066% of the weight of the molten iron by weight of Sb, 0.055-0.065% of Sn and 0.15% of crushed steel particles are added to the molten iron after insulation to cover the molten iron.

6. The ductile iron according to claim 1, characterized in that The specific operation of step 4 is: pouring at 1340-1350° C., and adding 0.1% of the weight of the molten iron into the second special-effect inoculant to perform in-stream inoculation during the pouring process.

7. A method for preparing a casting, characterized in that: The steps include: Step a: pouring the ductile iron according to any one of claims 1 to 6 into a furan resin sand mold and cooling the mold to obtain a casting; Step b: performing laser quenching treatment after finishing the die surface of the ingot.

8. The preparation method of the casting according to claim 7, characterized in that, The power of the laser quenching treatment is 3000-3200W, and the scanning speed is 360-390mm / min.

9. A casting, characterized in that, The casting is prepared by the method for preparing the casting according to claim 7 or 8, wherein the casting has a hardened layer with a thickness of 0.4-0.5 mm and a hardness of 350-400 HBW obtained by laser quenching treatment.

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