High-strength nitrogen-increasing gray cast iron and method for manufacturing the same

Abstract

The application belongs to the technical field of gray cast iron materials, and particularly relates to high-strength nitrogen-increased gray cast iron and a preparation method thereof, which comprises the following components in mass: C 3.2-3.4%, Si 2.0-2.4%, Mn 0.7-1.0%, P ≤0.1%, S 0.06-0.08%, Cr 0.15-0.3%, Cu 0.2-0.3%, N 90-120ppm, and the balance of Fe and inevitable impurities; wherein, the N is dissolved in ferrite and enriched in graphite tips, and hinders the growth of graphite; the high-strength nitrogen-increased gray cast iron and the preparation method thereof can effectively hinder the growth of graphite by increasing nitrogen in molten iron, so as to refine the graphite morphology, increase the volume fraction of pearlite, and significantly strengthen the gray cast iron. Compared with alloy elements such as copper and chromium, the nitrogen element has a significant cost advantage, and under the combined action of alloy copper and nitrogen-increased molten iron, high-performance gray cast iron can be more stably obtained.

Description

Technical Field

[0001] This invention belongs to the technical field of gray cast iron materials, specifically relating to a high-strength nitrogen-enriched gray cast iron and its preparation method. Background Technology

[0002] Gray cast iron refers to cast iron containing flake graphite. It is named for its dark gray fracture surface. Its main components are iron, carbon, silicon, manganese, sulfur, and phosphorus. It is the most widely used type of cast iron, accounting for over 80% of total cast iron production.

[0003] With product updates and iterations, the mechanical properties, especially hardness, of existing material-controlled products can no longer meet customer requirements. The mechanical properties have been improved from tensile strength ≥250MPa and hardness (170HBW-224HBW) to tensile strength ≥250MPa and hardness (200HBW-241HBW).

[0004] Existing technical solutions mainly use the addition of copper to improve the mechanical properties of gray cast iron. However, there is a threshold upper limit to the amount of copper added to gray cast iron. The strength peak is reached when the amount of copper added is around 0.4%. After exceeding 1.0%, the excess copper precipitates as free particles, the grain boundaries become embrittled, the tensile strength drops, the hardness increase slows down, but the brittleness continues to deteriorate.

[0005] Therefore, overcoming the limitation that the tensile strength and hardness of copper-containing gray cast iron cannot be further improved by increasing the copper content is a technical problem that urgently needs to be solved in this field.

[0006] It should be noted that the information disclosed in this background section is only for understanding the background technology of the present application concept, and therefore, the above description is not considered to constitute prior art information. Summary of the Invention

[0007] This disclosure provides at least one high-strength nitrogen-enriched gray cast iron and its preparation method.

[0008] In a first aspect, embodiments of this disclosure provide a gray cast iron comprising, by mass: 3.2–3.4% C, 2.0–2.4% Si, 0.7–1.0% Mn, ≤0.1% P, 0.06–0.08% S, 0.15–0.3% Cr, 0.2–0.3% Cu, 90–120 ppm N, with the balance being Fe and unavoidable impurities; wherein the N is dissolved in ferrite and enriched at the graphite tips, and hinders graphite growth.

[0009] In one optional embodiment, the tensile strength of the single-cast test bar of gray cast iron is not less than 322 MPa and the hardness is not less than 234 HBW.

[0010] In one optional embodiment, the tensile strength of the gray cast iron casting body is not less than 295 MPa and the hardness is not less than 202 HBW.

[0011] Secondly, the present disclosure also provides a method for preparing gray cast iron as described above, wherein: S1, low manganese briquettes, scrap steel plates, gray iron, ferrosilicon, ferrochrome, ferrosulfide, copper, and nitrogen-adjusting and carbon-increasing agents are added to the reactor as furnace charge; S2, the reactor is heated to not less than 1520°C, and after sufficient reaction, ferromanganese nitride is added to a casting ladle at 1430-1450°C, slag is removed, and iron is tapped at 1460-1480°C to obtain gray cast iron.

[0012] In one optional embodiment, the nitrogen-regulating and carbon-enhancing agent comprises, by mass: fixed carbon ≥ 98.4%, ash content ≤ 1.0%, volatile matter ≤ 0.6%, moisture content ≤ 0.3%, sulfur content ≤ 0.5%, and nitrogen content 4000-6000 ppm.

[0013] In one optional embodiment, the particle size of the nitrogen-regulating and carbon-raising agent is 1-5 mm.

[0014] In one optional embodiment, the manganese iron nitride comprises, by mass: N 7.5-8.5%, Mn ≥80%, Si ≤1.0%, C ≤1.5%, S ≤0.05%, and P ≤0.2%.

[0015] In one optional embodiment, the manganese nitride iron has a particle size of 1 to 10 mm.

[0016] In one optional embodiment, the amount of copper added in S1 is 0.4 to 0.5% of the total mass of the furnace charge.

[0017] In one optional embodiment, the amount of single-bag ferromanganese nitride added in S2 is 0.05 to 0.15% of the total mass of the furnace charge.

[0018] The beneficial effects of this invention are that the high-strength nitrogen-enriched gray cast iron and its preparation method introduce nitrogen into the molten iron. The introduced nitrogen dissolves in ferrite and accumulates at the graphite tips, effectively hindering graphite growth, thereby refining the graphite morphology and increasing the pearlite volume fraction, resulting in a significant strengthening effect on the gray cast iron. Compared to alloying elements such as copper and chromium, nitrogen has a significant cost advantage. Furthermore, the combined effect of copper alloy and nitrogen enrichment in the molten iron allows for a more stable and high-performance gray cast iron.

[0019] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description and the drawings.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 Metallographic image of sample 1 gray cast iron provided in the embodiments of this disclosure; Figure 2 Corrosion metallographic image of sample 1 gray cast iron provided in the embodiments of this disclosure; Figure 3 Metallographic image of sample 2 gray cast iron provided in the embodiments of this disclosure; Figure 4 Corrosion metallographic image of sample 2 gray cast iron provided in the embodiments of this disclosure; Figure 5 Metallographic image of sample 4 gray cast iron provided in the embodiments of this disclosure; Figure 6 Corrosion metallographic image of sample 4 gray cast iron provided in the embodiments of this disclosure; Figure 7 Metallographic image of sample 5 gray cast iron provided in the embodiments of this disclosure; Figure 8 Corrosion metallographic image of sample 5 gray cast iron provided in the embodiments of this disclosure. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] As used herein, the phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” etc., generally refer to the fact that a particular feature, structure, or characteristic following the phrase can be included in at least one embodiment of this disclosure. Therefore, a particular feature, structure, or characteristic can be included in more than one embodiment of this disclosure, such that these phrases do not necessarily refer to the same embodiment. As used herein, the terms “example,” “exemplary,” etc., are used to “serve as an example, instance, or illustration.” Any implementation, aspect, or design described herein as “example” or “exemplary” is not necessarily to be construed as preferred or superior to other implementations, aspects, or designs. Rather, the use of the terms “example,” “exemplary,” etc., is intended to present concepts in a specific manner.

[0025] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0026] This disclosure provides a gray cast iron comprising, by mass: 3.2–3.4% C, 2.0–2.4% Si, 0.7–1.0% Mn, ≤0.1% P, 0.06–0.08% S, 0.15–0.3% Cr, 0.2–0.3% Cu, 90–120 ppm N, with the balance being Fe and unavoidable impurities; wherein the N is dissolved in ferrite and enriched at the graphite tips, and hinders graphite growth.

[0027] In some embodiments, specifically, the tensile strength of the single-cast test bar of gray cast iron is not less than 322 MPa, and the hardness is not less than 234 HBW.

[0028] In some embodiments, specifically, the tensile strength of the gray cast iron casting body is not less than 295 MPa, and the hardness is not less than 202 HBW.

[0029] This disclosure also provides a method for preparing gray cast iron as described above, wherein: S1, low-manganese briquettes, scrap steel plates, gray iron, ferrosilicon, ferrochrome, ferrosulfide, copper, and nitrogen-adjusting and carbon-increasing agents are added to the reactor as furnace charge; S2, the reactor is heated to not less than 1520°C, and after full reaction, ferromanganese nitride is added to a casting ladle at 1430-1450°C, slag is removed, and iron is tapped at 1460-1480°C to obtain gray cast iron.

[0030] Specifically, the function of the low-manganese briquettes is that the ladle contains manganese nitride. When molten iron is poured into the ladle from the electric furnace, the manganese content in the molten iron is relatively high. Low-manganese briquettes are used to reduce the manganese content in the original molten iron. After adding manganese nitride ferronitride in the later stage, the manganese content of the final molten iron is kept within the control range.

[0031] In some embodiments, specifically, the nitrogen-regulating and carbon-enhancing agent comprises, by mass: fixed carbon ≥ 98.4%, ash content ≤ 1.0%, volatile matter ≤ 0.6%, moisture content ≤ 0.3%, sulfur content ≤ 0.5%, and nitrogen content 4000-6000 ppm.

[0032] In some embodiments, specifically, the particle size of the nitrogen-regulating and carbon-raising agent is 1-5 mm.

[0033] In some embodiments, specifically, the manganese iron nitride comprises, by mass: N 7.5-8.5%, Mn ≥80%, Si ≤1.0%, C ≤1.5%, S ≤0.05%, and P ≤0.2%.

[0034] In some embodiments, specifically, the particle size of the manganese ferronitride is 1 to 10 mm.

[0035] In some embodiments, specifically, the amount of copper added in S1 is 0.4 to 0.5% of the total mass of the furnace charge.

[0036] In some embodiments, specifically, the amount of a single bag of manganese ferronitride added in S2 is 0.05 to 0.15% of the total mass of the furnace charge.

[0037] Specifically, the term "single ladle" refers to a ladle of molten iron in the ironmaking process. A single ladle is defined as one batch of molten iron and is used to measure the amount of molten iron.

[0038] Example: A method for preparing gray cast iron as described above. S1, take 500Kg of low manganese briquettes, 3000Kg of scrap steel plates, 3500Kg of gray iron, 75Kg of ferrosilicon, 15Kg of ferrochrome, 7.5Kg of ferrosulfide, 17.5Kg of copper and 150Kg of nitrogen-adjusting and carbon-increasing agent, and add them to the reactor as furnace charge. S2. Heat the reactor to a temperature not lower than 1520℃. After the reaction is complete, add 1.5Kg of manganese nitride ferronitride to the casting ladle at 1430~1450℃, remove the slag, and tap the iron at 1460~1480℃ to obtain 1440Kg of gray cast iron.

[0039] The nitrogen-regulating and carbon-enhancing agent is selected from Henan Weiye's nitrogen-regulating and carbon-enhancing agent ZTJ-3-5.

[0040] The low-manganese briquettes, scrap steel plates, and gray iron are weighed using a crane with a tolerance of ±50 kg. The ferrosilicon, ferrochrome, ferrous sulfate, and ferromanganese nitride are weighed using an electronic scale with an error of ±0.5 kg.

[0041] The composition of the manganese iron nitride, by mass, includes: N 7.5-8.5%, Mn ≥80%, Si ≤1.0%, C ≤1.5%, S ≤0.05%, and P ≤0.2%.

[0042] The resulting gray cast iron includes samples 1, 2 and 3, and its mechanical properties and metallographic structure are shown in Table 1 below.

[0043] Table 1 Mechanical properties and metallographic features of the examples

[0044] Please see Figures 1-4 The image shows the metallographic and corrosion diagrams of sample 1, where the tips of the flake graphite are blunt.

[0045] Comparative example, grade HT250 The ingredients are as follows: 3500Kg scrap steel plate, 3500Kg gray scrap iron, 75Kg ferrosilicon, 15Kg ferrochrome, 7.5Kg ferrous sulfate, 28Kg copper and 140Kg medium-temperature graphitization recarburizer.

[0046] The components of the medium-temperature graphitization carbon raiser, by mass, include: fixed carbon ≥98.4%, ash ≤1.0%, volatile matter ≤0.6%, moisture ≤0.3%, sulfur content ≤0.5%, nitrogen content ≤2000ppm; and particle size of 1-5mm.

[0047] Add the above ingredients, heat the reactor to no less than 1520°C, and after the reaction is complete, remove the slag and tap the iron at 1460-1480°C to obtain gray cast iron.

[0048] The chemical composition of the resulting gray cast iron is as follows: C 3.2-3.4%, Si 2.0-2.4%, Mn 0.7-1.0%, P ≤0.1%, S 0.06-0.08%, Cr 0.15-0.3%, Cu 0.4-0.5%, with the balance being Fe and unavoidable impurities.

[0049] The resulting gray cast iron includes samples 4, 5 and 6, and its mechanical properties and metallographic structure are shown in Table 2 below.

[0050] Table 2 Comparative mechanical properties and metallographic features

[0051] Please see Figures 5-8 The tips of unnitrogenated flake graphite exhibit a relatively sharp characteristic.

[0052] As can be seen from the comparison, the embodiments effectively improved the mechanical properties of gray cast iron by increasing nitrogen and reducing the amount of copper used, while modifying the tips of the flake graphite.

[0053] In summary, this high-strength nitrogen-enriched gray cast iron and its preparation method introduce nitrogen into the molten iron. The introduced nitrogen dissolves in ferrite and accumulates at the graphite tips, effectively inhibiting graphite growth. This refines the graphite morphology and increases the pearlite volume fraction, significantly strengthening the gray cast iron. Compared to alloying elements such as copper and chromium, nitrogen offers a significant cost advantage. Furthermore, the combined effect of copper alloy and nitrogen enrichment in the molten iron allows for a more stable and high-performance gray cast iron production.

[0054] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A type of gray cast iron, characterized in that, By mass, including: C 3.2-3.4%, Si 2.0-2.4%, Mn 0.7-1.0%, P ≤0.1%, S 0.06-0.08%, Cr 0.15-0.3%, Cu 0.2-0.3%, N 90-120ppm, balance being Fe and unavoidable impurities; The N is dissolved in ferrite and enriched at the graphite tip, thus hindering graphite growth.

2. The gray cast iron as described in claim 1, characterized in that, The tensile strength of the single-cast test bar of the gray cast iron shall not be less than 322 MPa and the hardness shall not be less than 234 HBW.

3. The gray cast iron as described in claim 1, characterized in that, The tensile strength of the gray cast iron casting body is not less than 295 MPa, and the hardness is not less than 202 HBW.

4. A method for preparing gray cast iron as described in any one of claims 1-3, characterized in that, S1, take low manganese briquettes, scrap steel plates, gray iron, ferrosilicon, ferrochrome, ferrous sulfate, copper and nitrogen-adjusting and carbon-increasing agents, and add them to the reactor as furnace charge; S2. Heat the reactor to a temperature not lower than 1520℃. After the reaction is complete, add manganese ferronitride to the casting ladle at 1430-1450℃, remove the slag, and tap the iron at 1460-1480℃ to obtain gray cast iron.

5. The preparation method according to claim 4, characterized in that, The nitrogen-regulating and carbon-raising agent comprises, by mass: Fixed carbon ≥98.4%, ash ≤1.0%, volatile matter ≤0.6%, moisture ≤0.3%, sulfur content ≤0.5%, nitrogen content 4000-6000ppm.

6. The preparation method according to claim 4, characterized in that, The particle size of the nitrogen-regulating and carbon-raising agent is 1-5 mm.

7. The preparation method according to claim 4, characterized in that, The manganese ferronitride comprises, by mass: N 7.5~8.5%, Mn ≥80%, Si ≤1.0%, C ≤1.5%, S ≤0.05%, P ≤0.2%.

8. The preparation method according to claim 4, characterized in that, The particle size of the manganese nitride iron is 1-10 mm.

9. The preparation method according to claim 4, characterized in that, The amount of copper added in S1 is 0.4 to 0.5% of the total mass of the furnace charge.

10. The preparation method according to claim 4, characterized in that, The amount of single-bag ferromanganese nitride added in S2 is 0.05 to 0.15% of the total mass of the furnace charge.

Images