High-hardness mining round-link chain steel and preparation method thereof

Abstract

The invention relates to high-hardness mining round-link chain steel and a preparation method thereof, and belongs to the technical field of steel preparation. In order to solve the problem that the hardness of a product produced by an existing mining round-link chain steel hot rolling process is too low, the high-hardness mining round-link chain steel is provided and comprises the following chemical components in percentage by weight: 0.21-0.29% of C, 0.15-0.40% of Si, 1.10-1.55% of Mn, 0.10-0.25% of V, 0.010-0.035% of Al, less than or equal to 0.025% of P, less than or equal to 0.025% of S and the balance of Fe and inevitable impurities. According to the manufactured high-hardness mining round-link chain steel, in the state of natural cooling after rolling, the hardness of the steel ranges from 210 HBW to 240 HBW, the hardness of the surface and the hardness of the center are basically consistent, the machining performance is good, and the use requirements of current small-specification mining round-link chain steel can be completely met.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material preparation, and in particular relates to a high-hardness round-link chain steel for mining and a preparation method thereof. Background Art

[0002] High-hardness mining round link chain steel is widely used in the mining industry. However, with the advancement of technology, the mining industry's demand for coal mining efficiency and continuous service time is increasing. As the core component of coal mining machines, mining round link chain steel has increasingly stringent requirements in terms of wear resistance, tensile strength and hardenability.

[0003] At present, the mining round link chain steel commonly used in the market is mostly made of traditional hot-rolled annealed 23MnNiMoCr54, SAE8620H steel bars and 25MnV wires. The mechanical properties of 23MnNiMoCr54 steel are relatively high, and its preparation requires the addition of a lot of precious metals, which is costly. However, the requirements for mechanical properties of small-sized mining round link chains are slightly lower, so 25MnV steel is often used as the raw material.

[0004] At present, the production of 25MnV steel is divided into two types: bars and wires. The hardness of bars is generally lower than 180HBW, which is suitable for cold ring processing technology, but cannot be applied to hot ring equipment, and the production efficiency is low. During production, wires have better air cooling effect and their hardness is generally higher than 270HBW. Annealing is required to reduce the hardness before processing. Traditional annealing and straightening processes will cause residual stress in the steel during the processing process, and the production cost is high.

[0005] Therefore, it is necessary to develop a high-hardness hot-rolled round steel for mining round link chains, which can meet the increasingly stringent market demand while ensuring comprehensive performance, and can solve the environmental pollution and resource waste problems in the current processing technology, provide stronger guarantees for the durability and reliability of mining equipment, and promote the sustainable development of the industry. Summary of the invention

[0006] In order to solve the problem that the products produced by the existing hot rolling process for mining round link chain steel have too low hardness, and the products produced by the wire process have too high hardness and need annealing heat treatment and cannot be directly processed, the present invention provides a high-hardness mining round link chain steel and a preparation method thereof.

[0007] The technical solution of the present invention:

[0008] A high-hardness round-link chain steel for mining, the chemical composition of which includes, by weight percentage, C: 0.21-0.29%, Si: 0.15-0.40%, Mn: 1.10-1.55%, V: 0.10-0.25%, Al: 0.010-0.035%, P≤0.025%, S: ≤0.025%, and the rest is Fe and unavoidable impurities.

[0009] A method for preparing high-hardness round link chain steel for mining, the preparation process comprises electric furnace or converter smelting → LF refining → VD vacuum degassing → continuous casting → rolling → material production, during the smelting process, the final composition of the steel is controlled to be not less than 0.08% C, P≤0.015%, and the steel tapping temperature is not less than 1560°C, and the steel tapping enters LF refining;

[0010] During the LF refining process, argon gas is passed through, and the white slag is kept for no less than 40 minutes; samples are taken for component analysis, and the components are fine-tuned according to the internal control component requirements based on the component results; when the components meet the requirements, the temperature is 1650-1660℃ and enters the VD vacuum degassing;

[0011] During the VD vacuum degassing process, vacuum is drawn, and the vacuum degree is maintained at ≤67Pa for not less than 30 minutes before breaking the vacuum. After breaking the vacuum, Al is added to the steel, and after the end, weak argon is stirred for 25 minutes before casting. The pouring temperature is 1520-1550℃;

[0012] When the obtained steel is rolled, high-temperature diffusion treatment is adopted, the heating temperature is controlled at 1170-1205°C, and the high-temperature diffusion time is controlled at 1.5-2.0 hours; in order to achieve the ideal structure after rolling, the steel is cooled to 350°C on a cooling bed and then pile-cooled.

[0013] Furthermore, in the smelting process, the steel charge is composed of returned steel and pig iron, the carbon content of the steel charge is 1.0-1.5%, the slag is composed of lime and light-burned dolomite, and the total amount of slag is 1550Kg / 100 tons of steel; after the slag is fully melted, the temperature is 1620°C and oxidation begins; the oxygen blowing pressure is controlled at 0.3-0.7MPa; the decarburization amount is not less than 0.35%; the oxidation end point C is 0.19-0.23%, and P≤0.015%.

[0014] Furthermore, during the smelting process, 1600-1630kg / 100 tons of ferromanganese is added for manganese boiling; 250kg / 100 tons of ferrosilicon, 350kg / 100 tons of aluminum ingots, and 210-230kg / 100 tons of steel are added for deoxidation and alloying; the slag removal temperature is 1630°C, and the slag removal amount is not less than 95%.

[0015] Furthermore, during the LF refining process, the temperature of the molten steel entering the LF is not less than 1500° C., argon is passed, the argon pressure is controlled at 0.5-0.8 MPa, and electric heating is applied for not less than 35 minutes; diffusion deoxidizers SiC powder and SiFe powder are added for diffusion deoxidation, with a total amount of 58-80 kg / 100 tons of steel. After the refined slag turns white, SiC powder is added in multiple batches, 5-8 kg / time.

[0016] Furthermore, during the LF refining process, before entering the VD degassing, S is controlled below 0.005% and the steam pressure is controlled at 0.85-1.2 MPa.

[0017] Furthermore, the argon flow rate control during the VD vacuum degassing operation is as follows: when the vacuum degree is greater than 67Pa, the argon flow rate is 70 to 120NL / min; when the vacuum degree is less than or equal to 67Pa, the argon flow rate is 230 to 350NL / min.

[0018] Furthermore, Al is added to the steel after the VD vacuum degassing, and the Al content is controlled to be 0.010-0.035%.

[0019] Furthermore, the starting rolling temperature is 1100-1150°C, and the final rolling temperature is 880-950°C.

[0020] Beneficial effects of the present invention:

[0021] The present invention obtains ferrite + pearlite structure through reasonable chemical composition design, as well as control of ingredients during smelting, LF furnace deoxidizer type, alloy addition order, deoxidizer addition time, aluminum content in molten steel, vacuum degassing, microalloying, precise control of pouring temperature and speed, heating temperature during rolling and pit entry temperature, etc., and the manufactured high-hardness mining round link chain steel does not need to be annealed or other heat treatments after rolling. The hardness of the steel is 210-240HBW under natural cooling, and the surface and core hardness are basically the same, and the processing performance is good, which can fully meet the current small-size mining round link chain steel use requirements. After inspection and analysis, the high-hardness mining round link chain steel prepared by the present invention has dense low-multiple structure, low inclusion level, high flaw detection quality grade, and high material cleanliness. The high-hardness mining round link chain steel of the present invention has simple preparation process, low cost, energy saving and environmental protection, and has positive significance for promoting the development of mining round link chain steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a microscopic photograph of the structure morphology of the high-hardness mining round link chain steel prepared in Example 1, magnified 200 times;

[0023] Figure 2 This is a microscopic photograph of the structure morphology of the high-hardness mining round link chain steel prepared in Example 1, magnified 500 times;

[0024] Figure 3 This is a microscopic photograph of the organizational morphology of the high-hardness mining round link chain steel prepared in Example 1, magnified 1000 times. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below in conjunction with the embodiments, but it is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention shall be included in the protection scope of the present invention. The process equipment or devices not specifically noted in the following embodiments are all conventional equipment or devices in the art. If not specifically specified, the raw materials used in the embodiments of the present invention can be obtained commercially; if not specifically specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0026] Example 1

[0027] This embodiment provides a method for preparing high-hardness mining round link chain steel, and the preparation process includes converter BOF smelting → LF → VD → continuous casting → insulation → material production.

[0028] During the electric furnace smelting process of this embodiment:

[0029] The steel charge consists of 5wt% return steel and 95wt% pig iron, with a carbon content of 1.5-1.8%.

[0030] The slag is composed of lime and light-burned dolomite. The amount of lime and light-burned dolomite is adjusted according to the slag conditions. The total amount of slag is 1550Kg / 100 tons of steel.

[0031] After the slag is fully melted, the temperature reaches 1620°C and oxidation begins; the oxygen blowing pressure is controlled at 0.3-0.7 MPa; the decarburization amount is ≥0.35%.

[0032] The components and contents at the end of oxidation: C is 0.19%, P is 0.012%;

[0033] Add 1600-1630kg ferromanganese / 100 tons of steel to perform manganese boiling;

[0034] 250kg of ferrosilicon per 100 tons of steel, 350kg of aluminum ingots per 100 tons of steel, and 210-230kg of ferrovanadium per 100 tons of steel are used for deoxidation and alloying; the slag removal temperature is 1630℃, and the slag removal amount is ≥95%.

[0035] The composition is appropriate, the steel is tapped at a temperature ≥1560°C, and the final composition of the steel is controlled at C: 0.19-0.23%, P: 0.012%.

[0036] During the LF refining process of this embodiment:

[0037] The temperature of the molten steel entering the LF is 1550°C, argon is passed, the argon pressure is controlled at 0.5-0.8MPa, and electric heating is applied for 35 minutes.

[0038] Lime is added appropriately to adjust the slag according to the S content in the steel and the slag condition. Diffusion deoxidizers SiC powder and SiFe powder are added according to the requirements of the variety and composition for diffusion deoxidation, with a total amount of 58kg / 100 tons of steel.

[0039] During LF refining, the white slag is kept for ≥40 minutes. After the slag turns white, SiC powder is added in batches, 5 kg / time.

[0040] According to the analysis results of the bulk sample, the composition is adjusted according to the internal control composition requirements, and the aluminum content is adjusted to 0.040%-0.060%. Heating and heating, sampling and composition analysis, according to the composition results, fine-tuning the composition according to the internal control composition requirements; the composition meets the requirements, the temperature is 1670-1680℃, and VD is degassed. Before degassing, S is controlled below 0.005%, and the steam pressure is controlled at 0.85-1.2Mpa.

[0041] During the VD vacuum degassing process in this embodiment:

[0042] During vacuum (VD) degassing, evacuate the air and keep the vacuum degree ≤67Pa for 30min before breaking the vacuum; argon flow control during degassing operation: when the vacuum degree is greater than 67Pa, the argon flow rate is 70-120NL / min, and when the vacuum degree is ≤67Pa, the argon flow rate is 230-350NL / min.

[0043] After VD, it is not allowed to add Al ingots, and only feeding Al wire is allowed to adjust the Al content in the steel.

[0044] After breaking the vacuum, Al is added to the steel, and the Al content is controlled at 0.010-0.035%. In order to allow the inclusions to fully float and to make the chemical composition of the molten steel uniform, weak argon stirring is performed for 25 minutes after the addition of Al is completed before casting.

[0045] During the continuous casting process of this embodiment:

[0046] The pouring temperature of the steel is controlled at the ladle temperature: 1530℃ and the pouring temperature 1525℃.

[0047] During the rolling and slow cooling process of this embodiment:

[0048] During rolling, the steel obtained by continuous casting is subjected to high temperature diffusion treatment in order to reduce segregation and make carbides evenly distributed in the steel. The heating temperature is controlled at 1170-1205°C and the high temperature diffusion time is controlled at 1.5-2.0 hours.

[0049] The starting rolling temperature is 1100-1150°C, and the final rolling temperature is 880-950°C;

[0050] In order to achieve the ideal structure of steel after rolling, the steel is cooled to 350℃ on a cooling bed and then pile cooled.

[0051] The chemical composition of the steel prepared in this example is shown in Table 1.

[0052] Table 1 Composition of steel materials / %

[0053]

[0054] Figure 1 , Figure 2 and Figure 3 This is a microscopic photograph of the organizational morphology of the high-hardness mining round link chain steel prepared in Example 1. As can be seen from the figure, the obtained organization is ferrite + pearlite (extremely fine).

[0055] The hardness of the steel obtained in this embodiment was tested by conventional methods in the art. The results are shown in Table 2.

[0056] Table 2 Hardness and structure of steel / %

[0057]

[0058] Example 2

[0059] This embodiment provides a method for preparing high-hardness mining round link chain steel, and the preparation process includes electric furnace EAF smelting → LF → VD → continuous casting → insulation → material production.

[0060] In the converter smelting process of this embodiment:

[0061] The steel charge consists of 33wt% return steel and 67wt% pig iron, with a carbon content of 1.5-1.7%.

[0062] The slag is composed of lime and light-burned dolomite. The amount of lime and light-burned dolomite is adjusted according to the slag conditions. The total amount of slag is 1550Kg / 100 tons of steel.

[0063] After the slag is fully melted, the temperature reaches 1620°C and oxidation begins; the oxygen blowing pressure is controlled at 0.3-0.7 MPa; the decarburization amount is ≥0.35%.

[0064] The components and contents at the end of oxidation: C is 0.15%, P is 0.007%;

[0065] Add 1600-1630kg ferromanganese / 100 tons of steel to perform manganese boiling;

[0066] 290kg ferrosilicon / 100 tons of steel, 350kg aluminum ingot / 100 tons of steel, 210-230kg ferrochrome / 100 tons of steel are used for deoxidation and alloying; the slag removal temperature is 1630℃, and the slag removal amount is ≥95%.

[0067] The composition is appropriate, the steel is tapped at a temperature ≥1560°C, and the final composition of the steel is controlled at C: 0.15%, P: 0.007%.

[0068] During the LF refining process of this embodiment:

[0069] The temperature of the molten steel entering the LF is 1550°C, argon is passed, the argon pressure is controlled at 0.5-0.8MPa, and electric heating is applied for 35 minutes.

[0070] Lime is added appropriately to adjust the slag according to the S content and slag condition in the steel. Diffusion deoxidizer SiC powder is added for diffusion deoxidation according to the requirements of the steel type and composition, with a total amount of 78kg / 100 tons of steel.

[0071] During LF refining, the white slag is kept for ≥40 minutes. After the slag turns white, SiC powder is added in batches, 8 kg / time.

[0072] According to the analysis results of the bulk sample, the composition is adjusted according to the internal control composition requirements, and the aluminum content is adjusted to 0.040%-0.060%. Heating and heating, sampling and composition analysis, according to the composition results, fine-tuning the composition according to the internal control composition requirements; the composition meets the requirements, the temperature is 1670-1680℃, and VD is degassed. Before degassing, S is controlled below 0.005%, and the steam pressure is controlled at 0.85-1.2Mpa.

[0073] During the RH vacuum degassing process of this embodiment:

[0074] During vacuum (RH) degassing, evacuate the air and keep the vacuum degree ≤67Pa for 20min before breaking the vacuum; argon flow control during degassing operation: when the vacuum degree is greater than 67Pa, the argon flow rate is 70-120NL / min; when the vacuum degree is ≤67Pa, the argon flow rate is 230-350NL / min.

[0075] After RH, it is not allowed to add Al ingots, and only feeding Al wire is allowed to adjust the Al composition in the steel.

[0076] After breaking the vacuum, Al is added to the steel, and the Al content is controlled at 0.010-0.035%. In order to allow the inclusions to fully float and to make the chemical composition of the molten steel uniform, weak argon stirring is performed for 30 minutes after the addition of Al is completed before casting.

[0077] During the continuous casting process of this embodiment:

[0078] The pouring temperature of the steel is controlled at the ladle temperature: 1530℃ and the pouring temperature 1525℃.

[0079] During the rolling and slow cooling process of this embodiment:

[0080] During rolling, the steel obtained by continuous casting is subjected to high temperature diffusion treatment in order to reduce segregation and make carbides evenly distributed in the steel. The heating temperature is controlled at 1170-1205°C and the high temperature diffusion time is controlled at 1.5-2.0 hours.

[0081] The starting rolling temperature is 1100-1150°C, and the final rolling temperature is 880-950°C;

[0082] In order to achieve the ideal structure of steel after rolling, the steel is cooled to 350℃ on a cooling bed and then pile cooled.

[0083] The chemical composition of the steel prepared in this example is shown in Table 3.

[0084] Table 3 Composition of steel materials / %

[0085]

[0086] The hardness of the steel obtained in this embodiment was tested by conventional methods in the art. The results are shown in Table 4.

[0087] Table 4 Hardness and structure of steel / %

[0088]

[0089] Comparative Example 1

[0090] This comparative example provides a method for preparing round link chain steel for mining, and the preparation process includes electric furnace EAF smelting→LF→continuous casting→insulation→material production.

[0091] In the converter smelting process of this embodiment:

[0092] The steel charge consists of 23wt% return steel and 77wt% pig iron, with a carbon content of 1.3-1.5%.

[0093] The slag is composed of lime and light-burned dolomite. The amount of lime and light-burned dolomite is adjusted according to the slag conditions. The total amount of slag is 1350Kg / 100 tons of steel.

[0094] After the slag is fully melted, the temperature reaches 1610°C and oxidation begins; the oxygen blowing pressure is controlled at 0.3-0.7 MPa; the decarburization amount is ≥0.35%.

[0095] The components and contents at the end of oxidation: C is 0.08%, P is 0.016%;

[0096] Add 1200-1270kg ferromanganese / 100 tons of steel to perform manganese boiling;

[0097] Ferrosilicon 230kg / 100 tons of steel, aluminum ingot 100kg / 100 tons of steel, ferrochrome 200-220kg / 100 tons of steel are used for deoxidation and alloying.

[0098] The composition is appropriate, the steel is tapped at a temperature ≥ 1560°C, and the final composition of the steel is controlled at C: 0.15%, P: 0.016%.

[0099] During the LF refining process of this embodiment:

[0100] The temperature of the molten steel entering the LF is 1550°C, argon is passed, the argon pressure is controlled at 0.5-0.8MPa, and electric heating is applied for 25 minutes.

[0101] Lime is added appropriately to adjust the slag according to the S content and slag condition in the steel. Diffusion deoxidizer SiC powder is added for diffusion deoxidation according to the requirements of the steel type and composition, with a total amount of 38kg / 100 tons of steel.

[0102] During LF refining, the white slag retention time is ≥20 minutes.

[0103] According to the analysis results of the bulk sample, adjust the composition according to the internal control composition requirements. Take samples for composition analysis, and fine-tune the composition according to the internal control composition requirements based on the composition results; if the composition meets the requirements, the temperature is 1550-1580℃, and the ladle is poured.

[0104] During the continuous casting process of this embodiment:

[0105] The pouring temperature of the steel is controlled at the ladle temperature: 1553℃ and the pouring temperature 1535℃.

[0106] During the rolling and slow cooling process of this embodiment:

[0107] During rolling of the steel obtained by continuous casting, in order to make the carbides evenly distributed in the steel, high temperature diffusion treatment is adopted, the heating temperature is controlled at 1120-1170°C, and the high temperature diffusion time is controlled at 1.5-2.0 hours;

[0108] The starting rolling temperature is 930~980℃, and the final rolling temperature is ≤850℃;

[0109] In order to achieve the ideal structure of steel after rolling, the steel is cooled to 650℃ on a cooling bed and then slow cooled in a slow cooling pit.

[0110] The chemical composition of the steel prepared in this comparative example is shown in Table 5.

[0111] Table 5 Composition of steel materials / %

[0112] C Si Mn V Al P S 0.27 0.26 1.36 0.145 0.015 0.017 0.005

[0113] The hardness of the steel obtained in this embodiment was tested by conventional methods in the art. The results are shown in Table 6.

[0114] Table 6 Hardness and structure of steel / %

[0115]

[0116] By comparison, it can be seen that the present invention further improves the hardness of the steel through reasonable chemical composition design and control of various parameters in the smelting, refining, continuous casting and rolling processes.

Claims

1. A high-hardness round-link chain steel for mining, characterized in that: The chemical composition by weight percentage includes: C: 0.21-0.29%, Si: 0.15-0.40%, Mn: 1.10-1.55%, V: 0.10-0.25%, Al: 0.010-0.035%, P≤0.025%, S: ≤0.025%, and the rest is Fe and unavoidable impurities.

2. A method for preparing the high-hardness round link chain steel for mining as claimed in claim 1, characterized in that: Including smelting → LF refining → VD vacuum degassing → continuous casting → rolling → material production; During the smelting process, when the final composition of the steel is controlled to be not less than 0.08% C, P≤0.015%, and the steel temperature is not less than 1560°C, the steel enters LF refining; During the LF refining process, argon is passed, and the white slag is kept for no less than 40 minutes; sampling is performed to analyze the composition, and the composition is fine-tuned according to the internal control composition requirements based on the composition results; when the composition meets the requirements, the temperature is 1650-1660° C. and enters the VD vacuum degassing; During the VD vacuum degassing process, vacuum is drawn, and the vacuum degree is maintained at ≤67Pa for not less than 30 minutes before breaking the vacuum. After breaking the vacuum, Al is added to the steel, and after the end, weak argon stirring is performed for 25 minutes before casting, and the pouring temperature is 1520-1550°C; When the obtained steel is rolled, high-temperature diffusion treatment is adopted, the heating temperature is controlled at 1170-1205°C, and the high-temperature diffusion time is controlled at 1.5-2.0 hours; after rolling, the steel is cooled to 350°C on a cooling bed and then pile-cooled.

3. The method for preparing a high-hardness round link chain steel for mining according to claim 2, characterized in that: In the smelting process, the steel charge is composed of returned steel and pig iron, the carbon content of the steel charge is 1.0-1.5%, the slag is composed of lime and light-burned dolomite, and the total amount of slag is 1550 kg / 100 tons of steel; after the slag is fully melted, the temperature is 1620°C and oxidation begins; the oxygen blowing pressure is controlled at 0.3-0.7 MPa; the decarburization amount is not less than 0.35%; and the oxidation end point C is 0.19-0.23%.

4. A method for preparing a high-hardness round link chain steel for mining according to claim 2 or 3, characterized in that: During the smelting process, 1600-1630kg ferromanganese is added per 100 tons of steel for manganese boiling; 250kg ferrosilicon is added per 100 tons of steel, 350kg aluminum ingots are added per 100 tons of steel, and 210-230kg ferrovanadium is added per 100 tons of steel for deoxidation and alloying; the slag removal temperature is 1630°C, and the slag removal amount is not less than 95%.

5. The method for preparing a high-hardness round link chain steel for mining according to claim 4, characterized in that: During the LF refining process, the temperature of the molten steel entering the LF is not less than 1500° C., argon gas is passed, the argon gas pressure is controlled at 0.5-0.8 MPa, and electric heating is applied for not less than 35 minutes; diffusion deoxidizers SiC powder and SiFe powder are added for diffusion deoxidation, with a total amount of 58-80 kg / 100 tons of steel. After the refined slag turns white, SiC powder is added in multiple batches, 5-8 kg / time.

6. The method for preparing a high-hardness round link chain steel for mining according to claim 5, characterized in that: During the LF refining process, before entering the VD degassing, S is controlled below 0.005% and the steam pressure is controlled at 0.85-1.2 MPa.

7. The method for preparing a high-hardness round link chain steel for mining according to claim 6, characterized in that: The argon flow rate control during the VD vacuum degassing operation is as follows: when the vacuum degree is greater than 67Pa, the argon flow rate is 70 to 120NL / min; when the vacuum degree is less than or equal to 67Pa, the argon flow rate is 230 to 350NL / min.

8. The method for preparing a high-hardness round link chain steel for mining according to claim 7, characterized in that: After the VD vacuum degassing, Al is added to the steel to control the Al content to 0.010-0.035%.

9. The method for preparing a high-hardness round link chain steel for mining according to claim 8, characterized in that: The starting rolling temperature of the rolling is 1100-1150°C, and the final rolling temperature is 880-950°C.

Images