Large-specification mining round-link chain steel and preparation method thereof

Abstract

The invention relates to large-specification mining round-link chain steel and a preparation method thereof, and belongs to the technical field of steel preparation. In order to solve the problems of low hardness and poor hardenability of the large-specification mining round-link chain steel, the invention provides a preparation method of the large-specification mining round-link chain steel, which comprises the steps of electric furnace or converter smelting, LF refining, VD or RH vacuum degassing, continuous casting, rolling and heat preservation, heat treatment and material production. Through reasonable chemical component design and accurate control over smelting, refining, vacuum degassing, rolling, heat preservation and heat treatment procedures, the obtained large-specification mining round-link chain steel is subjected to heat treatment after rolling, the metallographic structure of the steel subjected to heat treatment is changed into tempered sorbite from bainite obtained through rolling, the hardness of the cross section is 340-375 HBW, and the tensile strength of the steel is higher than that of the steel. And the hardness of the surface is basically consistent with that of the center, the macrostructure is compact, the inclusion level is low, the flaw detection quality level is high, and the material cleanliness is high.

Description

Technical Field

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

[0002] Mining round link chain steel is used for coal mining machines in mines. The weight that the chain can pull is positively correlated with the output of the coal mining machine. There are a large number of large coal mines with a capacity of tens of millions of tons in my country, so there are great requirements for the working capacity of coal mining machines. The steel bars of mining round link chain steel currently used in the market are rolled from steel mills, with small specifications and limited weight that can be pulled.

[0003] With the advancement of technology, the output requirements of coal mining machines in mines are gradually increasing, so there is an urgent need to increase the weight of the chain traction. The larger the chain size, the greater the weight it can haul to a certain extent. However, due to the problem of diameter, the heat treatment effect of large-sized mining round link chain steel is often not ideal, and the hardness of the cross section and the hardenability of the steel are difficult to guarantee. Summary of the invention

[0004] In order to solve the problem of low hardness and poor hardenability of large-sized round-link chain steel for mining, the present invention provides a large-sized round-link chain steel for mining and a preparation method thereof.

[0005] The technical solution of the present invention:

[0006] A large-size round link chain steel for mining, the chemical composition of which is as follows by weight percentage: C: 0.22-0.25%, Si: 0.10-0.25%, Mn: 1.15-1.45%, Cr: 0.50-0.75%, Mo: 0.50-0.60%, S≤0.15%, P≤0.15%, and the rest is Fe and unavoidable impurities.

[0007] Furthermore, the specification of the large-size mining ring steelmaking is Φ48mm.

[0008] A method for preparing the large-size mining round link chain steel comprises electric furnace or converter smelting → LF refining → VD or RH vacuum degassing → continuous casting → rolling and heat preservation → heat treatment → material production;

[0009] During the smelting process, the final composition of the steel is controlled to be not less than 0.06% C, P ≤ 0.015%, and the steel temperature is not less than 1500℃, and the steel enters LF refining;

[0010] During the LF refining process, argon gas is passed through, and the white slag is kept for no less than 20 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 1630-1680℃ and enters the VD vacuum degassing;

[0011] During the VD or RH vacuum degassing process, vacuum is drawn and the vacuum degree is maintained at ≤67Pa for not less than 25 minutes before breaking the vacuum. After breaking the vacuum, the composition of the steel is not allowed to be adjusted. Casting is performed after weak argon stirring for 35 minutes;

[0012] When the obtained steel is rolled, high temperature diffusion treatment is adopted, the heating temperature is controlled at 1250-1280°C, and the high temperature diffusion time is controlled at 3.5-4.0 hours; in order to achieve the ideal structure after rolling, the steel is cooled to 450°C on the cooling bed and then put into the insulation pit, and the insulation time in the pit is not less than 72 hours;

[0013] When the obtained steel is heat treated, a hood annealing furnace and a hood tempering furnace are used. The heat treatment process includes an annealing process and a tempering process. The annealing process is 650-670°C, 1.5h, the tempering process is 870-890°C, 1h, water quenching, 390-410°C tempering, 1.5h, and water cooling.

[0014] 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 1350Kg / 100 tons of steel; after the slag is fully melted, the temperature begins to oxidize at 1650°C; the oxygen blowing pressure is controlled at 0.3-0.7MPa; the decarburization amount is not less than 0.35%; and the oxidation end point C is 0.12-0.15%.

[0015] Furthermore, during the smelting process, 630-650 kg / 100 tons of ferromanganese is added for manganese boiling; 750 kg / 100 tons of ferrosilicon, 270 kg / 100 tons of aluminum ingots, and 630-650 kg / 100 tons of ferrochrome are added for deoxidation and alloying; the slag removal temperature is 1650° C., and the slag removal amount is not less than 95%.

[0016] Furthermore, during the LF refining process, the temperature of the molten steel entering the LF is not less than 1550°C, argon is passed, the argon pressure is controlled at 0.6-0.9 MPa, and electric heating is applied for not less than 30 minutes; diffusion deoxidizers SiC powder and SiFe powder are added for diffusion deoxidation, with a total amount of 48 kg / 100 tons of steel.

[0017] Furthermore, the target composition of the refined slag is: CaO: 50-55%, SiO2: 5-10%, MgO: 5-8%, Al2O3: 20-25%. After the slag turns white, SiC powder is added in batches, 5 kg / time.

[0018] Furthermore, during the LF refining process, before entering the VD or RH vacuum degassing, S is controlled below 0.005% and the steam pressure is controlled at 0.85-1.2 MPa.

[0019] Furthermore, the argon flow rate control during the VD or RH vacuum degassing operation is: 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.

[0020] Furthermore, the starting rolling temperature is 980-1120°C, and the final rolling temperature is 900-950°C.

[0021] Beneficial effects of the present invention:

[0022] The present invention obtains bainite structure through reasonable chemical composition design, as well as control of ingredients during smelting, LF furnace deoxidizer type, alloy addition order, slag composition, 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. The manufactured large-scale mining round link chain steel is heat treated after rolling. After heat treatment, the metallographic structure of the steel changes from bainite obtained by rolling to tempered troostite, the hardness of the cross section is 340-375 HBW, and the surface hardness is basically the same as the core hardness. After inspection and analysis, the large-scale mining round link chain steel prepared by the present invention has dense macrostructure, low inclusion level, high flaw detection quality grade, and high material cleanliness. The preparation process of the large-scale mining round link chain steel of the present invention is reasonable and low cost, which has positive significance for promoting the development of large-scale mining round link chains. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a micrograph of the hot-rolled structure morphology of the steel prepared in Example 1;

[0024] Figure 2 This is a microscopic photograph of the structural morphology of the steel prepared in Example 1 after annealing during heat treatment;

[0025] Figure 3 This is a microscopic photograph of the structure morphology of the steel prepared in Example 1 after heat treatment;

[0026] Figure 4 This is a micrograph of the structural morphology of the steel prepared in Example 2 after heat treatment. DETAILED DESCRIPTION

[0027] 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.

[0028] Example 1

[0029] This embodiment provides a method for preparing large-size mining round link chain steel, and the preparation process includes electric furnace EAF smelting → LF → VD → continuous casting → insulation → heat treatment → material production.

[0030] During the electric furnace smelting process of this embodiment:

[0031] The steel charge consists of 15wt% return steel and 85wt% pig iron, with a carbon content of 1.0%.

[0032] 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.

[0033] After the slag is fully melted, the temperature reaches 1650°C and oxidation begins; the oxygen blowing pressure is controlled at 0.3MPa; the decarburization amount is ≥0.35%.

[0034] The components and contents at the end of oxidation: C is 0.12%, P is 0.015%;

[0035] Add 630kg / 100 tons of ferromanganese for manganese boiling; 750kg / 100 tons of ferrosilicon, 270kg / 100 tons of aluminum ingots and 630kg / 100 tons of ferrochrome for deoxidation and alloying; the slag removal temperature is 1650℃ and the slag removal amount is ≥95%.

[0036] The composition is appropriate, the steel is tapped at a temperature ≥1600°C, and the final composition of the steel is controlled to be C ≥0.06% and P ≤0.015%.

[0037] During the LF refining process of this embodiment:

[0038] The temperature of the molten steel entering the LF is 1580℃, argon is passed, the argon pressure is controlled at 0.6MPa, and electric heating is applied for 35 minutes.

[0039] 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 for diffusion deoxidation according to the requirements of the steel type and composition, with a total amount of 48kg / 100 tons of steel.

[0040] Target composition of refined slag: CaO: 50%, SiO2: 5%, MgO: 5%, Al2O3: 20%.

[0041] During LF refining, the white slag is kept for ≥35 minutes. After the slag turns white, SiC powder is added in batches, 5 kg / time.

[0042] 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%. Heating and heating, sampling and composition analysis, according to the composition results, the composition is fine-tuned according to the internal control composition requirements; the composition meets the requirements, the temperature is 1670℃, and VD is degassed. Before degassing, S is controlled below 0.005%, and the steam pressure is controlled at 0.85Mpa.

[0043] During the VD vacuum degassing process in this embodiment:

[0044] During vacuum (VD) degassing, evacuate the air and keep the vacuum degree ≤67Pa for 25min before breaking the vacuum. Argon flow control during degassing operation: when the vacuum degree is greater than 67Pa, the argon flow rate is 70NL / min; when the vacuum degree is ≤67Pa, the argon flow rate is 230NL / min.

[0045] After breaking the vacuum, the steel composition is not allowed to be adjusted, and casting is performed after weak argon stirring for 35 minutes.

[0046] During the continuous casting process of this embodiment:

[0047] The pouring temperature of the steel is controlled at the ladle temperature: 1532℃ and the pouring temperature 1525℃.

[0048] During the rolling and slow cooling process of this embodiment:

[0049] 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 1250°C and the high temperature diffusion time is controlled at 4.0 hours.

[0050] The starting rolling temperature is 980℃ and the final rolling temperature is 900℃;

[0051] In order to achieve the ideal structure after rolling, the steel is cooled to 450℃ on a cooling bed and then put into a holding pit for ≥72h.

[0052] During the heat treatment process of this embodiment:

[0053] The heat treatment process of steel is divided into annealing process and tempering process.

[0054] Annealing process of bell annealing furnace: 650℃, 1.5h, cooling with the furnace;

[0055] Hood-type tempering furnace tempering process: 870℃, 1h, water quenching, 390℃ tempering, 1.5h, water cooling.

[0056] The chemical composition of the steel prepared in this example is shown in Table 1.

[0057] Table 1 Composition of steel materials / %

[0058] Steel Type C Si Mn P S Cr Ni Mo Al Example 1 0.23 0.19 1.22 0.009 0.005 0.57 1.04 0.56 0.025

[0059] Figure 1 This is a micrograph of the hot-rolled structure morphology of the steel prepared in Example 1. As can be seen from the 500-fold image, the obtained structure is bainite.

[0060] Figure 2 This is a micrograph of the structural morphology of the steel prepared in Example 1 after annealing during heat treatment. From the 500-fold image, it can be seen that the obtained structure is troostite + granular bainite (very small).

[0061] Figure 3 This is a micrograph of the structure morphology of the steel prepared in Example 1 after heat treatment. It can be seen from the 500-fold image that the obtained structure is tempered troostite.

[0062] The hardness and hardenability of the steel obtained in this example were tested using conventional methods in the art. The results are shown in Tables 2 and 3.

[0063] Table 2 Hardness and structure of steel / %

[0064]

[0065] Table 3 Hardenability of steel / HRC

[0066] Steel Type J5 J7 J9 J11 J13 Example 1 47.6 46.9 46.3 46.0 45.8

[0067] Example 2

[0068] This embodiment provides a method for preparing large-size mining round link chain steel, and the preparation process includes converter BOF smelting → LF → VD → continuous casting → insulation → heat treatment → material production.

[0069] In the converter smelting process of this embodiment:

[0070] The steel charge consists of 5wt% return steel and 95wt% pig iron, with a carbon content of 1.5%.

[0071] 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.

[0072] After the slag is fully melted, the temperature reaches 1650°C and oxidation begins; the oxygen blowing pressure is controlled at 0.7MPa; the decarburization amount is ≥0.35%.

[0073] The components and contents at the end of oxidation: C is 0.15%, P is 0.015%;

[0074] Add 650kg / 100 tons of ferromanganese for manganese boiling; 750kg / 100 tons of ferrosilicon, 270kg / 100 tons of aluminum ingots and 650kg / 100 tons of ferrochrome for deoxidation and alloying; the slag removal temperature is 1650℃ and the slag removal amount is ≥95%.

[0075] The composition is appropriate, the steel is tapped at a temperature ≥1600°C, and the final composition of the steel is controlled to be C ≥0.06% and P ≤0.015%.

[0076] During the LF refining process of this embodiment:

[0077] The temperature of the molten steel entering the LF is 1580℃, argon is passed, the argon pressure is controlled at 0.9MPa, and electric heating is applied for 35 minutes.

[0078] 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 for diffusion deoxidation according to the requirements of the steel type and composition, with a total amount of 48kg / 100 tons of steel.

[0079] Target composition of refined slag: CaO: 55%, SiO2: 10%, MgO: 8%, Al2O3: 25%.

[0080] During LF refining, the white slag is kept for ≥35 minutes. After the slag turns white, SiC powder is added in batches, 5 kg / time.

[0081] 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 0.070%. 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 1680℃, and VD degassing is carried out. Before degassing, S is controlled below 0.005%, and the steam pressure is controlled at 1.2Mpa.

[0082] During the RH vacuum degassing process of this embodiment:

[0083] During vacuum (RH) degassing, evacuate the air and keep the vacuum degree ≤67Pa for 25min before breaking the vacuum. Argon flow control during degassing operation: when the vacuum degree is greater than 67Pa, the argon flow rate is 120NL / min; when the vacuum degree is ≤67Pa, the argon flow rate is 350NL / min.

[0084] After breaking the vacuum, the steel composition is not allowed to be adjusted, and casting is performed after weak argon stirring for 35 minutes.

[0085] During the continuous casting process of this embodiment:

[0086] The pouring temperature of the steel is controlled at the ladle temperature: 1550℃ and the pouring temperature 1535℃.

[0087] During the rolling and slow cooling process of this embodiment:

[0088] During rolling, the steel obtained by continuous casting is treated with high temperature diffusion to reduce segregation and make carbides evenly distributed in the steel. The heating temperature is controlled at 1280°C and the high temperature diffusion time is controlled at 3.5 hours.

[0089] The starting rolling temperature is 1120℃ and the final rolling temperature is 950℃;

[0090] In order to achieve the ideal structure after rolling, the steel is cooled to 450℃ on a cooling bed and then put into a holding pit for ≥72h.

[0091] During the heat treatment process of this embodiment:

[0092] The heat treatment process of steel is divided into annealing process and tempering process.

[0093] Annealing process of bell annealing furnace: 670℃, 1.5h, cooling with the furnace;

[0094] Hood-type tempering furnace tempering process: 890℃, 2h, water quenching, 410℃ tempering, 1.5h, water cooling.

[0095] The chemical composition of the steel prepared in this example is shown in Table 4.

[0096] Table 4 Composition of steel materials / %

[0097] Steel Type C Si Mn P S Cr Ni Mo Al Example 2 0.23 0.19 1.21 0.009 0.005 0.56 1.04 0.55 0.025

[0098] Figure 4 This is a microscopic photograph of the structural morphology of the steel prepared in Example 2. As can be seen from the 500-fold image, the obtained structure is fine tempered troostite.

[0099] The hardness and hardenability of the steel obtained in this example were tested using conventional methods in the art. The results are shown in Tables 5 and 6.

[0100] Table 5 Hardness and structure of steel / %

[0101]

[0102] Table 6 Hardenability of steel / HRC

[0103] Steel Type J5 J7 J9 J11 J13 Example 2 46.6 46.2 45.8 45.3 44.8

[0104] Comparative Example 1

[0105] The preparation method of this comparative example 1 is completely consistent with that of Example 1, and the preparation process includes electric furnace EAF smelting

[0106] →LF→VD→continuous casting→insulation→heat treatment→material production.

[0107] The chemical composition of the steel prepared in this comparative example is shown in Table 7.

[0108] Table 7 Composition of steel materials / %

[0109] Steel Type C Si Mn P S Cr Ni Mo Al Comparative Example 1 0.23 0.11 1.25 0.009 0.004 0.45 1.04 0.53 0.033

[0110] The hardness and hardenability of the steel obtained in this comparative example were tested by conventional methods in the art. The results are shown in Tables 8 and 9.

[0111] Table 8 Hardness and structure of steel / %

[0112]

[0113] Table 9 Hardenability of steel / HRC

[0114] Steel Type J5 J7 J9 J11 J13 Example 1 46.2 45.6 45.0 44.6 44.2

Claims

1. A large-size round link chain steel for mining, characterized in that: The chemical composition by weight percentage includes: C: 0.22-0.25%, Si: 0.10-0.25%, Mn: 1.15-1.45%, Cr: 0.50-0.75%, Mo: 0.50-0.60%, S≤0.15%, P≤0.15%, and the rest is Fe and unavoidable impurities.

2. A large-size round link chain steel for mining according to claim 1, characterized in that: The specification of the large-size mining ring steelmaking is Φ48mm.

3. A method for preparing large-size round link chain steel for mining as claimed in claim 1 or 2, characterized in that: Including electric furnace or converter smelting → LF refining → VD or RH vacuum degassing → continuous casting → rolling and insulation → heat treatment → material production; During the smelting process, the final composition of the steel is controlled to be not less than 0.06% C, P ≤ 0.015%, and the steel temperature is not less than 1500℃, and the steel enters LF refining; During the LF refining process, argon gas is passed through, and the white slag is kept for no less than 20 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 1630-1680℃ and enters the VD vacuum degassing; During the VD or RH vacuum degassing process, vacuum is drawn and the vacuum degree is maintained at ≤67Pa for not less than 25 minutes before breaking the vacuum. After breaking the vacuum, the composition of the steel is not allowed to be adjusted. Casting is performed after weak argon stirring for 35 minutes; When the obtained steel is rolled, high temperature diffusion treatment is adopted, the heating temperature is controlled at 1250-1280°C, and the high temperature diffusion time is controlled at 3.5-4.0 hours; in order to achieve the ideal structure after rolling, the steel is cooled to 450°C on the cooling bed and then put into the insulation pit, and the insulation time in the pit is not less than 72 hours; When the obtained steel is heat treated, a hood annealing furnace and a hood tempering furnace are used. The heat treatment process includes an annealing process and a tempering process. The annealing process is 650-670°C, 1.5h, the tempering process is 870-890°C, 1h, water quenching, 390-410°C tempering, 1.5h, and water cooling.

4. The method for preparing a large-size round link chain steel for mining according to claim 3, 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 1350 kg / 100 tons of steel; after the slag is fully melted, the temperature is 1650°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 0.12-0.15%.

5. The method for preparing a large-size round link chain steel for mining according to claim 4, characterized in that: During the smelting process, 630-650kg / 100 tons of steel ferromanganese is added for manganese boiling; 750kg / 100 tons of steel ferrosilicon, 270kg / 100 tons of steel aluminum ingots and 630-650kg / 100 tons of steel ferrochrome are added for deoxidation and alloying; the slag removal temperature is 1650°C and the slag removal amount is not less than 95%.

6. The method for preparing a large-size round link chain steel for mining according to claim 5, characterized in that: During the LF refining process, the temperature of the molten steel entering the LF is not less than 1550°C, argon gas is passed, the argon gas pressure is controlled at 0.6-0.9 MPa, and electric heating is applied for not less than 30 minutes; diffusion deoxidizers SiC powder and SiFe powder are added for diffusion deoxidation, with a total amount of 48kg / 100 tons of steel.

7. A method for preparing a large-size round link chain steel for mining according to claim 6, characterized in that: Target composition of refined slag: CaO: 50-55%, SiO2: 5-10%, MgO: 5-8%, Al2O3: 20-25%. After the slag turns white, add SiC powder in batches, 5kg / time.

8. A method for preparing a large-size round link chain steel for mining according to claim 7, characterized in that: During the LF refining process, before entering the VD or RH vacuum degassing, S is controlled below 0.005% and the steam pressure is controlled at 0.85-1.2 MPa.

9. A method for preparing a large-size round link chain steel for mining according to claim 8, characterized in that: The argon flow rate control during the VD or RH 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.

10. A method for preparing large-size round link chain steel for mining according to claim 9, characterized in that: The starting rolling temperature is 980-1120°C, and the final rolling temperature is 900-950°C.

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