Steel for engineering machinery and preparation method thereof

Abstract

The invention relates to steel for engineering machinery and a preparation method thereof, and belongs to the technical field of steel preparation. In order to solve the problems of high hardness and poor hardenability of the existing steel for the engineering machinery, the invention provides the steel for the engineering machinery, which comprises the following chemical components in percentage by weight: 0.16 to 0.21 percent of C, 0.20 to 0.35 percent of Si, 0.70 to 0.95 percent of Mn, 0.95 to 1.25 percent of Cr, 0.16 to 0.25 percent of Mo, 0.020 to 0.035 percent of S, less than or equal to 0.10 percent of Ni and the balance of Fe and inevitable impurities. The manufactured steel for the engineering machinery does not need to be subjected to annealing heat treatment after being rolled, the hardness of the steel in a heat preservation state is lower than 185 HBW, the hardness of the surface and the hardness of the center are basically consistent, cutting is easy, the machining performance is good, and the use requirements of the current steel for the engineering machinery can be completely met.

Description

Technical Field

[0001] The invention belongs to the technical field of steel preparation, and in particular relates to steel for engineering machinery and a preparation method thereof. Background Art

[0002] The field of engineering machinery involves urban and rural roads, urban infrastructure construction, national defense, water conservancy, electricity, transportation, energy industry, etc. It has a wide range of applications and a wide variety of products. With the rapid development of my country's industry and the need for energy conservation and environmental protection, the quality requirements for steel used in engineering machinery are constantly increasing.

[0003] The steel bars currently used in the market are rolled from steel mills. They have low technical requirements and are consumed in large quantities during use. For ease of processing, annealing is generally performed to keep the hardness of the material below 200HBW. If the hardness is higher than this, higher requirements are placed on the processing equipment. At present, the materials used for engineering machinery are mainly annealed 45Mn, 20CrMo and other steels. The hardness of 45Mn, 20CrMo and other steels used in hot rolling is generally around 200-240HBW, and the wear on the tool is high during cutting.

[0004] With the advancement of technology, downstream users have gradually increased their requirements for the hardenability of steel for engineering machinery. Steel needs to avoid bending before quenching and tempering, so it needs to be straightened. However, higher hardness steel will have residual stress inside after straightening, which will become the cause of quenching cracks during quenching, resulting in increased production costs. Annealing-straightening adds a heat treatment process, which is not good for the environment. Summary of the invention

[0005] In order to solve the problem that the existing steel for engineering machinery has high hardness and poor hardenability, the present invention provides a steel for engineering machinery and a preparation method thereof.

[0006] The technical solution of the present invention:

[0007] A steel for engineering machinery, the chemical composition of which is as follows by weight percentage: C: 0.16-0.21%, Si: 0.20-0.35%, Mn: 0.70-0.95%, Cr: 0.95-1.25%, Mo: 0.16-0.25%, S: 0.020-0.035%, Ni≤0.10%, and the rest is Fe and unavoidable impurities.

[0008] A method for preparing steel for engineering machinery, the preparation process includes electric furnace or converter smelting → LF refining → VD vacuum degassing → continuous casting → rolling and heat preservation → 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 1600°C, and the steel enters LF refining;

[0009] 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 1670-1680℃ and enters the VD vacuum degassing;

[0010] During the VD vacuum degassing process, vacuum is drawn, and the vacuum degree is maintained at ≤67Pa for not less than 10 minutes before breaking the vacuum. After breaking the vacuum, Al and S are added to the steel. After the vacuum is broken, weak argon is stirred for 15 minutes before casting. The pouring temperature is 1520-1550℃;

[0011] When the obtained steel is rolled, high-temperature diffusion treatment is adopted, the heating temperature is controlled at 1150-1205°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 650°C on a cooling bed and then entered into a holding pit, and the holding time in the pit is not less than 72 hours.

[0012] Furthermore, in the smelting process, the steel charge is composed of returned steel and pig iron, the carbon content of the steel charge is 1.0-1.2%, the slag is composed of lime and light-burned dolomite, and the total amount of slag is 1750Kg / 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 ≥0.35%; the oxidation end point C is 0.12-0.15%, and P≤0.015%.

[0013] Furthermore, during the smelting process, 130-150 kg / 100 tons of ferromanganese is added for manganese boiling; 90 kg / 100 tons of ferrosilicon, 100 kg / 100 tons of aluminum ingots, and 110-130 kg / 100 tons of ferrochrome are added for deoxidation and alloying; the slag removal temperature is 1630° C., and the slag removal amount is ≥95%.

[0014] 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 0.5-0.8MPa, and the electric heating is not less than 20 minutes; diffusion deoxidizer SiC powder and SiFe powder are added for diffusion deoxidation, with a total amount of 58kg / 100 tons of steel. The target composition of the refined slag is: CaO: 50-65%, SiO2: 5-10%, MgO: 3-6%, Al2O3: 20-30%, and after the slag turns white, SiC powder is added in multiple batches, 5kg / time.

[0015] 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.

[0016] 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.

[0017] Furthermore, Al and S are added to the steel after the VD vacuum degassing, and the order of addition is as follows: sulfur line needs to be added to the steel during the smelting process, and the Al content is first controlled to be 0.015-0.030%. After adding aluminum, weak argon is stirred for 10 minutes, and then sulfur line is added in three batches, each time with an interval of 3 minutes and medium argon stirring is maintained.

[0018] Furthermore, the starting rolling temperature of the rolling is not lower than 1150°C, and the final rolling temperature is not lower than 950°C.

[0019] Beneficial effects of the present invention:

[0020] The present invention obtains bainite + ferrite + a small amount of pearlite 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., and the manufactured engineering machinery steel does not need to be annealed and heat treated after rolling. The hardness of the steel in the insulation state is lower than 185HBW, and the hardness of the surface and the core is basically the same. It is easy to cut, has good processing performance, and excellent hardenability, which can fully meet the current use requirements of engineering machinery steel. After inspection and analysis, the engineering machinery steel prepared by the present invention has dense macrostructure, low inclusion level, high flaw detection quality grade, high material cleanliness, and can replace 45Mn, 20CrMo and other steels. The engineering machinery steel of the present invention has a simple preparation process, low cost, energy saving and environmental protection, and has positive significance for promoting the development of engineering machinery steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a microscopic photograph of the structure morphology of the steel for engineering machinery prepared in Example 1, magnified 100 times;

[0022] Figure 2 This is a microscopic photograph of the structure morphology of the steel for engineering machinery prepared in Example 1, magnified 500 times;

[0023] Figure 3 This is a microscopic photograph of the structure morphology of the steel for engineering machinery prepared in Example 2, magnified 100 times;

[0024] Figure 4 This is a microscopic photograph of the structural morphology of the steel for engineering machinery prepared in Example 2, magnified 500 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 steel for engineering machinery, and the preparation process includes electric furnace EAF smelting→LF→VD→continuous casting→insulation→material production.

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

[0029] The steel charge consists of 15wt% return steel and 85wt% pig iron, with a carbon content of 1.0-1.2%.

[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 1750Kg / 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 0.13%, P is 0.015%;

[0033] Add 130-150kg ferromanganese per 100 tons of steel to perform manganese boiling;

[0034] 90kg of ferrosilicon per 100 tons of steel, 100kg of aluminum ingots per 100 tons of steel, and 110-130kg of ferrochrome 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 ≥1600°C, and the final composition of the steel is controlled at C: ≥0.06%, P: ≤0.015%.

[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 20 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] Target composition of refined slag: CaO: 50-65%, SiO2: 5-10%, MgO: 3-6%, Al2O3: 20-30%.

[0040] During LF refining, the white slag is kept for ≥20 minutes. After the slag turns white, SiC powder is added in batches, 5 kg / time.

[0041] 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 0.020%-0.040%. 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.

[0042] During the VD vacuum degassing process in this embodiment:

[0043] During vacuum (VD) degassing, evacuate the air and keep the vacuum degree ≤67Pa for 15min 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.

[0044] 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.

[0045] After breaking the vacuum, Al and S are added to the steel in the following order: sulfur line needs to be added to the steel during the smelting process. First, the Al content is controlled at 0.015-0.030%. After adding aluminum, weak argon stirring is performed for 10 minutes, and then sulfur line is added in three batches, with an interval of 3 minutes each time and medium argon stirring is maintained. In order to allow inclusions to fully float and to uniformly mix the chemical composition of the molten steel, Al and S are added to the steel and weak argon stirring is performed for 15 minutes before casting.

[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 1150-1205°C and the high temperature diffusion time is controlled at 1.5-2.0 hours.

[0050] The starting rolling temperature is ≥1150℃, and the final rolling temperature is ≥950℃;

[0051] In order to achieve the ideal structure of steel after rolling, the steel is cooled to 650℃ on a cooling bed and then put into a holding pit for ≥72h.

[0052] The chemical composition of the steel prepared in this example is shown in Table 1.

[0053] Table 1 Composition of steel materials / %

[0054]

[0055] Figure 1 and Figure 2 The microscopic photos of the structure morphology of the steel for engineering machinery prepared in this embodiment are magnified 100 times and 500 times respectively. It can be seen from the 100 times and 500 times pictures that the obtained structure is bainite + ferrite + a small amount of pearlite.

[0056] 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.

[0057] Table 2 Hardness and structure of steel / %

[0058]

[0059] Table 3 Hardenability of steel / HRC

[0060] J1.5 J3 J5 J7 J9 J11 J13 45.0 44.3 42.6 35.3 31.8 29.5 28.0 J15 J20 J25 J30 J35 J40 26.5 23.8 21.2 19.5 18.0 17.2

[0061] Example 2

[0062] This embodiment provides a method for preparing steel for engineering machinery, and the preparation process includes converter BOF smelting→LF→VD→continuous casting→insulation→material production.

[0063] During the electric furnace smelting process of this embodiment:

[0064] The steel charge consists of 5wt% return steel and 95wt% pig iron, with a carbon content of 1.5-1.8%.

[0065] 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.

[0066] After the slag is fully melted, the temperature reaches 1675°C and oxidation begins; the oxygen blowing pressure is controlled at 0.3-0.7 MPa; the decarburization amount is ≥0.35%.

[0067] The components and contents at the end of oxidation: C is 0.15%, P is 0.015%;

[0068] Add 130-150kg ferromanganese per 100 tons of steel to perform manganese boiling;

[0069] Ferrosilicon 90kg / 100 tons of steel, aluminum ingot 230kg / 100 tons of steel, ferrochrome 110-130kg / 100 tons of steel are used for deoxidation and alloying; the slag removal temperature is 1630℃, and the slag removal amount is ≥95%.

[0070] The composition is appropriate, the steel is tapped at a temperature ≥1600°C, and the final composition of the steel is controlled at C: ≥0.06%, P: ≤0.015%.

[0071] During the LF refining process of this embodiment:

[0072] The temperature of the molten steel entering the LF is 1570℃, argon is passed, the argon pressure is controlled at 0.5-0.8MPa, and electric heating is applied for 20 minutes. Lime is added to adjust the slag according to the S content and slag condition in the steel, and diffusion deoxidizer 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.

[0073] Target composition of refined slag: CaO: 50-65%, SiO2: 5-10%, MgO: 3-6%, Al2O3: 20-30%.

[0074] During LF refining, the white slag is kept for ≥20 minutes. After the slag turns white, SiC powder is added in batches, 5 kg / time.

[0075] 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 0.020%-0.040%. 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.

[0076] During the VD vacuum degassing process in this embodiment:

[0077] During vacuum (VD) degassing, evacuate the air and keep the vacuum degree ≤67Pa for 15min 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.

[0078] 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.

[0079] After breaking the vacuum, Al and S are added to the steel in the following order: sulfur line needs to be added to the steel during the smelting process. First, the Al content is controlled at 0.015-0.025%. After adding aluminum, weak argon stirring is performed for 10 minutes, and then sulfur line is added in three batches, with an interval of 3 minutes each time and medium argon stirring is maintained. In order to allow inclusions to fully float and to uniformly mix the chemical composition of the molten steel, Al and S are added to the steel and weak argon stirring is performed for 15 minutes before casting.

[0080] During the continuous casting process of this embodiment:

[0081] The pouring temperature of the steel is controlled at the ladle temperature: 1532℃ and the pouring temperature 1525℃.

[0082] During the rolling and slow cooling process of this embodiment:

[0083] 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 1150-1205°C and the high temperature diffusion time is controlled at 1.5-2.0 hours.

[0084] The starting rolling temperature is ≥1170℃, and the final rolling temperature is ≥980℃;

[0085] In order to achieve the ideal structure of steel after rolling, the steel is cooled to 680℃ on a cooling bed and then put into a holding pit for ≥72h.

[0086] The chemical composition of the steel prepared in this example is shown in Table 4.

[0087] Table 4 Composition of steel materials / %

[0088]

[0089] Figure 3 and Figure 4 The microscopic photos of the structure morphology of the steel for engineering machinery prepared in this embodiment are magnified 100 times and 500 times respectively. It can be seen from the 100 times and 500 times pictures that the obtained structure is bainite + ferrite.

[0090] 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.

[0091] Table 5 Hardness and structure of steel / %

[0092]

[0093] Table 6 Hardenability of steel / HRC

[0094] Steel Type J1.5 J3 J5 J7 J9 J11 J13 45.8 44.8 43.5 39.2 34.8 31.5 30.5 Steel Type J15 J20 J25 J30 J35 J40 29.5 27.6 26.2 25.2 23.4 23.0

[0095] Comparative Example 1

[0096] The preparation method of this comparative example 1 is completely consistent with that of the embodiment 1, and the preparation process includes electric furnace EAF smelting→LF→VD→continuous casting→insulation→material production.

[0097] The chemical composition of the steel prepared in this comparative example is shown in Table 7.

[0098] Table 7 Composition of steel materials / %

[0099] Steel Type C Si Mn P S Cr Ni Mo Al 20CrMo 0.20 0.34 0.45 0.013 0.008 1.01 0.10 0.20 0.025

[0100] The hardenability of the steel obtained in this comparative example was tested by conventional methods in the art. The results are shown in Table 8.

[0101] Table 8 Hardenability of steel / HRC

[0102] Steel Type J1.5 J3 J5 J7 J9 J11 J13 20CrMo 44.0 43.3 40.6 34.3 30.1 27.8 26.0 Steel Type J15 J20 J25 J30 20CrMo 25.5 22.0 17.2 16.5

[0103] By comparison, it can be seen that the present invention further improves the hardenability of steel through reasonable chemical composition design and control of various parameters during smelting, refining, continuous casting and rolling, obtains a deeper hardened layer, thereby ensuring that the mechanical properties of the resulting engineering machinery steel are uniform.

Claims

1. A steel for engineering machinery, characterized in that: The chemical composition by weight percentage includes: C: 0.16-0.21%, Si: 0.20-0.35%, Mn: 0.70-0.95%, Cr: 0.95-1.25%, Mo: 0.16-0.25%, S: 0.020-0.035%, Ni≤0.10%, and the rest is Fe and unavoidable impurities.

2. According to claim 1, a method for preparing steel for engineering machinery, the preparation process comprises electric furnace or converter smelting → LF refining → VD vacuum degassing → continuous casting → rolling and heat preservation → material production, characterized in that: During the smelting process, when the final composition of the steel is controlled at C not less than 0.06%, P ≤ 0.015%, and the steel temperature is not less than 1600℃, 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 1670-1680℃ 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 10 minutes before breaking the vacuum. After breaking the vacuum, Al and S are added to the steel. After the vacuum is broken, weak argon is stirred for 15 minutes before casting. The pouring temperature is 1520-1550℃; When the obtained steel is rolled, high-temperature diffusion treatment is adopted, the heating temperature is controlled at 1150-1205°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 650°C on a cooling bed and then entered into a holding pit, and the holding time in the pit is not less than 72 hours.

3. The method for preparing steel for construction machinery according to claim 2, characterized in that: In the smelting process, the steel charge consists of returned steel and pig iron, the carbon content of the steel charge is 1.0-1.2%, the slag consists of lime and light-burned dolomite, and the total amount of slag is 1750 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 ≥0.35%; the oxidation end point C is 0.12-0.15%, and P is ≤0.015%.

4. A method for preparing steel for engineering machinery according to claim 2 or 3, characterized in that: During the smelting process, 130-150kg / 100 tons of steel ferromanganese is added for manganese boiling; 90kg / 100 tons of steel ferrosilicon, 100kg / 100 tons of steel aluminum ingots and 110-130kg / 100 tons of steel ferrochrome are added for deoxidation and alloying; the slag removal temperature is 1630°C and the slag removal amount is ≥95%.

5. The method for preparing steel for engineering machinery 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 1550° 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 20 minutes; diffusion deoxidizers SiC powder and SiFe powder are added for diffusion deoxidation, with a total amount of 58 kg / 100 tons of steel; the target composition of the refined slag is: CaO: 50-65%, SiO2: 5-10%, MgO: 3-6%, Al2O3: 20-30%, and after the slag turns white, SiC powder is added in multiple batches, 5 kg / time.

6. The method for preparing steel for engineering machinery 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 steel for engineering machinery 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 steel for engineering machinery according to claim 7, characterized in that: After the VD vacuum degassing, Al and S are added to the steel in the following order: sulfur line needs to be added to the steel during the smelting process, and the Al content is first controlled to be 0.015-0.030%. After adding aluminum, weak argon is stirred for 10 minutes, and then sulfur line is added in three batches, each time with an interval of 3 minutes and medium argon stirring is maintained.

9. The method for preparing steel for engineering machinery according to claim 8, characterized in that: The starting rolling temperature of the rolling is not lower than 1150°C, and the final rolling temperature is not lower than 950°C.

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