Method for improving comprehensive mechanical performance of 30CrMoA round steel

Abstract

The invention discloses a method for improving the comprehensive mechanical performance of 30CrMoA round steel. The method comprises the steps of molten iron pretreatment, converter smelting, LF furnace refining, square billet continuous casting production, heating, bar continuous rolling unit rolling and air cooling. The 30CrMoA round steel comprises the following chemical components in percentage by weight: 0.26% of C, 0.25% of Si, 0.65% of Mn, 0.80% of Cr, 0.15% of Mo, 0.020% of P, 0.018% of S, 0.15% of Ni, 0.10% of Cu and the balance of iron and inevitable trace chemical elements. The invention aims to provide the method for improving the comprehensive mechanical performance of the 30CrMoA round steel, so that the 30CrMoA round steel has good strength, hardness, toughness, plasticity and corrosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical materials, and in particular relates to a method for improving the comprehensive mechanical properties of 30CrMoA round steel. Background Art

[0002] 30CrMoA round steel is an alloy structural steel material with excellent performance, which plays a vital role in many industrial fields. In the machinery manufacturing industry, it is often used to manufacture various important parts, such as high-strength shaft parts, such as the transmission shaft of automobile engines, the main shaft of machine tools, etc. With its good strength and toughness, it can work stably under high-speed operation and large torque conditions, ensuring the reliable operation of mechanical equipment. At the same time, it is also suitable for the manufacture of various gears, whether it is the transmission gears in engineering machinery or the gears in industrial reducers. The gears made of 30CrMoA round steel can better resist wear, bite, etc., and transmit power accurately and efficiently. Moreover, its toughness can resist the impact loads generated by the gears during starting, stopping and speed changing, and extend the service life of the gears.

[0003] In the field of petrochemicals, many high-pressure pipelines, valves, and connection parts of reaction vessels are made of 30CrMoA round steel. It has excellent fatigue resistance and corrosion resistance, and can be used for a long time in complex and harsh chemical environments, high temperature and high pressure environments, ensuring the safety and continuity of petrochemical production processes.

[0004] In the automotive industry, 30CrMoA round steel can be used to manufacture key components such as engine crankshafts and connecting rods. When the engine is working, the crankshaft must withstand the gas pressure, reciprocating inertia force and rotational inertia force transmitted from the piston connecting rod group. Its force conditions are complex and it is subject to huge alternating loads. The high strength and good toughness of 30CrMoA round steel can ensure the normal operation of the crankshaft under high-speed rotation and complex force conditions. The connecting rod needs to convert the reciprocating motion of the piston into the rotational motion of the crankshaft. The performance of 30CrMoA round steel can meet its reliability requirements under the action of multiple forces such as tension, pressure and inertia.

[0005] In addition, it can also be used in some structural parts in the aerospace field, meeting the stringent requirements on material strength, weight, reliability, etc., helping to build the aircraft structure stably and contributing to the development of the aerospace industry. It is a widely used and indispensable high-quality metal material.

[0006] However, 30CrMoA round steel without heat treatment has obvious disadvantages. First, in terms of strength, it only relies on the original organizational structure after conventional processing such as rolling to provide bearing capacity, and the yield strength and tensile strength are at a relatively low level, which makes it difficult to be competent for key mechanical parts that need to withstand high tension, high pressure and complex alternating loads. For example, in the core transmission parts of large-scale engineering machinery or in the manufacture of shaft components under high-intensity working environments, it is likely to deform or even break due to insufficient strength, and the stable operation of the equipment cannot be guaranteed. The hardness is also poor, which makes its wear resistance poor. In situations where frequent contact and friction with other parts are required, such as when participating in power transmission as a gear, it is easy to have surface scratches and excessive wear, which in turn affects the transmission efficiency and service life of the entire mechanical system. In addition, when facing a certain extrusion force, it is also difficult to maintain the integrity of its own shape and is prone to deformation. Furthermore, its organizational stability is relatively limited. Since it has not been heat-treated to optimize and adjust its internal organizational structure, its internal organization may gradually change when subjected to external forces for a long time or in a specific working environment, such as high temperature, high humidity and other complex working conditions, which will lead to further weakening of performance. The reliability of the material is greatly reduced, and it cannot function as long-term and stably as the same steel that has undergone heat treatment. In addition, in some precision machinery application scenarios that require high dimensional accuracy and shape stability, 30CrMoA round steel that has not been heat-treated is difficult to meet the requirements with its existing performance. Because it lacks the stress relief and organizational strengthening brought by heat treatment, it is more likely to have dimensional deviations and shape changes during subsequent processing or use, which limits its application in the field of high-precision machinery manufacturing. Summary of the invention

[0007] The purpose of the invention is to provide a method for improving the comprehensive mechanical properties of 30CrMoA round steel so that the steel has good strength, hardness, toughness, plasticity and corrosion resistance.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The present invention discloses a method for improving the comprehensive mechanical properties of 30CrMoA round steel, comprising: molten iron pretreatment - converter smelting - LF furnace refining - billet continuous casting production - heating - bar continuous rolling unit rolling - air cooling; wherein:

[0010] Before smelting, the molten iron is first desulfurized to reduce the sulfur content in the molten steel, reduce the pressure of the refining furnace, and ensure that the tapping w[S] is ≤0.025%; in order to meet the high-drawing re-blowing operation and avoid overoxidation of the molten steel, the w[Si] is required to be 0.46%-0.56% and the temperature is greater than 1250℃; in the converter smelting process, the slag washing process is adopted, lime and refining slag are added, and the good dynamic conditions of the converter steel are used to prepare the pre-slag for the refining furnace smelting;

[0011] Pour the molten iron from the blast furnace into the converter, and add a certain amount of scrap steel as needed. Then blow oxygen into the converter from the top to remove the excess carbon, silicon and manganese elements in the molten iron through oxidation reaction between oxygen and these elements, reduce the carbon content of the molten iron and adjust the content of other elements to make it close to the composition requirements of steel. In the LF refining process, lime slag-making materials are added to facilitate the collection and removal of impurities generated by the reaction, forming slag for discharge. At the same time, argon is blown from the bottom for stirring throughout the process. Steel tapping temperature: 1600℃~1610℃ for the first furnace of the pouring, 1590℃~1600℃ for the continuous pouring furnace.

[0012] After LF steel is tapped, the temperature is measured on the continuous casting platform and Ar is blown. The intensity of Ar blowing is based on the condition that the steel surface is not exposed. The Ar blowing time is ≥8min~15min. The existing low-carbon and low-basicity covering agent is still used in the tundish. The covering agent should be added in time and should not be exposed or turn red.

[0013] The refined molten steel is injected into the tundish of the continuous casting machine, and then distributed to each crystallizer through the tundish. The crystallizer is cooled by water, so that the molten steel gradually solidifies on its inner wall to form a round billet. With the traction of the continuous casting machine, the billet is continuously pulled out of the crystallizer, and continues to be sprayed with water in the subsequent secondary cooling zone until it is completely solidified. Finally, it is cut into billets of the required length according to the fixed length. The continuous casting process adopts full-process protective casting to prevent secondary oxidation of the molten steel; the H content in the billet is less than 2.5ppm;

[0014] The obtained steel billet needs to be rolled to be processed into round steel products. First, the steel billet is heated in a heating furnace and then sent to a rolling mill. Through multiple rolling passes, the steel billet is gradually rolled into 30CrMoA round steel of the required diameter under the action of rollers of different diameters. During the rolling process, the dimensional accuracy and surface quality of the round steel are accurately controlled by controlling the parameters of the roller spacing and rolling speed. Finally, after cooling, straightening, and trimming, the round steel meets the quality and appearance requirements of the finished product.

[0015] During the steel rolling process, the technical parameters controlled in the high-speed wire rolling process are:

[0016] Rolling temperature: 1150±20℃;

[0017] Final rolling temperature 920±20℃;

[0018] The cooling beds are densely packed with spacing less than 10mm.

[0019] Furthermore, the chemical composition percentages of the 30CrMoA round steel are: C: 0.26%, Si: 0.25%, Mn: 0.65%, Cr: 0.80%, Mo: 0.15%, P: 0.020%, S: 0.018%, Ni: 0.15%, Cu: 0.10%, and the rest are iron and inevitable trace chemical elements.

[0020] Furthermore, the rolling temperature is 1165°C.

[0021] Furthermore, the final rolling temperature is 930°C.

[0022] Furthermore, a heat treatment process is also included: quenching + tempering heat treatment is performed on the 30CrMoA round steel.

[0023] Furthermore, the quenching temperature is 880°C and the tempering temperature is 540°C.

[0024] Furthermore, the produced 30CrMoA round steel has good strength, hardness, toughness, plasticity and corrosion resistance, and better comprehensive mechanical properties.

[0025] Carbon (C) is one of the key elements that determine the strength of steel. An appropriate amount of carbon can improve the hardness, strength, wear resistance and other properties of steel.

[0026] Silicon (Si) can enhance the strength, hardness and elastic limit of steel. It also has a positive effect on the deoxidation of steel, helps to improve the purity of steel, improve the quality of steel, make its internal structure more uniform, and facilitate the stable performance of steel in subsequent processing and use.

[0027] Manganese (Mn) can improve the strength, toughness and hardenability of steel, make it easier for steel to obtain an ideal organizational state during heat treatment, and to a certain extent reduce the hot brittleness effect caused by sulfur, making the steel more stable and reliable during operations such as hot processing.

[0028] The chromium (Cr) element can significantly improve the hardenability, strength, oxidation resistance, and corrosion resistance of steel. In 30CrMoA round steel, the presence of chromium helps to improve the durability of steel in different use environments, and cooperates with other elements to better improve the internal structure of steel during heat treatment, thereby improving its comprehensive mechanical properties.

[0029] Molybdenum (Mo) can refine grains, improve the hardenability, heat strength and temper softening resistance of steel, so that the strength and toughness of steel can be well maintained after heat treatment, especially under complex working conditions such as high temperature, it can still ensure that the steel has good mechanical properties and play a stabilizing role.

[0030] Compared with the prior art, the beneficial technical effects of the present invention are:

[0031] The 30CrMoA round steel produced by the invention has good strength, hardness, toughness, plasticity and corrosion resistance, and has better comprehensive mechanical properties. DETAILED DESCRIPTION

[0032] Below in conjunction with embodiment, the present invention is described in further detail:

[0033] The purpose of the invention is to provide a method for improving the comprehensive mechanical properties of 30CrMoA round steel so that the steel has good strength, hardness, toughness, plasticity and corrosion resistance.

[0034] The 30CrMoA round steel production process of the present invention specifically includes: molten iron pretreatment - converter smelting - LF furnace refining - billet continuous casting production - heating - bar continuous rolling unit rolling - air cooling;

[0035] The chemical composition percentages of the 30CrMoA round steel are: C: 0.26%, Si: 0.25%, Mn: 0.65%, Cr: 0.80%, Mo: 0.15%, P: 0.020%, S: 0.018%, Ni: 0.15%, Cu: 0.10%, and the rest are iron and inevitable trace chemical elements.

[0036] The rolling process parameters of 30CrMoA round steel are shown in Table 1:

[0037] Table 1: 30CrMoA round steel rolling process parameters

[0038]

[0039] The mechanical properties of 30CrMoA round steel are shown in Table 2:

[0040] Table 2: Mechanical properties of 30CrMoA round steel

[0041]

[0042] The impact properties of 30CrMoA round steel are shown in Table 3:

[0043] Table 3: Impact properties of 30CrMoA round steel

[0044]

[0045] The hardness values ​​of 30CrMoA round steel are shown in Table 4:

[0046] Table 4: Brinell hardness of 30CrMoA round steel

[0047]

[0048]

[0049] The corrosion rate of 30CrMoA round steel is shown in Table 5:

[0050] Table 5: Corrosion rate of 30CrMoA round steel

[0051]

[0052] After the quenching process, 30CrMoA round steel inhibits the transformation of austenite to pearlite and ferrite, and forms martensite instead. Martensite has high hardness, high strength and low toughness. Its hardness can be significantly improved, and its yield strength can also be greatly increased, so that the round steel can withstand higher loads and stresses. After quenching, the round steel is heated to an appropriate temperature for tempering. During the tempering process, the martensite structure will decompose, carbides will precipitate from the supersaturated martensite and grow together, and the residual austenite will also transform to form a tempered troostite structure. The tempered troostite structure has good comprehensive mechanical properties, which not only maintains a high strength, but also significantly improves toughness and plasticity. The elongation and cross-sectional shrinkage will also be significantly improved, making the round steel safer and more reliable during use, and not prone to brittle fracture. After quenching + tempering, the internal structure of the steel is denser, making it more difficult for corrosive media to invade the interior of the steel. At the same time, the increase in surface hardness also helps to resist some corrosion caused by friction. For example, in the case of wear, a harder surface can reduce the aggravation of corrosion caused by the destruction of the protective film.

[0053] Therefore, in this embodiment, 30CrMoA round steel is subjected to quenching + tempering heat treatment. The heat treatment test process parameters are shown in Table 6:

[0054] Table 6: 30CrMoA round steel heat treatment test process parameters

[0055]

[0056] The mechanical properties of 30CrMoA round steel after heat treatment test are shown in Table 7:

[0057] Table 7: Mechanical properties of 30CrMoA round steel after heat treatment test

[0058]

[0059] The impact properties of 30CrMoA round steel after heat treatment test are shown in Table 8:

[0060] Table 8: Impact properties of 30CrMoA round steel after heat treatment test

[0061]

[0062] The hardness values ​​of 30CrMoA round steel are shown in Table 9:

[0063] Table 9: Brinell hardness of 30CrMoA round steel

[0064]

[0065] The corrosion rate of 30CrMoA round steel is shown in Table 10:

[0066] Table 10: Corrosion rate of 30CrMoA round steel

[0067]

[0068] Through the above mechanical, impact, hardness and corrosion test results, it can be analyzed that the 30CrMoA round steel produced by the present invention has good strength, hardness, toughness, plasticity and corrosion resistance, and has better comprehensive mechanical properties.

[0069] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for improving the comprehensive mechanical properties of 30CrMoA round steel, characterized in that: include: Hot metal pretreatment - converter smelting - LF furnace refining - billet continuous casting production - heating - bar continuous rolling unit rolling - air cooling; Among them: Before smelting, the molten iron is first desulfurized to reduce the sulfur content in the molten steel, reduce the pressure of the refining furnace, and ensure that the tapping w[S] is ≤0.025%; in order to meet the high-drawing re-blowing operation and avoid overoxidation of the molten steel, the w[Si] is required to be 0.46%-0.56% and the temperature is greater than 1250℃; in the converter smelting process, the slag washing process is adopted, lime and refining slag are added, and the good dynamic conditions of the converter steel are used to prepare the pre-slag for the refining furnace smelting; Pour the molten iron from the blast furnace into the converter, and add a certain amount of scrap steel as needed. Then blow oxygen into the converter from the top to remove the excess carbon, silicon and manganese elements in the molten iron through oxidation reaction between oxygen and these elements, reduce the carbon content of the molten iron and adjust the content of other elements to make it close to the composition requirements of steel. In the LF refining process, lime slag-making materials are added to facilitate the collection and removal of impurities generated by the reaction, forming slag for discharge. At the same time, argon is blown from the bottom for stirring throughout the process. Steel tapping temperature: 1600℃~1610℃ for the first furnace of the pouring, 1590℃~1600℃ for the continuous pouring furnace. After LF steel is tapped, the temperature is measured on the continuous casting platform and Ar is blown. The intensity of Ar blowing is based on the condition that the steel surface is not exposed. The Ar blowing time is ≥8min~15min. The existing low-carbon and low-basicity covering agent is still used in the tundish. The covering agent should be added in time and should not be exposed or turn red. The refined molten steel is injected into the tundish of the continuous casting machine, and then distributed to each crystallizer through the tundish. The crystallizer is cooled by water, so that the molten steel gradually solidifies on its inner wall to form a round billet. With the traction of the continuous casting machine, the billet is continuously pulled out of the crystallizer, and continues to be sprayed with water in the subsequent secondary cooling zone until it is completely solidified. Finally, it is cut into billets of the required length according to the fixed length. The continuous casting process adopts full-process protective casting to prevent secondary oxidation of the molten steel; the H content in the billet is less than 2.5ppm; The obtained steel billet needs to be rolled to be processed into round steel products. First, the steel billet is heated in a heating furnace and then sent to a rolling mill. Through multiple rolling passes, the steel billet is gradually rolled into 30CrMoA round steel of the required diameter under the action of rollers of different diameters. During the rolling process, the dimensional accuracy and surface quality of the round steel are accurately controlled by controlling the parameters of the roller spacing and rolling speed. Finally, after cooling, straightening, and trimming, the round steel meets the quality and appearance requirements of the finished product. During the steel rolling process, the technical parameters controlled in the high-speed wire rolling process are: Rolling temperature: 1150±20℃; Final rolling temperature 920±20℃; The cooling beds are densely packed with spacing less than 10mm.

2. The method for improving the comprehensive mechanical properties of 30CrMoA round steel according to claim 1, characterized in that: The chemical composition percentages of the 30CrMoA round steel are: C: 0.26%, Si: 0.25%, Mn: 0.65%, Cr: 0.80%, Mo: 0.15%, P: 0.020%, S: 0.018%, Ni: 0.15%, Cu: 0.10%, and the rest are iron and inevitable trace chemical elements.

3. The method for improving the comprehensive mechanical properties of 30CrMoA round steel according to claim 1, characterized in that: The rolling temperature is 1165℃.

4. The method for improving the comprehensive mechanical properties of 30CrMoA round steel according to claim 1, characterized in that: Final rolling temperature is 930℃.

5. The method for improving the comprehensive mechanical properties of 30CrMoA round steel according to claim 1, characterized in that: It also includes a heat treatment process: quenching + tempering heat treatment of 30CrMoA round steel.

6. The method for improving the comprehensive mechanical properties of 30CrMoA round steel according to claim 5, characterized in that: Quenching temperature is 880℃ and tempering temperature is 540℃.

7. The method for improving the comprehensive mechanical properties of 30CrMoA round steel according to claim 1, characterized in that: The produced 30CrMoA round steel has good strength, hardness, toughness, plasticity and corrosion resistance, and better comprehensive mechanical properties.

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