A kind of round steel for engineering machinery half axle and a preparation method thereof

Abstract

The application discloses a kind of round steel for engineering machinery half axle and its preparation method, the chemical composition of the steel grade, by mass percentage, includes: C:0.24~0.32%, Si:0.20~0.30%, Mn:0.90~1.10%, Cr:1.00~1.30%, Ti:0.04~0.1%, Cu≤0.15%, Al:0.03~0.05%, P≤0.020%, S≤0.020%, O≤20×10 ‑4 % , H≤2×10 ‑4 % , the rest is Fe and other inevitable impurity elements, the preparation method includes converter smelting, rolling into bar material.The application adds Cr, Mn, Ti element in low carbon steel, greatly reduces heat treatment cost.Its static torsion strength K>1.8, torsional fatigue reaches B 50 ≥30×10 4 times.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a round steel bar for half-shafts of engineering machinery and its preparation method. Background Technology

[0002] With the rapid development of heavy industries such as petroleum and mining, construction machinery, as a key piece of equipment in these industries, faces increasingly stringent performance and quality requirements. As one of the core components of construction machinery, the performance of the half-shaft directly affects the overall operating efficiency and lifespan of the machine. In particular, with the increasing complexity and heavy loads of operating conditions, the fatigue resistance requirements for construction machinery half-shafts are gradually rising. The construction machinery half-shaft is a crucial component connecting the drive axle and drive wheels, bearing multiple stresses from the engine and road surface. These stresses include not only static loads but also dynamic vibrations and impacts. Fatigue refers to the phenomenon where the properties of a material change in a localized area under cyclic stress or cyclic strain, ultimately leading to failure when the stress is far below the material's static strength. For construction machinery half-shafts, fatigue failure typically manifests as surface spalling, crack propagation, and fracture. These forms of failure not only lead to a decline in mechanical performance but may also cause safety accidents. Many factors contribute to half-shaft fatigue, primarily including the material's composition, microstructure, structure, manufacturing process, and operating environment. Among these, the material's composition and microstructure are key factors affecting fatigue life. For example, excessively high levels of elements such as carbon, sulfur, and phosphorus in steel can lead to a decrease in its toughness and fatigue resistance. Similarly, an unreasonable microstructure in steel, such as coarse grains or excessive inclusions, can also reduce its fatigue resistance. Especially during operation, the half-shafts of construction machinery are subjected to the squeezing and wear effects of mutual stress between workpieces. Prolonged operation under these conditions makes them prone to surface spalling and breakage. Once surface spalling and breakage occur, the noise and vibration of the machinery increase, and the contact temperature between the samples gradually rises, exacerbating the damage. Excessive breakage further aggravates the workpiece's destruction, reducing its service life. This phenomenon is the main manifestation of fatigue in construction machinery half-shafts. Despite the increasing importance of construction machinery half-shafts, research and development on round steel for half-shafts remains insufficient. A search reveals few studies and patents related to round steel for construction machinery half-shafts. This may be due to various reasons, such as insufficient investment in technological research and development, a lack of in-depth understanding of the performance requirements of half-shafts within the industry, and limitations of traditional manufacturing processes.

[0003] In conclusion, as a key component in heavy industry, improving the fatigue resistance of construction machinery half-shafts is crucial for enhancing overall machinery operating efficiency and extending service life. Therefore, strengthening the research and development of round steel for construction machinery half-shafts, particularly focusing on optimizing fatigue resistance, is key to promoting the sustainable and healthy development of heavy industry. Currently, many factors influence the fatigue life of half-shafts, such as material composition, microstructure, structure, manufacturing process, and operating environment. Among these, material composition and microstructure are critical factors affecting fatigue life. Composition determines the basic properties of the material, such as strength, toughness, and wear resistance; while microstructure determines the material's microstructure, thus affecting its macroscopic properties. It can be seen that a suitable material composition ensures sufficient strength and toughness for the half-shaft, while a reasonable microstructure helps improve its fatigue resistance. Therefore, developing a high-quality, fatigue-resistant steel for construction machinery half-shafts is extremely important and a vital way to improve half-shaft performance and service life. Summary of the Invention

[0004] Based on the aforementioned shortcomings, the purpose of this invention is to address the problems of insufficient strength and susceptibility to fatigue fracture in traditional steel materials used for axle shafts of engineering machinery, which to some extent limits the performance and service life of the machinery. To solve this problem, this invention provides a round steel bar for axle shafts of engineering machinery and its preparation method. The steel grade of this invention significantly improves the tensile strength of the steel by adding Cr, Mn, and Ti elements to low- and medium-carbon steel. The addition of these alloying elements not only enhances the mechanical properties of the steel but also endows it with better fatigue resistance. This invention also optimizes the preparation process. By controlling key process technologies and parameters such as smelting and rolling, the microstructure and properties of the steel are ensured to reach their optimal state, resulting in round steel bars for axle shafts of engineering machinery that possess fatigue resistance and high cleanliness.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a round steel bar for axle shafts of engineering machinery. The chemical composition of this round steel bar, by mass percentage, includes: C: 0.24–0.32%, Si: 0.20–0.30%, Mn: 0.90–1.10%, Cr: 1.00–1.30%, Ti: 0.04–0.1%, Cu≤0.15%, Al: 0.03–0.05%, P≤0.020%, S≤0.020%, O≤20×10⁻⁶. -4 %, H≤2×10 -4 %, the remainder being Fe and other unavoidable impurity elements; wherein, the W Si W represents the mass percentage of Si. Ti This represents the mass percentage of Ti. The specifications of the steel used for the half-shaft of the engineering machinery are as follows.

[0007] Preferably, the chemical composition of the round steel for the half-shaft of the engineering machinery, by mass percentage, includes: C: 0.27–0.30%, Si: 0.23–0.29%, Mn: 0.95–1.00%, Cr: 1.05–1.10%, Ti: 0.045–0.070%, Cu≤0.15%, Al: 0.03–0.05%, P≤0.015%, S≤0.015%, O≤15×10⁻⁶. -4 %, H≤2×10 -4 %, the remainder being Fe and other unavoidable impurity elements.

[0008] The functions of each element in the round steel for the half-shaft of engineering machinery in this invention are as follows:

[0009] The role of Cr: Chromium is a carbide-forming element that improves the overall performance of steel by forming fine chromium carbides that are evenly distributed in the steel matrix.

[0010] The role of manganese: an appropriate amount of manganese can cause fine and high-strength pearlite to precipitate in steel during hot deformation and cooling, increasing the pearlite content in steel; during the heat treatment of steel, manganese can greatly enhance the quenching performance of steel; when manganese combines with cementite, it will form high-strength and stable alloy cementite distributed in the material structure, thereby significantly improving the strength and wear resistance of steel.

[0011] The role of Ti: Titanium exists mostly in the form of TiC or Ti(C,N), and its precipitation strengthening effect is obvious, thereby refining the austenite grains and improving the mechanical properties of the material.

[0012] Preferably, the round steel used for the half-shaft of the engineering machinery has the following specifications. Its hardness is 170–207 HBW, grain size ≥ 6, banded structure ≤ 2.0, tensile strength ≥ 1470 MPa, elongation ≥ 9%, shrinkage ≥ 30%, impact energy ≥ 47 J; non-metallic inclusion grades are: A (fine) ≤ 2.0, A (coarse) ≤ 1.5, B (fine) ≤ 1.5, B (coarse) ≤ 1.0, C (≤ 0.5), D (≤ 1.0), Ds (≤ 1.0); its static torsional strength K > 1.8, further optimized K = 2.13, and torsional fatigue reaches B... 50 ≥30×10 4 Second-rate.

[0013] This invention provides a round steel bar for axle shafts of engineering machinery. The chemical composition of the round steel bar for axle shafts of engineering machinery, by mass percentage, includes: C: 0.24–0.32%, Si: 0.20–0.30%, Mn: 0.90–1.10%, Cr: 1.00–1.30%, Ti: 0.04–0.1%, Cu≤0.15%, Al: 0.03–0.05%, P≤0.020%, S≤0.020%, O≤20×10⁻⁶. -4 %, H≤2×10 -4 %, the remainder being Fe and other unavoidable impurity elements.

[0014] As a further preference of the present invention, the chemical composition of the round steel for the half-shaft of the engineering machinery, by mass percentage, includes: C: 0.27-0.30%, Si: 0.23-0.29%, Mn: 0.95-1.00%, Cr: 1.05-1.10%, Ti: 0.045-0.070%, Cu≤0.15%, Al: 0.03-0.05%, P≤0.015%, S≤0.015%, O≤15×10⁻⁶. -4 %, H≤2×10 -4 %, the remainder being Fe and other unavoidable impurity elements.

[0015] As a further preference of the present invention, the

[0016] W Si W represents the mass percentage of Si. Ti This represents the mass percentage of Ti. The specifications of the steel used for the half-shaft of the engineering machinery are as follows.

[0017] As a further preference of the present invention, the steel used for the engineering machinery half-shaft has a hardness of 170-207 HBW, a grain size ≥6, a banded structure ≤2.0, a tensile strength ≥1470 MPa, an elongation ≥9%, a shrinkage rate ≥30%, and an impact energy ≥47 J; the non-metallic inclusion grades are: A (fine) ≤2.0, A (coarse) ≤1.5, B (fine) ≤1.5, B (coarse) ≤1.0, C (class) ≤0.5, D (class) ≤1.0, and Ds (class) ≤1.0; its static torsional strength K >1.8, and its torsional fatigue reaches B... 50 ≥30×10 4 Second-rate.

[0018] This invention provides a method for preparing round steel for axle shafts of engineering machinery, the method comprising the following steps:

[0019] 1) Converter smelting: tapping conditions: final C ≥ 0.08%, P ≤ 0.018%; tapping temperature 1600-1680℃;

[0020] 2) Rolling: The heating process includes the following in sequence: preheating section, heating section I, heating section II, and soaking section.

[0021] As a further preference of the present invention, in step 2), the rectangular blank is 320×420mm.

[0022] As a further preference of the present invention, in step 2), the pulling speed is 0.40 to 0.75 m / min.

[0023] As a further preference of the present invention, in step 2), the heating regime of the cold billet is as follows: the temperature of the preheating section is 500-900℃, the temperature of heating section I is 950-1150℃, the temperature of heating section II is 1140-1260℃, the temperature of the soaking section is 1120-1260℃, and the heating time is ≥2.9h.

[0024] As a further preference of the present invention, in step 2), the heating regime of the hot-charged billet is as follows: the temperature of the preheating section is 500-1000℃, the temperature of heating section I is 950-1150℃, the temperature of heating section II is 1140-1260℃, the temperature of the soaking section is 1120-1260℃, and the heating time is ≥2.5h.

[0025] As a further preference of the present invention, it also includes step 3) fatigue test: torsional fatigue loading torque range: 1800Nm±5Nm~19860Nm±10Nm, loading waveform: sine wave, loading frequency: 4Hz.

[0026] Specifically, the preparation method of the present invention includes converter smelting, LF refining, VD vacuum degassing, continuous casting, and rolling into bars.

[0027] More specifically, the present invention also provides a method for preparing round steel for half-shafts of engineering machinery. The preparation method includes processes such as converter smelting, rolling rectangular continuous casting billets into bars, and fatigue testing, wherein: 1) Converter smelting: tapping conditions: endpoint C≥0.08%, P≤0.018%, residual element content meets standard requirements; tapping temperature 1600-1680℃. 2) Rolling: Rectangular billet shape 320×420mm, drawing speed 0.40~0.75m / min; Cold-charged billet heating regime: preheating section 500~900℃, heating section I 950~1150℃, heating section II 1140~1260℃, soaking section 1120~1260℃, heating time ≥2.9h; Hot-charged billet heating regime: preheating section 500~1000℃, heating section I 950~1150℃, heating section II 1140~1260℃, soaking section 1120~1260℃, heating time ≥2.5h. 3) Fatigue testing: Torsional fatigue loading torque range: 1800Nm±5Nm~19860Nm±10Nm, loading waveform: sine wave, loading frequency: 4Hz.

[0028] The steel grade in this application improves the strength of the steel by adding Cr, Mn and Ti elements to low carbon steel, controlling the cleanliness of molten steel and normalizing after hot rolling, while also taking into account the fatigue resistance of the steel.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) This invention utilizes the aforementioned rational composition design, smelting, rolling, and fatigue testing processes to achieve a grain size ≥6, banded structure ≤2.0, tensile strength ≥1470MPa, elongation ≥9%, reduction of shrinkage ≥30%, and impact energy ≥47J for round steel used in engineering machinery half-shafts; non-metallic inclusion grades A (fine) ≤2.0, A (coarse) ≤1.5, B (fine) ≤1.5, B (coarse) ≤1.0, C (cate) ≤0.5, D (cate) ≤1.0, and Ds ≤1.0; its static torsional strength K >1.8, and torsional fatigue reaches grade B. 50 ≥30×10 4 The steel prepared by this invention has the characteristics of high strength, high cleanliness, and fatigue resistance, enabling the round steel for half-shafts of engineering machinery to work more durablely in long-term reciprocating service environments.

[0031] 2) The preparation method of the present invention specifies the tapping conditions and requirements of converter smelting, as well as the specifications of the rolled billet and the rolling process parameters, and the fatigue detection process parameters, etc., which provides a guarantee for the strength, cleanliness, fatigue resistance, machinability and other characteristics of the subsequent steel.

[0032] 3) The steel grade of the present invention is well adapted to the needs of engineering machinery used in harsh environments, and provides technical support for the development of round steel for the front axle of engineering machinery with good mechanical properties, fatigue resistance and machinability. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments.

[0034] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application are clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0035] The following lists three chemical composition ratios of round steel for engineering machinery half-shafts produced using the production process of the present invention, namely Examples 1, 2 and 3. The chemical composition ratios of the round steel for engineering machinery half-shafts obtained in the three examples are shown in Table 1, the specific production process is shown in Table 2, and the physical properties are shown in Tables 3 and 4.

[0036] Examples 1-3

[0037] This invention provides a round steel bar for half-shafts of engineering machinery. The chemical composition of the steel, by mass percentage, includes: C: 0.24–0.32%, Si: 0.20–0.30%, Mn: 0.90–1.10%, Cr: 1.00–1.30%, Ti: 0.04–0.1%, Cu≤0.15%, Al: 0.03–0.05%, P≤0.020%, S≤0.020%, O≤20×10⁻⁶. -4 %, H≤2×10 -4 %, the remainder being Fe and other unavoidable impurity elements; among which, W Si W represents the mass percentage of Si. Ti This represents the mass percentage of Ti. Specifications for steel.

[0038] This invention provides a method for preparing round steel for half-shafts of engineering machinery, comprising the following steps:

[0039] 1) Converter smelting: tapping conditions: final C: 0.16~0.19%, P: 0.015~0.017%, residual element content meets standard requirements; tapping temperature 1640~1645℃.

[0040] 2) Rolling: Rectangular billet shape 320×420mm, drawing speed 0.60m / min, heating regime for cold-charged billets: preheating section 729~734℃, heating section I 1053~1062℃, heating section II 1174~1176℃, soaking section 1187~1190℃, heating time 4.7~4.8h; heating regime for hot-charged billets: preheating section 729~734℃, heating section I 1053~1062℃, heating section II 1174~1176℃, soaking section 1187~1190℃, heating time 4.7~4.8h.

[0041] 3) Fatigue testing: Torsional fatigue loading torque range: 1800Nm~19800Nm.

[0042] Table 1 Chemical composition of round steel in Examples 1-3

[0043]

[0044] Table 2. Converter smelting process, rolling process, and fatigue testing process for round steel in Examples 1-3.

[0045]

[0046] Table 3 Grain size and mechanical properties of round steel in Examples 1-3

[0047]

[0048] Table 4. Inclusions and fatigue resistance of round steel bars in Examples 1-3

[0049]

[0050]

[0051] In summary, the specifications of the round steel for the half-shaft of engineering machinery obtained by this invention are as follows: The grain size reaches grade 6-7, the banded structure is grade 0-1, the tensile strength is 1558-1591 MPa, the elongation is 12.5%, the shrinkage is 54.5-56.5%, the impact energy is 90.5-99.3 J, the non-metallic inclusions are grade A (fine 1), A (coarse 0-0.5), B (fine 0.5), B (coarse 0), C (fine / coarse 0), D (fine 0.5), D (coarse 0-0.5), Ds (0), static torsional strength K: 2.04-2.13, torsional fatigue strength 30.1×10⁻⁶. 4 Second-rate.

[0052] This invention adds Cr, Mn, and Ti elements to low-carbon steel, making its strength comparable to that of 20CrMnTi steel after quenching and tempering, thus greatly reducing heat treatment costs.

[0053] The upper and lower limits of the process parameters (such as temperature, time, etc.) and the range values ​​of the present invention can all achieve the method, and examples are not listed here.

[0054] All aspects not described in detail in this invention can be covered using conventional technical knowledge in the field.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing round steel for half-shafts of engineering machinery, characterized in that, The chemical composition of the round steel for the half-shaft of the engineering machinery, by mass percentage, includes: C: 0.24–0.32%, Si: 0.20–0.30%, Mn: 0.90–1.10%, Cr: 1.00–1.30%, Ti: 0.04–0.1%, Cu≤0.15%, Al: 0.03–0.05%, P≤0.020%, S≤0.020%, O≤20×10⁻⁶. -4 %, H≤2×10 -4 %, the remainder being Fe and other unavoidable impurity elements; The Cr = 1.2223 + 0.000109 × M φ +0.353924×W Si -0.34724×W Mn +0.486808×W Ti W Si W represents the mass percentage of Si. Ti W represents the mass percentage of Ti. Mn Mn is the mass percentage of Mn. φ For the steel specifications, the steel used for the half-shaft of the engineering machinery has a specification of 20mm ≤ M. φ ≤100mm; The preparation method includes the following steps: 1) Converter smelting: tapping conditions: final C≥0.08%, P≤0.018%; tapping temperature 1600-1680℃; 2) Rolling: The heating process includes, in sequence: preheating section, heating section I, heating section II, and soaking section; In step 2), the heating regime for cold-filled billets is as follows: the temperature of the preheating section is 500-900℃, the temperature of heating section I is 950-1150℃, the temperature of heating section II is 1140-1260℃, the temperature of the soaking section is 1120-1260℃, and the heating time is ≥2.9h. In step 2), the heating regime for the hot-charged billet is as follows: the temperature of the preheating section is 500-1000℃, the temperature of heating section I is 950-1150℃, the temperature of heating section II is 1140-1260℃, the temperature of the soaking section is 1120-1260℃, and the heating time is ≥2.5h.

2. The method for preparing round steel for half-shafts of engineering machinery according to claim 1, characterized in that, The chemical composition of the round steel for the half-shaft of the engineering machinery, by weight percentage, includes: C: 0.27–0.30%, Si: 0.23–0.29%, Mn: 0.95–1.00%, Cr: 1.05–1.10%, Ti: 0.045–0.070%, Cu≤0.15%, Al: 0.03–0.05%, P≤0.015%, S≤0.015%, O≤15×10⁻⁶. -4 %, H≤2×10 -4 %, the remainder being Fe and other unavoidable impurity elements.

3. The method for preparing round steel for half-shafts of engineering machinery according to claim 1 or 2, characterized in that, The steel used for the half-shafts of the engineering machinery has a hardness of 170~207HBW, grain size ≥6, banded structure ≤2.0, tensile strength ≥1470MPa, elongation ≥9%, reduction of area ≥30%, and impact energy ≥47J; non-metallic inclusions are graded as follows: A fine ≤2.0, A coarse ≤1.5, B fine ≤1.5, B coarse ≤1.0, C ≤0.5, D ≤1.0, and Ds ≤1.0; its static torsional strength K>1.8, and torsional fatigue reaches grade B. 50 ≥30×10 4 Second-rate.

4. The method for preparing round steel for half-shafts of engineering machinery according to claim 1, characterized in that, In step 2), the rectangular billet shape is 320×420mm.

5. The method for preparing round steel for half-shafts of engineering machinery according to claim 1, characterized in that, In step 2), the pulling speed is 0.40 to 0.75 m / min.

6. The method for preparing round steel for half-shafts of engineering machinery according to claim 1, characterized in that, It also includes step 3) fatigue test: torsional fatigue loading torque range: 1800Nm~19800Nm, loading waveform: sine wave, loading frequency: 4Hz.

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