Steel for high-precision semitrailer axle, preparation method and semitrailer axle

Abstract

The invention relates to high-precision steel for a semitrailer axle, a preparation method of the high-precision steel and the semitrailer axle, and belongs to the technical field of preparation of automobile parts. The steel for the axle comprises the following chemical components in percentage by mass: 0.15%-0.37% of C, 0.15%-0.40% of Si, 1.1%-1.4% of Mn, less than or equal to 0.015% of P, less than or equal to 0.002% of S, 0.05%-0.50% of Cr, 0.01%-0.5% of Mo, 0.02%-0.05% of Nb, 0.002%-0.03% of Ti, 0.002%-0.05% of V and a matrix element Fe. Chemical components of steel are accurately controlled, especially the content of harmful elements such as P and S is reduced, Cr and Mo elements beneficial to improvement of hardenability and strength are increased, and microelements Ti, Nb and V with grain refining and precipitation strengthening effects are increased, so that the mechanical property and weldability of the steel plate are improved, and the steel plate is suitable for large-scale production. The size precision of the axle obtained through the high-frequency pipe welding technology is remarkably improved.

Description

Technical Field

[0001] The present application relates to the technical field of the preparation of automotive parts, and particularly relates to a steel for a high-precision semi-trailer axle, a preparation method thereof, and a semi-trailer axle. Background Art

[0002] In recent years, the severe domestic energy environment has put forward higher requirements for the safety and light weight of heavy-duty trucks. The axle is an important component for the load-bearing and braking of a semi-trailer. The axle plays a load-bearing and connecting role in the axle assembly. It bears the weight of the vehicle and transfers this weight to the wheels. At the same time, it connects the wheel-end structures on both sides, acting as a bridge to tightly connect different parts of the vehicle together. The quality of the axle is crucial for the service performance of the axle. The axle not only needs to have sufficient load-bearing strength, but also should have high dimensional accuracy, fatigue resistance, and collision energy absorption ability.

[0003] At present, semi-trailer axles are generally made of seamless steel pipes (20Mn2, 27Mn2). The manufacturing process of seamless pipes is relatively complex and the manufacturing cost is high. Problems such as unstable temperature and pressure, inaccurate rolling center line, and improper inclination angle of the two rolls during the production process will all lead to uneven wall thickness of the seamless pipe, resulting in problems such as poor dimensional accuracy of the axle and discrete bench fatigue life. With the development of semi-trailers towards high load-bearing, light weight, and long life, the traditional steel for axles and the preparation method of axles can no longer meet the requirements of high-precision dimensions and long life under high load-bearing conditions. Summary of the Invention

[0004] The present application provides a steel for a high-precision semi-trailer axle, a preparation method thereof, and a semi-trailer axle, so as to solve the following technical problem: how to improve the accuracy of a semi-trailer axle.

[0005] In a first aspect, an embodiment of the present application provides a steel for a high-precision semi-trailer axle. In terms of mass fraction, the chemical composition of the steel for the axle is: C: 0.15% - 0.37%, Si: 0.15% - 0.40%, Mn: 1.1% - 1.4%, P ≤ 0.015%, S ≤ 0.002%, Cr: 0.05% - 0.50%, Mo: 0.01% - 0.5%, Nb: 0.02% - 0.05%, Ti: 0.002% - 0.03%, V: 0.002% - 0.05%, and the matrix element Fe.

[0006] Optionally, the thickness of the steel for the axle is 9 mm - 16 mm.

[0007] In a second aspect, the present application provides a preparation method of the steel for the axle described in the first aspect. The method includes:

[0008] Obtaining a slab having the chemical composition;

[0009] The slab is heated, rough rolled, finish rolled, cooled and coiled in sequence to obtain the steel for semi-trailer axles.

[0010] Optionally, the temperature of the heating is 1200°C to 1260°C.

[0011] Optionally, the finishing rolling temperature of the rough rolling is 980°C to 1100°C.

[0012] Optionally, the finish rolling is 6 - pass to 7 - pass rolling, and the finishing rolling temperature of the finish rolling is 840°C to 900°C.

[0013] Optionally, the temperature of the coiling is 580°C to 640°C.

[0014] In a third aspect, the present application provides a semi - trailer axle, which is made of the steel for semi - trailer axles described in the first aspect.

[0015] Optionally, the semi - trailer axle meets at least one of the following performances: fatigue bench test ≥ 800,000 times, wall thickness difference on four sides of the middle section ≤ 0.2 mm, yield strength difference on four sides of the middle section < 20 MPa, tensile strength difference on four sides of the middle section

[0016] < 20 MPa, - 20°C impact absorption work difference on four sides of the middle section < 20 J.

[0017] In a fourth aspect, the present application provides a preparation method of the semi - trailer axle described in the third aspect, and the method includes:

[0018] Obtain the steel for semi - trailer axles;

[0019] The steel for semi - trailer axles is high - frequency welded into a pipe, heated and deformed, and heat - treated in sequence to obtain a semi - trailer axle.

[0020] Optionally, the welding speed of the high - frequency welded pipe is 16 m / min to 25 m / min, the welding power of the high - frequency welded pipe is 550 W to 650 W, the frequency of the high - frequency welded pipe is 190 KHz to 210 KHz, the extrusion amount of the high - frequency welded pipe is 4 mm to 8 mm, and the induction normalizing temperature of the high - frequency welded pipe is 920°C to 960°C.

[0021] Optionally, the heat treatment includes quenching and tempering; wherein, the temperature of the quenching is 900°C to 980°C, and the temperature of the tempering is 500°C to 560°C.

[0022] The above - mentioned technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0023] An embodiment of the present application provides a steel for high-precision semi-trailer axles. In terms of mass fraction, the chemical composition of the steel for axles is as follows: C: 0.15% - 0.37%, Si: 0.15% - 0.40%, Mn: 1.1% - 1.4%, P ≤ 0.015%, S ≤ 0.002%, Cr: 0.05% - 0.50%, Mo: 0.01% - 0.5%, Nb: 0.02% - 0.05%, Ti: 0.002% - 0.03%, V: 0.002% - 0.05%, and the matrix element Fe. By precisely controlling the chemical composition of the steel, especially reducing the contents of harmful elements such as P and S, increasing the Cr and Mo elements that are beneficial to improving hardenability and strength, and the trace elements Ti, Nb, and V with the functions of refining grains and precipitation strengthening, the mechanical properties and weldability of the steel plate are improved, and the dimensional accuracy of the axle obtained by high-frequency welded pipe technology is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings herein are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a schematic flow chart of a preparation method for a semi-trailer axle provided by an embodiment of the present application;

[0027] Figure 2 It is a metallographic structure diagram of adjacent two sides of the middle section square pipe of the semi-trailer axle provided in Embodiment 1 of the present application;

[0028] Figure 3 It is a metallographic structure diagram of adjacent two sides of the middle section square pipe of the semi-trailer axle provided in Comparative Example 1 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts fall within the scope of protection of the present application.

[0030] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range; in addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0031] In this text, terms including "comprising" etc. mean "including but not limited to". Relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the association relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, and "a plurality" means two or more; "at least one kind", "at least one of the following (items)" or similar expressions refer to any combination of these items, including any combination of single item (s) or plural item (s); for example, "at least one of a, b, or c", or, "at least one of a, b, and c" can both mean: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. "Parts representation method" such as parts by weight, parts by mass, etc. represents the proportional relationship between each component. In the proportional relationships involved in this text, the parameters that need to be described by proportion should be understood as the antecedents of the proportion formula in the order of description, and the proportional numbers should be understood as the consequents of the proportion formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportion formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0032] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in this text can be obtained through market purchase or can be prepared by existing methods.

[0033] In a first aspect, an embodiment of the present application provides a high-precision steel for a semi-trailer axle. The chemical composition of the axle steel, measured by mass fraction, is: C: 0.15% to 0.37%, Si: 0.15% to 0.40%, Mn: 1.1% to 1.4%, P≤0.015%, S≤0.002%, Cr: 0.05% to 0.50%, Mo: 0.01% to 0.5%, Nb: 0.02% to 0.05%, Ti: 0.002% to 0.03%, V: 0.002% to 0.05%, and matrix element Fe.

[0034] The positive effects of limiting the carbon (carbon) content to 0.15% to 0.37% by mass: Carbon is one of the most important strengthening elements in steel, significantly increasing its strength. When the carbon content exceeds 0.37%, the steel is susceptible to cracking and brittle fracture during welding because high-carbon steel tends to form a hard and brittle martensite structure in the heat-affected zone. Limiting the carbon content to 0.15% to 0.37% significantly improves steel weldability, reduces weld defects, and enhances the quality of welded joints.

[0035] The positive effects of limiting the mass fraction of Si (silicon) to 0.15% to 0.40% are as follows: Si exists primarily in steel as a solid solution, which can improve the strength and hardness of the steel. Especially during heat treatment, Si can hinder the growth of austenite grains, refine the grains, and thus improve the strength and toughness of the steel.

[0036] The positive effects of limiting the mass fraction of Mn (manganese) to 1.1% to 1.4% are as follows: Mn is one of the important alloying elements in steel and can significantly improve the hardenability of steel. Hardenability refers to the ability of steel to acquire a martensitic structure during quenching. Improving hardenability means that under the same quenching conditions, steel containing an appropriate amount of Mn can form more martensitic structure, thereby increasing the hardness and strength of the steel. In addition, Mn exists in steel primarily in the form of a solid solution, which has a solid solution strengthening effect on the steel. Solid solution strengthening is the phenomenon of increasing the strength and hardness of a metal by dissolving alloying elements in the base metal to form a solid solution. The solid solution strengthening effect of Mn can further increase the tensile strength and yield strength of steel, meeting the high strength requirements of semi-trailer axles.

[0037] The positive impact of limiting phosphorus to 0.015% or less: High phosphorus content can easily lead to cold cracks in the heat-affected zone (HAZ), thereby reducing the quality of the welded joint. Limiting the phosphorus content to below 0.015% can reduce phosphorus segregation at grain boundaries during welding, lowering the risk of weld cracking and improving the strength and toughness of the welded joint.

[0038] Positive effects of limiting S ≤ 0.002%: A high sulfur content easily leads to hot cracks in the heat-affected zone of welding because sulfide inclusions are prone to expanding at high temperatures and generating stress concentration. Limiting the mass fraction of S below 0.002% can reduce the crack sensitivity in the heat-affected zone of welding and improve the quality of the welded joint.

[0039] Positive effects of limiting the mass fraction of Cr (chromium) to 0.05% - 0.50%: Cr is one of the important elements for improving the hardenability of steel. For components like semi-trailer axles that need to bear high loads, improving the hardenability can ensure sufficient mechanical properties in a high-strength working environment.

[0040] Positive effects of limiting the mass fraction of Mo (molybdenum) to 0.01% - 0.5%: Mo is a strong carbide-forming element, which can significantly improve the hardenability of steel. Steel with good hardenability can obtain a deeper and more uniform martensite structure after quenching, thereby increasing the hardness and strength of the steel. Additionally, the addition of Mo can not only increase the strength of the steel but also maintain or improve its toughness to a certain extent. This is very important for semi-trailer axles because they need to bear high loads and complex stress states, requiring both sufficient strength to support the weight and good toughness to resist impact and fatigue.

[0041] Positive effects of limiting the mass fraction of Nb (niobium) to 0.02% - 0.05%: Nb is a strong carbonitride-forming element, which can combine with carbon and nitrogen in steel to form stable carbides and nitrides. These fine precipitates can effectively pin the grain boundaries and hinder grain growth, thus refining the grains of the steel. Grain refinement is one of the effective ways to improve the strength and toughness of steel, contributing to enhancing the load-bearing capacity and impact resistance of semi-trailer axles.

[0042] Positive effects of limiting the mass fraction of Ti (titanium) to 0.002% - 0.03%: Ti is a strong carbide-forming element, which can combine with carbon in steel to form stable titanium carbide. These titanium carbide particles can play a role in refining the grains in steel, hindering grain growth. Grain refinement can significantly improve the strength and toughness of steel, enabling semi-trailer axles to have better load-bearing capacity and impact resistance. Titanium carbide particles can also act as effective precipitation strengthening phases in steel, enhancing the strength of the steel by hindering dislocation movement. This precipitation strengthening effect is of great significance for improving the load-bearing capacity and wear resistance of semi-trailer axles.

[0043] Positive effects of limiting the mass fraction of V (vanadium) to 0.002% - 0.05%: V is a strong carbide-forming element, which can combine with carbon in steel to form vanadium carbide (VC). Vanadium carbide particles play a role in pinning the grain boundaries and hindering grain growth in steel, thus refining the grains of the steel.

[0044] Fe is the matrix element, and the specific content / content range of Fe can be obtained through the upper and lower limit formulas of the components, that is:

[0045] The sum of the percentage contents of each component in a composition should be equal to 100%, and the content ranges of several components should meet the following conditions: the upper limit value of a certain component + the lower limit values of other components ≤ 100; the lower limit value of a certain component + the upper limit values of other components ≥ 100.

[0046] In some embodiments, the thickness of the steel for axles is 9 mm to 16 mm.

[0047] The thickness of the steel plate has a significant impact on its mechanical properties. In the embodiments of the present application, the thickness of the steel for axles is 9 mm to 16 mm, which can maintain good toughness while ensuring strength. If the thickness of the steel for axles is less than 9 mm, the strength may be insufficient and it is difficult to meet the load-bearing requirements; while if the thickness of the steel for axles is greater than 16 mm, it may lead to a decrease in toughness, increasing the processing difficulty and cost.

[0048] In a second aspect, the present application provides a method for preparing the steel for axles described in the first aspect, and the method includes:

[0049] Obtaining a slab with the described chemical composition;

[0050] Successively heating, rough rolling, finish rolling, cooling, and coiling the slab to obtain the steel for semi-trailer axles.

[0051] In some embodiments, the temperature of the heating is 1200 °C to 1260 °C.

[0052] The heating temperature is one of the key factors affecting the austenitization of the steel plate. In the temperature range of 1200 °C to 1260 °C, carbon and other alloy elements in the steel plate can be fully dissolved into austenite to form a uniform austenite structure. This is crucial for the subsequent rolling and heat treatment processes because it can ensure the tissue uniformity and mechanical properties of the steel plate.

[0053] In some embodiments, the finishing rolling temperature of the rough rolling is 980 °C to 1100 °C.

[0054] During the rough rolling process, steel undergoes large amounts of plastic deformation. Setting the final rolling temperature between 980°C and 1100°C ensures that the steel maintains a sufficient temperature during the rough rolling process to allow the austenite to recrystallize. This not only facilitates the plastic deformation of the steel but also effectively prevents cracks caused by work hardening. Furthermore, a final rolling temperature of 980°C to 1100°C helps control the growth of austenite grains, ensuring a fine-grained structure in the steel, thereby improving its mechanical properties and toughness. If the final rolling temperature exceeds 1100°C, the steel may overheat or even burn. Overheating can cause abnormal grain growth and severely deteriorate its mechanical properties. Overburning, on the other hand, can lead to melting, oxidation, and decarburization within the steel, seriously affecting its quality and processing performance. Finally, the final rolling temperature of rough rolling directly affects the smooth progress of subsequent finishing rolling. If the final rolling temperature is lower than 980℃, the plasticity of the steel will drop significantly, increasing the difficulty and risk of finishing rolling. Setting the final rolling temperature within the range of 980℃ to 1100℃ can ensure that the steel maintains sufficient plasticity and deformation ability before finishing rolling, which is conducive to the stable progress of the finishing rolling process and the control of steel dimensional accuracy.

[0055] In some embodiments, the finishing rolling is performed in 6 to 7 passes, and the final rolling temperature of the finishing rolling is 840° C. to 900° C.

[0056] Multi-pass rolling effectively refines the steel's grain structure. Each rolling pass causes a certain amount of deformation, which promotes dynamic recrystallization and refines the grains. Grain refinement is an effective way to improve steel's strength and toughness. Multi-pass rolling also helps achieve uniform deformation of the steel, reducing internal stress and defects caused by uneven deformation. This not only improves the steel's mechanical properties but also its processing properties.

[0057] If the finishing temperature of the finishing rolling is lower than 840℃, the steel may suffer a reduction in plasticity due to work hardening, increasing the difficulty and risk of subsequent processing. Controlling the finishing rolling temperature within the range of 840℃ to 900℃ can ensure that the steel maintains sufficient plasticity during the finishing rolling process, which is conducive to achieving stable rolling. In addition, within the temperature range of 840℃ to 900℃, the austenite structure of the steel is relatively stable and is not prone to phase transformation or decomposition, which is conducive to maintaining the structural stability of the steel. At the same time, the finishing rolling temperature of 840℃ to 900℃ can also promote the formation and distribution of precipitation phases such as carbides in the steel, further improving its mechanical properties.

[0058] In some embodiments, the coiling temperature is 580°C to 640°C.

[0059] Coiling is carried out in the temperature range of 580°C to 640°C, which can ensure that appropriate phase transformations occur in the steel during subsequent cooling. By controlling the phase transformation process, the microstructure of the steel can be adjusted, thereby affecting its mechanical properties.

[0060] In a third aspect, the present application provides a semi-trailer axle, which is made of the steel for semi-trailer axles described in the first aspect.

[0061] In some embodiments, the semi-trailer axle meets at least one of the following performances: fatigue bench test ≥ 800,000 times, wall thickness difference on four sides of the middle section ≤ 0.2 mm, yield strength difference on four sides of the middle section < 20 MPa, tensile strength difference on four sides of the middle section < 20 MPa, -20°C impact absorption work difference on four sides of the middle section < 20 J.

[0062] Figure 1 It is a schematic flow chart of a preparation method of a semi-trailer axle provided by an embodiment of the present application.

[0063] Please refer to Figure 1 , In a fourth aspect, the present application provides a preparation method of the semi-trailer axle described in the third aspect, and the method includes:

[0064] S1. Obtain the steel for the semi-trailer axle;

[0065] S2. Sequentially perform high-frequency welded pipe making, heating deformation and heat treatment on the steel for the semi-trailer axle to obtain a semi-trailer axle.

[0066] In some embodiments, the welding speed of the high-frequency welded pipe is 16 m / min to 25 m / min, the welding power of the high-frequency welded pipe is 550 W to 650 W, the frequency of the high-frequency welded pipe is 190 KHz to 210 KHz, the extrusion amount of the high-frequency welded pipe is 4 mm to 8 mm, and the induction normalizing temperature of the high-frequency welded pipe is 920°C to 960°C.

[0067] The welding speed is an important factor affecting welding quality and efficiency. A speed faster than 25 m / min may lead to poor weld fusion, and a speed slower than 16 m / min may increase the width of the heat-affected zone and reduce welding efficiency. Controlling the welding speed within the range of 16 m / min to 25 m / min can ensure stable weld quality and improve production efficiency at the same time.

[0068] The welding power determines the heat input during the welding process. A welding power of 550W - 650W can ensure that the weld metal is fully melted, forming a good metallurgical bond. A power lower than 550W may result in incomplete fusion or poor fusion of the weld, while a power higher than 650W may cause hot cracks or coarse weld microstructure. Controlling the welding power within the range of 550W - 650W can ensure stable welding quality.

[0069] The welding frequency affects the skin effect and proximity effect of the high-frequency current, thus affecting the heating speed and depth of the weld.

[0070] A welding frequency of 190KHz - 210KHz can make the current evenly distributed in the weld, ensuring the weld quality.

[0071] The extrusion amount refers to the amount by which the diameter of the welded pipe decreases due to the pressure it receives during the welding process. An extrusion amount of 4mm - 8mm can eliminate the internal stress and deformation generated during the welding process, improving the dimensional accuracy and roundness of the welded pipe.

[0072] Induction normalizing is a heat treatment process in which the welded pipe is rapidly heated to the normalizing temperature through electromagnetic induction heating, held at that temperature, and then rapidly cooled. A normalizing temperature of 920°C - 960°C can improve the microstructure and mechanical properties of the welded pipe, enhancing its strength and toughness.

[0073] In summary, by precisely controlling the various parameters of high-frequency welded pipes (welding speed, welding power, welding frequency, extrusion amount, and induction normalizing temperature), the quality and performance of the welded pipes can be ensured to meet the requirements of high-precision semi-trailer axles. The control of these parameters not only affects the production efficiency and cost of the welded pipes but also directly relates to the dimensional accuracy, mechanical properties, and fatigue life of the final axle products.

[0074] In some embodiments, the heat treatment includes quenching and tempering; wherein, the temperature of the quenching is 900°C - 980°C, and the temperature of the tempering is 500°C - 560°C.

[0075] The main purpose of quenching is to heat the axle steel above the austenitizing temperature, transform its internal structure into uniform austenite, and then obtain martensite or bainite structure through rapid cooling (water or oil can be used as the cooling medium), thereby increasing the hardness and strength of the steel.

[0076] The main purpose of tempering is to eliminate the internal stress and brittleness generated during the quenching process, and at the same time adjust the hardness and toughness of the steel to the optimal balance state to meet the usage requirements of the axle.

[0077] The present application will be further described below in conjunction with specific embodiments. For the experimental methods without specific conditions indicated in the following embodiments, they are usually determined in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out in accordance with general international standards, conventional conditions or the conditions recommended by the manufacturer.

[0078] Example 1

[0079] The chemical composition of the steel for semi-trailer axles includes: C: 0.18%, Si: 0.17%, Mn: 1.26%, P: 0.011%, S≤0.002%, Cr: 0.32%, Mo: 0.003%, Nb: 0.011%, Ti: 0.013%, V: 0.002%.

[0080] The slab of the steel for semi-trailer axles is obtained and successively undergoes heating, rough rolling, finish rolling and coiling. The specific process is as follows: the heating temperature is 1240°C, the finishing temperature of rough rolling is 1060°C, finish rolling is carried out in 7 passes, the finishing temperature of finish rolling is 880°C, and the coiling temperature is 620°C.

[0081] The above-mentioned steel for semi-trailer axles is welded into a pipe by high-frequency welding. The welded pipe size is Φ178×10.2mm, the welding speed is 22m / min, the welding power is 538kW, the frequency is 204KHz, the extrusion amount is 7mm, and the induction normalizing temperature is 920°C. Both ends of the welded pipe are heated to 950°C by medium frequency, extruded to Φ116mm by a press, and then heated to 600°C and extruded to Φ96mm to form an axle head. The middle section of the welded pipe is cold-pushed into a square. The whole axle is heat-treated, the quenching temperature is 910°C, and the tempering temperature is 520°C to obtain a finished semi-trailer axle. The tensile strength of the axle is 830 - 850MPa, and the fatigue bench test reaches 1,198,137 times.

[0082] Example 2

[0083] The chemical composition of the steel for semi-trailer axles includes: C: 0.22%, Si: 0.14%, Mn: 1.12%, P: 0.010%, S≤0.002%, Cr: 0.15%, Mo: 0.006%, Nb: 0.006%, Ti: 0.003%, V: 0.011%.

[0084] The slab of the steel for semi-trailer axles is obtained and successively undergoes heating, rough rolling, finish rolling and coiling. The specific process is as follows: the heating temperature is 1240°C, the finishing temperature of rough rolling is 1100°C, finish rolling is carried out in 6 passes, the finishing temperature of finish rolling is 920°C, and the coiling temperature is 680°C.

[0085] The steel for semi-trailer axles is made into a welded pipe by high-frequency welding. The dimensions of the welded pipe are Φ178×13.7mm, the welding speed is 18m / min, the welding power is 627kW, the frequency is 209KHz, the extrusion amount is 8mm, and the induction normalizing temperature is 920°C. Both ends of the welded pipe are heated to 950°C by medium-frequency heating, and then extruded to Φ116mm by a press, and then heated to 600°C and extruded to Φ96mm to form the axle head. The middle section of the welded pipe is cold-pushed into a square shape. The entire axle is heat-treated, with the quenching temperature at 950°C and the tempering temperature at 560°C, obtaining the finished semi-trailer axle. The tensile strength of the axle is 800 - 820MPa, and the fatigue bench test reaches 1,239,628 times.

[0086] Example 3

[0087] The chemical composition of the steel for semi-trailer axles includes: C: 0.19%, Si: 0.14%, Mn: 1.34%, P: 0.010%, S≤0.002%, Cr: 0.17%, Mo: 0.006%, Nb: 0.005%, Ti: 0.015%, V: 0.010%.

[0088] The slab of the steel for semi-trailer axles is obtained and successively undergoes heating, rough rolling, finish rolling, and coiling. The specific process is as follows: the heating temperature is 1240°C, the final rolling temperature of rough rolling is 1100°C, finish rolling is carried out in 7 passes, the final rolling temperature of finish rolling is 920°C, and the coiling temperature is 680°C.

[0089] The steel for semi-trailer axles is made into a welded pipe by high-frequency welding. The dimensions of the welded pipe are Φ178×10.3mm, the welding speed is 20m / min, the welding power is 605kW, the frequency is 205KHz, the extrusion amount is 8mm, and the induction normalizing temperature is 940°C. Both ends of the welded pipe are heated to 950°C by medium-frequency heating, and then extruded to Φ116mm by a press, and then heated to 600°C and extruded to Φ96mm to form the axle head. The middle section of the welded pipe is cold-pushed into a square shape. The entire axle is heat-treated, with the quenching temperature at 940°C and the tempering temperature at 530°C, obtaining the finished semi-trailer axle. The tensile strength of the axle is 820 - 840MPa, and the fatigue bench test reaches 1,235,438 times.

[0090] Comparative Example 1

[0091] The chemical composition of the steel for semi-trailer axles includes: C: 0.21%, Si: 0.16%, Mn: 1.15%, P: 0.010%, S≤0.002%, Cr: 0.14%, Mo: 0.006%, Nb: 0.008%, Ti: 0.06%, V: 0.01%.

[0092] The slab of the steel for semi-trailer axles is obtained and successively undergoes heating, rough rolling, finish rolling, and coiling. The specific process is as follows: the heating temperature is 1240 °C, the final rolling temperature of rough rolling is 1100 °C, finish rolling is carried out in 6 passes, the final rolling temperature of finish rolling is 920 °C, and the coiling temperature is 680 °C.

[0093] The steel for semi-trailer axles is welded into a pipe by high-frequency welding. The pipe size is Φ178×13.7 mm, the welding speed is 18 m / min, the welding power is 627 kW, the frequency is 209 KHz, the extrusion amount is 8 mm, and the induction normalizing temperature is 920 °C. Both ends of the welded pipe are heated to 950 °C by intermediate frequency, extruded to Φ116 mm by a press, then heated to 600 °C and extruded to Φ96 mm to form the axle head, and the middle section of the welded pipe is cold-pushed into a square shape. The entire axle is heat-treated, with the quenching temperature being 950 °C and the tempering temperature being 560 °C, obtaining the finished semi-trailer axle. The tensile strength of the axle is 830 - 850 MPa, and the fatigue bench test reaches 692380 times.

[0094] Comparative Example 2

[0095] The steel for seamless steel pipes has the following chemical composition: C: 0.25%, Si: 0.26%, Mn: 1.36%, P: 0.014%, S: 0.002%, Cr: 0.076%, Mo: 0.01%, Nb: 0.002%, Ti: 0.002%, V: 0.005%.

[0096] The steel for seamless steel pipes is made into a pipe blank through processes such as heating, piercing, and tube rolling. The pipe blank is obtained with the same hot deformation and heat treatment processes as in Example 1 above to obtain a semi-trailer axle.

[0097] For the semi-trailer axles prepared in the examples and comparative examples, measure the wall thickness of the middle section of the semi-trailer axles. The measurement results of the wall thicknesses of the four side walls are shown in Table 1. According to "GBT 228.1-2021 Metallic materials - Tensile testing - Part 1: Method of test at room temperature" and "GB / T 229—2020 Metallic materials - Charpy pendulum impact test method", tensile and impact property tests are carried out on the four sides of the square tube of the axle. The test results are shown in Table 2.

[0098] Table 1

[0099] serial number Wall thickness 1(mm) Wall thickness 2(mm) Wall thickness 3 (mm) Wall thickness 4 (mm) Example 1 10.24 10.18 10.33 10.22 Example 2 13.73 13.81 13.69 13.71 Example 3 10.32 10.43 10.29 10.34 Comparative Example 1 13.50 13.62 13.57 13.54 Comparative Example 2 9.67 9.79 10.31 10.34

[0100] Table 2

[0101]

[0102] As can be seen from Tables 1 to 2, the wall thickness difference of the semi-trailer axle in the examples is within 0.2 mm, and the dimensional accuracy of the axle is high. During implementation, the fluctuations in the yield strength and tensile strength of the semi-trailer axle are less than 20 MPa, and the maximum difference in the impact absorption energy at -20°C is less than 20 J. Compared with Examples 1 to 3, in Comparative Example 1, the Ti content is 0.06%, exceeding the range in the claims, and the fatigue bench test does not meet the requirement of ≥ 800,000 times. For the semi-trailer axle provided in Comparative Example 2, the maximum difference in wall thickness is 0.67 mm, the maximum difference in yield strength is 68 MPa, and the maximum difference in tensile strength is 42 MPa, which are much larger than those in the examples.

[0103] Appendix Figure 2-3 Detailed description:

[0104] Figure 2 This is the metallographic structure diagram of the adjacent two sides of the square tube in the middle section of the semi-trailer axle provided in Embodiment 1 of the present application; as Figure 2 shown, the metallographic structures of the adjacent two sides are both proeutectoid ferrite + bainite, and the structure is uniform.

[0105] Figure 3 This is the metallographic structure diagram of the adjacent two sides of the square tube in the middle section of the semi-trailer axle provided in Comparative Example 1 of the present application; as Figure 3 shown, the metallographic structures of the adjacent two sides are proeutectoid ferrite + bainite along the austenite grain boundary (left) and bainite (right) respectively, and there are obvious differences in the structure.

[0106] One or more technical solutions in the embodiments of the present invention at least further have the following technical effects or advantages:

[0107] The embodiments of the present invention adopt high-frequency welded pipe technology to replace the seamless steel pipe manufacturing process, simplify the production process, and reduce the production cost.

[0108] The above are only specific implementation manners of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A steel for semi-trailer axles with high precision. In terms of mass fraction, the chemical composition of the steel for axles is as follows: C: 0.15% - 0.37%, Si: 0.15% - 0.40%, Mn: 1.1% - 1.4%, P ≤ 0.015%, S ≤ 0.002%, Cr: 0.05% - 0.50%, Mo: 0.01% - 0.5%, Nb: 0.02% - 0.05%, Ti: 0.002% - 0.03%, V: 0.002% - 0.05%, and the matrix element Fe.

2. The steel for axles according to claim 1, characterized in that, The thickness of the steel for axles is 9 mm - 16 mm.

3. A preparation method for the steel for semi-trailer axles according to any one of claims 1 - 2, the method comprising: Obtaining a slab with the above chemical composition; Successively heating, rough rolling, finish rolling, cooling, and coiling the slab to obtain the steel for semi-trailer axles.

4. The method according to claim 3, characterized in that, The heating temperature is 1200°C - 1260°C; and / or, The finishing rolling temperature of the rough rolling is 980°C - 1100°C; and / or, The finish rolling is 6 - 7 passes of rolling, and the finishing rolling temperature is 840°C - 900°C.

5. The method according to claim 3, characterized in that, The coiling temperature is 580°C - 640°C.

6. A semi-trailer axle, which is made of the steel for semi-trailer axles according to any one of claims 1 - 2.

7. The semi-trailer axle according to claim 6, wherein, The semi-trailer axle meets at least one of the following performances: fatigue bench test ≥ 800,000 times, wall thickness difference on four sides of the middle section ≤ 0.2 mm, yield strength difference on four sides of the middle section < 20 MPa, tensile strength difference on four sides of the middle section < 20 MPa, -20°C impact absorption work difference on four sides of the middle section < 20 J.

8. A preparation method for the semi-trailer axle according to any one of claims 6 - 7, the method comprising: Obtaining the steel for semi-trailer axles; Successively subjecting the steel for semi-trailer axles to high-frequency welded pipe making, heating deformation, and heat treatment to obtain a semi-trailer axle.

9. The method according to claim 8, wherein The welding speed of the high-frequency welded pipe making is 16 m / min - 25 m / min, the welding power of the high-frequency welded pipe making is 550 W - 650 W, the frequency of the high-frequency welded pipe making is 190 KHz - 210 KHz, the extrusion amount of the high-frequency welded pipe making is 4 mm - 8 mm, and the induction normalizing temperature of the high-frequency welded pipe making is 920°C - 960°C.

10. The method according to claim 8, wherein The heat treatment includes quenching and tempering; wherein, the quenching temperature is 900°C - 980°C, and the tempering temperature is 500°C - 560°C.

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