Seamless steel tube for high-strength and high-toughness automobile stabilizer bar and manufacturing method of seamless steel tube

Abstract

The invention discloses a high-toughness seamless steel tube for an automobile stabilizer bar, which contains Fe and inevitable impurities, and also contains the following chemical elements in percentage by mass: 0.30 to 0.40 percent of C, less than or equal to 0.35 percent of Si, 1.2 to 1.8 percent of Mn, 0.10 to 0.45 percent of Cr, 0.01 to 0.35 percent of Cu, 0.02 to 0.35 percent of Ni, 0.01 to 0.06 percent of Ti, 0.0005 to 0.005 percent of B, 0.015 to 0.045 percent of Al and 0.001 to 0.006 percent of Ca. The invention further discloses a manufacturing method of the seamless steel tube for the high-strength and high-toughness automobile stabilizer bar, which comprises the following steps: heating a tube blank, preserving heat, perforating, hot-rolling and sizing to obtain a hot-rolled tube; annealing is conducted; performing cold machining to the size of a finished product in a cold-drawing machining mode; and normalizing.

Description

Technical Field

[0001] The present invention relates to a steel pipe and a manufacturing method thereof, and particularly to a seamless steel pipe and a manufacturing method thereof. Background Art

[0002] The function of the stabilizer bar of an automobile is to prevent excessive lateral roll of the vehicle body during turning and keep the vehicle body as balanced as possible. When the vehicle turns, the vehicle body rolls, the two-side suspensions bounce inconsistently, the outer suspension presses against the stabilizer bar, and the stabilizer bar will be distorted. The elastic force of the bar body will prevent the wheel from lifting, so as to keep the vehicle body as balanced as possible and play a role in lateral stability.

[0003] The stabilizer bar will bear extremely large torsional moments, vibration impact forces and other loads. Therefore, the material is required to have high strength and toughness to ensure that the stabilizer bar has sufficient anti-torsion and anti-fatigue properties. The stabilizer bar usually needs to be bent by cold working into the required shape. Therefore, high strength and toughness, high fatigue performance and good cold working performance must be considered simultaneously in the material design.

[0004] In the prior art, most stabilizer bars are made of solid bar materials and forgings, which are relatively heavy. However, with the increasingly strict requirements for energy conservation and emission reduction in the automotive industry, components with a relatively small proportion in the total vehicle weight, such as stabilizer bars, are also included in the weight reduction category. Therefore, it is necessary to use hollow tubes to replace solid bar materials and forgings.

[0005] In the prior art, there have been some technical solutions using hollow tubes for automotive stabilizer bars. For example: Chinese patent document with publication number CN102782172A, publication date November 14, 2012, and title "Solid Stabilizer Bar, Steel for Solid Stabilizer Bar and Manufacturing Method of Solid Stabilizer Bar" discloses a solid stabilizer bar, steel for solid stabilizer bar and manufacturing method of solid stabilizer bar. The chemical composition disclosed in this invention patent is C: 0.24 - 0.40%, Si: 0.15 - 0.40%, Mn: 0.5 - 1.2%, Ti: 0.0010 - 0.030%, Cr: ≤0.30%, P: ≤0.03%, B: 0.0005 - 0.005%. The hardness at the tempering center of this steel is ≥400HV, and the proportion of martensite structure is ≥80%.

[0006] For another example, a Chinese patent document with the publication number CN104395487A, publication date of March 4, 2015, and title "Hollow Stabilizer Bar, Steel Pipe for Hollow Stabilizer Bar, and Manufacturing Method Thereof" discloses a hollow stabilizer bar and its manufacturing method. The disclosed chemical composition by mass percentage is as follows: C: 0.26 - 0.30%, Si: 0.005 - 0.35%, Mn: 0.5 - 1.0%, Cr: 0.05 - 1.0%, Ti: 0.005 - 0.05%, B: 0.0005 - 0.005%, Ca: 0.0005 - 0.005%, Al: ≤0.08%, P: ≤0.05%, S: ≤0.003%, N: ≤0.06%, O: ≤0.04%. [Mn][S] ≤0.0025%. The steel pipe for the hollow stabilizer bar is obtained by cold drawing of an electric welded steel pipe. This technical solution adds a relatively large number of alloying elements. Summary of the Invention

[0007] One of the objectives of the present invention is to provide a seamless steel pipe for high-strength and high-toughness automotive stabilizer bars. This steel pipe has good plasticity and toughness and cold bending processing performance, and is particularly suitable for automotive components such as stabilizer bars that bear high torsional loads.

[0008] To achieve the above objective, the present invention proposes a seamless steel pipe for high-strength and high-toughness automotive stabilizer bars, which contains Fe and inevitable impurities, and also contains the following chemical elements by mass percentage:

[0009] C: 0.30 - 0.40%, Si ≤0.35%, Mn: 1.2 - 1.8%, Cr: 0.10 - 0.45%, Cu: 0.01 - 0.35%, Ni: 0.02 - 0.35%, Ti: 0.01 - 0.06%, B: 0.0005 - 0.005%, Al: 0.015 - 0.045%, Ca: 0.001 - 0.006%;

[0010] In addition, the mass percentage of each chemical element also satisfies Ti ≥ 5(N + B).

[0011] Furthermore, in the seamless steel pipe for high-strength and high-toughness automotive stabilizer bars of the present invention, the mass percentage of each chemical element is as follows:

[0012] C: 0.30 - 0.40%, Si ≤0.35%, Mn: 1.2 - 1.8%, Cr: 0.10 - 0.45%, Cu: 0.01 - 0.35%, Ni: 0.02 - 0.35%, Ti: 0.01 - 0.06%, B: 0.0005 - 0.005%, Al: 0.015 - 0.045%, Ca: 0.001 - 0.006%; the balance is Fe and inevitable impurities.

[0013] In the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, the design principles of each chemical element are as described below:

[0014] C: In the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, an increase in the C content is beneficial to improving the material strength and fatigue resistance. However, if the C content is too high, the toughness and plasticity will decrease, and it is not conducive to bending cold working, easily resulting in quality problems such as processing difficulties and surface decarburization. Therefore, in the present invention, the C content is controlled to be C: 0.30 - 0.40%, which can ensure the quenching hardness and hardenability of the material, thus ensuring both the hardenability of the material and reducing the quenching crack sensitivity, and ensuring that cold working performance can be achieved.

[0015] Si: In the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, the Si element has a greater impact on the bending cold working performance. The lower the Si content, the better the cold working performance. Therefore, Si is a residual element in the present invention, and its upper limit is controlled to be 0.35%.

[0016] Mn: In the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, an increase in the Mn content can improve the material strength, and Mn can stabilize P and S elements, avoiding the formation of low-melting-point sulfides and improving the hot working performance of the material. However, if the Mn content is too low, P and S elements cannot be well stabilized, and the desired effect cannot be achieved; in addition, if the Mn content is too high, cold working strain hardening is serious. Based on this, in the present invention, the Mn content is controlled to be 1.2 - 1.8%.

[0017] Cr: In the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, an increase in the Cr content can improve the hardenability of the material, improve the material strength and fatigue resistance. In addition, the Cr element also cooperates with C to jointly ensure the strength and toughness of the material. Based on this, in the present invention, the Cr content is controlled to be 0.10 - 0.45%.

[0018] Cu: In the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, an increase in the Cu content, in cooperation with the Ni element, can improve the corrosion resistance of the material in the atmospheric environment, but too high may cause the problem of hot brittleness in hot working. Based on this, in the present invention, the content of Cu is controlled to be 0.01 - 0.35%.

[0019] Ni: In the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, an increase in the Ni content can improve the impact performance of the material, and in cooperation with elements such as Cu and Ti, can improve the corrosion resistance of the material in the atmospheric environment. In the present invention, the content of Ni is controlled to be 0.01 - 0.35%.

[0020] Ti: In the seamless steel tube for high-strength and high-toughness automotive stabilizer bars of the present invention, an increase in the Ti content, especially in combination with B, can improve the hardenability of the material. At the same time, the generated nano-scale Ti carbides and carbonitrides can improve the strength and other properties of the material. However, if the Ti content is too high, it is difficult to control the non-metallic inclusions of Ti. Based on this, the present invention controls the Ti content to be 0.01 - 0.06%.

[0021] B: In the seamless steel tube for high-strength and high-toughness automotive stabilizer bars of the present invention, an increase in the B content, especially in combination with Ti, can improve the hardenability of the material. However, if the B content is too high, it will reduce the plasticity of the material. Based on this, the present invention controls the B content to be 0.0005 - 0.005%.

[0022] Al and Ca: As described above, Si is a residual element after steel smelting and deoxidation. If a lower Si content is required, the deoxidation method during the steelmaking process needs to be changed. The present invention controls the Al content to be 0.015 - 0.045% and the Ca content to be 0.001 - 0.006% to ensure the deoxidation level and ensure that the corresponding non-metallic inclusions have no adverse effect on the fatigue resistance.

[0023] Furthermore, in the seamless steel tube for high-strength and high-toughness automotive stabilizer bars of the present invention, the mass percentage contents of its various chemical elements also satisfy at least one of the following items:

[0024] C: 0.33 - 0.38%,

[0025] Si ≤ 0.30%,

[0026] Mn: 1.25 - 1.45%,

[0027] Cr: 0.15 - 0.35%,

[0028] Cu: 0.01 - 0.3%,

[0029] Ni: 0.02 - 0.25%,

[0030] Ti: 0.02 - 0.05%,

[0031] B: 0.001 - 0.004%.

[0032] Furthermore, in the seamless steel tube for high-strength and high-toughness automotive stabilizer bars of the present invention, among other inevitable impurities: N ≤ 0.005%, O ≤ 0.0035%, P ≤ 0.015%, S ≤ 0.003%.

[0033] In the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, the main impurities are N, O, P, and S. Under the condition that conditions permit, it is desirable that their contents are as low as possible. Among them, P and S are impurity elements introduced during the steel raw materials or the production process. P can embrittle the grain boundaries, deteriorating the toughness and workability of the material. The S element forms low-melting sulfides, reducing the workability of the material and its mechanical properties. In some embodiments, it is possible to control N ≤ 0.005%, O ≤ 0.0035%, P ≤ 0.015%, and S ≤ 0.003%.

[0034] Furthermore, in the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, its microstructure is ferrite + lamellar pearlite.

[0035] Furthermore, in the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, its yield strength is 400 - 500 MPa, its tensile strength is 650 - 780 MPa, and its elongation at fracture ≥ 25%.

[0036] Furthermore, in the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, its microstructure after quenching and tempering is martensite.

[0037] Furthermore, in the seamless steel pipe for high-strength and tough automotive stabilizer bars according to the present invention, its hardness after quenching and tempering is 50 - 58 HRC, and the product of strength and plasticity is greater than 15000 MPa·%.

[0038] Correspondingly, another object of the present invention is to provide a manufacturing method for the seamless steel pipe for high-strength and tough automotive stabilizer bars. By using this method in combination with the above-mentioned component ratios, a seamless steel pipe with good plasticity, toughness, and cold bending workability can be obtained.

[0039] To achieve the above object, the present invention proposes a manufacturing method for a seamless steel pipe for high-strength and tough automotive stabilizer bars, which includes the steps of:

[0040] Heating and holding the tube blank, piercing, hot rolling, and sizing to obtain a hot-rolled tube;

[0041] Annealing;

[0042] Cold working to the finished size by means of cold drawing;

[0043] Normalizing: The normalizing temperature is 780 - 820 °C, holding for 20 - 60 min, controlling the furnace atmosphere to be a reducing atmosphere so that the total decarburization depth of the steel pipe ≤ 20 μm and the semi-decarburization depth ≤ 150 μm. After normalizing, air cooling or air quenching is carried out to obtain a ferrite + lamellar pearlite structure.

[0044] Furthermore, in the manufacturing method according to the present invention, the heating temperature of the tube blank is 1200 - 1260 °C, and the holding time is 30 - 60 min.

[0045] Further, in the manufacturing method of the present invention, the temperature of the perforation is 1000 - 1200 °C.

[0046] Further, in the annealing step of the manufacturing method of the present invention, the annealing temperature is controlled to be 740 - 800 °C, and the heat preservation time is 20 - 60 min.

[0047] Further, in the manufacturing method of the present invention, after the normalizing step, quenching + tempering heat treatment is further included.

[0048] The seamless steel pipe for high-strength and tough automotive stabilizer bars of the present invention has the following advantages and beneficial effects compared with the prior art:

[0049] The seamless steel pipe for high-strength and tough automotive stabilizer bars of the present invention has good room-temperature mechanical properties, cold working properties, and good torsional resistance.

[0050] In some embodiments, the yield strength of the seamless steel pipe for high-strength and tough automotive stabilizer bars in the normalized state is 400 - 500 MPa, the tensile strength is 650 - 780 MPa, and the fracture elongation rate is ≥ 25%.

[0051] In some embodiments, the seamless steel pipe for high-strength and tough automotive stabilizer bars can obtain tempered martensite structure after quenching and tempering heat treatment, its hardness is 50 - 58 HRC, and the product of strength and plasticity is greater than 15000 MPa.%.

[0052] Therefore, the seamless steel pipe for high-strength and tough automotive stabilizer bars of the present invention is particularly suitable for automotive parts such as stabilizer bars that bear high torsional loads. Specific Embodiments

[0053] The following will further explain and illustrate the seamless steel pipe for high-strength and tough automotive stabilizer bars of the present invention and its manufacturing method in combination with specific embodiments. However, this explanation and illustration shall not unduly limit the technical solution of the present invention.

[0054] Examples A1 - A12 and Comparative Examples B1 - B2

[0055] The seamless steel pipes for high-strength and tough automotive stabilizer bars in Examples A1 - A12 and the comparative steel pipes in Comparative Examples B1 - B2 were all prepared by the following steps:

[0056] (1) Using an electric furnace or a converter for smelting + refining and casting into a tube blank, and the mass percentage of chemical elements of the tube blank is shown in Tables 1 - 1 and 1 - 2;

[0057] (2) Heat the tube blank at 1200 - 1260 °C for heat preservation for 30 - 60 min, and then perform high-temperature deformation such as high-temperature piercing, hot rolling, and sizing at 1000 - 1200 °C to process it into a hot-rolled tube;

[0058] (3) Anneal, control the annealing temperature at 740 - 800 °C, and the heat preservation time at 20 - 60 min;

[0059] (4) Cold work it to the finished product size by cold drawing;

[0060] (5) Normalize: The normalizing temperature is 780 - 820 °C, heat preservation is 20 - 60 min, control the furnace atmosphere as a reducing atmosphere, so that the total decarburization depth of the steel pipe ≤ 20 um, the semi-decarburization depth ≤ 150 um, and after normalizing, air-cool or air-cool to obtain a ferrite + lamellar pearlite structure.

[0061] It should be noted that in some embodiments, quenching + tempering and hardening treatment can also be performed after the normalizing step.

[0062] Table 1-1 and Table 1-2 list the mass percentage distributions of various chemical elements of the seamless steel pipes for high-strength and tough automotive stabilizer bars in Examples A1 - A12 and the comparative steel pipes in Comparative Examples B1 - B2.

[0063] Table 1-1. (wt%, the balance is Fe and other unavoidable impurities except P, S, O, and N)

[0064]

[0065] Table 1-2

[0066]

[0067]

[0068] Note: 5(N + B) in Table 1-2 is substituted for the mass percentage contents of these two elements.

[0069] Table 2 lists the specific process parameters of the seamless steel pipes for high-strength and tough automotive stabilizer bars in Examples A1 - A12 and the comparative steel pipes in Comparative Examples B1 - B2.

[0070] Table 2.

[0071]

[0072] Samples were taken from the seamless steel pipes for high-strength and tough automotive stabilizer bars in Examples A1 - A12, and microstructure observation was carried out. It was found that the microstructures of each example were all ferrite + lamellar pearlite.

[0073] In addition, seamless steel pipes for high-strength and tough automotive stabilizer bars of Examples A1 - A12 and comparative steel pipes of Comparative Examples B1 - B2 were sampled, their mechanical properties were tested, and the test results are listed in Table 3.

[0074] In addition, the seamless steel pipes for high-strength and tough automotive stabilizer bars of Examples A1 - A12 and the comparative steel pipes of Comparative Examples B1 - B2 were subjected to adjustment treatment using a quenching and tempering treatment process of high-frequency quenching at 900 ± 20°C and low-temperature tempering at 250 ± 50°C, their mechanical properties were tested, and the test results are also listed in Table 3.

[0075] The relevant performance testing methods are as follows:

[0076] Tensile test: At room temperature, the mechanical properties of the steel pipes were tested in accordance with GB / T 228.1 - 2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature".

[0077] Hardness test: The Rockwell hardness of the test was measured using INNOVATEST6200.

[0078] Table 3 lists the test results of the seamless steel pipes for high-strength and tough automotive stabilizer bars of Examples A1 - A12 and the comparative steel pipes of Comparative Examples B1 - B2.

[0079] Table 3.

[0080]

[0081] Combining Tables 1 - 1, 1 - 2, 2, and 3, it can be seen that for the seamless steel pipes for high-strength and tough automotive stabilizer bars of Examples A1 - A12, due to the use of the mass percentages of chemical elements designed in this case and in combination with the corresponding manufacturing method processes, the properties of each seamless steel pipe for high-strength and tough automotive stabilizer bars in this case can all reach: the yield strength in the normalized state is 412 - 500 MPa, the tensile strength is 698 - 780 MPa, the fracture elongation rate ≥ 25%. After quenching and tempering heat treatment, tempered martensite structure is obtained, its yield strength is 1151 - 1361 MPa, the tensile strength is 1413 - 1782, the fracture elongation rate ≥ 8%, the product of strength and plasticity ≥ 15000 MPa.%, and the hardness is 50 - 58 HRC.

[0082] On the contrary, for the comparative steel pipes of Comparative Examples B1 - B2, either the mass percentage does not meet the range defined in this case, or the manufacturing process parameters do not meet the range defined in this case, resulting in the comprehensive performance of these comparative steel pipes being inferior to the comprehensive performance of the seamless steel pipes for high-strength and tough automotive stabilizer bars in this case.

[0083] It should be noted that the prior art in the protection scope of the present invention is not limited to the embodiments given in the present application documents. All prior art that does not contradict the scheme of the present invention, including but not limited to prior patent documents, prior public publications, prior public uses, etc., can be included in the protection scope of the present invention.

[0084] In addition, the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0085] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A seamless steel tube for a high-strength and tough automotive stabilizer bar, which contains Fe and inevitable impurities, and is characterized in that, It also contains the following chemical elements by mass percentage: C: 0.30 - 0.40%, Si ≤ 0.35%, Mn: 1.2 - 1.8%, Cr: 0.10 - 0.45%, Cu: 0.01 - 0.35%, Ni: 0.02 - 0.35%, Ti: 0.01 - 0.06%, B: 0.0005 - 0.005%, Al: 0.015 - 0.045%, Ca: 0.001 - 0.006%; In addition, the mass percentages of the chemical elements also satisfy Ti ≥ 5(N + B).

2. The seamless steel pipe for high-strength and tough automotive stabilizer bars according to claim 1, characterized in that, The mass percentages of its chemical elements are: C: 0.30 - 0.40%, Si ≤ 0.35%, Mn: 1.2 - 1.8%, Cr: 0.10 - 0.45%, Cu: 0.01 - 0.35%, Ni: 0.02 - 0.35%, Ti: 0.01 - 0.06%, B: 0.0005 - 0.005%, Al: 0.015 - 0.045%, Ca: 0.001 - 0.006%; the balance is Fe and unavoidable impurities.

3. The seamless steel pipe for high-strength and tough automotive stabilizer bars according to claim 1 or 2, characterized in that, The mass percentages of its chemical elements also satisfy at least one of the following: C：0.33～0.38％， Si ≤ 0.30%, Mn: 1.25 - 1.45%, Cr：0.15～0.35％， Cu: 0.01 - 0.3%, Ni: 0.02 - 0.25%, Ti: 0.02 - 0.05%, B：0.001～0.004％。 4. The seamless steel pipe for high-strength and tough automotive stabilizer bars according to claim 1 or 2, characterized in that, Among other unavoidable impurities: N ≤ 0.005%, O ≤ 0.0035%, P ≤ 0.015%, S ≤ 0.003%.

5. The seamless steel pipe for high-strength and tough automotive stabilizer bars according to claim 1 or 2, characterized in that, Its microstructure is ferrite + lamellar pearlite.

6. The seamless steel pipe for high-strength and tough automotive stabilizer bars according to claim 1 or 2, characterized in that, Its yield strength is 400 - 500 MPa, tensile strength is 650 - 780 MPa, and elongation at break ≥ 25%.

7. The seamless steel pipe for high-strength and tough automotive stabilizer bars according to claim 1 or 2, characterized in that, Its microstructure after quenching and tempering treatment is martensite.

8. The seamless steel pipe for high-strength and tough automotive stabilizer bars according to claim 7, characterized in that, Its hardness after quenching and tempering treatment is 50 - 58 HRC, and the product of strength and plasticity is greater than 15000 MPa.%.

9. The manufacturing method of the seamless steel pipe for a high-strength and tough automotive stabilizer bar according to any one of claims 1-6, characterized in that, It includes the steps: Heating and holding the tube blank, piercing, hot rolling and sizing to obtain a hot-rolled tube; Annealing; Cold working to the finished size by cold drawing; Normalizing: The normalizing temperature is 780 - 820 °C, holding for 20 - 60 min, controlling the furnace atmosphere to be a reducing atmosphere so that the total decarburization depth of the steel tube ≤ 20 μm and the semi-decarburization depth ≤ 150 μm, and air cooling or air cooling after normalizing to obtain a ferrite + lamellar pearlite structure.

10. The manufacturing method according to claim 9, characterized in that, The heating temperature of the tube blank is 1200 - 1260 °C, and the holding time is 30 - 60 min.

11. The manufacturing method according to claim 9, characterized in that, The temperature of the piercing is 1000 - 1200 °C.

12. The manufacturing method according to claim 9, characterized in that, In the annealing step, control the annealing temperature to be 740 - 800 °C, and the holding time is 20 - 60 min.

13. The manufacturing method according to claim 9, characterized in that, After the normalizing step, it also includes quenching + tempering treatment.

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