DE112020004121T5 - HOT ROLLED STEEL FOR WHEELS WITH A TENSILE STRENGTH EXCEEDING 500 MPA AND PRODUCTION PROCESS THEREOF - Google Patents

Abstract

Disclosed is a hot-rolled steel for wheels with a tensile strength above 500 MPa, containing the following chemical elements in mass percentage: C: 0.09% to 0.2%, Mn: 0.8% to 1.2%, Al : 0.025% to 0.060%, Nb: 0.01 to 0.10%; the balance being Fe and other unavoidable impurities. Further, a manufacturing method for manufacturing the hot-rolled steel for wheels is disclosed, the manufacturing method having no heat treatment step and comprising the steps of: (1) melting and casting; (2) heating a disk blank; (3) hot rolling; (4) Segmented cooling: in a first stage, a steel plate is cooled to 650°C to 750°C at a rate of 60°C/s to 150°C/s; in a second stage, the steel plate is cooled in air for 5 to 20 seconds; in a third stage, the steel plate is cooled to 350°C to 500°C at a rate of 60°C/s to 150°C/s; and in a fourth stage, the steel plate is air-cooled to room temperature.

Description

technical field

The present invention relates to a steel plate and a manufacturing method thereof, more particularly to a hot-rolled steel for wheels and a manufacturing method thereof.

State of the art

In recent years, reduction of fuel consumption of automobiles and emission of CO ₂ is becoming a worldwide demand due to increasing awareness of environmental protection. Among the measures to achieve this goal, reducing the weight of automobiles is a very effective means. This global trend combined with the emphasis on automobile safety brings the requirement for various novel advanced steel materials with high strength and good workability.

Hot-rolled steel plate is mainly used for the chassis, wheels, suspension and surrounding parts of various passenger or commercial vehicles, and their weight can account for more than 25% of the total weight of a vehicle body. Since many components in these areas are relatively thick and heavy, there is great potential for weight reduction.

In the past, in order to meet the usage conditions of the steel plates on wheels, there were generally two ways: a steel plate with reduced strength (≤300MPa) is used to achieve better weldability and formability; or alternatively, the amount of working in the wheel design is reduced to reduce the requirements on the weldability and formability of the steel plate. With the continuous improvement in the strength of steel for automobiles, the formability of conventional beam for automobile wheels is declining. At the same time, it is difficult to meet the requirements of car wheels for formability of steel plates. In order to meet the increasing demands on the strength of the steel plate due to the weight reduction of automobiles, it is desired to obtain a special high-strength steel with high formability for wheels.

For example, a high-strength hot-rolled plate is known from Japanese Patent Literature Publication No. JPS 56130455 A published on Oct. 13, 1981, the title of which is "high-strength hot-rolled steel plate having good flash butt weldability and workability". In the technical solution disclosed in this patent literature, the components Ca and Ce are contained, with a strength of 560 to 580 MPa being achieved and the elongation being 27%.

Another example: A high-strength hot-rolled plate is known from Japanese Patent Literature Publication No. JPS 57155347 A, published on September 25, 1982, the title of which is "high-strength hot-rolled steel plate for wheel rims having excellent flash butt weldability". In the technical solution disclosed in this patent literature, the C content in the composition is 0.067 to 0.082% and the Mn content is 1.52 to 1.70%. However, no hot rolling and cooling process is affected.

Another example: From Japanese Patent Literature Publication No. JPS 57155348 A published on September 25, 1982, the title of which is "high-strength hot-rolled steel plate suitable for manufacturing rims by flash butt welding", a hot-rolled plate with high strength known. In the technical solution disclosed in this patent literature, rare earth components are added to the steel composition using a coiling temperature below 500°C.

content of the invention

One of the objects of the present invention is to provide a hot-rolled steel for wheels with a tensile strength of over 500 MPa, the hot-rolled steel for wheels having uniform properties, good sheet shape, good cold workability, simple composition and low production costs, and the process requirements of car wheels Processing processes such as forming, expanding and welding can perform well.

• C: 0,09% bis 0,2%, Mn: 0,8% bis 1,2%, Al: 0,025% bis 0,060%, Nb: 0,01% bis 0,10%, 0 < Si ≤ 0,3%; wobei der Rest Fe und andere unvermeidliche Verunreinigungen ist.

In order to achieve the above object, the present invention proposes a hot-rolled steel for wheels having a tensile strength of over 500 MPa, containing the following chemical elements by mass percentage:

• C: 0.09% to 0.2%, Mn: 0.8% to 1.2%, Al: 0.025% to 0.060%, Nb: 0.01% to 0.10%, 0 < Si ≤ 0, 3%; the balance being Fe and other unavoidable impurities.

• C: In dem erfindungsgemäßen warmgewalzten Stahl für Räder wird C verwendet, um eine ausreichende Carbid-Verstärkungsphase zu bilden, so dass das Festigkeitsniveau von Stahl sichergestellt wird. Ferner kann C auch eine Rolle bei der Stabilisierung von Austenit spielen und dazu beitragen, Restaustenit zu bilden. Auf dieser Grundlage wird der Massenprozent von C in dem erfindungsgemäßen warmgewalzten Stahl für Räder auf 0,09% bis 0,2% geregelt.
• Mn: Bei dem erfindungsgemäßen warmgewalzten Stahl für Räder stellt Mn ein wichtiges Mn ein wichtiges Element für die Festlösungsverfestigung dar. Ein zu niedriger Massenprozent von Mn wird zur unzureichenden Festigkeit des Stahls führen. Ein zu hoher Massenprozent von Mn kann jedoch zur Reduzierung der Plastizität führen, was auch eine Abnahme der Schweißleistung des Materials verursacht. Auf dieser Grundlage wird der Massenprozent von Mn in dem erfindungsgemäßen warmgewalzten Stahl für Räder auf 0,8% bis 1,2% geregelt.
• Al: Bei der technischen Lösung der vorliegenden Erfindung stellt Al ein desoxidierendes Element in dem Stahl dar, weswegen sein Massenprozent auf 0,025% bis 0,060% geregelt wird.
• Nb: Bei dem erfindungsgemäßen warmgewalzten Stahl für Räder stellt Nb ein Element dar, das Körner wirksam verfeinert und Festigkeit sowie Zähigkeit verbessert, und das in Form von Carbiden und Carbonitriden im Strahl vorliegt. Da die Zugabe von Nb weniger als 0,01% ist, ist dessen Verstärkungswirkung gering. Daher wird der Massenprozent von Nb in der technischen Lösung der vorliegenden Erfindung auf 0,01% bis 0,10% geregelt. In einigen Ausführungen liegt der Massenprozent von Nb im Bereich von 0,01% bis 0.08%.
• Si: In Anbetracht der Tatsache, dass Si in Stahl eine Wirkung der Festlösungsverfestigung ausüben kann, führt ein zu hoher Massenprozent von Si leicht zu Oberflächendefekten wie z. B. rotem Eisenbelag auf der Oberfläche der Stahlplatte, wodurch die Schweißeigenschaft beeinträchtigt wird. Auf dieser Grundlage kann bei einigen Ausführungsformen der Massenprozent von Si so geregelt werden, dass es ≤ 0,3% ist. In einigen Ausführungen liegt der Massenprozent von Si im Bereich von 0,05% bis 0.30%. Ferner ist vorgesehen, dass der erfindungsgemäße warmgewalzte Stahl für Räder mit einer Zugfestigkeit von über 500 MPa ferner mindestens eines der folgenden chemischen Elemente aufweist: Ti ≤ 0,05%, und Cr ≤ 0,5%.

In the hot-rolled steel for wheels with a tensile strength of more than 500 MPa of the present invention, the design principles of each chemical element are as follows:

• C: In the hot-rolled steel for wheels of the present invention, C is used to form a sufficient carbide reinforcing phase so that the strength level of steel is secured. Further, C can also play a role in stabilizing austenite and contributing to the formation of retained austenite. Based on this, the mass percentage of C in the hot-rolled steel for wheels of the present invention is controlled to 0.09% to 0.2%.
• Mn: In the hot-rolled steel for wheels of the present invention, Mn is an important element for solid-solution strengthening. Too low a mass percent of Mn will result in insufficient strength of the steel. However, too high a mass percentage of Mn can lead to the reduction in plasticity, which also causes a decrease in the welding performance of the material. Based on this, the mass percentage of Mn in the hot-rolled steel for wheels of the present invention is controlled to 0.8% to 1.2%.
• Al: In the technical solution of the present invention, Al is a deoxidizing element in the steel, so its mass percentage is controlled to 0.025% to 0.060%.
• Nb: In the hot-rolled steel for wheels of the present invention, Nb is an element which effectively refines grains and improves strength and toughness, and is present in the form of carbides and carbonitrides in the beam. Since the addition of Nb is less than 0.01%, its reinforcing effect is small. Therefore, the mass percentage of Nb in the technical solution of the present invention is controlled to 0.01% to 0.10%. In some implementations, the mass percent of Nb ranges from 0.01% to 0.08%.
• Si: Considering that Si can exert an effect of solid-solution strengthening in steel, too high a mass percentage of Si easily leads to surface defects such as pitting. B. Red iron coating on the surface of the steel plate, which affects the welding property. Based on this, in some embodiments, the mass percent of Si can be controlled to be ≦0.3%. In some implementations, the mass percent of Si ranges from 0.05% to 0.30%. Furthermore, it is contemplated that the hot-rolled steel for wheels of the present invention having a tensile strength greater than 500 MPa further comprises at least one of the following chemical elements: Ti≦0.05%, and Cr≦0.5%.

In the above solution, Cr partially replaces the function of Si, widens the temperature range for ferrite transformation, and is beneficial to the stability of the structure and properties.

Considering that Ti can also effectively refine grains, improve strength and toughness, and also exist in steel in the form of carbides and carbonitrides, too small an addition amount has an adverse effect on the strengthening effect. Based on this, in some preferred embodiments, the mass percent of Ti can be controlled to be ≦0.05%.

Further, in the hot-rolled steel for wheels of the present invention having a tensile strength of more than 500 MPa, in the other unavoidable impurities, it is envisaged that S≦0.005%, P≦0.035%, N≦0.0060%, and O≦0.0030%.

In the technical solution of the present invention, the unavoidable impurities should be controlled as little as possible. Here, as impurity elements in steel, P and S may each have a mass percentage, which is preferably controlled to S≦0.005% and P≦0.035%.

O as an impurity element in steel easily reacts with Al to form oxide inclusions. Therefore, its mass percentage can be preferably controlled to 0 ≤ 0.0030%.

N can expand the austenite phase range of steel and is a strong element that forms and stabilizes austenite; however, too high a residual nitrogen content in the steel leads to loose macrostructure or pores. Based on this, in the present invention, the mass percentage of N can preferably be controlled to ≦0.0060%.

It should also be noted that the hot-rolled steel for wheels of the present invention having a tensile strength greater than 500 MPa may also contain at least one of the following chemical elements: Cu≦0.5%, Mo≦0.2%, and B≦0.005%, so that the Properties of steel can be further improved.

Furthermore, it is provided that in the case of the hot-rolled steel for wheels according to the invention with a tensile strength of more than 500 MPa, the microstructure is formed from ferrite, bainite and retained austenite.

Further, in the hot-rolled steel for wheels of the present invention having a tensile strength of over 500 MPa, the phase ratio of retained austenite is 5% to 10% and the phase ratio of bainite is 30% to 45%, with the balance being ferrite.

Furthermore, it is provided that in the hot-rolled steel for wheels according to the invention with a tensile strength of more than 500 MPa, the tensile strength is 500 MPa to 700 MPa and the elongation is ≧30%. It is further contemplated that the hot rolled steel for wheels of the present invention having a tensile strength greater than 500 MPa has a yield strength greater than 400 MPa, such as in the range of 400 MPa to 650 MPa. Furthermore, it is provided that the hot-rolled steel for wheels according to the invention with a tensile strength of more than 500 MPa has an elongation ≥ 32% and preferably ≥ 34%. In some embodiments, the inventive hot-rolled steel for wheels with a tensile strength above 500 MPa has a tensile strength of ≥ 600 MPa, such as in the range 600 MPa to 700 MPa, while its elongation is ≥ 32%, preferably its yield strength in the range from 500 MPa to 650 MPa. In some embodiments, the inventive hot-rolled steel for wheels with a tensile strength above 500 MPa has a tensile strength of ≥ 600 MPa, such as in the range 600 MPa to 700 MPa, while its elongation is ≥ 34%, preferably its yield strength in the range from 500 MPa to 650 MPa. In some embodiments, the hot rolled steel for wheels of the present invention has a tensile strength greater than 500 MPa, an elongation ≥ 35%, its tensile strength being in the range 500 MPa to 620 MPa, preferably its yield strength being in the range 400 MPa to 550 MPa .

Accordingly, another object of the present invention is to provide a manufacturing method for manufacturing a foregoing hot-rolled steel for wheels. The manufacturing method is simple in process, does not require heat treatment, and does not require complicated cooling process after hot rolling; and the obtained hot-rolled steel for wheels has high strength and excellent formability at the same time, and can avoid the occurrence of cracks during the wheel forming process.

1. (1) Schmelzen und Gießen;
2. (2) Heizen eines Plattenrohlings;
3. (3) Warmwalzen;
4. (4) Segmentiertes Abkühlen: in einer ersten Stufe wird eine Stahlplatte auf 650°C bis 750°C mit einer Geschwindigkeit von 60°C/s bis 150°C/s abgekühlt wird; in einer zweiten Stufe wird die Stahlplatte 5 bis 20 Sekunden lang in der Luft abgekühlt; und in einer dritten Stufe wird die Stahlplatte auf 350°C bis 500°C mit einer Geschwindigkeit von 60°C/s bis 150°C/s abgekühlt und dann aufgerollt; und
5. (5) Luftkühlen der Stahlplatte auf Raumtemperatur.

In order to achieve the above object, the present invention proposes a manufacturing method for manufacturing a foregoing hot-rolled steel for wheels, the manufacturing method not having a heat treatment step, the manufacturing method comprising the steps of:

1. (1) melting and casting;
2. (2) heating a disk blank;
3. (3) hot rolling;
4. (4) Segmented cooling: in a first stage, a steel plate is cooled to 650°C to 750°C at a rate of 60°C/s to 150°C/s; in a second stage, the steel plate is cooled in air for 5 to 20 seconds; and in a third stage, the steel plate is cooled to 350°C to 500°C at a rate of 60°C/s to 150°C/s and then rolled up; and
5. (5) Air cooling the steel plate to room temperature.

In the manufacturing method of the present invention, in the first stage, the steel plate after finish rolling is cooled to a temperature of 650°C to 750°C at a cooling rate of 60°C/s to 150°C/s so that part of the austenite becomes ferrite is converted. If the temperature is lower than 650°C or higher than 750°C, the ferrite transformation in the structure of the steel plate is insufficient, which is not good for the formability and welding performance of the material. In the third stage, the steel plate is rolled up to a temperature of 350°C to 500°C at a speed of 60°C/s to 150°C/s, after which the steel plate is air-cooled to room temperature. During this process, most of the remaining austenite is converted to bainite, but a small amount of austenite (e.g. 5% to 10%) remains and forms retained austenite.

Furthermore, it is provided that the heating temperature for the plate blank is 1150° C. to 1250° C. in step (2) of the production method according to the invention.

In the above solution, the micro-alloy elements are insufficiently dissolved at a heating temperature for the plate blank below 1150°C, so that their effects are not utilized and the strength lowers; and at a blank plate heating temperature over 1250°C, the grains are liable to coarsening, which is disadvantageous for increasing the strength of the steel plate. On this basis, the heating temperature for the plate blank is controlled at 1150° C. to 1250° C. in the production method according to the invention.

Furthermore, it is provided that in the production method according to the invention in step (3) the rolling deformation is greater than 80%.

Furthermore, it is provided that the final rolling temperature is regulated to 830° C. to 900° C. in step (3) in the production method according to the invention.

Considering that in the above solution in step (3), the plate blank is subjected to rough rolling in a boundary of austenite recrystallization and the austenite grains are refined by recrystallization after rolling deformation, the rolling deformation is increased to more than 80% or the Finish rolling temperature in a non-recrystallized austenite range controlled to 830°C to 900°C, so that by the rolling deformation in the low-temperature austenite range, the deformation zone is formed in the austenite grains, and due to strain-induced carbonitride precipitation of micro-alloying elements, an austenite phase change product is refined, thereby improving toughness of the steel plate is improved.

Compared with the prior art, the hot-rolled steel for wheels having a tensile strength of more than 500 MPa and manufacturing methods thereof according to the present invention have the following advantages and advantageous effects:

The hot-rolled steel for wheels of the present invention has the features of high strength and good formability, and the hot-rolled steel for wheels has good cold workability and high elongation.

In addition, the hot-rolled steel for wheels of the present invention cannot be heat-treated, and its manufacturing cost is low. In addition, complex controlled cooling technology is not required after hot rolling. The hot rolled steel for wheels can be made by general laminar cooling process and is easy to produce.

Detailed Embodiments

Hereinafter, the hot-rolled steel for wheels having a tensile strength exceeding 500 MPa according to the present invention and manufacturing methods thereof will be explained and given with reference to specific examples. But this explanation and indication do not form an unacceptable limitation of the technical solutions of the present invention.

Examples 1 to 8

1. (1) Schmelzen und Gießen gemäß der in Tabelle 1 gezeigten chemischen Zusammensetzung.
2. (2) Heizen eines Plattenrohlings: Die Heiztemperatur für das Plattenrohling beträgt 1150°C bis 1250°C.
3. (3) Warmwalzen: Die Walzverformung ist größer als 80%, und die Endwalztemperatur liegt im Bereich von 830°C bis 900°C.
4. (4) Segmentiertes Abkühlen: in einer ersten Stufe wird eine Stahlplatte auf 650°C bis 750°C mit einer Geschwindigkeit von 60°C/s bis 150°C/s abgekühlt wird; in einer zweiten Stufe wird die Stahlplatte 5 bis 20 Sekunden lang in der Luft abgekühlt; und in einer dritten Stufe wird die Stahlplatte auf 350°C bis 500°C mit einer Geschwindigkeit von 60°C/s bis 150°C/s abgekühlt und dann aufgerollt; und
5. (5) Luftkühlen der Stahlplatte auf Raumtemperatur.

The hot-rolled steel for wheels in Embodiments 1 to 8 are manufactured through the following steps:

1. (1) Melting and casting according to the chemical composition shown in Table 1.
2. (2) Heating a blank plate: The heating temperature for the blank plate is 1150°C to 1250°C.
3. (3) Hot rolling: The rolling deformation is greater than 80%, and the finish rolling temperature is in the range of 830°C to 900°C.
4. (4) Segmented cooling: in a first stage, a steel plate is cooled to 650°C to 750°C at a rate of 60°C/s to 150°C/s; in a second stage, the steel plate is cooled in air for 5 to 20 seconds; and in a third stage, the steel plate is cooled to 350°C to 500°C at a rate of 60°C/s to 150°C/s and then rolled up; and
5. (5) Air cooling the steel plate to room temperature.

Table 1 lists the mass percentage of each chemical element in the hot-rolled steel for wheels of Working Examples 1 to 8. Table 1. (% by weight, the balance is Fe and other unavoidable impurities except P, S, O and N) Execution examples chemical composition C si Mn P S Cr Al N Ti Nb O 1 0.15 0.28 1.20 0.008 0.0031 - 0.035 0.0035 - 0.030 0.0020 2 0.15 0.28 1.20 0.008 0.0031 - 0.035 0.0035 - 0.030 0.0020 3 0.13 0.20 1:15 0.007 0.0030 - 0.043 0.0032 0.031 0.029 0.0025 4 0.13 0.20 1:15 0.007 0.0030 - 0.043 0.0032 0.031 0.029 0.0025 5 0.20 0.05 1.20 0.007 0.0030 0.35 0.052 0.0034 0.033 0.031 0.0017 6 0.20 0.05 1.20 0.007 0.0030 0.5 0.052 0.0034 0.033 0.031 0.0017 7 0.09 0.24 1:18 0.012 0.0045 - 0.043 0.0051 - 0.010 0.0030 8th 0.18 0.19 0.87 0.018 0.0041 - 0.025 0.0030 - 0.078 0.0021

Note that although no other elements such as Cu, Mo, B, etc. are contained in the above-mentioned working examples 1 to 8, the steel of the present invention may contain at least one of the following chemical elements: Cu≦0.5%, Mo≦ 0.2%, and B ≤ 0.005% to further improve the properties of steel.

Table 2 lists specific process parameters of the hot-rolled steel for wheels of working examples 1-5. Table 2: Execution examples blank plate heating (°C); Roll deformation (%) End roll temperature (°C) Cooling rate (°C/s) of the first stage Cooling rate (°C/s) of the second stage Air cooling time (s) of the second n stage Cooling rate (°C/s) of the third stage Rolling up temperat ure (°C) 1 1200 90 870 80 683 10 60 500 2 1150 88 853 150 738 16 150 350 3 1150 80 850 60 657 5 70 430 4 1250 87 850 120 705 18 80 464 5 1200 86 883 60 665 8th 120 358 6 1150 84 895 120 748 15 120 454 7 1250 87 832 150 725 20 80 487 8th 1150 86 865 100 689 12 110 400

• Vergleichsbeispiel 1 bezieht sich auf die Zusammensetzung und die Parameter des Herstellungsprozesses vom Ausführungsbeispiel 1 in der japanischen Patentliteratur mit der Veröffentlichungsnummer JPS 5935653 A, veröffentlicht am 27. Februar 1984 und betitelt „hochfeste warmgewalzte Stahlplatte“.
• Vergleichsbeispiel 2 bezieht sich auf die Zusammensetzung und die Parameter des Herstellungsprozesses vom Ausführungsbeispiel 1 in der japanischen Patentliteratur mit der Veröffentlichungsnummer JPS 57155347 A, veröffentlicht am 25. September 1982 und betitelt „hochfeste warmgewalzte Stahlplatte für Radfelgen mit hervorragender Abbrennstumpfschweißbarkeit“.
• Vergleichsbeispiel 3 bezieht sich auf die Zusammensetzung und die Parameter des Herstellungsprozesses vom Ausführungsbeispiel A in der j apanischen Patentliteratur mit der Veröffentlichungsnummer JPS 56130455 A, veröffentlicht am 13. Oktober 1981 und betitelt „hochfeste warmgewalzte Stahlplatte mit guter Abbrennstumpfschweißbarkeit und Bearbeitbarkeit“.

In order to verify the implementation effect of the present invention and at the same time prove the superior effect of the present invention compared to the prior art, the hot-rolled steels for wheels of Embodiments 1 to 8 and Comparative Examples 1 to 3 were tested. The test specimen represents the process control during rolling and the mechanical properties ten of the obtained steel plate with a thickness of 3 mm. The test is carried out according to the standard GB6397-86. Note that the gauge length of the tensile specimens of each embodiment and the comparative example is 50 mm. Included:

• Comparative Example 1 refers to the composition and manufacturing process parameters of Example 1 in Japanese Patent Literature Publication No. JPS 5935653 A published on February 27, 1984 and entitled "High Strength Hot-Rolled Steel Plate".
• Comparative Example 2 refers to the composition and manufacturing process parameters of Working Example 1 in Japanese Patent Literature Publication No. JPS 57155347 A, published September 25, 1982 and entitled "High Strength Hot-Rolled Steel Plate for Wheel Rims Excellent in Flash Butt Weldability".
• Comparative Example 3 refers to the composition and manufacturing process parameters of Embodiment A in Japanese Patent Literature Publication No. JPS 56130455 A published on Oct. 13, 1981 and entitled "High Strength Hot-Rolled Steel Plate Having Good Flash Butt Weldability and Workability".

Table 3 lists the test results of various working examples and comparative examples. Table 3: number Yield Strength (MPa) Tensile Strength (MPa) Strain (%) microstructure Example 1 558 638 34 7% Ar - 40% B - 53% F Example 2 562 657 34 7% Ar - 40% B - 53% F Example 3 634 701 30 5% Ar - 45% B - 50% F Example 4 623 675 32 5% Ar - 45% B - 50% F Example 5 578 653 34 7% Ar - 40% B - 53% F Example 6 530 605 36 10% Ar - 30% B - 60% F Example 7 407 508 40 5% Ar - 30% B - 65% F Example 8 498 572 39 8% Ar - 35% B - 57% F Comparative example 1 510 674 29 F+P Comparative example 2 - 599 30 F+P Comparative example 3 448 574 27.6 F+P
Notes: In Table 3, Ar stands for retained austenite, B for bainite, F for ferrite and P for pearlite.

It can be seen from Table 3 that the microstructure of the hot-rolled steel for wheels of various embodiments of the present invention is formed of ferrite, bainite and retained austenite, wherein the phase ratio of retained austenite is 5% to 10% and the phase ratio of bainite is 30% to 45%, with the balance being ferrite. Therefore, as compared with Comparative Examples 1 to 3, the mechanical properties and formability of various embodiments of the present invention are excellent. The tensile strength of the hot-rolled steel for wheels of various embodiments of the present invention is 500 MPa to 700 MPa and its elongation is ≥ 30%. Although the tensile strength of Comparative Example 1 is similar to that of Working Example 4, the elongation of this Comparative Example is 3% lower than that of Working Example 4, and the workability and cold workability in this Comparative Example are significantly reduced. Although the elongation of Comparative Example 2 is the same as that of Working Example 3 and is 30%, the tensile strength of this Comparative Example is significantly lower than that of Working Example 3.

It should be noted that Table 2 shows that the hot-rolled steels for wheels in various embodiments of the present invention do not need to be subjected to heat treatment during the manufacturing process, so the process is simple and the manufacturing cost is low.

In summary, the hot-rolled steel for wheels of the present invention has the features of high strength and good formability, and the hot-rolled steel for wheels has good cold workability and high elongation.

In addition, the hot-rolled steel for wheels of the present invention cannot be heat-treated, and its manufacturing cost is low. In addition, complex controlled cooling technology is not required after hot rolling. The hot-rolled steel for wheels can be made by a general laminar cooling process, so it is easy to produce.

It should be noted that the "prior art" part in the scope of the present invention is not limited to the embodiments given in the present disclosure, and all prior art that does not contradict the solution of the present invention, including but not limited to prior patent literature, prior publications, prior public uses, etc., can be included within the scope of the present invention.

In addition, the combination of each technical feature of the present invention is not limited to the combination described in the claims of the present invention or the combination described in the specific embodiments. All technical features described herein can be freely combined or combined in any way, unless there is a contradiction between them.

It should also be noted that the embodiments listed above are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments. And the following similar changes or transformations can be directly derived or easily conceived by those skilled in the art from the contents disclosed in the present invention and are intended to fall within the scope of the present invention.

Claims (15)

Hot-rolled steel for wheels with a tensile strength above 500 MPa, characterized in that it contains the following chemical elements in percentage by mass: C: 0.09% to 0.2%, Mn: 0.8% to 1.2%, Al : 0.025% to 0.060%, Nb: 0.01% to 0.10%, 0<Si≦0.3%; the balance being Fe and other unavoidable impurities. Hot rolled steel for wheels with tensile strength over 500 MPa claim 1 , characterized in that it further comprises at least one of the following chemical elements: Ti ≤ 0.05% and Cr ≤ 0.5%. Hot rolled steel for wheels with tensile strength over 500 MPa claim 1 , characterized in that it further comprises at least one of the following chemical elements: Cu ≤ 0.5%, Mo ≤ 0.2%, and B ≤ 0.005%. Hot rolled steel for wheels with tensile strength over 500 MPa claim 1 , characterized in that in the other unavoidable impurities: S ≤ 0.005%, P ≤ 0.035%, N ≤ 0.0060%, and O ≤ 0.0030%. Hot rolled steel for wheels with tensile strength over 500 MPa claim 1 , characterized in that 0.05% ≤ Si ≤ 0.3% applies. Hot rolled steel for wheels with tensile strength over 500 MPa claim 1 , characterized in that Nb is 0.01% to 0.08%. Hot rolled steel for wheels with tensile strength over 500 MPa claim 1 , characterized in that its microstructure is formed from ferrite, bainite and retained austenite. Hot rolled steel for wheels with tensile strength over 500 MPa claim 7 , characterized in that the phase fraction of retained austenite is 5% to 10% and the phase fraction of bainite is 30% to 45%, the balance being ferrite. Hot rolled steel for wheels with a tensile strength exceeding 500 MPa according to any of Claims 1 until 8th , characterized in that its tensile strength is 500 MPa to 700 MPa and its elongation is ≥ 30%. Hot rolled steel for wheels with a tensile strength exceeding 500 MPa according to any of Claims 1 until 9 , characterized in that its yield point is 400 MPa to 650 MPa. Hot rolled steel for wheels with a tensile strength exceeding 500 MPa according to any of Claims 1 until 10 , characterized in that its elongation is ≥ 32% and preferably ≥ 34%. Production method for producing a hot-rolled steel for wheels according to any one of Claims 1 until 11 , characterized in that the manufacturing method has no heat treatment step, and the manufacturing method comprises the following steps: (1) melting and casting; (2) heating a disk blank; (3) hot rolling; (4) Segmented cooling: in a first stage, a steel plate is cooled to 650°C to 750°C at a rate of 60°C/s to 150°C/s; in a second stage, the steel plate is cooled in air for 5 to 20 seconds; and in a third stage, the steel plate is cooled to 350°C to 500°C at a rate of 60°C/s to 150°C/s and then rolled up; and (5) air cooling the steel plate to room temperature. manufacturing process claim 12 , characterized in that in the step (2), the heating temperature for the plate blank is 1150°C to 1250°C. manufacturing process claim 12 , characterized in that in step (3) the rolling deformation is greater than 80%. manufacturing process claim 12 , characterized in that in step (3) the final rolling temperature is controlled to 830°C to 900°C.