800mpa grade steel for wheel rim and method for manufacturing the same

Abstract

The application relates to an 800MPa-grade steel for a wheel rim and a preparation method thereof, and the chemical components of the steel for the wheel rim include C, Si, Mn, P, S, Als, Cr, Nb, Ti and Fe; wherein, the content of C is 0.08%-0.10% in mass fraction, the content of Si is 0.05%-0.20% in mass fraction, the content of Mn is 1.65%-1.90% in mass fraction, the content of Cr is 0.45%-0.65% in mass fraction, the content of Nb is 0.041%-0.060% in mass fraction, and the content of Ti is 0.031%-0.080% in mass fraction; the microstructure of the steel for the wheel rim includes ferrite and bainite, the volume fraction of the ferrite is 70%-75%, and the volume fraction of the bainite is 25%-30%. The 800MPa-grade steel for the wheel rim has good cold forming performance and a higher fatigue strength limit.

Description

Technical Field

[0001] This application relates to the field of steel preparation technology, and in particular to an 800MPa grade steel for wheel rims and its preparation method. Background Technology

[0002] Tubeless car wheel rims mostly use high-strength steel with a tensile strength of 500MPa and above as raw materials, and there is an increasing emphasis on achieving lightweight tubeless car wheel rims by upgrading material strength.

[0003] Currently, the production and processing of lightweight tubeless wheel rims for commercial vehicles requires complex cold deformation processes such as rolling, welding, drawing, and roll forming. For 22.5×9.0J commercial vehicle wheel rims weighing 28-31kg, the rim material thickness is reduced from 5.0-6.0mm to 4.0-5.0mm. To ensure that the fatigue life of the wheel is not reduced, the tensile strength of the material is upgraded to 800MPa. However, after rolling and welding, cracking and micro-crack defects are very likely to occur during the flaring, drawing, and roll forming processes. Micro-crack defects will lead to a reduction in the service life of the wheel, which wastes materials and increases safety hazards. Summary of the Invention

[0004] This application provides an 800MPa grade steel for wheel rims and a method for preparing the same, in order to solve the following technical problem: how to improve the formability of 800MPa grade steel for wheel rims.

[0005] In a first aspect, this application provides an 800MPa grade steel for wheel rims, the chemical composition of which includes:

[0006] C, Si, Mn, P, S, Als, Cr, Nb, Ti, and Fe; wherein, by mass fraction,

[0007] The C content is 0.08%–0.10%, the Si content is 0.05%–0.20%, the Mn content is 1.65%–1.90%, the Cr content is 0.45%–0.65%, the Nb content is 0.041%–0.060%, and the Ti content is 0.031%–0.080%.

[0008] The microstructure of the steel used for the wheel rim includes ferrite and bainite, with the volume fraction of ferrite being 70% to 75% and the volume fraction of bainite being 25% to 30%.

[0009] Optionally, the content of P is ≤0.010%, the content of S is ≤0.005%, and the content of Als is 0.02% to 0.05%.

[0010] Optionally, the grain size of the steel used for the wheel rim is grade 13 to 14.

[0011] Optionally, the steel used for the wheel rim meets the following mechanical properties: tensile strength of 780MPa to 830MPa, elongation A50 of 18% to 23%, yield strength ratio of 0.82 to 0.89, and fatigue strength limit of 431MPa to 454MPa.

[0012] Optionally, the thickness of the steel used for the wheel rim is 2mm to 6mm.

[0013] Secondly, this application provides a method for preparing the 800MPa grade wheel rim steel described in the first aspect, the method comprising:

[0014] The slab is heated and rolled to obtain a hot-rolled plate;

[0015] The hot-rolled plate is sequentially cooled by a first water cooling, an air cooling, and a second water cooling, and the process parameters of the first water cooling, the air cooling, and the second water cooling are controlled. Then it is coiled to obtain 800MPa grade steel for wheel rims.

[0016] Optionally, the process parameters of the first water cooling include: a cooling rate of 50℃ / s to 80℃ / s, an initial cooling temperature of 840℃ to 900℃, and an end cooling temperature of 680℃ to 740℃.

[0017] Optionally, the air cooling process parameters include: air cooling time of 6s to 10s.

[0018] Optionally, the process parameters for the second water cooling include: a cooling rate of 50℃ / s to 80℃ / s, an initial cooling temperature of 630℃ to 690℃, and an end cooling temperature of 420℃ to 500℃.

[0019] Optionally, the heating temperature is 1200℃~1250℃; and / or,

[0020] The rolling process includes roughing and finishing, wherein the finishing temperature of the roughing is 1060℃~1100℃ and the finishing temperature is 840℃~900℃; and / or,

[0021] The winding temperature is 420℃~500℃.

[0022] The technical solutions provided in this application have the following advantages compared with the prior art:

[0023] The 800MPa grade wheel rim steel provided in this application embodiment has the following chemical composition: C, Si, Mn, P, S, Als, Cr, Nb, Ti, and Fe; wherein, by mass fraction, the content of C is 0.08%–0.10%, the content of Si is 0.05%–0.20%, the content of Mn is 1.65%–1.90%, the content of P is ≤0.010%, the content of S is ≤0.005%, the content of Als is 0.02%–0.05%, the content of Cr is 0.45%–0.65%, the content of Nb is 0.041%–0.060%, and the content of Ti is 0.031%–0.080%; the microstructure of the wheel rim steel includes ferrite, and the volume fraction of the ferrite is 70%–75%. In the chemical composition of wheel rim steel, C and Mn are used as the basic strengthening elements. C, Mn, and Cr ensure the hardenability of the wheel rim steel to form bainite structure, thereby improving the strength of the 800MPa grade wheel rim steel. Si plays a solid solution strengthening role. A higher Si content can inhibit the precipitation of C compounds, thereby promoting the formation of ferrite and allowing C to diffuse into the retained austenite, ensuring the plasticity of the 800MPa grade wheel rim steel. Nb and Ti elements can increase the temperature of the non-recrystallized austenite region during the subsequent finishing rolling stage, increase the deformation of the non-recrystallized austenite region, thereby refining the grains of the 800MPa grade wheel rim steel. At the same time, appropriate precipitation and solid solution in ferrite can improve the strength of ferrite. A ferrite content of 70% to 75% can ensure the plasticity of the wheel rim steel and improve its elongation, thus giving the wheel rim steel good deformability and preventing cracking problems during subsequent cold forming. In summary, the formability of steel for 800MPa grade wheel rims has been improved. Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic flowchart illustrating a method for preparing 800MPa grade wheel rim steel according to some embodiments of this application;

[0027] Figure 2The metallographic structure of the 800MPa grade wheel rim steel according to Embodiment 1 of this application is located at 1 / 4 of the thickness and magnified by 1000 times.

[0028] Figure 3 The metallographic structure of the steel used for the wheel rim according to Comparative Example 1 of this application is shown at 1 / 4 of the thickness, with a magnification of 500x.

[0029] Figure 4 The metallographic structure of the steel used for the wheel rim according to Comparative Example 2 of this application is located at 1 / 4 of the thickness and magnified by 1000 times.

[0030] Figure 5 The metallographic structure of the steel used for the wheel rim according to Comparative Example 3 of this application is located at 1 / 4 of the thickness and magnified by 1000 times.

[0031] Figure 6 The metallographic structure of the steel used for the wheel rim according to Comparative Example 4 of this application is shown at 1 / 4 of the thickness, magnified 1000 times. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical 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 single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0034] In this application, the terms "comprising," "including," etc., mean "including but not limited to." Relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0036] In a first aspect, this application provides an 800MPa grade steel for wheel rims, the chemical composition of which includes:

[0037] C, Si, Mn, P, S, Als, Cr, Nb, Ti, and Fe; wherein, by mass fraction,

[0038] The C content is 0.08%–0.10%, the Si content is 0.05%–0.20%, the Mn content is 1.65%–1.90%, the Cr content is 0.45%–0.65%, the Nb content is 0.041%–0.060%, and the Ti content is 0.031%–0.080%.

[0039] The microstructure of the steel used for the wheel rim includes ferrite and bainite, with the volume fraction of ferrite being 70% to 75% and the volume fraction of bainite being 25% to 30%.

[0040] In some embodiments, the content of P is ≤0.010%, the content of S is ≤0.005%, and the content of Als is 0.02% to 0.05%.

[0041] In the embodiments of this application, the functions of the above-mentioned chemical elements are as follows:

[0042] C: The content of carbon (C) has a significant impact on the hardenability, compositional segregation, tensile strength, hardness, elongation, and other microstructural properties of steel. To achieve high formability and fatigue resistance while ensuring strength, and to obtain a uniform ferrite-bainite microstructure, the composition needs to guarantee hardenability without increasing the tendency for microstructure segregation. Therefore, the C content is controlled within the aforementioned range. For example, the C content can be 0.08%, 0.085%, 0.09%, 0.095%, 0.10%, etc.

[0043] Si: Si plays a solid solution strengthening role in steel. A higher Si content can inhibit carbide precipitation and promote ferrite formation, allowing carbon to diffuse into the retained austenite and ensuring a certain degree of plasticity in the steel. However, excessive Si content can lead to severe oxidation of the strip surface, affecting surface quality. For example, the Si content can be 0.05%, 0.1%, 0.15%, 0.2%, etc.

[0044] Mn: Mn plays a solid solution strengthening role in steel, improving the strength of the steel plate after quenching. Mn is an austenite stabilizing element, lowering the austenite transformation temperature and promoting the dissolution of carbon in austenite. If its content is too low, the material strength requirements cannot be met; however, adding excessive Mn will reduce elongation and increase the severity of component segregation in the slab. For example, the Mn content mentioned above can be 1.65%, 1.70%, 1.75%, 1.80%, 1.85%, 1.90%, etc.

[0045] P and S: P and S are harmful elements in steel. P severely impairs the plasticity and toughness of steel plates; S combines with Mn and other compounds in steel to form manganese sulfide, a plastic inclusion, which is particularly detrimental to the transverse plasticity and toughness of steel. Therefore, the content of P and S should be as low as possible. For example, the content of P can be 0.010%, 0.009%, 0.008%, or 0.007%; the content of S can be 0.005%, 0.004%, or 0.003%, etc.

[0046] Als: Als mainly plays a deoxidizing role in liquid steel. For example, the Al content can be 0.02%, 0.03%, 0.04%, 0.05%, etc.

[0047] Cr: Cr improves the hardenability of steel and ensures its strength. While forming ferrite, Cr also enhances the formation of retained austenite and inhibits the transformation of pearlite. For example, the Cr content can be 0.45%, 0.5%, 0.55%, 0.60%, 0.65%, etc.

[0048] Nb and Ti: Nb is a strong carbon compound-forming element that can delay the recrystallization process of hot-rolled austenite. Nib in solution state delays both static and dynamic recrystallization during hot deformation, increases the non-recrystallization temperature, and helps refine austenite grains during the finishing rolling stage. In the subsequent air-cooling stage of the steel plate and after coiling, both Nb precipitation and solution can improve ferrite strength and reduce the hardness difference between ferrite and martensite, which is beneficial to fatigue performance. Ti has a similar effect to Nb; Ti can preferentially precipitate by combining with nitrogen at high temperatures, thus refining austenite. Simultaneously, its carbides precipitate in the ferrite matrix, playing a precipitation strengthening role. However, excessively high Ti content can easily cause significant fluctuations in mechanical properties. For example, the Nb content can be 0.041%, 0.045%, 0.050%, 0.055%, 0.060%, etc., and the Ti content can be 0.031%, 0.035%, 0.040%, 0.045%, 0.050%, 0.055%, 0.060%, 0.065%, 0.070%, 0.075%, 0.080%, etc.

[0049] Ferrite is a relatively soft phase that gives wheel rim steel good plasticity and increases elongation, thus providing good formability. A large amount of ferrite ensures the material's plasticity, increases elongation, and provides good formability, preventing cracking during cold deformation. Bainite is a relatively hard phase that gives dual-phase steel high strength, making it less prone to cracking during service and further improving fatigue performance. For example, the volume fraction of ferrite can be 70%, 71%, 72%, 73%, 74%, 75%, etc., and the volume fraction of bainite can be 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0050] In some embodiments, the grain size of the steel used for the wheel rim is grade 13 to 14.

[0051] In this embodiment, a larger grain size grade corresponds to a smaller grain size. Controlling the grain size grade to 13-14 allows for a smaller grain size, which is beneficial for improving the strength and toughness of the steel used in wheel rims. Conversely, a smaller grain size results in a larger grain size, which weakens the fine-grain strengthening effect and reduces the strength and toughness of the steel used in wheel rims. For example, the grain size of the steel used in wheel rims can be grade 13, 13.5, or 14, etc.

[0052] In some embodiments, the steel used for the wheel rim meets the following mechanical properties: tensile strength of 780MPa to 830MPa, elongation A50 of 18% to 23%, yield strength ratio of 0.82 to 0.89, and fatigue strength limit of 431MPa to 454MPa.

[0053] In some embodiments, the thickness of the steel used for the wheel rim is 2mm to 6mm.

[0054] In the embodiments of this application, the steel used for wheel rims possesses the aforementioned excellent mechanical properties, and the steel used for wheel rims is used for welding, exhibiting excellent weldability with a weld cracking rate ≤3%. The thickness of the steel used for wheel rims can be 2mm, 3mm, 4mm, 5mm, 6mm, etc.

[0055] Figure 1 This is a schematic flowchart illustrating a method for preparing 800MPa grade wheel rim steel according to some embodiments of this application; please refer to... Figure 1 This application provides a method for preparing the 800MPa grade wheel rim steel described in the first aspect, the method comprising:

[0056] S1. The slab is heated and rolled to obtain a hot-rolled plate;

[0057] S2. The hot-rolled plate is sequentially cooled by first water cooling, air cooling and second water cooling, and the process parameters of the first water cooling, the air cooling and the second water cooling are controlled. Then it is coiled to obtain 800MPa grade steel for wheel rims.

[0058] In some embodiments, the process parameters of the first water cooling include: a cooling rate of 50°C / s to 80°C / s, an initial cooling temperature of 840°C to 900°C, and an end cooling temperature of 680°C to 740°C.

[0059] In some embodiments, the air cooling process parameters include an air cooling time of 6s to 10s.

[0060] In some embodiments, the process parameters of the second water cooling include: a cooling rate of 50°C / s to 80°C / s, an initial cooling temperature of 630°C to 690°C, and an end cooling temperature of 420°C to 500°C.

[0061] In this embodiment, a three-stage cooling method is used in the cooling process: first water cooling + air cooling + second water cooling. The first water cooling stage allows a large amount of ferrite to form in the wheel rim steel, giving it good cold formability. The second water cooling stage transforms residual austenite in the wheel rim steel into bainite, resulting in good fatigue strength. If the first water cooling rate is too low, production efficiency is low; if the first water cooling rate is too high, it is detrimental to sheet shape control. The end temperature of the first water cooling is the ferrite transformation temperature. If the end temperature is too low, pearlite is easily formed; if the end temperature is too high, it is difficult for austenite in the steel to form ferrite. For example, in the process parameters of the first water cooling described above, the cooling rate can be 50℃ / s, 55℃ / s, 60℃ / s, 65℃ / s, 70℃ / s, 75℃ / s, 80℃ / s, etc., the initial cooling temperature can be 840℃ / s, 850℃ / s, 860℃ / s, 870℃ / s, 880℃ / s, 890℃ / s, 900℃ / s, etc., and the initial cooling temperature can be 680℃ / s, 690℃ / s, 700℃ / s, 710℃ / s, 720℃ / s, 730℃ / s, 740℃ / s, etc.

[0062] The air cooling time should not be too long, otherwise it will increase the ferrite volume fraction and reduce the strength, and at the same time shorten the water cooling time of the second stage, making it impossible to cool to the coiling temperature due to insufficient cooling line length; if the air cooling time is too short, the ferrite content will be insufficient. For example, the air cooling time can be 6s, 7s, 8s, 9s, 10s, etc.

[0063] If the second water cooling rate is too high, it will hinder sheet shape control; if the second water cooling rate is too low, it will form a pearlite structure, reducing strength. Furthermore, it will affect production efficiency because insufficient cooling line length will prevent cooling to the coiling temperature. If the second water cooling end temperature is too low, the retained austenite will not completely transform into bainite, but will partially transform into martensite, worsening weldability; if the second water cooling end temperature is too high, the retained austenite will not completely transform into bainite, but will partially transform into pearlite, reducing strength. For example, in the process parameters of the second water cooling described above, the cooling rate can be 50℃ / s, 55℃ / s, 60℃ / s, 65℃ / s, 70℃ / s, 75℃ / s, 80℃ / s, etc., the initial cooling temperature can be 630℃ / s, 640℃ / s, 650℃ / s, 660℃ / s, 670℃ / s, 680℃ / s, 690℃ / s, etc., and the initial cooling temperature can be 420℃ / s, 430℃ / s, 450℃ / s, 440℃ / s, 460℃ / s, 470℃ / s, 480℃ / s, 490℃ / s, 500℃ / s, etc. As one embodiment, in the first stage of water cooling, the cooling rate can be 60℃ / s, the ending temperature can be 720℃, and the air cooling time can be 10s; in the second stage of water cooling, the cooling rate can be 60℃ / s.

[0064] In some embodiments, the heating temperature is 1200°C to 1250°C; and / or,

[0065] The rolling process includes roughing and finishing, wherein the finishing temperature of the roughing is 1060℃~1100℃ and the finishing temperature is 840℃~900℃; and / or,

[0066] The winding temperature is 420℃~500℃.

[0067] In the embodiments of this application, the heating temperature can be 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, 1250℃, etc.; the finishing temperature of the rough rolling can be 1060℃, 1070℃, 1080℃, 1090℃, 1100℃, etc.; the finishing temperature of the finishing rolling can be 840℃, 850℃, 860℃, 870℃, 880℃, 900℃, etc.; and the coiling temperature can be 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, etc.

[0068] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0069] The specific chemical composition of an 800MPa grade steel for wheel rims is shown in Table 1.

[0070] Table 1. Chemical composition (wt%) of steel used for 800MPa grade wheel rims, the remainder being Fe and unavoidable impurities.

[0071]

[0072]

[0073] A method for preparing 800MPa grade steel for wheel rims, comprising:

[0074] (1) After KR desulfurization, the molten iron undergoes double refining treatment of LF refining + RH refining, followed by Ca treatment with pure Ca wire; after soft blowing, it enters the tundish, and then is cast under full protection using a continuous casting crystallizer; after casting, it is placed in a slow cooling pit for slow cooling to obtain a slab, the chemical composition of which is shown in Table 1, with the balance being Fe and unavoidable impurities; the Si-Fe alloy used in the LF refining furnace is FeSiAl2.0 alloy, the Mn-Fe alloy used is FeMn78C2.0 alloy, the Nb-Fe alloy used is FeNb60-A alloy (65% Nb), and the Cr-Fe alloy used is FeCr55C400. The Mn-Fe alloy used in the RH refining furnace is FeMn78C2.0 alloy, the Nb-Fe alloy used is FeNb60-A alloy (65% Nb), and the Ti-Fe alloy used is FeTi30-A.

[0075] (2) After heating the slab, it undergoes homogenization heat treatment, followed by descaling and width determination. Then, it is subjected to rough rolling (passes 1+5) and finish rolling (passes 5). After finish rolling, laminar flow cooling is performed using a three-stage cooling method: water cooling in the first stage, air cooling in the second stage, and water cooling in the third stage. After laminar flow cooling, the slab is coiled and cooled to room temperature to obtain steel for wheel rims. The control of process parameters in the above steps is shown in Tables 2 and 3.

[0076] Table 2 Process parameters for heating and rolling

[0077]

[0078]

[0079] Table 3 Process parameters for cooling and winding

[0080]

[0081] Table 4. Microstructure and Grain Size Grade of Steel for 800MPa Grade Wheel Rim

[0082]

[0083]

[0084] Table 5 Properties of 800MPa Grade Steel for Wheel Rim

[0085]

[0086] Samples of the steel used for wheel rims prepared in Examples 1-9 and Comparative Examples 1-4 were taken. After grinding and polishing, the metallographic samples were etched with a 4% nitric acid alcohol solution and then photographed using a Leica-DMI5000M metallographic microscope to obtain the metallographic structure and evaluate the grain size grade. The results are shown in Table 4.

[0087] Mechanical properties, including yield strength, tensile strength, and elongation, were tested according to GB / T 228; cold bending performance was tested according to GB / T 232; and the fatigue strength limit was tested according to GB / T 3075-2008, Axial Force Control Method for Fatigue Testing of Metallic Materials. The results are shown in Table 5. In the 180° transverse cold bending in Table 5, b = 35 mm and d = 2a, where b is the bending radius and a is the material thickness. The samples were welded into rims, then flared, rolled three times, and expanded for shaping. The cracking rate at the weld is shown in Table 5. A lower cracking rate indicates better weldability and formability of the material.

[0088] In summary, the 800MPa grade wheel rim steel provided in this application embodiment has excellent tensile strength of 780-830MPa, A50 elongation of 18-23%, yield strength ratio of 0.82-0.89, good formability, fatigue strength limit of 431-454MPa, high fatigue strength, and weld cracking rate ≤3%. For example, Figure 2 The metallographic structure of the 800MPa grade wheel rim steel according to Embodiment 1 of this application is located at 1 / 4 of the thickness, with a magnification of 1000x. Please refer to [link to documentation]. Figure 2 .

[0089] In Comparative Example 1, the Mn content is too low, the Cr content is too low, and the Ti content is too high; the second cooling rate is too low, the second cooling end temperature is too high, resulting in a high yield strength ratio, a low fatigue strength limit, and a high cracking rate. For example, Figure 3 For the metallographic structure of the steel used for the wheel rim according to Comparative Example 1 of this application, located at 1 / 4 of the thickness, at a magnification of 500x, please refer to [link / reference]. Figure 3 The ferrite content is relatively high.

[0090] Comparative Example 2, lacking Cr and having excessively high Ti content, did not employ the three-stage cooling method described in this application's embodiments, resulting in a high yield strength ratio, low fatigue strength limit, and high cracking rate. For example, Figure 4For the metallographic structure of the steel used for the wheel rim according to Comparative Example 2 of this application, located at 1 / 4 of the thickness, at a magnification of 1000x, please refer to [link / reference]. Figure 4 Pearlite is precipitated, but bainite is not present.

[0091] In Comparative Example 3, the Mn content was too low, the Cr content was too low, and the Ti content was too high. Using the three-stage cooling method described in this application, the tensile strength was low, the fatigue strength limit was low, and the cracking rate was high. For example, Figure 5 For the metallographic structure of the steel used for the wheel rim according to Comparative Example 3 of this application, located at 1 / 4 of the thickness, at a magnification of 1000x, please refer to [link / reference]. Figure 5 The ferrite content is relatively high.

[0092] In Comparative Example 4, the second cooling rate is too low and the second cooling end temperature is too high. The three-stage cooling method used in this embodiment of the application results in high tensile strength, high yield strength ratio, and high cracking rate. For example, Figure 6 For the metallographic structure of the steel used for the wheel rim according to Comparative Example 4 of this application, located at 1 / 4 of the thickness, at a magnification of 1000x, please refer to [link / reference]. Figure 6 The ferrite content is relatively high.

[0093] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A type of 800MPa grade steel for wheel rims, characterized in that, The chemical composition of the steel used for the wheel rim is as follows: The composition includes C, Si, Mn, P, S, Als, Cr, Nb, Ti, and the remainder being Fe and unavoidable impurities; wherein, by mass fraction, the content of C is 0.08%~0.10%, the content of Si is 0.05%~0.20%, the content of Mn is 1.65%~1.90%, the content of Cr is 0.45%~0.65%, the content of Nb is 0.041%~0.060%, and the content of Ti is 0.031%~0.080%. The microstructure of the steel used for the wheel rim consists of ferrite and bainite, with the volume fraction of ferrite being 70%~75% and the volume fraction of bainite being 25%~30%. The steel used for the wheel rims meets the following mechanical properties: tensile strength of 780MPa~830MPa, elongation A50 of 18%~23%, yield strength ratio of 0.82~0.89, and fatigue strength limit of 431MPa~454MPa.

2. The steel for wheel rims according to claim 1, characterized in that, The content of P is ≤0.010%, the content of S is ≤0.005%, and the content of Als is 0.02%~0.05%.

3. The steel for wheel rims according to claim 1, characterized in that, The 800MPa grade wheel rim The grain size of the steel used is grade 13 to 14.

4. The steel for wheel rims according to claim 1, characterized in that, The 800MPa grade wheel rim The thickness of the steel used is 2mm to 6mm.

5. A method for preparing 800MPa grade wheel rim steel according to any one of claims 1 to 4, characterized in that, The method includes: The slab is heated and rolled to obtain a hot-rolled plate; The hot-rolled plate is sequentially cooled by a first water cooling, an air cooling, and a second water cooling, and the process parameters of the first water cooling, the air cooling, and the second water cooling are controlled. Then it is coiled to obtain 800MPa grade steel for wheel rims. The process parameters for the first water cooling include: a cooling rate of 50℃ / s to 80℃ / s, an initial cooling temperature of 840℃ to 900℃, and an end cooling temperature of 680℃ to 740℃. The air cooling process parameters include: air cooling time of 6s to 10s; The process parameters for the second water cooling include: a cooling rate of 50℃ / s to 80℃ / s, an initial cooling temperature of 630℃ to 690℃, and an end cooling temperature of 420℃ to 500℃.

6. The method according to claim 5, characterized in that, The heating temperature is 1200℃~1250℃; And / or, The rolling process includes roughing and finishing, wherein the finishing temperature of the roughing is 1060℃~1100℃, and the finishing temperature is... The final temperature is 840℃~900℃; and / or, The winding temperature is 420℃~500℃.

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