Method for reducing the flash welding forming cracking rate of 590mpa grade rim wheel steel

Abstract

The application discloses a method for reducing the flash welding forming cracking rate of 590MPa grade wheel rim wheel steel, and the chemical components of the wheel steel are as follows in percentage by weight: C: 0.06-0.10%, Si: 0.05-0.30%, Mn: 1.40-1.60%, P: 0.020% or less, S: 0.010% or less, Alt: 0.020-0.040%, Nb: 0.035-0.055%, Ti: 0.010-0.025%, N: 0.0040-0.0060%, Ti / N: 2.0-4.0, and the balance is Fe and inevitable impurities; and the manufacturing process comprises the following steps: final rolling temperature: 840-880 DEG C, cooling speed after final rolling: 20-30 DEG C / s, and coiling temperature: 570-600 DEG C. The application aims to provide a method for reducing the flash welding forming cracking rate of 590MPa grade wheel rim wheel steel, improving the welding process adaptability of products, reducing the welding forming cracking rate, and reducing the waste product rate.

Description

Technical Field

[0001] This invention relates to the field of high-strength steel welding technology, and in particular to a method for reducing the cracking rate of flash welding of wheel steel for 590MPa grade wheel rims. Background Technology

[0002] With the rapid development of the automotive industry and the increasing environmental awareness of the public, lightweighting, safety, energy conservation, and environmental protection have become the mainstream directions for automotive development. In the field of automotive lightweighting, the lightweighting of automotive components is key, and wheels, as an important part of a car, have great potential for lightweighting. As a rotating component, the wheel rim achieves a lightweighting effect 1.2-1.3 times that of other non-rotating parts. Therefore, the lightweighting of automotive wheels mainly focuses on the rim, primarily through the use of higher-strength materials to significantly reduce weight while meeting load-bearing requirements.

[0003] In the production of steel wheels, high-strength steel rims primarily utilize flash butt welding to join materials. Flash butt welding eliminates the need for filler material, is simple to operate, highly efficient, and produces excellent weld quality. Its advantages, including good weld quality, no need for filler material, fast welding speed, and ease of operation, have led to its widespread use in automotive wheel rim production. Stable and reliable weld quality is a prerequisite for ensuring the safety and lifespan of automotive products. However, with the rise of lightweighting concepts, the strength grades of low-alloy high-strength steel plates are continuously increasing, while the thickness of the steel plates is also decreasing. This results in some weldability issues still existing during the rim production process. For example, weld cracking can occur during the forming process after flash welding, a disadvantage of flash butt welding of wheel rims, particularly in terms of fracture toughness, which is a common challenge faced by major wheel rim manufacturers.

[0004] Weld cracking is mostly caused by factors such as weld composition segregation, abnormal structure and micro-defects due to the quality of the base material itself or improper welding process. The reasons are generally considered to be as follows: (1) The joint interface did not completely remove liquid metal or other oxides, inclusions, etc. during the upsetting process. This can be improved by appropriately adjusting the upsetting pressure and upsetting amount parameters; (2) The joint interface area and heat-affected zone have structures that are highly sensitive to cracking after welding, such as Widmanstätten, martensite or bainite. Increasing the preheating before welding and appropriately controlling the cooling rate will help improve the cracking; (3) The influence of materials, such as the rolling temperature, grain size and carbon and other alloying element content of the material, all have a certain impact on the comprehensive performance of the welded joint of automobile wheel rims. However, it is rare to form a comprehensive evaluation method for the welding cracking of high-strength wheel hub steel.

[0005] The steel used for wheels must solve a series of problems, such as weld cracking and softening of the heat-affected zone during forming and welding assembly.

[0006] Patent CN 111334715A discloses a wheel steel adapted to welding heat effects and its production method. It mainly solves the problems of wheel steel from the aspects of composition design, smelting and rolling and microstructure control. The designed steel grades are 380CL-540CL. This invention patent has a higher strength level and more evaluation methods and means.

[0007] Patent CN 107675088 B discloses steel for thick wheel rims with a tensile strength ≥590MPa and its production method. The thickness specifications involved are not less than 10mm, and it mainly focuses on manufacturing fine-grained wheel steel through chemical composition and heating / rolling processes, without providing other evaluation methods. This invention patent, however, covers thickness specifications of 3-6mm and proposes an evaluation method to reduce the flash welding cracking rate of 590MPa wheel rim steel from aspects such as composition design, microstructure type, and weld quality.

[0008] Patent CN 10912417A discloses a hot-rolled steel plate for automobile wheels with a tensile strength of 590MPa. This patent focuses on its manufacturing process and fatigue performance, but does not provide an evaluation method for its flash welding performance.

[0009] In summary, the aforementioned patents focus on the production technology, surface quality, and fatigue performance of the 590MP grade wheel steel, but rarely address welding performance, particularly the evaluation system for the proportion of forming cracks after flash welding. Summary of the Invention

[0010] The purpose of this invention is to provide a method for reducing the cracking rate of flash welding of wheel steel for 590MPa grade wheel rims, thereby improving the adaptability of the product to welding processes, reducing the cracking rate during welding, and reducing the scrap rate.

[0011] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0012] This invention discloses a method for reducing the cracking rate of flash welding forming of wheel steel for 590MPa grade wheel rims. The chemical composition and weight percentage of the wheel steel are as follows: C: 0.06-0.10%, Si: 0.05-0.30%, Mn: 1.40-1.60%, P≤0.020%, S≤0.010%, Alt: 0.020-0.040%, Nb: 0.035-0.055%, Ti: 0.010-0.025%, N: 0.0040-0.0060%, Ti / N: 2.0-4.0, with the balance being Fe and unavoidable impurities. The manufacturing process includes: final rolling temperature: 840-880℃, cooling rate after final rolling: 20-30℃ / s, coiling temperature: 570-600℃.

[0013] Furthermore, the thickness specifications are: 3-6mm.

[0014] Furthermore, the strength properties meet the following requirements: lower yield strength: ≥450MPa, tensile strength: 610-700MPa.

[0015] Furthermore, the longitudinal microstructure consists of ferrite + pearlite + a small amount of bainite, with the ferrite grain size grade being 11.0-13.0 and the pearlite banding segregation grade being ≤2.0.

[0016] Furthermore, for the 590MPa grade wheel rim steel used in flash welding, the inclusions in the center of the weld in the thickness direction are tested, and the requirements are: Class B inclusions must be level 0, Class C inclusions must be level 0, and Class D inclusions must be ≤0.5.

[0017] Furthermore, the 590MPa grade wheel steel used for wheel rims is subjected to flash welding, and the microhardness of the weld in the thickness direction, the heat-affected zone, the tempered zone, and the substrate is tested.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0019] This invention proposes an evaluation method to reduce the cracking rate of flash welding of 590MPa grade wheel steel for rims, considering factors such as chemical composition design (specifically, the Ti / N ratio range is defined, specifying the weight percentage content of titanium and nitrogen and the Ti / N ratio, primarily to ensure dispersed precipitation of TiN and refine the microstructure of the coarse-grained heat-affected zone during flash welding), base material production process and microstructure type, grain size level and pearlite banding segregation level, inclusion level in the weld and heat-affected zone, and hardness difference assessment. The implementation of this invention ensures that 590MPa grade wheel steel for rims maintains strength while possessing excellent weldability and cold forming performance, reducing the cracking rate of high-strength wheel steel after welding, and providing a solution to improve the weldability of wheel steel for rims. Attached Figure Description

[0020] The present invention will be further described below with reference to the accompanying drawings.

[0021] Figure 1 The microstructure of the 590MPa grade wheel steel base material for wheel rims in Example 1;

[0022] Figure 2 The pearlitic banded structure of the 590MPa grade wheel steel base material for wheel rims in Comparative Example 6;

[0023] Figure 3 This is a comparative example of the inclusions and microstructure of the weld seam in the 590MPa grade wheel steel used for wheel rims. Detailed Implementation

[0024] An evaluation method for reducing the cracking rate of flash welding in wheel steel for 590MPa grade wheel rims specifically includes:

[0025] (1) The chemical composition and weight percentage of wheel steel are as follows: C: 0.06-0.10%, Si: 0.05-0.30%, Mn: 1.40-1.60%, P≤0.020%, S≤0.010%, Alt: 0.020-0.040%, Nb: 0.035-0.055%, Ti: 0.010-0.025%, N: 0.0040-0.0060%, Ti / N: 2.0-4.0, with the balance being Fe and unavoidable impurities.

[0026] (2) The production process of wheel steel for 590MPa grade wheel rims, with a final rolling temperature of 840-880℃, a cooling rate of 20-30℃ / s after final rolling, and a coiling temperature of 570-600℃.

[0027] (3) The thickness specifications of wheel steel for 590MPa grade wheel rims are: 3-6mm, lower yield strength: ≥450MPa, tensile strength: 610-700MPa.

[0028] (4) The longitudinal microstructure of the 590MPa grade wheel steel for wheel rims is ferrite + pearlite + a small amount of bainite. The ferrite grain size is 11.0-13.0 grade, and the pearlite banding segregation grade is ≤2.0 grade.

[0029] (5) For 590MPa grade wheel rims, flash welding is performed on wheel steel. The inclusions in the center of the weld in the thickness direction are tested. The inclusion level of Class B inclusions is required to be 0, the inclusion level of Class C inclusions is required to be 0, and the inclusion level of Class D inclusions is ≤0.5.

[0030] (6) Flash welding was performed on 590MPa grade wheel steel for wheel rims, and the microhardness of the weld in the thickness direction, heat-affected zone, tempered zone and matrix was tested.

[0031] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0032] Examples 1-3 and Comparative Examples 1-2 mainly investigated the effect of Ti / N ratio on the welding cracking rate of 590MPa grade wheel rim steel, including its production process, microstructure type, grain size level, base metal segregation band level, weld inclusion level, etc.

[0033] Basically the same.

[0034] Table 1. Chemical composition (wt%), Ti / N ratio, thickness (mm), and post-weld cracking rate (‰) of Examples 1-3 and Comparative Examples 1-2 of the present invention.

[0035]

[0036]

[0037] Comparing the results of Examples 1-3 and Comparative Examples 1-2, the Ti / N ratio in the 590MPa grade wheel steel for wheel rims has a certain impact on the post-weld forming crack rate of the wheel rim. The main reason is that the 590MPa grade wheel steel for wheel rims undergoes micro-Ti treatment. Only a reasonable Ti / N ratio can promote the precipitation of dispersed fine TiN or (Nb, Ti)(C, N) during the welding process, hinder the growth of austenite grains in the heat-affected zone, improve the deformation coordination ability during subsequent forming, and stabilize the forming crack rate within a certain range.

[0038] Examples 4-6 and Comparative Examples 5-6 are of the same thickness (6mm), using similar chemical compositions, rolling processes, welding processes, and weld inclusion levels.

[0039] Similar to this, the main analysis focuses on the influence of the pearlite banding segregation level of the base material on the forming crack rate after welding of 590MPa grade wheel steel for wheel rims.

[0040] Table 2. Chemical composition (wt%), pearlite banding grade (grade), and post-weld forming cracking rate (‰) of Examples 4-6 and Comparative Examples 5-6 of the present invention.

[0041]

[0042]

[0043] Comparing the results of Examples 4-6 and Comparative Examples 5-6, the pearlite banding segregation in the base material of 590MPa grade wheel rim steel has a certain impact on the cracking rate of the wheel rim after welding. The main reason is that the pearlite segregation is the segregation of C and Mn elements. Since the wheel rim is relatively thin, flash welding is a local instantaneous heating and cooling process. In particular, the pearlite segregation band in the weld and heat-affected zone will generate bainite and martensite with high hardness during the air cooling process. The deformation coordination ability is poor during the subsequent forming process, which leads to a certain increase in the cracking rate.

[0044] Examples 7-8 and Comparative Example 7 had the same chemical composition (C: 0.07, Si: 0.11, Mn: 1.52, P: 0.013, S: 0.05, Al: 0.026, Nb: 0.037, Ti: 0.015, N: 0.0051 wt%), thickness (4 mm), similar rolling and welding processes, and comparable mechanical properties, microstructure, pearlite banding grade, and other characteristics of the base material.

[0045] Similarly, this study mainly analyzes the influence of weld inclusion level on the forming crack rate of 590MPa grade wheel steel after welding.

[0046] Table 3 shows the inclusion levels (grades) at the welds of Examples 7-8 and Comparative Example 7 of the present invention and the cracking rate (‰) after rim welding.

[0047]

[0048]

[0049] Comparing the results of Examples 7-8 and Comparative Example 7, the inclusions in the weld seam of the 590MPa grade wheel rim after welding of wheel steel have a significant impact on the cracking rate of the wheel rim after welding. If B or C inclusions or high-level D inclusions appear in the middle of the weld seam, it indicates that the molten metal that has been oxidized during the welding process has not been squeezed out. The remaining inclusions reduce the bonding strength of the weld seam and are prone to becoming crack sources during the forming of the wheel rim after welding, leading to cracking.

[0050] Examples 9-11 and Comparative Examples 8-9 have the same chemical composition (C: 0.07, Si: 0.11, Mn: 1.52, P: 0.013, S: 0.05, Al: 0.026, Nb: 0.037, Ti: 0.015, N: 0.0051 wt%), thickness (3 mm), similar rolling and welding processes, and similar mechanical properties, microstructure, pearlite banding level, and weld inclusion level of the base material. The main analysis...

[0051] The effect of welding on the forming crack rate of wheel steel for 590MPa grade wheel rims.

[0052] Table 4 is... Cracking rate (‰) after welding of wheel rim

[0053]

[0054]

[0055] The results of Examples 9-11 and Comparative Examples 8-9 show that after welding 590MPa grade wheel rims with wheel steel... The welding process of wheel steel for 590MPa grade wheel rims has a certain impact on the cracking rate after forming. The weld and heat-affected zone metal have undergone melting, recrystallization and cooling processes. In particular, compared with the tempering zone adjacent to the base material of high-grade wheel steel for wheel rims, soft spots are prone to appear. During the subsequent deformation process of the wheel rim, it is easy to thin and crack.

[0056] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for evaluating reduction of flash welding forming cracking rate of 590 MPa grade rim wheel steel, characterized by: The chemical composition of the wheel steel is C: 0.06-0.10%, Si: 0.05-0.30%, Mn: 1.40-1.60%, P≤0.020%, S≤0.010%, Alt: 0.020-0.040%, Nb: 0.035-0.055%, Ti: 0.010-0.017%, N: 0.0040-0.0060%, Ti / N: 2.0-4.0, and the balance being Fe and inevitable impurities; The manufacturing process comprises: finish rolling temperature: 840-880℃, cooling speed after finish rolling: 20-30℃ / s, and coiling temperature: 570-600℃; The 590MPa grade rim wheel steel is subjected to flash welding, and the inclusion in the central part of the thickness direction weld is detected, and the B class inclusion level is 0, the C class inclusion level is 0, and the D class inclusion level is ≤0.

5. The 590MPa grade rim wheel steel is subjected to flash welding, and the microhardness of the thickness direction weld, heat affected zone, tempering zone and matrix is detected, .

2. The method of evaluating the flash welding forming cracking rate of a 590 MPa grade wheel rim for a vehicle wheel steel according to claim 1, characterized by: The thickness specification is 3-6mm.

3. The method of evaluating the flash welding forming cracking rate of a 590 MPa grade wheel rim wheel steel according to claim 1, characterized by: The strength performance satisfies: lower yield strength: ≥450MPa, and tensile strength: 610-700MPa.

4. The method of evaluating the flash welding forming cracking rate of a 590 MPa grade wheel rim wheel steel according to claim 1, characterized by: The longitudinal microstructure is ferrite+pearlite+small amount of bainite, the ferrite grain size level is 11.0-13.0, and the pearlite banding segregation level is ≤2.0.

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