Hot rolled steel sections for automobile wheel rims
Hot-rolled steel sections for automotive wheel rims are specialized, special-shaped steels designed for manufacturing rims. These sections feature U-shaped or deep groove profiles, forming the critical contact point between the wheel and tire. They must withstand the full weight of the vehicle and the radial and tangential forces experienced during driving, placing extremely high demands on strength, ductility, and dimensional accuracy. These sections are typically manufactured from low-alloy, high-strength steels such as Q345 and Q355, or automotive structural steels such as 510L and 590L. They offer a tensile strength of 450-650 MPa, a yield strength ≥345 MPa, and an elongation ≥20%, meeting the processing requirements of cold bending and roll forming. Compared to conventional hot-rolled sections, rim sections have more complex cross-sectional dimensions, with groove depths ranging from 80-150 mm. Wall thickness deviations must be controlled within ±0.3 mm, and flange parallelism deviations must be ≤0.5 mm/m to ensure roundness and a precise fit with the tire after forming.
The production process for hot-rolled steel sections for automotive wheel rims is one of the most technically challenging in special-shaped steel rolling, requiring precise pass design and multiple rolling passes. First, the cross-sectional shape is designed based on the rim’s specifications (13-24 inches in diameter). Finite element simulation software is used to analyze the metal flow patterns within the pass, optimizing the pass parameters and ensuring full fill in all sections of the section. Continuously cast square or rectangular billets are heated to 1180-1220°C before entering the roughing mill. Three to five rolling passes are used to reduce the billet to an approximate intermediate cross-section. During roughing, the width must be carefully controlled to avoid wavy flange defects. Intermediate and finishing rolling utilize a universal mill and an edger mill to gradually adjust the cross-sectional dimensions. The finishing temperature is controlled at 850-920°C, and the rolling speed is determined by the section’s specifications (1-3 m/s) to ensure cross-sectional accuracy. After rolling, the steel sections are cooled to 600-650℃ by a controlled cooling system, then straightened and cut to length. Finally, they undergo ultrasonic testing and cross-sectional dimension inspection to ensure that the product has no internal defects and that the dimensions meet the design requirements.
Hot-rolled steel sections are most widely used in the rims of passenger cars and light commercial vehicles, particularly for steel wheels. Compact car rims (13-16 inches in diameter) are typically made of Q345 low-alloy steel. After cold bending and roll forming, the rim’s roundness tolerance is controlled within 0.5mm, ensuring uniform load distribution after tire installation. Tests by a car manufacturer showed that wheels using high-quality rim steel only experienced a 0.2mm increase in radial runout after 100,000 kilometers of driving. Due to their heavy loads, 510L automotive structural steel sections are used for SUV and MPV rims. With a yield strength of ≥355MPa, they meet the strength requirements under full load and exhibit excellent weldability, with the rim’s butt weld strength exceeding 90% of the parent material.
In the heavy-duty commercial vehicle and specialty vehicle sectors, the specifications and performance of hot-rolled steel sections used in automotive wheel rims require specialized design. Heavy-duty truck rims (19-22.5-inch diameter) utilize thick-walled hot-rolled steel sections (8-12mm thick) made from 590L high-strength steel with a tensile strength of ≥590 MPa, ensuring no permanent deformation even when fully loaded (gross mass of 49 tons). By adopting this steel section, one heavy-duty truck manufacturer has extended the service life of its rims to over 200,000 kilometers. Bus rims, subject to frequent starting, stopping, and braking, require excellent fatigue performance. By controlling the steel’s inclusion content (≤ Grade 2) and grain size (≥ Grade 7), the fatigue life of the rims can be increased by 40%. For specialized vehicles such as ambulances and emergency repair vehicles, the rim steel sections also require a certain level of corrosion resistance. The addition of trace alloying elements (copper, chromium, and nickel) enhances their resistance to rust in outdoor environments.
With the development of the automotive industry, the performance and production technology of hot-rolled steel sections used in automotive wheel rims are constantly innovating. Steel companies are developing ultra-high-strength steels (such as 700L and 980L) to reduce wheel rim weight while maintaining rim strength. A wheel manufacturer using 700L steel is reportedly 15% lighter than traditional Q345 steel, meeting the lightweighting requirements of new energy vehicles. To address competition from aluminum alloy wheels, a complex-section rim steel section has been developed. This single-step hot-rolling process reduces subsequent processing steps and lowers the manufacturing cost of steel wheels. In terms of production technology, an automated hot rolling control system is employed to achieve online closed-loop control of steel section dimensions. One steel mill can now maintain a wall thickness tolerance of ±0.2mm for its wheel rim steel, increasing material utilization to over 85%. In the future, with the advancement of electrification and intelligent vehicles, hot-rolled steel sections for wheel rims will develop towards higher strength, more precise dimensions, and improved fatigue performance, providing key material support for the safety and lightweighting of automotive wheels.
