Hot rolled steel plates are mainly used in automotive linings, linings, joints and other parts. The performance requirements for the outer lining are very strict, including strength, formability, corrosion resistance, weldability, sprayability, impact resistance, shock resistance, uniformity, and recyclability. Recently, there have been more and more environmental and safety requirements. Despite this, some requirements are indeed contradictory, like formability and high strength, recyclability and corrosion resistance. The main steel used in automobile bodies are cold-rolled steel sheets and coated steel sheets with corrosion resistance. The
hot rolled steel sheet is generally thick and thinnest hot rolled steel sheet is 1.2 mm, so it is limited to the frame, side parts, wheel rims and relatively heavy gear parts of the automobile.
High-strength steel plates with various strength levels have been widely used in different parts of the automobile body, and steel plates with a strength of 340 MPa or more are also widely used in the impact-resistant parts of the body. In order to provide safety during the collision and avoid increasing the weight of the vehicle, it is necessary to develop and adopt high-performance and high-strength steel plates. Steel sheets for automotive bodies should have three main properties, high tensile strength, large dent resistance and compression set breaking strength (breaking strength). Generally, materials with high tensile strength have high resistance to deformation. Therefore, high-strength steel plate instead of a normal-strength steel plate does not contribute to the improvement of the stretch forming, but contributes to the improvement of the dent resistance and the breaking strength of the vehicle body. Correspondingly, when the high-strength steel plate is used instead of the ordinary steel plate in the anti-pit and compression-breaking strength parts of the vehicle body, the thinning of the steel plate is also facilitated, and the road of weight reduction of the vehicle body is created, and the cost of the material is not increased. High-strength steel sheets are to be used for the body. Besides the strength properties, they must have good stamping properties, weldability and corrosion resistance. Stamping performance is the most important requirement when we select materials. In addition, the spot weldability and the simple metal coating process impose strict requirements on the chemical composition of the material, which in turn affects the manufacturing conditions.