In order to achieve the goals of automobile weight reduction, energy saving, anti-corrosion, anti-pollution, anti-noise, safety and comfort, etc., a series of cold-rolled automobile sheets with different characteristics have been gradually formed, among which the main ones include: deep-drawing steel plate series aimed at improving formability; High-strength steel plate series aimed at vibration reduction and energy saving; surface-treated steel plate series aimed at improving automobile anti-corrosion capabilities; special steel plates aimed at developing high-performance automobiles, etc.
Deep drawn steel plate
Cold-rolled plates are divided according to stamping grade: commercial grade (CQ), ordinary stamping grade (DQ), deep drawing grade (DDQ), extra deep drawing grade (EDDQ) and super deep drawing grade (S-EDDQ). Among the sheets for cars, about 72% of the cold-rolled sheets are required to have deep drawing properties of DQ level and above, and more than 95% of the galvanized sheets are required to have deep drawing properties of DQ level and above.
High strength steel plate
High-strength automotive sheets are divided into three categories: ordinary stamping grade, deep drawing grade and ultra-deep drawing grade according to the stamping grade. According to the strengthening mechanism, there are four main types:
Solid solution strengthened phosphorus-added steel plate
By adding phosphorus, the ferrite is solid solution strengthened to improve the strength. Its strength levels are 320MPa and 360MPa. Phosphorus-added high-strength steel plates have excellent formability. The plastic strain ratio r value of deep-drawing grade high-strength steel plates is 1.4~1.6, and the plastic strain ratio r-value of ultra-deep drawing grade high-strength steel plates can reach 2.0.
Dispersion strengthened high strength low alloy steel plate
By adding Mn, Cu, Mo, V, Ti, Co and appropriate controlled rolling and cooling process, dispersion strengthening, grain refinement and recovery strengthening are produced to improve the strength. Its strength levels are 380MPa, 420MPa, 460MPa, 500MPa and 540MPa. The tensile strength of Cu precipitation strengthened steel can reach 610MPa, and the plastic strain ratio r value can reach 1.9. After adding Mn, the tensile strength of IF steel reaches 440MPa, and the plastic strain ratio r value is 1.5~2.0.
Phase transformation strengthened dual-phase steel plate and martensitic steel plate
Dual-phase steel is composed of 80% to 90% ferrite and 10% to 20% martensite through appropriate alloying elements and production processes. It has low yield strength, high work hardening index, good formability, and resistance to The tensile strength can reach 560~1030MPa. Martensitic steel is a steel with high manganese content (0.8%~1.6%). It controls the A→M transformation under rapid cooling to obtain more than 80% martensite structure and extremely high strength (689~1034MPa). TRIP steel is a variant of dual-phase steel. The main structures are ferrite, bainite and retained austenite. The content of retained austenite is 5%~15%, and the strength range is 600~800 MPa.
Bake hardened BH steel plate
The number of solid solution C atoms is controlled through an appropriate annealing process to achieve a low yield strength before stamping. The yield strength increases by 40~80MPa during the baking process, thereby improving the material's dent resistance. BH plate has good formability and the plastic strain ratio r value is as high as 2.3.
Coated steel plate
The use of cold-rolled surface-treated steel plates can greatly improve the anti-corrosion capabilities of automobiles. Cold-rolled coated steel plates can be divided into three series: hot dip plating series, electroplating series and organic coating series.
Special steel plate
In order to improve the performance of automobiles, special automobile panels with potential competitiveness have been developed and produced. For example, vibration-damping steel plates for the purpose of safe vibration reduction can effectively reduce the thunder effect produced when cars are running at high speeds, eliminate noise, and improve comfort; tailor-welded steel plates are used for the purpose of producing wide-width automobile panels, reducing weight, and reducing costs. The overall performance and safety performance of the car are greatly improved; the surface defect-free steel plate (O5) with improved surface quality requirements greatly meets the development needs of high-end cars.
