Steel for automobile body

1. Steel for the outer plate of the automobile body

Automobile body outer plate steel is mainly used for manufacturing front, rear, left, right door plate, engine hood outer plate, trunk cover outer plate and other parts. It should have good formability, corrosion resistance, concave resistance and good electric weldability. The outer plate of the automobile body is mainly coated to meet the anticorrosion requirements. In order to improve the concave resistance, baking hardened steel, high strength IF steel and high formability cold rolled annealed dual-phase steel (such as DP450) are often used. Coating plate is used for hot galvanized plate, hot galvanized iron plate, galvanized plate, galvanized - nickel plate and so on.

2, the body of the inner plate steel

Through the outer panel of the automobile, we can see that the parts of the inner panel of the automobile body have more complex shapes, which requires the steel used for the inner panel of the automobile body to have higher formability and deep drawing performance. Therefore, the inner panel of the automobile body is mainly used IF steel with excellent stamping formability and deep drawing performance, and a small amount of high-strength IF steel is used. The coating requirements of the inner panel are similar to those of the outer panel.

3, the car body structure parts

Further in, we can see the body structure of the car, as shown in the picture below. It is closely related to the safety and lightweight of cars. Therefore, the material selection needs both high strength and high plasticity. Advanced high strength steel (AHSS) is commonly used in body structure because of its good strong plastic bonding, good collision characteristics and longer fatigue life. For example, it has been widely used in the front and rear bumper skeleton, as well as A pillar, B pillar and other key parts, in the impact, especially in the front and side impact, can effectively reduce the deformation of the cockpit, to protect the safety of drivers and passengers. Advanced automotive high strength includes biphasic steel, martensitic steel, phase change induced plastic steel, multiphase steel, quenched ductile steel.

Cold rolling and hot rolling concepts

1. Hot rolled

The continuous casting slab or the first rolled slab is used as raw material, which is heated by a stepping furnace and dephosphorized by high pressure water, and then enters the roughing mill. The roughing material enters the finishing mill after cutting head, tail and then enters the finishing mill to implement computer-controlled rolling. After the final rolling, it passes through laminar cooling (computer-controlled cooling rate) and coiling machine to become a straight roll. The head and tail of straight hair roll are often tongue and fish tail, the thickness and width accuracy is poor, and the edge often has wave shape, hem, tower shape and other defects. The coil weight is heavier and the inner diameter of the steel coil is 760mm. (The general pipe industry likes to use.) After finishing the straight hair coil by cutting the head, cutting the tail, cutting the edge, straightening and leveling several times, then cutting the plate or rewinding, it becomes: hot rolled steel plate, flat hot rolled steel coil, slitting strip and other products. The hot rolled pickling plate roll is formed after removing the oxide skin by pickling and applying oil.

2. The cold rolling

The HOT rolled steel coil is used as raw material, the oxide skin is removed by pickling, and the finished product is rolled hard coil. The cold work hardening caused by continuous cold deformation increases the strength and hardness of rolled hard coil, decreases the toughness and plastic index, and deteriorates the stamping performance, so it can only be used for simple deformed parts. Hard rolling coil can be used as raw material for hot dip galvanizing plant because hot dip galvanizing units are equipped with annealing line. The rolling coil weight is generally 6~13.5 tons, and the inner diameter of the steel coil is 610mm. In order to eliminate cold working hardening and rolling STRESS and reach THE mechanical properties SPECIFIED in the STANDARD, the plate and reel should be annealed by continuous annealing (CAPL unit) or hood furnace. The surface quality, appearance and dimensional accuracy of cold rolled steel plate are better than those of hot rolled steel plate.