Introduction to Commonly Used Steel Types of Automotive Steel

Hot-rolled low-alloy high-strength steel (HSLA) thin steel plate, application parts: truck chassis, also used for bus wheels, hubs and other components, yield strength: between 350MPa and 550MPa, organizational structure: with ferrite processing A small amount of pearlite tissue. Recently, a 690MPa-class truck frame steel has been developed that utilizes all the strengthening mechanisms in bainite steel rolled directly from a hot strip mill.

DP steel plate, main structure: ferrite and martensite, of which the content of martensite is 5% to 20%. , Strength: 500~1200MPa. Features: DP steel has the characteristics of low yield-to-strength ratio, high work hardening index, high bake hardening performance, no yield extension and room temperature aging. It is generally used for products that require high strength, high collision resistance and energy absorption, and also have certain forming requirements. Auto parts such as wheels, bumpers, suspension systems and their reinforcements, etc. Advantages of DP steel plate: ① low yield point, high tensile strength, low yield-to-strength ratio; ② no yield point elongation or yield elongation, smooth stress-strain curve; ③ high elongation; ④ initial work hardening rate High, good processing strengthening performance; ⑤ Good fatigue resistance. Therefore, DP steel is particularly suitable for parts with good stamping and flanging properties. It has always been concerned by the automotive industry and may become the first choice of cold-rolled high-strength steel plates for automobiles. TRIP steel, including hot-rolled, cold-rolled, electroplated and hot-dip galvanized products. Main structures: ferrite, bainite and retained austenite, of which the content of retained austenite is 5% to 15%, and the strength is 600 to 800MPa. Main components: C, Si and Mn. The main function of Si is to inhibit the precipitation of cementite during bainite transformation, but it is detrimental to the surface quality of the steel plate.

In Japan, TRIP steel plates have been used in about 80 parts of the concept car chassis. Compared with traditional steel plates, parts made of this steel plate are about 12% lighter. TRIP steel has high elongation. Compared with DP steel, the initial work hardening index is smaller than that of DP steel. The work hardening index remains high over a long strain range and is particularly suitable for bulging forming.

Complex phase CP steel, main structure: similar to the structure of TRIP steel, except that CP steel contains martensite instead of retained austenite. Strengthening mechanism: through the composite effect of martensite, bainite and precipitation strengthening. The strength of CP steel can reach 800-1000MPa, and it is especially suitable for safety parts such as door anti-collision bars, bumpers and B-pillars. Martensitic (M) steel is transformed into a lath martensite structure by rapid quenching of high-temperature austenite structure. It can be produced by hot rolling, cold rolling, continuous annealing or post-forming heat treatment. It is currently among the commercial high-strength steel plates. The highest strength grade of steel. Main use: Replace tubular parts such as door anti-collision bars with low molding requirements to reduce manufacturing costs.

MnB steel or hot-formed steel, main elements: Mn and B and other elements, have very good hardenability. Hot forming process: including heating the blank to austenitize it, stamping the steel plate into a red-hot state, and then using the cooling capacity of the mold to harden the part into martensite. The entire forming process takes about 15 to 25 seconds.

Corrosion-resistant steel plate, main purpose: to enhance the corrosion resistance of ordinary steel plate stamping parts. Main categories: One category is corrosion-resistant steel plates that add new elements, such as atmospheric corrosion-resistant steel plates. Among the atmospheric corrosion-resistant steel plates developed in my country, there are 10CuPCrNi (cold rolled) and 9CuPCrNi (hot rolled), whose corrosion resistance is 3 to 5 times that of ordinary carbon steel plates; the second type is to coat or plate a layer of anti-corrosion material on the surface , also a type of coated board.