Duplex steel for automobile wheels

Duplex steel for automobile wheels

Dual-phase steel was first proposed in the United States in 1968, was recognized in 1975, and has since been developed in the automotive industry. Dual-phase steel is generally used in automotive parts that require high strength and performance, such as B-pillars, bumpers, and suspension systems. With the research on the formability of dual-phase steel, dual-phase steel is also used in automobile wheels and requires automobiles. Wheels have high strength and excellent formability. DP540, DP590 and DP600 steels are commonly used dual-phase steels for automobile wheels, so the study of their mechanical properties and formability is of great significance.

Mechanical properties
Effect of alloying elements on mechanical properties

Alloying elements play an important role in the microstructure and mechanical properties of duplex steels. C is an important strengthening element in dual-phase steel. By increasing the C content, the strength of dual-phase steel can be improved, but the toughness will be reduced. C is an element that generates martensite structure through phase transformation. The carbon content directly affects the volume fraction of martensite, the carbon content level in martensite and the morphology of martensite, thereby affecting the mechanical properties of dual-phase steel. The Si element in steel has the function of inhibiting the formation of carbides and maintaining a good combination of strength and plasticity of dual-phase steel. The presence of Si can not only improve the continuity of ferrite, but also increase the activity of C in ferrite. Mn has a positive effect on improving the strength and hardenability of dual-phase steel. The addition of Mn can play the role of fine grain strengthening and solid solution strengthening, thereby improving the strength of dual-phase steel. Mn element has an influence on the formation of austenite during critical zone annealing. It is a stabilizing element for austenitization and improves the hardenability of austenite. However, too high Mn content will cause martensite to be distributed in a banded manner, affecting the plasticity of dual-phase steel. Although P is a harmful element, it can improve the strength of dual-phase steel. P can promote the uniform distribution of ferrite and martensite and increase the C content in ferrite, thereby improving the strength of dual-phase steel. However, excessive P element easily forms Fe3P, which increases the brittleness of dual-phase steel. Al element can reduce the hardenability of dual-phase steel because Al element reduces the stability of austenite, thereby reducing the content of retained austenite. Cr element not only affects austenite hardenability, but also reduces the strength of dual-phase steel. This is because the addition of Cr delays bainite transformation and pearlite transformation, shifts the CCT curve to the right, and also reduces the yield strength of ferrite. The addition of Mo can improve the hardenability and reduce the yield ratio of dual-phase steel. Mo element can not only promote the precipitation of ferrite, thereby improving the plasticity of dual-phase steel, but also hinder the transformation of austenite into pearlite during cooling. However, the cost of Mo element is higher.

Effect of heat treatment process on mechanical properties

Heat treatment is a commonly used metal processing process that improves material properties by changing the microstructure without changing the shape and chemical composition of the material. Therefore, it is necessary to study the effect of heat treatment process on the mechanical properties of dual-phase steel. The study found that as the heating rate increases, the ferrite undergoes a process transition from complete recrystallization to incomplete recrystallization and the evolution mechanism. At lower heating rates, the dynamic recrystallization process is almost complete before austenite nucleation begins; at higher heating rates, the dynamic recrystallization process will be delayed and the microstructure consists of more deformed ferrite grains. ; After the heating rate reaches a high enough level, the ferrite is almost completely unrecrystallized before austenite nucleation occurs. Therefore, the number of austenite nucleation increases with the increase of heating rate, which can produce more martensite to improve the strength of steel.

The welding process is widely used in automobile wheels, and the welding process parameters affect the formability of the steel. Regarding the influence of heat input on the performance of DP600 steel welded joints, it was found that the degree of softening of the heat-affected zone and the range of the heat-affected zone increased with the increase in heat input, while changes in heat input had little effect on the mechanical properties and formability of DP600 steel. When the heat input is high, the martensite in the heat affected zone will undergo tempering aging, resulting in a small amount of tempered martensite and some cementite dispersed in the ferrite; when the heat input is low, the martensite will not Decomposition or a small amount of decomposition causes the hardness of the heat affected zone to increase, but the decomposition of martensite has less impact on the heat affected zone.

In summary, the differences in mechanical properties and formability of dual-phase steel for automobile wheels are not only related to the content of alloy elements, but also to the austenite transformation.

GNEE STEEL Company was established in Anyang, China in 2008, specializing in automotive duplex steel coils and related products to meet customer needs. The company management and sales staff have more than 15 years of international trading experience in steel coils, steel plates and various steel products, and we have won the trust and good reputation of our customers. Welcome to inquire and place an order!