·New breakthroughs in automotive lightweight steel research and development

Recently, the high-strength plastic-plastic automobile steel developed by Xu Yunbo, a professor of Northeastern University, successfully rolled off the production line of Hegang's Tangshan high-strength automobile plate. The mechanical properties all reached the target and received user orders, which marked the first time in China. The third-generation automotive steel with excellent mechanical properties was successfully developed on the traditional continuous annealing line characterized by cooling rate and one-step overaging treatment.
In recent years, the world's major steel companies have increased the research and development of the third generation of automotive steel, and strive to achieve the goal of "more fuel-efficient and safer" through the body weight reduction. Quenching component (Q&P) steel, one of the typical representatives of the third generation steel, has become the most prominent "star" due to its excellent plastic properties and technical characteristics suitable for industrial mass production.
However, according to the classical quenching partition theory, in order to obtain excellent ferroplastic properties, the traditional continuous annealing line must have special functions such as high-speed cooling and rapid temperature increase after quenching (two-step dispensing). The investment in a high-strength steel special annealing production line with such luxury is 890 million yuan, and some even more than one billion yuan, which makes most steel enterprises only "looking at the ocean."
The development of the third generation of high-strength steel in the traditional continuous annealing production line with low cooling rate and no quenching and re-heating function has gradually become the common goal pursued by the academic community and the industry. In order to solve the common technical problems in this industry, Xu Yunbo, a professor of the State Key Laboratory of Rolling Technology and Continuous Rolling Automation of Northeastern University, conducted in-depth research on quenching partition theory and key industrialization technologies, breaking through the dependence on martensite to austenite carbon alone. The traditional framework proposes a new concept and new process of “ferritic, bainite and martensite synergistic carbon partitioning”. It is based on the alloy composition design, austenite stabilization and precise regulation of multiphase microstructure. QP980 steel was successfully developed in the lower continuous cooling rate and one-step overaging treatment of the traditional continuous annealing line of Hegang Steel. The yield strength of this steel product board is ≥600MPa, the tensile strength is ≥980MPa, the elongation after fracture is 21%~28%, and the comprehensive performance is excellent.
Compared with the commercialized Q&P steel of the same level of "two-step distribution", the new technology has a simple temperature control path, flexible distribution window, smooth and efficient production connection, and reduced process cost. Only by canceling the "induction heating" can save electricity costs 50~ 100 yuan / ton. Moreover, the new product has excellent structural and mechanical properties, low fluctuations in the coiling performance, and strong anti-tempering stability. The volume fraction of the Paralyzed objects in the microstructure is increased by 2% to 6%, and the elongation after the elongation is increased by 2% to 4%. The strong plastic product can reach more than 27GPa%. The resistance spot welding and forming performance are basically the same as the typical values ​​of the “two-step matching” product. Among them, the bending and rebounding properties are better, the critical bending radius of the 1.6mm plate is reduced to about 1.5mm, and the 90° bending back angle is It can reach about 14°.
In addition, compared with the same grade cold rolled dual phase steel (DP) and phase change induced plastic steel (TRIP), not only the alloy cost is greatly reduced, but also the toughness, formability and stretch flangeability of the steel are significantly improved, especially The elongation rate is more than twice that of the same grade DP steel.
The new Q&P steel can be used for automotive structural parts such as beams, stringers, window frames, bumpers and floor reinforcements. It can effectively reduce energy consumption and reduce consumption by reducing the thickness of parts and reducing fuel consumption. For example, using the QP980 instead of the DP600, the thickness of the workpiece is reduced from 1.2mm to 1.0mm, which can reduce the weight of the car by 10%~20%. At the same time, the safety of automobiles has increased significantly, and the mortality rate of personnel has dropped significantly under normal collisions.

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