Along with the increasing demand from the automotive industry for the strength and formability of automotive steels, the second and third generation advanced high-strength steels with superior performance have drawn much attention from steel makers and researchers. Based on the knowledge of the development trend of automotive steel and its own technical accumulation, Baosteel has developed a serial of innovative steels with different composition and performance. Among them, Q&P steel is the most promising candidate for 3rd Gen. steels, due to its excellent manufacturability and usability.

Baoseel’s QP steel is produced in a ultra-high-strength steel special production line. After cold rolling, the steel sheet is heated for austenization, and then quenched to an intermediate temperature between Ms and Mf, in order to obtain a microstructure mixed of martensite and austenite. Next, the sheet is reheated to a partitioning temperature over Ms, which allows C to partition from the martensite into untransformed austenite. The higher C content stabilizes the austenite at room temperature after final cooling. Therefore, a final microstructure of martensite + remained austenite or ferrite + martensite + retained austenite could be achieved.

The microstructure of Q&P steel contains martensite, ferrite and retained austenite. Aided with the ultra-strength of martensite and the TRIP (Transformation introduced plastic deformation ) effect of retained austenite, Q&P steel has a higher n value and elongation. At the same time, it has a good hole expanding performance, which guarantees the performance of flange and hole expansion.

Due to the TRIP effect, QP steel has high strength along with a high elongation and a high n. QP steel has a better formability and stronger strain homogenization ability. Compared with other UHSS, QP steels is very suitable for the auto-parts with complicated shape by cold stamping. The combination of strength and formability makes Q&P steels suitable for frame parts and safety parts of car body requiring complicated shapes and high strength.

QP steel is suitable for automotive safety parts and structural parts with complex shapes. 980MPa grade QP steel is the first “world –first” product of Baosteel. At present, it has been commercially supplied for the manufacturing of the parts of many domestic models, such as B-pillar reinforcement, A-pillar reinforcement and hinge pillar reinforcement.

This B-pillar reinforcement is located between the side wall outer plate and the B-pillar inner panel, which is an important part of the B-pillar, which could improve the strength and impact performance of the B-pillar. Generally, the B-pillar reinforcements are made of HSS or UHSS sheets with high formability. QP steel was successfully applied to a domestic brand car B-pillar reinforcement plate.