Advanced High Strength Steel (AHSS) has been developed toward the simultaneous improvement of increasing strength and ductility. In particular, retention of austenite at room temperature is a reliable and well-known method to maximize both strength and ductility by TRIP effect. Quenching and Partitioning (Q&P) is one of the processes for manufacturing AHSS utilizing retained austenite phase. After the formation of primary martensite at quenching process, austenite is chemically stabilized by carbon enrichment from the primary martensite during partitioning process.

Addition of alloying elements such as Si and Al in the AHSS is critical in order to suppress the cementite precipitation during partitioning process, which leads to securing high fraction of stable austenite. However, recent studies have shown that the addition of high Si in AHSS is necessary to be avoided due to the possibility of several problems such as degradation of weldability and liquid metal embrittlement (LME). Therefore, it is essential to examine the effect of Si contents and the process parameters on the tensile properties in order to optimize Q&P process conditions for securing desired combination of strength and ductility.

In the present study, we report the change of tensile properties of cold-rolled steel depending on Si contents and process conditions. It is found that the characteristics of tempered martensite and bainite mainly determined the tensile properties in steels with low Si contents, whereas those of retained austenite determined the tensile properties in steels with high Si contents. Detailed analysis will be discussed with respect to the microstructure of Q&P steel and characteristics of each constituent phases.