Mechanical Properties and Microstructures Development of Quenching and Partitioning (Q&P) Steels During Galvannealing Process

Quenching and Partitioning (Q&P) steels are regarded as one of the promising candidates for 3rd generation advanced high strength steels (AHSSs) for their lean alloy elements and excellent mechanical properties. Carbon partitioning from the quenched martensite to the retained austenite during annealing is believed as a key process for Q&P steel mass production. However, galvannealing (GA) process of Q&P steels is quite challenging. The mechanical property of Q&P steels tends to degrade when they are galvanized via the traditional GA process because the heat cycle in this process is unfavorable for carbon partitioning. In the present work, we applied various modified GA heat cycles to two grades of Q&P steel, studied the effects of the GA process on the tensile properties and microstructures of the samples, and proposed optimal GA heat cycles for both grades of Q&P steels. It is found that high alloying temperature in GA process promotes carbide precipitation and retained austenite decomposition, and is the main reason for mechanical properties degradation of galvannealed Q&P steels.