Abstract: Continuous-annealing process was simulated to treat 1.4 mm chilled steel strips with different chemical composition by Using Gleeble-3500 thermal simulation machine, and the mechanical properties and microstructure of the simulating annealed specimens were analyzed by means of universal tensile testing machine, optical microscope, scanning electron microscope and EDS. The results show that other annealing parameters are the same, under the premise of low C and high Mn composition, the C-Mn-Si(high)+Cr+Mo steel with alloying elements Cr, Mo and high Si content and the C-Mn-Si(low) steel without alloying elements Cr, Mo and with low Si content can obtain 980 MPa grade dual-phase steel with mechanical properties meeting requirements when annealed at soaking temperature of 760 ℃ and 780 ℃. The microstructure of the C-Mn-Si(high)+Cr+Mo steel is composed of ferrite, island-like martensite and a small amount of bainite at different soaking temperatures. The difference is that the ferrite at high soaking temperature has small grain size and a large amount, uneven morphology, and the martensite content is relatively less, and the bainite is needle-like or cluster-like. The microstructure of the C-Mn-Si(low) steel is composed of ferrite, martensite and a small amount of bainite and retained autensite. The difference lies in the refinement of ferrite grain at high soaking temperature, not obvious rolling characteristics, less martensite content, and less granular bainite. The retained autensite is bright white stripes, which is mainly caused by local enrichment of Mn. In essence, the difference of microstructure between the C-Mn-Si(high)+Cr+Mo steel and C-Mn-Si(low) steel is caused by the different content of alloying elements Cr, Mo and Si, which affects the stability of undercooled austenite.

Key words: annealing thermal simulation, soaking temperature, 980 MPa grade dual-phase steel, mechanical properties, microstructure, alloying elements