Abstract
This study investigates the strengthening mechanism and carbide precipitation behavior of medium Mn steel with Nb-Mo microalloy after cyclic quenching and austenite reverse transformation treatment. The results show that the Nb/Mo element not only precipitates (Nb,Mo)C in the grains, hindering the movement of dislocations and increases the strength, but also segregates at the austenite/ferrite grain boundary, thus delaying the transformation from austenite to ferrite. In addition, a large amount of nano-scale cementite is retained after cyclic quenching and austenite reverse transformation, which has a positive effect on the proportion of retained austenite in medium Mn steel. Moreover, the carbides with small size and low Mn content are dissolved, and the decomposed C and Mn content are beneficial to the nucleation of austenite during the intercritical annealing process at a temperature of 690 °C.
Highlights
With the intensification global energy crisis and environmental deterioration, countries around the world continue to attach importance to the research and development of lightweight and high-strength materials [1,2,3,4]
Three processes of cold rolling samples were separately carried out as follows: For CQ1- sample, it was rapidly reheated to austenitization temperature at 900 ◦ C for 30 min, and water quenched to room temperature; for CQ2 sample, a similar cyclic quenching heat treatment was used for 10 min based on CQ1, and water quenched to room temperature; with regard to the
Cementite is thermodynamically unstable and easy to dissolve in the intercritical region, while the results show that cementite particles with a diameter of 7~88 nm formed after martensite was rapidly heated to the intercritical temperature for annealing, accompanied by a large amount of Mn distribution between cementite, ferrite, and austenite phases
Summary
With the intensification global energy crisis and environmental deterioration, countries around the world continue to attach importance to the research and development of lightweight and high-strength materials [1,2,3,4]. More and more researchers have used Nb, V, Ti, Mo, and other elements for microalloying to further improve the strength of medium-manganese steel through main strengthening methods such as solid solution, fine grain, and precipitation. Cao et al [22] reported that during the coiling process of hot-rolled steel, Nb-Mo composite can better obtain the precipitation strengthening increment of microalloy carbides than Nb-Ti composite addition, and improve the yield strength of steel. Cai et al [24] studied Fe-0.17C-6.5Mn-1.1Al-0.22Mo0.05Nb medium manganese steel and found that the addition of Mo and Nb microalloys controlled the ratio of retained austenite and the mechanical stability during tensile deformation, and has the effect of improving the yield strength
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