Three steels were prepared using Ti–Mg, V and Ti–Mg–V microalloying treatments and rolled into steel plates with a thickness of 20 mm. In this article, the inclusions, second phase particles, grain size and mechanical properties of three steels were studied. It was shown that Mg was able to refine inclusions in steel, and the average sizes of inclusions in Ti–Mg-microalloyed and Ti–Mg–V-microalloyed steels were 2.56 μm and 2.87 μm respectively, which were smaller than the average size of inclusions in V-microalloyed steel (3.58 μm). The austenite grain sizes of Ti–Mg-microalloyed and Ti–Mg–V-microalloyed steels (73.34 μm and 68.70 μm) were significantly smaller than those of V-microalloyed steel (289.38 μm) because of the ability of TiN precipitated at high temperatures to pin austenite. V-microalloyed steel had the largest number of second phase particles with the smallest particle size, resulting in the best precipitation strengthening effect. Ti–Mg-microalloyed steel had TiN particles that grow and had a weakened precipitation strengthening effect. Ti and V tend to form larger sized (Ti, V) (C, N), which reduces the amount of precipitates and thus makes the precipitation strengthening effect weaker.
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