The compound CaCl2 plays a significant role in the process of direct calciothermic reduction of Ti2O3 to prepare porous titanium. In this paper, the effect of CaCl2 on reduction products by calciothermic reduction of Ti2O3 was investigated. Results show that the distribution of CaCl2 in reduction preform influences particle size and morphology differences in reduction products both on the surface and the inside. The CaCl2 is transferred to the surface of the Ti2O3 preform due to its volatilization before and throughout reduction. The content of CaCl2 in the surface zone of Ti2O3 preform is significantly higher than that in the interior during the reduction process, contributing to the formation of large Ti particles with a smooth shape on the surface, and small Ti particles with inherited morphology of Ti2O3 inside. More CaCl2 causes the aggregation of Ti particles to form large Ti particles which are advantageous as they connect and form a more solid porous titanium structure. The presence of a small amount of CaCl2 in the interior also results in the coexistence of small Ti and CaO particles, forming a loose structure with uniform distribution.

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Herein, the precipitation characteristic of sulfide is investigated by confocal laser scanning microscopy for a typical medium‐carbon sulfur‐containing 42CrMo steel under different cooling rates (100, 200, 600 °C min−1) and sulfur contents (0.0018 and 0.0249 wt%). Thermodynamic calculations show that increasing sulfur content can enlarge the liquid–solid‐phase zone and enhance the initial precipitation temperature of MnS in 42CrMo steel. Phase diagram of Mn–Mo–S demonstrates that the sulfides contain Mn, Mo, and S elements can be formed. The experimental results indicate that with an increase of the sulfur content from 0.0018 to 0.0249 wt%, more (Mn, Mo)S sulfides are formed in the steel due to the significant enhancement of supersaturation. Moreover, it is revealed that the average size of (Mn, Mo)S inclusions decreases from 16.11 to 3.55 μm when the cooling rate increases from 100 to 600 °C min−1. The typical of large‐size rodlike (Mn, Mo)S inclusions is observed in a low cooling rates of 100–200 °C min−1. As the cooling rate increases to 600 °C min−1, smaller globular (Mn, Mo)S inclusions with an average size of 3.55 μm are appeared which can act as a core to promote the ferrite formation.

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