“…After the bloom reaches the air-cooling section, the cooling rate inside the bloom is already very small, so the quantity density of manganese sulphide tends to be stable. This relationship has also been proven in other studies [21,22]. Figure 2. Variation of manganese sulphide number density along bloom thickness direction.…”
In this paper, the characteristics of manganese sulphide in the continuous casting bloom of 38MnS6 steel were revealed. Manganese sulphide in low oxygen (w(O) = 7 ppm) bloom mainly exists in the form of pure manganese sulphide distributed along grain boundaries. The morphology changes from fine droplets/rods to dendrites with large size and the aspect ratio gradually increases. The thermodynamic calculation results show that manganese sulphide precipitates at the end of solidification (f s = 0.86), and its morphology is related to local supersaturation and extrusion of solid-phase boundary. The solid-phase first transforms from high-temperature ferrite to austenite, then austenite grows up, which compresses the liquid phase boundary enriched with Mn and S and finally forms a large amount of manganese sulphide at the grain boundary. Dendritic, angular and droplet/rod manganese sulphide have different growth processes. Different types of morphological growth processes of manganese sulphide are described by combining crystal growth mechanism and solidification process.
“…After the bloom reaches the air-cooling section, the cooling rate inside the bloom is already very small, so the quantity density of manganese sulphide tends to be stable. This relationship has also been proven in other studies [21,22]. Figure 2. Variation of manganese sulphide number density along bloom thickness direction.…”
In this paper, the characteristics of manganese sulphide in the continuous casting bloom of 38MnS6 steel were revealed. Manganese sulphide in low oxygen (w(O) = 7 ppm) bloom mainly exists in the form of pure manganese sulphide distributed along grain boundaries. The morphology changes from fine droplets/rods to dendrites with large size and the aspect ratio gradually increases. The thermodynamic calculation results show that manganese sulphide precipitates at the end of solidification (f s = 0.86), and its morphology is related to local supersaturation and extrusion of solid-phase boundary. The solid-phase first transforms from high-temperature ferrite to austenite, then austenite grows up, which compresses the liquid phase boundary enriched with Mn and S and finally forms a large amount of manganese sulphide at the grain boundary. Dendritic, angular and droplet/rod manganese sulphide have different growth processes. Different types of morphological growth processes of manganese sulphide are described by combining crystal growth mechanism and solidification process.
“…Shen et al [20]- [21]) revealed the effect of C and Mn on the segregation toward the liquid phase in TWIP steel, and Luo [22]) predicted the size and distribution of MnS inclusion precipitation in the rail steel. The effect of cooling rate and temperature gradient were considered to analyze the distribution mechanism [23]- [24]) . Wang et al [25]- [28]) qualitatively studied the precipitation behavior of inclusions during directional solidification.…”
In order to reasonably control the precipitation of inclusions during solidification in TWIP steels, the precipitation behavior of typical MnS inclusions in high manganese steel was investigated by unidirectional solidification experiments. Through the combined analyses using ASEM-EDS, optical microscope, and thermodynamic calculation, it was found that Mn concentration in the liquid metal region were higher than those in the solid metal region. Furthermore, closer to the inclusion the liquid phase was, higher its Mn content was. In Fe-18mass%Mn-1Al-0.3C, MnS inclusions can precipitate at the positions located in the junction of dendrites at the end of the solidification (solid fraction f s =0.96), Mn content reaching 34.88 mass%. Already existing Al 2 O 3 particles could become the core of MnS to form composite inclusions to promote the MnS precipitation during the solidification process. When f s achieved 0.7 leading the Mn segregation in the liquid phase to 25 mass%, MnS starts to precipitate to attach the Al 2 O 3 surface to form composite inclusion.
“…They can avoid the problems of quenching deformation and cracking of long-axis parts, which is conducive to improving the quality of products. Therefore, researchers in the automotive industry at home and abroad are committed to applying non-tempered steel in automotive forgings [3][4][5][6][7][8][9].…”
The microstructure, mechanical properties, and heat treatment process relationships of 45MnVS non-tempered steel were investigated. Different grain sizes and tissue ratios were obtained after heating and holding at 950, 1050, and 1150 °C for 30 min, respectively, and cooling at different cooling conditions and cooling rates. As the austenitizing temperature increased, the grain size and the elongation and section shrinkage of the experimental steels decreased. At the same time, the content of ferrite and pearlite in the tissue gradually decreases, the content of sorbite and troostite rises, and the strength and hardness of the experimental steel increase. With the increase of cold speed, ferrite's content decreases, sorbite and troostite's content increases, and strength and hardness increase. The original austenite grain size also influences the tissue ratio. As the austenite grain refines, the ferrite transformation temperature increases during cooling and the ferrite content in the tissue rises after cooling.
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