抄録
Following the previous paper, Tetsu-to-Hagané vol, 42 (1956) No. 10, p. 956-961, some experimeats are achieved on the nitrogen-blowing process. Results obtained are summarized as follows:
1) Surface appearances of rolled billets: Surface appearances of rolled billets made by the nitrogen-blowing process are superior to those by the ordinary and floating boards processes.
2) Appearances of sub-surface defects of rolled billets: Appearances of sub-surface defects of rolled billets by the nitrogen-blowing and floating boards processes are both clean. Applying the nitrogen-blowing process, the surface appearances of rolled billets are clean and the sub-surface defects don't occur, so that the mold dressings are unnecessary.
3) Gas contents in inside and outside parts of rolled billets, -oxygen and nitrogen: Oxygen contents of rolled billets are nearly equal between the nitrogen-blowing process and the ordinary one. Sand contents of rolled billets made by the nitrogen-blowing process are somewhat lower than those by the ordinary process. However, this point must be checked by the abovementioned sampling methods, analytical methods and ingot size. Nitrogen contents of rolled billets are nearly equal between the nitrogen-blowing and ordinary processes.
4) Cleanliness and grain size in inside and outside parts of rolled billets; Cleanliness of rolled billets by the nitrogen-blowing process are better than the ordinary one. Grain size of rolled billets are nearly equal between the nitrogen-blowing and ordinary pyocesses.
5) Effects of nitrogen on the properties of finished products: Effects of nitrogen on the properties of finished products must not be considered, because nitrogen contents of rolled billets made by the nitrogen-blowing process are nearly equal to other processes.
Following the above mentioned experiments, some theoretical considerations on the nitrogenblowing process are achieved as follows:
1) Oxidation of molten steel by the atmosphere in mold;
2) Beginning temperature of oxidation for active elements in molten steel
3) Nitrogen absorption of molten steel.
