熱延鋼板の製造プロセスにおけるNb炭化物の析出挙動
1993 年 79 巻 1 号 p. 83-89
詳細
1993 年 79 巻 1 号 p. 83-89
The precipitation of NbC during hot rolled steel production process was examined by the laboratory simulation for Nb-bearing low carbon steels.
For a 0.03%C-0.1%Mn-0.13%Nb steel, finely dispersed NbC precipitates and the precipitate free zone (PFZ) were observed in the ferrite matrix. On the other hand, for the Mn and B bearing steel the NbC precipitaion was suppressed considerably. However by aging treatment in a temperature range between 550 and 700°C the fine precipitates became visible and in the specimens aged at 700°C PFZ was also observed. The addition of Mn and B was also found to lower the austenite/ferrite transformation temperature.
The suppression of the precipitation by Mn and B addition is explained by the effect of these elements on the transformation temperature, not by the effect on the Nb diffusion rate and solubility product in ferrite.
The formation of PFZ is explained as follows:
The coarse particles already precipitate in rows along austenite grain boundaries and deformation bands. Through the austenite/ferrite transformation, the coarse particles grow rapidly and the amount of Nb in solution in the neighborhood decreases, resulting in the formation of PFZ along the rows of the coarse particles.
