Bainite transformation progresses with the nucleation accompanying carbon diffusion and the growth without carbon diffusion, and the increase in volume fraction is due to the successive nucleation of sub-units whose size depends on the transformation temperature and austenite strength. The heat-affected zone (HAZ) is susceptible to deterioration in toughness since the fine microstructure imparted to the steel plates during the manufacturing process is demolished. A layer in which alloying elements are depleted around other precipitates of sulfides (CuS), carbides and nitrides is also formed. In the case of carbides and nitrides, however, the rates of C and N diffusion are extremely high even at low temperatures and hence, there is not much possibility that such depleted zones will be formed. By the quantitative evaluation of element-depleted zones which have been reported on the bainite formation as well, it will become possible to control the refinement of microstructures via the utilization of intragranular transformation and to manufacture high-function and high-strength steel materials having excellent HAZ toughness.
|ジャーナル||Nippon Steel Technical Report|
|出版ステータス||出版済み - 11月 2012|
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