| Abstract Scope |
Since the local harness in martensitic steels is widely distributed, in this study, the relationship between local harness distribution and microstructure formation process during martensitic transformation was investigated by combining hardness evaluation and in-situ observation. Steels with different carbon contents (0.002C and 0.12C, in mass%) were prepared. The formation process was observed by a confocal laser microscopy, the crystal orientation for observed area was analyzed by EBSD, and the micro Vickers hardness test was also conducted. For 0.002C steel, coarse blocks were observed and each block was formed to expand gradually. In each block, the hardness of area where it was formed initially is low. For 0.12C steel, a single block formed to divide austenite grain in the early stage of transformation, and multiple blocks were generated simultaneously in the later stage to form a packet. In each austenite grain, the local harness increased as the formation temperature decreased. |