Deformation Behavior of Cementite in Deformed High Carbon Steel Observed by X-ray Diffraction with Synchrotron Radiation

The deformation behavior of cementite in drawn pearlitic steel and spheroidal cementite steel, which have hypereutectoid composition, was investigated by X-ray diffraction using synchrotron radiation. A detailed analysis of diffraction peak profiles reveals that the deformation behavior strongly depends on the shape of cementite in steel. The unit cell volume of the cementite in the drawn pearlitic steel compressively and elastically deforms by 1.5 to 2 pct of the initial volume at the early stage of drawing, whereas that in the drawn spheroidal cementite steel is compressed by 1 pct of the initial volume even at a large true strain. The cementite in the drawn pearlitic steel fragments into small pieces with increasing the true strain, and these pieces change to amorphous cementite. The dislocation densities of the cementite in the drawn pearlitic steel and in the drawn spheroidal cementite steel are estimated to be ~10¹³/m² before drawing and ~10¹⁴/m² after drawing. Although the large strain is induced in the cementite by drawing, the maximum strain energy in the cementite is too small to contribute to the dissolution of the cementite.