Strengthening of Pearlitic Steel by Ferrite/Cementite Elastic Misfit Strain

Abstract

The strength of pearlitic steel was clearly reduced by annealing, even though cementite stably maintained a lamellar structure. In response, lattice strain of the ferrite phase in pearlite monotonically decreased with increasing annealing time. As a result, a good linear relationship was established between the strength and ferrite lattice strain independent of the interlamellar spacing and morphology of cementite. This suggests that the ferrite/cementite elastic misfit strain contributes to the high strength of pearlitic steel.

Internal Stress and Elastic Strain Energy in Pearlite and Their Accommodation by Misfit Dislocations

“…However, most of the elastic strain energy still remains in pearlite. This agrees well with the results in previous researches [23][24][25] and suggests that the misfit dislocation interval of 20 nm is insufficient to effectively reduce the coherency strain energy. On the other hands, it is understood that E 1 increases as interlamellar spacing becomes finer due to the increase in E 1 dis .…”

“…As a result, it is interesting to find that the strength of pearlitic steel has a good linear relationship with the lattice strain in pearlitic ferrite rather than with the interlamellar spacing. 25) These results strongly suggest that the elastic strain and internal stress are very important factors affecting the microstructure and the mechanical properties of pearlitic steel. It seems that the internal stress in pearlite is inhomogeneously distributed among pearlite colonies, and each colony possesses different anisotropic internal stress.…”

“…This means that Type 2 accommodation is more reasonable to explain the fact that ferrite lattice strain in pearlite clearly decreases with increasing interlamellar spacing. 25) E 2 is concave down function of L and becomes almost constant when interlamellar spacing is finer than 200 nm. This is because we have assumed for simplicity that the interval of misfit dislocations is simply proportional to the pearlite growth rate, as expressed by Eq.…”

Effects of Mn on Isothermal Transformation Microstructure and Tensile Properties in Medium- and High-carbon Steels

“…Moreover, the authors recently reported that 0.2% proof stress linear increase with respect to the lattice strain (micro-strain) in the pearlitic ferrite, as evaluated by X-ray diffractometry, regardless of the interlamellar spacing and cementite morphology. 26) Thus, authors proposed that the internal stress generated by the misfit between ferrite and cementite has large influence on the strength of pearlite steels. [26][27][28][29][30][31] Figure 12 shows X-ray (211) ferrite diffraction peak containing Kα1 and Kα2 of 40C0Mn and 100C2Mn with IF steel as a reference.…”

“…26) Thus, authors proposed that the internal stress generated by the misfit between ferrite and cementite has large influence on the strength of pearlite steels. [26][27][28][29][30][31] Figure 12 shows X-ray (211) ferrite diffraction peak containing Kα1 and Kα2 of 40C0Mn and 100C2Mn with IF steel as a reference. As shown above in Table 2, 40C0Mn and 100C2Mn have the lowest and highest 0.2% proof stress, respectively.…”