遊離フェライト中に硬質領域が存在する鋼の下降伏点

抄録

The influences of microstructural parameters on the lower yield point σ were investigated, in the microstructure containing tempered martensite patches in free ferrite matrix. The results obtained are as follows:
(1) σ is not affected by the difference of hardness in the tempered martensite patches. (2) σ rises with the increasing of f, the volume ratio of total tempered martensite, when the ferrite grain size α₁ is kept at a constant value. However, σ does not vary, when the mean free path between the tempered martensite patches α₂ is kept at a constant value. (3) There is an approximately linear relationship between (α₁)^-1/2 and σ in the presence of tempered martensite patches. And the sensitivity of σ to α₁ increases with the increasing of f. (4) There is a linear relationship between (α₂)^-1/2 and σ, and better correlation is demonstrated compared with the relationship between (α₁)^-1/2 and σ. Furthermore, when the values of f are with in the range of 15 to 40%, the values of σ are plotted on a straight line irrespective of f. (5) These results can be understood under the consideration that, in the propagation of Lüders band, α₂ is the effective length of slip band to produce the stress concentration for forcing a dislocation out from a boundary of free ferrite and tempered martensite patch, when the tempered martensite patches are contained.