抄録
This paper describes the structural dependence of ψ-splitting behavior observed in the X-ray stress measurement of worked surfaces. In order to investigate at first the effect of the cementite phase on the X-ray residual strain distribution, the lattice spacings at many orientations (φ, ψ) were measured for the ground or orthogonally planed surfaces of annealed S55C and pure iron. The variation of measured interplanar spacing against sin2ψ for S55C was closely approximated by the following fundamental triaxial stess-strain relation:
εφψ=1/2s2[σ11cos2φ+σ12sin2φ+σ22sin2φ-σ33]sin2ψ+1/2s2σ33
+s1[σ11+σ22+σ33]+1/2s2[σ31cosφ+σ23sinφ]sin2ψ.
However, the values for pure iron showed remarkable deviations from the elliptic distribution in sin2ψ diagram because of sharp preferred orientations produced by hard mechanical working.
Secondly, the effect of morphology of the cementite phase on the sin2ψ diagram was investigated for SK 3 specimens which were prepared by four different heat treatments in order to include the spheroidized structure and the pearlite structure. The interplanar spacings showed the ψ-splitting behavior between positive and negative ψ angles along the grinding direction and distributed approximately in the form of ellipse. The extent of the ψ-splitting was the greatest for the pearlite structure and became smaller with increasing mean interparticle spacing for the spheroidized structure. This can be understood by a high impediment in dislocation motion within the lamellate or fine dispersed structure, which causes the large back stress due to dislocation pile-up at the cementite phase.
