X線による多結晶金属の変形に関する研究

炭素鋼のX線的弾性定数に及ぼす含有炭素量の影響

抄録

The X-ray elastic constants are found to be affected by many factors due to the selective nature of X-ray diffraction measurements. It is important to measure quantitatively the effect of these factors, not only to improve the accuracy of X-ray stress measurements, but also to elucidate the deformation mechanisms of polycrystalline aggregates.
In a previous paper, an experimental and analytical investigation of the X-ray elastic constants was presented. The dependence of the constants on the diffracting plane as well as the change in these constants caused by uniaxial plastic deformation were observed experimentally and interpreted on the basis of crystal orientation, anisotropic elastic constants and deformation texture.
In the present investigation, similar experimental techniques have been employed to determine the influence of carbon content (or cementite phase) and the effect of pre-working on the X-ray elastic constants of plain carbon steels. The results are reported for five compositions of hot-rolled plain carbon steel ranging in carbon content from 0.01 to 0.91%, and a forged 0.13% carbon steel. All the specimens were fully annealed and electropolished to remove the surface layer affected by machining.
The following conclusions have been reached as the result of this investigation:
(1) The absolute values of the X-ray elastic constants, S₁ and S₂/2, decrease with increasing carbon content, while the X-ray elastic modules, E, increases gradually. This phenomenon cannot be explained by the difference between the elastic constants of ferrite and cementite. It can be explained, however, by the constraint of deformation due to grain boundaries, since ferrite grains of the steels used in this investigation are smaller in size in proportion as the carbon content is larger. The smaller the grain size, the more prodominantly the deformation of the grain is influenced by the grain boundary and the deformation behavior approaches the Voigt's condition (uniform strain).
(2) The absolute values of S₁ and S₂/2 of annealed hot-rolled steel decrease in the early stages of plastic deformation until they reach a nearly constant value at large strains.
(3) In the case of the annealed forged steel, on the contrary, the plastic deformation causes the value to increase.
(4) The absolute values of S₁ and S₂/2 of annealed forged steel are smaller at first than those of annealed hot-rolled steel of the same carbon content, but they approach the same constant level at high strain, as the plastic deformation causes change in the values. It is concluded that the X-ray elastic constants are affected according to the type of the pre-working employed before the annealing.
(5) The values of the constants of the steels used depend upon the diffracting plane. In other words the absolute values of S₁ and S₂/2 measured on {211} by Cr-K_α radiation are considerably smaller than those measured on {310} by Co-K_α.