X線応力測定に及ぼすX線透過深さの影響

抄録

The residual stresses of the hardened high carbon steels are very sensitive to grinding processes, and the stress gradients near the ground surface are found to be very steep. In the suitably ground surfaces of middle carbon steels which are case-hardened by the high-frequency induction heat treatment, there is no appearance of the tensile residual stress, but under the unsuitable grinding conditions, tensile stresses are discovered at about 10 to 30μ depth under the ground surfaces. These residual stresses can be satisfactorily measured by the X-ray diffraction technique, on successively electropolished surfaces.
However, the penetration depth of X-rays must be taken into consideration because the stress varies in the distance of X-ray penetration. With Cr-Kα-rays the very thin surface stress could be determined, because they are heavily attenuated in steel. With more penetrable X-rays, Co-Kα, Fe-Kα and Mo-Kα, the measured stresses are influenced by the steep gradient of stresses. These relations are discussed theoretically and experimental results using Fe-Kα and Cr-Kα are compared, and it is shown that the 2θ-sin²ψ plot for Fe-Kα is not in a straight line because of the stress gradient.
It is discovered that these facts can be utilized for the non-destructive measurement of tensile stresses whick may be existent just under the unsuitably ground surfaces. In the usual method the stress is measured on the electro-polished surface and it gives some failures to the precisely ground surfaces, but using the more penetrable X-ray, Fe-Kα, the stress under the surface is estimated from the non treated surface.