焼入鋼の表面硬度におよぼす加工変質層の影響

抄録

When the steel surface was finished by mechanical process, for example, turning, grinding and mechanical polishing, its surface is covered by the layer in which the physical and mechanical properties differ from those in mother material. The authors tentatively called this layer in terms of the “machined-surface-layer”. Although it is said that the influence of this layer on mechanical strength of a material is of no negligible amount, but many questions are still left unsolved. Especially in previous studies, only discussions on the influence of residual stress in the surface layer were described, and no attention was paid to the work hardening and other factors.
This paper presented the results of an investigation into the influence of the machinedsurface-layer on hardness of the surface of hardened steel.Distribution of the half-value breadth of X-ray diffraction patterns on the ground surface layer was obtained with small specimens heat-treated under various conditions.Then, hardness tests were carried out on the surface layer of Sendzimir rolls finished by some mechanical process.The results of these studies were as follows:
(1) Two types of machined-surface-layer were obsereved.One of these had a monotonous distribution of half-value breadth under the surface and the other had the minimum value of half-value breadth directly under the surface.This phenomenon was explained by a “competition” happened between mechanical action and thermal action.
(2) The distribution of half-value breadth corresponded with the distribution of hardness. Therefore, the depth of the machined-surface-layer could be determined by the measurements of the distribution of half-value breadth.
(3) The strong work-hardening was observed on the machined-surface-layer of a Sendzimir roll finished by turning.It is necessary to remove the surface about 300μ thickness by grinding in order to obtain the reasonable value of Shore hardness.