抄録
It is necessary to minimize thermal deformation of machinery in order to carry out high-precise processing. For this reason, use of low thermal expansion material is effective, and wide applications of low thermal cast iron to mechanical structures are anticipated. To apply to machine structure components, fatigue strength must be evaluated.
In this study, rotating bending fatigue tests and fatigue crack propagation tests were carried out in low thermal expansion cast irons subject to two kinds of heat treatments, normalizing and solution treatment. The grain size decreased by solution treatment, and static strength improved slightly. The fatigue limit ratio of low thermal expansion cast iron is 0.27 to 0.31, and is smaller than 0.57 in FCD450. The fatigue strength improved by solution treatment, because the fracture origin was slip from crystal grain in materials subject to normalizing and solution treatment. The decrease in grain size by solution treatment seemed to improve fatigue strength. The improvement in fatigue strength by the solution heat treatment also drastically increased the threshold stress intensity factor range ΔKth because crack propagates in curvature and bifurcation in two materials. Threshold stress intensity factor range, ΔKth, was drastically increased by the solution treatment due to the roughness induced crack closure seen markably in this material.
