Abstract
This work was made to clarify the influences of grinding, annealing after grinding and buff-finishing on fatigue strengths of electrolytic and carbonyl iron powder compacts sintered at 1123 and 1423 K for 3.6 ks.
The results obtained were as follows:
(1) The plastic flow induced by the grinding occurred on the surface layers of sintered iron compacts toward the grinding direction and the worked surface layers were formed in the region about 10μm thickness under the surfaces of them. The pores near the surface of specimens were collapsed to the grinding direction and became a linear-like microcrack.
(2) From X-ray residual stress measurement, the residual stress in the surface layer of as-sintered specimen was slight, but that of as-ground specimen induced a very higher tensile and compressive stress, respectively, in parallel and transverse to the length of specimens. In the other specimens, the tensile residual stress disappeared and varied to compressive side.
(3) In all fatigue strengths of specimens prepared by various processes, that of annealed specimen after grinding was the largest. This was caused by the reduction of the residual stress, the formation of some surface layers without pores and the nucleation of a few fine grain due to the recrystallization during annealing process.
