抄録
Studies have been made of the fatigue strength of the tufftrided steel which is widely used as structural material of machine parts,
The material of the specimens used in the present experiment is SFA 55 carbon steel, and the forms of tested specimens are 20mmφ smooth specimen and 15mmφ V-notched specimen (notch radius is 0.3, 0.6, and 1.0mm). The heat-treatments of specimens are of three kinds, i. e; tufftrided and water-cooled, tufftrided and air-cooled, neutralized heat-treatment and water-cooled.
Further, the residual stress of the specimen near the surface was measured by means of an X-ray stress measurement apparatus.
The test results are as follows;
(1) The fatigue limit of the tufftrided smooth specimen is about 40 percent higher than that of the non-tufftrided one.
(2) In the case of the sharp V-notched specimen, the fatigue limit of the tufftrided specimen is about twice the fatigue limit of the non-tufftrided one. But, under the condition of cooling treatment after heat-treatment, the fatigue limit falls considerably and becomes smaller than the value of σw0/α.
(3) The effective hardened layer of the tufftrided specimen is about 2 to 3mm.
(4) The residual stress near the surface of the tufftrided specimens is about-40kg/mm2. The 70 to 75% of its value has been caused by the cooling treatment. The residual stress caused by the combinated layer or the diffusion layer is about -10kg/mm2.
