Concerning Cr-Mo steels used actually for motor shafts, etc. by Japanese National Railways, we examined their mechanical properties with the same test material, especially tensile strengths, strains, contractions and rotational bending fatigue strengths.
As a result of our experiments, in which we compared the effects of the difference of forging ratio and heat treatment conditions, or those of standard specimens and sectional parts of large size materials given on statical tension and fatigue strengths, we found various differences in data.
About the standard specimens, we could not find any difference in influences of heat treatment conditions on statical tension data. But the fatigue strengths of materials oil-or water-tempered were larger than those of materials air-tempered.
Also, the effects of the difference in forging ratio did not appear in the statical tension experiments, but appeared a little in the rotational bending fatigue tests.
On the other hand, about the sectional parts of large size specimens (840°C HWQ-680°C OT or AT), we found fairly large differences, namely in yielding p't σs, tensile strength σB, and fatigue strength σwb; data of outer layer parts were larger than those of inner parts.
The tensile strength was in a range of 78-92kg/mm2, and the fatigue strength was about 37-41kg/mm2.