Electron-microscopic Observations on the Fatigue-Fracture Surfaces of Low-Alloy Steels and High-Carbon Steels (Microfractography of Fatigue-Fracture Surfaces of Metals, 2nd Report)

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  • 低合金鋼および高炭素鋼の疲労破面の電子顕微鏡による観察
  • テイゴウキン コウ オヨビ コウタンソ コウ ノ ヒロウハメン ノ デンシ ケンビキョウ ニ ヨル カンサツ

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Abstract

It was mentioned in the first report that the fatigue fracture surfaces of low carbon steels could be classified roughly in five types according to the different patterns of their electron-microfractographs and that their characteristic features were remarkably different from those of the fracture surfaces obtained by tensile or impact tests. This report refers to the observations which we conducted on the fatigue-fracture surfaces of low-alloy steel and high carbon steel brought about by the rotating-beam fatigue tester, using the electron-microfractographs of the fatigue-fracture surfaces, as in the case of the previous report, and comparing the fatigue fracture surfaces with those of low-carbon steel. The results obtained are as follows; (1) The electron microfractographs of fatigue fracture surfaces of low alloy steel in quenched and tempered conditions were classified in five types as in the instance of low-carbon steel. (2) The fatigue fracture surfaces of hardened carbon steel (0.6% carbon) did not show the characteristics of a fatigue fracture, but the river pattern whicd usually appears in brittle fracture surfaces was noticed. (3) In the case of high-carbon steel in annealed condition, a pattern like lamellar pearlite was observed appearing in the fatigue-fracture surfaces, though the surfaces were not treated by etching. A part of the surface which corresponded to ferrite took on an appearance of fine stripes at intervals of less than 200 Å while the remaining part corresponding to cementite was smooth and no pattern of stripes was seen in it.

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