Fatigue of two heats of vacuum-melted iron (one containing 170 wt.ppm C and the other 50 ppm C) produced a rumpled surface with grain boundary cracks in ultrahigh vacuum. In oxygen, prominent slip lines and transgranular cracks were observed. Also, the samples with a larger carbon content (170 wt.ppm) showed coarser slip lines in oxygen than did the samples with a smaller carbon content (50 wt.ppm). Interstitial-free samples fatigued in dry air showed very fine slip lines with the surface resembling the rumpled structure of fatigue in ultrahigh vacuum. It was suggested that CO clusters affect the dislocation motion during fatigue and control the surface structure.
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