Thermal Fatigue Behaviour of a Chromium Electroplated 32NiCrMo145 Steel

Thermal fatigue behavior of hard chromium electroplated steel in three different crack intensities of high contraction (HC), medium contraction (MC) and Iow contraction (LC) was studied. Maximum and minimum temperatures during thermal cycle were 800 and 100℃, respectively. The topography and cross sections of the samples exposed to 50, 100 and 200 thermal cycles were studied. The thermal fatigue behavior was analyzed using the data obtained from surface roughness, crack networks and stress induced during cycles. Although the as-coated sample with LC chromium contained no crack, it appeared to have a high crack density after only 50 cycles. The crack depth and width in cyclically oxidized LC coating were much less than those in MC and HC coatings. It was concluded that the LC coating protected the substrate from having cracks or subsurface oxidation during thermal fatigue. The cracks in the HC and MC coatings increased in density as well as in depth by thermal cycles. Moreover, the opening of the cracks to the substrate resulted in sub-surface oxidation.