Hydrogen‐ion image features of tempered martensite

SUMMARY Hydrogen‐ion microscopy has been used to study first and third stage tempered ferrous martensite. Both ε‐carbide and cementite particles resulting from the tempering process appeared dark in the images. The image characteristics of the matrix phases in these specimens were intermediate between those of pure iron and as‐quenched ferrous martensite. The sharpness of the (111) zone lines and the ‘butterfly’ pattern in {110} regions, the development of high index planes and the regularity of low index net plane edges decreased continuously with increasing carbon content of the matrix phase. The effects of carbon content and lattice strain on specimen geometry, field evaporation, hydrogen etching and field ionization are discussed. It is suggested that carbon atoms in random solid solution lead to an irregular evaporation, similar to that previously proposed for other solid solution alloys, and that the irregular evaporation is enhanced by the associated lattice strain and hydrogen etching process. The irregular end form thus produced lacks the sharp image features found in the smoother end form of the pure metal.