**1. Introduction**

Chemical vapor deposition (CVD) diamond is a prospective thin film material for cutting tools applications due to the extreme combination of hardness, chemical inertness, and thermal conductivity [1]. However, the CVD diamond cutting ability of ferrous materials is strongly limited due to its extreme affinity to iron, cobalt, or nickel [2] attributed to the phase transformation of diamond to graphite and subsequent diffusion of carbon into the metal [3]. This phenomenon is frequently used for diamond catalytic etching [4,5], patterning [6], or polishing [7]. Jin et al. [8] report the thinning of CVD diamond, caused by the reaction with iron foil with a speed up to 2 μm/h at 900 ◦C in argon. Ralchenko et al. [9] show that for the CVD diamond–Fe system in a hydrogen atmosphere the etching speed increases up to 8 μm/min due to the formation of gaseous hydrocarbons, primarily methane. Giménez et al. [10] show an extreme increase of the chemical wear rate of polycrystalline diamond during iron-based materials machining in the temperature range from 700 to 1300 ◦C. Most of these experiments were carried out at extreme temperatures up to 1000 ◦C, while the diamond–iron interaction and diffusion behavior in the diamond–Fe system at lower temperatures are not well studied and are believed to be similar to the graphite–iron mechanism.

In the article, we are focused on the interaction between CVD grown microcrystalline diamond and thermally evaporated Fe at elevated temperatures in the range of 400–800 ◦C under vacuum conditions. We show that in this temperature range, etching of CVD diamond is not as strong as for the 900–1000 ◦C interval [8,10], making a CVD diamond applicable for the cutting of ferrous materials under medium-temperature conditions.
