Surface modifications and the mechanical properties of carbon steels implanted with nitrogen

Abstract

Discusses the relationships between the surface composition and the mechanical properties of carbon steels implanted with nitrogen. Conversion electron and X-ray Mossbauer spectroscopy (CEMS and CXMS) were used to investigate the surface modifications of the implanted samples. Thermal annealing was performed in high vacuum, at temperatures between 250 and 500 degrees C, in order to simulate the temperature increase in real tribological processes. It is shown that the improved performance of nitrogen-implanted carbon steels against wear and fatigue is mainly due to the action of finely dispersed iron carbonitrides ( theta - and epsilon -Fe3(C,N)). It is shown also that the persistence of the protective action at greater depths is associated with the in-diffusion of nitrogen released by thermal decomposition of the compounds formed at the surface.

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“…Early interest in iron nitrides came from the steel industry to improve the abrasive strength of steels by nitridizing the surface. 1,2 Recently, however, the magnetic properties of iron nitrides, especially high saturation magnetization and high coercivity, have received more attention than their mechanical properties because they are amenable to high-density magnetic recording.…”

Dissolution and reprecipitation of carbonitride precipitates in carbon steel by low-dose α bombardment

“…In [13] it was found that &-Fe3 2(C, N) obtained by N: implantation into 1020 steel are stable up to 400°C. For higher temperatures, they dissolve as a consequence of N diffusion out of the implanted region.…”

Carbonitride precipitation by successive implantation of carbon and nitrogen into pure iron

“…In particular, steels implanted with nitrogen ions exhibited greatly improved resistance to wear (Dearnaley and Hartley 1978, Hirvonen 1978, Hartley 1979, Herman 1981. It was shown that nitrogen implantation into low carbon steels induces the formation of avery fine dispersion of precipitates with grain size ranging from 10 to 100 A (Herman 198l), and on the basis of Mossbauer measurements several authors have interpreted these precipitates as carbonitrides (Principi et ai 1980, Frattini et a1 1982, dos Santos eta1 1982,1984. Recently a key role was attributed to these compounds in the properties of nitrogen-implanted steels (dos Santos et ai 1984).…”