The oxidation and carburisation of Fe-9%Cr-1%Mo steel
The mechanisms involved in the breakdown of the protective ccides
formed on Fe-9%Cr l%Mo have been investigated in both air and high
pressure CO 2' The initial research programme was to investigate the
microstructural changes which occurred with breakaway oxidation, a new
EELS detector being cxi missioned to detenni. ne oxygen and raXbon levels.
Oxidation in air was performed at temperatures between 500 and 1000'C.
SEM and sane TEN cross sectional work was performed to determine the
role of oxygen ingression, but prcblems in sample preparation made
With cDcidation in high pressure OD2 the change from protective growth
to breakaway is accanpanied by massive oxide growths usually at
specimen corners. Microstructural changes also occur, with massive
carbide growth acccrnpanying the changes in oxide structure. During
oxidation, chemical exchanges between the oxidising gas, the metal and
the inner oxide all contribute to the deposition of carbon at the
metal/ oxide interface. This process generates internal stresses in the
oxide, allowing microcracks to develop this enhancing the inward
movement of the 002 and causing more, oxidation and carbon deposition.
TEM cross sections were prepared to determine the mode of oxidation and
the process by which carbon reaches the interface.
In theory, EELS analysis allows identification of light elements Mi
and above) but in practice the system proved very sample dependent,
working well on thin films but very poorly on thick specimens
(carbides). Evidence of the range of EELS mapping facilities are
presented together with work on a new particle extraction system