Corrosion investigations and testing standards normally use standard surface pre-treatments, e.g.
ground samples. This is in order to be able to determine the impact of various elements. The end users
of materials therefore generally have access to good data regarding the impact of the alloy
composition. The problem is that alloys are almost never used in a ground condition, as the surface
condition strongly depends on the production route used. This study addresses this problem.
The metal dusting resistance of wrought and spun cast 20Cr32NiFe with different surface states has
been investigated. The samples came from commercially available tubes with their standard surface
condition; the wrought alloys in a pickled state and the spun cast deep hole drilled. Samples with the
original and ground surfaces were exposed for 300 h at 600 °C in a CO/CO2/H2/H2O mixture, Ptot=5.5
bar (ac: Boudouard/COred/Water-Gas-Shift: 558/232/379), corresponding to conditions in some furnaces
used for the direct reduction of iron ore. The results clearly show that that 20Cr32NiFe is not suitable
for high carbon activities. However, the pickled surface was sensitive toward metal dusting attack while
the drilled and the ground samples had better resistance. This shows that the surface pre-treatment
plays a crucial role.
Key words: metal-dusting, surface pre-treatment, wrought alloys, cast alloys, pickling, machining