The Influence of Surface Pre-Treatment on the Metal Dusting Behavior of Cast and Wrought 20Cr32NiFe

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, P_tot=7.0 bar (a_c: Boudouard/COred/WGS: 558/232/379), corresponding to conditions in some direct reduction furnaces. The results clearly show that that 20Cr32NiFe is not suitable for high carbon activities, cast 35Cr45NiFe is more suitable. 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.