Hydrogen trapping in low alloy steel and 9%Cr steel - a comparison

BRUZZONI, PABLO; RAMUNNI, V.P.; CASTAÑO RIVERA, PATRICIA; C. HURTADO-NOREÑA

Rio de Janeiro

Workshop; The 3nd International Workshop on Degradation in Metallic Materials DEMAT 2012; 2012

Universidad Federal de Rio de Janeiro - COPPE

The hydrogen trapping behavior of two steels, namely an API 5L X60 low carbon steel used for gas pipelines and a P91-9Cr steel used in thermal power plants, has been studied by means of the hydrogen permeation technique. The low carbon steel presents two types of traps: low energy traps and high energy traps. Low energy traps (binding energy up to 35 kJ/mol) can be ascribed mainly to dislocations, as suggested by results of cold-rolled specimens. High energy traps (60 kJ/mol) are probably related with monovacancies or vacancy clusters which are also created during cold work and might undergo subsequent aging at room temperature. The Presence of Cr as sustitutional solute in the 9Cr steel causes a change in the matrix, which makes dislocation trapping less important. The application of different thermal treatments reveals that submicron coherent carbonitrides precipitated in the temperature range of 500 tp 600C. are the main trap sites in this steel. These hypothesis are supported by electron microscopy and ab initio calculations.