Changes in Corrosion Resistance of 18%Cr-12%Ni-Type Stainless Steels After Sensitization

• Published in: Corrosion (Houston, Tex.) Vol. 57; no. 10; pp. 874 - 883
• Main Authors: Záhumensk´y, P., Tuleja, S., Országhová, J., Janovec, J., Magula, V.
• Format: Journal Article
• Language: English
• Published: Houston, TX NACE International 01.10.2001; NACE
• Subjects: Activation; Analytical methods; Annealing; Applied sciences; Austenitic stainless steels; Chromium; Corrosion; Corrosion environments; Corrosion resistance; Corrosion resistant steels; Cycles; Deformation; Electrochemistry; Electron diffraction; Exact sciences and technology; Intergranular corrosion; Metals. Metallurgy; Molybdenum; Nickel; Sensitizing; Sigma phase; Stainless steel; Steel construction; Thermal simulation; Titanium; Welding; X-ray spectroscopy; Corrosion resistance; Austenitic stainless steel; Sensitization; Stainless steel; Intergranular corrosion
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3290314

ABSTRACTAustenitic stainless steels (SS) represent the largest group (65% to 70%) of SS in use.1 Their dominant position is based on a generally high level of corrosion resistance, good mechanical properties, workability, and the ability to obtain various specific combinations of properties by different compositions within the group. However, these steels can become sensitized to intergranular corrosion (IGC) after undergoing treatment in the temperature range between 723 K and 1,123 K or by slow-cooling from annealing temperatures of 1,273 K to 1,473 K. The sensitization of SS is the result of microstructural changes, particularly at grain boundaries (GB), and is still the subject of many studies.2-8 M23C6 carbide precipitation on GB is known to be the critical factor influencing the resistance of SS to IGC. The most common way to combat sensitization to IGC in austenitic SS is by using stabilizing elements such as Nb or Ti, which are stronger carbide formers than Cr. Stabilized austenitic SS are used regularly in welded constructions. Welding affects the material and it can cause susceptibility to IGC, particularly in the weld heat-affected zone (HAZ). Knifeline corrosion is a specific manifestation of IGC in weld HAZ in stabilized austenitic SS, which can occur in the high-heated region at the interface between the base material and weld metal. At high temperatures, particles of carbides of stabilizing elements dissolve, and consequently, their stabilizing effect disappears. During subsequent cooling, dendritic eutectic carbides of the stabilizing elements and -ferrite are formed coincident with grain growth.9 Repeated heating (i.e., by multipass welding or exposures at highoperating temperatures) can give rise to heavy knife corrosion in severe oxidizing acidic media (e.g., nitric acid [HNO3]).