Factors affecting initiation of pitting corrosion in super martensitic stainless steel weldments

Abstract

In the present investigation optical microscopy, in combination with sputtered neutral mass spectrometry (SNMS), has been used to examine the conditions for initiation of pitting corrosion in the heat affected zone (HAZ) of two super martensitic (SM) stainless steel weldments. It is shown that the corrosion resistance depends mainly on the nature of the surface oxide, as determined by the oxygen potential in the shielding gas and the HAZ temperature–time relationship, and less strongly on the underlying microstructure. In the absence of H2S the initiation is associated with spalling of the iron enriched chromium oxide within a narrow region approximately 6 mm from the fusion line, where the contaminated oxide layer is thinnest. As H2S is introduced, the region close to the fusion boundary becomes susceptible to localised corrosion because of the more extensive metal oxidation. Thus, the high temperature oxidation and iron oxide scale formation accompanying the welding operation appear to be the main factors affecting pitting corrosion initiation in SM stainless steel weldments.

Residual stress and microstructure in welds of 13%Cr–4%Ni martensitic stainless steel

“…As pointed out before, the somewhat lower hardness in HAZ5B compared to base metal is most probably due to some decomposition of base metal martensite in stable austenite on heating. This microhardness profile is quite different from the one presented by Enerhaug et al (2001) a much smaller HAZ 3 was found, no significant drop in hardness and a higher hardness in all HAZ zones were measured. The smaller HAZ3 can be explained by the higher molybdenum content of the alloy studied by Enerhaug et al (2001) which shrinks the ␥ loop and expand the ␦-␥ zone so that the ␦-ferrite formed has less time to transforms in austenite upon cooling.…”

“…This microhardness profile is quite different from the one presented by Enerhaug et al (2001) a much smaller HAZ 3 was found, no significant drop in hardness and a higher hardness in all HAZ zones were measured. The smaller HAZ3 can be explained by the higher molybdenum content of the alloy studied by Enerhaug et al (2001) which shrinks the ␥ loop and expand the ␦-␥ zone so that the ␦-ferrite formed has less time to transforms in austenite upon cooling. The higher hardness of the rest of the HAZ is most probably due to the higher carbon and nitrogen content of the steel used in the present study.…”

Influência da refusão por plasma na microestrutura de um revestimento Fe-Mn-Cr-Si depositado por aspersão térmica arco elétrico sobre aço inoxidável ASTM A743-CA6NM

“…A formação de martensita na região aquecida no campo monofásico, a partir da transformação parcial da austenita em martensita produz uma elevação no valor de dureza. Resultados similares obtidos em aços supermartensíticos de composição semelhante foram observados em trabalhos anteriores com soldagem TIG (tungsten inert gas) e Plasma PTA [12,13,28].…”

Reliability of pipe steels with different amounts of C and Cr during onshore carbon dioxide injection

“…It is known from thermal energy production that the CO 2 -corrosion is sensitively dependent on alloy composition (in particular Cr and C), contamination of alloy and media, environmental conditions like temperature, CO 2 partial pressure, flow conditions and protective corrosion scales (Cui et al, 2006;Zhang et al, 2008;Lopez et al, 2003a;Mu and Zhao, 2010;Bonis, 2008;Enerhaug, 2002;Neubert, 2008;Kirchheiner and Wölpert, 2008;Zhang et al, 2005;Alhajji and Reda, 1993;Choi and Nešić, 2008;Moreira et al, 2004;Jiang et al, 2008;Ahmad et al, 2000). Generally a high Cr-content (above 12%) leads to a passivating Cr-oxide layer (Cr 2 O 3 ) on the steels surfaces if Cr is part of the regular atomic structure and not trapped in secondary phases such as carbides.…”