Investigation on the Correlation between Inclusions and High Temperature Urea Corrosion Behavior in Ferritic Stainless Steel

Abstract

The influence of inclusion size and number density on high-temperature urea corrosion (HTUC) behavior of ferritic stainless steels was investigated in a simulated working environment of selective catalytic reduction (SCR) system in commercial vehicles. There is a positive correlation between the control level of inclusions and the resistance of HTUC. By slightly increasing the content of Nb in ferritic stainless steels, the inclusions, especially TiN, were significantly refined, and thus displayed an improvement in HTUC resistance. The interface between inclusions and the matrix becomes a fast channel for chromium precipitation during high-temperature nitriding induced by the decomposition of urea. Chromium nitrides will precipitate around the inclusions and wrap the inclusions, which will decrease the chromium equivalent of the matrix and reduce the resistance of ferritic stainless steels to HTUC. In addition, the high-temperature oxidation accompanied with thermal fatigue also makes the inclusions more likely to become the crack nucleation source, which can accelerate the material thinning and reduce its service life.

Study on Grain Growth Tendency and Its Correlation with Recrystallization and Precipitation in High‐Nb 444‐Type Ferritic Stainless Steel during Brazing

“…It is consistent with the precipitates previously formed in 439 ferritic stainless steel. [ 3 ] The fine NbC precipitates are also uniformly distributed within the grains and at the grain boundaries of sample 2#, and the precipitates at the grain boundaries can effectively inhibit grain boundary migration. Moreover, from Figure 3a,b, it can be seen that ferrite grain boundaries also exhibit two patterns, namely, line grain boundary (black arrow) and wide grain boundary with higher density of dislocations (yellow arrow).…”

“…Ferritic stainless steels are widely used in automotive industries, especially for exhaust systems including manifolds, catalytic converters, mufflers, and tail pipes. [ 1–3 ] According to the performance of different grades of ferritic stainless steels, various types of ferritic stainless steel such as 409, 436, 439, and 441 have been used to replace austenitic stainless steel applied in automotive exhaust systems, achieving performance improvement and cost reduction. [ 4,5 ] Accompanying this, Nb–Ti dual‐stability technology has gradually been developed and applied to the development of high‐performance ferritic stainless steels.…”

“…The composite addition of Nb and Ti can refine inclusions and improve the ability to resist high‐temperature oxidation and condensate corrosion. [ 3,5 ] Moreover, another study indicated that the addition of Nb and Mo is very beneficial to improve the high‐temperature urea corrosion resistance of ferritic stainless steel, attributing it to the reduction of the reactivation rate. [ 6 ] However, the application environments of ferritic stainless steel involved in the above studies are generally below 1000 °C.…”

Numerical Investigation on Coalescence Behavior of Liquid Inclusion Particles in Argon Bubble Wake Flow

“…This, in turn, significantly deteriorates the mechanical properties of the steel. [ 1–4 ] Furthermore, during the rolling process, the presence of nonmetallic inclusions in the steel may lead to imperfections in the final product. In some cases, it may also result in severe nozzle clogging, causing interruption in continuous casting.…”

Long-Term Oxidation Studies on Porous Stainless Steel 430L Substrate Relevant to Its Application in Metal-Supported SOFC

“…However, a major challenge in using the porous 430L substrate as a symmetrical SOFC support for long-term operation is its significantly larger surface area compared to the dense 430L stainless steel of the same size, which can lead to oxidation of the porous stainless steel skeleton over extended use and trigger cell degradation. However, extended operation at higher temperatures results in the formation of a protective Cr 2 O 3 scale on the substrate surface [15][16][17]. This leads to a depletion of chromium in the substrate and breakaway oxidation as the oxidation exposure time increases.…”