New Ferritic Stainless Steel for Service Temperatures up to 1050 °C Utilizing Intermetallic Phase Transformation

Abstract

A large number of thermodynamic simulations has been used to design a new Nb-Ti dual stabilized ferritic stainless steel with excellent creep resistance at 1050 °C through an optimal volume fraction of Laves (η) phase stabilized by the alloying elements Nb, Si and Mo. By raising the dissolution temperature of the phase, which also corresponds to the onset of rapid grain growth, the steel will better maintain the mechanical properties at higher service temperature. Laves phase precipitates can also improve creep resistance through precipitation strengthening and grain boundary pinning depending on the dominant creep mechanism. Sag tests at high temperatures for the designed steel showed significantly better results compared to other ferritic stainless steels typically used in high temperature applications at present.

Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

“…NbFe 2 -containing ferritic stainless steels with Cr contents in the range 15 to 19 wt% and low C contents of 0.01 wt% or less were developed for application in automotive exhaust systems, which currently are working at temperatures in the range of up to 900°C [740][741][742][743][744][745][746][747][748][749][750][751][752][753][754][755][756]. Typical Nb additions are in the range 0.4 to 0.8 wt% and lead to significant solid solution strengthening of the ferrite matrix with precipitation of NbFe 2 Laves phase and small amounts of Nb(C,N) and Fe 3 Nb 3 C during aging.…”

“…Typical Nb additions are in the range 0.4 to 0.8 wt% and lead to significant solid solution strengthening of the ferrite matrix with precipitation of NbFe 2 Laves phase and small amounts of Nb(C,N) and Fe 3 Nb 3 C during aging. Owing to the low C and high Cr contents, the Laves phase can-compared to 9-12Cr steels-exist as stable phase up to much higher temperatures ([ 1000°C depending on composition [750,754]). While the incongruently growing Laves phase was reported to be detrimental for the long-term strength at 700°C [742], its formation along grain boundaries was found to effectively prevent grain growth at higher temperatures, thus preserving the high-temperature strength over a long time period [750,755].…”

Manufacturing and Applications of Stainless Steels

“…The review papers focus on the state of the art and perspectives in repairing and reinforcing historic timber structures by stainless steels [1], on duplex and super-duplex stainless steel microstructures and the evolution of their properties by surface modification processes [2], on the process and properties of reversion-heated austenitic stainless steels [3] and on the 3D printing of stainless steels by the laser powder bed fusion technique [4]. A group of research papers deal with physical metallurgy and advancedcharacterization techniques [5], others with process aspects [6][7][8] or property application items related to stainless steels [9][10][11][12][13][14]. The paper by Fava et al [5] presents and discusses the results of mechanical spectroscopy tests carried out on Cr martensitic steel.…”

“…Peng et al [9] report an experimental data assessment and fatigue design recommendation for stainless steel welded joints. Juuti et al [10] present a new family of ferritic stainless steels for service temperatures up to 1050 • C, utilizing intermetallic phase transformation. Cianetti et al [11] report a novel method for the evaluation of the surface fatigue strength of a stainless steel component.…”

Caracterização da ductilidade em fluência dos aços inoxidáveis AISI 321 e AISI 441 pela metodologia Sag Test

“…Em automóveis com motorização não turbinada à gasolina, os componentes do escapamento, como coletores e catalizadores, podem atingir temperaturas de trabalho de até 900 °C. No entanto, com a introdução do sistema turbo, uma consequência imediata é o aumento da temperatura de trabalho desses componentes, podendo a chegar até 1050 °C [2][3][4][5].…”