Alumina-Forming Austenitic Stainless Steels Strengthened by Laves Phase and MC Carbide Precipitates

Yamamoto, Yukinori; Brady, Michael P.; Lu, Z. P.; Liu, Chang; Takeyama, Masao; Maziasz, P.J.; Pint, Bruce A.

doi:10.1007/s11661-007-9319-y

Cited by 154 publications

(78 citation statements)

References 16 publications

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“…Such understanding is needed, because the high-temperature strength of AFA alloys cannot be further improved by nitrogen additions, which are typically used to form M(C, N)-type carbonnitrides (M: Nb, Ti, V)-strengthening precipitates in advanced austenitic stainless steel alloys such as alloy 709, [14][15][16] because of acicular, coarse AlN formation. [17] The AFA alloy compositions of interest are based on Fe- (12)(13)(14)Cr- (2.5-4) [18,19] Copper was added for further stabilizing the austenitic matrix, tungsten was added for solution hardening, and very small amounts of Ti and V (<~0.1 to 0.2 wt pct) were also added to enhance the MC-type carbide formation without the loss of Al 2 O 3 scale formability.…”

Section: Introductionmentioning

confidence: 99%

Effect of Alloying Additions on Phase Equilibria and Creep Resistance of Alumina-Forming Austenitic Stainless Steels

Yamamoto

Santella

Brady

et al. 2009

Metall Mater Trans A

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102

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The high-temperature creep properties of a series of alumina-forming austenitic (AFA) stainless steels based on Fe-20Ni-(12-14)Cr-(2.5-4)Al-(0.2-3.3)Nb-0.1C (weight percent) were studied. Computational thermodynamics were used to aid in the interpretation of data on microstructural stability, phase equilibria, and creep resistance. Phases of MC (M: mainly Nb), M 23 C 6 (M: mainly Cr), B2 [b-(Ni,Fe)Al], and Laves [Fe 2 (Mo,Nb)] were observed after creep-rupture testing at 750°C and 170 MPa; this was generally consistent with the thermodynamic calculations. The creep resistance increased with increasing Nb additions up to 1 wt pct in the 2.5 and 3 Al wt pct alloy series, due to the stabilization of nanoscale MC particles relative to M 23 C 6 . Additions of Nb greater than 1 wt pct decreased creep resistance in the alloy series due to stabilization of the Laves phase and increased amounts of undissolved, coarse MC, which effectively reduced the precipitation of nanoscale MC particles. The additions of Al also increased the creep resistance moderately due to the increase in the volume fraction of B2 phase precipitates. Calculations suggested that optimum creep resistance would be achieved at approximately 1.5 wt pct Nb in the 4 wt pct Al alloy series.

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Section: Introductionmentioning

confidence: 99%

Effect of Alloying Additions on Phase Equilibria and Creep Resistance of Alumina-Forming Austenitic Stainless Steels

Yamamoto

Santella

Brady

et al. 2009

Metall Mater Trans A

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102

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“…Wrought aluminum forming austenitic (AFA) alloys were developed at ORNL in 2006, based on the matrix composition of the HT-UPS steels described earlier [19][20][21] (Table II). The AFA alloys won an R&D 100 Award in 2009.…”

Section: Development Of Aluminum-modified Cf8c-plus Steelmentioning

confidence: 99%

Development of Creep-Resistant and Oxidation-Resistant Austenitic Stainless Steels for High Temperature Applications

Maziasz

2017

JOM

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Austenitic stainless steels are cost-effective materials for high-temperature applications if they have the oxidation and creep resistance to withstand prolonged exposure at such conditions. Since 1990, Oak Ridge National Laboratory (ORNL) has developed advanced austenitic stainless steels with creep resistance comparable to Ni-based superalloy 617 at 800-900°C based on specially designed ''engineered microstructures'' utilizing a microstructure/composition database derived from about 20 years of radiation effect data on steels. The wrought high temperature-ultrafine precipitate strengthened (HT-UPS) steels with outstanding creep resistance at 700-800°C were developed for supercritical boiler and superheater tubing for fossil power plants in the early 1990s, the cast CF8C-Plus steels were developed in 1999-2001 for land-based gas turbine casing and diesel engine exhaust manifold and turbocharger applications at 700-900°C, and, in 2015-2017, new Al-modified cast stainless steels with oxidation and creep resistance capabilities up to 950-1000°C were developed for automotive exhaust manifold and turbocharger applications. This article reviews and summarizes their development and their properties and applications.

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“…Austenitic stainless steels have an FCC crystal structure which allows them to have good high-temperature creep resistance, which can be improved significantly with dispersions of MC carbides (M can be Nb, Ti, or V) [1][2][3][4][5][6][7]. They also have lower cost when compared with Ni-based superalloys.…”

Section: Introductionmentioning

confidence: 99%

“…Alumina is thermodynamically more stable and generally offers the potential for greater protection in many aggressive environments. The main problem with creating an aluminaforming austenitic (AFA) stainless steel is that aluminum is highly bcc stabilizing in iron [1][2][3][4][5][6][7]. These alloys also require significant quantities of chromium to help promote the formation of an alumina scale.…”

Section: Introductionmentioning

confidence: 99%

“…Oak Ridge National Laboratory (ORNL) has developed a class of AFA alloys for use in highly aggressive atmospheres [1][2][3][4][5][6][7]. The baseline alloys were a family of austenitic stainless steels called the high-temperature ultrafine-precipitationstrengthened steel (HTUPS) [15], which have typical compositions of (wt%) Fe14Cr-16Ni-2.5Mo-2Mn with additions of B, C, Nb, P, Ti, and V in order to balance mechanical properties and oxidation resistance as well as form nanoscale precipitates (such as Fe 2 Nb Laves phase, B2-NiAl, c 0 -Ni 3 Al, M 23 C 6 and MC) for strength at high temperatures.…”

Section: Introductionmentioning

confidence: 99%

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The Effects of Water Vapor on the Oxidation Behavior of Alumina Forming Austenitic Stainless Steels

et al. 2015

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The isothermal oxidation behavior of three alumina forming austenitic (AFA) stainless steels with varying composition was studied at 650 and 800°C in dry air and gases which contained water vapor. The AFA alloys exhibited better oxidation resistance than a ''good chromia former'' at 650°C, particularly in H 2 Ocontaining atmospheres by virtue of alumina-scale formation. Although the AFA alloys were more resistant than chromia formers, their oxidation resistance was degraded at 650°C in the presence of water vapor. In dry air the AFA alloys formed, thin continuous alumina scales, whereas in Ar-4%H 2 -3%H 2 O the areas of continuous alumina were reduced and Fe oxide-rich nodules and regions of Cr, Mnrich oxides formed. In some regions internal oxidation of the aluminum occurred in the H 2 O-containing gas. The alloy OC8 had slightly better resistance than OC4 or OC5 in this atmosphere. The alumina-forming capability of the AFA alloys decreases with increasing temperature and, at 800°C, they are borderline alumina formers, even in dry air. The oxidation resistance of all three alloys was degraded at 800°C in atmospheres, which contained water vapor (Air-10%H 2 O, Ar-3%H 2 O and Ar-4%H 2 -3%H 2 O). The areas, which formed continuous alumina, were reduced in these atmospheres and areas of internal oxidation occurred. However, as a result of the borderline alumina-forming capability of the AFA alloys it was not possible to determine which of the H 2 O-containing atmospheres was more severe or to rank the alloys in terms of their performance. The experimental results indicate that the initial microstructure of the AFA alloys also plays a role in their oxidation performance. Less protective oxides formed at 800°C when alloy OC8 was equilibrated before exposure rather than being exposed in the as-processed condition.

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Alumina-Forming Austenitic Stainless Steels Strengthened by Laves Phase and MC Carbide Precipitates

Cited by 154 publications

References 16 publications

Effect of Alloying Additions on Phase Equilibria and Creep Resistance of Alumina-Forming Austenitic Stainless Steels

Effect of Alloying Additions on Phase Equilibria and Creep Resistance of Alumina-Forming Austenitic Stainless Steels

Development of Creep-Resistant and Oxidation-Resistant Austenitic Stainless Steels for High Temperature Applications

The Effects of Water Vapor on the Oxidation Behavior of Alumina Forming Austenitic Stainless Steels

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