Precipitation during long time ageing in the austenitic stainless steel 310

A 20%Cr-25%Ni-1.5%Mo-Nb-N austenitic stainless steel tube, NF709, has been developed for boiler tube applications. The calculated maximum allowable stress values for NF709 is much higher than those for other austenitic stainless steel tubes. NF709 test tubes were exposed for 75,075 hours in Eddystone Unit No.1 boiler with a steam temperature of 615°C at the superheater outlet. The removed tubes were investigated metallurgically and mechanically. No severe corrosion was observed on the outer surface. No exfoliation of the outer layer of the steam oxidation scale was observed. One percent of Mo was in solid-solution state even after long-time exposure, which is useful for improving the creep strength. Cr23C6, Nb(C,N), NbCrN and TiN were the main precipitates and the σ(Sigma) phase was slightly detected only in the flame side. Charpy impact values at 20°C of NF709 tubes after exposure was over 40 J/cm2, acceptable for boiler tube use. The time to rupture for the exposed NF709 tubes became closer to that for unexposed ones at lower stresses. The above results indicate that NF709 is a promising material for superheaters and reheaters of power plants with advanced steam conditions.

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On Embrittlement of Stabilized Austenitic Stainless Steel after Long Time Service at Elevated Temperature

Journal of The Japan Petroleum Institute ◽

10.1627/jpi1958.16.130 ◽

1973 ◽

Vol 16 (2) ◽

pp. 130-137

Author(s):

Takeharu Watanabe ◽

Tamotsu Saita

Keyword(s):

Stainless Steel ◽

Elevated Temperature ◽

Austenitic Stainless Steel ◽

Time Service ◽

Long Time

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The Effects of Long-Term Operation and High Temperature on Material Properties of Austenitic Stainless Steel Type 321H

Al-Khwarizmi Engineering Journal ◽

10.22153/kej.2017.11.005 ◽

2017 ◽

Vol 13 (2) ◽

Author(s):

Ahmed Naif Al-Khazraji ◽

Samir Ali Amin ◽

Husam Ahmed Al-Warmizyari

Keyword(s):

Mechanical Properties ◽

Tensile Strength ◽

Stainless Steel ◽

High Temperature ◽

Austenitic Stainless Steel ◽

Yield Strength ◽

Mechanical Testing ◽

Tube Material ◽

Absorbed Energy ◽

Long Time

Changes in mechanical properties of material as a result of service in different conditions can be provided by mechanical testing to assist the estimation of current internal situation of these materials, or the degree of deterioration may exist in furnaces serviced at high temperature and exceed their design life. Because of the rarity works on austenitic stainless steel material type AISI 321H, in this work, ultimate tensile strength, yield strength, elongation, hardness, and absorbed energy by impact are evaluated based on experimental data obtained from mechanical testing. Samples of tubes are extracted from furnace belong to hydrotreaterunit, also samples from un-used tube material are used to make comparisons between these properties. Tensile properties of stainless steel (AISI 321H) were decreased as temperature increases; the trend of properties decreasing for the samples of un-used tube material is the same for the ex-used material. The trend of stress-strain curve will not change due to elevated temperature exposure for long time of service, except the yield strength will be higher in this diagram. The yield strength increased under these conditions, but the ability of material which is elongated will decrease. Hardness and absorbed energy increased by 11.28 and 14% respectively when the material is aged for long time under effect of high temperature accompanied with creep effect. Keywords: Hardness, Impact, Mechanical Properties, Stainless Steel 321H, Mechanical Properties, Tensile Strength, Tube Furnace.

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Some aspects of the defect structure in an austenitic stainless steel

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108714 ◽

1978 ◽

Vol 36 (1) ◽

pp. 314-315

Author(s):

R. Gonzalez ◽

L. Bru

Keyword(s):

Stainless Steel ◽

Austenitic Stainless Steel ◽

Cellular Structures ◽

Total Strain Amplitude ◽

Total Deformation ◽

Density Of Dislocations ◽

Planar Arrays ◽

Stacking Fault Tetrahedra ◽

Distribution Of Dislocations ◽

Very High

The analysis of stacking fault tetrahedra (SFT) in fatigued metals (1,2) is somewhat complicated, due partly to their relatively low density, but principally to the presence of a very high density of dislocations which hides them. In order to overcome this second difficulty, we have used in this work an austenitic stainless steel that deforms in a planar mode and, as expected, examination of the substructure revealed planar arrays of dislocation dipoles rather than the cellular structures which appear both in single and polycrystals of cyclically deformed copper and silver. This more uniform distribution of dislocations allows a better identification of the SFT.The samples were fatigue deformed at the constant total strain amplitude Δε = 0.025 for 5 cycles at three temperatures: 85, 293 and 773 K. One of the samples was tensile strained with a total deformation of 3.5%.

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A TEM microscopical investigation of the magnetic domain structure of a metastable austenitic stainless steel

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100171213 ◽

1994 ◽

Vol 52 ◽

pp. 696-697

Author(s):

G. Fourlaris ◽

T. Gladman

Keyword(s):

Tensile Strength ◽

Stainless Steel ◽

Austenitic Stainless Steel ◽

Cold Rolling ◽

Solution Treatment ◽

Magnetic Domain ◽

High Strength ◽

Medium Carbon Steel ◽

Magnetic Characteristics ◽

Metastable Austenitic Stainless Steel

Stainless steels have widespread applications due to their good corrosion resistance, but for certain types of large naval constructions, other requirements are imposed such as high strength and toughness , and modified magnetic characteristics.The magnetic characteristics of a 302 type metastable austenitic stainless steel has been assessed after various cold rolling treatments designed to increase strength by strain inducement of martensite. A grade 817M40 low alloy medium carbon steel was used as a reference material.The metastable austenitic stainless steel after solution treatment possesses a fully austenitic microstructure. However its tensile strength , in the solution treated condition , is low.Cold rolling results in the strain induced transformation to α’- martensite in austenitic matrix and enhances the tensile strength. However , α’-martensite is ferromagnetic , and its introduction to an otherwise fully paramagnetic matrix alters the magnetic response of the material. An example of the mixed martensitic-retained austenitic microstructure obtained after the cold rolling experiment is provided in the SEM micrograph of Figure 1.

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