Microstructural and microchemical aspects of the solid-state decomposition of delta ferrite in austenitic stainless steels

1985 ◽  
Vol 16 (8) ◽  
pp. 1363-1369 ◽  
Author(s):  
J. Singh ◽  
G. R. Purdy ◽  
G. C. Weatherly
Keyword(s):  
Solid State ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Delta Ferrite ◽  
Solid State Decomposition

scholarly journals Fracture Resistance of Cast Austenitic Stainless Steels

2016 ◽  
Author(s):  
Y. Chen ◽  
W-Y. Chen ◽  
A. S. Rao ◽  
Z. Li ◽  
Y. Yang ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Growth Rate ◽  
Corrosion Resistance ◽  
Neutron Irradiation ◽  
Stainless Steels ◽  
Thermal Aging ◽  
Austenitic Stainless Steels ◽  
Light Water Reactor ◽  
Delta Ferrite ◽  
Light Water

Cast austenitic stainless steels (CASS) possess excellent corrosion resistance and mechanical properties and are used alongside with wrought stainless steels (SS) in light water reactors for primary pressure boundaries and reactor core internal components. In contrast to the fully austenitic microstructure of wrought SS, CASS alloys consist of a dual-phase microstructure of delta ferrite and austenite. The delta ferrite is critical for the service performance since it improves the strength, weldability, corrosion resistance, and soundness of CASS alloys. On the other hand, the delta ferrite is also vulnerable to embrittlement when exposed to reactor service temperatures and fast neutron irradiations. In this study, the combined effect of thermal aging and neutron irradiation on the degradation of CASS alloys was investigated. Neutron-irradiated CASS specimens with and without prior thermal aging were tested in simulated light water reactor environments for crack growth rate and fracture toughness. Miniature compact-tension specimens of CF-3 and CF-8 alloys were tested to evaluate the extent of embrittlement resulting from thermal aging and neutron irradiation. The materials used are static casts containing more than 23% delta ferrite. Some specimens were thermally aged at 400 °C for 10,000 hours prior to the neutron irradiation to simulate thermal aging embrittlement. Both the unaged and aged specimens were irradiated at ∼320°C to a low displacement damage dose of 0.08 dpa. Crack growth rate and fracture toughness J-integral resistance curve tests were carried out on the irradiated and unirradiated control samples in simulated light water reactor environments with low corrosion potentials. While no elevated crack propagation rates were detected in the test environments, significant reductions in fracture toughness were observed after either thermal aging or neutron irradiation. The loss of fracture toughness due to neutron irradiation seemed more evident in the samples without prior thermal aging. Transmission electron microscope (TEM) examination was carried out on the thermally aged and neutron irradiated specimens. The result showed that both neutron irradiation and thermal aging can induce significant changes in the delta ferrite. A high density of G-phase precipitates was observed with TEM in the thermally aged specimens, consistent with previous results. Similar precipitate microstructures were also observed in the neutron-irradiated specimens with or without prior thermal aging. A more extensive precipitate microstructure can be seen in the samples subjected to both thermal aging and neutron irradiation. The similar precipitate microstructures resulting from thermal aging and neutron irradiation are consistent with the fracture toughness results, suggesting a common microstructural origin of the observed embrittlement after thermal aging and neutron irradiation.

Effect of strain paths and residual delta ferrite on the failure of cold rolled austenitic stainless steels, type 304L

2013 ◽  
Vol 48 (7) ◽  
pp. 410-419 ◽  
Author(s):  
Ismaila I Ahmed ◽  
Joao Q da Fonseca ◽  
Andrew H Sherry
Keyword(s):  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Delta Ferrite ◽  
Strain Paths ◽  
Cold Rolled

Influence of Process Parameter on Microstructural Characteristics and Tensile Properties of Friction Welded ASS304L Alloy

2015 ◽  
Vol 766-767 ◽  
pp. 745-750 ◽  
Author(s):  
K. Umanath ◽  
K. Palanikumar
Keyword(s):  
Mechanical Properties ◽  
Solid State ◽  
Stainless Steels ◽  
Friction Welding ◽  
Welding Process ◽  
Austenitic Stainless Steels ◽  
Microstructural Characteristics ◽  
Solid State Joining ◽  
Joining Process ◽  
Rotary Type

The rotary type continuous friction welding process is a solid state joining process by mechanically. It produces a joint in the forging pressure contact with rotating and motionless workpiece. The solid state joining process it produces welds with reduced distortion and improved mechanical properties. The austenitic stainless steels are widely used in shipbuilding field, nuclear field and automobile field because of their special mechanical and metallurgical properties. In this work, friction welding of austenitic stainless steel rods of 10mm diameter was investigated with an aim to understand the influence of friction welding process parameters. The details of microstructure analysis using optical microscopy are discussed.

Corrosion Resistance of Molybdenum Modified Cr-Ni-Mn Austenitic Stainless Steels

CORROSION ◽  
1963 ◽  
Vol 19 (6) ◽  
pp. 210t-216t ◽  
Author(s):  
F. NAIR ◽  
M. SEMCHYSHEN
Keyword(s):  
Mechanical Properties ◽  
Corrosion Resistance ◽  
Sulfuric Acid ◽  
Nitric Acid ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Delta Ferrite ◽  
Ferritic Stainless Steels ◽  
Acidic Conditions

Abstract The corrosion resistance of nine Cr-Ni-Mn austenitic and duplex austenitic-ferritic stainless steels, containing up to 5 percent molybdenum, in hot deaerated sulfuric acid and boiling concentrated nitric acid was determined and compared to the behavior of recognized commercial grades. A limited evaluation of mechanical properties was performed. The corrosion resistance of these alloys was affected by molybdenum additions in a manner similar to that observed in Cr-Ni austenitic steels:The ability to tolerate minimal oxidizing environments such as sulfuric acid was markedly improved.The resistance toward strongly oxidizing acidic conditions was reduced. The presence of delta ferrite effected improved resistance in sulfuric acid and materially diminished corrosion resistance in hot nitric acid.

Unraveling the Effect of Thermomechanical Treatment on the Dissolution of Delta Ferrite in Austenitic Stainless Steels

2015 ◽  
Vol 47 (2) ◽  
pp. 641-648 ◽  
Author(s):  
Mohammad Rezayat ◽  
Hamed Mirzadeh ◽  
Masih Namdar ◽  
Mohammad Habibi Parsa
Keyword(s):  
Thermomechanical Treatment ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Delta Ferrite

scholarly journals Microstructure Evolution during Annealing Treatment of Austenitic Stainless Steels

2012 ◽  
Vol 715-716 ◽  
pp. 913-913 ◽  
Author(s):  
Clara Herrera ◽  
Angelo Fernando Padilha ◽  
R.L. Plaut
Keyword(s):  
Grain Size ◽  
Microstructure Evolution ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Thickness Reduction ◽  
Recrystallization Temperature ◽  
Delta Ferrite ◽  
Aisi 304L ◽  
316L Steel ◽  
304L Steel

Austenitic stainless steels of the AISI 304 and 316 grades, amongst over other hundred compositions of stainless steels available in the market, are the most frequently used ones worldwide. They are selected for numerous applications due to their favorable combination of characteristics such as low price, moderate to good corrosion resistance, excellent ductility and toughness along with good weldability. Their major limitation is in the yield strength, which is relatively low (about 200 MPa), in the annealed condition. Through cold working, this value can be easily multiplied by a factor of up to six, however ductility drops. The cold worked sub-structure of the austenitic stainless steels is formed by a planar array of dislocations and strain induced martensites, α (BCC) and ε (HCP). The microstructure evolution of austenitic stainless steels, AISI 304L and 316L, during cold rolling and subsequent annealing was studied (maximum thickness reduction - 90%). Samples were initially solution annealed at 1100°C for one hour with subsequent water quenched. Following, they have been cold rolled at room temperature, with cold reductions varying between 10 and 90%. After rolling, samples with approximately 90% thickness reduction have been submitted to annealing treatments in order to study martensite reversion, recovery and recrystallization. Annealing treatments have been performed between 200 and 900°C, with 100°C interval for one hour. The resulting microstructures were investigated by optical microscopy, scanning electron microscopy (with EBSD), magnetic measurements and hardness evaluation. As received (hot rolled) austenitic stainless steel sheet presented recrystallized equiaxial grains with austenite and islands of delta ferrite, in larger quantities mainly in the centre of the sheet. The solution annealing at 1100°C for one hour eliminated delta ferrite. During rolling, the austenite partially transforms into α martensite. The 50% αmartensite reversion temperature is close to 550°C for both steels. This temperature is practically independent of the amount of αmartensite present in the steel. The 50% recrystallization temperature of the 304L steel is lower than that of the 316L steel, about 700 and 800°C, respectively. The 316L steel shows a higher recrystallization resistance, due to its higher SFE and lower storage deformation energy than the 304L steel. Recrystallization temperature is about 150°C higher that the αmartensite reversion temperature. The percentage of αmartensite has a strong influence on the recrystallized grain size, the higher the percentage of this phase the smaller will be the grain size.

Delta Ferrite Formation in Austenitic Stainless Steel Castings

2012 ◽  
Vol 730-732 ◽  
pp. 733-738 ◽  
Author(s):  
Angelo Fernando Padilha ◽  
Caio Fazzioli Tavares ◽  
Marcelo Aquino Martorano
Keyword(s):  
Stainless Steel ◽  
Chemical Composition ◽  
Cooling Rate ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Magnetic Method ◽  
Empirical Formulas ◽  
Delta Ferrite ◽  
Ferrite Formation ◽  
Steel Castings

The effects of chemical composition and cooling rate on the delta ferrite formation in austenitic stainless steels have been investigated. Ferrite fractions measured by a magnetic method were in the range of 0 to 12% and were compared with those calculated by empirical formulas available in the literature. The delta ferrite formation (amount and distribution) was strongly affected by the steel chemical composition, but less affected by the cooling rate. Among several formulas used to calculate the amount of delta ferrite, the best agreement was obtained with those proposed independently by Schneider and Schoefer, the latter being recommended in the ASTM 800 standard.

Transformation of Delta Ferrite Into Sigma Phase in Metastable Austenitic Stainless Steels After Long-Term High-Temperature Service Exposure

2014 ◽  
Vol 51 (4) ◽  
pp. 259-279 ◽  
Author(s):  
A. Neidel ◽  
B. Fischer ◽  
S. Riesenbeck ◽  
E. Cagliyan
Keyword(s):  
High Temperature ◽  
Stainless Steels ◽  
Sigma Phase ◽  
Austenitic Stainless Steels ◽  
Delta Ferrite ◽  
Service Exposure
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