scholarly journals Quantitative metallographic method for determining delta ferrite content in austenitic stainless steels. Final report

1986 ◽  
Author(s):  
G. Pressly
Keyword(s):  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Ferrite Content ◽  
Final Report ◽  
Delta Ferrite ◽  
Metallographic Method

Fracture Toughness and Deformation Behavior of Cast Austenitic Stainless Steels After Thermal Aging

2017 ◽  
Author(s):  
Yiren Chen ◽  
Wei-Ying Chen ◽  
Chi Xu ◽  
Xuan Zhang ◽  
Zhangbo Li ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Stainless Steels ◽  
Thermal Aging ◽  
Cooling System ◽  
Austenitic Stainless Steels ◽  
Ferrite Content ◽  
Delta Ferrite ◽  
Light Water ◽  
Water Reactors ◽  
The Impact

Cast austenitic stainless steels (CASSs) are used in the cooling system of light water reactors (LWRs) for components with complex shapes, such as pump casings, valve bodies, coolant piping, etc. The CF grades of CASS alloys are the cast equivalents of 300-series stainless steels (SSs) and show excellent mechanical properties and corrosion resistance. In contrast to the fully austenitic microstructure of wrought SSs, CASS alloys consist of a dual-phase microstructure of delta ferrite and austenite and are vulnerable to thermal aging embrittlement. The service performance of CASS alloys is of concern after long-term exposure to high-temperature coolant. In this work, we studied the effects of thermal aging and ferrite content on the fracture resistance of CASS alloys. Crack growth rate and fracture toughness J–R curve tests were performed on aged and unaged CASS alloys in simulated light water reactor environments. The impact of thermal aging on the cracking susceptibility was investigated and the effect of ferrite content was evaluated. Significant embrittlement was observed in the CASS alloys after aging at 400°C. To understand the embrittlement mechanism, microstructural characterizations were performed with transmission electron microscope. The thermal aging produced G-phase precipitates and phase separation in the ferrite, but did not affect the microstructure of austenite. Consequently, the ferrite was hardened considerably after thermal aging while the hardness of austenite phase remained unchanged. The difference in hardness created a high incompatible strain at the interface between ferrite and austenite, leading to fracture at phase boundaries.

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.

Effects of Primary Water Environment on the Thermal Aged Cast Austenitic Stainless Steels

2015 ◽  
Author(s):  
Yuichi Fukuta ◽  
Hiroshi Kanasaki ◽  
Takahisa Yamane
Keyword(s):  
Fracture Toughness ◽  
Stainless Steels ◽  
Water Environment ◽  
Prediction Method ◽  
Austenitic Stainless Steels ◽  
Charpy Impact ◽  
Tensile Tests ◽  
Ferrite Content ◽  
Pressurized Water ◽  
Primary Water

This report summarizes the results of a scoping fracture toughness tests at high and low temperature for thermally aged cast austenitic stainless steels (CASSs) in a pressurized water reactor (PWR) environment. CF8M (ferrite content = 10.1%, 18.9%) and CF8 (ferrite content = 10.5%) were thermally aged up to 5,000 hours at 465°C. Tensile tests, Charpy impact tests and fracture toughness tests were conducted in air at 325°C and 50°C. Fracture toughness tests were also performed in simulated PWR primary water. Although the effect of 325°C and 50°C in simulated PWR primary water and dissolved hydrogen on the fracture toughness (JIc and J-Δa relationship) were slightly observed, fracture toughness was greater than that predicted by the thermally aged fracture toughness prediction method (Hyperbolic-Time-Temperature-Toughness (H3T) model).

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

Stainless Steel Processing to Meet Advanced Applications

2013 ◽  
Vol 794 ◽  
pp. 135-158 ◽  
Author(s):  
G. Balachandran ◽  
V. Balasubramanian
Keyword(s):  
Grain Size ◽  
Stainless Steel ◽  
Stainless Steels ◽  
Size Control ◽  
High Technology ◽  
Alloy Design ◽  
Ferrite Content ◽  
Delta Ferrite ◽  
Grain Size Control ◽  
Advanced Applications

Stainless steel bar and wire products that cater to the high technology application in defence, nuclear, aerospace, oil field and chemical engineering is an area poised for rapid growth in India. The advancing capabilities of alloy steel plants in India have enabled mastering of techniques to make a wide variety of stainless steels. However, there are increasing challenges to meet the advanced property requirements, which call for a basic understanding on the structure property relationship that are influenced by appropriate alloy design and down-stream processing. The special steel industry cater to a wide variety of stainless steels namely ferritic, martensitic, austenitic and precipitation hardenable categories for meeting requirements of high technology. One of the process for making the primary stainless steels is Vacuum Oxygen Decarburisation process. For advanced applications, the primary melted steel is again secondary refined using electroslagremelting for the management of solidification structures and control of inclusions. In the austenitic grades, the hot forged and hot rolled heat treated steels, careful choice of chemistry controls the delta ferrite content and ensures uniformity of the grain size in the product during deformation processing and heat treatment. In the martensitic stainless steel grades, focus is given to delta ferrite, grain size control and appropriate tempering treatment. In the precipitation hardenable steels grades the aging reactions and hot deformation range have to be optimised for deriving specified mechanical properties. Special grades are produced using non ESR and ESR routes to meet high temperature applications such as turbine blades and bolting. In these grades control of delta ferrite content, carbides, carbo-nitrides in the matrix has a deep influence on the mechanical and sub zero fracture properties. In the ferritic stainless steel grade grain size control is critical. The presentation would bring forth the correlation between the alloy design, processing and properties that were achieved in the products mentioned above to meet some of the challenging requirements.

Microstructural and Property Changes During Short-Term Ageing of Cast Austenitic Stainless Steels

1983 ◽  
Vol 21 ◽  
Author(s):  
M. Hodgkinson ◽  
T.A. Towers
Keyword(s):  
Impact Energy ◽  
Structural Changes ◽  
Fine Particles ◽  
Ageing Time ◽  
Austenitic Stainless Steels ◽  
Ferrite Content ◽  
Delta Ferrite ◽  
Microstructural Investigation ◽  
Property Changes ◽  
The Impact

ABSTRACTThe Charpy ν-notch impact properties at -196°C of casts of Type 316 austenitic stainless steel have been compared, after ageing at 650°C for time periods up to 90 minutes. The impact energy of all steels depends on ageing time; the degree of response to ageing depends on original delta ferrite content, which varied from −0.5% to 5.0% in the steels studied. For steels with delta ferrite content in the lower half of this range the impact energy, during ageing, initially decreases to a minimum, subsequently rises to a maximum and finally decreases. Steels with delta ferrite contents near 5% suffer a continuous decrease in impact energy as ageing time increases.Microstructural investigation reveals, during early stages of ageing, the rapid formation of sigma phase, at the ferrite-austenite interphase boundaries. Some delta concurrently transforms to new austenite. Microfractographs indicate a change in the nature of the fracture as ageing progresses. Initially, fractures have large dimples, but as ageing progresses, a finer dimpling appears and extends in area. These dimples contain fine particles, identified mainly as MnS. The variations in impact behaviour are explained on the basis of the structural changes observed.

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.

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