HYDROGEN EFFECTS ON THE FRACTURE TOUGHNESS PROPERTIES OF FORGED STAINLESS STEELS. PDF Download
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Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The effect of hydrogen on the fracture toughness properties of Types 304L, 316L and 21-6-9 forged stainless steels was investigated. Fracture toughness samples were fabricated from forward-extruded forgings. Samples were uniformly saturated with hydrogen after exposure to hydrogen gas at 34 MPa or 69 and 623 K prior to testing. The fracture toughness properties were characterized by measuring the J-R behavior at ambient temperature in air. The results show that the hydrogen-charged steels have fracture toughness values that were about 50-60% of the values measured for the unexposed steels. The reduction in fracture toughness was accompanied by a change in fracture appearance. Both uncharged and hydrogen-charged samples failed by microvoid nucleation and coalescence, but the fracture surfaces of the hydrogen-charged steels had smaller microvoids. Type 316L stainless steel had the highest fracture toughness properties and the greatest resistance to hydrogen degradation.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The effect of hydrogen on the fracture toughness properties of Types 304L, 316L and 21-6-9 forged stainless steels was investigated. Fracture toughness samples were fabricated from forward-extruded forgings. Samples were uniformly saturated with hydrogen after exposure to hydrogen gas at 34 MPa or 69 and 623 K prior to testing. The fracture toughness properties were characterized by measuring the J-R behavior at ambient temperature in air. The results show that the hydrogen-charged steels have fracture toughness values that were about 50-60% of the values measured for the unexposed steels. The reduction in fracture toughness was accompanied by a change in fracture appearance. Both uncharged and hydrogen-charged samples failed by microvoid nucleation and coalescence, but the fracture surfaces of the hydrogen-charged steels had smaller microvoids. Type 316L stainless steel had the highest fracture toughness properties and the greatest resistance to hydrogen degradation.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The deformation and fracture toughness properties of forged stainless steels pre-charged with tritium were compared to the deformation and fracture toughness properties of the same steels heat treated at 773 K or 873 K and precharged with hydrogen. Forged stainless steels pre-charged with tritium exhibit an aging effect: Fracture toughness values decrease with aging time after precharging because of the increase in concentration of helium from tritium decay. This study shows that forged stainless steels given a prior heat treatment and then pre-charged with hydrogen also exhibit an aging effect: Fracture toughness values decrease with increasing time at temperature. A microstructural analysis showed that the fracture toughness reduction in the heat-treated steels was due to patches of recrystallized grains that form within the forged matrix during the heat treatment. The combination of hydrogen and the patches of recrystallized grains resulted in more deformation twinning. Heavy deformation twinning on multiple slip planes was typical for the hydrogen-charged samples; whereas, in the non-charged samples, less twinning was observed and was generally limited to one slip plane. Similar effects occur in tritium pre-charged steels, but the deformation twinning is brought on by the hardening associated with decay helium bubbles in the microstructure.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Forged stainless steels are used as the materials of construction for tritium reservoirs. During service, tritium diffuses into the reservoir walls and radioactively decays to helium-3. Tritium and decay helium cause a higher propensity for cracking which could lead to a tritium leak or delayed failure of a tritium reservoir. The factors that affect the tendency for crack formation and propagation include: Environment; steel type and microstructure; and, vessel configuration (geometry, pressure, residual stress). Fracture toughness properties are needed for evaluating the long-term effects of tritium on their structural properties. Until now, these effects have been characterized by measuring the effects of tritium on the tensile and fracture toughness properties of specimens fabricated from experimental forgings in the form of forward-extruded cylinders. A key result of those studies is that the long-term cracking resistance of stainless steels in tritium service depends greatly on the interaction between decay helium and the steels' forged microstructure. New experimental research programs are underway and are designed to measure tritium and decay helium effects on the cracking properties of stainless steels using actual tritium reservoir forgings instead of the experimental forgings of past programs. The properties measured should be more representative of actual reservoir properties because the microstructure of the specimens tested will be more like that of the tritium reservoirs. The programs are designed to measure the effects of key forging variables on tritium compatibility and include three stainless steels, multiple yield strengths, and four different forging processes. The effects on fracture toughness of hydrogen and crack orientation were measured for type 316L forgings. In addition, hydrogen effects on toughness were measured for Type 304L block forgings having two different yield strengths. Finally, fracture toughness properties of type 304L stainless steel were measured for four different forging strain rates which and two forging temperatures. Tritium exposures have been and are being conducted on companion specimens for property measurements in the upcoming years.
Author: Publisher: ISBN: Category : Languages : en Pages : 28
Book Description
High-energy-rate-forged (HERF) austenitic stainless steels are used for the containment of hydrogen and its isotopes. Embrittlement of these materials by hydrogen has been a source of concern for some time. The nature and the degree of embrittlement by hydrogen varies considerably and, among other factors, is a complicated function of material composition and processing variations. Helium, the radioactive decay product of tritium, will also embrittle stainless steels. Precipitation of microscopic helium bubbles tends to increase the material's flow stress, through dislocation pinning, as well as weaken interfaces like grain and twin boundaries. Since fracture toughness tends to decrease with increasing yield strength, at least part of the helium-embrittlement problem may be due to strength effects. The relationship between a material's yield strength and toughness and, the incremental strength increase and corresponding toughness decrease imparted by helium is not known. The purpose of this study was to measure the combined effects of strength, hydrogen isotopes, and helium on the room temperature mechanical and fracture toughness properties of HERF 21-6-9 stainless steel.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
The fracture toughness properties of Type 21-6-9 stainless steel were measured for forgings in the unexposed, hydrogen-exposed, and tritium-exposed-and-aged conditions. Fracture toughness samples were cut from conventionally-forged and high-energy-rate-forged forward-extruded cylinders and mechanically tested at room temperature using ASTM fracture-toughness testing procedures. Some of the samples were exposed to either hydrogen or tritium gas (340 MPa, 623 K) prior to testing. Tritium-exposed samples were aged for up to seven years and tested periodically in order to measure the effect on fracture toughness of 3He from radioactive tritium decay. The results show that hydrogen-exposed and tritium-exposed samples had lower fracture- toughness values than unexposed samples and that fracture toughness decreased with increasing decay 3He content. Forged steels were more resistant to the embrittling effects of tritium and decay 3He than annealed steels, although their fracture-toughness properties depended on the degree of sensitization that occurred during processing. The fracture process was dominated by microvoid nucleation, growth and coalescence; however, the size and spacing of microvoids on the fracture surfaces were affected by hydrogen and tritium with the lowest-toughness samples having the smallest microvoids and finest spacing.
Author: Ellis E. Fletcher Publisher: ISBN: Category : Steel Languages : en Pages : 82
Book Description
This report deals with the deleterious effects of hydrogen gas on steel at elevated temperatures and/or pressures. Hydrogen attack on steels is manifest as decarburization, intergranular fissuring, or blistering. These conditions result in lowered tensile strength, ductility, and impact strength. The reaction of hydrogen with iron carbide to form methane is probably the most important chemical reaction involved in the attack on steel by hydrogen. Attack of steel at elevated temperatures and pressures is limited or prevented by the following measures: (1) use of steel alloyed with strong carbide-forming elements, (2) use of liners of resistant alloy steels, and (3) substitution of resistant nonferrous alloys.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
This study reports on the effects of hydrogen isotopes, crack orientation, and specimen geometry on the fracture toughness of stainless steels. Fracture toughness variability was investigated for Type 21-6-9 stainless steel using the 7K0004 forging. Fracture toughness specimens were cut from the forging in two different geometric configurations: arc shape and disc shape. The fracture toughness properties were measured at ambient temperature before and after exposure to hydrogen gas and compared to prior studies. There are three main conclusions that can be drawn from the results. First, the fracture toughness properties of actual reservoir forgings and contemporary heats of steel are much higher than those measured in earlier studies that used heats of steel from the 1980s and 1990s and forward extruded forgings which were designed to simulate reservoir microstructures. This is true for as-forged heats as well as forged heats exposed to hydrogen gas. Secondly, the study confirms the well-known observation that cracks oriented parallel to the forging grain flow will propagate easier than those oriented perpendicular to the grain flow. However, what was not known, but is shown here, is that this effect is more pronounced, particularly after hydrogen exposures, when the forging is given a larger upset. In brick forgings, which have a relatively low amount of upset, the fracture toughness variation with specimen orientation is less than 5%; whereas, in cup forgings, the fracture toughness is about 20% lower than that forging to show how specimen geometry affects fracture toughness values. The American Society for Testing Materials (ASTM) specifies minimum specimen section sizes for valid fracture toughness values. However, sub-size specimens have long been used to study tritium effects because of the physical limitation of diffusing hydrogen isotopes into stainless steel at mild temperatures so as to not disturb the underlying forged microstructure. This study shows that fracture toughness values of larger specimens are higher and more representative of the material's fracture behavior in a fully constrained tritium reservoir. The toughness properties measured for sub-size specimens were about 65-75% of the values for larger specimens. While the data from sub-size specimens are conservative, they may be overly so. The fracture toughness properties from sub-size specimens are valuable in that they can be used for tritium effects studies and show the same trends and alloy differences as those seen from larger specimen data. Additional work is planned, including finite element modeling, to see if sub-size specimen data could be adjusted in some way to be more closely aligned with the actual material behavior in a fully constrained pressure vessel.
Author: Anthony W. Thompson Publisher: John Wiley & Sons ISBN: 1118803272 Category : Technology & Engineering Languages : en Pages : 1090
Book Description
Proceedings of the Fifth International Conference on the Effect of Hydrogen on the Behavior of Materials sponsored by the Structural Materials Division (SMD) Mechanical Metallurgy and Corrosion & Environmental Effects Committees of The Minerals, Metals & Materials Society held at Jackson Lake Lodge, Moran, Wyoming, September 11-14, 1994.
Author: G. Wicks Publisher: John Wiley & Sons ISBN: 0470483415 Category : Technology & Engineering Languages : en Pages : 258
Book Description
This volume contains papers presented at the Materials Innovations in an Emerging Hydrogen Economy Conference in Februrary 2008 in Cocoa Beach, Florida. It provides a useful one-stop resource for understanding the most important issues in the research and applications of materials innovations. The text features logically organized and carefully selected articles, organized into: International Overviews; Hydrogen Storage; Hydrogen Production; Hydrogen Delivery; and Leakage Detection/Safety. This comprises an essential resource for industrial and academic chemists and engineers.
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Author: Ellis E. Fletcher
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Author: Anthony W. Thompson
Author: G. Wicks