Carbide precipitation and chromium depletion on coherent twin boundaries in deformed 304 stainless steels

1992 ◽  
Vol 50 (2) ◽  
pp. 1216-1217
Author(s):  
A.H. Advani ◽  
L.E. Murr ◽  
D.J. Matlock ◽  
W.W. Fisher ◽  
P.M. Tarin ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Stainless Steels ◽  
Interfacial Free Energy ◽  
Carbide Precipitation ◽  
Twin Boundaries ◽  
Invariant Structure ◽  
Heat Treated ◽  
Constant Structure ◽  
Cr Depletion

Coherent annealing-twin boundaries are constant structure and energy interfaces with an average interfacial free energy of ∼19mJ/m2 versus ∼210 and ∼835mJ/m2 for incoherent twins and “regular” grain boundaries respectively in 304 stainless steels (SS). Due to their low energy, coherent twins form carbides about a factor of 100 slower than grain boundaries, and limited work has also shown differences in Cr-depletion (sensitization) between twin versus grain boundaries. Plastic deformation, may, however, alter the kinetics and thermodynamics of twin-sensitization which is not well understood. The objective of this work was to understand the mechanisms of carbide precipitation and Cr-depletion on coherent twin boundaries in deformed SS. The research is directed toward using this invariant structure and energy interface to understand and model the role of interfacial characteristics on deformation-induced sensitization in SS. Carbides and Cr-depletion were examined on a 20%-strain, 0.051%C-304SS, heat treated to 625°C-4.5h, as described elsewhere.

Some comparative observations of carbide precipitation morphology related to coherent twin boundaries and high-energy grain boundaries in stainless steels

1993 ◽  
Vol 51 ◽  
pp. 1166-1167
Author(s):  
R. J. Romero ◽  
E. A. Trillo ◽  
A. H. Advani ◽  
L. E. Murr ◽  
W. W. Fisher
Keyword(s):  
Grain Boundaries ◽  
Stainless Steels ◽  
High Energy ◽  
Carbide Precipitation ◽  
304 Stainless Steel ◽  
Twin Boundaries ◽  
Transmission Electron ◽  
Wide Range ◽  
Annealing Twins ◽  
Precipitation Morphology

Stickler and Vinckier showed more than three decades ago that there is a very consistent relationship between the boundaries upon which carbides (M23 C6) precipitate in 300 series stainless steels (having carbon contents ranging from 0.02 to 0.08 wt%). For example, carbides first appear on regular (high-energy) grain boundaries, then non-coherent boundaries and steps on annealing twins, and finally on coherent twin boundaries at a constant temperature above about 600° C, and at aging times which, correspondingly, change by orders of magnitude (1,10, 100 hrs. respectively at 675°C for 304 stainless steel). We have examined a wide range of precipitation features on these various boundaries in 316 and 304 stainless steels which have not been described previously because there have been limited observations comparing carbide morphologies in the transmission electron microscope (TEM) for high-energy grain boundaries (γgb ∼ 800 mJ/m2), non-coherent steps on twin boundaries (γTB ∼ 200 mJ/m2), and coherent twin boundaries (γtb ∼ 20 mJ/m2) for 316 and 304 stainless steels.

Strain-induced martensite effects on transgranular carbide precipitation in type 304 stainless steels

1991 ◽  
Vol 49 ◽  
pp. 604-605
Author(s):  
A.H. Advani ◽  
L.E. Murr ◽  
D. Matlock
Keyword(s):  
Heat Treatment ◽  
Grain Boundary ◽  
Stress Corrosion Cracking ◽  
Stainless Steels ◽  
Deformation Twin ◽  
Austenitic Stainless Steels ◽  
Carbide Precipitation ◽  
Strain Induced Martensite ◽  
Type 304

Thermomechanically induced strain is a key variable producing accelerated carbide precipitation, sensitization and stress corrosion cracking in austenitic stainless steels (SS). Recent work has indicated that higher levels of strain (above 20%) also produce transgranular (TG) carbide precipitation and corrosion simultaneous with the grain boundary phenomenon in 316 SS. Transgranular precipitates were noted to form primarily on deformation twin-fault planes and their intersections in 316 SS.Briant has indicated that TG precipitation in 316 SS is significantly different from 304 SS due to the formation of strain-induced martensite on 304 SS, though an understanding of the role of martensite on the process has not been developed. This study is concerned with evaluating the effects of strain and strain-induced martensite on TG carbide precipitation in 304 SS. The study was performed on samples of a 0.051%C-304 SS deformed to 33% followed by heat treatment at 670°C for 1 h.

Deformation effects on transgranular carbide precipitation in 304 stainless steels

1992 ◽  
Vol 50 (1) ◽  
pp. 260-261
Author(s):  
A.H. Advani ◽  
L.E. Murr ◽  
D.J. Matlock ◽  
W.W. Fisher ◽  
P.M. Tarin ◽  
...  
Keyword(s):  
Stainless Steels ◽  
True Strain ◽  
Carbide Precipitation ◽  
Material Research ◽  
Chromium Depletion ◽  
Engineering Strain ◽  
Twin Fault ◽  
Heat Treated ◽  
Strain Induced Martensite ◽  
The Relationship

Plastic deformation is a key variable producing accelerated intergranular (IG) carbide precipitation and chromium-depletion (sensitization) development in stainless steels. Deformation above 20% also produces transgranular (TG) carbides and depletion in the material. Research on TG carbides in SS is, however, limited and has indicated that the precipitation is site-specific preferring twin-fault intersections in 316 SS versus deformation-induced martensite and martensite lath-boundaries in 304 SS. Evidences indicating the relation between martensite and carbides were, however, sketchy.The objective of this work was to fundamentally understand the relationship between TG carbides and strain-induced martensite in 304 SS. Since strain-induced martensite forms at twin-fault intersections in 304 SS and the crystallography of the transformation is well understood, we believed that it could be key in understanding mechanisms of carbides and sensitization in SS. A 0.051% C, 304 SS deformed to ∽33% engineering strain (40% true strain) and heat treated at 670°C/ 0.1-10h was used for the research. The study was carried out on a Hitachi H-8000 STEM at 200 kV.

Structural Integrity of a Standpipe Component in a Petrochemical Catalytic Cracking Unit: Part 1—Assessment of Creep Rupture Properties

2000 ◽  
Vol 122 (3) ◽  
pp. 264-268
Author(s):  
Levi de O. Bueno ◽  
Luiz Marino ◽  
Flavio A. S. Serra ◽  
Fernando T. Gazini
Keyword(s):  
Thermal Treatment ◽  
Grain Boundaries ◽  
Creep Behavior ◽  
Catalytic Cracking ◽  
Structural Integrity ◽  
Carbide Precipitation ◽  
Remaining Life ◽  
Heat Treated ◽  
Rupture Properties ◽  
Relevant Section

During a shutdown for general maintenance of a catalytic cracking unit, intergranular cracks were observed to occur during welding of the regenerator’s standpipe component manufactured from 2 1/4 Cr-1Mo steel. The cracking was observed to be related to intensive carbide precipitation in grain boundaries. To overcome the problem it was decided to heat-treat the relevant section of the component to dissolve these carbides and make possible its welding to a new virgin section of the tube. Samples of the material in its various conditions (virgin, ex-service, heat-treated and welded) were taken to check the efficiency of the thermal treatment in reducing the embrittlement effects and to carry out a general assessment of the remaining life of the component related to creep behavior considering smooth bar creep specimens. [S0094-4289(00)00403-5]

Twin boundaries in GaAs grown on Ge

1987 ◽  
Vol 45 ◽  
pp. 338-339
Author(s):  
N.-H. Cho
Keyword(s):  
Grain Boundaries ◽  
Growth Surface ◽  
Polycrystalline Materials ◽  
High Electron ◽  
Face Centered Cubic ◽  
Twin Boundaries ◽  
Direct Band ◽  
Dynamical Coupling ◽  
Face Centered

Interest in the structure of grain boundaries in semiconductors has been increasing for many reasons including the important role of boundaries on the electrical behavior of polycrystalline materials. GaAs is of interest because of its particular electrical properties such as its direct band gap and high electron mobility. Specific bicrystals of GaAs were produced on substrates cut from Czochralski-grown germanium bicrystals in a low-pressure organometallic vapor- phase epitaxy system. When the growth surface was parallel to the (110) plane, many microtwins were produced in the GaAs epilayer. The structure of twin boundaries in GaAs can take two forms depending on the relative polarities of the two adjoining grains because GaAs has a sphalerite structure which is a face-centered cubic lattice with a two atom basis. The polarity of the two grains meeting at the grain boundaries can be determined by using the dynamical coupling effects of high-order Laue-zone reflections on the (200) and (200) diffracted beams.

Influences of Twin Boundaries on Microstructural Characteristics of ZnO Varistors Simulated by Voronoi Network

2008 ◽  
Vol 368-372 ◽  
pp. 490-492 ◽  
Author(s):  
Jin Liang He ◽  
Jun Hu ◽  
Feng Chao Luo
Keyword(s):  
Standard Deviation ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Relative Standard Deviation ◽  
Potential Role ◽  
Twin Boundaries ◽  
Relative Standard ◽  
Zno Varistors ◽  
Different Content

The presence of twins in ZnO varistors raises interesting questions concerning the potential role of those electrically distinctive twin boundaries in the characteristics of ZnO varistors. The paper uses Voronoi networks to simulate the microstructures of ZnO varistors. The relation between the relative standard deviation of grain size and the ratio of twin number to grain number is obtained. It indicates that the relative standard deviation decreases with the increasing of the twin ratio. On the other hand, ZnO varistor samples with different content of Al2O3 additive were prepared to gain different twin ratios. The simulation has the same conclusion as that obtained from experiments. The probable mechanism of ZnO grain growth inhibition by twins is that the twins increase the mobility viscosity of ZnO grains and grain boundaries, and drag ZnO grains and liquid grain boundaries during the sintering course, then the grain growth is inhibited, and the microstructure becomes more uniform.

Structural Integrity of a Standpipe Component in a Petrochemical Catalytic Cracking Unit: Part 2—Assessment of Embrittlement Effects

2000 ◽  
Vol 122 (3) ◽  
pp. 269-272
Author(s):  
Levi de O. Bueno ◽  
Luiz Marino ◽  
Flavio A. S. Serra ◽  
Fernando T. Gazini
Keyword(s):  
Thermal Treatment ◽  
Grain Boundaries ◽  
Creep Behavior ◽  
Catalytic Cracking ◽  
Structural Integrity ◽  
Carbide Precipitation ◽  
Remaining Life ◽  
Heat Treat ◽  
Heat Treated ◽  
Relevant Section

During a shutdown for general maintenance of a catalytic cracking unit, intergranular cracks were observed to occur during welding of the regenerator’s standpipe component manufactured from 2 1/4 Cr-1Mo steel. The cracking was observed to be related to intensive carbide precipitation in grain boundaries. To overcome the problem it was decided to heat-treat the relevant section of the component to dissolve these carbides and make possible its welding to a new virgin section of the tube. Samples of the material in its various conditions (virgin, ex-service, heat-treated, and welded) were taken to check the efficiency of the thermal treatment in reducing the embattlement effects and to carry out a general assessment of the remaining life of the component related to creep behavior considering notched bar creep specimens. [S0094-4289(00)00503-X]

Mechanisms of transgranular carbide precipitation in deformed 304 stainless steels

1993 ◽  
Vol 51 ◽  
pp. 1168-1169
Author(s):  
A. H. Advani ◽  
L.E. Murr ◽  
W.W. Fisher
Keyword(s):  
Recent Work ◽  
Stainless Steels ◽  
High Strain ◽  
Lath Martensite ◽  
Austenitic Stainless Steels ◽  
Carbide Precipitation ◽  
Carbide Formation ◽  
Lattice Image ◽  
Site Specific ◽  
Heat Treated

Transgranular (TG) carbides form in thermomechanically processed austenitic stainless steels (SS) when the material is plastically deformed to high strain levels, typically above 20%, and for heat treatments that lie within the 500-850°C sensitization range of the SS. In recent work, we have shown that the TG carbide precipitation is site-specific, and favors deformation-induced sites created during the straining process. Specifically, twin-faults and their intersections, and dislocation intersections have been indicated to be preferred sites forTG carbide formation in 304 and316 SS, while clustered regions containing a mix of fine-austenite and lath martensite were also observed to be critical sites for the TG precipitation in 304 SS. In this paper, we present lattice image observations of carbide precipitates in the TG fme-austenite/lath martensite regions of 40% deformed, 670°C/0.1-10h heat treated, 0.051%C 304 SS, as a means to understand the mechanisms of TG carbide precipitation in the SS.

EM study of carbon content effects on carbide precipitation and chromium depletion in type 304 stainless steels

1993 ◽  
Vol 51 ◽  
pp. 1164-1165
Author(s):  
E.A. Trillo ◽  
A.H. Advani ◽  
L.E. Murr ◽  
W.W. Fisher
Keyword(s):  
Carbon Content ◽  
Stainless Steels ◽  
Test Methods ◽  
Carbide Precipitation ◽  
Valuable Insight ◽  
Chromium Depletion ◽  
Electrochemical Test ◽  
Heat Treated ◽  
Precipitation Characteristics ◽  
Type 304

Carbon content is the most critical compositional variable in carbide precipitation and sensitization development in stainless steels (SS). Quantitative electrochemical test methods have conclusively demonstrated that an increase in carbon content enhances the susceptibility of SS to sensitization development. The increase in sensitization has been considered to be caused by the influence of carbon on the thermodynamics of the precipitation-depletion process. This has been supported by limited TEM work. In this research, we are using electron microscopy to quantify the effects of carbon content on carbide precipitation and chromium-depletion development in SS. Initial observations that compare precipitation characteristics and depletion profiles in 0.011% C, 0.025% C, 0.051% C, and 0.07% C-containing, 304 SS heat treated at 775°C for 0.1-500 h are presented in this paper, and will be enhanced by a statistical analysis of carbon content effects on precipitate sizes, densities, and depletion profiles, to provide a valuable insight into the precipitation-depletion phenomena.

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