scholarly journals A dislocation density-based model for the work hardening and softening behaviors upon stress reversal

2021 ◽  
Vol 21 (2) ◽  
Author(s):  
Paulina Lisiecka-Graca ◽  
Krzysztof Bzowski ◽  
Janusz Majta ◽  
Krzysztof Muszka
Keyword(s):  
Dislocation Density ◽  
Electron Backscatter Diffraction ◽  
Microstructural Analysis ◽  
Back Stress ◽  
Carbon Steels ◽  
Internal Variables ◽  
Low Carbon ◽  
Average Dislocation Density ◽  
Calculation Results ◽  
Mechanical Behaviours

AbstractThe mechanical behaviours of microalloyed and low-carbon steels under strain reversal were modelled based on the average dislocation density taking into account its allocation between the cell walls and cell interiors. The proposed model reflects the effects of the dislocations displacement, generation of new dislocations and their annihilation during the metal-forming processes. The back stress is assumed as one of the internal variables. The value of the initial dislocation density was calculated using two different computational methods, i.e. the first one based on the dislocation density tensor and the second one based on the strain gradient model. The proposed methods of calculating the dislocation density were subjected to a comparative analysis. For the microstructural analysis, the high-resolution electron backscatter diffraction (EBSD) microscopy was utilized. The calculation results were compared with the results of forward/reverse torsion tests. As a result, good effectiveness of the applied computational methodology was demonstrated. Finally, the analysis of dislocation distributions as an effect of the strain path change was performed.

A New Approach Using EBSD to Quantitatively Distinguish Complex Transformation Products Along the HAZ in X80 Linepipe Steel

2014 ◽  
Author(s):  
Jennifer M. Reichert ◽  
Matthias Militzer ◽  
Warren J. Poole ◽  
Laurie Collins
Keyword(s):  
Orientation Relationship ◽  
Transformation Temperature ◽  
Retained Austenite ◽  
Electron Backscatter Diffraction ◽  
High Strength ◽  
Transformation Products ◽  
Carbon Steels ◽  
Low Carbon ◽  
Structure Property ◽  
Linepipe Steel

State-of-the-art linepipe steels are microalloyed low-carbon steels that combine high strength and fracture toughness with good weldability. During welding of pipe sections the heat affected zone (HAZ) experiences rapid thermal cycles resulting in a graded microstructure that can be significantly different from that of the base metal. In particular a variety of bainitic microstructures can form in the HAZ. Depending on the type of bainite mechanical properties may be improved or may lead to poor fracture resistance and be detrimental to the overall HAZ performance. Optical microscopy is not sufficient to differentiate bainitic morphologies which vary with the transformation temperature. The investigated X80 linepipe steel also contains retained austenite at room temperature. Based on the retained austenite it is possible to characterize the orientation relationship (OR) between austenite and the transformation products. It is found that bainite shows an orientation relationship near Kurdjumov-Sachs with the prior austenite. Variant selection is related to the driving force for the bainite reaction and hence depends on the transformation temperature. In the current study Electron BackScatter Diffraction (EBSD) mapping is used to characterize transformation products based on their orientation relationship. This approach offers a quantitative way to determine volume fractions of different types of bainite in complex HAZ microstructures which is necessary to establish structure-property relationships of the HAZ.

scholarly journals Effect of Nb addition and Pre-strain on Hydrogen Embrittlement of Low-carbon Steels with Ferrite-pearlite Structure

2020 ◽  
Vol 58 (11) ◽  
pp. 752-758
Author(s):  
Seok-Woo Ko ◽  
Ji-Min Lee ◽  
Byoungchul Hwang
Keyword(s):  
Hydrogen Embrittlement ◽  
Dislocation Density ◽  
Significant Loss ◽  
Electron Back Scatter Diffraction ◽  
Carbon Steels ◽  
Low Carbon ◽  
Hydrogen Distribution ◽  
Low Carbon Steels ◽  
Reduction Of Area ◽  
Nb Addition

The effect of pre-strain on the hydrogen embrittlement of Nb-free and Nb-added low-carbon steels with ferrite-pearlite structure was investigated in this study. After the steels were electrochemically charged with hydrogen, slow-strain rate tensile (SSRT) tests were conducted on them to examine hydrogen embrittlement behavior. The SSRT test results revealed that the Nb-added steel had a lesser decrease of elongation and reduction of area than the Nb-free steel. The formation of NbC carbide and grain refinement caused by the Nb addition improved resistance to hydrogen embrittlement. The loss of elongation and the reduction of area after hydrogen charging occurs when pre-strain is increased. The pre-strain increases dislocation density and thus increases the amount of reversible hydrogen trap sites associated with hydrogen embrittlement. 10% pre-strained specimens exhibited a significant loss in elongation and reduction of area, regardless of Nb addition. Based on the results of electron back-scatter diffraction, fractographic, and silver decoration analyses for Nb-free and Nb-added steels, the hydrogen embrittlement mechanism in low-carbon steels with different amounts of pre-strain is discussed in terms of dislocation density and hydrogen distribution.

scholarly journals Modeling of Precipitation Hardening during Coiling of Nb–Mo Steels

Metals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 758 ◽  
Author(s):  
Jean-Yves Maetz ◽  
Matthias Militzer ◽  
Yu Chen ◽  
Jer-Ren Yang ◽  
Nam Goo ◽  
...  
Keyword(s):  
Electron Backscatter Diffraction ◽  
Bainitic Ferrite ◽  
High Strength Steels ◽  
High Strength ◽  
Carbon Steels ◽  
Age Hardening ◽  
Precipitation Strengthening ◽  
Low Carbon ◽  
Coiling Temperature ◽  
Hsla Steels

Nb–Mo low-alloyed steels are promising advanced high strength steels (AHSS) because of the highly dislocated bainitic ferrite microstructure conferring an excellent combination of strength and toughness. In this study, the potential of precipitation strengthening during coiling for hot-strip Nb–Mo-bearing low-carbon steels has been investigated using hot-torsion and aging tests to simulate the hot-rolling process including coiling. The obtained microstructures were characterized using electron backscatter diffraction (EBSD), highlighting the effects of Nb and Mo additions on formation and tempering of the bainitic ferrite microstructures. Further, the evolution of nanometer-sized precipitates was quantified with high-resolution transmission electron microscopy (HR-TEM). The resulting age hardening kinetics have been modelled by combining a phenomenological precipitation strengthening model with a tempering model. Analysis of the model suggests a narrower coiling temperature window to maximize the precipitation strengthening potential in bainite/ferrite high strength low-alloyed (HSLA) steels than that for conventional HSLA steels with polygonal ferrite/pearlite microstructures.

Formation of the {111} and {111} Recrystallization Texture in Deep Drawing Low Carbon Steel

2012 ◽  
Vol 535-537 ◽  
pp. 687-691 ◽  
Author(s):  
Xiao Li ◽  
Ping Yang ◽  
Li Meng
Keyword(s):  
Recrystallization Texture ◽  
Electron Backscatter Diffraction ◽  
Early Stage ◽  
Low Carbon Steel ◽  
Carbon Steels ◽  
Low Carbon ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cold Rolled ◽  
Backscatter Diffraction

The formation of 111-112 and 111-110 recrystallization textures during annealing of cold rolled low carbon steels at low heating rate was investigated by electron backscatter diffraction (EBSD) and X-ray diffraction techniques. The orientation characteristics during recrystallization of this steel were determined, results show that there is a strong competition between the 111-112 component and the 111-110 component along the γ-fiber. The former was developed from the deformed matrix with the same orientation by means of subgrain coalescence at early stage of recrystallization, while the latter nucleated at the grain boundary areas of deformed grains with 111-112 or 112-110 orientations by means of preferred nucleation and evolved into stable recrystallization texture at later stage of recrystallization.

Strain Localizations in Ultra Low Carbon Steel

2011 ◽  
Vol 702-703 ◽  
pp. 782-785
Author(s):  
Rajesh Khatirkar ◽  
Karri V. Mani Krishna ◽  
Leo Kestens ◽  
Roumen H. Petrov ◽  
Prita Pant ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Low Carbon Steel ◽  
Carbon Steels ◽  
Low Carbon ◽  
Dislocation Dynamic ◽  
Dynamic Simulations ◽  
Discrete Dislocation ◽  
Resolution Electron ◽  
Different Strains ◽  
Grain Misorientation

Ultra low carbon (ULC) steel samples were deformed in near plane-strain compression mode with different strains, strain rates and temperatures. Different aspects of microstructural developments, for deformed γ (ND//) and θ (ND//) fibre grains, were investigated using X-ray line profiles and high resolution electron diffraction. The study clearly showed increase in grain interior strain localizations and in-grain misorientation at the intermediate deformation temperature. This effect was more apparent in γ-fibre and can best be explained through orientation sensitive recovery. γ-fibre also demonstrated higher potential for increase in dislocation density. This was observed experimentally and simulated through discrete dislocation dynamic simulations. Higher textural softening with stronger increase in dislocation density and possible effects of orientation sensitive recovery appears to define the orientation dependent recovery in low carbon steels.

Lattice Imaging of Twin, Lath and α/Martensite Boundaries in Duplex Low Carbon Steels

1977 ◽  
Vol 35 ◽  
pp. 118-119
Author(s):  
J. Y. Koo ◽  
G. Thomas
Keyword(s):  
High Resolution Electron Microscopy ◽  
Ferrite Matrix ◽  
Carbon Steels ◽  
Bright Field Image ◽  
Low Carbon ◽  
Lattice Imaging ◽  
Bright Field ◽  
Lattice Image ◽  
New Information ◽  
Resolution Electron

High resolution electron microscopy has been shown to give new information on defects(1) and phase transformations in solids (2,3). In a continuing program of lattice fringe imaging of alloys, we have applied this technique to the martensitic transformation in steels in order to characterize the atomic environments near twin, lath and αmartensite boundaries. This paper describes current progress in this program.Figures A and B show lattice image and conventional bright field image of the same area of a duplex Fe/2Si/0.1C steel described elsewhere(4). The microstructure consists of internally twinned martensite (M) embedded in a ferrite matrix (F). Use of the 2-beam tilted illumination technique incorporating a twin reflection produced {110} fringes across the microtwins.

Precipitation at the transformation interface of pearlite in steel

1990 ◽  
Vol 48 (4) ◽  
pp. 912-913
Author(s):  
F. A. Khalid ◽  
D. V. Edmonds
Keyword(s):  
Thin Foil ◽  
Carbon Steels ◽  
Model Alloy ◽  
Low Carbon ◽  
High Carbon ◽  
Growth Interface ◽  
Medium Carbon ◽  
Interphase Precipitation ◽  
Solution Treated ◽  
Wide Range

The austenite/pearlite growth interface in a model alloy steel (Fe-1lMn-0.8C-0.5V nominal wt%) is being studied in an attempt to characterise the morphology and mechanism of VC precipitation at the growth interface. In this alloy pearlite nodules can be grown isothermally in austenite that remains stable at room temperature thus facilitating examination of the transformation interfaces. This study presents preliminary results of thin foil TEM of the precipitation of VC at the austenite/ferrite interface, which reaction, termed interphase precipitation, occurs in a number of low- carbon HSLA and microalloyed medium- and high- carbon steels. Some observations of interphase precipitation in microalloyed low- and medium- carbon commercial steels are also reported for comparison as this reaction can be responsible for a significant increase in strength in a wide range of commercial steels.The experimental alloy was made as 50 g argon arc melts using high purity materials and homogenised. Samples were solution treated at 1300 °C for 1 hr and WQ. Specimens were then solutionised at 1300 °C for 15 min. and isothermally transformed at 620 °C for 10-18hrs. and WQ. Specimens of microalloyed commercial steels were studied in either as-rolled or as- forged conditions. Detailed procedures of thin foil preparation for TEM are given elsewhere.

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