Microstructural Control of Ductile Crack Propagation in TMCP HSLA Pipeline Steels

Control of ductile fracture propagation is one of the major concerns for pipeline industry, particularly with the increasing demand of new control rolled steel grades required to maintain integrity at high operational pressures. The objective of this research is to understand which microstructural features govern crack propagation, and to analyse the effect of two of them (average grain size, and volume fraction of pearlite). The main disadvantage during classical Charpy test was to discriminate the crack initiation and propagation energy during fracture of a notched sample. The initiation appears to be caused by the stress state in the neighbouring of Ti-containing precipitates or pearlite particles (no presence of M/A constituents or MnS inclusions was detected in the evaluated grades), propagation-arrest of the crack is assumed to play the main role concerning the control of fracture. Our approach to characterize the fracture resistance is to measure the energy absorbed during the crack propagation stage by means of load-displacement curves obtained via instrumented Charpy test. It was observed that the energy absorbed during crack propagation is not influenced by the average grain size but by the fraction and the morphological (banded-not banded) distribution of second pearlitic phase. This suggests that a different approach to characterize the heterogeneities in grain size clustering might be followed to correlate the energy measured during crack propagation and the morphological features of the steel.

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Study on Dynamic Recrystallization Behavior in Deformed Austenite of 52100 Steel by Using JMAK-Model

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.275-277.1833 ◽

2013 ◽

Vol 275-277 ◽

pp. 1833-1837

Author(s):

Ke Lu Wang ◽

Shi Qiang Lu ◽

Xin Li ◽

Xian Juan Dong

Keyword(s):

Grain Size ◽

Dynamic Recrystallization ◽

Hot Deformation ◽

Volume Fraction ◽

True Strain ◽

Strain And Strain Rate ◽

Average Grain Size ◽

Dynamic Recrystallization Behavior ◽

Simulation And Experiment ◽

Good Agreement

A Johnson-Mehl-Avrami-Kolmogorov (JMAK)-model was established for dynamic recrystallization in hot deformation process of 52100 steel. The effects of hot deformation temperature, true strain and strain rate on the microstructural evolution of the steel were physically studied by using Gleeble-1500 thermo-mechanical simulator and the experimental results were used for validation of the JMAK-model. Through simulation and experiment, it is found that the predicted results of DRX volume fraction, DRX grain size and average grain size are in good agreement with the experimental ones.

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Static Recrystallization Microstructure Evolution in a Cold-Deformed Ni-Based Superalloy during Electropulsing Treatment

Crystals ◽

10.3390/cryst10100884 ◽

2020 ◽

Vol 10 (10) ◽

pp. 884

Author(s):

Hongbin Zhang ◽

Chengcai Zhang ◽

Baokun Han ◽

Kuidong Gao ◽

Ruirui Fang ◽

...

Keyword(s):

Grain Size ◽

Thermal Effect ◽

Static Recrystallization ◽

Volume Fraction ◽

Heating Effect ◽

Wind Force ◽

Average Grain Size ◽

Higher Temperature ◽

Electropulsing Treatment ◽

Electron Wind

The influence of electropulsing treatment (EPT) parameters on the static recrystallization (SRX) microstructure in a cold-deformed Ni-based superalloy was investigated. During EPT, both the volume fraction of SRX grains and the average grain size increased with the increasing EPT temperature, which was attributed to the thermal effect and athermal effect induced by EPT. The mobility of SRX grain boundaries was promoted at the higher temperature due to the thermal effect, while the nucleation rate would be increased by EPT through decreasing the thermodynamic barrier. The formation of parallel dislocations caused by electron wind force could also play an indirect role in promoting SRX process. Moreover, the volume fraction of SRX grains increased significantly with the extension of EPT time at 700 °C, while the EPT time had a trivial effect on the average grain size. In addition, the sufficient deformation was essential to the occurrence of SRX behavior during EPT, and the localized Joule heating effect could promote the SRX behavior in the samples with the larger strains. Besides that, the influence of twining and carbides on the SRX behaviors was also investigated.

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Enhanced Mechanical Properties of Mg-6Sn-3Al-1Zn Alloy with Bimodal Grain Size Disturbed in the Microstructure Uniformly through Changing the Rolling Temperature

Advances in Materials Science and Engineering ◽

10.1155/2020/6635507 ◽

2020 ◽

Vol 2020 ◽

pp. 1-13

Author(s):

Fuan Wei ◽

Jinhui Wang ◽

Ping Li ◽

Bo Shi

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Yield Strength ◽

Volume Fraction ◽

Rolling Temperature ◽

Average Grain Size ◽

Small Grains ◽

Mg2sn Phase ◽

Average Size ◽

Bimodal Grain Size

The mechanical properties of Mg-6Sn-3Al-1Zn alloy were enhanced with bimodal grain size disturbed in the microstructure uniformly; the Mg-6Sn-3Al-1Zn alloys were rolled with 60% thickness reduction at different rolling temperatures. The results have shown that the Mg-6Sn-3Al-1Zn alloys are composed of Mg2Sn phase and α-Mg matrix phase. When the rolling temperature was less than or equal to 400°C, with the rolling temperature increasing, the average size and volume fraction of Mg2Sn phase and the average grain size of small grains remained unchanged, the average grain size of large grains decreased, the volume fraction of small grains increased, and the yield strength of the alloy increased. When the rolling temperature reached 450°C, the average size and volume fraction of Mg2Sn phase and the average grain size of large grains increased, and the volume fraction of small grains and the yield strength of the alloy decreased. The elongation increased with the rolling temperature increasing, but the change trend of hardness was just opposite. When the alloy was rolled at 400°C, the average sizes of small grains, large grains, and Mg2Sn phases were 3.66 μm, 9.24 μm, and 19.5 μm, respectively. The volume fractions of small grains, large grains, and Mg2Sn phases were 18.6%, 77.6%, and 3.8%, respectively. And the tensile properties reached the optimum; for example, the tensile strength, yield strength, elongation, and Vickers hardness were 361 MPa, 289.5 MPa, 20.5%, and 76.3 HV, respectively.

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Finite Element Analysis of Dynamic Recrystallization of Casting Slabs during Hot-Core Heavy Reduction Rolling Process

Metals ◽

10.3390/met10020181 ◽

2020 ◽

Vol 10 (2) ◽

pp. 181

Author(s):

Haijun Li ◽

Tianxiang Li ◽

Meina Gong ◽

Zhaodong Wang ◽

Guodong Wang

Keyword(s):

Grain Size ◽

Dynamic Recrystallization ◽

Volume Fraction ◽

Rolling Process ◽

Reduction Ratio ◽

Secondary Development ◽

Innovative Technology ◽

Element Analysis ◽

The Core ◽

Average Grain Size

Hot-core heavy reduction rolling (HHR2) is an innovative technology, where a two-high rolling mill is installed after the solidification end of a strand, which can significantly eliminate the core defects of the slab. The mill exhibits a heavy reduction ratio, which promotes the dynamic recrystallization (DRX) of the slab. This study aims to optimize the parameters of the HHR2 process considering the effect of DRX on microstructure homogeneity. The secondary development of commercial software DEFORM-3D is conducted to calculate the deformation and DRX behavior of HHR2 for different reduction ratios. The parameters of DRX volume fraction and DRX grain size are compared, and finer DRX grains are obtained when the greater reduction ratios are conducted in HHR2. Then, corresponding to the deformation conditions in the HHR2, the thermal–mechanical simulations are conducted on the Gleeble3800 to obtain the average grain sizes before and after this process. When the reduction amount increases from 20 mm to 50 mm, the difference of average grain size between the core and the surface reduces by 52%. In other words, appropriately enhancing the reduction ratio is helpful to reduce the average austenite grain and promote the microstructure uniformity of the slab. These results provide some valuable information on the design of deformation parameters for HHR2.

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Effect of Annealing on Microstructure and Corrosion Behavior of Interstitial Free Steel

Materials ◽

10.3390/ma15010024 ◽

2021 ◽

Vol 15 (1) ◽

pp. 24

Author(s):

Qiongyao He ◽

Xiaojuan Jiang ◽

Pengzhan Cai ◽

Ling Zhang ◽

Tao Sun ◽

...

Keyword(s):

Grain Size ◽

Corrosion Resistance ◽

Corrosion Behavior ◽

Corrosion Potential ◽

Volume Fraction ◽

Interstitial Free ◽

Stored Energy ◽

Interstitial Free Steel ◽

Average Grain Size ◽

Nyquist Plots

Interstitial free steels with various grain sizes and textures were prepared by cold-rolling followed by an annealing process. The effect of grain size, crystallographic orientations and stored energy on corrosion behavior of interstitial free steel was investigated. It was found that the deformed microstructure and dislocation boundaries were consumed by recrystallizing grains during annealing. The average grain size increase ranging from 0.61 μm to 11 μm and the volume fraction of recrystallized grains was about 96% after annealing for 64 h; meanwhile, the γ fiber was the dominated recrystallized texture component. The stored energy gradually decreased due to the reduction in dislocation density by annealing. The potentiodynamic polarization and Nyquist plots show that the corrosion potential exhibits a more positive shift and depressed capacitive semicircle radius increase with rising annealing time. The 64 h annealed specimens had the biggest depressed semicircle in the Nyquist plots and the highest positive corrosion potential, which indicates the enhancement of corrosion resistance. Such an improvement of corrosion resistance is attributed to the increase in the volume fraction of the γ fiber and decrease in the stored energy.

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Effects of Repetitive Upsetting Extrusion on the Microstructure and Texture of GWZK124 Alloy under Different Starting Temperatures

Materials ◽

10.3390/ma12152437 ◽

2019 ◽

Vol 12 (15) ◽

pp. 2437

Author(s):

Guanshi Zhang ◽

Zhimin Zhang ◽

Yingze Meng ◽

Zhaoming Yan ◽

Xin Che ◽

...

Keyword(s):

Grain Size ◽

Dynamic Recrystallization ◽

Grain Refinement ◽

Volume Fraction ◽

Bimodal Microstructure ◽

Continuous Dynamic Recrystallization ◽

Average Grain Size ◽

Second Phases ◽

Continuous Dynamic ◽

Weak Texture

The effects of repetitive upsetting extrusion under different starting temperatures on the microstructure and texture of GWZK124 alloy were investigated. The results clearly showed that the particles and second phases induced dynamic recrystallization (DRX), which can be explained by the particle-stimulated nucleation (PSN) mechanism. It was shown that grain refinement during repetitive upsetting extrusion (RUE) is dominated by a complicated combination of continuous dynamic recrystallization and discontinuous dynamic recrystallization. The RUEed alloys under different starting temperatures exhibited a bimodal microstructure comprising fine DRXed grains with weak texture and coarse deformed grains with strong texture. The DRXed grains could weaken the texture. As the RUE starting temperature decreased, the average grain size increased and the volume fraction of DRXed grains decreased.

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Hot Deformation Behavior and Microstructural Evolution of Twin-Roll-Casting Mg Alloy during High-Temperature Compression

Advances in Materials Science and Engineering ◽

10.1155/2019/1820671 ◽

2019 ◽

Vol 2019 ◽

pp. 1-7

Author(s):

Qingshan Yang ◽

Jiahong Dai ◽

Sensen Chai ◽

Daliang Yu ◽

Bin Jiang ◽

...

Keyword(s):

Grain Size ◽

Flow Stress ◽

Microstructural Evolution ◽

Deformation Behavior ◽

Volume Fraction ◽

Mg Alloy ◽

Twin Roll Casting ◽

Roll Casting ◽

Average Grain Size ◽

Twin Roll

The deformation behavior and microstructural evolution of twin-roll-casting AZ31 Mg alloy sheets were investigated via hot compression tests at 0°, 5°, and 10° from the normal direction. Compression strains of 5%, 15%, 25%, and 35% were employed at high temperatures of 450°C and 500°C. The flow stress as well as the difference in the flow stress associated with different sampling directions decreased when the temperature was increased. Furthermore, the volume fraction of dynamically recrystallized grains increased with increasing deformation, whereas the average grain size decreased. The DRX grain size and the volume fraction of dynamically recrystallized grains increased with increasing deformation temperature. During ultrahigh temperature compression, the effect of sampling direction on the compression microstructure is relatively small.

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Dynamic Precipitation Behaviors and Mechanical Properties of Mg-12Gd-3Y-0.5Zr Alloy Processed by Secondary Extrusion

Materials Science Forum ◽

10.4028/www.scientific.net/msf.747-748.192 ◽

2013 ◽

Vol 747-748 ◽

pp. 192-197

Author(s):

De Jiang Li ◽

Yin Peng Zhou ◽

Xiao Qin Zeng ◽

Wen Jiang Ding ◽

Bin Chen ◽

...

Keyword(s):

Grain Size ◽

Volume Fraction ◽

Extrusion Process ◽

Extrusion Ratio ◽

Water Quenching ◽

Age Hardening ◽

Metallographic Analysis ◽

Air Cooling ◽

Dynamic Precipitation ◽

Average Grain Size

Secondary extrusion at 350 °C with the extrusion ratio of 12.25, 25 and 44 was carried out on the Mg-12Gd-3Y-0.5Zr (GW123K) alloy, and the cooling method of the secondary extruded alloys was air cooling and water quenching. Quantitative metallographic analysis method was also employed to study the distribution and volume fraction of dynamic precipitates during the extrusion process. The results showed that secondary extrusion could result in significant grain refinement and the grain size increased with extrusion ratio, which the minimum average grain size was about 5.4μm in the alloy under λ=12.25. The volume fraction of dynamic precipitates decreased with increasing extrusion ratio and the maximum volume fraction was measured to be about 49.2% in the alloy under λ =12.25. Water quenching after extrusion can effectively inhibit dynamic precipitation and the volume fraction of the precipitates ratio decreased from 41.1% after air cooling to 19.6% after water quenching in the same extrusion condition. Tensile properties results showed that the age hardening response of the alloys was decreased by dynamic precipitation and water quenching was an efficient method which is able to avoid this behavior in some extent.

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Finite Element Analysis on Microstructure Evolution of Hot Ring Rolling Process

Materials Science Forum ◽

10.4028/www.scientific.net/msf.575-578.1455 ◽

2008 ◽

Vol 575-578 ◽

pp. 1455-1460 ◽

Cited By ~ 2

Author(s):

Zhi Chao Sun ◽

He Yang ◽

Xin Zhe Ou

Keyword(s):

Grain Size ◽

Microstructure Evolution ◽

Volume Fraction ◽

Small Deformation ◽

Local Area ◽

Rolling Process ◽

Ring Rolling ◽

Rigid Plastic ◽

Element Analysis ◽

Average Grain Size

Hot ring rolling (HRR) is a 3D unsteady-state and coupled thermo-mechanical process, the metal undergoes complicated unequal deformation and microstructure evolution. In this paper a 3D rigid-plastic and coupled thermo-mechanical FEM model for hot ring rolling was developed based on DEFORM3D platform, taking dynamic recrystallization (DRX) volume fraction, DRX grain size, recystallization volume fraction and average grain size as objects, the mechanism of material microstructure evolution and distributions in HRR process are thoroughly studied. The results show that: with the HRR progressing, the DRX volume fraction, volume fraction, DRX grain size and average grain size have the similar distributing characteristic, and the distribution zones expand from a small local area into the whole ring strip, then diffuse to the mid-layer of ring with small deformation, their distributions become more uniform. Meanwhile with increase of deformation, the values of the DRX volume fraction and recrystallization volume fraction augment, i.e. the degree of recystallization increases. The DRX grain size also augments due to local high temperature, while the average grain size decreases. In general during HRR process the distributions of DRX volume fraction, recrystallization volume fraction, DRX grain size, and average grain size are ununiform due to unequal deforming in HRR process.

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Microstructure of Al2O3-Fe FGM Obtained by Modified Slip-Casting Method

Materials Science Forum ◽

10.4028/www.scientific.net/msf.492-493.665 ◽

2005 ◽

Vol 492-493 ◽

pp. 665-672 ◽

Cited By ~ 4

Author(s):

A. Ozieblo ◽

Tomasz Wejrzanowski ◽

K. Konopka ◽

Mikolaj Szafran ◽

Krzysztof Jan Kurzydlowski

Keyword(s):

Magnetic Field ◽

Grain Size ◽

Magnetic Force ◽

Volume Fraction ◽

Slip Casting ◽

Functionally Graded ◽

Casting Method ◽

Average Grain Size ◽

Field Lines ◽

The Magnetic Field

This paper describes the technology and microstructure of Al2O3-Fe functionally graded composites, FGM, obtained by slip-casting under magnetic field. Alumina a-Al2O3, provided by Alcoa (symbol A16SG), with average grain size of 0.5 µm, and iron powder, (symbol Distaloy AB) from Hoganas, with average grain size of 35 µm, were used to produce a series of specimens which differed in contents of Fe particles in Al2O3. As a source of magnetic force a permanent magnet was used. Preforms were sintered in a vacuum at temp. 1470oC. The microstructures of the specimens were quantitatively described via stereological methods. Sections, parallel to the magnetic field lines were analyzed using special image analysis software. Stereological methods presented in this work have been used to determine gradient in the volume fraction of the Fe particles and variation in their size and dispersion. These parameters are essential for controlling the technological process of interest and to design microstructure for needed properties (fracture toughness).

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