Transformation behavior and microstructural characteristics of acicular ferrite in linepipe steels

Kim, Young Min; Lee, Hakcheol; Kim, Nack J.

doi:10.1016/j.msea.2007.06.035

Cited by 126 publications

(82 citation statements)

References 22 publications

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“…This is consistent with other previous research results, [12,17,18] although in that research, the changes of grain refinement were observed from optical micrographs. However, the result of this research differs from previous studies, [14][15][16] which indicate that a coarser transformed microstructure forms after austenite deformation.…”

Section: Controversial Effect Of Austenite Deformation On Effectivsupporting

confidence: 93%

“…[16] More importantly, it was revealed from these investigations that even after significant amounts of austenite deformation, the transformation product still consists of parallel BF laths. Contradicting this were the prior research results [12,17,18] in which the transformed microstructures mainly were nonequiaxed AF laths with an irregular arrangement and the transformed microstructure was refined after austenite deformation. However, it should be noted that in earlier research, [12,17,18] the changes of grain refinement were observed directly from optical micrographs, which are not accurate enough, because for displacive transformation products, the boundaries revealed in the optical micrographs after etching are not necessarily HAGBs (h > 15 deg, where h is the boundary disorientation angle) and a substantial part of the boundaries are low-angle grain boundaries (LAGB, h £ 15 deg).…”

Section: Introductionmentioning

confidence: 85%

“…This indicates that with the increase of austenite deformation, a transition from BF to AF occurs, consistent with previous research. [12,17,18] Finally, in Figure 4(e), despite the further increased strain 2, the fraction of AF is not increased and the microstructure becomes inhomogeneous with coarse BF packets surrounding fine AF laths.…”

Section: B Transformed Microstructuresmentioning

confidence: 90%

“…The adjacent laths with disorientation below 15 deg make up the effective grains. [12] Since the effective grain boundaries (h ‡ 15 deg) act as obstacles to cleavage crack propagation, the reduction of effective grain size can result in better toughness, especially in terms of the ductile-brittle transition temperature. [12] …”

Section: Ebsd Mappingmentioning

confidence: 99%

“…Despite the unique morphology of AF, many investigations have shown that the transformation mechanism of AF is similar to that of BF. [8][9][10][11][12][13] As for the grain refinement of low-temperature transformation products, although the effect of austenite deformation has been studied by many researchers, the results are still controversial. In a prior investigation, [14] it was shown that the effective grain size of bainite increases from 3.2 to 3.8 lm when austenite was deformed by 30 pct.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Austenite Deformation on the Microstructure Evolution and Grain Refinement Under Accelerated Cooling Conditions

Zhao

Palmiere

2017

Metall and Mat Trans A

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Although there has been much research regarding the effect of austenite deformation on accelerated cooled microstructures in microalloyed steels, there is still a lack of accurate data on boundary densities and effective grain sizes. Previous results observed from optical micrographs are not accurate enough, because, for displacive transformation products, a substantial part of the boundaries have disorientation angles below 15 deg. Therefore, in this research, a niobium microalloyed steel was used and electron backscattering diffraction mappings were performed on all of the transformed microstructures to obtain accurate results on boundary densities and grain refinement. It was found that with strain rising from 0 to 0.5, a transition from bainitic ferrite to acicular ferrite occurs and the effective grain size reduces from 5.7 to 3.1 lm. When further increasing strain from 0.5 to 0.7, dynamic recrystallization was triggered and postdynamic softening occurred during the accelerated cooling, leading to an inhomogeneous and coarse transformed microstructure. In the entire strain range, the density changes of boundaries with different disorientation angles are distinct, due to different boundary formation mechanisms. Finally, the controversial influence of austenite deformation on effective grain size of low-temperature transformation products was argued to be related to the differences in transformation conditions and final microstructures.

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Section: Controversial Effect Of Austenite Deformation On Effectivsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 85%

Section: B Transformed Microstructuresmentioning

confidence: 90%

Section: Ebsd Mappingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Effect of Austenite Deformation on the Microstructure Evolution and Grain Refinement Under Accelerated Cooling Conditions

Zhao

Palmiere

2017

Metall and Mat Trans A

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A Review of the Factors That Can Increase the Risk of Sulfide Stress Cracking in Thermomechanical Controlled Processed Pipeline Steels

Hiew Sze Kei,

van Haaften,

Britton

et al. 2023

Adv Eng Mater

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This review aims to improve our understanding of the important factors which influence the susceptibility of thermomechanical controlled processed (TMCP) steels to sulfide stress cracking (SSC). Mechanisms involved in hydrogen embrittlement (HE) from three perspectives are focused on: the microstructure constituents of TMCP steels; environmental factors; and fracture mechanism of SSC. Microstructures are reviewed as they affect the diffusion and trapping of hydrogen that can reduce the resistance to fracture. Environmental factors discussed highlight that when exposed to an aqueous H2S environment, a sulfide layer can form and influence the ingress of hydrogen, and this is affected by pH, temperature, and H2S partial pressure. Fracture is influenced by the nature of the crack tip and the crack tip plastic zone during crack propagation, and hydrogen can significantly affect crack tip growth. This review provides a critical assessment of the interplay between these three factors and aims to provide understanding to enhance our engineering approaches to manage and mitigate against fracture of TMCP steels.

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Isochronal Phase Transformations of Low‐Carbon High Strength Low Alloy Steel upon Continuous Cooling

Hou

Liu

Zhang

et al. 2012

steel research int.

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Aimed to acquire optimum comprehensive properties for the oil and gas pipeline steels, thermal treatment should be controlled to achieve ideal microstructures. Effects of cooling rates on transformation kinetics and microstructures of the low-carbon high strength low alloy (HSLA) steel were investigated to obtain an optimized thermal treatment technology. Dilatometric measurements, light microscopy, scanning electron microscopy, and transmission electron microscopy were employed in present work. The transformed microstructures contained polygonal ferrite þ pearlite, acicular ferrite (AF), and bainitic ferrite (BF) due to the cooling rates increasing from 5 to 30008C min À1 , in present investigated HSLA steel. The result shows that, the increase of cooling rate accelerates AF transformation and refines the steel's matrix. The morphology of martensite/austenite structures transformed from islands in AF to films in BF with the increase of cooling rate.

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Transformation behavior and microstructural characteristics of acicular ferrite in linepipe steels

Cited by 126 publications

References 22 publications

Effect of Austenite Deformation on the Microstructure Evolution and Grain Refinement Under Accelerated Cooling Conditions

Effect of Austenite Deformation on the Microstructure Evolution and Grain Refinement Under Accelerated Cooling Conditions

A Review of the Factors That Can Increase the Risk of Sulfide Stress Cracking in Thermomechanical Controlled Processed Pipeline Steels

Isochronal Phase Transformations of Low‐Carbon High Strength Low Alloy Steel upon Continuous Cooling

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