Effects of Molybdenum and Vanadium Addition on Tensile and Charpy Impact Properties of API X70 Linepipe Steels

Kim, Young Min; Shin, Sang Yong; Lee, Hakcheol; Hwang, Byoungchul; Lee, Sunghak; Kim, Nack J.

doi:10.1007/s11661-007-9197-3

Cited by 63 publications

(35 citation statements)

References 25 publications

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“…Additionally, it was found in many TEM observations that AF laths contain a higher density of dislocations than those associated with reconstructive transformation products [12,[42][43][44], and the AF microstructure consists of several parallel subunits with a size less than 1 lm [12,42] resembling the sheaf morphology of bainitic ferrite [5]. In summary, AF shows similar transformation behaviours and microstructure characteristics to those of bainite; therefore, it is reasonable to say that the AF transformation mechanism is in fact bainitic, which is also agreed by many other researchers [2,3,12,[44][45][46].…”

Section: Discussion Acicular Ferrite Transformation Mechanismsupporting

confidence: 74%

Conditions for the occurrence of acicular ferrite transformation in HSLA steels

2017

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For the class of steels collectively known as high strength low alloy (HSLA), an acicular ferrite (AF) microstructure produces an excellent combination of strength and toughness. The conditions for the occurrence of the AF transformation are, however, still unclear, especially the effects of austenite deformation and continuous cooling. In this research, a commercial HSLA steel was used and subjected to deformation via plane strain compression with strains ranging from 0 to 0.5 and continuous cooling at rates between 5 and 50°C s -1 . Based on the results obtained from optical microscopy, scanning electron microscopy and electron backscattering diffraction mapping, the introduction of intragranular nucleation sites and the suppression of bainitic ferrite (BF) laths lengthening were identified as the two key requirements for the occurrence of AF transformation. Austenite deformation is critical to meet these two conditions as it introduces a high density of dislocations that act as intragranular nucleation sites and deformation substructures, which suppress the lengthening of BF laths through the mechanism of mechanical stabilisation of austenite. However, the suppression effect of austenite deformation is only observed under relatively slow cooling rates or high transformation temperatures, i.e., conditions where the driving force for advancing the transformation interface is not sufficient to overcome the austenite deformation substructures.

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Section: Discussion Acicular Ferrite Transformation Mechanismsupporting

confidence: 74%

Conditions for the occurrence of acicular ferrite transformation in HSLA steels

2017

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“…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%

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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“…Studies on the microstructure of microalloyed steels with a view to improving their mechanical properties had been conducted by many researchers. [8][9][10] Steels used for large-scale structures, such as the tower flanges of wind turbines, are usually produced by hot forging followed by air cooling. For meeting the structural safety requirements, such structural steels require excellent strength to bear static and dynamic heavy loads.…”

Section: Jingwei Zhao Taekyung Lee Jeong Hun Lee Zhengyi Jiang Anmentioning

confidence: 99%

Effects of Tungsten Addition on the Microstructure and Mechanical Properties of Microalloyed Forging Steels

Zhao

Lee

et al. 2013

Metall Mater Trans A

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In the current study, the effects of tungsten (W) addition on the microstructure, hardness, and room/low [223 K and 173 K (-50 C and -100 C)] temperature tensile properties of microalloyed forging steels were systematically investigated. Four kinds of steel specimens were produced by varying the W additions (0, 0.1, 0.5, and 1 wt pct). The microstructure showed that the addition of W does not have any noticeable effect on the amount of precipitates. The precipitates in W-containing steels were all rich in W, and the W concentration in the precipitates increased with the increasing W content. The mean sizes of both austenite grains and precipitates decreased with the increasing W content. When the W content was equal to or less than 0.5 pct, the addition of W favored the formation of allotriomorphic ferrite, which subsequently promoted the development of acicular ferrite in the microalloyed forging steels. The results of mechanical tests indicated that W plays an important role in increasing the hardness and tensile strength. When the testing temperature was decreased, the tensile strength showed an increasing trend. Both the yield strength and the ultimate tensile strength obeyed an Arrhenius type of relation with respect to temperature. When the temperature was decreased from 223 K to 173 K (from -50 C to -100 C), a ductile-to-brittle transition (DBT) of the specimen with 1 pct W occurred. The addition of W favored a higher DBT temperature. From the microstructural and mechanical test results, it is demonstrated that the addition of 0.5 pct W results in the best combination of excellent room/low-temperature tensile strength and ductility. 2013 The Minerals, Metals & Materials Society and ASM International. Effects of Tungsten Addition on the Microstructure and Mechanical Properties of Microalloyed Forging Steels JINGWEI ZHAO, TAEKYUNG LEE, JEONG HUN LEE, ZHENGYI JIANG, and CHONG SOO LEEIn the current study, the effects of tungsten (W) addition on the microstructure, hardness, and room/low [223 K and 173 K (À50°C and À100°C)] temperature tensile properties of microalloyed forging steels were systematically investigated. Four kinds of steel specimens were produced by varying the W additions (0, 0.1, 0.5, and 1 wt pct). The microstructure showed that the addition of W does not have any noticeable effect on the amount of precipitates. The precipitates in W-containing steels were all rich in W, and the W concentration in the precipitates increased with the increasing W content. The mean sizes of both austenite grains and precipitates decreased with the increasing W content. When the W content was equal to or less than 0.5 pct, the addition of W favored the formation of allotriomorphic ferrite, which subsequently promoted the development of acicular ferrite in the microalloyed forging steels. The results of mechanical tests indicated that W plays an important role in increasing the hardness and tensile strength. When the testing temperature was decreased, the tensile strength showed an increasing trend. Both...

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Effects of Molybdenum and Vanadium Addition on Tensile and Charpy Impact Properties of API X70 Linepipe Steels

Cited by 63 publications

References 25 publications

Conditions for the occurrence of acicular ferrite transformation in HSLA steels

Conditions for the occurrence of acicular ferrite transformation in HSLA steels

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

Effects of Tungsten Addition on the Microstructure and Mechanical Properties of Microalloyed Forging Steels

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