Thermomechanical Processing of Pipeline Steels with a Reduced Mn Content

Schambron, Thomas; Phillips, Andrew W.; O’Brien, Denis; Burg, Joshua; Pereloma, Elena V.; Killmore, Chris C.; Williams, Jim A.

doi:10.2355/isijinternational.49.284

Cited by 19 publications

(10 citation statements)

References 42 publications

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“…7 shows the microstructure of two other nital-etched samples that went through the same schedules 3a and 3c but were slowly cooled in an argon flow from 750 • C. The cooling rate during transformation was near 3.5 • C/s, which is similar to the reported cooling rate for the core of a heavy plate [12]. The effect of austenite strengthening at the end of hot rolling is observed again: ferrite grains are finer and more equiaxed when austenite is more heavily deformed (higher values of ), which agrees with previous results that proved the remarkable refinement of final microstructure by hot deformation of austenite [9,28,29]. On the other hand, lower values of generate more acicular structures after cooling.…”

Section: Resultssupporting

confidence: 91%

“…This also impedes the growth of /˛interfaces and accelerates the diffusion of carbon to the /˛interface, which can give rise to carbonenriched austenite due to the partitioning of carbon [20]. On the other hand, it is known that the refinement of ferritic microstructure is enhanced by a fine-grained austenite before transformation, and especially by a microstructure of strengthened austenite with elongated grains, high dislocation density and ledges in the grain boundaries that increase the density of nucleation sites and promote high nucleation rates for ferrite [9,28,29]. The total degree of roughing and especially the final deformation degree have a great influence on the toughness and strength properties, more than the deformation degree of the single passes.…”

Section: Introductionmentioning

confidence: 97%

“…These steels include a strict combination of alloying and microalloying elements to obtain good weldability, adequate strength in corrosive environment and a precise balance of microconstituents in order to achieve excellent mechanical properties at a reduced cost [4][5][6][7]. To obtain an adequate fine-grained final microstructure, the strict control of thermomechanical processing (reheating temperature, percentage reduction, interpass times, roughing and finishing temperatures) and accelerated cooling (delay time between finish rolling and the onset of accelerated cooling, cooling start temperature, cooling rate, cooling stop temperature) is also crucial for the strength and toughness properties [8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

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Evolution of microstructure and precipitation state during thermomechanical processing of a X80 microalloyed steel

Gómez¹,

Vallés

Medina³

2011

Materials Science and Engineering: A

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a b s t r a c tA series of anisothermal hot torsion tests were carried out to simulate hot rolling on a high-strength low-carbon CMnNbMoTi microalloyed steel corresponding to an industrial X80 grade for pipeline construction. Mean Flow Stress was graphically represented against the inverse of temperature to characterize the evolution of austenite microstructure during rolling, which was also studied by optical microscopy and SEM on samples quenched from several temperatures. On the other hand, particles precipitated at different temperatures during rolling were analyzed by means of TEM using the carbon extraction replica technique and their size distribution and mean size were determined, as well as their morphology, nature and chemical composition. The effect of rolling temperature and austenite strengthening obtained at the end of thermomechanical processing on final microstructure and precipitation state was studied. Austenite strengthening was characterized by means of the parameter known as accumulated stress ( ). It was found that ferrite grains are finer and more equiaxed when the austenite is more severely deformed during finishing (higher values of ) but lower values of generate a higher density of acicular structures after cooling, which should improve the balance of mechanical properties. The increase in strength associated to acicular ferrite compared to polygonal ferrite is revealed by the higher values of Vickers microhardness measured on samples corresponding to low . On the other hand, (Ti, Nb)-rich carbonitrides can be found from reheating and their size keeps a constant value near 20-30 nm during thermomechanical processing. A second population of much finer (Nb, Mo)-rich carbonitrides whose size is close to 5 nm forms from lower temperatures, near 1000 • C. The accomplishment of two different levels of at the end of hot rolling schedule does not seem to introduce major differences in precipitation state before final cooling.

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Section: Resultssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Evolution of microstructure and precipitation state during thermomechanical processing of a X80 microalloyed steel

Gómez¹,

Vallés

Medina³

2011

Materials Science and Engineering: A

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“…Samples were taken from the quarter thickness position of 230 mm thick Al killed and continuously cast slabs and machined to 20 mm × 15 mm × 8 mm blocks with the long edge parallel to the casting direction. Plain strain compression tests were carried out using a Gleeble 3500 thermo‐mechanical simulator using the method described elsewhere …”

Section: Materials and Experimental Proceduresmentioning

confidence: 99%

Effect of Mo Concentration on Dynamic Recrystallization Behavior of Low Carbon Microalloyed Steels

Schambron¹,

Chen

Gooch

et al. 2013

steel research int.

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The cover shows a simulated slip traces plot on a (011) oriented single crystal surface after a nanoindentation. More details can be found in the article by M. Liu and co-workers. 1191 Dynamic recrystallization (DRX) and mechanical properties of microalloyed Nb-Ti-steels with different Mo contents are investigated, and the effects of Mo, deformation temperature and strain rate quantifi ed. The typical signs of DRX are observed over a wide range of deformation conditions, but at higher strain rates and/or lower deformation temperatures, dynamic recovery occurred. It is shown that Mo has a retarding effect on DRX. A crystal plasticity fi nite element method model has been developed to investigate the effect of the initial orientation on the surface profi le patterns of aluminum single crystal during nano-indentation. This 3D model has been validated by comparison with experimental observations. The slip traces are analyzed to provide detailed explanations of the anisotropy of the piling-up patterns.

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“…To obtain an adequate fine-grained final structure, the strict control of thermomechanical processing and accelerated cooling is crucial [1][2][3]. Depending on the thermomechanical processing conditions and chemical composition, pipeline steels can present different microstructures.…”

mentioning

confidence: 99%

Evolution of Microstructure and Precipitation State During Thermomechanical Processing of a Low Carbon Microalloyed Steel

Vallés¹,

Gómez²,

Medina³

et al. 2012

Microsc Microanal

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The increasing demand of sources of energy such as oil and natural gas induces at the steel industry a development on low carbon microalloyed steels for pipeline applications in order to achieve excellent mechanical properties of strength and toughness at a reduced cost. To obtain an adequate fine-grained final structure, the strict control of thermomechanical processing and accelerated cooling is crucial [1][2][3]. Depending on the thermomechanical processing conditions and chemical composition, pipeline steels can present different microstructures. Several authors have found that the microstructure of acicular ferrite usually provides an optimum combination of mechanical properties [4,5]. Higher levels of austenite strengthening before cooling promote a refinement of final microstructure but can also restrict the fraction of low temperature transformation products such as acicular ferrite.A series of anisothermal multipass hot torsion were carried out to simulate hot rolling on a low-carbon high-Mn (Nb, Ti)-microalloyed steel with increased hardenability obtained thanks to Mo, Ni and Cu additions, designed for pipeline construction. Mean Flow Stress (Fig. 1) was graphically represented against the inverse of temperature to characterize the evolution of austenite microstructure during rolling. This combined effect gives rise to a wide range of final microstructures and mechanical properties depending on the composition, processing schedule and cooling rates applied. On the other hand, it is known that strain-induced precipitates formed by microalloying elements play a very important role on the microstructure evolution and final mechanical properties [5,6,7] Precipitation state at different stages of thermomechanical processing was studied on different samples obtained by means quench-interrupted hot rolling simulations.The samples were studied by optical microscopy and scanning electron microscopy (SEM), after were prepared by metallographic techniques on a longitudinal surface (Figs. 2, 3). The primitive austenite grain boundaries were revealed by etching. The evolution of austenite microstructure during hot rolling simulation was obtained. The characteristics of the precipitates were determined by transmission electron microscopy (TEM), using the carbon extraction replica technique (Figs. 4, 5). In each replica a population of no less than 400 particles was counted and their size was measured with the aim of calculating the mean size. Energy dispersive X-ray (EDX) analysis was carried out to characterize the chemical composition of the particles observed. SAED patterns were also obtained.

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Thermomechanical Processing of Pipeline Steels with a Reduced Mn Content

Cited by 19 publications

References 42 publications

Evolution of microstructure and precipitation state during thermomechanical processing of a X80 microalloyed steel

Evolution of microstructure and precipitation state during thermomechanical processing of a X80 microalloyed steel

Effect of Mo Concentration on Dynamic Recrystallization Behavior of Low Carbon Microalloyed Steels

Evolution of Microstructure and Precipitation State During Thermomechanical Processing of a Low Carbon Microalloyed Steel

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