Quantitative analysis of complex carbo-nitride precipitates in steels

Scott, Colin; Chaleix, D.; Barges, P.; Rebischung, V

doi:10.1016/s1359-6462(02)00219-1

Cited by 29 publications

(14 citation statements)

References 2 publications

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“…9c). Based on the compositions given in Table 1 and previous work [16,17], the precipitates are probably Ti, Nb and V carbides/nitrides (or carbonitrides). Moreover, the spectrum shows high Cu, Si and O peaks.…”

Section: Microstructural Evolutionmentioning

confidence: 80%

“…9a and c). In fact, because Ti, Nb and V carbides, nitrides or carbonitrides have similar crystal structures, co-precipitation is very common in multi-microalloyed steels [16,17]. When the reheating temperature is elevated to 1230℃, all V-and most Nb-containing particles dissolve from the outside layer of the complex precipitates and return to the austenite solid solution.…”

Section: Microstructural Evolutionmentioning

confidence: 99%

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Enhancing impact fracture toughness and tensile properties of a microalloyed cast steel by hot forging and post-forging heat treatment processes

2013

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In the present work, the effects of hot forging and post-forging heat treatment on the impact fracture toughness and tensile properties of a microalloyed cast steel were investigated. Mechanical tests were used to evaluate the room temperature impact fracture toughness and tensile properties of the steel. The resulting microstructures were analysed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The extraction replica technology was used to investigate the characterisation of complex precipitates formed during heat treatment. The obtained results showed that the coarse-grained microstructure of the forged specimen was significantly refined after post-forging heat treatment. Presence of complex precipitates had a favourable effect on the formation of refined austenite grains, and consequently refined final microstructure. Hot forging was beneficial to enhance the impact fracture toughness and tensile properties of the microalloyed cast steel. After 920 °C-treatment followed by air cooling, the impact energy of the forged specimen was significantly increased from 19.3 to 208.3 J, and further enhancement in tensile properties was obtained. The enhanced impact fracture toughness and tensile properties of the microalloyed cast steel after hot forging and post-forging heat treatment were closely related to the refined and homogenised ferritic-pearlitic microstructure. Republic of Korea AbstractIn the present work, the effects of hot forging and post-forging heat treatment on the impact fracture toughness and tensile properties of a microalloyed cast steel were investigated. Mechanical tests were used to evaluate the room temperature impact fracture toughness and tensile properties of the steel. The resulting microstructures were analysed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The extraction replica technology was used to investigate the characterisation of complex precipitates formed during heat treatment. The obtained results showed that the coarse-grained microstructure of the forged specimen was significantly refined after post-forging heat treatment. Presence of complex precipitates had a favourable effect on the formation of refined austenite grains, and consequently refined final microstructure. Hot forging was beneficial to enhance the impact fracture toughness and tensile properties of the microalloyed cast steel. After 920℃-treatment followed by air cooling, the impact energy of the forged specimen was significantly increased from 19.3 to 208.3 J, and further enhancement in tensile properties was obtained. The enhanced impact fracture toughness and tensile properties of the microalloyed cast steel after hot forging and post-forging heat treatment were closely related to the refined and homogenised ferritic-pearlitic microstructure.

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Section: Microstructural Evolutionmentioning

confidence: 80%

Section: Microstructural Evolutionmentioning

confidence: 99%

Enhancing impact fracture toughness and tensile properties of a microalloyed cast steel by hot forging and post-forging heat treatment processes

2013

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“…Measurements of C/N ratios in V(C, N) were performed using Electron Energy Loss Spectroscopy (EELS) on precipitates extracted on sub-stoichiometric alumina replicas. 15,16) Quantitative image analysis of TEM micrographs for precipitate size distribution determination was performed as follows: image magnification 66 K, negatives scanned at 800 dpi, manual identification of precipitates using a graphical analysis package and finally quantitative image analysis of the manually treated images. …”

mentioning

confidence: 99%

Vanadium Precipitation During Intercritical Annealing in Cold Rolled TRIP Steels

Perrard

Scott

2007

ISIJ Int.

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Flat carbon steel manufacturers are currently developing new TRansformation Induced Plasticity (TRIP) steels as a response to strong demands for vehicle lightening and security reinforcement from the automobile sector. Compared to conventional high strength steels these advanced grades exhibit a very favourable compromise between strength and ductility and can therefore be produced in thinner, lighter gauge strips with equivalent functional properties. The excellent mechanical properties of TRIP steels are attributed to the high strain hardening coefficient generated by the progressive transformation of metastable retained austenite to martensite during plastic deformation. Further improvements in mechanical properties can be obtained by microalloying, especially with vanadium and nitrogen additions. In this paper we discuss the rather complex evolution of vanadium carbonitride V(C, N) precipitation during continuous annealing of cold rolled strip. Transmission electron microscopy (TEM) and selective chemical dissolution are used to characterise the precipitation state during interrupted intercritical annealing cycles. The experimental results are compared with calculations made using a recent kinetic precipitation model. We show that reasonable agreement can be achieved using a simple uncoupled model, however a complete description of the precipitation sequence during continuous annealing will require fully coupled kinetic models describing the interactions between cementite dissolution, the ferrite to austenite transformation and V(C, N) precipitation.KEY WORDS: cold rolled TRIP; microalloying; V(C, N) precipitation; kinetics modelling. ISIJ International, Vol. 47 (2007), No. 8, pp. 1168-1177 Points 1-4 and 6 require that the precipitating species should be highly soluble in austenite. Points 5, 7 and 8 require the maximum possible precipitation driving force to generate a high particle nucleation density. Concerning point 7, intragranular precipitation will dominate if the precipitation step occurs in a deformed matrix, for example during annealing after cold rolling. Finally, point 9 would seem to favour the precipitation of nitrides or carbonitrides rather than pure carbides, which would tend to reduce the amount of carbon available to stabilise the residual austenite during the bainitic transformation. Taking into account all of the above criteria, the microalloying element which best satisfies these criteria is vanadium. Precipitation of VanadiumThe equilibrium solubility products for microalloy carbides and nitrides in austenite show that VN is the nitride which has the greatest solubility in austenite and that VC is even more soluble in austenite and in ferrite.10) For the purposes of precipitation strengthening in TRIP grades, it is the precipitates formed in the soft ferrite phase that are the most effective. It is therefore desirable to maintain the V in solution in the hot coil and to precipitate during continuous annealing after cold rolling. Due to the short holding times available in commercial c...

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“…Para la observación e identificación de los precipitados existentes en las fronteras de los granos austeníticos, se prepararon réplicas de carbono por un método de extracción en dos etapas [32][33][34][35][36] . En la primera, se desprenden las películas delgadas de triacetíl-celulosa que han sido previamente aplicadas sobre la superficie de la muestra (unas gotas de metíl acetato mejora la adherencia de las películas sobre la superficie de la muestra); a continuación, se realiza la evaporación de carbono sobre la película plástica en una cámara de alto vacío.…”

Section: Aunclassified

Study and modelling of the influence of second phase particles on the austenite grain growth in a niobium microalloyed steel

Martín¹,

Caballero

Capdevila

et al. 2006

Rev. metal.

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ResumenEn este trabajo se ha estudiado el crecimiento de grano austenítico producido durante el calentamiento continuo de un acero CMnNb. Se ha analizado la influencia de la velocidad de calentamiento sobre dicho proceso y se ha calculado la temperatura de crecimiento libre del grano austenítico, a la cual desaparece la influencia del pinzamiento provocado por los precipitados de carbonitruro de niobio. Finalmente, se propone un modelo del proceso de crecimiento de grano austenítico bajo pinzamiento que permite predecir el tamaño de grano austenítico (TGA) que se alcanza en el acero a una determinada temperatura por calentamiento continuo a velocidad conocida. Palabras ClaveCrecimiento de grano austenítico. Aceros microaleados con Niobio. Temperatura de crecimiento libre. Modelización. Calentamiento continuo.Study and modelling of the influence of second phase particles on the austenite grain growth in a niobium microalloyed steel AbstractThe austenite grain growth occurred during continuous heating in a niobium microalloyed steel has been investigated in this work. The effect of temperature and heating rate on the grain size is studied. The free grain coarsening temperature is determined as a function of the heating rate. It is found that unpinning by precipitates occurs around 40-70K below the temperature of complete dissolution of carbonitrides. Furthermore, a new model has been proposed to describe the austenite grain coarsening under the influence of niobium carbonitrides during continuous heating at different rates.

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Quantitative analysis of complex carbo-nitride precipitates in steels

Cited by 29 publications

References 2 publications

Enhancing impact fracture toughness and tensile properties of a microalloyed cast steel by hot forging and post-forging heat treatment processes

Enhancing impact fracture toughness and tensile properties of a microalloyed cast steel by hot forging and post-forging heat treatment processes

Vanadium Precipitation During Intercritical Annealing in Cold Rolled TRIP Steels

Study and modelling of the influence of second phase particles on the austenite grain growth in a niobium microalloyed steel

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