Topic
Microalloyed steel
About: Microalloyed steel is a research topic. Over the lifetime, 2183 publications have been published within this topic receiving 33586 citations.
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15 Sep 2017
TL;DR: In this article, different amounts of rare earth (RE) elements were added to a niobium microalloyed steel in as-cast condition to investigate its influence on the type of inclusions and precipitation of Niobium carbides.
Abstract: The main role of Rare Earth (RE) elements in the steelmaking industry is to affect the nature of inclusions (composition, geometry, size and volume fraction), which can potentially lead to the improvement of some mechanical properties such as the toughness in steels. In this study, different amounts of RE were added to a niobium microalloyed steel in as-cast condition to investigate its influence on: (i) type of inclusions and (ii) precipitation of niobium carbides. The characterization of the microstructure by optical, scanning and transmission electron microscopy shows that: (1) the addition of RE elements change the inclusion formation route during solidification; RE > 200 ppm promote formation of complex inclusions with a (La,Ce)(S,O) matrix instead of Al2O3-MnS inclusions; (2) the roundness of inclusions increases with RE, whereas more than 200 ppm addition would increase the area fraction and size of the inclusions; (3) it was found that the presence of MnS in the base and low RE-added steel provide nucleation sites for the precipitation of coarse niobium carbides and/or carbonitrides at the matrix–MnS interface. Thermodynamic calculations show that temperatures of the order of 1200 °C would be necessary to dissolve these coarse Nb-rich carbides so as to reprecipitate them as nanoparticles in the matrix.
31 citations
TL;DR: In this paper, the effect of temperature and heating rate on the grain size is studied, assuming a random distribution of carbonitrides in the matrix and niobium volume diffusion as the rate controlling process for the coarsening of precipitates.
Abstract: This work investigates grain growth behaviour under the influence of pinning carbonitrides in a niobium microalloyed steel. The effect of temperature and heating rate on the grain size is studied. The grain coarsening temperature is determined as a function of the heating rate. It is found that unpinning by precipitates occurs around 40-70 K below the temperature of complete dissolution of carbonitrides. It has been found that experimental results are best described assuming a random distribution of carbonitrides in the matrix and niobium volume diffusion as the rate controlling process for the coarsening of precipitates. Austenite grain growth is explained theoretically taking as a basis the model proposed by Zener, which has been adapted for non-equilibrium kinetics, taking into account the experimental evidence that during a continuous heating, the amount of microalloyed element in solid solution is altered and different from that predicted by the solubility product.
31 citations
TL;DR: In this paper, the ferrite grain refinement in a low carbon Nb-microalloyed steel was investigated using hot compression experiments for various deformation temperatures, and the results indicated that very fine ferrite grains of about 2-4μm can be obtained by deformation at 760-850°C, due to the occurrence of strain-induced transformation of austenite to ferrite.
31 citations
TL;DR: In this article, single-hit hot compression and stress relaxation after deformation on a Gleeble 1500D thermomechanical simulator, the curves of flow stress and stress relaxations, the microstructure and the recrystallization behavior of Nb-V-Ti high strength microalloyed low carbon pipeline steel were studied.
Abstract: Using methods of single-hit hot compression and stress relaxation after deformation on a Gleeble 1500D thermomechanical simulator, the curves of flow stress and stress relaxation, the microstructure and the recrystallization behavior of Nb-V-Ti high strength microalloyed low carbon pipeline steel were studied, and the influence of the thermomechanical treatment parameters on dynamic and static recrystallization of the steel was investigated. It was found that microalloying elements improved the deformation activation energy and produced a retardation of the recrystallization due to the solid solution and precipitation pinning. The deformation conditions such as deformation temperature, strain, and strain rate influenced the recrystallization kinetics and the microstructure respectively. Equations obtained can be used to valuate and predict the dynamic and static recrystallizations.
30 citations
TL;DR: In this article, the effect of Si on the rate of Nb(C, N) precipitation was investigated by using fractional softening measurements, and it was found that the precipitation rate in hot deformed austenite increases with Si concentration.
Abstract: The effect of Si on the rate of Nb(C, N) precipitation was investigated by using fractional softening measurements. Compression specimens, with diameters of 7.6 mm and lengths of 11.4 mm, were prepared from four Nb microalloyed steels containing a range of Si concentrations from 0.01 mass% to 0.41 mass%. Double-hit compression tests, with a strain of 0.3 for each pass and a strain rate of 0.1/sec., were employed. A solution heat treatment was applied immediately prior to each test. It was found that the rate of Nb(C,N) precipitation in hot deformed austenite increases with Si concentration. This phenomenon is attributed to the increases in the activities of C and N that result from Si addition.
30 citations