Surface microstructure evolution during phase transformation on Mn, Al and Si alloyed ultra low carbon steel

This paper investigates the surface texture evolution after a short alpha-gamma-alpha phase transformation annealing in low vacuum on ultra low carbon steel sheets alloyed with high Mn and Al and the cold rolled steel sheets of industrial composition alloyed with silicon. The ultra low carbon steel sheets with high Mn and Al show surface monolayer which has a characteristic surface texture components //ND texture and microstructure with special grain morphology. Contrastingly, the industrial composition alloyed with silicon does not show specific surface texture components inspired by surface energy anisotropy at the surface. The composition depth profiling investigations performed on the all steel sheet surface shows that oxidation characteristics of alloying elements at the metal vapour interface have played a decisive influence on surface texture evolution. Further, transformation annealing in higher vacuum reveals that surface texture can be obtained in an industrial composition alloyed with silicon

Surface energy controlled α-γ-α transformation texture and microstructure character study in ULC steels alloyed with Mn and Al

In this article, an ultralow-carbon steel grade alloyed with Mn and Al has been investigated during alpha-gamma-alpha transformation annealing in vacuum. Typical texture and microstructure has evolved as a monolayer of grains on the outer surface of transformation-annealed sheets. This monolayer consists of //ND and //ND fibre, which is very different from the bulk texture components. The selective driving force is believed to reside in the anisotropy of surface energy at the metal-vapour interface. The grain morphology is very different from the bulk grains. Moreover, 30-40% of the grain boundary interfaces observed in the RD-TD surface sections are tilt incoherent 70.5 boundaries, which are known to exhibit reduced interface energy. Hence, the conclusion can be drawn that the orientation selection of surface grains is strongly controlled by minimization of the interface energy; both metal/vapour and metal/metal interfaces play a roll in this

Nucleation and growth of surface texture during alpha-gamma-alpha transformation in ultra low carbon steel alloyed with Mn, Al and Si

It is well known that surface energy anisotropy is one of the driving forces for the orientation selection at the metal-vapour interface. This affects the microstructure and texture evolution at the surface during phase transformation, which is an inherent feature of low-alloyed low-carbon steels. This paper investigates the nucleation and growth of the surface texture by orientation contrast microscopy. It has been found that the surface texture is dominated by {001} oriented grains, which exhibit a remarkable orientation gradient from the centre of the grain towards the edge. The {001} oriented grain centre gradually rotates around a axis in small incremental steps when nearing the edge of the grain. Towards the edge the accumulated rotation angle has commonly reached a value of 30 degrees. Underneath the surface grains (similar to 30 mu m) the bulk texture consists of a strong gamma-fibre

Texture control in non-oriented electrical steels by severe plastic deformation

Although plenty of research has already been carried out on the issue of texture control in non-oriented electrical steels, there is not yet a universally applied industrial process to obtain an optimized {001} fibre texture. Among the various laboratory processes that have been studied so far, cross rolling seems to be one of the most promising approaches. For evident reasons cross-rolling cannot be implemented on a conventional continuous rolling line of an industrial plant. In the present study a potential interesting alternative is presented which may deliver a similar texture evolution as the cross rolling process, but can be applied in a continuous line of hot and cold rolling operations followed by recrystallization annealing. By applying severe rolling reductions a very strong rotated cube texture is obtained very much similar to the one that is observed after cross rolling. After annealing, the rotated cube texture changes to a {h11} fibre texture with a maximum on the {311} component which implies the potential to develop a {001} fibre texture after further processing. It is argued that the appearance of the {311} recrystallization texture component can be attributed to oriented nucleation in the vicinity of grain boundaries between slightly misoriented rotated cube grains

Strain induced inward grain growth during recrystallisation in steel sheets with BCC crystal structure

The present paper investigates the potential application of Strain Induced Boundary Migration mechanism on the two different types of surface textures developed after alpha-gamma-alpha phase transformation annealing, one with preferred cube and Goss orientation at the surface and the other with random surface texture without preferred orientations. It has been demonstrated that these surface texture components grow in across the thickness of the sheet after an appropriate combinations of a critical amount of rolling reductions and an annealing treatment at the recrystallisation temperature

Surface microstructure and texture evolution during interrupted annealing in ultra low carbon steels

The austenite-to-ferrite phase transformation, which is an inherent feature of low-alloyed ultra low carbon steels, has scarcely been investigated to control surface texture and microstructure evolution. This paper investigates the systematic evolution of texture and microstructure at the metal-vapour interface during interrupted annealing in vacuum. Interrupted annealing experiments were carried out on three ultra low carbon steel sheets alloyed with Mn, Al and Si. The texture and microstructures have been investigated by X-ray diffraction and SEM-EBSD techniques. These results reveal a very clear variation in the surface texture components as well as in the surface microstructure after BCC recrystallisation and double alpha-gamma-alpha transformation interrupted annealing. The recrystallisation texture consists mainly of a //ND fibre, while the transformation texture at the surface exhibits a //ND fibre in combination with components of the //ND fibre. It has been revealed that the latter specific surface texture was present in a monolayer of outer surface grains which were in direct contact with the vapour atmosphere. This observed phenomenon could be explained by considering the role of surface energy anisotropy occurring during phase transformation annealing

A first-principles reassessment of the Fe-N phase diagram in the low-nitrogen limit

Nitriding of steels has been widely used for almost a century. However, insight in two important precipitating phases for low concentration through-thickness nitriding is still lacking, hindering further development of the process. Due to their metastable nature, manufacturing large homogeneous samples of Fe4N and Fe16N2 is very challenging. Consequently, measuring thermodynamic properties, such as heat capacity and free energy, has proven difficult at best. In this work, we have calculated those thermodynamic properties using density-functional theory (DFT) for Fe4N, Fe16N2 and ferrite with nitrogen in solid solution. This information is a prerequisite to improve the accuracy of larger-scale modeling approaches of iron nitrides. We used the free energies to construct the temperature/concentration phase diagram for low nitrogen concentrations from to . Both the range of metastability for Fe16N2 and the nitrogen solvus confirm the experimental data. On the other hand, it was concluded that the experimental Curie temperature for Fe16N2 is severely underestimated because of the thermodynamic instability above 400 K

Effect of Mn on the Nanoprecipitation in Binary Fe-Cu alloys

International audienceEffect of the third alloying element Mn on Cu-precipitation was studied in a binary Fe-1.3% Cu alloy. Precipitation in both the alloys was investigated after homogenization treatment and subsequent artificial aging. Advanced characterization techniques such as Positron Annihilation Spectroscopy (PAS) and Tomographic Atom Probe (TAP) were used to establish the chemical composition, morphology, size and number density of the Cu-rich phases. Combined results of PAS and TAP were particularly useful in order to follow the Cu precipitation in the binary alloy. At short aging times, addition of Mn significantly increased the kinetics of hardening while its effect on the magnitude of precipitation strengthening is only marginal. It further increases the over-aging kinetics

Effect of Mn on the Nanoprecipitation in Binary Fe-Cu alloys

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Surface microstructure evolution during phase transformation on Mn, Al and Si alloyed ultra low carbon steel

This paper investigates the surface texture evolution after a short alpha-gamma-alpha phase transformation annealing in low vacuum on ultra low carbon steel sheets alloyed with high Mn and Al and the cold rolled steel sheets of industrial composition alloyed with silicon. The ultra low carbon steel sheets with high Mn and Al show surface monolayer which has a characteristic surface texture components //ND texture and microstructure with special grain morphology. Contrastingly, the industrial composition alloyed with silicon does not show specific surface texture components inspired by surface energy anisotropy at the surface. The composition depth profiling investigations performed on the all steel sheet surface shows that oxidation characteristics of alloying elements at the metal vapour interface have played a decisive influence on surface texture evolution. Further, transformation annealing in higher vacuum reveals that surface texture can be obtained in an industrial composition alloyed with silicon.This paper investigates the surface texture evolution after a short alpha-gamma-alpha phase transformation annealing in low vacuum on ultra low carbon steel sheets alloyed with high Mn and Al and the cold rolled steel sheets of industrial composition alloyed with silicon. The ultra low carbon steel sheets with high Mn and Al show surface monolayer which has a characteristic surface texture components //ND texture and microstructure with special grain morphology. Contrastingly, the industrial composition alloyed with silicon does not show specific surface texture components inspired by surface energy anisotropy at the surface. The composition depth profiling investigations performed on the all steel sheet surface shows that oxidation characteristics of alloying elements at the metal vapour interface have played a decisive influence on surface texture evolution. Further, transformation annealing in higher vacuum reveals that surface texture can be obtained in an industrial composition alloyed with silicon.C