Tribological properties of magnetite precipitate from oxide scale in hot-rolled microalloyed steel

et al. 2013

AMM

Oxidation characteristics of a microalloyed low carbon steel were investigated by a hot rolling mill combined with acceleration cooling system over the cooling rate range from 20 to 70°C/s. The effects of cooling rate after hot rolling on microstructure and phase composition of oxide scale were examined. The results showed that the increase of the cooling rate has a significant influence on the decrease of the grain size and surface roughness of oxide scale. A higher cooling rate promotes the formation of retain wustite and primary magnetite precipitation while suppression of eutectoid α-iron precipitates. This provides the possibility to enhance potential contribution of magnetite precipitates with preferable ductility, and hence fabricates a desired oxide-scale structure under continuous post cooling conditions considering a suitable cooling rate. Abstract. Oxidation characteristics of a microalloyed low carbon steel were investigated by a hot rolling mill combined with acceleration cooling system over the cooling rate range from 20 to 70°C/s. The effects of cooling rate after hot rolling on microstructure and phase composition of oxide scale were examined. The results showed that the increase of the cooling rate has a significant influence on the decrease of the grain size and surface roughness of oxide scale. A higher cooling rate promotes the formation of retain wustite and primary magnetite precipitation while suppression of eutectoid α-iron precipitates. This provides the possibility to enhance potential contribution of magnetite precipitates with preferable ductility, and hence fabricates a desired oxide-scale structure under continuous post cooling conditions considering a suitable cooling rate. IntroductionDuring hot rolling, oxidation occurs inevitably on the surface of steel strips, and hence forms the oxide scale which is a complex mixture of three iron oxide phases: hematite (Fe 2 O 3 ), magnetite (Fe 3 O 4 ) and wustite (Fe 1-x O, x=0.84-0.95) [1,2]. The mechanical properties and subsequent descalability intimately depend on phase distribution and microstructure of these oxides. Correspondingly, oxidation behaviour of steel strips is well known to be highly sensitive to both steel composition and oxidation conditions, in particular the post cooling conditions at the exit of the last finishing stand of the rolling mill [3]. Throughout the run-out laminar cooling, the three-layer oxides structure is maintain until an eutectoid point of Fe-O phase equilibrium diagram is reached if oxygen is available at the temperature of around 570C [4,5]. The microstructure of oxide scale is complicated further by the instability of wustite below 570C, which results in wustite decomposition to magnetite or eutectoid structure of magnetite and proeutectoid iron [6,7]. Under various cooling regimes, different reaction paths taking place in the oxide layer lead to particular phase compositions of the oxide scale. In order to achieve desired phase constitution of the final oxide scale, some elegant studies ha...

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of Cooling Rate on Oxidation Behaviour of Microalloyed Steel

Xiang

et al. 2013

AMM

“…9) These surface properties include surface energy, crystallographic orientation, grain boundaries, texturing of surface and crystal structure. 10,11) For instance, some results demonstrate that Fe3O4 (100) plane is a very rich and complex system, and its surface structure depends critically on surface preparation in the magnetoelectronics field.…”

Section: Introductionmentioning

confidence: 99%

Crystallographic Texture Based Analysis of Fe3O4/α-Fe2O3 Scale Formed on a Hot-rolled Microalloyed Steel

et al. 2015

ISIJ Int.

Self Cite

Oxide scale formed on the strip surface during hot rolling has posed a serious obstacle to ensure a defect-free surface of steel products in an ecologically friendly way. Recently, an influential idea is that the tertiary oxide scale with a tailored texture can be expected to enhance surface quality and tribolgoical properties during particular lubrication. In this study, texture evolutions of magnetite (Fe3O4) and hematite (α-Fe2O3) in deformed oxide layers formed on a hot-rolled microalloyed steel were investigated by electron back-scattering diffraction (EBSD). Fe3O4 develops a strong θ fibre parallel to the oxide growth, and α-Fe2O3 has a dominant {0001}<1010> texture component. This could be explained by surface energy minimisation during oxides growth and transformation between two oxides, which can also be affected by propagation of cracks along high angle grain boundaries in Fe3O4. Our data further demonstrate that a high thickness reduction (>28%) can reduce α-Fe2O3 wedging through Fe3O4 cracks, and tailoring Fe3O4 texture to {111} components can prevent the α-Fe2O3 growth titling 54.76° from the <001> crystal direction of Fe3O4. As such, these means can dramatically alleviate disturbance from 'red scale' (α-Fe2O3) during high-temperature steel processing.

“…In the case of hot rolling, the surface properties include the surface energy, crystallographic orientation, grain boundaries, texturing of the surface and crystal structure [6]. It is therefore widely expected that tailoring the atomic structure of the oxide layers can enhance tribological properties during environmentally friendly nanoparticle lubrication and further improve the surface quality of the final products [7].…”

Section: Introductionmentioning

confidence: 99%

“…In most cases, the tertiary oxide scale consists of a thin outer layer of hematite (α-Fe 2 O 3 ), an intermediate layer of magnetite (Fe 3 O 4 ), and an inner layer of wustite (Fe 1-x O, with 1-x ranging from 0.83 to 0.95) just above the steel substrate [2,8,9]. These layers of oxide scales may evolve further and undergo structural changes if oxygen is available during air-cooling after coiling [7,8]. Hence, the distribution of these oxide phases depends largely on the heat treatment and atmospheric conditions during hot rolling and the alloying elements contained in the steel compositions [8,10].…”

Section: Introductionmentioning

confidence: 99%

Dependence of texture development on the grain size of tertiary oxide scales formed on a microalloyed steel

Surface and Coatings Technology

et al. 2015

Self Cite

Q. (2015). Dependence of texture development on the grain size of tertiary oxide scales formed on a microalloyed steel. Surface and Coatings Technology, Dependence of texture development on the grain size of tertiary oxide scales formed on a microalloyed steel AbstractBoth orientational and geometrical characteristics of grains in tertiary oxide scales have been quantitatively investigated using the electron backscatter diffraction (EBSD) technique. Phase and orientation mappings demonstrate that the {001} planes of magnetite and the {0001} planes of hematite are parallel to the direction of oxide growth. Pole figures (PFs) as scattering plots clearly display the direct correlation between the orientations and microstructure sites of magnetite grains. Magnetite grains develop a strong rotated cube texture component that shifts to the {100} component, whereas those with the grain size of 1-5. μm develop the {001} cube texture component. The refined magnetite grains surrounding the abnormal ones can be a combined process, including magnetite pro-eutectoid during hot rolling and cooling and re-oxidation during air-cooling. Our findings offer insights toward further understanding of the link between the geometrical and orientation parameters of grains with respect to the deformation behaviour of oxide scales formed at elevated temperatures.