Effect of Cooling Rate on Oxidation Behaviour of Microalloyed Steel

Xiang

et al. 2014

AMR

Self Cite

The composition and phase transformation of oxide scale in cooling process (after hot rolling) of rolled microalloyed steels affect tribological features of rolled strip and downstream process, and the produced steel surface quality. In this study, physical simulation of surface roughness transfer during cooling process with consideration of ultra fast cooling (UFC) was carried out in Hille 100 experimental rolling mill, the obtained oxide scale was examined with SEM to show its surface and phase features. The results indicate that the surface roughness of the oxide scale increases as the final cooling (coiling) temperature increases, and the flow rate of the introduced air decreases. The cracking of the surface oxide scale can be improved when the cooling rate is 20 °C/s, the strip reduction is less than 12%, and the thickness of oxide scale is less than 15 μm, independent of the surface roughness. A cooling rate of more than 70 °C/s can increase the formation of retained wustite and primary magnetite precipitates other than the precipitation of α-iron. This study is helpful in optimising the cooling process after hot rolling of microalloyed steels to obtain quality surface products. KeywordsOxide scale, Surface roughness, Ultra fast cooling, Microalloyed steel, Tribology Abstract. The composition and phase transformation of oxide scale in cooling process (after hot rolling) of rolled microalloyed steels affect tribological features of rolled strip and downstream process, and the produced steel surface quality. In this study, physical simulation of surface roughness transfer during cooling process with consideration of ultra fast cooling (UFC) was carried out in Hille 100 experimental rolling mill, the obtained oxide scale was examined with SEM to show its surface and phase features. The results indicate that the surface roughness of the oxide scale increases as the final cooling (coiling) temperature increases, and the flow rate of the introduced air decreases. The cracking of the surface oxide scale can be improved when the cooling rate is 20 C/s, the strip reduction is less than 12 %, and the thickness of oxide scale is less than 15 µm, independent of the surface roughness. A cooling rate of more than 70 C/s can increase the formation of retained wustite and primary magnetite precipitates other than the precipitation of α-iron. This study is helpful in optimising the cooling process after hot rolling of microalloyed steels to obtain quality surface products. IntroductionMicroalloyed steels are widely used in various structures and automotive components. Promising potential for the Ni-V-Ti microalloyed steels lies in the tight oxide scale formed on the surface of hot-rolled strip due to thermal oxidation at elevated temperature [1][2][3][4]. The tight oxide scale is expected to deform with steel substrate without cracking, and may act as self-lubricant at tribological contact surfaces between the workpiece and tool during downstream processing [5,6]. Thus lower shear strength, good adhesion and den...

Section: Methodsmentioning

confidence: 99%

Tribological Analysis of Oxide Scales during Cooling Process of Rolled Microalloyed Steel

Xiang

et al. 2014

AMR

Self Cite

“…Full details of the experimental instruments can be found elsewhere [20,21]. The following procedure was carried out for every HR-AC test.…”

Section: Materials and Hr-ac Testsmentioning

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

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.

“…Flat steel sheets (400 × 100 × 3 mm 3 ) with an average surface roughness of about 0.5 µm were hot rolled on a 2-high Hille 100 experimental mill combined with an accelerated cooling system. Full details of the experimental instruments can be found elsewhere [39,40]. The following procedure was conducted for every HR-AC test.…”

Section: Materials and Hr-ac Testmentioning

confidence: 99%

Effects of grain boundaries in oxide scale on tribological properties of nanoparticles lubrication

et al. 2015

Wear

The characters of grain boundaries in oxide layers formed on substrates influence adhesion and friction behaviour, surface fracture and wear during high temperature steel processing. In this work, an electron backscattered diffraction (EBSD) analysis was conducted to investigate the role of surface grain boundary and orientation in magnetite (Fe 3 O 4 )/haematite (α-Fe 2 O 3 ) scale during hot rolling, and further evaluate their effects on tribological properties of water-based nanoparticles lubrication. The results demonstrate that Fe 3 O 4 (100) plane is strongly sensitive to the surface characteristics as the minimisation of surface energy. Coincident site lattice (CSL) boundaries in microstructure is in presence of Σ3 in the Fe 3 O 4 and Σ13b in the Fe 2 O 3 of the substrates subjected to a thickness reduction of 28% and cooling rate of 28 ° C/s. This is due in great part to the changes in crystal slip systems. These low-Σ CSL boundaries in oxide scale offer obstacles to the propagation of cracks, where some of nanoparticles collected would be trapped at the interface and thereby may cause high wear rates. A lubrication mechanism is proposed to explain the grain boundary effect on nanoparticles lubrication, and further to determine the dependence of frictional behaviour on surface energy, crystallographic preferred orientation (microtexture) and crystal structure. These results provide an intriguing new insight into the application of water-based lubricant with graphite nanoparticles. AbstractThe characters of grain boundaries in oxide layers formed on substrates influence adhesion and friction behaviour, surface fracture and wear during high temperature steel processing. In this work, a thickness reduction of 28% and cooling rate of 28 °C/s. This is due in great part to the changes in crystal slip systems. These low-Σ CSL boundaries in oxide scale offer obstacles to the propagation of cracks, where some of nanoparticles collected would be trapped at the interface and thereby may cause high wear rates. A lubrication mechanism is proposed to explain the grain boundary effect on nanoparticles lubrication, and further to determine the dependence of frictional behaviour on surface energy, crystallographic preferred orientation (microtexture) and crystal structure. These results provide an intriguing new insight into the application of water-based lubricant with graphite nanoparticles.