Browsing by Subject "hot rolling"

Now showing 1 - 4 of 4

Access status: Open Access ,
Mechanical properties and structure evolution of the AZ91 magnesium alloy after hot rolling and annealing
(2015) Sułkowski, Bartosz; Boczkal, Grzegorz
The AZ91 magnesium alloy was processed up to 87.5% of total thickness reduction in several thermodynamic routes, consisted of hot rolling and intermediate annealing. The hot-rolling process was performed at a high strain rate equal to 1.6 s−1 and at a temperature of 430°C. The intermediate annealing was performed at 430°C for 15 minutes after each route. It was found that, during hot rolling, the hardness of the material increased from 32 HV to 40 HV, and the structure investigations showed a huge amount of twins formed inside the grains (which were not observed after annealing). Tensile tests have shown strong anisotropy in mechanical properties of the “as-rolled” samples dependent onthe orientation between tension direction (TD) and rolling direction (RD). The samples with TD perpendicular to RD provedhigher ultimate tensile strength (UTS) and (on the other hand) worse plastic properties as compared to the samples with TD parallel to RD. The annealing has an effect on the reduction of mechanical properties anisotropy. X-ray investigations have shown texture changes from the basal type with the additional (0001) <1120> component for “as-rolled” samples to the texture with the main (0001) <1010> component for annealed samples. The texture changes had a great impact on the anisotropy of mechanical properties of the investigated AZ91 magnesium alloy.
Access status: Open Access ,
Scaling behaviour of Si-alloyed steel slabs under reheating conditions
(AGH University of Science and Technology Press, 2021) Mikl, Gregor; Höfler, Thomas; Gierl-Mayer, Christian; Danninger, Herbert; Linder, Bernhard; Angeli, Gerhard
Reheating of steel slabs for further processing such as hot rolling usually takes place in gas-fired pusher furnaces. Temperatures well above 1000°C, combined with an atmosphere containing $H_{2}O$, $CO_{2}$, and $O_{2}$, lead to substantial oxidation of most steel grades. Newly developed advanced steels often contain significant amounts of Si. This element plays a dominant role in the scaling behaviour near the steel-scale-interface, since fayalite $(Fe_{2}SiO_{4})$ forms a eutectic with wuestite $(Fe_{1-x}O)$ that melts as low as 1177°C. To better understand the high temperature oxidation behaviour, lab-scale trials were performed with different steel grades containing up to 3 wt.% Si. Possible interactions of Si with other alloying elements present in the samples such as Cr, Mn and Al were also of interest. The atmosphere contained 20% $H_{2}O$, 7% $CO_{2}$, and 3% $O_{2}$, resembling reheating conditions in pusher furnaces, and temperatures ranged from 1100 to 1240°C. For metallographic investigation, the oxidised samples were cold mounted under vacuum using taper section angles. After preparation, the sections were examined through light microscopy, SEM/EDS, XRD, and TEM. The local distribution of the alloying elements could be mapped efficiently, and phase identification was successful in most parts. Under the applied experimental conditions, the elements of interest were present in their oxidic form either as pure or as mixed oxides. Higher Si-contents led to an increased build-up of eutectic melting phase at the steel-scale-interface at temperatures above 1177°C, which in turn further accelerated the oxidation.
Access status: Open Access ,
Structure and properties of hot-rolled and annealed AZ61 magnesium alloy
(2017) Sułkowski, Bartosz
Magnesium alloy AZ61 was processed by hot rolling up to a large thickness reduction (~89%) in several routes with intermediate annealing. The hot rolling process was conducted at 450°C and at a 1.5 s−1 strain rate. The structure and texture evolution as well as the mechanical properties during processing were investigated. The structure studies showed that, during the hot-rolling process, a large number of twins formed, which had an impact on the mechanical properties of the hot-rolled samples. After annealing for 15 minutes, the twins were no longer observed in the annealed samples, causing a significant decrease in hardness. Moreover, an investigation of the hardness showed that annealing for 15 minutes did not remove all of the hardening effects nor did the hardness of the annealed samples decrease to the value before hot rolling. The texture investigations showed that the texture of the hot-rolled samples was a typical basal-type texture. However, the basal pick was split into two tilted towards the rolling direction (RD). The texture changed during annealing while the new strong texture components evolved. The annealing led to an increased intensity of <1010>{1120} texture component and enhanced ductility. It was concluded that the texture changes observed in the present investigations may lead to the enhanced ductility of magnesium alloys and, therefore, help us design a deformation scheme for magnesium alloys consisting of several thermomechanical routes.
Access status: Open Access ,
Thermal-mechanical finite element simulation of flat bar rolling coupled with a stochastic model of microstructure evolution
(Wydawnictwa AGH, 2022) Szeliga, Danuta; Czyżewska, Natalia; Kusiak, Jan; Kuziak, Roman; Morkisz, Paweł M.; Oprocha, Piotr; Pietrzyk, Maciej; Piwowarczyk, Michał; Poloczek, Łukasz; Przybyłowicz, Paweł; Rauch, Łukasz; Wolańska, Natalia
It is generally recognized that the kinetics of phase transformations during the cooling of steel products depends to a large extent on the state of the austenite after rolling. Austenite deformation (when recrystallization is not complete) and grain size have a strong influence on the nucleation and growth of low-temperature phases. Thus, the general objective of the present work was the formulation of a numerical model which simulates thermal, mechanical and microstructural phenomena during multipass hot rolling of flat bars. The simulation of flat bar rolling accounting for the evolution of a heterogeneous microstructure was the objective of the work. A conventional finite-element program was used to calculate the distribution of strains, stresses, and temperatures in the flat bar during rolling and during interpass times. The FE program was coupled with the stochastic model describing austenite microstructure evolution. In this model, the random character of the recrystallization was accounted for. Simulations supplied information about the distributions of the dislocation density and the grain size at various locations through the thickness of the bars.