Recrystallization of a cold-rolled low-carbon steel by cold-plasma-discharge rapid annealing
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Recrystallization of a Cold-Rolled Low-Carbon Steel by Cold-Plasma-Discharge Rapid Annealing JOËLLE STOCKEMER and PIERRE VANDEN BRANDE A new annealing technology has been developed by the authors in order to conduct fast steel annealing. This process consists of steel heating by cold-plasma discharge. It allows the opportunity for new annealing cycles with higher heating rates (up to 300 K/s), shorter soaking times, and controlled cooling rates, so that well-recrystallized samples have been achieved in less than several seconds of total process time. This article reports the influence of various parameters of the annealing cycle (heating rate, maximum annealing temperature, and cooling rate) on the recrystallization and properties of a cold-rolled low-carbon steel. This study shows that the annealing time can be significatively reduced using this new technology, compared to the industrial continuous annealing technology used today, to obtain equivalent metallurgical properties.
I. INTRODUCTION
THE steel annealing process has been improved during the last 50 years, with a considerable annealing-time decrease. Nowadays, two different processes are commonly used in the industry: batch annealing and continuous annealing. The process-time decrease brought by the continuous annealing is a consequence of the heating-rate and coolingrate increase, as well as the soaking-time decrease. Numerous publications report recrystallization studies vs annealing cycle in an attempt to shorten the total process time by increasing the heating rate to several thousand K/s.[1–6] The influence of heating rate on the maximum temperature necessary to fully recrystallize steel is not yet completely understood. Some publications report an increase of this maximum temperature with the heating-rate increase,[1,2,3] while others report no influence[4] or a decrease of the maximum temperature.[5,6] In the same way, the influence of the heating rate on the recrystallization texture development is still not generally accepted.[7,8,9] During recrystallization, nucleation and growth are responsible for the steel-properties evolution (e.g., texture development). These processes have been the subject of numerous publications trying to demonstrate if there were oriented mechanisms and to which extent each mechanism contributed to the recrystallization texture development.[10–19] It is generally accepted that oriented nucleation gives rise to nuclei development within high-stored-energy deformed grains, i.e., grains belonging to the γ fiber ({111}uvw) and grains of similar orientation ({554}110 and {554}225). This leads to a nucleation texture presenting a fiber whose skeleton line shows a curvature with respect to the ideal γ fiber.[10–13] On the other hand, the oriented growth is a consequence of the presence of high-mobility grain boundaries between deformed grains and nuclei. This mechanism leads to preferential growth of these nuclei and explains, for instance, the JOËLLE STOCKEMER and PIERRE VANDEN BRANDE are with Cold Plasma Applications,
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