Simulated hot working, cold working,
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I.
INTRODUCTION
THE significant influence that precipitation can have on restoration processes, such as recovery and recrystallization, is well established and has been exploited commercially in many alloy systems. For example, the "controlled" hot rolling of Nb-, V-, or Ti-containing microalloyed steels imparts attractive properties to the material in the as-hot-rolled condition, and this is achieved by preventing austenite recrystallization and grain growth through careful manipulation of the carbonitride precipitation behavior. Iq Aluminum is not usually thought of as a microalloying element in steel, but the precipitation of A1N can influence the properties at least as significantly as Nb, V, or Ti additions. Among other effects, A1N precipitation has been implicated in the inhibition of recrystallization during the annealing of cold-worked material, as well as the promotion of crystallographic textures favorable for deep drawing. A recent detailed review of A1N in steel is provided in Reference 2. High-temperature torsion testing has been established as a convenient laboratory method of studying precipitation behavior in microalloyed steels during hot working. This is because the high strains typical of most industrial metal working operations can be readily attained. Torsion testing has been used particularly effectively to simulate the main metallurgical aspects of the hot rolling of microalloyed steel plate and strip, providing useful information for optimizing alloy compositions and roll pass designs. [3-6] The present article summarizes a recent study of the effects of changing the hot-working, cold-working, and annealing parameters on the interaction between A1N precipitation and recrystallization in low-carbon steels containing significant amounts of A1 and N. The primary T.M. MACCAGNO, Research Associate, S. YUE, Associate Professor, and J.J. JONAS, Professor, are with the Department of Metallurgical Engineering, McGill University, Montreal, QC, Canada H3A 2A7. K. DYCK, Supervisor of Metallurgical Services, is with the Ivaco Rolling Mills Division of Ivaco Inc., L'Orignal, ON, Canada. Manuscript submitted September 30, 1992. METALLURGICAL TRANSACTIONS A
aim of the work was to determine whether torsion testing can also be helpful in studying precipitation behavior in Al-containing steels. The approach taken was first to establish the baseline annealing behavior of material that was hot- and cold-worked in a mill and then to compare this with the behavior of material that was hot- and coldworked in the lab by torsion testing. II. H O T AND C O L D W O R K I N G UNDER INDUSTRIAL CONDITIONS
A. Inhibition of Recrystallization by AIN Precipitation When steels containing significant amounts of A1 and N are cold-worked, the strength of the material is increased by strain hardening, and annealing is normally expected to restore the microstructure to the undeformed condition by recovery and recrystallization, t7] However, very fine (submicron) precipitates of A1N can impede recrystallization by pinning the g
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