High temperature grain growth during slab reheating of oriented 3 pct Si-Fe made using continuous casting
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INTRODUCTION
IN the manufacture of grain oriented 3 pct silicon-iron products with (110) [001 ] or Goss orientation, two essential provisions must be met to foster the process of secondary grain growth. First, a grain growth inhibitor such as MnS, MnSe, or AIN in the form of small, dispersed inclusions or solid solution inhibitors such as Sb, B, or N ~ is needed to restrain primary grain growth in the early portion of the final anneal. Second, a suitable structure of completely recrystallized grains with a sufficient number of these grains having a cube-on-edge orientation must be present prior to the final anneal.2 These two factors in turn are affected by the slab reheating and hot rolling processes. In the typical processes used for slab reheating and hot rolling of oriented 3 pct silicon-iron, slabs or ingots are reheated to temperatures near 1400 ~ prior to roughing and finish hot rolling. These unusually high temperatures are employed to dissolve rapidly the grain growth inhibitors which are subsequently reprecipitated as a fine dispersion of particles during hot rolling. While the primary concern at this step is to establish a suitable inhibitor, the grain structure is also beginning its evolution. To a great extent, after hot rolling is completed, little can be done to offset the effects of hot rolling on either the inhibitor or the grain structure of the hot rolled strip. Goss oriented 3 pct siliconiron products have been produced since the 1950's using ingot casting. The processing of these products had developed such that stable and complete secondary grain growth could be obtained, providing a product with good and consistent magnetic quality. During the 1970's most producers of oriented 3 pct silicon iron converted to continuous (or strand) casting as the means of producing slabs. However, the initial attempts to produce high quality (110) [001] oriented 3 pct silicon iron with continuous casting resulted in a product with highly variable and generally J. W. SCHOEN is Senior Research Engineer with Armco Inc., Research and Technology, Middletown, OH 45043. This paper is based on a presentation made at the symposium "Physical Metallurgy of Electrical Steels" held at the 1985 annual AIME meeting in New York on February 24-28, 1985, under the auspices of the TMS Ferrous Metallurgy Committee. METALLURGICAL TRANSACTIONS A
poorer texture than the ingot processes. 3 The nonuniformity of the product made by continuous casting consisted of normal (110)[001] oriented grains interspersed with "streaks" of small, poorly oriented grains. Littmann reported that the results obtained with continuous casting were caused by an inordinantly large grain size, about 25 mm, which developed when the slabs were reheated above 1280 ~ For comparison, the grain size in slabs rolled from ingots was much smaller, about 10 mm, after similar reheating. 3,4 The larger grain size was found to produce large, elongated grains in the hot rolled structure which resulted in a more irregular recrystallized grain size at each step in pr
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