Microstructure and crystallographic texture of strip-cast and hot-rolled austenitic stainless steel
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I.
INTRODUCTION
F L A T products of austenitic stainless steels are conventionally manufactured by continuous casting, hot rolling, subsequent cold rolling, and final recrystallization. Recent progress in strip-casting technology, tl,:] however, provides three main improvements in comparison to the customary processing method. First, it supplies an austenitic steel band with the same thickness and width as that which is produced by hot rolling. This permits the entire hot-rolling process to be bypassed. Second, the weak initial crystallographic texture of the strip-cast steel, which predetermines the deep drawing properties and strength of the final sheet as well as its weak through-thickness texture gradient, is responsible for a more homogeneous behavior when compared to hot-rolled sheets.t3"4] Third, it is not economical to produce small amounts of highly alloyed stainless steels by continuous casting and hot rolling. Strip casting is therefore likely to be a competitive method in the production of stainless steel sheets. Whereas the texture and microstructure of cold rolled and recrystallized austenitic stainless steels have already been subject to detailed investigations in the past (e.g., References 5 and 6), the corresponding microstructural features resulting from the recently introduced strip-casting technology as well as from the hot-rolling process have not yet been discussed in the literature. In the present work, therefore, the microstructure and crystallographic texture of a strip-cast sample were compared to those of a continuously cast and subsequently hot-rolled specimen. Both types of samples had a chromium (Cr) content of 18 wt pct and a nickel (Ni) content of 8.5 wt pct (Table I). The microstructure and texture were measured with high local resolution through the sheet thickness of both materials. D. RAABE, Group Head, Research Group "Computer Simulation," is with the Institut f'tir Metallkunde und Metallphysik, RWTH Aachen, 52056 Aachen, Germany. Manuscript submitted June 9, 1994. METALLURGICAL AND MATERIALS TRANSACTIONS A
II.
EXPERIMENTAL PROCEDURE AND MEASUREMENT OF C R Y S T A L L O G R A P H I C TEXTURES
A. Processing of the Samples The hot rolling of the austenitic stainless steel (Table I) was industrially carded out after continuous casting, slab reheating, and initial reversing hot rolling in a conventional hot-strip mill, where the band is unidirectionally deformed in seven subsequent rolling passes. The temperature was between 1420 and 1470 K during the first hot-rolling pass and between 1050 and 1200 K during the last pass. The thickness of the hot band was 2.2 mm. The austenitic strip cast samples (Table I) were industrially produced by casting liquid steel into a preheated tundish, which contacts two rotating, water-cooled steel rolls. The two casting rolls with different diameters are located in an "eleven o'clock position." The steel solidifies as a thin film on the roll surfaces. The process is controlled in such a way that the contact length between the liquid metal and th
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