Influence of strain-induced phase transformation on the surface crystallographic texture in cold-rolled-and-aged austeni
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I. INTRODUCTION
AUSTENITIC stainless steels (SSs) are important as a class of industrial metallic alloys because of their resistance to corrosion (by many of the chemicals and gases used in the industry in the presence or absence of stress), high temperature, and cyclic loading. Basically, they are alloys of Cr, Ni, and C with varying amounts of other elements such as Mo, Ti, Nb, W, etc. Among these, the steels based on 304 SS and 316 SS are more common. Such steels typically contain 18 to 20 pct Cr, 8 to 10 pct Ni, and 0.08 pct C in their normal varieties and 0.03 pct in the low-carbon varieties.[1] Austenitic SS is mainly used in process industries such as the nuclear, chemical, fertilizer, and petrochemical industries in the form of pipes, tubes, vessels, and plates. The SSs having large amounts of expensive alloying elements are considered high-value items. For this and because the SS components function as important modules in a plant, special care is needed during the fabrication of the SS components. During fabrication, the SS materials are subjected to various schemes of thermomechanical treatment and welding designed to impart suitable properties in the components, as mentioned earlier. Weldability and formability are the two important attributes that the SS materials should have. Preferred crystallographic orientations in the grains developed in a SS component are a natural consequence of the fabrication process, and it plays a very important role in giving the desired properties to the components. Therefore, studies on texture in various SS materials have been an important subject of investigation. Although the term “austenitic” implies that the austenitic SS is constituted of a single phase in the microstructure, the steels often behave as metastable alloys in which cold deforB. RAVI KUMAR and B. MAHATO are with the MST Division, National Metallurgy Laboratory, Jamshedpur – 831007, India. Contact e-mail: [email protected] N.R. BANDYOPADHYAY, Professor, is with the MN Dastur School of Materials Science, Bengel Engineering College, Howrah, India. and D.K. BHATTACHARYA, Deputy Director, is with Central Glass & Ceramics Research Institute, Kolkata, India. Manuscript submitted September 2, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
mation and/or high-temperature exposure leads to the formation of a second phase. For example, in a type 304 SS, the austenite phase transforms to - or a¿-martensite phase either by subzero temperature quenching or by plastic deformation.[2–4] On the other hand, in a type 316 SS, cold deformation or subzero treatment does not lead to any significant second-phase formation. The properties of SSs are affected by a combination of various microstructural features, namely, the dislocation density and morphology, grain size and shape, grain-boundary susbstructure, types of various phases, texture, etc.[6] In the case of 304 SS, the changes in the various features will be important during the cold deformation, when the martensite phase forms from austenite, as well as during th
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