It is important that the material used to produce high-integrity pressure vessels has homogeneous properties which are reproducible and within specification. Most heavy pressure vessels comprise large forgings derived from ingots, and are consequently affected by the chemical segregation that occurs during ingot casting. Of particular concern are the compositional variations that arise from macrosegregation, such as the channels of enriched material commonly referred to as A-segregates. By causing corresponding variations in microstructure, the segregation may be detrimental to mechanical properties. It also cannot be removed by any practically feasible heat treatments because of the large scale on which it forms. Here we describe an investigation on the consequences of macrosegregation on the development of microstructure in a pressure-vessel steel, SA508 Grade 3. It is demonstrated that the kinetics of transformation are sensitive to the segregation, resulting in a dramatic spatial variations in microstructure. It is likely therefore that some of the scatter in mechanical properties as observed for such pressure vessels can be attributed to macroscopic casting-induced chemical segregation.
The Consequences of Macroscopic Segregation on the Transformation Behavior of a Pressure-Vessel Steel
Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received July 26, 2013; final manuscript received January 6, 2014; published online February 27, 2014. Assoc. Editor: Osamu Watanabe.
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Pickering, E. J., and Bhadeshia, H. K. D. H. (February 27, 2014). "The Consequences of Macroscopic Segregation on the Transformation Behavior of a Pressure-Vessel Steel." ASME. J. Pressure Vessel Technol. June 2014; 136(3): 031403. https://doi.org/10.1115/1.4026448
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