Research Papers: Materials and Fabrication

Coalesced Martensite in Pressure Vessel Steels

[+] Author and Article Information
Hector Pous-Romero

Department of Materials Science & Metallurgy,
University of Cambridge,
Cambridgeshire CB2 3QZ, UK
e-mail: hp323@cam.ac.uk

Harry Bhadeshia

Department of Materials Science & Metallurgy,
University of Cambridge,
Cambridgeshire CB2 3QZ, UK
e-mail: hkdb@cam.ac.uk

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received July 24, 2013; final manuscript received December 4, 2013; published online February 27, 2014. Assoc. Editor: Marina Ruggles-Wrenn.

J. Pressure Vessel Technol 136(3), 031402 (Feb 27, 2014) (6 pages) Paper No: PVT-13-1121; doi: 10.1115/1.4026192 History: Received July 24, 2013; Revised December 04, 2013

An alloy commonly used for large pressure vessels, known as SA508 Grade 3, has a microstructure after heat treatment consisting of a mixture of tempered bainite and martensite at fast cooled regions near surfaces subject to water quenching. These two phases are conventionally recognized to consist of fine platelets, each of which is approximately 0.2 μm in thickness, enhancing strength and leading to good toughness properties. We have discovered in our experimental work that there are circumstances where the adjacent platelets of a similar orientation can coalesce as the austenite transforms, to produce much coarser structures which are believed to be detrimental to toughness. An examination of published micrographs reveals that such coalesced regions existed but were not noticed in previous studies. The mechanism of coalescence is described and methods to ameliorate the coarsening are discussed.

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Cogswell, D., Swan, D., Mitchell, R., and Garwood, S., 2010, “Materials and Structural Integrity Challenges for the Next Nuclear Generation,” 63rd Annual Assembly and International Conference of the International Institute of Welding.
Lee, B., Hong, J., Yang, W., Huh, M., and Chi, S., 2000, “Master Curve Characterization of the Fracture Toughness in Unirradiated and Irradiated RPV Steels Using Full- and 1/3-Size Pre-Cracked Charpy Specimens,” Int. J. Pressure Vessels Piping, 77, pp. 599–604. [CrossRef]
Bhadeshia, H. K. D. H., Keehan, E., Karlsson, L., and Andrén, H. O., 2006, “Coalesced Bainite,” Trans. Indian Inst. Metals, 29, pp. 689–694. Available at: http://citeseerx.ist.psu.edu/viewdoc/download?doi=
Pak, J. H., Bhadeshia, H. K. D. H., and Karlsson, L., 2012, “Mechanism of Misorientation Development Within Coalesced Martensite,” Mater. Sci. Technol., 28(8), pp. 918–923. [CrossRef]
Pak, J. H., Bhadeshia, H. K. D. H., Karlsson, L., and Keehan, E., 2008, “Coalesced Bainite by Isothermal Transformation of Reheated Weld Metal,” Sci. Technol. Weld. Joining, 13(7), pp. 593–597. [CrossRef]
Caballero, F. G., Chao, J., Cornide, J., García-Mateo, C., Santofimia, M. J., and Capdevila, C., 2009, “Toughness Deterioration in Advanced High Strength Bainitic Steels,” Mater. Sci. Eng. A, 525, pp. 87–95. [CrossRef]
Keehan, E., Bhadeshia, H. K. D. H., and Thuvander, M., 2008, “Electron Backscatter Diffraction Study of the Coalesced Bainite i High Strength Steel Weld Metals,” Mater. Sci. Technol., 24(10), pp. 1183–1188. [CrossRef]
Keehan, E., Karlsson, L., and Andrén, H. O., 2006, “Influence of Carbon, Manganese and Nickel on Microstructure and Properties of Strong Steel Weld Metal. Part 1—Effect of Nickel Content,” Sci. Technol. Weld. Joining, 11(1), pp. 1–8. [CrossRef]
Suzuki, K., 1982, “Neutron Irradiation Embrittlement of ASME SA508 Cl. 1 Steel,” J. Nucl. Mater., 109, pp. 443–450. [CrossRef]
Park, S. G., Kim, M. C., Lee, B. S., and Wee, D. M., 2010, “Correlation of the Thermodynamic Calculation and the Experimental Observation of Ni-Mo-Cr Low Alloy Steel Changing Ni, Mo, and Cr contents,” J. Nucl. Mater., 407, pp. 126–135. [CrossRef]
Hawthorne, J., 1985, “Composition Influences and Interactions in Radiation Sensitivity of Reactor Vessel Steels,” Nucl. Eng. Des., 89, pp. 223–232. [CrossRef]
Chang, L. C., and Bhadeshia, H. K. D. H., 1996, “Microstructure of Lower Bainite Formed at Large Undercooling Below Bainite Start Temperature,” Mater. Sci. Technol., 12, pp. 233–236. [CrossRef]
Pak, J. H., 2012, “Coalesced Bainite and Martensite,” Ph.D. thesis, GIFT, POSTECH, Pohang, South Korea.
Christian, J. W., 1958, “Accommodation Strains in Martensite Formation, the Use of the Dilatation Parameter,” Acta Metall., 6, pp. 377–379. [CrossRef]
Bhadeshia, H. K. D. H., David, S. A., Vitek, J. M., and Reed, R. W., 1991, “Stress Induced Transformation to Bainite in Fe-Cr-Mo-C Pressure Vessel Steel,” Mater. Sci. Technol., 7, pp. 686–698. [CrossRef]
Pak, J., Suh, D. W., and Bhadeshia, H. K. D. H., 2012, “Promoting the Coalescence of Bainite Platelets,” Scr. Mater., 66, pp. 951–953. [CrossRef]
Pous-Romero, H., Lonardelli, I., Cogswell, D., and Bhadeshia, H. K. D. H., 2013, “Austenite Grain Growth in a Nuclear Pressure Vessel Steel,” Mater. Sci. Eng., A, 567, pp. 72–79. [CrossRef]
Yang, H. S., and Bhadeshia, H. K. D. H., 2007, “Uncertainties in Dilatometric Determination of Martensite Start Temperature,” Mater. Sci. Technol., 23(5), pp. 556–560. [CrossRef]
Peet, M., and Bhadeshia, H. K. D. H., 1982, “Software for Transformations in Steels.” Available at: http://www.msm.cam.ac.uk/map/steel/programs/mucg83.html
Kim, S., Kang, S. Y., Oh, S. J., Kwon, S., Lee, S., Kim, J. H., and Hong, J. H., 2000, “Correlation of the Microstructure and Fracture Toughness of the Heat-Affected Zones of an SA508 Steel,” Metall. Mater. Trans. A, 31A, pp. 1107–1119. [CrossRef]
Kim, S., Im, Y.-R., Lee, S., Lee, H.-C., Kim, S.-J., and Hong, J. H., 2004, “Effects of Alloying Elements on Fracture Toughness in the Transition Temperature Region of Base Metals and Simulated Heat-Affected Zones of Mn-Mo-Ni Low Alloy Steels,” Metall. Mater. Trans., 35A, pp. 2027–2037. [CrossRef]
Kim, S., Im, Y.-R., Lee, S., Lee, H.-C., Oh, Y. J., and Hong, J. H., 2001, “Effects of Alloying Elements on Mechanical and Fracture Properties of Base Metals and Simulated HAZ of SA508 Steels,” Metall. Mater. Trans. A, 32A, pp. 903–911. [CrossRef]
Jang, H., Kim, J.-H., Jang, C., Lee, J. G., and Kim, T. S., 2013, “Low-Cycle Fatigue Behaviours of Two Heats of SA508 Gr. 1a Low Alloy Steel in 310 °C Air Deoxygenated Water—Effects of Dynamic Strain Aging and Microstructures,” Mater. Sci. Eng., A, 580, pp. 41–50. [CrossRef]
ASTM, 2004, “Standard Specification for Quenched and Tempered Vacuum-treated Carbon and Alloy Steel Forgings for Pressure Vessel Components A508A/A548M.”


Grahic Jump Location
Fig. 1

SEM of the SA508 Grade 3 studied in this work showing clear bimodal size distribution of martensitic plates. Sample austenitized at 1200 °C for 48 h and water quenched. The arrows indicate regions where structures have coalesced.

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Fig. 2

Austenite grain size revealed by thermal etching. (a) Austenitized at 860 °C for 1 h. (b) Austenitized at 1150 °C for 10 min. (c) Austenitized at 1200 °C for 48 h. Arrows point at thermal grooves defining austenite grain boundaries.

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Fig. 3

Dilatometric curves after austenitization at 1150 °C for 10 min, showing the transformation behaviour during continuous cooling at 4, 7, 10, and 30 °C s−1. Hardness Vickers (Hv) values are also shown.

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Fig. 4

SEM micrographs of SA508 Grade 3 steel austenitized at 1150 °C for 10 min showing coalesced martensite. (a) Cooled at 10 °C s−1, (b) cooled at 30 °C s−1, (c) high magnification image of (b) showing serrated edges.

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Fig. 5

Calculated driving force versus transformation temperature for SA508 Grade 3 steel calculated using MUCG83

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Fig. 6

Size differences in coalesced martensite plates for different austenitic grain sizes. (a) Austenitized at 860 °C for 1 h. (b) Austenitized at 1200 °C for 48 h.

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Fig. 7

Unnoticed case of coalesced martensite in the HAZ of a SA508 Grade 3 steel, resulting in an unexplained very low value of impact energy [22]

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Fig. 8

SEM micrographs of SA508 Grade 3 steel austenitized at 1150 °C for 10 min showing coalesced martensite after tempering



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