Research Papers

The Corrosion Behavior of 9Cr Ferritic–Martensitic Heat-Resistant Steel in Water and Chloride Environment

[+] Author and Article Information
Z. Zhang, Z. F. Hu

School of Materials Science and Engineering,
Tongji University,
Shanghai 201804, China

P. M. Singh

School of Materials Science and Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332-0245

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received July 31, 2014; final manuscript received April 17, 2015; published online May 8, 2015. Assoc. Editor: Georges Cailletaud.

J. Eng. Mater. Technol 137(3), 031009 (Jul 01, 2015) (7 pages) Paper No: MATS-14-1156; doi: 10.1115/1.4030430 History: Received July 31, 2014; Revised April 17, 2015; Online May 08, 2015

The corrosion behavior of 9Cr ferritic–martensitic heat-resistant steel was investigated in water and chloride environment at room temperature (RT). The results of linear polarization, electrochemical impedance spectroscopy (EIS), and potentiodynamics (PD) polarization tests on long-term exposure show that 9Cr ferritic–martensitic steel has weaker corrosion resistance and greater pitting corrosion tendency in higher chloride concentrations. Corresponding scanning electron microscopy (SEM) observation displays that higher concentration chloride promotes the pitting initiation. During long-term exposure, pitting susceptibility decreases, the average pit size increases, and the density declines in higher chloride concentrations. Pits in the grains and along the grain boundaries are observed by optical microscope (OM), and it indicates that inclusions in grains and carbide particles at grain boundaries are the sites susceptible to pitting initiation.

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Fig. 1

Metallurgical structure and schematic diagram of P92 steel-tempered martensite [8,9]

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Fig. 2

OCP evolution with time under various NaCl concentrations

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Fig. 3

LPR evolution with time under water and different NaCl concentrations

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Fig. 4

The Nyquist plots of P92 steel during 296 hr immersion in water and various NaCl concentrations: (a) distilled water, (b) 1.0% NaCl, and (c) 3.5% NaCl

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Fig. 5

The Bode plots of P92 steel immersed in different NaCl concentrations: (a) 1.0% NaCl and (b) 3.5% NaCl

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Fig. 6

Rp as a function of time. Rp resistance was calculated using Rp = R1 + R2, where R1 and R2 were parameters from the fitting procedure of P92 steel chloride solutions, as indicated.

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Fig. 7

(a) PD for P92 steel before exposure in water and chloride solution and (b) PD after 22 days exposure

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Fig. 8

The breakdown potentials Ebd as a function of NaCl content

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Fig. 9

The macroscopic profile of surface of specimen after 22 days immersion in water and chloride solutions: (a) distilled water, (b) 1.0% NaCl solution, and (c) 3.5% NaCl solution

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Fig. 10

Scanning electron micrographs of P92 steel after 22 days immersion in water and chloride solutions: (a) distilled water; (b) 1.0% NaCl solution; and (c) and (d) 3.5% NaCl solution

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Fig. 11

Metallographic microstructure of P92 steel after 22 days immersion in chloride solutions: (a) and (c) 1.0% NaCl solution and (b) and (d) 3.5% NaCl solution




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