Materials Performance

JUN 2016

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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Page 52 of 100

50 JUNE 2016 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 55, NO. 6 MATERIALS SELECTION & DESIGN A The stress corrosion behavior of S355 steel in 3.5% sodium chloride (NaCl) solution was investigated with slow strain rate testing. The fracture mor- phologies of stress corrosion cracking and chemical compositions of corro- sion products were analyzed with a scanning electron microscope and energy dispersive spectrometer, re- spectively. The results showed that the stress corrosion susceptibility in- dex of S355 steel in 3.5% NaCl solu- tion was 12.5%, with no signifcant stress tendency; and the fracture was caused by a combination of mechani- cal stress and chemical corrosion. When secondary cracks appeared, the stress corrosion resistance de- creased and the section was reduced by 9.8%. As a low-alloy steel, S355 is extensively used in marine engineering structures, w hich require high-strength structural steel 1-2 and subject it to long-term tensile stresses. In complex marine environments, S355 is easily corroded by Cl – . 3 Test results h av e sh ow n th at th e hi g h er a st e el 's strength, the higher its stress corrosion sensitivity will be. Research on the stress corrosion of S355 steel is one of the most important topics in the field of marine plat- form security. At present, research on S355 steel is still in its initial stage. The proper- ties of S355 steel welded joints have been reported, 4-5 but research on sensitive frac- ture has not been carried out. Therefore, the slow tensile stress corrosion behavior of S355 steel in sodium chloride (NaCl) solutions has practical significance. 6 The stress fracture behavior of S355 steel in 3.5% NaCl solution was studied with a slow strain rate tensile test (SSRT). The fracture morphologies were observed and the fracture mechanism was investi- gated. This provided a theoretical basis for S355 steel use on marine platforms. Experimental Procedures The experiment used European stan- dard S355 structural steel with the follow- ing chemical composition ( by mass %): 0.17% C, 0.94% Mn, 0.55% Si, 0.30% Mo, 0.065% Cr, 0.065% Ni, 0.15% Zr, 0.035% S, and the remainder Fe. The mechanical properties of S355 steel are as follows: ten- sile strength ≥345 MPa, yield strength of 470 to 630 MPa, and elongation ≥20%. SSRT was conducted on a WDML-3 type SST † stress corrosion testing machine. The test was conducted in 3.5% NaCl solution and at atmospheric pressure. The tempera- ture was 25 ± 1 °C and the strain rate was 5 × 10 –6 . The length of the samples was 200 mm, and the standard distance and di- ameter were 25.4 mm and 6.35 ± 0.01 mm, respectively, when fully immersed in the 3.5% NaCl solution. After the samples were broken, the fractures were washed with ac- etone and ultrasonically cleaned. The mor- Slow Tensile Stress Corrosion Behavior of S355 Steel in 3.5% NaCl Solution Kong dejun, Jiangsu Key Laboratory of Materials Surface Science and Technology, Changzhou University, Changzhou, P.R. China Sheng Tianyuan, Jiangsu Key Laboratory of Materials Surface Science and Technology, Changzhou University, Changzhou, P.R. China † Trade name.

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