EH40 Stress Corrosion Data

Test materialsThe experimental material in the paper was marine EH40 steel, with a yield strength of 410 MPa and a tensile strength of 559 MPa.The metal matrix was etched using a 25% nitric acid aqueous solution, followed by metallographic observation under room temperature. The metallographic image of EH40 steel was presented in Fig.1. The light brownish-yellow structures were the ferrite matrix phase, while the gray-black structures were lamellar pearlite. The distribution of these phases was relatively homogeneous, and the proportion of the pearlite was approximately 25%.Fig.1 Microstructure of EH40 steelCorrosion weight loss testThe effect of typical polar environments on the corrosion rate of EH40 steel was investigated by corrosion test. The specimens were designed according to the NACE TM0169/G31 standard, with a length, height and thickness of 25 mm × 50 mm × 3 mm, , as shown in Fig.2.(a) Dimensions of test pieces (mm)(b) Test specimenFig.2 Corrosion weightlessness hanging piece specimensIn order to simulate typical polar environments, a high-precision temperature-controlled tank and a constant-temperature system were used to regulate the test temperature. The test container was placed in the constant-temperature water tank, and the specimens were suspended in the solution using nylon ropes. The main test surface of each specimen was placed vertically with a minimum distance of 10 mm between adjacent specimens and between the specimen and the inner wall of the container. A schematic diagram of this test setup is shown in Fig.3.Fig.3 Schematic diagram of coupon corrosion test1 day, 2 days, 4 days, 10 days, 20 days, and 30 days were selected to investigate the time-dependent characteristics of the corrosion rate. Three parallel specimens were prepared for each cycle to minimize experimental errors. The specimens were weighed using a high-precision balance. The corrosion rate was calculated from the mass loss of the specimens before and after the experiment. To obtain the quality loss, special treatment was required for the specimens after the test, and the treatment method was as follows.First, the loose corrosion products were removed from the specimen surface with clean water and a soft brush. The dense corrosion products were then cleaned with an acidic solution and an ultrasonic cleaner. The acid cleaning solution was mixture of 500 mL of HCl (ρ = 1.19 g/mL) and 5 g of 1,3-dibutyl-2-thiourea and diluted with distilled water to a total volume of 1000 mL. The specimens were rinsed sequentially with distilled water and anhydrous ethanol, and dried in an oven.Electrochemical testElectrochemical tests were employed in this paper to investigate the corrosion characteristics of EH40 steel in typical polar environments. The specimens were dimensions of 25 mm × 40 mm × 3 mm, and the corrosion reaction surface was 25 mm × 40 mm. The non-test surfaces were sealed with epoxy resin, and electrical contact was established by spot-welded wires, as shown in Fig.4. 3 parallel specimens were used for each test.(a) Specimen processing size(mm)(b)Test specimenFig.4 Electrochemical test specimensThree-electrode system were used for electrochemical tests, with a saturated calomel electrode (SCE) as the reference electrode, a Pt electrode as the auxiliary electrode, and the specimen as the working electrode. The test temperature was regulated by a temperature-controlled tank and a constant-temperature water bath system. Corrtest CS310M was used to measure the linear polarization curves (potential range ±10 mV vs. OCP, scan rate 0.1 mV/s), Tafel polarization curves (potential range ±200 mV vs. OCP, scan rate 0.1 mV/s), and electrochemical impedance spectra (frequency range10 mHz-10 kHz, AC excitation amplitude 5 mV), as shown in Fig.5.Fig.5 Electrochemical test diagramSlow strain rate tensile testSSRT tests were conducted on EH40 steel under different typical polar environments according to GB/T 15970.7. The dimensions of the test specimens were shown in Fig.6. The specimens were polished using sandpaper to eliminate the influence of surface conditions on the test results.Fig.6 Specimen size diagramThe SSRT tests were performed using an RPL100 creep-fatigue testing machine with a maximum load capacity of 100 kN and a measurement error of ±0.5%. The test temperature was regulated by a low-temperature-controlled tank with the temperature range of -60°C to 10°C. The specific test setup was illustrated in Fig.7, where the lower end of the environmental tank was kept sealed to prevent leakage.Fig.7 SSRT testing deviceThe specimens were pre-corroded in the corrosive solution for 12 hours before the SSRT test. During the test, the strain rate was set to . The elongation and shrinkage of the specimens were obtained after the experiment. The fractured sections of the specimens were cut off, and the corrosion products on the fractured sections were removed with a rust-removing solution. The fractured sections were rinsed with deionized water and acetone. After drying, the fractured sections were subjected to SEM to examine the surface morphology, fracture characteristics, and crack patterns.