According to the ISO3183 standard, a 7-furnace 1 t steel ingot is smelted in the laboratory by immersion method, and a tube is produced by forging, piercing, pipe jacking and tension reduction, and a thickness of 20 mm × 100 mm × 5 mm or a tube thickness test is taken on the steel pipe. The sample was immersed in a solution prepared according to the standard. After 96 h, it was taken out and rolled vertically to take a cross section. Three parameters (CLR, CTR, CSR) were calculated by the metallographic method to compare the HIC sensitivity.
2, Factors affecting HIC performance
2.1 Media factors
1) pH value. A large number of studies have shown that the sensitivity of hydrogen bubbling decreases with increasing pH in the range of pH 1-6. When pH>6, hydrogen bubbling does not occur [1].
2) H2S concentration. The higher the concentration of hydrogen sulfide, the greater the sensitivity of hydrogen bubbling.
3) Chloride ion. In the range of pH 3.5 to 4.5, the presence of Cl- increases the corrosion rate and increases the sensitivity of hydrogen bubbling.
4) Temperature. The CLR is the largest at 25 ° C, and the hydrogen bubbling sensitivity is the highest. When the temperature is lower than 25 ° C, the temperature rise causes the corrosion reaction and the hydrogen diffusion rate to increase, and the sensitivity of hydrogen bubbling increases. When the temperature is higher than 25 ° C, the sensitivity of hydrogen bubbling is lowered due to the decrease in the concentration of H 2 S.
5) Time. The test was carried out using 96 h as a comparison. Under normal circumstances, the degree of corrosion tends to be severe with the increase of test time.
2.2 Material factors
2.2.1 Effects of chemical composition
In the laboratory, a round of steel grades designed according to different grades was smelted. The specific components are shown in Table 1, and HIC immersion tests were carried out. From the surface of the sample after soaking, the bubbling area of B2, B6 and B7 was significantly more than that of B9 and B10. The results of crack sensitivity index are shown in Table 2. It can be seen from Table 2 that the anti-HIC performance of B2, B6 and B7 is significantly inferior to that of B9 and B10. In Table 1, B2, B6, and B7 steels do not contain Cu or Ni, while B9 and B10 steels contain Cu and Ni. It can be seen that the addition of Cu and Ni causes the corrosion product to form a protective film on the surface of the steel, which inhibits the corrosion reaction of the surface, thereby reducing the escape of hydrogen, reducing the entry of hydrogen from the environment into the steel matrix, and reducing the hydrogen drum. Foam sensitivity increases anti-HIC performance, which is in good agreement with Oriani's findings [2], and Oriani also pointed out that only 0.2% Ni and greater than 0.2% Cu can produce effects.
2.2.2 Effect of sulfur content in steel
The chemical composition of the two steel grades B2 and D2 is almost the same, except that the S content of D2 is much lower than that of B2. After soaking test (Table 3), it was found that the anti-HIC performance of D2 was much better than that of B2. It can be seen that improving the purity of the steel and reducing the sulfur content are beneficial to reduce the sensitivity of hydrogen bubbling. This is mainly due to the fact that hydrogen atoms are easily accumulated in the strips of MnS inclusions or alumina inclusions to form a large hydrogen pressure, resulting in internal bubbling inside the material, and hydrogen induced cracks along the stress perpendicular to the stress. The axial direction is stacked and arranged to form a chain-like bubble, and finally a stepped fracture. Therefore, reducing the sulfur content in the steel reduces the MnS formed, thereby reducing the sensitivity of hydrogen bubbling.
2.2.3 Effect of calcium treatment on HIC performance
The composition of B6 and C6 is equivalent, except that B6 is not treated with sprayed silicon calcium powder, and C6 is treated with Ca. B6 and C6 were simultaneously immersed in the artificial seawater solution specified by TM0284 for 96 h. It was found that the surface area of C6 was significantly reduced and no cracks were generated. The specific HIC test results are shown in Table 4. It can be seen from Table 4 that the corrosion resistance of the steel treated with Ca is significantly better than that of the steel without Ca treatment. This is mainly caused by the change of the shape of the sulfide and oxide inclusions after the treatment of the silicon-silicate powder, and the concentrated corner inclusions become dispersed particles, thereby reducing the sensitivity of hydrogen bubbling and improving the resistance. HIC performance.
3, Conclusion
1) The media factors affecting HIC performance are pH, H2S concentration, chloride ion, temperature and time.
2) The addition of Cu and Ni can improve the anti-HIC performance.
3) Reducing the S content in the steel and improving the purity of the steel can reduce the sensitivity of hydrogen bubbling.
4) Spraying silicon calcium powder is one of the most effective measures to reduce hydrogen bubbling sensitivity.