Research Of High Strength Steel Welding Electrode For Repair Of Ultra-high Pressure Vessel

The application scope of ultrahigh pressure vessel is extremely broad, which plays a veryimportant role in the national economy and social production. However, the weld metal has poortoughness reserve when the high strength steel is used to manufacture ultrahigh pressure vessel. Inorder to improve the toughness reserve of the high strength steel’s weld metal, this thesis was basedon the C-Ni-Cr-Mo-V-Re alloy system, and a kind of high strength steel welding electrode of100kgwas developed, which had the same strength as high strength steel of ultrahigh high pressure vessel,but the former had higher toughness reserve. By changing the content of nickel, chromium,molybdenum and rare-earth yttrium oxide, microscopic structure and mechanical properties ofwelding electrode’s metal deposits were studied and explored.The microstructure observation, scanning electron microscope energy spectrum analysis, X-raydiffraction analysis and transmission electron microscopy were used to study the microscopicstructure of high strength steel welding electrode’s deposited metal. The result showed that, when thecontents of nickel, chromium, molybdenum and rare-earth yttrium oxide were3.5wt%,1.2wt%,0.6wt%and1.0wt%respectively, the electrode’s deposited metal had the best microscopic structure with alarge number of tiny and uniform distribution acicular ferrites and a small amount of tiny lowerbainites in the weld metal deposits.The approaches of tensile test, impulse test (20℃) and scanning electron microscope energyspectrum analysis were applied to study the mechanical properties of high strength steel weldingelectrode s deposited metal. The result showed that, when the contents of nickel, chromium,molybdenum and rare-earth yttrium oxide were3.5wt%,1.2wt%,0.6wt%and1.0wt%respectively,the electrode’s deposited metal had the same strength with parent metal; yield strength was1031MPa;tensile strength was1149MPa; the deposited metal’s elongation was23%; reduction of area was65%;impact absorbing energy was81J, and the fractograph was the typical ductile fracture with hightoughness reserve.By hardness testing, mercury determination of diffusible hydrogen and cracking sensitivity testwith oblique Y groove, the welding crack sensitivity of high strength steel welding electrode’sdeposited metal was studied. The result showed that, when the contents of nickel, chromium,molybdenum and rare-earth yttrium oxide were3.5wt%,1.2wt%,0.6wt%and1.0wt%respectively,the content of diffusion hydrogen of the electrode’s deposited metal was1.2ml/100g, which could meet the standards of ultra-low hydrogen. However, hardness and micro residual stressso was higherso that the weld metal deposits of the high strength steel had a certain welding crack rate.Comparing to high-strength steel electrode of J107and J107Cr usually used in the domesticmarket, high-strength steel electrode of this thesis had the best performance and the almost the samestrength value, and furthermore it had the higher toughness reserve, and lower welding cold crackingtendency.