30N8K4KhMF (VKS-6) steel, design for replacing 30KhGSN2A steel in heavily loaded structures, is characterised by identical hot and cold cracking resistance in welding (cold cracks appear at a hydrogen content in the weld of 4.5 cm~3/100 g) and approximately the same level of standard mechanical properties with higher cold strength and fracture toughness.The special feature of welding 30N8K4KhMF (VKS-6) steel is the susceptibility to the formation in the weld metal of a stable crystallisation structure with the appearance of large macrograins and woody structure on the fracture surface. This decreases the impact toughness by 30-40 percent and the low-cycle fatigue endurance decreases 2-3 times. An increase of the welding speed above 4 mm/sec, welding in long sections (with cooling of the individual layers), and two-pass welding with the second pass made on hot metal in EBW enables these phenomena to be eliminated.The application of FBW with subsequent heat treatment results in full strength of the welded joints in comparison with the parent metal, with similar low-cycle fatigue and fracture toughness values. It was shown possible to carry out EBW of components strengthened by heat treatment with a tensile strength of the welded joint of 1600 MPa at KCU~(20)> 0.60 MJ/m~2.In arc welding methods using Sv-18N8KhMF-VI filler wire, the strength of the joints is higher than 1300 MPa with or without subsequent heat treatment. The impact toughness of the metal of the welded joint is not lower than that of the parent metal.
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