PSI - Issue 16

Olena Berdnikova et al. / Procedia Structural Integrity 16 (2019) 89–96 Olena Berdnikova et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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joints, it was found that the most stable values of strength and ductility are characteristic of laser welding conditions. However, welded joints produced by hybrid laser-arc welding are characterized by the highest ultimate strength. Herewith, the optimal structure, from the point of view of phase composition (mainly B L , more than 50%) and a gradient-free dislocation density distribution, is formed at 363 J/mm with a maximum contribution to the heat input of the laser component.

Fig. 1. The microstructure of the weld metal (a, b, e, f, i, j) and HAZ (c, d, g, h, k, l) of welded joints produced by arc welding at 1519 J/mm (a) and 546 J/mm (b – d), laser welding at 880 J/mm (e) and 316 J/mm (f – h), and hybrid welding at 314 J/mm (i) and 363 J/mm (j – l).

6. Evaluation of strength and crack resistance properties

Based on the results of studies of the structure and phase composition of low-alloyed high-strength steel welded joints with various technological parameters of arc, laser and hybrid laser-arc welding, we made analytical assessments of the strength, fracture toughness and the level of local internal stresses in various components of microstructure (Markashova et al. (2012), Berdnikova et al. (2014)). It has been found the following. In conditions of arc welding at 546 J/mm (#4) in the metal of weld and HAZ, the calculated value of hardening is ∑σ T = 741...890 MPa, Fig. 2a. At the same time, the fracture toughness K 1C is 15...32 MPa∙m 1/2 . When using arc welding in modes with a maximum heat input of 1519 J/mm (#1), the welded joint was destroyed as a result of the formation of cold cracks in HAZ and embrittlement along the boundaries of grain structure. In this case, the nature of fracture is an intercrystalline cleavage fracture with secondary cracks along the grain boundaries, Fig. 2a. The fracture toughness K 1C in this case decreases noticeably, Fig. 2a.