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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concentrators of local internal stresses. Thus, we have shown how the microstructure affects the properties of welded joints of low-alloyed high-strength steels. The most influencing structural factors are the dispersion of the bainitic structure and substructure, the uniform distribution of the dislocation density and the absence of areas of nucleation and propagation of cracks.

7. Conclusions

The structure and properties of welded joints of low-alloyed high-strength steel depend on the welding methods (arc, hybrid laser-arc or laser) and the modes used. Under various welding conditions, the following structure transformations are observed: the ratio of the phase components forming in the welding zones (lower bainite, upper bainite, martensite), as well as their parameters and volume fraction, changes. Under arc welding conditions, predominantly upper bainite structures are formed with a general increase in the size of the grain and sub-grain structures with their uneven distribution and a large gradient of dislocation density. Hybrid laser-arc and laser welding is characterized by the formation of lower bainite structures with significant refinement of the grain and sub-grain structure with a uniform distribution of the dislocation density. A significant increase in strength, ductility and crack resistance of welded joints of low-alloyed high-strength steel at a decrease in heat input and a transition to laser and hybrid laser-arc welding evidences the validity of the relationship “welding method (modes) → structure → properties”. This is due to the prevailing influence of fine grained formations of lower bainite structures, the absence of dense extended dislocation clusters with prevailing of a uniform distribution of dislocations in the welded joint. To ensure high strength in arc welding of low-alloyed high-strength steels, it is necessary to strive to form an equiaxial grain fine-grained bainite-martensitic structure in welded joints, which is achieved by reducing the heat input welding to values below 500 J/mm that are characteristic of laser and hybrid laser-arc welding. Afkhami, S., Björk, T., Larkiola, J., 2019. Weldability of Cold -Formed High Strength and Ultra-High Strength Steels. Journal of Constructional Steel Research 158, 86 – 98. Alipooramirabad, H., Ghomashchi, R., Paradowska, A., Reid, M., 2016. Residual Stress-Microstructure-Mechanical Property Interrelationships in Multipass HSLA Steel Welds. Journal of Materials Processing Technology 231, 456 – 467. Alipooramirabad, H., Paradowska, A., Ghomashchi, R., Reid, M., 2017. Investigating the Effects of Welding Process on Residual Stresses, Microstructure and Mechanical Properties in HSLA Steel Welds. Journal of Manufacturing Processes 28 – 1, 70 – 81. Berdnikova, O., Sydorets, V., Alekseienko, T., 2014. Structure and Properties of Laser-Welded Joints from High-Strength Steels. Applied Mechanics and Materials 682, 240 – 245. Berdnikova, O., Pozniakov, V., Bushma, O., 2016. Laser and Hybrid Laser-Arc Welding of High Strength Steel NA-XTRA-70. Materials Science Forum 870, 630 – 635. Bhole, S.D., Fox, A.G., 1996. Influence of GTA Welding Thermal Cycles on HSLA-100 Steel Plate. Canadian Metallurgical Quarterly 35 (2), 151 – 158. Bright, G.W., Kennedy, J.I., Robinson, F., Evans, M., Whittaker, M.T., Sullivan, J., Gao, Y., 2011. Variability in the Mechanical Properties and Processing Conditions of a High Strength Low Alloy Steel. Procedia Engineering 10, 106 – 111. Bunaziv, I., Akselsen, O. M., Frostevarg, J., Kaplan, A. F. H., 2018. Laser-Arc Hybrid Welding of Thick HSLA Steel. Journal of Materials Processing Technology 259, 75 – 87. Bunaziv, I., Akselsen, O.M., Ren, X., Salminen, A., 2015. Hybrid Welding Possibilities of Thick Sections for Arctic Applications. Physics Procedia 78, 74 – 83. Doncheva, E., Medjo, B., Rakin, M., Sedmak, S., Trajanoska, B., 2018. Numerical Simulation of Crack Propagation in High-Strength Low Alloyed Welded Steel. Procedia Structural Integrity 13, 483 – 488. Dubovska, R., Jambor, J., Majerik, J., 2014. Qualitative Aspects of Machined Surfaces of High Strength Steels. Procedia Engineering 69, 646 – 654. Garcia, C. I., 2017. High Strength Low Alloyed (HSLA) Steels, in: “Automotive Steels. Design, Metallurgy, Processing and Applications”. Rana, R. and Singh, S. B. (Eds.). Woodhead Publishing, Cambridge, pp. 145 – 167. Gianetto, J.A., Goodall, G.R., Tyson, W.R., Fazeli, F., Quintana, M.A., Rajan, V.B., Chen, Y., 2012. Microstructure and Properties of High Strength Steel Weld Metals, in: 9th International Pipeline Conference-2012, September 24 – 28, 2012, Calgary. American Society of Mechanical Engineers, New York, pp. 515 – 526. Gomes, A.J.M., Jorge, J.C.F., de Souza, L.F.G., Bott, I.S., 2013. Influence of Chemical Composition and Post Welding Heat Treatment on the Microstructure and Mechanical Properties of High Strength Steel Weld Metals. Materials Science Forum 758, 21 – 32. References