The dissertation is devoted to the establishment of regularities of influence of
features of structural-phase composition of metal of welded joints of high-strength steels
of different strength class on their mechanical characteristics and crack resistance by
definition of the structural criteria providing a necessary complex of these properties.
In this work it is investigated structure and properties of welded joints of highstrength
steels with yield strength from 690 MPa to 1300 MPa depending on technological
parameters (cooling and welding speed, alloying of seams, heat treatment conditions) and
welding methods (mechanized arc, laser, hybrid laser-arc welding).
Researched structural steels of construction purpose of bainitic-ferritic and bainiticmartensitic
type (alform 620M; 17Х2М; 14KhGN2MDAFB; N-AXTRA-
700); high-carbon ferritic-pearlitic steel (wheel steel grade 2; 65G); alloyed
medium carbon steels of special purpose martensitic-bainite type (armor - steel 71 and
Miilux Protection 500).
The paper proposes an approach based on a set of methods of physical materials
science, including light, analytical scanning and transmission electron microscopy,
methods of quantitative metallography to determine structure parameters, quantitative
methods for determining the scalar density of dislocations and estimating the size of
dispersed phases; quantitative methods for estimating the distribution of chemical
elements in the welding zone, methods of statistical processing of results. In order to
improve the analysis of the results of fractographic studies, a methodological approach to
the classification of fractures by: type of force load; the nature of the destruction, macroand
microrelief of the destruction surface; micromechanisms of destruction; local
destruction hubs.
Regularities have been established formation of phase composition, grain, subgrain,
dislocation structures of welded joints of high-strength steels and the relationship of
structural parameters with a set of properties - strength, toughness, level of localized
deformation and local internal stresses in the metal welds of the studied steels. Have been
studied peculiarities of structural-phase components (ferrite, austenite, perlite, tempered
and hardening martensite, bainite upper and lower), their parameters - packet size, grains,
the corresponding values of microhardness, the nature of the destruction of the metal by
fracture zones, the volume fraction type, the size of trace elements fracture surface,
dislocation density and substructure.
Improvements have been made experimental-analytical methods for evaluating the
complex of physical and mechanical properties for specific structural parameters,
introduced mathematical data processing and analytical evaluations of strength, fracture
toughness, local internal stresses of welded joints of the studied steels.
In order to ensure the operational reliability of structures in the creation of scienceintensive
and promising technologies for welding high-strength steels on the basis of
experimental and theoretical studies, structural criteria are established to ensure the
necessary set of mechanical properties and crack resistance of these joints. Ensuring the
operational reliability of welded joints of high-strength steels makes it possible to use
them in structures of responsible purpose in mechanical engineering, railways, heavy
industry, shipbuilding, armaments, etc.
