UK: Дисертація присвячена вирішенню науково-прикладної проблеми отримання в
металопрокаті для зварних будівельних конструкцій підвищеного рівня міцністних
характеристик при збереженні пластичних та в’язкісних властивостей, шляхом
розробки удосконаленої технологічної схеми виробництва високоміцного прокату з
низьковуглецевих, низько-, мікро- та нелегованих сталей. Проблему вирішено
шляхом виявлення загальних закономірностей формування в області дифузійного
механізму розпаду переохолодженого аустеніту нанорозмірних структурних
елементів та особливостей їх впливу на підвищення механічних властивостей
будівельного металопрокату відповідального призначення.
Використаний в роботі комплексний підхід щодо з’ясування принципів
формування тонкої структури сталей в області дифузійного розпаду аустеніту
(фериту та перліту), дозволив розробити технологічну схему безперервної
контрольованої прокатки низьковуглецевих низько-, мікро та нелегованих сталей,
яка дозволяє розкрити резервні можливості вітчизняних технологій виробництва та
вдосконалити структуру і властивості високоміцного товстолистового прокату, що
задовольняє вимогам сучасної вітчизняної будівельної індустрії.
EN: The work deals with solving scientific-applied problem of getting in metal-roll for
welding building constructions of increased level of operating capacity by means of
elaboration of the improved technological production scheme of high-strength rolled metal
from low-carbon low-, micro- and non-alloyed steels. The problem is solved by means of
the detection of general regularities of nanoscale structural elements formation in the area
of diffusive mechanism of supercooled austenite decay and the peculiarities of their
influence on the increase in mechanic properties of building metal-roll from low-carbon
steels.
It is stated that ductile deformation starts from the places with the enlarged level of
free energy and spreads along crystallographic areas that make the smallest angle with the
direction of maximal tangential stress from outer loading. It is shown that ductile
deformation creates periodically inhomogeneous hardened environment, which will define
the direction of crack growth. Under the conditions of loading, which happen in standard
tensile tests, the resistance of material detachment is overcome in structural components
with a lower resistance of ductile deformation, i.e. in ferrite because during the process of
ductile deformation, residual strengths appear which gradually grow to reach the boundary
state. Such concentration of strengths is observed close to grain boundaries. At the even
strength spreading in the critical cross section of the steel part, ductile deformation can
develop almost simultaneously in a number of ferrite grains. At the monotonous increase
in loading a great number of micro cracks appear, which eventually unite, making the
fracture surface with a large number of imperfections and the change of the direction from
grain to grain. Grain boundaries create a net that evens the separation of the deformations
among the grains of poly-crystal structure.
The models of initiation and spreading the destruction in steels with ferrite-perlite
structure are perfected. It is found out that the initiation of viscous destruction can be
described by the activity of three mechanisms: the initial stage – the formation of
dislocation loops near the part (Broek`s model); the next stage of pore growth happens
owing to the accumulation of dislocations. Herewith, this stage occurs under the activity of
both strength components normal and sliding.
The urgency of the work is conditioned by the search for new additional
opportunities to improve the structure and the properties of metal-roll from low-carbon
low-, micro- and non-alloyed steels. The elaboration of new and improvement of the
existing technologies of production of high-strength plate metal-roll that satisfies the
modern demands of building industry was also of primary importance.
The peculiarities of structure-creation processes are analyzed, which happen in
metal-roll with low-carbon low-, micro- and non-alloyed steels during the use of the most
wide-spread technological production schemes: hot and controlled rolling. It is found out
that the effective and stable deformation influence on the steel structure is determined by
the presence and the size of three temperature intervals limited by critical points of
transformation and the temperatures of recrystallization of the deformed austenite.
With the application of mathematical apparatus of the theory of experimental data
array processing, the interconnection between the technological parameters of production
schemes of low-carbon low-, micro- and non-alloyed steels (hot rolling, controlled rolling)
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and the main mechanic metal-roll properties is quantitatively analyzed. Hereby, it is shown
that the change of the temperature interval of finish rolling leads to the change of strength
characteristics (for the technological scheme of controlled rolling). Ductile peculiarities
remain constant. With the application of mathematic apparatus of one-parameter (for hot
rolling) and multiparmetry regression analysis (for controlled rolling), mathematic models
of interconnection between mechanic characteristics and temperatures of the beginning
and the end of finish rolling are created.
The analysis of the models showed that the increase in the temperature of the
beginning of finish rolling (for controlled rolling) would lead to the increase in the level of
mechanic characteristics, particularly strength. For the technological scheme of hot rolling,
widening of temperature range of hot deformation will have a positive influence on the
properties complex.
On the basis of the obtained results, temperature-deformation regime of hot rolling
in intercritical temperature interval is theoretically grounded, which leads to the
conservation of the dislocation austenite substructure to the lowest boundary of
intercritical temperature interval. As a result, the deformation in intercritical temperature
interval will enable to obtain a fine structure of the deformed ferrite and perlite, the peculiarity of which is the absence of ferrite-perlite striation. This conception is realized for low-, micro- and almost non-alloyed steels.
Thus, the analysis of the research results proved the possibility to correct the
processes of the formation of structure and substructure components by means of constant deformation in intercritical temperature interval. Herewith, the decrease in the temperature of the end of hot rolling to the lowest boundary of intercritical interval will make it possible to improve further and stabilize the complex of mechanic characteristics of rolling for building constructions. The conservation of a stable polygonal structure during the deformation in the intercritical temperature interval leads to the formation of a developed ferrite-perlite structure with a certain type of cementite carcass of the perlite component.
The complex approach, applied in the work, as for the clarification of principles of thin structure steel formation in the area of diffusive decay of austenite (ferrite and perlite) made it possible to work out the technological scheme of rolling production with lowcarbon low-, micro- and non-alloyed steels, which enables to reveal the backup capabilities of domestic production technologies and to improve the structure and properties of high-strength roll from low-carbon steels the way to meet the demands of modern domestic building industry. The obtained results can be classified as the solution to the important scientific-applied problem, which has a significant importance in terms of rolling improvement with low-carbon low-, micro- and non-alloyed steels produced by domestic enterprises.
