Zakharova I. A drop in the amount of defects in low alloyed steel through welding conditions optimization.

Українська версія

Thesis for the degree of Candidate of Sciences (CSc)

State registration number

0402U000341

Applicant for

Specialization

  • 05.03.06 - 3варювання та споріднені процеси і технології

11-01-2002

Specialized Academic Board

К 12.052.01

Essay

The work is aimed to the perfection of automatic submerget welding technique and to a drop in crack amound in the weld proper and in the thermal influence zone in the process of welding calcium modified steel tubs for gas and pipelines. Object of research - the factors responsible for the cleclin in mechanical properties of submerged multi - arc welded joints as well as the welding process facilitating guaranteed high quality of gas and oil pipes have been investigated. Subject of research -heat exchange process, weld formation, as well transformations taking pluce in the.thermal influence zone in submerged multi-arc twelding; anizothermal diagrams of austenit and NV trans-formations under the influence of WTC for low-alloyed calcium steels; choice technique and algorithm for proper operating condition in sheet steel welding were the subject of investigation. Research techniques-high speed dila-tometering, optical and electronic metallography, electron microscopy, mathematical simulation were the rese arch methods. Personal computer were used for all the calcula-tion according to mathematical models. The results of the calculation were compared to the results of the experi-ments oftined in the industrial tube welding. Up-to-date methods of chemical analysis were used to define metal composition. Anizothermal diagrams of austenit decompo-sition for calcium modified steel under welding thermal cycle condition have been spesified. Crack formation thermal influence zone under various temperatures, have been studied and the influence of calcium content in metal on the amount of crack in thermal influence zone has been shown. Three-dimensional dynamic model of heat ex-change in the welding bath and in TІZ, permitting is devel-oped to calculate the form both sizes of a welding bath and thermal influence zone has been worked out. The model makes it possible to calcium both the configuration and demisions of the welding bath and the areus of the two-phase condition of metale and the weld proper and in the final sec tion of it. Due to the mathematical simulation of heat exchange and the industrial experiments it has been found out that the main characteristic of the weld and the liquid metal bath relates to the condition of submerged tree-arc welding. The technique of a optimum welding conditions choice has been worked out. The optimum con-dition for making outside welds in gas and vil pipelines have been tested in Khartsizk tube work

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