Svařitelnost termomechanicky zpracovaných ocelí

Abstract

The non-alloyed or microalloyed thermomechanically treated steels for the production of the steel´s constructions have been used in the last years. The main reason for their application is the increase of the mechanical qualities without the necessity of alloy element content’s increasing. The possibility of thickness reduction is related to increasing of mechanical quality, the weight of construction as well as the price. The thermomechanically treated plates, strips, reinforcing steel bars belong to the main types. For the reinforcing steel bar´s constructions the important parameter is the planned service lifetime for 100 years. The thesis work deals with the welding issues of the reinforcing steel bars, includes the study of the welded transit zones and the study of the defect‘s formation . In the theoretical part the history and the development of the reinforcing steel bars in The Czech republic have been described becouse of the possibility of old construction’s reconstructions. Further, the theoretical part includes the characteristic of the reinforcing steel bars, the ways of production, the influence of the macrostructure and microstructure and phase’s transformations during the cooling. During the welding of the reinforcing steel bars the changes of the material‘s qualities and the defect’s formations are created. The practical part of thesis work deals with welded joint making and their appraisal. The work more includes review of mechanical qualities of welded joints. There have been tensile, bend, shear tests and the meassurment of the hardness made. For some welded joints the testing was broaden. The meassurement of the microhardness and local chemical composition of some parts of the welded joints have been made. On the basis of this thesis work, discussion and result’s summary, the heat input influence on defects, the local chemical changes and the changes of microhardness have been determined regarding the lifetime of the reinforcing steel bar’s constructions which are proposed for 100 years. From the final results there have been defined new fields of this research for the development of the Mechanical Engineering branch. The practical aim of this thesis work is the defining of welding process specifications (WPS) in accordance to the valid standards and the rules.