STUDY OF THE INFLUENCE OF THE CONCENTRATOR ORIENTATION RELATIVE TO THE PIPELINE AXIS ON THE COMPONENTS OF THE FRACTURE ENERGY AND THE DUCTILE-BRITTLE TRANSITION TEMPERATURE OF THE OF THE SHARPY SPECIMENS FROM THE STEEL 22K

Abstract

The world experience shows, that the standard basis available in Ukraine needs improvements for more correct interpreting of strength and durability of the power-station 1-st contour elements. Nowadays different numerical and experimental methods are being developed and improved for solving the problems of broadening the power-stations equipment operation life looking for the additional spare strength.
While calculating the brittle fracture resistance it is necessary to know the value of the critical brittleness temperature Тk0 of the material in the initial state in order to build the curve of the permissible values of the stress intensity factor ( SIF ). Usually Тk0 is found according to the results of the impact tests of the Charpy specimens, the methods of finding Тk0 and other factors affecting the value of Тk0 being of special attention nowadays. The result of the bending tests of the specimens with concentrators differ from those cut in the longitudinal and transversive directions. That is why the investigation of the effect of the cutting direction of the Sharpy specimens and the cut orientation on the results of the impact tests, as well as the determination of the critical brittleness temperature, are the pressing problems.
Charpy specimens impact tests are one of more simple and inexpensive method to determine the mechanical properties of materials. The results of these tests can be used to estimate the strength and durability of large-scale structures. A series of Charpy specimens impact test from high-alloyed high-temperature resistant steel 22К were carried out in the temperature range of –50 ÷ +100ºС with control of rolling direction. Tests were conducted on instrumented vertical impact machine, which can record a full diagram of specimen’s deformation and fracture. The values of total energy of deformation and fracture and its components: energy of crack initiation, energy of ductile crack growth, brittle cracks energy and ductile rupture energy were determined. It was found, that ductile-brittle transition temperature for specimens cuted along the rolling direction (group КK) higher than for specimens of group КO. It is shown, that the direction of rolling Charpy specimens significantly influences the values of total energy of deformation and fracture and its components, and the values of the ductile-brittle transition temperature for 22К steel.