Diagnostic Examination of P265GH Boiler Steel Plate Using the Barkhausen Method
The article presents the results of diagnostic examination of P265GH boiler steel plate. During blanking, cutting and cold forming of elements from this plate, their spontaneous plastic deformation and warping took place, indicating an unfavourable internal stress state of a considerable magnitude occurring in the steel plate. In order to identify the causes of this situation, examinations were carried out, which included a microstructure assessment and a Vickers hardness test. In view of the absence of clear differentiation, in terms of both structure and hardness, in different steel plate areas, diagnostic examination was performed by the Barkhausen magnetic method, which included the determination of the principal direction of residual stresses and the determination of their anisotropy based on the measurement of the effective value of Barkhausen noise. As their result, a significant anisotropy of residual stresses was revealed on the steel plate surface. Moreover, the adverse phenomenon of perpendicularity of the principal directions of stresses was found to occur on the opposite plate surfaces, being the direct cause of warping of elements cut out from the plate
The paper presents the results of two new in-situ methods of Fe-Al intermetallic compounds layers fabrication on the steel substrates. The layers were produced by hardfacing of pure aluminum and titanium on the steel (S235JR) substrate as well as in the two-step process: the thermal spraying of pure aluminum on a steel substrate and subsequent remelting of aluminum coating with iron from the substrate using AC TIG method. As a result of the synthesis of Fe, Al and Ti components (for the hardfacing method) the new layer material based on the ordered intermetallic phases was achieved. The effects were confirmed by metallographic examinations, hardness tests and the diffraction patterns of the analyzed remelted layers. In addition, measurements of residual stresses in the layer and substrate were carried out.
The results of a microstructure examination and mechanical properties of 15HM (13CrMo4-5) steel are presented in the article. The examined elements are the samples taken from the live steam pipeline serviced for about 420 000 hours at the temperature of about 510°C, and pressure of 11 MPa. It has been shown that after long-term operation the examined steel has a ferritic-pearlitic microstructure with a dominant content of quasipolygonal ferrite. The processes of fragmentation of lamellar precipitates and their spheroidization were observed in pearlite. On the grain boundaries, single lamellar precipitations were observed. Moreover, numerous precipitations at the interface of three grain boundaries were revealed. The examined steel, despite its long-term service time, was characterized by the strength properties (YS, TS) slightly lower than the required minimum, the impact energy value KV equal to 20 J, and the transition temperature shifted to a temperature above zero. Relatively low level of degradation of the microstructure and mechanical properties of the investigated steel can result from high stability of the ferritic-pearlitic microstructure.