PSI - Issue 16

Vitalii Knysh et al. / Procedia Structural Integrity 16 (2019) 73–80 Vitalii Knysh et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Experimental results affirmed that HFMI treatment is useful for welded joints, both at initial stage and after a long-term service. It can be assumed that additional protection of HFMI-strengthened metal layer against atmospheric influence, for instance, by a lacquer-paint coating, will increase the fatigue strength of welded joint to the level of specimens tested in air (curve 2, Fig. 6).

4. Conclusions

1. The corrosion rate of as-welded and treated by HFMI surfaces of base metal of low-alloyed 15KhSND steel changes non-monotonically over time, but has a tendency to lowering. After 2400 hours, the corrosion rate of surface treated by HFMI is somewhat lower, than that of a ground surface – approximately 0.184 mm/y and 0.162 mm/year, respectively. 2. The metallographic investigations revealed that the welded T-joints of 15KhSND steel treated by HFMI along the fusion line causes intensive deformation (elongation) of grains in the weld metal and heat-affected zone. The depth of plastically deformed layer of metal with essential changes of the grain shape (grain form factor К f_ = _ 5…17) reaches 390…650 μm. 3. It is found that HFMI is an effective method to increase the fatigue strength of the welded T-joints at the stage of fabrication of metal structures, which will be exposed to simultaneous influence of alternating loads and artificial atmospheric conditions of temperate climatic zone in service. Strengthening of the welded T-joints of 15KhSND steel before exposure to high humidity of air (98%) and temperature ( 40°C ) during 1200 hours leads to increasing of their fatigue limit 2·10 6 cycles by 32% (from 157 up to 230 MPa) and of cy clic fatigue life in 5…7 times. 4. Effectiveness of HFMI treatment to increase the fatigue life of welded joints in long-term service structures with corrosion-fatigue damage that resulted from simultaneous impact of alternating loading and atmospheric factors of temperate climate zone was experimentally grounded. HFMI of welded T-joints of 15khSND steel after cyclic pre- loading (2·10 6 cycles) and exposure to high humidity of air and temperature during 1200 hours leads to 10 times increase of their fatigue life and fatigue limit at 2·10 6 cycles – by 82% (from 135 to 246 MPa).

Acknowledgement

The work was carried out within the framework of the departmental order program of the National Academy of Sciences of Ukraine by E.O. Paton Electric Welding Institute (basic research no.6541230) titled “Support in development of priority research areas”.

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