PSI - Issue 13

Fidan Smaili et al. / Procedia Structural Integrity 13 (2018) 1347–1352 Fidan Smaili, Tomaž Vuherer / Structural Integrity Procedia 00 ( 2018) 000 – 000

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 The threshold for long crack fatigue propagation in CG HAZ microstructure is 10.50 MPam 0.5 while the threshold for long crack fatigue propagation in FG HAZ is 4.33 MPam 0.5 , what is almost 2.5 lower threshold.  Some cracks, which had been initiated, stopped to propagate in CG HAZ but in case of FG HAZ they propagated without stopping.  Small cracks in CG HAZ and FG HAZ can easily initiate from the defect but early crack propagation in FG HAZ is faster than in CG HAZ due to stronger microstructural barriers (grain boundary) in CG HAZ.  Microstructural barriers (grain boundary) in CG HAZ can be so strong that can retard and even stop the small crack propagation of the small crack (non-propagating cracks).  In FG HAZ microstructural barriers (grain boundary) are so weak that initiated small crack propagate all the time and non-propagating cracks do not occurred.  At the beginning the long crack growth is faster in FG HAZ microstructure than in CG HAZ microstructure. When the crack overcome the microstructural barriers in CG HAZ crack propagate faster in CG HAZ which has lower toughness. Vuherer T., 2008. Analysis of influence of micro defects on fatigue strength of coarse grain HAZ in welds. PhD Thesis, University of Maribor, Faculty of Mechanical Engineering. Vuherer T., Maruščak P.O., Samardžić I., 2012. Behaviour of coarse grain heat affected zone (HAZ) during cycle loading. Metalurgija 51 3 301 304. Vuherer T., Dunđer M., Milović Lj., Zrilić M., Samardžić I., 2013. Microstructural investigation of the heat -affected zone of simulated welded joint of P91 steel. Metalurgija 52 3, 317-320. Vuherer T., Milović Lj., Gliha V., 2011 Behaviour of small cracks during their propagation from Vickers indentations in coars e-grain steel: an experimental investigation. International journal of fatigue 33 12,1505-1513. References