MICROSTRUCTURE-FATIGUE CRACK-GROWTH RATE CORRELATION IN MULTIPASS SUBMERGED-ARC C-MN STEEL WELD DEPOSIT

All-weld blocks of C-Mn steel were prepared by multipass submerged arc weld deposit, using different welding currents (500-750 A) and speeds (40-60 cm/min), filler wire of 4 mm diameter and a basic bonded type flux. The dendrite content of the weld blocks was estimated by quantit ative metallography technique. The fatigue crack growth rate of the we ld at LT direction of the block was evaluated by using C-T specimens a nd correlated with the area fraction of dendrite (D(f)) of the matrix. The increase in dendrite content of the matrix was found to reduce th e crack growth rate by influencing significantly the material constant C and exponent m of Paris law, da/dN = c(DELTAK)m, where, 'a' is the crack length, 'N' is the number of Loading cycle and DELTAK is the str ess intensity factor range. The modification of C and m with D(f) was found to provide a satisfactory basis for the evaluation of fatigue cr ack growth rate of multipass C-Mn steel weld deposit having a given am ount of dendrite.