Experimental and numerical investigation on cold cracking susceptibility of naval grade high strength steel welds for lightweight shipbuilding structures

Abstract

In this study the cold cracking (CC) susceptibility of naval grade high strength steel (HSS) welds developed using flux core wires of different yield strength levels was analyzed for lightweight shipbuilding structures. The steel plates of the PCE500 TM grade were welded in T-joint configuration using automatic flux core arc welding under the shielding gas. The CC susceptibility of weld metals was evaluated using Tekken weldability test. The microstructure of weld metal and the hardness of welded joint were analyzed using optical microscope and Vickers microhardness tester, respectively. Software package Sysweld was used for finite element simulation of CC susceptibility of weld metals. Results showed that the probability of CC increases with increase in the strength of filler wires, especially under conditions of limited welding deformations and exposure to low temperatures. The maximum resistance to the formation of cold cracks (CCs) in microstructure of the weld metal is observed in the presence acicular ferrite of at least 60%. To assess the structural strength of T-joint with soft welds, a calculation method has been developed, which allows ranking various structural and technological solutions of the T-joint from the condition of resistance to various types of fracture. Numerical calculation showed that the margin for brittle fracture at 11–23% and the gain in fatigue durability at 40% for welded joint with soft weld greater than for a welded joint with an equally strong weld. The use of low strength filler wires for welding thick plates of HSSs can successfully resolve the problem of CCs and ensure structural strength of joints.