Fracture Toughness Of Welded Joints Research Articles

Effect of the welding process and heat input on the fracture toughness of welded joints in high strength low alloy steel

Fracture toughness studies were conducted in high strength, low alloy steel weldments obtained by using two different welding techniques namely CO 2 welding and manual metal arc welding. The heat input was varied in order to study its effect on the fracture toughness of the weld zone (WZ) and the heat-affected zone (HAZ). The crack-tip-opening displacement and the J integral were used as the characterizing toughness parameters. The tensile properties of the weldments were obtained and the hardness profiles through the various zones were determined. The fracture toughness values for the HAZ and the WZ were compared under different welding conditions. Microstructural studies and fractographic studies were also conducted to correlate the micromechanism of fracture with the fracture toughness values. The effect of heat input was found to be predominant in the WZ toughness and the HAZ toughness for CO 2 welding. Also, manual metal arc welding provided a higher fracture toughness than did CO 2 welding for a similar heat input. The microvoid coalescence mode of fracture led to higher fracture toughness values for the WZs than for the HAZs which exhibited a cleavage mode of fracture mixed with microvoid coalescence. In all conditions the WZs exhibited higher fracture toughness values than the HAZs.

Fracture Toughness of Welded Joints of 9% Ni Steel for the Tank of LNG Carriers

The basic premise of the MOSS-Rosenberg LNG containment system and other spherical LNG tank system is “leak-before-failure”. In other words, the design concept applied to this type of pressure vessel is basically “fail-safe”.Therefore, to evaluate the structural safety of the spherical LNG tank, it is neccesary to obtain the fracture toughness of the tank shell plate and the welded joints, quantitatively. Considering the strength of brittle fracture initiation of 9% Ni steel LNG tank, the fracture toughness in the heat affected zone is the most important problem.Accordingly, the authors carried out the tension test with wide center-notched plate test specimens, notched in the heat affected zone of submerged arc welding with heat input values of about 1050 KJ/cm, in order to evaluate the fracture toughness of welded joints of 9% Ni steel.The following conclusions were obtained.(1) It is reasonable to calculate the critical crack length, using the experimental results obtained from the standard size specimens (about 400 mm wide) on the basis of Linear Elastic Fracture Mechanics.(2) For the butt-welded joints produced with the most practical heat input values of about 1040 KJ/cm, the lowest Kc values at the cryogenic temperature of LNG, -62°C, will be 775500 kg, √mm/mm2, and the critical crack length for brittle fracture initiation of 9% Ni steel LNG tank is satisfactorily long.