Abstract
A thermal-metallurgical-mechanical model was developed to study the effects of dilution in each weld pass for multipass gas tungsten arc and submerged arc welding in low alloy steel (i.e. SA508) plates. Hardness distributions and residual stresses were measured on the transverse sections perpendicular to the welding direction of the manufactured weldments. The predicted hardness and residual stresses were compared with the measurement data and shown to be reasonably accurate. The results showed that dilution can significantly affect both the hardness and the residual stress field in the weld metal. It was found that, for the base and filler materials used, increased dilution led to greater weld-metal hardness and reduced the magnitude of tensile stress or promoted compressive stress in the as-deposited and reheated weld metals. This mechanical behaviour is associated with the tendency for diluted weld metal to experience delayed austenite decomposition, owing to the high hardenability of SA508 steel relative to the filler materials used. Although dilution is irrelevant for the hardness of the base material and its transformation products adjacent to the weld metal, it affected the full-field residual stresses via the equilibrium interaction between the stresses in the base and weld metals.
Highlights
The mechanical properties of welds and the residual stresses in weldments have significant effects on structural integrity, and they are of particular concern for safety-critical structures such as those found in nuclear reactor pressure vessels [1,2]
The coarse-grained heat affected zone (HAZ) (CGHAZ) that originated in the base material exhibits the highest hardness, as the SA508 steel (Ceq = 0.3) is more prone to forming martensite when compared against the filler material (Ceq = 0.22)
Effects of dilution on hardness and residual stresses in multipass weldments have been investigated for gas tungsten arc (GTA) and submerged arc (SA) welding processes in grooved SA508 steel plates
Summary
The mechanical properties of welds and the residual stresses in weldments have significant effects on structural integrity, and they are of particular concern for safety-critical structures such as those found in nuclear reactor pressure vessels [1,2]. Unfor tunately, the mitigation of weld residual stress is difficult and expensive for large structures (e.g. nuclear reactor pressure vessels and steam generators), and it is often necessary to consider these stresses in structural integrity assessments [5]. Since mechanical properties (e.g. yield strength and fracture toughness) are strongly dependent on micro structure, it is necessary to evaluate the resultant heterogeneity of me chanical properties in the fusion zone (FZ) and heat affected zone (HAZ) of a weldment [12,13,14]. Its origin and development in ferritic steel weldments are complicated by multi-physics factors, which include the thermal expansion mismatch, transformation-induced deformation and plastic distortion
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