Simulation Research On The Law Of Angular Distortion Of D36 Steel For Shipbuilding During Multi-pass Welding

As a low-alloy and high-strength steel, D36 steel is widely used in shipbuilding due to its good mechanical properties and strong resistance to corrosion. When multi-pass welding is adopted to thicker plate of D36 steel, using automatic submerged arc welding, there tend to be larger distortion, mainly angular distortion. Currently, the prediction of angular distortion is mainly based on experience, which is highly limited. In this study, the prediction formula of angular distortion is derived using the basic theory of mechanics of materials, and the influencing factors in the theoretical formula are verified by finite element method simulation, and the effects of other relevant parameters for the correction coefficient in the formula are studied, which provided the basis to the theoretical analysis and engineering application of the prediction of the angular distortion of D36 steel during multi-pass welding.Based on the transverse shrinkage force model and the calculation formula of the transverse shrinkage, using the theory of mechanics of materials, the formula of the angular distortion during the multi-pass welding on the plate with plate butt joint and Tshaped joint is derived. During this study, the angular distortion of T-shaped joints is divided into two parts, which are the angular distortion of the plate due to the nonuniform transverse shrinkage in the thickness direction, and the angular distortion due to the selfshrinkage of the fillet weld. The formula shows that, the angular distortion of the plate with butt joint and the plate part of T-shaped joint is in direct proportion to the heat input during welding, and is in inverse proportion to the thickness of the plate, while the angular distortion of the T-shaped joint due to the self-shrinkage of the fillet weld is relevant to the size of the fillet weld and the properties of materials.Establishing the finite element model of the butt joint with V-shaped groove and Yshaped groove and the T-shaped joint, and determining the expression of the correction coefficient in the formula which predicts the angular distortion of D36 steel during multipasses welding by simulation. The result of simulation shows that, the welding power and the thickness of plate are the main factors in the correction coefficient of the formula which predicts the angular distortion of butt joint, while the size of the fillet weld and the material properties are the main factors in the correction coefficient of the formula which predicts the angular distortion of T-shaped joint. Carried out the experiments of welding by one side and by both sides, to verify the finite element model of butt joint with Vshaped groove and the T-shaped joint. The angular distortion results of simulation match well with the experimental results so that the accuracy of the finite element model is verified. This provides the basis to analyze the factors of the correction coefficient using the finite element model.Establishing the finite element model of 10 mm thickness-plate with I-shaped groove and obtaining the relation curve of the angular distortion on both sides and the heat input, which can be used to predict the final angular distortion. Also studying the effects of welding power on both sides, positioned welding and the thickness of plate on the angular distortion, and then providing the best match of welding power and the best form of positioned welding.On this basis, improving the expression of the angular distortion. Exploring the law of the variation of the angular distortion through the length direction of plate, and analyzing the reasons of this variation, then fitting a curve which provides the expression of the angular distortion thought the length direction of plate. In the case of certain heat input, analyzing the effects of welding power and welding speed on angular distortion respectively, and studying the variation of the molten pool’s shape with different welding parameters. The results shows that, when constant heat input is provided, different matches of welding power and welding speed have effects on the shape of the molten pool and then influence the angular distortion. This provides the basis for a better application of the formula in practice.