Research On Welding Process Of Heterogeneous Butt Girth Weld Between Main Chord And Joint Of Crawler Crane Boom

Crawler crane is a kind of lifting equipment widely used in various fields of the national economy,used for material lifting,loading and unloading and installation operations.Among them,the crane boom is the most important load-bearing structure,and the welding method of low-alloy high-strength steel is mostly used,but the use of low-alloy high-strength steel to reduce the weight of the boom will also bring a series of welding problems,such as welding cracks,which will adversely affect production practice.In this thesis,numerical simulation method is used to study the welding temperature field and stress field distribution law of the heterogeneous butt ring weld of the main chord and the joint of the crawler crane boom,and the welding process scheme is optimized,which effectively reduces the proportion of welding crack defects,and the main work is as follows:(1)The weldability of 20 CrMnTi and BJ890 dissimilar steel was theoretically analyzed,and through the analysis of the carbon equivalent and cold crack sensitivity index of the steel,it was shown that the weldability of 20 CrMnTi and BJ890 was poor,and the dissimilar steel between the two was welded and needed to be preheated before welding.(2)Combined with the chemical composition and mechanical properties of the test steel and welding wire,the welding matching analysis of the base metal and the welding wire was carried out,and the T Union GM110 welding wire was selected according to the principle of "low strength matching".Based on Marc finite element software,a numerical model of slope Y groove crack test was established,and the distribution of temperature field and stress field at different preheating temperatures was analyzed,and the appropriate preheating temperature was determined,and175～275 °C was selected.(3)The numerical model of heterogeneous butt ring weld welding of the main chord and the joint of the crawler crane boom was established,and the distribution law of welding temperature field and stress field was studied.The temperature field simulation results conform to the general law,the temperature of each weld is1900～2600 °C,the same layer of weld,due to the different heat transfer methods,the temperature of the first few welds is higher than that of the last weld,and the equivalent residual stress at the weld is in the range of 480～550 MPa.On the inner surface of the weldment,the axial residual stress of the weld and the heat-affected zone is the tensile stress,and the circumferential residual stress is mainly the compressive stress.On the outer surface of the weldment,the weld first forms a circumferential tensile stress in the welding area,and then forms a circumferential compressive stress in the welded area,which indicates that the welding sequence has a certain influence on the distribution of residual stress.(4)Based on orthogonal test methods combined with numerical simulations,the welding process parameters are obtained.The primary and secondary orders of the influence of the three factors on the residual stress of the specimen are welding speed,welding power,and welding sequence.The optimized process parameters are: the welding sequence is IV,the welding power is 6750 W,and the welding speed is 12mm/s.The welding test was carried out by using the best welding process parameters,5 groups of samples were welded on site,and the weldment was detected for cracks after welding,and no cracks appeared.By comparing the actual welding production data before and after optimizing the process parameters,the proportion of weld cracks decreased by 50%,which has far-reaching significance for actual production.The thesis has 67 figures,17 tables,and 88 references.