Design On Draining Water Device And Its Welding Procedure Research In Umderwater Laser Welding Of 304 Stainless Steel

There are more and more restrictions to the conventional underwater welding methods as the scope of human activities extends to deeper,wider areas of the ocean and large use of new materials.In addition,water environment with high pressure and high radiation in nuclear power plants also put forward higher requirements for the underwater welding techniques.Compared with the underwater arc welding,underwater laser welding has the advantages of smaller influence by hydraulic pressure,wider welding material,lower heat input,higher cooling rate,smaller heat affected zone,lower residual stress.However,the underwater laser welding technology of China is still in a very backward position because of techni cal blockade and other reasons.Especially,it has not yet achieved substantial breakthrough in the research of interaction mechanism between the high-power laser beam and the metal in water and the design of draining water device in underwater laser welding.Firstly,the interaction mechanism between the high-energy laser beam and the metal in water is studied in this paper.The video sequence and the welding plasma shape image of underwater wet laser welding under different water depth are obtained using the traditional visible light imaging system.The force balance and energy balance model of “beam channel” formation,growth and closure are established in underwater wet laser welding.It is found that the welding stability and weld quality of underwater wet laser welding process are gradually deteriorated with the increase of water depth.The available water depth of underwater wet laser welding is over 20 mm with 6.0 k W laser power,0.1 m/min welding speed and 0 mm defocusing distance.Based on the above,two sets of draining water device in underwater laser welding——single layer gas-assisted draining water device and double layer gasassisted draining water device are designed starting from the inflation mode design and the internal fluid dynamics simulation calculation utilizing Solid Works and ANSYS Workbench 14.5.The gas-liquid two phase flow numerical simulation of flow field is carried out for the designed drainage device respectively.The reliability of the drainage device designing is verified by analyzing the fluid streamline image,speed vector image,speed contour image and pressure contour image.Among them,for single layer gas-assisted draining water device,the inflation mode is ring direction inflation with an equal distance of the hole;for double layer gas-assisted draining water device,the inflation mode of outer cylinder is side tangent direction inflation,the inflation mode of inner cylinder is oblique tangent direction inflation.Finally,the local dry underwater laser welding test system is established.The underwater laser welding procedure of 304 stainless steel is studied based on the two sets of designed draining water device in underwater laser welding.The results show that the underwater welding joint with good appearance,no defect and excellent performance can get with the two sets of designed draining water devices in this paper in underwater laser welding.Among them,the tensile strength and impact toughness of the weld obtained by the single layer gas-assisted draining water device are 665 MPa and 107 J/cm2 respectively;the tensile strength and impact toughness of the weld obtained by the double layer gas-assisted draining water device are 620 MPa and 152 J/cm2 respectively.Compared with the weld in air,the ferrite in underwater weld exist not only in the form of dendrites,but also in the form of lathies.Meanwhile,weld strength meets requirements while toughness is decreased and microhardness is not much different.