The Study On The Cold Rolling Process Of The Nickel N6Plate Welded Joint

Nickel N6panel after welding joined together become big-volume, then need to cold-rolled to the finished product delivery status. In the process of the cold rolling, the failure rate of the belt is very high. The failure rate of the belt will influence the whole product efficiency and reduce the production capacity, in order to improve the yield of the product, and effectively solve these production actual problems, in this experiment, we have optimized and adjusted the cold rolling process.Earlier experiments, use the plasma to weld the nickel N6plate, with the optimal welding parameters for subsequent cold rolling experiments. Use the same cold rolling process of the base metal, the joint with filler wire and the joint without filler wire. And research their mechanical properties and microstructure.It will rolling8times from5.5mm to1.5mm, each time rolling down0.5mm. And analysis the tensile strength and the microstructure of the joint, analysis the result of the experiment data, it showed that in the process of cold rolling. The base metal, the joint with filler wire and the joint without filler wire, their mechanical properties have the same change rule, that tensile strength is more and more big, the elongation is more and more small. Contrast5.0mm and1.5mm, the tensile strength of base metal increased from358.9MPa to580.4MPa, the elongation rate from12.9%down to1.2%. The tensile strength of the joint with filler wire increased from388.4MPa to629.8MPa, the elongation rate from1.5%down to20.0%.The tensile strength of the joint without filler wire increased from239MPa to614MPa, the elongation rate from14.7%down to14.7%. SEM analysis of the tensile fracture shows that the toughening nest is reducing gradually in the cold rolling process, and the toughening nest becomes shallowly gradually, the fracture mode transited from ductile fracture primarily to brittle fracture predominantly. This suggests that in the process of cold rolling the plasticity and the toughness of the joint are gradually reduced. Analysis the microstructure, it shows that, the cold rolling can refine the crystalline grain of the joint, and the trend of this phenomenon is obvious. When cold rolled to the thickness of1.5mm, the crystalline grain looks like the thin line.When the cold rolled to the thickness of1.5mm, it need to stress relieving. This experiment used vacuum annealing furnace, selecting800℃,900℃,1000℃three different temperatures, each with furnace cooling to room temperature after heat preservation for15min. After annealing analysis shows that, at the temperature of900℃the mechanical properties of the joint is better, and the crystalline grain is smaller. So the optimal annealing process is:the heating temperature is900℃, holding time is15min, the cooling way is along with the furnace.From1.5mm to0.2mm the process is divided into6times, the total working rate reached87%. The data of the experiment shows that, in this process, the mechanical properties of each joint have the similar change law with the process before annealing, that the tensile strength increased gradually, and the elongation decreased gradually. The crystalline grain become more and more small. When cold rolled to0.2mm, the tensile strength of the joint with filler wire increased to725.5MPa, and the elongation rate down to0.57%. At this time, the SEM analysis of the tensile fracture shows that, there is litter toughening nest can be seen, and the fracture like the river pattern obvious, it is the typical brittle fracture. In the microstructure pictures, the size of the crystalline grain is obvious flat, and like the thin strips.