Influence of Cold Rolling on Microstructure and Properties of Industrial Pure Titanium coil Weld
Industrial pure titanium has excellent corrosion resistance in oxidizing and neutral media, and has been widely used in various fields such as petrochemical industry and salt production. It has been reported in the literature that after argon arc welding of industrial pure titanium, there will be a molten pool area and a heat-affected zone. Corrosion phenomenon is preferred. Plasma welding has the advantages of high energy density, large line energy, and high efficiency. Using this method to weld pure titanium plates can overcome the tungsten electrode that may occur when the tungsten electrode is closer to the molten pool when welding with single-pass tungsten argon arc welding. Corrosion, making the weld penetrate into tungsten inclusions and other defects.
The coil production line of a company's strip factory adopts sheet tailor welding technology to make titanium coils, so there will be several deformed welds in the Cold rolled titanium coil product. Whether these deformed welds can be used normally with other parts of the coil is a question Coil usage has a major impact. The researchers conducted research on the organization and performance of the weld processing area and the base metal area, aiming to provide reference for the production and use of tailor-welded coils.
The experimental material is 3.5mm thick industrial pure titanium plate, the grade is TA1. The Nertamatic 450 automatic plasma welding machine is used to weld two annealed pure titanium plates into a cold-rolled slab with a size of 3.5mm×1350mm×1520mm. The XXH2005 X-ray flaw detector was used to conduct non-destructive inspection on the weld seam of the welded sample plate, and the microstructure of the base metal and weld seam was observed with a metallographic microscope. The slabs that have passed the flaw detection inspection are cold-rolled in two rolling passes on a 1780mm cold rolling mill: the deformation in the first rolling pass is 43%, the thickness of the plate is reduced to 2mm, and annealing is performed at 680°C×30min/AC after rolling; The deformation amount in the second rolling process is 50%, and the finished plate with a thickness of 1mm is obtained, which is annealed at 650°C×30min/AC after rolling.
Carry out X-ray non-destructive flaw detection inspection on the plate weld processing area of the two rolling processes; conduct metallographic microstructure observation on the cold-rolled and annealed weld samples of the two rolling processes; Hardness and room temperature mechanical properties test; use Meters ETC1604 cupping test machine to conduct cupping test on the annealed finished plate to investigate the process performance; use PARSTAT-2273 electrochemical comprehensive test system (the reference electrode is a saturated calomel electrode, The auxiliary electrode is a platinum electrode, and the corrosion solution is 3.5% NaCl aqueous solution), and the anodic polarization test is carried out on the annealed finished plate to investigate the corrosion resistance. test results:
(1) The weld quality of the pure titanium plate after plasma welding and the pure titanium plate after two times of cold deformation and annealing all meet the requirements of Class I of JB/T 4730.2 standard.
(2) After the two times of cold deformed plate annealing, the grain size of the weld processing area is slightly smaller than that of the base metal area, the strong plasticity is slightly better, and the Vickers microhardness is also slightly higher.
(3) After cold deformation and annealing in two rolling passes, the elongation of the weld processing zone of the plate is not much different from that of the base metal, the cupping value is similar, and the process performance is comparable to that of the base metal.
(4) There is no significant difference between the anodic polarization behavior of the weld processing zone and the base metal, and the corrosion resistance of the two in 3.5% NaCl aqueous solution is basically the same.
In the cold rolled titanium coil rolling production process, pickling is a necessary and very important process. The main function of pickling is to remove the oxide layer and dirt on the surface of the titanium coil from the hot rolling factory, and obtain a titanium coil with a clean surface to avoid Defects occur during rolling. The oxide layer is removed by chemical reaction with the acid solution after the titanium is rolled into the pickling tank, but because the chemical reaction needs to be activated at a certain temperature, the temperature is too low, the reaction will be slow, and the rust removal effect will be poor. If the temperature is too high, it will cause over-pickling, which cannot meet the production requirements; therefore, in order to ensure the best pickling effect, it is necessary to continuously heat the acid solution to meet the temperature requirements of the rust removal reaction, and keep the acid at a certain temperature. within range.
The traditional pickling process uses a graphite heat exchanger to heat the acid liquid. During production, the boiler generates high-temperature steam to transfer heat to the acid liquid through the graphite heat exchanger. However, in production and application, graphite heat exchangers have major disadvantages such as low heating efficiency, troublesome operation, environmental pollution caused by boiler combustion, and excessive carbon emissions. The microwave heating method is used to heat the acid liquid, which changes the heating method of the acid liquid and fundamentally solves the problems in the traditional process. Compared with traditional heating, microwave heating has the advantages of selective heating, fast heating rate, high heating efficiency, and easy automatic control. The Microwave Application Research Institute of Kunming University of Science and Technology has developed a new type of microwave heating device for cold rolling pickling solution of titanium coils, as well as the matching control cabinet, operating table and cooling system. The main structure of the device is cavity, microwave generator, temperature sensor, heating tube and so on. The cavity is designed as a heptahedron structure, and the microwave generators are arranged on the seven surfaces of the cavity in a ring shape. The number of microwave generators determines the maximum power of the microwave heating device. The heating tube is made of PPH material and placed in the cavity of the microwave heating device. In the body, temperature sensors are respectively arranged in the input end and the output end of the heating tube.
