Short process preparation method for titanium and titanium alloy pipes

Titanium and titanium alloy have excellent properties such as corrosion resistance, high specific strength and low permeability, and titanium alloy seamless pipes are widely used in aircraft piping systems, chemical transmission pipes and ship heat exchanger pipes and other special industries. In recent years, it has also been gradually applied to high value-added civilian fields such as condenser for power station, drill pipe for oil opening and heater for seawater desalination, with broad market prospects. According to statistics, the global Titanium Seamless Pipe market size in 2021 exceeded 2 billion yuan, and is expected to reach 2.9 billion yuan in 2027.

It is difficult to extract titanium from ore, and the traditional seamless tube preparation process is complex and costly, which limits the wider application of titanium and titanium alloy seamless tubes in the market. Due to cost constraints, many domestic and foreign civilian product industries still choose traditional stainless steel pipes or titanium welded pipes, rather than titanium and titanium alloy seamless pipes with better performance.

At this stage, in addition to titanium and titanium alloy seamless pipe preparation mainly refer to the stainless steel pipe industry equipment and processing technology for processing, high process maturity, small improvement space, can not effectively shorten the processing cycle and reduce processing costs. In order to reduce cost and increase efficiency, this paper decided to improve from the source, avoiding the traditional melting, forging, perforation and other processes, and carried out the process innovation and optimization of the whole process. The titanium alloy tube is obtained by smelting cast hollow tube billet, radial forging, double annealing and machining process, which can shorten the processing cycle and effectively reduce the production cost.

The traditional seamless preparation process of titanium alloy first produces cylindrical titanium alloy ingot through melting, and adopts hot forging process to prepare the bar, which requires heating, heat preservation, deformation and skinning at each fire. After the finishing of the bar blank, the tube blank is prepared by the method of cross rolling perforation and hot extrusion. Finally, the finished seamless pipe is prepared by auxiliary processes such as hot rolling, cold rolling and machining

The bar preparation technology has high energy consumption, long production cycle, large raw material production loss and low yield. When the hot extrusion method is used to perforate the tube billet, because the extrusion method eventually needs to leave the material head, the material utilization rate is low, the process flow is long, and the deformation resistance of titanium alloy is large, the need for larger tonnage extrusion equipment is limited, and the production of titanium alloy seamless tube is limited. The use of diagonal rolling perforation process to prepare the tube billet, this process has a short processing cycle, but because of the high temperature during processing, the obtained product organization is poor, most of them are basket organization or Weil organization, and the equipment covers a large area and has high energy consumption.

In order to solve the above technical problems and produce high-strength and high-toughness titanium alloy seamless pipe with low cost quickly and efficiently, a short process preparation method of titanium alloy and titanium alloy pipe is proposed in this paper, including: casting Titanium Tube billet production, radial forging, double annealing and machining processes, to obtain titanium alloy pipe, as shown in Figure 2. The concrete performance is to directly use plasma gun or electron beam gun to melt raw materials to produce hollow tube billet, and then improve the structure of the tube billet through radial forging, then double annealing to uniform the structure and eliminate the internal stress of radial forging, and finally adopt machining to ensure the surface quality and size of the finished tube. Direct smelting can not only shorten the process, but also effectively remove high and low density inclusions and obtain products with higher purity. Different from the traditional forging, radial forging can directly forge the tube blank, improve the processing efficiency and material utilization. Double annealing first promotes recrystallization of the product through high temperature, and then performs low temperature treatment to homogenize the tissue while eliminating internal stress.

In order to solve the above technical problems and produce high-strength and high-toughness titanium alloy seamless pipe with low cost quickly and efficiently, a short process preparation method of titanium alloy and titanium alloy pipe is proposed in this paper, including: casting titanium tube billet production, radial forging, double annealing and machining processes, to obtain titanium alloy pipe, as shown in Figure 2. The concrete performance is to directly use plasma gun or electron beam gun to melt raw materials to produce hollow tube billet, and then improve the structure of the tube billet through radial forging, then double annealing to uniform the structure and eliminate the internal stress of radial forging, and finally adopt machining to ensure the surface quality and size of the finished tube. Direct smelting can not only shorten the process, but also effectively remove high and low density inclusions and obtain products with higher purity. Different from the traditional forging, radial forging can directly forge the tube blank, improve the processing efficiency and material utilization. Double annealing first promotes recrystallization of the product through high temperature, and then performs low temperature treatment to homogenize the tissue while eliminating internal stress.

The cast tube billet was heated above the titanium alloy β phase transition point, then radial forging was carried out three times, and then double heat treatment was performed to obtain the finished tube billet, as shown in Figure 4. Different from the traditional forging, radial forging can directly forge the tube billet, improve the processing efficiency and material utilization rate, and at the same time, the cast grain of the tube billet is fully destroyed through a large number of deformation, and then the use of high-speed hammer, so that the grain is refined, so that the density, continuity and mechanical properties of the tube billet are improved, and excellent organization is obtained.

Before radial forging, a mandrel is inserted in the middle of the tube blank and clamped to the radial forging machine, and the first chuck is clamped on one end of the tube blank, the hammer is located on the other end of the tube blank, and the second chuck is clamped on the mandrel at the same end as the hammer head. Before forging three times, it is necessary to replace the mandrel, and the diameter of the mandrel is 15 ~ 20 mm smaller than the inner diameter of the clamped tube blank.

The heating temperature is 80 ~ 100 ℃ above the titanium alloy β phase transition point, and the holding time is ≥ 2 h; Multiple radial forging includes three radial forging. in the first radial forging, four flat hammer heads are used, and the tube blank is controlled to move along the central axis, the moving speed is 1 ~ 3 m/Mi n, the hammer speed is 1 000 ~ 2 000 n/min, and the deformation of the tube blank is controlled at 40% ~ 80%. After the first radial forging, the section of the tube blank is square on the outside and round on the inside.

in the second radial forging, four flat hammer heads are used to control the tube blank to rotate 40 ~ 50° around its own axis, then forging begins, and the tube blank moves along the central axis, the moving speed is 3 ~ 5 m/Mi n, and the hammer speed is 2 000 ~ 3 000 n/Mi N. The deformation of tube billet is controlled at 30% ~ 60%. After the second radial forging, the section of the tube blank is octagonal and circular.

Before the third radial forging, it is necessary to replace the mandrel, and the diameter of the mandrel is 15 ~ 20 m smaller than the inner diameter of the clamped tube blank. When forging, four curved hammer heads are used, and the surface diameter of the curved hammer head is 80 ~ 120 m larger than the outer diameter of the tube blank. The temperature of the waiting part is reduced to 40 ~ 60 ℃ below the titanium alloy β phase transition point, and the tube blank is controlled to rotate and move along the central axis, the rotation speed is 300 ~ 600 r p m, the moving speed is 3 ~ 5 m/Mi n, and the hammer speed is 50 ~ 100 n/Mi n. The deformation of tube billet is controlled at 30% ~ 40%. After the third radial forging, the product is restored to round tube blank, and the overall shape variable of Ti Tube or Ti Pipe is ≥ 100%.

The tube billet is heated to 80 ~ 100 ℃ above the phase transition point of titanium alloy β, and then radial forging is carried out three times. After high-speed hammer, the temperature of the tube billet is increased, thus reducing the deformation resistance, but at the same time, the situation of overheating will not burn the workpiece; In addition, in the process of three forging, the outer tube of the tube blank is forged from round to square, then from square to octagon, and finally from octagon to round again, so that the cast grain of the tube blank is fully destroyed, and after high-speed hammer, the deformation of the tube blank is increased, so that the grain is refined. As a result, the density, continuity and mechanical properties of the tube billet are improved, and the mechanical properties are increased by more than 15%, and the equiaxial or bimodal structure is directly obtained.