Electron beam and plasma beam cold hearth smelting are two basic methods of active metal and refractory metal smelting. The two processes are basically similar, but the heat source is different. In these two processes, the raw material is first melted in a water-cooled copper bed, then the molten metal passes through the refining zone, and finally enters the ingot mold through the casting port, and solidifies in the ingot mold. Both processes can use a variety of raw materials, including cutting scraps, rolling, forging and other process returns, cutting heads, and sponge titanium and master alloys. Electron beam cold hearth melting is carried out under a vacuum of 1.3X103Pa or higher: those elements with high vapor pressure (such as aluminum) are easily evaporated under the high vacuum atmosphere of electron beam melting, so these elements must be added to compensate their volatilization loss. At present, the ingot produced by electron beam cold hearth melting can weigh up to 22.7t, and can produce round ingots and square ingots. The common ingot size of industrial pure titanium or unalloyed titanium is 660mm X1320mmX4000mm and weighs 16t. The melting capacities of pure titanium and titanium alloys are 3.6t / h and 2.3 / h respectively.
Cold hearth melting can use lower cost raw materials to reduce the cost of titanium alloys, and only one smelting is required. Although each of the above-mentioned processes is actively sought by people, there are still certain problems in directly rolling the ingot without completely cooling it. Because the rolling processing equipment is generally far away from the melting site, and the ingots generally need to be descaled before rolling. The diameter of titanium hearth production is 76cm. For the Ti-6Al-4V ingot weighing 4000 kg, a sample is taken every 125 mm along the direction of the ingot for chemical composition analysis during the smelting process.
Chemical composition of ingot
Element Al V O
Average 6.28 4.16 0.176
Standard deviation 0.145 0.068 0.004
Maximum 6.66 4.25 0.181
Minimum 6.05 3.97 0.166
Very bad 0.61 0.28 0.015
The raw material composition for producing the ingot is: 31.6% titanium sponge; 62.4% Ti-6Al-4V chips; the rest is aluminum and Al-V master alloy. First, turn the surface of the ingot to about 6mm, and then roll it on the traditional steel rolling equipment according to the following process system:
① Heat the ingot to 1150 ℃ and roll it into a square billet of 210mmX1030mmX 3810mm;
② Cut into 3 parts and heat to 940 ℃, roll into 25mm, 38mm and 64mm thick plates;
③The final rolling annealing is 760 ℃, 1h;
④Each board is cut into 2 pieces, and finally all are polished by belt.
Under this process system, the final yield from the ingot to the titanium plate is 71%. When the output is large and the plate is thick, the yield from ingot to titanium plate can also reach 80%. The yield rate is an important parameter that determines the final cost and the final rolled material price. Tests have shown that the tensile properties of the longitudinal and transverse specimens of the end of the titanium plate exceed the requirements of MIL-T-9046J AB-1 and MIL-DTL 46077F standards. For titanium plates for structural applications, solution treatment and aging treatment are generally required, but for armor applications, studies have found that the annealed structure has the best ballistic resistance. www.lh-ti.com studied the effect of annealing temperature on the ballistic performance of Ti-6Al-4V alloy, and evaluated the effect of different deformation heat treatment processes on the ballistic performance of Ti-6Al-4V alloy. The results show that the cross-rolling is better than the general rolling for the elastic properties of the sheet. Rolling in the α + β area is better than rolling in the β area; unannealed is better than annealing, and annealing in the α + β area is better than β annealing. Once the β area is annealed, it is annealed in the α + β area, and Can not restore the material properties; the rolled or annealed state is better than the solution treatment and aging state.