The TB3 Ti-10Mo-8V-1Fe-3.5Al and TB6 Ti -10V-2Fe-3Al two iron-containing titanium alloys were smelted in low voltage and small current for three times to analyze and discuss the quality and composition uniformity of the ingot and the ingot. The problem of component segregation and structural uniformity in alloys.
Keywords: TB3, TB6 iron-titanium alloy small current smelting macro and micro segregation
- 1 Metallurgical process analysis
TB3 and TB6 two alloys are nearly β alloys, Mo, V, Fe are β stable elements. The characteristics of near-beta alloys are as follows: high strength, plasticity, toughness; low phase transition point; small flow stress; beta spots are prone to occur, especially Fe element is limited in miscibility in beta-Ti, so beta is formed The chance of spots is relatively large. Under vacuum consumable arc melting conditions, the main factors affecting the crystallization segregation are: the distribution coefficient of the intermediate alloy element (the distribution coefficient of Fe element K = 0.3), the depth and shape of the molten pool, the cooling rate, the crystallization rate and direction , Size of transition zone of crystallization front, electromagnetic stirring current and time, etc. In other words, controlling the macro and micro segregation of the Fe element is mainly to formulate the corresponding smelting process parameters and control the area of the axial structure in the solidification process. When the ingot is smelted in a vacuum consumable furnace, most of the equiaxed structure is formed after the arc. Due to the different solidification methods and directions of the ingot during melting and after the arc is interrupted, it is easy to cause segregation of certain elements. In addition, the volume of the equiaxed crystal area of the ingot is determined by the depth and shape of the molten pool. The empirical formula for calculating the depth of the molten pool is: [7]
(D is the diameter of the ingot (m); H is the depth of the molten pool (m); ν is the melting speed (kg / s))
Known from the above formula, the melting rate is proportional to the bath depth, so reducing the melting speed can reduce the bath depth, which can reduce the equiaxed crystal area and prevent element segregation. Therefore, the use of small current smelting is the key to preventing the segregation of the components of this large-scale alloy TB6 and TB3. - 2 Selection of test melting parameters
This time uses three smelting, the finished ingot specification is Φ580, the ingot Φ580 after the second smelting adopts the rapid forging machine to open the forging to form (Φ500), and then performs three smelting after surface treatment. In the case of ensuring that the molten pool reaches the edge during the smelting process, take as little current as possible to reduce the melting rate and control the depth and shape of the molten pool. - 3 Analysis of crystal structure of ingot
After the second smelting, slice from the bottom of the secondary ingot and the billet after the billet is opened by the fast forging machine for low-magnification analysis. The low-magnification crystal structure is shown in Figures 2 and 3; after the finished ingot is forged to the corresponding fire time Carry out high-level tissue analysis, high-power organization as shown in Figure 4 and Figure 5.
It can be seen from the low magnification of the semi-finished product that the structure after the second smelting is relatively uniform and bright, and there is no obvious component segregation; the high magnification structure of the forged slab after the third smelting can also be seen that the α phase is in the β matrix The above is uniform precipitation, and there is no obvious white or gray β spot defect, that is, there is no or obvious segregation phenomenon of β stable element Fe. - 4 Sampling component analysis
Sampling from five parts on the side of the finished ingot after three smelting and nine-point sampling of the end face after the head riser (100 mm) sawing, the analysis data and results are as follows:
The following is the longitudinal component analysis data of TB6 and TB3 finished ingots (as shown in Figures 7 and 8)
The following is the horizontal component analysis data of nine-point sampling at the head end of the finished ingot of TB6 and TB3, that is, at the head 100 mm.
From the above data results, it can be seen that the intermediate alloy Fe elements in the TB6 and TB3 ingots are evenly distributed in the longitudinal direction of the ingot, and there is no large fluctuation; in the lateral distribution of the ingot, the third point of TB6 is slightly higher than the other points , But also within the scope of the standard requirements, which belongs to the normal fluctuation within the composition range (the maximum deviation error is 0.22), and does not belong to the phenomenon of component segregation. During vacuum consumable arc melting, the ingot has a wide range of solidification and cooling rate due to local solidification and cooling rate. It is very difficult to control the uniformity of the chemical composition of the ingot, and it is normal for the composition to fluctuate. Therefore, the two alloy ingots of this experiment do not have macroscopic segregation. - 5 Conclusion
(1) Use a small melting current (reduced by 4-7 kA current compared with other peers) to reduce the melting rate, supplemented by an appropriate arc-stabilizing stirring current, to prevent the iron element in high iron titanium near β alloy or β alloy from macro and micro The segregation above is effective;
(2) Small current smelting iron-titanium alloy can better ensure the uniformity of the ingot composition in the vertical and horizontal directions, thereby obtaining high-quality products;
(3) Low current smelting of alloys containing elements prone to segregation is the future research direction of smelting.
