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Production of large ingots of titanium-based creep-resisting alloys by electron beam melting.

World trends in the development of the technology of production of ingots of creep-resisting titanium alloys and semifinished products and its alloys for the manufacture of components are practically identical for the leading aviation companies, i.e., production technology is an important link in ensuring the stability and the required level of the service properties.

One of the promising directions of metallurgical production of creep-resisting titanium alloys is electron beam melting (EBM) which not only refines these materials to remove gas and volatile metallic impurities but also greatly simplifies the metallurgical processing processes and produces components with the quantitatively new physical-chemical and mechanical properties.

Electron beam melting can also be used to produce ingots of complexly alloyed titanium alloys by remelting the primary charge in the form of titanium sponge and master alloy (1).

In the conditions of the existing technological system of production of creep-resisting titanium alloys, special importance is attached to the examination of the process of solidification of ingots of various parameters.

The E.O. Paton Electric Welding Institute has carried out detailed investigations into the production of ingots of creep-resisting alloys by the EBM method (2). In the determination of the technological parameters of the melt special attention was given to the heating conditions of the surface of the ingot between the solidification mould, determined by mathematical modelling methods. Experiments were carried out with the production of ingots of VT8 creep-resisting titanium alloys with a diameter of 200 mm and also VT3-1 alloys with a diameter of 400 and 500 mm.

To optimise the melting process and pro-duce ingots with a guaranteed chemical com-position, and also minimise the losses of the alloying elements in EBM of large ingots of creep-resisting titanium alloys, the technological parameters of melting for ingots with a diameter of 840 mm were determined by mathematical calculations (3). The results of the calculations using the mathematical model were used to determine the temperature field in an ingot with a diameter of 840 mm made of VT3-1 creep-resisting titanium alloys for electron beam melting with an intermediate crucible (EBMIC) with different productivity ((Figure 1).

[FIGURE 1 OMITTED]

The dependence of the thermal state of the ingot in EBMIC on melting productivity was investigated. The dependence of the depth of the liquid bath and of the general losses of metal through evaporation on the productivity of the melting process was determined (Figures 2 and 3).

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The experimental results show that the depth of the liquid bath for a number of the working values of the productivity of the melting process does not exceed half the diameter of the ingot which is a satisfactory result from the viewpoint of solidification theory (2).

The ingots were produced in UE5010 industrial electron beam equipment (4). This equipment is characterised by high technological parameters in certain processes, achieved by simply replacement of one device by another, so that it is possible to carry out melting of circular cross-section ingots with a diameter of up to 1200 mm and right-angled section ingots up to 420X1300 and up to 4000 mm long.

The results of the theoretical and experimental investigations of the process of EBMIC of the ingots with a diameter of 200-500 mm were used to develop a technology of production of high-quality ingots of creep-resisting titanium alloys with a diameter of 840 mm, free from low and high density inclusions. Electron beam equipment UE5810 was used for the first time in the world to produce, from the primary charge, a large ingots of VT3-1 creep-resisting titanium alloys with a diameter of 840 mm (Figure 4).

[FIGURE 4 OMITTED]

The ingots of the clip-resisting titanium alloys, produced by the EBMIC methods, are free from discontinuities, nonmetallic inclusions larger than 1 mm and also high-density clusters of finer inclusions. The structure of the metal is dense, and there is no crystalline heterogeneity and zonal liquation in the ingots. The distribution of the alloying elements both along the length and in the cross-section of the ingots is uniform, and the content of the impurity elements is in the allowed range according to GOST 19807-91 (Table 1).
Table 1. The distribution of alloying elements and impurities along the
length in an 840 mm amateur ingot made of VT3-1 titanium alloys,
produced by electron beam melting in an intermediate container

Ingot Sampling Mass fraction of elements,%
section area

 Al Mo Cr Fe Si

Top A 6.25 2.28 1.72 0.29 0.32

 C 6.30 2.40 1.83 0.30 0.33

 P 6.15 2.35 1.63 0.30 0.33

Middle A 6.20 2.27 1.73 0.29 0.33

 C 6.27 2.38 1.70 0.29 0.35

 P 6.18 2.36 0.70 0.30 0.30

Bottom A 6.25 2.43 1.88 0.28 0.36

 C 6.26 2.50 1.95 0.28 0.35

 P 6.14 2.44 1.90 0.26 0.30

GOST 19807-91 5.57.0 2.0 3.0 0.8...2.0 0.2...0.7 0.15...0.40

Ingot Sampling
section area

 H o

Top A 0.001 0.09 0.011

 C

 P

Middle A 0.001 0.11 0.009

 C

 P

Bottom A 0.001 0.09 0.011

 C

 P

GOST 19807-91 <0.015 <0.15 < 0.05

Comment. A--in vicinity of ingot axis, C--at middle of
the radius, P--in peripheral zone (10 mm from ingot surface).


The ingots with a diameter of 840 mm were used to produce semifinished products in the form of forgings and bars (Figures 5 and 6).

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

The macrostructure of the forged bars with a diameter of 45 mm made of VT3-1 creep-resisting titanium alloys was determined on longitudinal and transverse templates. The grain size was No. 4 on the 10-number scale VIAM 1054-76 (Figure 7), which fully satisfies the standard requirements. The macro-structure of the bars was free from cracks, delamination, cavities, films, metallic and nonmetallic inclusions, determined by visual examination.

[FIGURE 7 OMITTED]

The experimental results show that the properties of the semifinished products, produced from the ingots melted by the pro-posed EBMIC technology correspond to all the requirements imposed by the industry on the quality of creep-resisting titanium alloys (Table 2).
Table 2. Mechanical properties of the forgings of VT3-1 creep
resisting titanium alloy

Forging [[sigma].sub.B] [sigma], [psi], KCU, J/ HB
No. MPa % % [cm.sub.2]

Ts812 1150...1160 10 23 35 360

Ts815 1100...1110 12 26 40 320

Kh479 1090...1100 13 25 38 316

Ts819 1120...1130 11 24 37 358

Kh490 1060...1065 12 26 40 332

Ts836 1160...1170 10 24 36 361

Ts840 1180...1190 9 22 32 363

Kh466 1060...1070 12 25 35 330

I255. 950...1200 >9 >22 > 30 269...363
105.091-87


The processes of electron beam melting, developed at the E.O. Paton Electric Welding Institute, can be used to produce high-quality ingots of titanium and its alloys with a homogeneous defect-free structure. The equipment, constructed at the Titan Scientific and Production Centre of the E.O. Paton Electric Welding Institute can be used to produce industrial batches of titanium ingots of different standard dimensions with the annual production volume of up to 5000 t.

The proposed technology reduces the production cost of titanium semifinished products as a result of the application of cheaper initial materials and increasing the yield of suitable metal and, consequently, increases the competition capacity and widens the areas of application of titanium in different branches of the industry.

Thus, as a result of the development of the technology of electron beam melting of creep-resisting titanium alloys and of equipment for producing high-quality ingots it has been possible to organise in Ukraine production high-quality ingots of creep-resisting titanium alloys capable of competition on the world markets.

Conclusions

1. The method of electron beam melting in an intermediate container (cold hearth) was used for the first time in the world to produce ingots of the VT 3-1 creep-resisting titanium alloys with a diameter of up to 840 mm.

2. The extensive investigations show that the properties of the semifinished products, produced from the ingots melted by the EB- MIC method satisfy the requirements, imposed by the industry on the quality of the creep resisting titanium alloys.

3. A technology has been developed for the electron beam melting of the ingots of creep-resisting titanium alloys, and specialised equipment has been constructed for this technology. Consequently, it has been possible to organise in Ukraine the production of high-quality ingots of titanium alloys capable of competition on the world market.

References

(1.) Trigub N.P. and Zhuk G.V.,Sovremen. Elektrometal-lurgiya, 2008, No. 4, 7-9.

(2.) Paton B.E., et al., Electron beam melting of titanium, Naukova Dumka, Kiev, 2008.

(3.) Paton B.E., et al., Sovremen. Elektrometallurgiya, 2008, No. 3, 22-24.

(4.) Paton B.E., et al., Electron beam melting of refractory and high-reactivity metals, Naukova Dumka, Kiev, 2008.

B.E. Paton, N.P. Trigub, V.A. Berezos, V.A. Kryzhanovskii and A.Yu. Severin

E.O. Paton Electric Welding Institute, Kiev
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Title Annotation:ELECTRON-BEAM PROCESSES
Author:Paton, B.E.; Trigub, N.P.; Berezos, V.A.; Kryzhanovskii, V.A.; Severin, A.Yu.
Publication:Advances in Electrometallurgy
Geographic Code:4EXUR
Date:Jul 1, 2010
Words:1534
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