TITANIUM'99: SCIENCE AND TECHNOLOGY

ELECTRON BEAM MELTING OF TITANIUM·

Paton B.E.,·Trigub N.P., Akhonin S.V. E.O.Paton Electric Welding Institute

Kyiv. Ukraine

One of the basic factors that restrict the application of titanium in different industries is a high cost of titanium semi-finished products. In this connection. the challenge now is to find ways for cutting the costs of the manufacture of the titanium semi-finished products.

The cost of titanium sponge and alloying elements constitute 40-75 % of the cost of the manufacture of titanium ingots [1]. Therefore. recycling of scrap and utilization of the lower-quality and, hence, less expensive grades of the titanium sponge are an important reserve for reducing the cost.of the manufacture of the titanium semi-finished products.

It is· a known fact that the capabilities of recycling of scrap using a traditional process of the manufacture of titanium ingots by the method of vacuum-arc melting (VAM) are limited to 20-30 %. Relatively low vacuum within the melting zone (10-100 Pa) and leakage of air into the melting chamber cause an additional contamination of titanium with. oxygen and nitrogen.

This prevents the use of a lower-quality (cheaper) titanium sponge combined with scrap as the consumable electrode. In addition. entrapment of inclusions of refractory metals (e.g. pieces of cutting tool hard alloy pla~es) and lumpy titanium sponge saturated with nitrogen and oxygen may be a problem in this case. These types of the inclusions in VAM pass to the ingot [2]. They persist in metal of the semi-finished products during further processing and may be a cause of an unexpected failure of a structure.

The radical method for removal of such inclusions during the

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process of ingot melting is electron beam melting using an intermediate crucible (EBMIC).

The E.O.Paton Electric Welding Institute developed the technology and commercial equipment (Fig. 1) to realize this process. In addition to melting ingots of round or rectangular section (slabs), the equipment is also intended for making· the operation of surface melting of the ingots, instead of machining.

Titanium sponge of different fractions, which does not need to be preliminarily pressed into a consumable electrode, and lumpy titanium scrap are used as the initial charge. The content of the scrap used in the charge can amount to 100 %.

During the time of. dwelling of .liquid .metal in the intermediate crucible the heavy particle§ (with a density of more than 4 g/cm3) settle down to tqe bot.tom and are· accumulated in the skull (Figs. · 2 and .3) ~ · while the itgh.ter particle~. (with a density of less than 4 g/cm3) float .up to the surface of the melt, where they are destructed, under the effect of the Blectron beam. The hydrogen content of the ingots is decreased 3-6 times, while the concentration of oxygen and nitrogen remains at a level of their content of the initial raw materials.

Therefore. owing to the use of the intermediate crucible, the metal is refined and cleaned from inclusions and gases. It should be emphasized that the concentration of impurities in the ingot is not higher than that required by specifications for commercially pure titanium applied as the charge for titanium sponge with a hardness of up to 130 HB, i.e. the lower-quality titanium sponge (TG-120 grade) can be used for the manufacture of the commercial-purity titanium ingots.

Technologies developed by the E.O.Paton Electric Welding Institute provide consistent chemical composition and high quality of the ingots of titanium-base alloys, despite evaporation of alloying elements. aluminium in particular (Table 1) .

Selective evaporation of aluminium during melting is compensated for by its increased content in the initial billet.

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TITANlUM'99: SCIENCE AND TECHNOLOGY

Fig. l. Electron beam furnace with power 1200 kW for remelting of

titamum sponge and scrap.

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TITANIUM'99: SCIENCE AND TECHNOLOGY

2

I

Fig.2. Mechanism of nonmetallic inclusions during electron beam-melting with could hearth: I - electron beam gun; 2 - melting electrod; 3 - low density inclusion; 4 - high density inclusion; 5 - could hearth; 6 - skull; 7 - ingot.

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Fig.3. High density inclusion into skull.

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TITANIUM'99: SCIENCE AND TECHNOLOGY

Table 1. Content of alloying and admixture elements in titanium electron beam

melting ingots.

Alloy Sampling Concentration of elements, %

place Al v c Fe Si 0 N

VT6 Top 5,90 4,38 0,01 0,08 0,02 0,08 0,02

Middle 6,00 4,30 0,02 0,10 0,02 0,08 0,02

Bottom 6,00 4,38 0,01 0,09 0,03 0,08 0,02

GOST Min 5,3 3,5

19807-74 Max 6,8 5,3 0,10 0,30 0,15 0,20 0,05

VTl-00 Top 0,27 0,03 0,08 0,04 0,07 0,02

Middle 0,30 0,02 0,10 0,02 0,06 0,02

Bottom 0,24 0,02 0,12 0,03 0,07 0,03

rocT Min

19807-74 Max 0,3 0,05 0,20 0,08 0,10 0,04

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H

0,001

0,001

0,001

0,015

0,001

0,001

0,001

0,008

TITANIUM'99: SCIENCE AND TECHNOLOGY .

As with other methods of melting titanium ingots. the ingots produced by EBMIC have surface defects ·of the 'buckle' type. Although in our case their depth does not exceed 2.5-3.0 mm, for further processing the ingots should be subjected to machining. Up to 8-10 % of metal go to chips. Since during EBMIC the ingots cool down in deeper vacuum, as compared with VAM. formation or a gas-saturated layer on the surface. avoid the above metal losses, we developed the

this prevents ·Therefore. to technology for

electron-beam surface melting to be used instead of machining (Fig. 4). This ~llows the cost of the manuf~ctur~ of th~ ingots to be reduced and. at the same time, contamination of the surface layer and, therefore. the loss in_ quality to be elimin~ted.

·Moreover, the process of surface me~ting, in addition to removing the surface defects, provides an improvement in a microstructure of the remelted layer by grain refining (Fig. 5).

The E.O.Paton Electric Welding ·Institute ·developed and manufactured a special machine for :electron beam melting of the surface layer of the titanium ingots. It is intended for surface melting of round ingots up .~o 600 mm in diameter and_ up to 2000 mm long and slabs up to 400x950x2000 mm in size. Productivity of one machine of this type is more than 1000 t of titanium ingot.s per year: Experience gained in operating this macpine shows that with this technology the yield of metal is increased and labour consumption is decreased by 25-35 %, as compared with machining.

. .

The possibility of producing ingots -· slabs ·with a . . rectangular· cross section allows the cost or production o-r·p1ates to be decreased (Fig. 6), as it excludes from the technology chain the operation of re-forging of cylindrical ingots into slabs and increases metal yield.

Plates 1500x5500 mm in size and 6 mm thick were produced from slabs by hot deformation. Tubes with an inside diameter of 10 to 3S mm and wall thickness of 0.8. to 2· mm were produced directly from a round cast billet of VT1-0 alloy by cold rolling. Mechanical characteristics of the cast and deformed metal are given in Table 2.

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TITANIUM'99: SCIENCE AND TECHNOLOGY

Fig.4. EB ingot diameter 600 mm, len!:,>th 2000 mm with glazed surtace.

f'ig.5. Macrostructure of EB ingot from Ti6Al4 V alloy with sLu-face

glazing.

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TITANIUM'99: SCIENCE AND TECHNOLOGY

Fig.6. EB ingot-slabs: thickness 160 mm, width 950 mm, length 2000 mm.

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TITANruM'99: SCIENCE AND TECHNOLOGY ·

The EBM processes developed by the E.O.Paton Welding Institute provide the high-quality titanium slabs with a homogeneous defect-free structure.

..

Electric ingots and Equipment

available at the Scientific-Production Centre 11 TITAN 11 makes it .· j.

possible to produce commercial'·· batches of titanium ingots of different standard sizes with an annual output of 1~00 t.

- "

Based on the developed technology for electron ~earn melting of titanium -·alloy ingots. in the .. last years -the E. o. Paton Electric'·Welding Institute has been active in research and development aimed at production of domestic high-strength titanium alloys with a good weldability.

Currently available are two new domestic alloys which in the level of strength borrespond to alloys VT6 and VT22 and. at the same time. have a more favourable combination of mechanical properties in the cast and deformed conditions (Fig. 7) .. improved weldability and corrosion resistance which is higher -tha~ that of commerc1al-pur1·ty titanium (Table 3).

It should be emphasized once more that. unlike the existing concepts that EBM can be applied only for processing of titanium

. . -'. ~

scrap or at l~ast for produttion of ingots of commercial-purity titanium. this technology makes it possible to produce ingots from multicomponent titanium ~lloy~ by remelting titanium sponge and alloying elements.

As to chemical . composition and mechanical properties. titanium. semi-finished products maqe fr.om- the EBM· metal meet in full all requirements of domestic and foreign standards.

The technology developed allows the cost of the manufacture of titanium semi-finished products to .be reduced and, hence. their competitiveness to be increased and fields of application of titanium in. different industries to be widened through using cheaper raw materials and increasing the total yield of metal.

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TITANIUM'99: SCIENCE AND TECHNOLOGY

Table 2. ~echanical properties of cast and deformed metal.

Characteristic of crs, Mila cro.2 , MIIa. 0 % ' \V, %

metal

Cast 237 330 27 65 Sheet 360 447 33 60 (thickness 6 MM)

Specification 275 345 20 ASTM B265-79 Tube 290 400 47 75 (diameter 38 MM,

wall thickness 2 MM)

GOST 22897-86 245 343 24

Table 3. Corrosion of titanium alloy Ti-Al-Nb-Fe-Zr.

Alloy Corrosion velocity, mm/year

(500 hour under 20 °c)

5% HCl 10% HCl · 5% H2S04 · 10% H2S04 spirits + 0,4% HCI

VTl-0

Ti-Al­

Nb-Fe-Zr

0,0050 0, 102 . 0,0045

0,0002 0,0083 0,0002

1382

0,0091

0,0005

<2000

>2000

-w 00 w

~ BT22

c=J 7Z-4e-#C-Fe-Z~

JIHTbe

KCV

KCU .3TB

EZ2J BT22

~ Tt,· -/le-#b-Ee-Z1-r

6a

_ ... '

1<.C IJ

KCU 3TB

/

rzz:za BT6

l=:J Ti -At-N6-ie-1r: 68

JIHCT

d /<.CU /(.CU

3T8

Fig. 7. Mechanical properties of titanium alloys.

!2Z3 8T6

c===i T; -At. -#6 ·Fe -Z""

JUiTbe

!(CU 3TB

/

TITANIUM'99: SCIENCE AND TECHNOLOGY

1. Anoshkin B. F. . __ ~9oanov .V. s. . Shiryaev E. P. State-of-the-art bf productio-r1· and a·pplication of titanium in the CIS countries// -1st Intern._ Scient.-Techn.· Conf. on titanium in

L • ' ~

the CIS Countries. -Science. production and application of .. - . . - ..

titanium under, the conversiort conditions. Part 1 - M.: VILS, 1994. - P. 3-17.

2. Musatov··M: I:. - . Chuchurkin .k D .. Fridman·- A."Sh. Development of melting of~-defect-free ingots II -1st-Intern.- Scient.-Techn. Conf. on Titaniu~ in the CIS Countries. Science. production and application of tit~nium under the conversion conditions. Part 1 -M. : VILS. 1994. P. -2-28,-233,-

·,, .

.. - .

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