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Application of plasma-arc remelting of technogenic waste in movable horizontal mould for producing quality ferroalloys and master alloys.

In the course of conversion of defense facilities nomenclature of alloys, used in the industry, reduces, that's why application of many kinds of waste for metallurgical conversion into ingots of required composition requires, is connected at present with certain difficulties.

Processing of technological waste into different alloys and master alloys is anyway expedient because of many reasons. Firstly, single-stage processing of complex alloyed alloys into ready product is possible. Secondly, in production of ferroalloys and master alloys key parameters of the process may be reduced [1], for example, melting point, activity of highly reactionary metals, heat conductivity, etc.

Increased interest was noted to processing of the wastes of chemically active metals, for example, titanium into high-percentage ferrotitanium.

New technologies of titanium melting in electronbeam and plasma-arc furnaces with intermediate skull unit and pouring metal over into the mould, in which an ingot is formed, provide for producers of titanium products additional possibilities for more full and efficient use of titanium waste, and this enables significant reduction of the amount of titanium waste, which is traditionally used in production of 70 % ferrotitanium.

Increasing demand for 70 % ferrotitanium, on one hand, and reducing amount of titanium waste, on the other hand, stimulate development of new technologies for melting 70 % ferrotitanium. One of the options of such technologies is melting of 30-40 % ferrotitanium from ilmenite or rutile with its subsequent fusion with titanium scrap in the proportions, which ensure production of 70 % ferrotitanium [2].

One more problem exists. For 70 % ferrotitanium, used in melting of special-purpose stainless steels, increased requirements are established concerning content of harmful impurities (carbon, oxygen, and nitrogen). Such ferrotitanium may be produced only by the method of skull melting (without contact of molten metal with lining) be means of fusion of titanium waste with iron, using "clean" sources of heating--electron beam or plasma [3].

Developed in the E.O. Paton EWI plasma-arc method of charge remelting in movable mould allows avoiding such shortcomings, inherent to commercial methods of melting of ferroalloys [4, 5] as contamination of the metal with carbon, components, which enter into composition of lining, slag inclusions, nitrogen, and oxygen. This makes it possible to significantly improve quality of ferroalloys and alloyed steels [6, 7].

Purpose of this work is study of possibility of producing ferroalloys and master alloys from waste of highly reactionary and refractory metals, and determination of main technological parameters of the process of plasma-arc remelting in a flat cooled mould. The experiments were carried out on experimental plasma-arc installation OB1957 of the E.O. Paton EWI (Figure 1), additionally equipped with copper water-cooled mould (internal dimensions 600 x x 300 x 70 mm), mounted on a movable bogie. The installation includes a melting chamber, a movable bogie, a group of plasmatrons located above the bogie, and mechanisms for moving the bogie and oscillation of plasmatrons. Power sources of the PD-110 plasmatrons are transformers A-1458 complete with rectifying units A-1557.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

Waste of steel St3 and metal titanium, vanadium, niobium, molybdenum or alloys thereof with weight share of the main element not less than 95 %, were used as the charge.

The charge was loaded directly into the flat mould, and iron and alloying elements were uniformly distributed over the mould area. Then the movable bogie with the mould was placed under the plasmatrons, the chamber was vacuumized and filled with argon, and a small excessive pressure was created.

Principle diagram of the process is shown in Figure 2. In the experiments one plasmatron, located in center of the mould, was used. Remelting was started in extreme point of the charge location and due to transverse oscillations of the arc molten metal pool was induced all over the width of the mould. After formation of general pool the bogie with the mould and the ingot was moved at assigned speed.

Level of current in the experiments varied from 900 to 1100 A, frequency of transverse oscillations of the plasmatron-from 0.5 to 2.5 oscillations per minute, speed of the mould movement-from 5 to 15 mm/min, arc length-from 70 to 210 mm, thickness of the charge layer-from 60 to 180 mm. Amplitude of the arc oscillation corresponded to the mould width.

In the process of remelting voltage in the arc and stability of its burning were registered. After termination of remelting, depth of penetration and length of the pool were measured, and quality of produced ingot was studied. Using chemical and spectral analysis of taken samples distribution of alloying elements and harmful impurities over length, width and depth of ingots was measured.

Carried out investigations allowed choosing optimal parameters of melting and technological parameters, which ensure guaranteed penetration all over the ingot at depth 20-50 mm, depending upon chemical composition of ferroalloys and master alloys, whereby, as one had to expect, the higher is melting point of the alloying element, which enters into composition of the ferroalloy, the lower is thickness of an ingot, which ensures its full penetration.

Width of an ingot is determined by dimensions of the mould and, taking into account shrinkage of the metal, varies within 293-296 mm.

It is confirmed that level of the plasmatron current exerts significant influence on the penetration depth, and speed of the mould movement--on length of the molten metal pool. Arc voltage depends upon its length and angle of the plasmatron inclination.

Optimization of parameters of described technology allowed producing homogeneous ingots: variation of weight share of alloying elements over the ingot length did not exceed 4 %, width-1 %, depth-0.3%, which is quite acceptable for ferroalloys and master alloys. Chemical composition of molten ferroalloys and master alloys is given in Table 1.

As it follows from the Table, mentioned method of melting allows producing ferroalloys and master alloys of assigned composition with low content of carbon, oxygen, nitrogen and other harmful impurities, which contributes to high quality of these materials. In all cases taken samples did not have slag inclusions and had metallic color.

In Figure 3 specimens of 70 % ferrotitanium and 60 % ferromolybdenum, produced by the method of plasma-arc remelting of charge in movable mould, are shown.

Values of specific electric power and argon consumption at optimum mass of remolten metal of different chemical composition of ferroalloys and master alloys are given in Table 2.

[FIGURE 3 OMITTED]

As one can see from the Table, the higher is temperature of the main alloying element, the lower is optimum mass of the remolten metal and the higher is specific consumption of electric power and argon.

If increase of titanium content in ferroalloy enables reduction of its density and melting point of the alloy changes insignificantly [8], in melting of ferrovanadium, ferroniobium and ferromolybdenum sharp increase of temperature of alloys is observed as content of the main alloying element increases, which causes reduction of the pool dimensions and need to reduce optimum mass of the metal being remolten. For improving energy and economic indices it is necessary to increase dimensions of the mould and develop multi-plasmatron scheme of remelting, whereby dimensions of technogenic waste lumps may be commeasurable with dimensions of the mould, which does not require for special preparation of the charge.

This method of remelting of bulky charge may be recommended for development of a commercial melting complex of up to 1 t capacity with acceptable energy and economic parameters of the process and high quality of produced ferroalloys and master alloys.

CONCLUSIONS

1. It is established that plasma-arc remelting of charge in a movable mould allows producing high-quality ferroalloys and master alloys with low content of slag inclusions, carbon, oxygen, nitrogen, and other harmful impurities.

2. Values of specific consumption of electric power and argon at optimum mass of ferroalloys and master alloys of different chemical composition are determined.

[1.] Gasik, L.N., Ignatiev, V.S., Gasik, N.I. (1975) Structure and quality of commercial ferroalloys and master alloys. Kiev: Tekhnika.

[2.] Rozhkov, D.E. (2004) Tendencies of development of production and consumption of ferrotitanium in Russia and abroad. In: Proc. of Int. Conf. on Ti-2004 in CIS (St.-Petersburg, 25-26 May, 2004). St.-Petersburg.

[3.] Lakomsky, V.I. (1974) Plasma-arc remelting. Ed. by B.E. Paton. Kiev: Tekhnika.

[4.] Edneral, F.P. (1963) Electrometallurgy of steel and ferroalloys. Moscow.

[5.] Durrer, F., Folkert, G. (1976) Metallurgy of ferroalloys. Moscow: Metallurgiya.

[6.] Meskin, V.S. (1964) Principles of steel alloying. Moscow.

[7.] Vinograd, M.I. (1963) Inclusions in steel and its properties. Moscow.

[8.] Shank, F.A. (1973) Structures of binary alloys. Moscow: Metallurgiya.

V.N. KOLEDA, V.A. SHAPOVALOV, G.F. TORKHOV and A.V. AKSINICHENKO

E.O. Paton Electric Welding Institute, NASU, Kiev, Ukraine
Table 1. Chemical composition of alloys

 Weight share of elements, %

Ti V Nb Mo Al Si Mn Cu

28--29 0.15 -- 0.03 0.095 0.72 0.035 0.10
34--35 0.11 -- 0.025 0.30 0.56 0.15 0.12
39--40 0.16 -- 0.07 2.12 0.81 0.80 0.12
60--61 0.12 -- 0.05 1.47 0.47 0.09 0.18
64--65 0.19 -- 3.70 0.94 0.75 0.09
70--72 0.15 -- 0.35 1.64 0.75 0.24 0.15
78--81 -- -- -- -- 0.35 0.07 0.10
-- 35--36 -- -- 0.80 0.95 0.54 0.15
-- 50--51 -- -- 0.95 0.78 0.47 0.082
-- 61--63 -- -- 0.17 0.29 0.64 0.09
-- -- 35--36 -- 0.07 0.15 0.83 0.17
-- -- 55--56 -- 0.09 0.63 0.35 0.085
-- -- 60--62 -- 1.15 0.81 0.80 0.11
-- -- 68--70 -- 1.75 0.95 0.56 0.16
-- -- -- 55--56 0.95 1.22 0.63 0.13
-- -- -- 60--62 1.34 0.87 -- 0.011
59--52 -- -- -- 48--50 0.02 0.03 --
-- 50--52 -- -- 48--50 0.015 0.07 --
-- -- 50--52 -- 48--50 0.04 0.045 --

 Weight share of elements, %

Ti Sn C P S O N

28--29 -- 0.10 0.015 0.012 0.17 0.070
34--35 -- 0.12 0.014 0.017 0.21 0.085
39--40 -- 0.05 0.015 0.012 0.23 0.100
60--61 -- 0.11 0.001 0.013 0.18 0.092
64--65 0.012 0.10 0.015 0.010 0.27 0.150
70--72 -- 0.07 0.013 0.011 0.25 0.110
78--81 -- 0.05 0.012 0.010 0.11 0.120
-- -- 0.12 0.015 0.013 0.14 0.015
-- -- 0.09 0.012 0.013 0.17 0.027
-- -- 0.11 0.015 0.012 0.21 0.016
-- -- 0.12 0.013 0.014 0.13 0.022
-- -- 0.14 0.013 0.012 0.18 0.017
-- -- 0.085 0.012 0.014 0.20 0.019
-- -- 0.07 0.012 0.014 0.25 0.025
-- -- 0.10 0.010 0.011 0.12 0.025
-- -- 0.09 0.010 0.011 0.12 0.031
59--52 -- 0.05 0.010 0.010 0.11 0.025
-- -- 0.07 0.010 0.010 0.07 0.016
-- -- 0.04 0.015 0.010 0.09 0.024

Note. The rest is iron.

Table 2. Technological parameters of remelting process

Type of Weight share of Mass of metal in one
alloy alloying element, % melting, kg

FeTi 28--40 60--70
FeTi 60--70 50--55
FeTi 70--80 45--50
FeV 30--40 50--55
FeV 50--60 45--50
FeV 60--70 40--45
FeNb 30--40 45--50
FeNb 50--60 40--45
FeNb 60--70 35--40
FeMo 50--60 30--35
Al--Ti 50--52 45--50
Al--V 50--52 45--50
Al--Nb 50--52 45--50

Type of Electric power Consumption of
alloy consumption, kWh/kg argon, 1/kg

FeTi 1.0--1.2 70--80
FeTi 1.2--1.5 80--90
FeTi 1.3--1.6 90--100
FeV 1.0--2.3 120--140
FeV 2.1--2.5 125--145
FeV 2.3--2.7 130--150
FeNb 2.2--2.6 120--140
FeNb 2.5--2.8 130--150
FeNb 2.8--3.1 140--160
FeMo 3.3--3.7 150--170
Al--Ti 0.8--1.0 70--80
Al--V 1.0--1.2 75--85
Al--Nb 1.2--1.4 80--90
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Title Annotation:PLASMA-ARC TECHNOLOGY
Author:Koleda, V.N.; Shapovalov, V.A.; Torkhov, G.F.; Aksinichenko, A.V.
Publication:Advances in Electrometallurgy
Article Type:Report
Date:Oct 1, 2006
Words:1992
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