Технические науки/1. Металлургия

Zhiguts Yu.Yu.¹, Lazar V.F.², Mojsyuk S.I.¹

¹Uzhgorod National University, Ukraine

²Mukathevo State University, Ukraine

SPECIAL GREY TERMITE CAST IRONS

The important problem for modern production is not only making up new materials and improving the properties of traditional ones but also supplying of the production with spare parts and tools of non-common applying, the need of selfproviding of those appears at small enterprises and in the shops where required base is absent.

Deep studying of the question makes it possible to consider that the problems mentioned above can be solved successfully when using as machine-building alloys the materials got by the process of burning of exothermic powder mixtures.

This method can be successfully used also for metal economy at the plants of large scale and mass production of machine-building parts and tools.

That is why the synthesis of materials on the basis of metallothermic processes as well as the investigation of the influence of new technological methods of getting metal on microstructure, chemical composition, mechanical properties of manufactured castings got great practical importance.

Metallothermic reactions further and further become of great appliance in science and technology. Under the lack of energetic and raw basis, of special melting and cast equipment such technological processes of creating the materials become economically expedient, and their usage in already existed methods of casting production e. g. in technique of producing steel and cast iron castings with termite addition greatly rises the efficiency of production.

Creating of the alloys on the basis of combined (metallothermic+SHS) processes allows getting materials with new technological properties the study of which has both scientific and practical importance.

While organizing the process of synthesis of steels and cast irons classic [1] termite reactions based on oxidation of aluminum and renovation of iron are used.

Fe₃O₄+Al→Fe+Al₂O₃

The task was to work up the method of calculating of burden composition on the basis of stechiometric relationship of reaction components with the introduction of suitable coefficients taking into account the component activity and the coefficients of its adoption by metal.

The method allows to establish the composition of metallothermic burdens and to calculate adiabatic temperature of its combustion. The main condition of the process is the necessity to have real temperature of burden combustion higher than the temperature of slag melting [2] (for Al₂O₃ 2400 K).

The main structure components in termite cast irons that influence greatly the wear resistance are the carbides. First of all these are cementite and more wear resistanceable carbides Cr, W, Mo, Ti and others.

If we assume that synthesized termite cast irons of carbide class have one-type phase composition, then to determine its ware resistance will be possible using the scheme: the more is their hardness, the more is the wear resistance. But while investigating the components of the structure and their influence on wear resistance it is necessary to use the principle of Sharpi-Bochvar, and, taking into account the necessity to shape the construction part the technological form (we mustn't forget that the rise of hardness leads simultaneously also to the deterioration of machining by cutting). Metal base of the alloy must contain a hard component and must prevent brittle break.

Wear resistance of synthesized cast irons under abrasive wear resistance depends on microhardness, form, replacement and quantity of structural components.

It is the most convenient to get grey cast irons by metallotermic or combined (metalloterming+SHS) methods because of the high temperature within the zone of reacting of the components that leads under synthesis of alloys in conditions of micromelting to fast cooling and that in its turn gives the speeds of cooling higher than the critical ones and simultaneously martensite or needle-shape microstructure. These are the structures that are of the highest wear resistance.

Grey termite cast iron is being manufactured very well by cutting, much better than chilled and white cast irons.

The burden composition for synthesis, chemical composition and components of the burden for getting wear resistant termite cast iron and its mechanical properties are shown in table 1 and 2.

Table 1

Chemical composition of the burden for synthesis of grey termite cast iron

№	Electrode powder, percent	Ferrosilicium (ФС 75)	Ferro-manganese (ФМн 75)	Ni powder	Ferrochrome	Ferroalumini-um termite
1	4,0–4,2	1,6–2,0	1,3–1,6	4,2–4,8	0,4–1,1 FeCr	The rest
2	4,0–4,2	3,3–3,8	1,0–1,5	4,0–4,5	0,7–1,4 FeCr	The rest
3	4,0–4,2	1,6–2,0	3,8–4,3	4,8–5,3	0,9–1,6 FeCr	The rest
4	4,0–4,2	1,6–6,0	4,0–4,3	5,5–6,1	–	The rest
5	4,0–4,2	2,0–2,7	4,3–5,1	5,5–6,0	0,7–1,4 FeMo	The rest

Table 2

Chemical composition and hardness of martensite grey cast iron

№	Element content, per cent							HB
	С	Si	Mn	S	P	Ni	Cr and Mo	In alloyed state	After tempering^1
1	3,0–3,2	1,2–1,5	1,0–1,2	<0,05	<0,1	4,2–4,8	0,3–0,8 Cr	390–430	–
2	3,0–3,3	2,5–2,8	0,7–1,1	<0,05	<0,1	4,0–4,5	0,5–1,0 Cr	370–440	–
3	3,0–3,2	1,2–1,5	2,7–3,2	<0,1	<0,1	4,8–5,3	0,7–1,2 Cr	270	390–400
4	3,0–3,2	1,2–1,5	3,0–3,2	<0,1	<0,1	5,5–6,1	–	280–292	–
5	3,0–3,3	1,5–2,0	3,2–3,8	<0,05	<0,1	5,5–6,0	0,5–1,0 Mo	290–310	–

¹Tempering was being done under 550ºC during 12 hours.

Within cast irons 1, 2 martensite is formed just during metallothermic melting without certain termomanufacturing which is furthermore connected with replacement of critical point regarding alloying of Ni.

Cast irons 4, 5 (table 2) contain great amount of austenite but after tempering we get the structure of martensite of tempering with hardness being 280-310 HB.

Cast iron 3 is being got with substantial chilled layer of material. Martensite in grey cast iron is being got without additional termomanufacturing (tempering) and this effect decreases with the increasing of mass of the burden for melting [2]. In fact, it gives the possibility for termite micromelting to decrease greatly the content of alloyed elements (Mn and Mo) not making tempering cracks while doing this.

Wear resistance of manufactured cast irons may be compared using table 3.

Cast iron manufactured by termite method may to some extend be classified as a grey iron not lower than «CЧ 30», and after tempering in cast irons 4 and 5, the limit of tension strength has been established at the level not less than 500 MPa.

Table 3

Wear resistance of special cast irons

№	Termite material	Conditional value of resistance
1	Carbon steel (analogue of steel «У8»)	100
2	Termically manufactured termite alloyed cast iron	85
3	Martensite termite cast iron	50
4	Alloyed Mn and Mo martensite cast iron	40

Table 3 data witness the increasing of conditional resistance for martensite termite cast irons and rather great increasing for termically manufactured cast iron.

Thus we may make a conclusion that aluminothermic ways can be used for producing of special termite alloyed cast irons expect for high-chromium cast irons during the synthesis of those the problems of technological character appear. Other types of special cast irons have in some cases even better properties than in cast irons produced by ordinary methods.

Designed compositions of termite mixtures are also suitable for technology of termite casting additives of high-temperature gradient [2]. The work that has been carried out allows making a conclusion that for their mechanical properties synthesized specialized cast irons don't yield to "common" and the methods themselves are available for synthesis in principle of any black alloy.

Literature:

1. Zhiguts Yu., Kurytnik I. Special thermite cast irons. Archives of foundry engineering. Polish Academy of Sciences. 2008. N 2. Vol. 8. P. 162-166.

2. Zhiguts Yu.Yu. Splavy, syntezovani metalotermieju I SVS-protsesamy (monografija). Uzhgorod: Grazhda, 2008. − 276 s.