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Zhiguts Yu.Yu., Skyba Yu.Yu., Feldeshi T.T.
WEAR
RESISTANCE OF THERMITE SPECIAL CAST IRONS
Abstract. The given paper deals with the
problems of the synthesis of cast iron by metallothermy.
On the basis of investigated method of calculations structures of charges have
been arranged and cast iron has been synthesized further.
1
Introduction. 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.
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 and mechanical
properties of manufactured castings got great practical importance.
2.
The methods of experiment. While organizing the process of synthesis of steels
and cast irons classic [1] thermite reactions based
on oxidation of aluminum and renovation of iron are used. 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
metalthermic 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 then the
temperature of slag melting [2] (for Al2O3 2400 K).
The main structure components in thermite 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.
3.
The directions of studies. Synthesized thermite wear
resistant cast irons in analogy with the cast irons dot by ordinary methods,
can be divided into the following groups: grey, white, including non-alloyed,
low-alloyed, nickel-chromium-plated; martensite and
high chromium-plated.
It is the most convenient to
get grey cast irons by metalthermic or combined (metallotherming+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 thermite cast iron is being
manufactured very well by cutting, much more better than chilled and white cast
irons.
The burden composition for
synthesis, chemical composition and components of the burden for getting wear
resistant thermite cast iron and its mechanical
properties are shown in table 1 and 2.
Table 1
Chemical composition of the burden for synthesis of grey thermite cast iron
|
¹ |
Electrode powder,
% |
Ferrosilicium (ÔÑ 75) |
Ferromanganese (ÔÌí 75) |
Ni powder |
Ferrochrome |
Ferroalumini-um thermite |
|
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 thermite cast
iron
|
¹ |
Element content, % |
HB |
|||||||
|
Ñ |
Si |
Mn |
S |
P |
Ni |
Cr and Mo |
In alloyed state |
After tempering* |
|
|
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 |
– |
*Tempering was
being done under 550ºC during 12 hours.
Within cast irons 1, 2 martensite (table 2) is formed just during metalthermic melting without certain temomanufacturing
which is furthermore connected with replacement of critical point regarding
alloying of Ni. Cast irons 4, 5 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 [3]. In fact, it gives the possibility for thermite
micromelting to decrease greatly the content of
alloyed elements (Mn and Mo) not making tempering
cracks while doing this. Cast iron mamufactured by thermite method may to some extend be classified as a grey
iron not lower than «C× 30», and after tempering in cast irons 4 and 5, the limit of tension
strength has been established at the level not less then 500 MPa.
4.
Conclusion. Thus we may
make a conclusion that aluminothermic ways can be
used for producing of special thermite 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 thermite
mixtures are also suitable for technology of thermite
casting additives of high-temperature gradient. 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.
References. [1] Beljaev A.I. Nikolaj
Nikolaevith Beketov. Metallurgizdat. Moskva. 1953. 137
s. [2] Zhiguts Yu. Termitnyje
nihardy, sintezirovannyje metalothermiej. Visnyk SumDU.