Технические науки/1. Металлургия

Zhiguts Yu.Yu., Beiresh Ya.Ya.

Uzhhorod National University, Ukraine

THE ALLOYED CAST IRONS SYNTHESIZED BY METALLOTHERMIC PROCESIS

Introduction. Synthesized materials are based on metallothermіс processes promising and use in the manufacture of cast billets, for saving doped cast iron and improving their quality when used in the technology of thermite casting profits of a high temperature gradient [1-4]. The great practical importance has the study of the influence of new technological methods of obtaining an alloy on the microstructure, the chemical composition, and the mechanical properties of the castings.

The purpose of the work. The main task of work is establishment of the possibility of obtaining high-quality cast materials (high-alloyed special cast irons) by metallothermic methods, as well as revealing the relationships between the structure, chemical composition and mechanical properties of the synthesized alloys.

The scheme for obtaining high-alloyed cast iron by metal-thermal processes using powdered ingredients for the composition of mixtures is shown below:

The aluminium powder was later replaced by grinding aluminium shavings, and carbon was introduced into the charge as a powder of graphite electrodes.

Experimental research. The conducting micromelting four types of chromium-nickel cast irons, analogues of industrial cast irons was synthesized. The chemical composition of the resulting alloys is shown in table 1. The synthesis reaction was carried out in a chill metal reactor and with graphite facing (table 2).

Pouring into a graphite crucible gives an insignificant increase in the strength of cast iron. In general, the conditions of micromelting lead to intensive cooling of the alloy. All castings from chromium-nickel cast irons had no external signs of a shrinkage shell, cutting them and macroanalysis confirmed these results.

Table 1

Chemical composition of thermite chromium-nickel cast irons (% by mass)

Synthesized cast iron	The content of alloying elements (%by weight)
	С	Si	Mn	Ni	Cr	Mo	S	P
1	3,2–3,5	0,4–0,7	0,3–0,5	4–4,5	2–2,5	–	£0,05	£0,05
2	2,7–3,2	0,4–0,7	0,3–0,5	4–4,7	2–2,5	–	£0,05	£0,05
3	1–1,5	0,4–0,7	0,3–0,5	4–4,5	1,4–1,6	–	£0,05	£0,05
4	3,2–3,5	0,4–0,7	1,2–2,0	3–3,5	1,5–2,0	0,8–1,0	£0,15	£0,40

The liquation of chemical composition wasn’t detected by the volume of castings. The graphitization is significantly reduced of castings from the thermal wear-resistant cast iron in them during the synthesis of the alloy by the aluminothermy method due to a significant temperature gradient and high heat dissipation rates.

Table 2

Mechanical properties of thermite alloyed cast irons

Synthesized cast iron	Casting technology	sв	НВ	su
		MPa
1	In the chill mold	270–320	570–640	470–890
	In a graphite crucible	280–320	600–670	490–710
2	In the chill mold	380–450	590–630	560–770
3	In a graphite crucible	–	370–410	–
4	In a graphite crucible	–	490–560	–

Microstructural analysis showed that in termite cast iron the cementite content is not less than 50%, and the microhardness is from 1000 to 1050 НV. The main phases in the structure of chromium-nickel cast-iron (as shown by X-ray spectral analysis) are cementite and more wear-resistant carbides Cr, Mo, etc. X-ray diffraction analysis has revealed, that provides microhardness of 15 GPa. The microhardness of carbides in HV is 10.0-17.5 GPa.

The getting isn’t difficult to obtain a martensitic structure in chromium-nickel cast-iron, because in the synthesis of alloys under micromelting conditions, rapid cooling occurs, and this in turn produces a martensitic or acicular structure. These structures give the greatest wear resistance.

It should be noted, also, that the mechanical properties of the termite chromium-nickel cast iron are higher than the corresponding properties of the chromium-nickel industrial iron, apparently in connection with the additional microalloying with aluminium, which is necessarily included in the charge. At the same time, in doped thermal iron with increasing manganese content [3-4], in spite of high synthesis temperatures, deterioration of fluidity is observed while shrinkage is maintained in the range of 1.6-2.2%.

Conclusions. 1) the principal possibility of thermite smelting of high-alloyed chromium-nickel cast irons is shown; 2) the quantitative composition of the metallothermic charge for their synthesis is established on the basis of the calculation technique; 3) the mechanical properties and microstructure of synthesized cast irons are investigated; 4) synthesized special termite cast irons are not inferior to industrial ones by mechanical properties.

Literature:

1. Zhiguts, Yu.Yu. Using the thermite doped cast iron to feed rolling rolls [Text] / Yu.Yu. Zhiguts // News of Sumu. – 2004. – No. 2 (61). – P. 134 - 140.

2. Zhiguts, Yu.Yu. Gray and white special thermite cast iron [Text] / Yu.Yu.Zhiguts // Bulletin of the National University "Lviv Polytechnic" "Optimization of production processes and technical control in machine-building and instrument making". – 2003. – No. 480. – P. 148 - 153.

3. Patent №2001129089. Metalothermic reactor [Text] / Zhiguts Yu.Yu. – 2003. – Bul. №1.

4. Zhiguts, Yu. Yu. Technologies of obtaining and features of alloys synthesized by combined processes [Text] / Yu. Yu. Zhiguts, V.F. Lazar. – Uzhhorod: Invasor, 2014. – 388 p.