Технические науки/1. Металлургия

Zhiguts Yu., Kadar V.

Uzhhorod National University, Ukraine

THERMITE HIGH-STRENGTH CAST IRON

Introduction. Termite reactions have been known for more than a century and they are used to produce ferroalloys and to heat exothermic foundry profits in the foundry industry [1-3]. The thermite reactions use for synthesis of materials and have wide opportunities for the production of cast alloys opens up of virtually any chemical composition and structure.

Purpose and statement of the research task. Taking into account the advantages and specific uses of thermite methods for obtaining high-carbon alloys, the problem of complex study of thermite irons, the determination of their mechanical, technological and service properties arose, and on the basis of the obtained data, the establishment of the most optimal areas for the use of these alloys.

Theoretical and experimental research. The thermite high-strength cast iron has distinctive feature not only its method productions, but also a very compact, nearly spherical form of graphite inclusions. The properties of the thermite high-strength cast iron can be controlled by changing the structure of the metal substrate, as in industrial cast iron [3,4]. Formed thermal iron with a ferrite, perlite, sorbite, martensitic, austenite structure and, accordingly, with specified strength and performance properties maybe varying the chemical composition of the charge with the metallothermic synthesis method, the cooling conditions of the casting.

The results of mechanical tests of the cast iron obtained are shown in table 1. Analysis and comparison of the obtained data testified that the main mechanical properties of thermal grades of high-strength cast irons are not worse than industrial ones. In the spherical form of graphite and the pearlite structure of the base, thermal irons showed the highest values of the tensile strength, and the maximum plasticity was obtained with the ferritic structure.

Table 1– Mechanical properties of thermite high-strength cast iron

№	Termite cast iron – analog of industrial	σb	σ0,2	б, %	а, МPа	НВ
		МPа
1	“ВЧ 45-0”	470	380	–	–	210–250
2	“ВЧ 45-5”	460	360	5	20	190–210
3	“ВЧ 50-1,5”	510	370	1,5	15	220–240
4	“ВЧ 60-2”	600	430	2	15	210–240

The thermite pig iron reached in the cast state the strength of with perlitic structure 600...700 MPa, the compressive strength of the thermite high-strength cast iron was ~ 2000 MPa, the bend was 700...1200 MPa, and the deflection bend varied within 4–30 mm, the tensile strength at torsion was 440 MPa with a ferritic structure and 700…800 MPa with pearlite structure and the yield point of termite iron is higher than that of carbon steel and was 320...430 MPa, and for some samples it reached 800 MPa. The ratio was of yield stress to tensile strength in termite cast iron 0,75...0,8 (for comparison, 0,55...0,61 in industrial steel). The relative elongation was 1,5–3,0% of the thermite high-strength cast iron in the cast state. The content phosphorus was formed more than 0,15% in termite cast iron, a friable phosphide eutectic with a microhardness of 11,000–14,100 MPa, which reduced the elongation. The hardness varied of termite cast irons depending on the structure of the matrix (for ferritic – 160...210 HB, for pearlitic – 190...260 HB, for bleached thermite cast iron – 280...340 HB), temperature and carbon content.

Simultaneously the study of technological properties, the possibility of organizing the thermal welding of high-strength cast iron was considered. It was found that its weldability was at the level of weldability of carbon steel (table 2). The authors managed to get a weld with properties better than those of the material to be welded.

Conclusions. 1. The using thermite high-strength cast iron possibility proved of theoretically and experimentally not only for the production of castings, but also for the technology of thermite welding.

Table 2 – The properties of thermite welded¹

№	Alloy	Properties of the welding zone
		The amount of globular graphite in the structure, %	Hardness, НВ	σb, МPа	σ10^1, %
1	Gray cast iron	0	170	210	0
2	Transition zone^2	30–70	–	–	–
3	High-strength thermite cast iron	85–95	190	550	4,5

¹Mechanical properties are determined on standard samples with a diameter of 10 mm.

²No bleach.

2. The mechanical properties are established of the thermite high-strength cast iron (strength, hardness, elongation, impact strength). 3. The technological properties were determined of thermite cast iron, namely, fluidity and the influence of temperature, machinability, etc. on it.

Literature:

1. 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. ISBN 978-966-8224-74-4.

2. Zhiguts, Yu. Special thermite cast irons [Текст] / Yu. Zhiguts, I. Kurytnik // Archives of foundry engineering. Polish Academy of Sciences. − 2008. − № 2. − V. 8. − Р. 162 – 166.

3. Zhiguts, Yu.Yu. Grey 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.

4. Patent №2001129089. Metallothermic reactor [Text] / Zhiguts Yu.Yu. – 2003. – Bul. №1.