Технические науки/1. Металлургия

Zhiguts Yu.Yu., Segeda Yu.M., PoroKhnavets V.P.

Uzhhorod National University, Ukraine

THERMITE HIGH STRENGTH CAST IRON: TECHNOLOGY OF OBTAINING AND PROPERTIES

Introduction

The 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, 2]. The thermite reactions use for the synthesis of materials opens up wide opportunities for the production of cast alloys of virtually any chemical composition and structure.

Purpose and statement of the research task.

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

Analysis of the research method

The termite alloys have many advantages and synthesis of thermite processes, namely, their autonomy, the absence of the need for electric power sources, the simplicity and cheapness of technological equipment, the high productivity of the process (the duration of the synthesis lasts depending on the mass and volume of the metallothermic charge from several tens of seconds to several minutes) [1‒3]. In addition to aforesaid, attention is drawn to the possibility of using metalworking and thermic industries (iron scale, aluminum chips and graphite electrode cadmium, cutting out alloyed steel dust from filters in foundries, etc.). Thus, the manufacture and repair of shaped parts and metallothermic methods from high-strength cast irons, it is possible using to production.

Theoretical and experimental research

Use of metallothermic methods change the chemical composition of the charge with the metallothermic synthesis method, the cooling conditions of the casting, allows formed thermite iron with a ferrite, perlite, sorbitol, martensitic, austenite structure and, accordingly, with specified strength and performance properties. The results of mechanical tests of the cast iron obtained in table 1 are shown. Analysis and comparison of the obtained data testified the main mechanical properties of thermite grades of high-strength cast irons are not worse than industrial ones.

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

No	Termite cast iron ‒ industrial analogue	σb	σ0,2	δ, %	аn, MPa	НВ
		MPa
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

¹The mechanical properties of cast iron were determined on samples Ø10 mm, 50 mm long, cut from samples of a shamrock.

The spherical form of graphite and the pearlite structure of the base showed in thermite irons the highest values of the tensile strength, and the maximum plasticity was obtained with the ferritic structure. The strength reached of the thermite cast iron with perlitic structure in the cast state ‒ 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. The yield point is of termite iron higher than that of carbon steel and was 320...430 MPa, and for some samples it reached 800 MPa. The ratio of yield stress to tensile strength in termite cast iron was 0,75...0,8 (for comparison, 0,55...0,61 in industrial steel). The relative elongation was of the thermite high-strength cast iron in the cast state 1,5‒3,0%. The termite cast iron was formed with a phosphorus content of more than 0,15% in, a friable phosphide eutectic with a microhardness of 11,000‒14,100 MPa, which reduced the elongation.

The hardness of termite cast irons varied 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. The investigation showed that the thermite cast iron had the highest impact strength with a ferritic structure, while the increased content of silicon, manganese, phosphorus and sulfur lowered the toughness.

Conclusions

1. The proved the possibility of using thermite high-strength cast iron not only for the production of castings, but also for the technology of thermite welding theoretically and experimentally. 2. The mechanical properties of the thermite high-strength cast iron (strength, hardness, elongation, impact strength) are established. 3. The technological properties are determined of thermite iron, namely the 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.