Технические науки/1. Металлургия

Zhiguts Yu.Yu.¹, Telythko V.F.², Muthithka A.Yu.¹

¹Uzhgorod National University, Ukraine

²Mukathevo State University, Ukraine

SOME FEATURES OF THERMITE CAST IRONS

Introduction. Thermite reactions are known already more than age and they are utilized for making of ferrous-alloys and warming-up of exothermic castings incomes in a casting production [1]. Use of thermite reactions for the synthesis of materials, opens wide possibilities of receipt of the cast alloys practically of any chemical composition and structure.

Purpose and raising of research task. Improvement of properties of materials is arrived mainly by the use of traditional technologies of receipt of alloys and subsequent thermal, chemical-thermal and by another ways of treatment. But their high power-hungriness, necessity of combination of a few technological stages of treatment, the observances of ecological requirements result in the necessity of search of other ways of receipt of necessary properties of materials, enabling to avoid the adopted failings. One of such perspective ways may be the use of the method of receipt of thermite highstrong cast-irons developed and experimentally grounded in theory as a result of high exothermic reactions.

Taking into account the advantages and specific areas of the use of thermite methods of receipt of high-carbon alloys there is a problem of complex research of thermite cast-irons, determinations of their physical and mechanical, technological and official properties, and on the basis of findings establishment of the most optimum areas of the use of these alloys.

Analysis of research method. Advantages of thermite processes talk in behalf on thermite alloys, namely, their noninteraction, absence of requirement in the sources of electric power, simplicity and cheapness of technological equipment, high performance of process (time of leadthrough of synthesis lasts depending on mass and volume of metallothermic mixture from a few ten of seconds to a few minutes) [1]. Except for transferred, pays attention on itself the possibility of the use for arrangement of mixture of offcuts of metal-working and thermal productions (ferrous dross, grade of the aluminium shaving and candle-ends of graphite electrodes, sifting out of dust of alloy steel from filters in castings workshops and other). The wide use of highstrong cast-irons is conditioned except for their high mechanical and technological properties with quite good welding. Thus, for making and shaped component overhaul possibility to utilize thermite methods which find all of greater distribution lately appears from highstrong cast-irons.

Materials and method of preparation of exothermic mixture. For arrangement of metallothermic mixture such materials were used: chrome metallic; ferrochrome; silicocalcium; aluminium for aluminotermic; silicomanganese; ferrosilicon; powder of aluminium; ferromanganese; soot is acetylene (technical carbon); powder of titanic chemical; powder of chrome; ferrous dross (blacksmith's and rental productions) of middle chemical composition (in % on mass): 0,05 C; 0,10...0,35 Si; 0,10...0,35 Mn; 0,01...0,03 S; 0,01...0,03 P; 40...50 Fe₂O₃; 50...60 FeO.

Experimental researches. As a result of leadthrough of the experimental thermite melting the shaped founding’s which probed complex were got. Chemical composition, mechanical, technological and some official properties of the synthesized alloy where set.

The distinctive feature of thermite highstrong cast-iron was not only it method of receipt but also very compact, near to spherical form of including of graphite. As well as in industrial cast-iron, regulating properties of thermite highstrong cast-iron is possible by changing the structure of metallic basis. Varying chemical composition of mixture at the metallothermic method of synthesis, the terms of cooling of founding was formed thermite cast-iron with a ferritic, pearlitic, sorbitum, martensitic, austenitic structure and accordingly with the set durability and operating properties.

It is set that thermite highstrong cast-iron possessed high durability on tension, compression and bend, by high enough plasticity and shock viscidity, by satisfactory castings properties (namely good fluidity of fusion, small linear and by volume shrinkage, small propensity to the firecracking). It was well processed mechanically except for welded, added the autogenously cutting, possessed high wearproofness, heat-tolerance and anti-friction properties.

Research of physical properties of thermite highstrong cast-iron rotined that it differed from properties of industrial. So, a closeness of it at a room temperature was 7000...7600 kg/m³.

At the spherical form of graphite and pearlitic structure of basis thermite cast-irons were rotined by the most high values of tensile strength, and maximal plasticity is got – at a ferritic structure.

As-cast tensile of thermite cast-iron strength with a pearlitic structure was arrived at 600...700 MPa (table 1). Tensile strength made at the compression of thermite highstrong cast-iron ~2000 MPa, on a bend – 700...1200 MPa, and a sagitta changed within the limits of 4...30 mm. Tensile strength at twisting was 440 MPa at a ferritic structure and 700...800 MPa at a pearlitic structure. The limit of fluidity of thermite cast-iron is higher, than at carbon steel and 320...430 made MPa, and for some standards 800 was arrived at MPa. The attitude of limit of fluidity toward tensile strength at tension at thermite cast-iron was 0,75...0,8 (for comparison at industrial steel 0,55...0,61). The relative lengthening of thermite highstrong cast-iron was 1,5...3,0%.

Table 1

Mechanical properties of thermite highstrong cast-irons

№	Thermite cast-iron, analogue of industrial	Σb	σ0,2	δ, %	ан, МPа	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

Hardness of thermite cast-irons changed depending on the structure of matrix (for ferritic – 160…210 НВ, for pearlitic – 190…260 НВ, for the bleached thermite cast-iron – 280…340 НВ), temperature and maintenance of carbon.

The synthesized highstrong cast-iron allowed to weld cast-iron purveyances with the receipt of the welded guy-sutures durability on tension ~550 MPa.

Thermite welding of cast-iron in this way is at 2,5...4 time dearer than traditional technology of welding of cast-iron details [2]. An economic effect is arrived only in that case, when cast-iron details must be welded in the conditions of absence of standard welding equipment, outsourcings of electric power and in the compressed terms.

In the process of welding high quality of guy-sutures turned out due to absence in him of area of white zone of acquisition of structure and properties of highstrong cast-iron guy-sutures.

Cutting speed for thermite highstrong cast-iron is rotined in table 2.

Table 2

Speed of cutting at treatment of thermite highstrong cast-iron

Structure of cast-iron	Cutting speed, m/mines
	Instrument from highspeeds steel of Р6М5	Instrument from the carboloy of ВК8^1
Ferritic	45...70	90...180
Ferritic-pearlitic	35...45	60...100
Pearlitic	35...45	60...90

¹A turning-off was made by plates of type 1 GOST 19045-80.

Conclusions: 1. In theory and possibility of the use of thermite highstrong cast-iron is experimentally well-proven not only for the receipt of foundings, welding but also for the use of the overheated fusion in technology of thermite incomes of high temperature gradient. 2. Mechanical properties of thermite highstrong cast-iron are set is a closeness, mechanical properties are durability, hardness, relative lengthening, shock viscidity, limit of fluidity depending on the structure of cast-iron and temperature of its use.

Literature:

1. Yu.Yu.Zhiguc Alloys, synthesized metalotermieyu and by SHS-processes. Grazhda, Uzhgorod (2008) [in Ukraine].

2. Yu.Yu.Zhiguts, Vіstі Akad. Inzh. Nauk Ukrajiny, 32 (2007) [in Ukraine].