Faculty:

Department:

Speciality:

Scientific adviser:

Theme of master's work:

Physical-and-metallurgycal

Physical material Sience

Applied material science

professor Vladimir Gorbatenko

Studying the structure and properties of bimetal steel-brass obtained by centrifugal casting

ABSTRACT:

High efficiency and durability of the created machines can be achieved by using of bimetal. Bimetals save expensive non-ferrous metals and alloy steels. Monolithic bimetallic products combines a variety of important properties such as high mechanical strength and corrosion resistance, high strength and frictional properties, etc. Thus, bimetallic materials have created a complex of different properties, the combination of which can not be obtained in some other alloys.

Nomenclature of the details that can be made of bimetallic compositions is rather wide. For example a group of parts such as bodies of rotation with the internal working surface.

One of the most advanced technological processes for obtaining bimetallic parts with the shape of bodies of rotation, is the centrifugal method with electric heating (Fig. 1).

1 – blank; 2 – charge; 3 – centering flange;

4 – graphite sealing insert; 5 – graphite electrodes

Figure 1. - Scheme of laminated blanks prepared for pouring

The essence of this method is: steel billets loaded into the batch (mixture of metal particles with flux), blank flanges at the ends closed with graphite or asbestos panels. Harvesting is installed on the machine and is rotated. Through the central hole into the end piece is introduced graphite electrodes, between which is excited by an electric arc is used as a heat source for melting the mixture and heating the work piece. The molten metal mixture by centrifugal forces are uniformly distributed on the inner surface of steel billets. Then the electricity supply to the electrodes is terminated before the complete solidification of the cast layer.

Layer of cladding metal gives a dense, without pores, pits and other defects. This method has also several other advantages: the cast-iron or steel base can be filled with more high-melting alloys, since the heating is independent of electric arc inside and the temperature difference comes from the inner surface of filled shells to the outside. Melting of the mixture (alloy) is poured directly on the surface. The melting of the charge is accompanied by the heating of filled blanks. In the burning of an electric arc between graphite electrodes in a closed space with limited air access formed a reducing atmosphere.

Material for research is bimetal bushing. Material composition is shown in Table 1.

Table 1. - Chemical composition of the material.

One of the main requirements for the bimetal, is a strong association of metals or alloys comprising bimetal. By measuring the microhardness was found that hardness either steel or brass parts of the sample increases in the direction of the free surface and the minimum hardness is observed near the boundary. So, the interface between the layers of brass hardness was 1160 - 1200 N/mm², in the middle layer 1230 - 1270 N/mm², the free surface in 1410 - 1450 N/mm². It can be explained by displacement of zinc in the direction of the free surface, with increasing concentration of zinc increased strength. The same pattern is observed in the steel part of the sample. Boundary layer of steel has a hardness of 1480 - 1550 N/mm², in the middle layer 2160 - 2240 N/mm², the free surface in 2530 - 2610 N/mm². Softening in the steel part of the sample may explained by heating during the pouring brass layer.

Technological process of obtaining bimetal by centrifugal casting provides a very strong bond steel base with brass. Melting the mixture poured directly on the steel surface, which is in the process is heated to the austenitic state. This creates good conditions for the diffusion of elements melt into a preheated steel substrate.

The literature list:

• Технология производства крупных центробежнолитых биметаллических валков. / Р.Х. Гималетдинов, С.П. Павлов, А.А. Гулаков и др. Труды VI съезда литейщиков России. Том 2. - Екатеринбург: Изд. УГТУ-УПИ, 2003. с. 186- 188.;
• Костенко Г.Д., Снежко A.A. Технологические основы процессов получения биметаллических отливок/ Литейное производство. 1979. № 5. С. 25;
• Диффузионное перераспределение легирующих элементов при формировании биметаллических отливок / Г.Д. Костенко, В.Б. Крик, В.В. Горский и др. // Литейное производство. 1986. № 8. С. 9 10.;
• Особенности кристаллизации двухслойных отливок. /A.M. Михайлов, Н.С. Беспалов, М.К. Сарлин и др. Литейное производство, 1973, №7, с 26-28.;
• Гарбуз Н.А. Металлические композиционные материалы. В кн.: Литые биметаллические детали машин: Тр. Кубанского гос. ун-та,- Краснодар, 1972, с. 3-8.;
• Поздняк Л.А., Ульшин В.И., Костенко Г.Д., Влияние С, Сг, Мп на процесс формирования переходного слоя биметаллических отливок на основе железа. В кн.: Литье биметаллических изделий. - Киев, 1976, с 39-50.;
• Суходольская Е.А., Даниленко Е.А. Некоторые вопросы формирования структуры литого биметалла. Вестник Харьковского политехи, ин-та. -Харьков: Вища школа, 1973, №5, с 139-140.;
• Снежко A.A., Костенко Г.Д., Ульшин В.И. Формирование переходного слоя в биметаллических отливках сталь-чугун. В кн.: Литье биметаллических изделий. - Киев, 1976, с. 26 - 32.;
• Лакедемонский A.B. Биметаллические отливки. М.: Машиностроение, 1984.- 180 с.;
• Фурман Е.Л. Создание и совершенствование технологий получения композиционных отливок на основе изучения капиллярного взаимодействия в литейной форме: Дис. . доктора техн. наук.