SU912447A1 - Friction welding method - Google Patents

Description

(54) METHOD OF WELDING THRESHOLD

one

This invention relates to friction welding.

There is a known method of friction welding of parts made of nodular cast iron, which is based on a cycle with a three-step change in pressure with uniform heating.

The structure of nodular cast iron provides an all-in-one connection with friction welding. Nodular cast iron (high-strength cast iron) is an alloy of iron with carbon. The carbon in this iron is mainly in the free state in the form of spherical graphite with a finely dispersed arrangement in the alloy matrix. The form of graphite and its location in high-strength cast iron leads at the initial stage of heating during friction welding to the burning of carbon from the welded ends. At the final stage of heating, when the access of air to the ends to be welded stops and the temperature reaches values close to melting points, carbon dissolves in austenite, phase transformation occurs, i.e., carbides of the type are formed. Thus, in the stage of heating at the welded ends of the parts

of nodular cast iron, no carbon is present in the free state and, therefore, no graphite film is formed. The absence of graphite film allows to obtain a high-quality connection of parts.

5 from nodular cast iron in the forging stage 1.

The disadvantage of this method is that it does not provide a permanent connection of gray cast iron parts.

, with gray cast iron and gray cast iron with steel due to the structure of gray cast iron, which is an alloy of iron with carbon. The carbon in this iron is mainly in a free state in the form of coarse grained graphite

15 location in the alloy matrix. The shape of graphite and its location in gray iron lead to the fact that during friction welding in the heating stage at the welded ends, graphite does not have time to completely burn out and go into another phase state, therefore a graphite film is formed which acts as a lubricant and reduces heat In the forging stage, when a permanent joint is formed, this film is not squeezed out of the joint. because of

insufficient heating of the workpieces to be welded and, due to the brittleness of the graphite film (graphite is a brittle phase), the strength of such a joint is very low (practically no joint is obtained).

Also known is a method of friction welding, in which a permanent connection of gray iron parts with steel is obtained; during the welding process, the length of the blanks is reduced by an amount equal to the welding allowance. In this method, a hole, the diameter of which is much larger than the diameter of the steel rod, is drilled into the gray iron parts at the place of the intended connection. Next, in the base of the hole milled annular groove. A rod is inserted into the hole to failure and pressed with the necessary force. The rod is contacted, and then dried, the plug is punched. The permanent connection is formed by filling the annular groove with a deformed metal 2.

The disadvantage of this method is that it allows you to weld parts of only different sizes, provides for special machining of large-sized gray cast iron parts and high steel consumption due to the fact that before welding a steel part must be inserted to a certain depth gray iron.

The purpose of the invention is to expand the range of products to be welded from gray cast iron, as well as gray cast iron with steel, eliminating special machining of parts before welding and reducing material consumption.

The goal is achieved by the fact that in the friction welding method, mainly of gray cast iron and gray cast iron with steel, in which during the welding process the length of the workpieces is reduced by an amount equal to the welding allowance, the ends of the gray iron workpieces are whitened to a depth greater than than welding allowance, and after welding, the bleached areas are heat treated.

Bleaching does not reduce the productivity of the production of gray iron castings.

Bleaching is performed as follows.

Cast iron is smelted. Then pour it into a two-part mold. The upper part of the mold is made of a material that provides a low cooling rate. . The lower part of the mold is made of a material that provides a high cooling rate. Crystallization of cast iron in this form makes it possible to obtain a blank of gray cast iron with a bleached area of a certain length. In this case, in the area of white iron, all carbon is in a bound state in the form of carbide of the type FejC. When welding on welded ends does not form

graphite film. The ends of the blanks are heated to the desired temperature. The strength of the permanent joint is satisfactory due to the fact that there is no fragile graphite film at the joint. Subsequent thermal treatment of the bleached layer in welded workpieces leads to the transformation of white iron into flaky graphite cast iron and an increase in the strength of the welded workpieces.

An example of a specific implementation. The proposed method is welded billet of gray iron with a content of C-3, 26% Si - 2.1%, Mp -0.62%; P-0.12%; S -0.12%. The cast iron is melted in a graphite crucible with heating by a high frequency current, the melted cast iron at 1320 ... 1390 ° C is poured into a two piece mold. The upper part is made of fireclay (brick of ShBV GS) ST 3272-71). The bottom is made of steel 45 to increase the cooling rate. Thus, blanks from gray cast iron of 18 Mm and 120 mm long were obtained. A gray cast iron structure was obtained at a length of 100 mm, and a white1; o cast iron structure with a transitional zone at a length of 20 mm. Billets of steel 15 -100 mm long and 5 f 18 mm.

Welding is performed on a semi-automatic MF-372A in the following modes: n 1550 rpm; RC 13 kgf / mm; Ррр 26 kgf / mm; tjj 10c; tnp. 3 with where.p - the number of revolutions of the workpiece in min; P „-the heating pressure;

RPR-pressure forging;

t is the heating time;

t pr-time forging.

Samples after welding are subjected to heat treatment in the following modes.

1parti images - heating to 650 ° C,

Exposure time 4 h and air cooling.

2 batches of samples - heating up. 900 ° C, holding time 20 min.,

cooling with oven to 300 ° C and air cooling.

Welded specimens were tested at 5 bend. The required strength was obtained on samples heat-treated at 900 ° C. In this case, the destruction of the sample occurs on the base metal, i.e., on gray cast iron and bend 36 ... 40 kgf / mm.

FIG. 1 shows the 66fr microstructure of gray cast iron + steel 15, cooled after welding in air; in fig. 2 microstructure of gray cast iron sample + steel 15, after heat treatment at 650 ° C; in fig. 3 - microstructure of gray cast iron sample + steel 15, after heat treatment at 900 ° C.

Claims (2)

Microstructural analysis shows that in these samples there are no cracks, lack of penetration and other welding defects. The proposed method of friction welding can be applied in the valve industry, for example, in the manufacture of valves. The application of the proposed method of welding, friction, reduces the complexity of manufacturing products and saves about 20,000 p. The invention of the method of welding by friction, mainly gray iron or gray iron with steel, in which the length of the workpieces during the welding process is reduced by an amount equal to the welding allowance, characterized in that, in order to expand the range of welded products, to eliminate special machining of parts before welding and reduce material consumption, the ends of gray iron billets are whitened to a depth greater than the welding allowance before welding, and after welding the bleached areas, heat treated. Sources of information taken into account In the examination 1. A. S. Gelman et al. Welding by friction of thick-walled pipes. “Mechanical Engineering Technologists, No. 8, 1960, p. 64-69. 2. US patent number 3444611, cl. 29-470.3, 20.05.69 (prototype). ig./