Heating steel blanks in molten glass. To make the forgings as close as possible in shape and size to the finished part, it is necessary to obtain billets after heating with minimum scale and decarburization. To do this, use a non-oxidative heating of the metal, for example, heating steel blanks in molten glass mass.
Heating steel blanks – the advantage of this method is as follows: a special atmosphere is not required (as in induction furnaces); ensures an efficient and uniform heating rate; profitability; use of glass as a heating medium; descaling of the workpiece. During the technological process of processing, the workpiece is isolated from the atmosphere by a protective glass film, which can be used as a glass lubricant during pressing .
Tests, heating of steel blanks in molten glass was carried out in a bath-type pelvic furnace with a working space size of 0.5 × 0.16 × 0.5 m and in a silicite furnace of size 0.2 × 0.25 × 0.3 m – in fireclay crucibles
The experiments were carried out with a punch of window glass, which, after averaging and heating the blanks in it, had the following composition: 65% SiO2; 1.42% Al 2 O 3; 3.13% Fe2O3; 6.5% CaO; 3.53% MgO; 0.1% SO3; 20.319% Na2O + K2O.
The heating time of the steel billet and the exposure in the molten glass melt were determined from the values of the heat transfer coefficient in the molten glass obtained experimentally (Img. 1).
Image1. The dependence of the average heat transfer coefficient when heating steel samples from the temperature of molten glass.
The samples were heated in a molten glass, in a BaCl2 melt and in a fiery gas furnace to 1160-1200 ° C. The results of the study for steel 45 are given in the table. It follows from the table that heating in molten glass masses is similar in degree of decarburization and grain size to heating in molten salts; the depth of the decarburized layer when heated in a fiery furnace with increasing exposure time increases more intensively than when heated in melts.
|Heat||Decarburization depth in mm||Grain size in points|
|Duration of heating in minutes|
|In molten glass||0..0,1||0..0,15||0,15..0,2||3||2||2..1|
Heating of steel blanks before processing found that with increasing exposure time the number of decarbonized areas increases. A similar process was observed on samples after heating in molten salts.
This can be explained by the fact that decarburization in molten media occurs due to the direct effect of the dissolved gases. Thus, the samples placed on the bottom of the crucible with a height of a layer of molten glass of 135 mm were not decarburized in 40 minutes.
Heating of steel blanks from steel 45 with a diameter of 70 mm after heating in a glass melt at 1250-1270 ° C and a shutter speed of 18 min was applied to a crank press with a nominal force of 2500 tons.
Induction heating of steel billets on crimped billets determined the depth of decarburization and grain size. The microstructure of the surface layer of the machined billets of steel 45 before and after heating for 35 minutes in molten glass at 1200 ° C is minimally decarbonated (Fig. 2). The blanks after heating in the molten glass and cleaning had a shiny surface, without scale. This is due to the fact that simultaneously with heating, chemical interaction of scale occurs on the surface of the workpiece, which has a basic character, with the melt of glass, which has acidic properties. When this occurs, a partial transition of the interaction products in a liquid medium.
Image2. The microstructure of the surface layer of machined specimens of steel 45 (× 100): a – before heating; b – after heating in molten glass.
Heating of steel blanks taken out of the melt, due to the strong adhesion of glass to the metal surface, a film is formed which protects against scale formation during transportation and cooling. With an appropriate viscosity and temperature of the melt, the glass film can be used as a lubricant during pressing.
1. Heating steel billets in molten glass has the following advantages: slight decarburization and slight losses from metal oxidation; good surface quality to minimize machining allowances; increase durability of dies and a sharp improvement in sanitary and hygienic working conditions.
2. Molten glass is a cheaper heating medium than non-oxidizing media.
L. B. EFIMOVA, A. I. KOZLOV
Gorky Polytechnic Institute
ISSN 0026-0819. “Metallurgy and heat treatment of metals”, № 6. 1965
Prozorov L.V. Pressed steel. M., Mashgiz, 1956.
This article was taken from this resource.