Effect of Ultrasonic Treatment on High-Speed Steel
Abstract Generated abstract
This study examines how ultrasonic treatment affects crystallization, transcrystallization, primary carbide morphology, and nonmetallic inclusion distribution in R9 high-speed steel castings. Paired castings from each heat were poured into identical molds, with one subjected to ultrasound throughout solidification, while cooling rates were varied using metal and heated ceramic molds and different ultrasonic concentrators. The results indicate that ultrasound refined grain size in all heats and promoted a more uniform distribution of nonmetallic inclusions, while substantial alteration of ledeburitic carbide morphology occurred mainly under slower cooling conditions. The best reported results were obtained with an exponential concentrator whose radiating face diameter was half the casting diameter.
Full Text
EFFECT OF ULTRASONIC TREATMENT ON HIGH-SPEED STEEL
G. V. SIMONOV, G. G. KREVSKII, N. D. TYUTEVA
(Presented by Prof. Dr. A. N. Dobrovidov)
The purpose of this work was to study the effect of ultrasonic treatment on: 1) crystallization at various cooling rates; 2) the structure of primary carbides; 3) transcrystallization; 4) the distribution of nonmetallic inclusions in high-speed steel.
The work also determined the optimal ratio between the diameter of the waveguide and the diameter of the casting billet.
To determine the nature of the effect of ultrasound, the metal of each melt was poured into two molds identical in all parameters, in one of which the metal was subjected to sonication.
To eliminate the influence of the mold material on the nature of the action of ultrasound during crystallization of the melt, the concentrator of the magnetostrictive transducer was in direct contact with the metal of the casting (Fig. 1). Ultrasound was supplied to the magnetostrictive—
Fig. 1.
—strictive transducer directly in contact with the metal of the casting (Fig. 1). Ultrasound was supplied to the magnetostrictive-
the converter before the start of pouring the metal into the mold. The treatment continued throughout the entire crystallization process, until the casting had cooled to 500°.
The cooling rate of the casting was varied over wide limits. Pouring was carried out into metal molds with wall thicknesses of 25 and 8 mm, and also into ceramic molds with a wall thickness of 25 mm. To increase the duration of the crystallization period, the ceramic mold was heated in an electric furnace to 700°.
All castings were examined for macro- and microstructure. The billet was cut lengthwise into two templates, one of which was prepared for determining the nature of the distribution of nonmetallic inclusions and for revealing transcrystallization. From the second, three specimens were made (from different locations over the height of the template) for microstructural investigation.
The dimensions of the billets used for the investigation were: diameter—38 mm; height—100–110 mm.
An ultrasonic generator of the UZG-6 type with a set of magnetostrictive transducers was used in the work. To increase the intensity of treatment, each of the transducers had a concentrator. Two magnetostrictors were provided with exponential concentrators, and the third had a cylindrical stepped concentrator. The diameter of the radiating end face of the exponential concentrator was 19 mm, or 0.5 of the casting diameter. The diameter of the radiating end face of the cylindrical concentrator was 38 mm.
The investigations were carried out on R9 steel. A total of 9 heats were made (two castings per heat).
The chemical composition of the heats is given in the table. These heats were sonicated using an exponential concentrator with a diameter ratio of 0.5.
| Heat No. | Pouring mold | Type of billet | C | W | V | Cr |
|---|---|---|---|---|---|---|
| 1 | Metallic, wall thickness 25 mm | Sonicated | 0.87 | 9.1 | 2.21 | 3.97 |
| 1 | Metallic, wall thickness 25 mm | Without sonication | 0.86 | 9.06 | 2.12 | 3.92 |
| 4 | Metallic, wall thickness 8 mm | Sonicated | 0.92 | 9.4 | 2.22 | 4.1 |
| 4 | Metallic, wall thickness 8 mm | Without sonication | 0.9 | 9.4 | 2.17 | 4.06 |
| 7 | Ceramic, heated | Sonicated | 0.89 | 9.02 | 2.43 | 4.18 |
| 7 | Ceramic, heated | Without sonication | 0.9 | 9.06 | 2.36 | 4.15 |
Results of the investigation of the macro- and microstructures of sonicated heats
I. MACROSTRUCTURE
a) Nature of transcrystallization.
In all three sonicated heats, no dendritic structure was found.
b) Distribution of nonmetallic inclusions.
In comparison with the non-sonicated heats, a certain refinement and more uniform distribution throughout the volume of the casting is observed.
II. MICROSTRUCTURE
In studying the microstructure, special attention was paid to the structure (shape) of the eutectic carbides. It was assumed that ultrasonic treatment would completely or partially destroy the network structure of the ledeburitic eutectic.
Sections of the investigated heats were etched with potassium permanganate. With rapid cooling of the castings (metal molds), under the action of ultrasound no sharp change was observed in the structure of the ledeburitic carbides. A sharp change in the structure of the ledeburitic carbides was obtained when the metal, while in the liquid state, was subjected to ultrasonic treatment for a longer time (ceramic mold). In this case, immediately after casting, the primary carbides had a granular form with a uniform distribution over the cross section. The shape, dimensions, and distribution of carbides in heat 7 are analogous to the structure of forged steel.
Conclusions
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The effect of ultrasound on highly alloyed steels of the ledeburitic class is strongly associated with the cooling rate during crystallization.
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During ultrasonic treatment, a decrease in grain size was observed in all heats.
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After ultrasonic treatment, provided that cooling is slow, the primary carbides have a granular form with a uniform distribution.
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The best results were obtained when using an exponential concentrator with a ratio of the diameter of the radiating end face to the diameter of the casting equal to 0.5.
REFERENCES
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I. I. Teumin. On the mechanism of the effect of elastic vibrations on the crystallization of metals. Izvestiya AN SSSR, No. 1, 1962.
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A. P. Kapustin. The influence of ultrasound on the kinetics of crystallization. Publishing House of the Academy of Sciences of the USSR, 1962.
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Mołdżieva Radka. The influence of ultrasound on the crystallization of high-speed steel. Tekhnika, II, No. 10, 1962.
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Ya. B. Gurevich et al. The influence of ultrasound on the structure and properties of a steel ingot. Stal’, No. 5, 1957.