US2228257A

US2228257A - Method of treating steel

Info

Publication number: US2228257A
Application number: US299882A
Authority: US
Inventors: Fred L Collins
Original assignee: Individual
Current assignee: Individual
Priority date: 1939-10-17
Filing date: 1939-10-17
Publication date: 1941-01-14
Anticipated expiration: 1958-01-14

Description

Jan. 14, 1941.

F. L. COLLINS METHOD OF TREATING STEEL Filed Oct. 17, 1939 v INVENTOR: 7650 L. COLL/N5,

BY: H '5 ATT NEY.

Patented Jan. 14, 1941 UNITED STATES PATENT OFFICE 3 Claims.

At the present time, most commercial steel is poured into cast iron molds set on heavy cast iron bases 10 inches to 12 inches thick. The molten steel, at a temperature of 2600 degrees Fahrenheit to 2800 degrees Fahrenheit, is teemed into a relatively cold mold until it is filled to the top. The time required for teeming each mold of approximately tons in weight is 1 minute to 1 minutes. Larger molds take proportionally longer time.

On account of the height of the mold (approximately 90 inches) the velocity with which the molten steel strikes the bottom causes much spattering. Tests indicate very clearly that the 15 molten steel spatters on the sides of the mold and chills, and some of the chunks freeze on the sides. Sometimes these frozen hunks fall oil as the steel rises up in the mold. However, most of the time, these chunks do not fall off, but stick to the mold and do not weld into the metal as the mold is filled. This results in a scabby surface on the ingot which never becomes an integral part thereof, but shows up in the finished product as surface defects. In reheating in the soaking pits, this scrappy surface readily oxidizes and reduces the carbon content in the surface which also affects the surface of the finished product.

Another serious drawback to this most prevalent method is the formation of crystals from the side and bottom of the mold. The growth of crystals from each side meet in diagonal lines.

Growth of crystals from the bottom of the mold upwardly meet obliquely on planes and form a four sided pyramid. All or these diagonal lines are rich in segregation and non-metallic impurities, elongated gas cavities, and shrinkage cavities. This causes weakness along these diagonal planes.

The surfaces due to crystallization from the outside surfaces constitute planes of weakness.

In a round ingot, the crystals form a cone and in an octagonal ingot they form an eight sided pyramid. Sometimes independent crystal clusters may be formed in the centers.

Shrinkage or contraction cavities are nearly always formed and are called pipes." High carbon steels are subject to much larger pipes than low carbon steels. Usually blow-holes formed by gases liberated in the steel are more numerous in low carbon steels than in highrcarbon steels. To overcome pipes and blow-holes in ingots, resort has been made to hot-tops, capping, and use of aluminum deoxidizers. Hot tops allow molten steel to feed into the shrinkage cavity and reduce the length of the pipe. Capping causes the top of the ingot to freeze over at once, and thereby creates a pressure on the inside of the ingot which reduces the formation of free gas in the steel, thus reducing the formation of pipes.

Shrinkage cavities in the ingot cause internal separation and result in blisters on the slab or sheets when rolled from the steel. This also causes lamination in rolled strip or sheets. These blisters are also coated with alumina or segregated impurities which cause failures in finished product. Inverted ingots are also used extensively to reduce piping, but they also show transverse cracks due to the bottom end cooling faster than the top. Hot top pouring must also be used to fill the cavity formed by shrinkage of the metal. Inverting the ingot creates added difiiculties in handling during stripping and charging into the soaking pits.

Many designs of corrugated inside mold surfaces have been tried in order to reduce the tendency of ingots to form shrinkage cracks. By giving the mold chamber a definite type of contour whereby a polygonal ingot 'of substantial rectangular cross-section is formed, the surface as well as the interior structure of the ingot is considerably improved. This prevents angular interferences of projecting dendrites, thereby reducing lines of weakness or cleavage planes.

With all of these developments in the art of teeming and casting steel ingots, there is much to be desired. There is great expense connected with cooling the steel down to a temperature of 1000 degrees Fahrenheit or less, stripping, and charging into blooming mill pits for reheating. The reheated ingot becomes heavily oxidized on the outside surface, which oxide is often rolled into the steel in the first two or three passes in the blooming mill, thereby causing surface defects. Rapid reduction in the early passes of the blooming mill often causes bad surface cracks which must be chipped or burned off by scarfing.

Reheating in soaking pits is sometimes the cause of transverse cracks in the ingot which may not be discovered and will cause failure in the finished product, especially in higher carbon steels.

It is among the objects of the present invention to eliminate the foregoing disadvantages.

Other objects will be apparent after referring to the drawing, in which:

Figure l. is an elevation of the apparatus use in practicing the method of the invention;

Figure 2 is a. fragmentary plan of part of the apparatus of Figure 1;- and Figure 3 is a sectional view on the line III-III of Figure 1.

Referring more particularly to the drawing, the numeral 2 designates a conventional bottom pouring hot metal ladle immediately beneath which there is disposed a hot metal spout 3.

Disposed immediately below the delivery or feeding end 4 of the hot metal spout 3, there is a trackway 6 extending at right-angles with respect thereto. A series of buggies 8 are mounted on, and for movement along, the trackway 6, each buggy 8 carrying a gang of horizontal billet molds I transversely disposed with respect thereto. These horizontal billet molds III are provided withremovable covers and ends in. the manner well-known in the art. By using the horizontal molds I0 and pouring the molten metal from the ladle 2 into the hot metal spout 3 and from the delivery or feeding end 4 thereof into the molds, all splashing is eliminated and accordingly scab on the surface of the ingot.

As soon as a mold I0 is filled, it is moved forwardly so that the next mold is in position under the spout. The full mold is capped at once to freeze the top surface as quickly as possible and prevent contact with the air.

As the teeming progresses, the first billet will have cooled sufiiciently to have a shell which is strong enough to support the metal.

Placed on the floor of the mill at a point adjacent which any given billet will have cooled sufiiciently to have a shell which is strong enough to support the metal, and on the side of the trackway 6 which is opposite that on which the ladle 2 and hot metal spout 3 are disposed, is a. heating furnace I5. This heating furnace I functions as a temperature holding furnace and is preheated to a temperature of approximately 2300 degrees Fahrenheit by any suitable medium. When the steel billets are ready to be charged into the furnace I5, the heating medium may be cut off, as no further heat will be needed since this holding furnace is tightly closed.

This furnace I5 has a door in alignment with the horizontal billet molds I0 and the billets, hereinafter designated II, are moved therethrough after the removable covers and ends of the aligned mold are removed. The transfer of the ingots (from mold to furnace) is accome plished by means of a conventional pusher cylinder I8, the piston I9 of which is aligned with the door of the furnace and on the opposite side of of the furnace. These bars comprise a pullover mechanism which includes a pair of links 24 which are connected on one of their ends to the adjacent end of one of the bars 20 and on their other ends to a suitably operated crank mechanism, generally designated at 2'6. Extending upwardly through the bottom of the furnace I5, and projecting through suitable apertures in the floor thereof, is a pair of vertical shafts which are provided at their lower ends with pivoted links 32 which are, in turn, connected with suitably operated crank mechanism, generally designated at 33. The shafts 30 are so constructed and arranged with respect to the shafts 20 that together they provide a kick-over device for the billets I I disposed in the furnace I5 and also a pull-over mechanism for use in connection therewith. Thus, it will be seen that any of the side surfaces of the billet or bloom may be brought to face the roof of the furnace I5. 5

The furnace I5 is provided with a removable roof 35 and disposed above this removable roof and exteriorly of the furnace is a trackway, generally designated at 40. This trackway carries a suitable wheeled truck 4I which supports 10 anair-hammer cylinder 42, the air hammer 43 of which is provided with an extensible shaft 44. According to the foregoing, the truck 4I may be brought into position immediately over the furnace roof 35 and, when the latter is removed, the 15 extensible shaft 44 of the air hammer 43 may be made to extend into the furnace and in close adjacency with respect to any of the billets charged thereinto. When in the adjacent position referred to, the air hammer 43 may be suitably operated by controlling the flow of air into the airhammer cylinder 42 through a conduit, generally designated at 45, in the manner well-known to the art.

The air hammer 43 is operated by short rapid 25 strokes and travels over the. top surface of the billet I! once or twice .to weld the surface and reduce the shell of the billet to make up for shrinkage. The kick-over and pull-over devices are then operated in the manner referred to hereinbefore to expose all four sides of the billet tov the action of the air hammer. Thus, all four sides are hammered as the billet slowly cools, thereby preventing the formation of cavities or pipes within the billet. By working the billet at or near the fiuid point, the formation of long dendrites is prevented, thus eliminating cleavage lines and surfaces.

By keeping the whole body of the billet close to the solidification point the tendency to form any shrinkage cavity is very small. By working the steel billet at this high temperature, the steel will have the same quality as now obtained when the ingot is rolled down from an ingot to the same size, and the power required will be comparatively 45 small when compared with that of conventional practice. Surface oxidation is practically eliminated because the billet has had very little exposure to the oxygen of the air. There has been no reheating as now takes place in the soaking pits in contact with oxidizing gases. The surface acquired is exceedingly good and free from seams, cracks, and deoxidation.

The chemical segregation within the billet is much less than with current practice. The larger 55 the mass of steel, such as in an ingot, the greater chance there is for segregation. An ingot cools much slower than a billet, thus. allowing more time for segregation.

While I have shown and described one specific .60 embodiment of the present invention, it will be seen that I do not wish to be limited exactly thereto, since various modifications may be made without departing from the scope of the invention, as defined by the following claims. 55

I claim:

1. The method of treating steel which includes teeming the same through a splash-preventing device into a horizontal mold, stripping the casting from said mold while the temperature of the casting is close to the point of solidification, and mechanically working the casting while its temperature is close to the point of solidification in a furnace which is closed to oxidizing influences.

2. The method of treating steel which includes teeming the same through a splash-preventing device into a horizontal mold, stripping the casting from said mold while the temperature of the casting is close to the point of solidification, mechanically working the casting while its temperature is close to the point of solidification in a furnace which is closed to oxidizing influences, and rolling the casting to the desired section.

, 3. The method of treating steel which includes 10 teeming the same through a splash-preventing,

device into a horizontal mold, stripping the casting from said mold while the temperature of the casting is close to the point of solidification, mechanically working the casting while its temperature is close to the point of solidification in a. furnace which is closed to oxidizing influences, and rolling the casting to the desired section without reheating. v

' FRED L. COLLINS.