US2516282A - Apparatus for heat-treating steel - Google Patents

Description

July 25, 1950 P. J. WILTON APPARATUS FOR I-iEAT-TREATING STEEL 2 Sheets-Sheet 1 Filed April 27, 1946 INVE N T0 R Pam d lV/L MN 0. m 0 m m PatentedJuly 25, 1950 UNITED STATES PATENT OFFl CE APPARATUS FOR HEAT-TREATING STEEL Percy J. Wilton, Gary, Ind., assignor to Carnegie- Illinois Steel Corporation, a corporation of New Jersey Application April 27, 1946, Serial No. 665,357

2 Claims. (01. 29a 106 The present invention is directed to an apparatus for carrying out a process for thermally steel into the alpha state by cooling at a rate suiliciently rapid for preventing migration of respective constituents throughout corresponding gains. Quenching and tempering may be mentioned as examples of such procedures.

Quenching in water and tempering, which is a satisfactory procedure for preventing banding in steels in many instances, fails to achieve the desired results when a final product is sought which is to have a maximum softness, particularly when high ductility requirements are equally present. The latter properties are associated conventionally with the spheroidized structure, specifically when the latter is achieved by straight annealing under the lower critical temperature. It has been found that the spheroidizing treatment of water-quenched steels has to be conducted at higher temperatures, which temperatures occasionally may convert the original martensitic areas into undesirable well-laminated pearlite in place of spheroidized cementite and partially restore its banded structure.

The deleterious effect of banding, and of changes in the properties of the metal induced by treatments resorted to for elimination of banding, is particularly noticeable in sheets and similar thin bodies of large dimensions during cold-forming operations to which they are subjected in the course of the usual manufacturing processes. There is not known any treatment industrially suitable for elimination of banding in sheets without undesirably ailecting the properties of the metal treated.

Application of treatments found efiective for banding elimination in bars and similar bodies, such as, for example. quenching followed by a tempering operation, is not feasible from the practical standpoint when applied to sheets, particularly during continuous operations. Two additional major obstacles have to be considered in this case, namely, excessive warping, warping induced by immersion in liquid cooling media,

2 and rusting induced by the use of aqueous quenching baths.

The aforementioned obstacles have been met in steel plants making alloy'steel sheets through a compromise consisting in the use of normalizing in place of quenching and drawing, at the cost of reduced mechanical properties and only a partial elimination of banding. In this method, strip or sheets were fed continuously into a, normalizing furnace confining a properly lected atmosphere for reducing surface oxidation. The material introduced was gradually heated to the temperature, or slightly below the temperature of the hot zone of the furance, usually ranging between 1700 F. and 1750 F., and then allowed to cool in the controlled atmosphere during the travel through cooler portions of the furnace to a temperature substantially preventive of surface oxidation of the sheets. Heat treated sheets were subjected to a spheroidizing anneal or used without this treatment, depending upon the requirements of the ultimate application. Spheroidizing annealing, when used, accentuated the degree of banding resulting from the primary treatment.

It has been found that the properties of steel can be improved greatly, particularly in respect to the yield point and handing removal, by increasing the cooling rate, after heating to the austenitizing temperature, above the rate required in normalizing, but below the rate induced by quenching in liquids.

After an extended investigation it has been discovered that the cooling rate induced by the application of supersaturated vapors, exemplified by wet steam. to sheets heated to austenitizing temperature induces a cooling rate that is optimum from the standpoint of banding elimination and mechanical properties produced, provided a proper control is exercised in steam application. Steam-cooled sheets possess a higher yield point, a substantially greater freedom from banding, and have an unimpaired surface.

Thepresent invention provides an apparatus for carrying out the above-outlined procedure in an efiective manner without requiring extensive modifications of existing equipment, and the invention relates more specifically to a nozzle or instrumentalities for directing quenching fluid, such as steam, upon the shapes being treated.

- The invention will be understood more readily by reference to the accompanying drawings, in

which:

Figure 3 is a transverse sectional elevation on the line III-III of Figure 1; and

Figure 4 is a diagrammatic longitudinal sectional elevation of a furnace embodying the present invention.

Referring more particularly to the drawings, the fluid-injection means of the present invention comprises a tube A having a closed end B and a plurality of nozzles for directing fluid on to the heated shapes to be quenched, not shown. It will be understood that the tube A is adapted to be inserted in a suitable heat treating furnace, indicated at C, or exteriorly of the furnace adjacent thereto. The furnace C is shown to be a conventional type of annealing furnace, having conveying instrumentalities D therein, which furnace has been modified for the purposes of the present invention by removal of a section of the cover and introduction of a stack E and quenching tubes A, constructed in accordance with the present invention.

Each tube A has a Venturi throat adjacent the open intake end 5 thereof. A fluid-supply pipe 9 enters said end and is secured therein by radial ribs I welded in place. A source of quenching fluid (not shown), e. g., steam, is connected to pipe 9 and fluid entering the tube A induces atmospheric air through the intake ports [5 in the end 5 thereof. A sliding valve H, mounted on the intake pipe 9 and provided with an end flange l3 positioned towards the end 5 of the Venturi tube A, is controlled as to its position relative to the end 5 by. means of a set screw it which engages the intake pipe 9 and may be tightened thereagainst for holding the valve II in proper adjusted position. The flange [3 on the valve H has a diameter suflicient to close the air intake ports I5 when the valve I l is moved against the intake end 5 of tube A; and the amount of air admitted through the ports [5 is controlled by the distance the flange i3 is positioned from the intake end 5 of the tube A.

The tube A has a plurality of holes i'l provided with nozzles IQ for directing quenching fluid against the shapes being quenched. For guiding the resulting jets of quenching fluid, deflector plates 2| are provided, which conveniently are welded to the pipe A and to nozzles l9, and serve to direct and to concentrate the quenching fluid onto the heated shapes being quenched.

When steel shapes such as a strip, sheets, or other shapes, heated to a temperature above the Ara critical point, pass under the quenching tubes of this invention, they are quenched by suitable number of jets of the fluid issuing through the parallel nozzles i9, and impinging on the shapes at an angleof substantially sixty degrees to the surface ofthe shapes as shown in Figure 4. The holes I1 may have in practice a diameter of substantially A; inch, for example, and where the quenching medium is water-bearing steam, it may be fed through the intake pipe 9 under seventy-five pounds pressure, for exports II; and it is found in practice that the general efllciency oi the quenching rests hea on the liquid content of the steam used.

Thus, representative photomicrographs of a specimen of steel which has been subjected to normalizing treatment followed by spheroidizing annealing, and to steam quenching and spheroidizing annealing, show that, inspite of identical temperatures in the heating zone of the furnace, the same speed of travel, and exactly similar steps during the spheroidizing annealing, the normalized specimens have a banded structure outlined by flne particles of cementite and incompletely coagulated pearlitic lamellas, while steam quenched samples are free from any suggestion of the former structure, and are characterized by uniformly distributed particles of cementite much coarser than those observed in normalized specimens.

This difference in structure of the same steel resulted in difierences in physical properties and marked differences in cold forming characteristics during deep drawing. The difference in cold forming characteristics of steels having a structure associated with a normalizing treatment as contrasted with steels having a structure produced by steam quenching is more marked than differences in tensile properties, since tensile properties and other physical tests are not the only true criteria for comparison of steels which exhibit poor deep drawing characteristics with steels having good deep drawing characteristics. Diflerences in microstructure resulting from normalizing and from steam quenching have been found to be very definite guides in predicting success or failure in deep drawing. This difierence, namely, the degree of banding present, often can be used as a criterion of formability when other steel characteristics are approximately similar.

There is established definitely a pronounced improvement in sheets as a structural material for cold forming applications by interposing the supersaturated vapor quenching step under properly regulated conditions in the series of processing operations used in heat treating the shapes; and it is found in practice that suitable regulation of steam temperature, its water content, and method of application to fit modifications in composition and gauge of the shapes, make steam quenching and the beneficial efiects derived therefrom applicable to both carbon and alloy steels.

It has been stated above that the general elliciency of the present invention rests heavily on the liquid content of the steam used, since it has been demonstrated that dry steam does not exert a cooling efiect sufliciently rapid for producing the desired results. The degree of saturation which is important from the standpoint of the present invention is the saturation in contact with the articles being quenched and independent of the properties of vapors in supply lines. On

. this account, a close attention must be paid to the pressure selected, the size of orifices delivering the vapors, the distance of the orifices from the quenched Objects, the angle of vapor impact a some instances, particularly with heavier sheets,

better quenching is attained by applying the steam from both sides of the shapes.

, In Figure 4 of the drawings, the stack E is shown as extending transversely of the heating chamber of the furnace to lead hot gases out of the furnace while permitting passage of the shapes through it. This stack structure forms no part of the present invention but is more fully described and claimed in Patent No. 2,466,870 issued on an application filed by Arthur E. Twiehaus and me. The tubes A are joined by straps 23 each-of which has an opening or eye 25 which are in registry to permit insertion of the suspension rod 2'! by which the tubes A are removably suspended in the furnace. The stack and quenching tube assemblies may be removed entirely from the furnace, which upon replacement of the removed cover, is directly restorable to conventional operaunderstood that the construction'of the spray pipe of the present invention is not limited rigidly to the specific details of the structure thathave been herein illustrated and described; and it will be understood that it 'is intended and desired to embrace within the scope of this invention such modifications and changes as may be necessary to adapt it to varying conditions and uses, as set forth in the appended claims.

I claim:

1. A quenching tube adapted to be mounted transversely of an elongated furnace chamber,

said tube having laterally directed nozzles spaced therealong and a Venturi throat at one end, the other end being closed, an elongated deflector plate extending along said tube, one edge of said plate being disposed tangential to the tube and the other edge of said plate projecting into the line of discharge from said nozzles, and a fluidsupply pipe smaller than said one end of said tube extending thereinto, leaving an annular air inlet between the pipe and said tube.

2. The apparatus defined by claim 1 characterized by means for removably mounting the tube in the furnace chamber including hangers spaced I along the tube.

PERCY J. WILTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 921,139 'Moore May 11, 1909 963,354 Braemer July 5, 1910 1,057,707 Cassidy Apr. 1, 1913 1,290,561 Jackman et al. Jan. 7, 1919 1,809,221 Snow et a1. June 9, 1931 1,819,109 Miller Aug. 18, 1931 1,826,590 Adams et a1 Oct. 6, 1931 1,859,802 Shanafelt et a1 May 24, 1932 1,888,960 Talley Nov. 22,1932 1,914,934 Whitney June 6, 1933 1,936,249 Leser Nov. 21, 1933 2,083,851 Marcy June 15, 1937 2,352,709 Haase July 4, 1944 Certificate of Correction Patent N 0. 2,516,282 July 25, 1950 PERCY J. WILTON It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 1, line 17, for the Word gains read grains;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 7th day of November, A. D. 1950.

THOMAS F. MURPHY,

Assistant Commz'ssz'oner of Patents.

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