US2466870A - Apparatus for heat-treating steel - Google Patents

Description

April 12, 1949. A. E. TwlEHAUs ETAL 2,466,870

APPARATUS FOR HEAT TREATING STEEL Filed Aprii 27, 194e 2 sheets-sheet 1 2 Sheets-Sheet 2 April 12,l 1949.l A. E. TwlEHAUs ET Al.

APPARATUS FOR HEAT TREATING STEEL Filed April 27. 1946 Patented Apr. 12, 1949 Azama-'1u UNITED, STATESA PATENT oI-Flce a 2,466,910 l I APPARATUS F R HEAT-TREATING STEEL v ix-thin' E, Twlehaus and Percy J. Wilton, Gary,

Ind., assignors to Carnegie-Illinois Steel Corporation, a corporation of New Jersey Application April 27, 194MB, Serial No. 665,470

l -This invention relates to an apparatus for thermally treating steel for the purposev of imparting to the metal advantageous cold-formin properties and particularly to apparatus for t e thermal treatment of alloy steels to prevent the formation of banding and induce additional corollary improvements in the mechanical characteristics thereof.

Commercial experience has taught the steelisfactory procedure for preventing banding in' steels in many instances, but fail to achieve thedesired results when a final product is sought which is to have a maximum softness, particu larly when high ductility requirements are equally present. These 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 m-artensitic areas into undesirable Weil-laminated pearlite in place 6i spheroidized cementite and partially restore its original banded structure,

The deleterious eiect of bandingl 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 suby lected in the course of the usual manufacturing processes. There is not known any treatment industrially suitable for elimination of banding in sheets without undesirably affecting the properties of the metal treated. i

Application of treatments found elective for banding elimination in bars and similar bodies, such as, for example, quenching followed by a tempering operation, is not feasible fromthe practical standpoint when applied tofsheets, particularly during continuous operations. Two additional major obstacles have .to be considered in this case, namely, excessive warping induced 4 Claims. (Cl. 263-10) 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 selected atmosphere for reducing surface oxidation. The material introduced is gradually heatked to the temperature, or slightly below the temperature, of the hot zone of the furnace, usually rangingbetween 1'700 deg. F. and 1750 deg. 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 are 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 banding removal, by in creasing 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, exemplied 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 afproper control is exercised in steam application. Steam quenched sheets possess a higher yield point, a substantially greater freedom from banding than normalized stock, and have an unimpaired surface.

Our invention provides an apparatus for carrying out the above-outlined procedure in an effective manner without requiring extensive modifications of existing equipment.

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

Figure 1 is a fragmentary side elevation of a furnace embodying the improved features of construction of the present invention;

` by immersion in liquid cooling media, and rustl5 Figure 2 is an enlarged longitudinal sectional andere elevation of of Figure I;

Figure 3 is a fragmentary elevation of'a stack removably disposable on the furnace showing details of the construction and mounting thereof, the view being taken at right angles to Figure 2, looking in the direction of the arrows and on the plane of line III-III of Figure 2;

Figure 4 is a plan view 'of the stack;

Figure 5 is a vertical section taken along the plane of line V-V of Figure 3, looking in the direction of the arrows;

Figure 6 is a plan view of steam injector pipes mounted in the furnace for quenching the heated steel passing through the furnacefand Figure 1 is an end elevation of the quenching pipe assembly shown in Figure 6.

Referring more particularly to the drawings, reference character A represents a furnace having heating, quenching, and cooling zones, and containing power driven conveyor rolls B by which the plates to be treated are conveyed through the furnace. The furnace A is generally f a standard continuous heat treating type, but modified in a manner which permits a convenient conversion from a conventional operation to the operation of the present invention.

For this purpose, two sections of the furnace roof are removed, and replaced by a sectionvof roof 9, corresponding to that marked cooling or soaking zone in Figure 2, and quenching assembly including a stack I I and quenching heads I3 beyond the stack.

The stack II is a box open at the top and bottom designed to discharge hot gases issuing from the furnace, and to prevent them from flowing out into the space about the quenching heads I3. It is composed of end posts in the form of channels I and I1, the lower ends of which penetrate the sand lling I9 in sealing channels 2i, 23 disposed at the sides of the furnace to prevent the escape of furnace gases. A front wall or plate 25 and a rear wall or plate 21 extend between the channels and are secured thereto. The front plate 25 terminates a short distance below the center of roof section 9 and defines an intake i o the quenching zone of the furnace opening 29 for the entry of furnace gases into the stack, while the rear plate 21 extends downwardly to within a short distance of the conveyor. The stack is supported by clips 30 on plate 25 adapted to nt over supporting angles 3| on the roof of the furnace. A plate welded in the top of the stack has an eye 33 adapted to be engaged by a crane hook for lifting the stack out of the furnace to permit replacement of the removable roof 4section when it is desired to return to .conventional operation.

The quenching heads I3 are more fullyl described and claimed in a copendiing application Serial No. 665,357, filed April 27, 1946, by Percy J. Wilton. They are composed of a pair of tubes 35 and 31, each closed at oneend as indicated 'at 39, and provided with a plurality of holes 4I which are adapted to direct quenching steam onto the plate P being treated. A suitable number of the holes 4I is provided, depending upon the size of the furnace, sufficient forvdirectingv the steam uniformly over the plates P. The tubes 35 and 31 have their open ends tapered inwardly as indicated at 43, so that air is drawn thereinto through suitable inlets (not shown) and commingled with lthe steam supplied thereto, by venturi action,

whereby the steam is condensed to a greater or less extent, as may be desired. Optimum results l in treatment of the plates P arel usually obtained pended from a beam in the form of a rod 45 extending through eyes 41 of straps 49 welded to the pipes 35, 31 transversely thereof. The rod 4l is carried by eye bolts 44 received in sockets 43 mounted in the furnace walls. This construction permits vertical adjustment of the tubes and also permits them to be readily removed for demounting when desired. Each o f the eyes 41 is welded to its strap 49 and is provided with a set screw 5I.

Preferably, the holes 4I are fitted with downwardly extending nozzles 53, and angularly disposed defiector plates 55 are provided to direct the resulting jets of steam onto the plates P being quenched, the angle of impingement being, in practice, about deg.

From the foregoing, it will be evident that the stack, by natural draft, deflects upwardly the hot gases issuing from the furnace and prevents their interfering with the application of steam to the heated plates. As shown, the stack extends across the entire width of the furnace and the rear plate 21 extends within a short distance above the rolls B sufficient only to provide clearance 51 for passage of the plates.

The bottom 59 of the heat treating furnace A is shown as being provided with expansion joints 60, and the furnace is mounted on foundation blocks or beams 3l.

It will be understood also that in addition to a vertical adjustment for proper application of steam to the plates P, the tubes 36 and 31 with their deflector plates 55, may be removed from; the furnace as a unit and replaced at will. Likewise, the stack II may be lifted out of the furnace and replaced as desired. When the stack II and the spray pipe assembly are removed from the furnace, and the removed cover sections restored, the furnace is ready for conventional use.

In this connection, it may be pointed out that the distance from the heating zone of the furnace to the quenching tubes 35 and 31 must be While certain specific embodiments of the present invention have been described yand illustrated as examples of one form of apparatus suitable for carrying out the invention, it will be understood that the apparatus is not limited rigidly to the specic details of the structure that have 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 ada/pt it to varying conditions and uses, as set forth in the appended claims.

We claim:

1. In apparatus for heat-treating flat-rolled metal including a continuous furnace composed of spaced side walls, a roof extending therebetween having a removable section intermediate the ends of the furnace and a conveyor for moving therethrough the material to be treated, the improvement comprising a stack removably disposable transversely on said furnace at one side of the opening left by removal of said section, said stack having end posts spaced apart about the width of the furnace and front and rear plates extending therebetween providing a vertical duct open at the top and bottom, said rear plate hav-v andere 5 ing its lower edge adjacent the conveyor to limit the escape of furnace spaced from the conveyor suiliciently to afford clearance for said material.

2. In. apparatus for heat-treating fiat-rolled metal including a continuous furnace composed of spaced side walls, a roof extending therebetween having a removable section intermediate the ends of the furnace and a conveyor-for moving therethrough the material to be treated, the improvement comprising a stack removably disposable transversely on said furnace at one side of the opening left by removal of said section, said stack being a box open at the bottom and top. having a length substantially equal to the width of the furnace, with front and rear side walls spaced along the conveyor, the rear side wall extending downwardly toward the conveyor farther than the front side wall.

3. In apparatus for 'heat-treating flat-rolled metal including a continuous furnace composed of spaced side walls, a roof extending therebetween having a removable section intermediate the ends of the furnace and a conveyor for moving therethrough the material to be treated, the improvement comprising a stack removably disposable transversely on said furnace at one side gases into said opening but of the opening left by removal of said section, said v stack 'being a box open at the bottom and top,

having a length substantially equal to die width of the furnace, with iront and rear side walls spaced along the conveyor, said front side wall having supporting means thereon adapted to en-A gage the portion of the roof adjoining said opening.

4. The apparatus defined by claim 1 characterized by sealing channels at the sides of the furnace,.said posts extending downwardly into said channels.

' A ARTHUR. E. TWIEHAUS.

PERCY J. WILTON. l

REFERENCES crrsn The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 381,575 Oldham Apr. 24, 1888 963,354 Brauner -s July 5, 1910 1,057,707 Cassidy Apr. 1, 1913 1,679,389 Watkins Aug. 7, 1928 1,914,934 Whitney s June 20, 1932 1,967,098 McFarland July 17, 1934 2,023,285 Otis Dec. 3, 1935 v 2,083,851 Mary June 15, 1937

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