US2271372A - Method of treating strip metal - Google Patents

Description

Jan. 27, 1942. F. J. HERMAN ErAL l '2,271,372A y METHOD 0F TREATING STRIP METAL Filed April 10, 1939 2 Sheets-Shes?l l Jan. 27, 1942. F. J. HERMAN ErAL- 2,271,372

METHOD OF TREATING'- STRIP METAL y I l 'File-d April 10, 1959 2 ShtSSh8Qt 2 l FIE. 2|.

J0 .55 77ME /N 77/75 HELD TO Patented Jan. 27, 1.942

Francis J. Herman, Youngstown, Ohio, William F. McGarrity, Hillcrest, Pa., and Woodworth, Youngstown, Ohio Application Aprii1o,'1939', serial No;- zsmss 4 2 Claims.

This invention relates. to the manufacture of steel, and, particularly, to a method of treating hot rolled strip steel whereby improved finished strip steel is obtained.

In fabricating strip steel to various forms and shapes, and particularly in the pressing of various steel products to shape, the manufacturer desires a steel that will be sufficiently ductilc in his power presses and a-steel that will retain its homogeneous structure. and continuity ofsurfaces as it is cold-drawn by the machine or press, and,-further; a steel that possesses the defined required strength to withstand the use intended of the finished fabricated product.

Therefore, the steel manufacturers must provide steel conforming to definite qualities and properties for use of the fabricating industry in order that these requirements may be inet.

oftentimes, the fabricating industry will specify a certain' grade of steel to test at a definite percentage of elongation and a stress yield consistent with its use and, of c ourse, these factors become a basis on which the finished steel must be produced. Generally, the steel produced by the steel industry to meet these requirements is a. low', carbon bearing metal,

present invention to provide a method of treating strip steel which produces steel having certain predetermined physical properties and characteristics withina narrow range and, at the same time, producing` consistently a steel having all the necessary requirementslof a good steel.

It isanother object of the invention to provide an improved method of treating strip steel soas to produce finished steel having certain predetermined physical properties and characteristcs by controlling the rate of cooling thereof.

Various other objects and -advantages of this i 1- invention will be more apparent in the course analyzing under .25- per cent, and metallurgically I compounded Iwith ingredients of manganese, phosphorus, and sulphur, bestknown to those skilled in the art. However when such steel is rolled in the conventional mnner, the steel will test in a latitude too variable and broad in its limits for optimum ductility. For example, in

'any given grade of fsteel or tin plate, thel yield stress may be from 41,000 to 50,000 pounds per similar uctuations in ductility inversely with square inch,'which is quite a wide variation with of the following Vspecification v and will be particularly pointed out in the appended claimsf In the accompanying drawings there is shown,

for the purpose of illustration; one embodiment which our` invention may assume in practice.

Inlthese drawings:

Figures I and 1'L are side elevations of a roller conveyor and associated apparatus that may be used in the practice of our invention;

Figure-2 lis a section taken on the line Ill-II of Figure 1; and,

Figure-3 is a graph illustrating the relation between the temperature-and time of cooling for a certain strip steel.`

Itv has been found that the required physical properties and characteristics of strip steel can..

be confined within a narrow range by accurately controlling the cooling ofthe finished steel strip. For the ideal grain structure of the steel by the hot finishing method, an upper criticaltempera- -ture at which the steel is to be finished has been established by means of considerable research and experimentation. Similarly, a definite temperature at which the strip st'eel should be the strength.. As is commonly known,. steel or tin plate of excessive strength and accompanied low ductility results in fractures of the'material when it is subjected to forming and deep-drawingI operations, which, of course,are objectionable the fabricating industry. A

According to the present invention, 'the strip steel is treated by a method whereby theyield produced thereby has a yield stress within 2,00

to 3,000 pounds per square inch of that desire A point thereof is definitely' controlled and the steel I stacked or piled has also been established, and, further, it has been found that the rate of abstraction or coolingA of the steel between its hot finishing .temperature and that-at which it is tb be piled m'ust be deiinitely controlled in order to obtain the required physical properties within a narrow range.

It has also been found that strip steel piled at a given'deined temperature and allowed to .cool normally in air at atmospheric temperature results in nov appreciable change in its physical of the steel for any particularl use, and, in` consequence thereof, the maximum- .degree of ductilityy thereof is denitely controlled,- and a steel having,

uniform physicalzpropertieand characteristics to meet the manufacturers*requirements is'con y sistentlylobtained.

`Accordin81y, it one of the objects of the properties or characteristics'.

According 4to the present invention, the hot .finished strip is rapidly cooled bymeans of a liquid through the upper 'critical range at a definite Pate of cooling so as to insure an equiaxed, unifform1y sized and' reaped. grain structure in the steel,"thus the hardness and the acvdenite temperature.

the strip is to be piled or stacked at a similarly predetermined controlled rate'ofcooling to keep these required physical properties within the desired The strip steel is then piled or .stacked and pile-annealed at a given definite cooled therein down through the upper critical temperature to a temperature of approximately 1400 degrees Fahrenheit, namely, a drop of about 150 degrees therein. Aftery the strip lengths leave the liquid or water spray and pass along the conveyor, they are cooled in air at atmospheric temperature as they pass therealong to a predetermined temperature at which the strip steel can be piled without resulting in any material temperature by cooling the same in air at atchange in its physical properties thereafter. In

The methodv of treating the :stripzsteelso as to,

control the rate of cooling thereof may be prac,`

' ticed by conventional apparatus as that shown in Figure l of the drawings, or-other suitable appa-l. ratus. There is shown therein the last or ilnish-` and a rotary shear 3 for cutting the continuous steel strip into predetermined lengths 4. The

lengths of strip steel l pass successively from the rotary shear 3 onto a power driven roller Atable 5, which may be driven in any suitable manner r y -fore piling had been seconds, the materialv such as by a motor 6, for conveying the strips therefrom vto a piler :I or to other suitable means for stacking the lengths of steel arranged at the opposite end lof the conveyor. 'I'here is arranged distance .from the rotary shear` 3, a cooling liquid or water spraying means, such as spray pipes 8, which are adapted to direct a coling liquid spray, preferably a water spray,y upon the lengths of strip steel as they passalong the conveyor thereunder; Y l A In operation, the lengths of strip` steel pass successively from the rotary shear or. cutter 3 onto the rollers 5 oi' the,con`veyor, under the water spray 8 where they are rapidly cooled .by 40'l means thereof, and along the roller conveyor y5 where they'are slowly cooled in the atmosphere to the pinch rolls 9 and thence to .the piler 'I where they are pile-annealed at a predetermined the amount of time at which the strip steel is cooled in the water spray and at which it is cooled in the atmosphereis predetermined and controllel by the speed or the conveyor. That is, the time of travel from the time the strip steel leaves' the rotary shear -until it is nally piled at the other end of the conveyor is determined by` the physical properties and 'characteristics desired of the finished strip.

' The present method of treating the strip as `55 shown in Figures 1 and 2 is illustrated further in Figure 3 of the drawingsby a g'raph illus-I l trating the relation between the temperature and time for the cooling of the strip steel for a'. certravel along the conveyor. From this graph it will be noticed that the strip is hot flnished in the finishing stand at about 1600 degreesFahrenheit, which is above the upper critical temperature of the steel. A slight drop in' temperature occurs in the lengths of strip steel as they pass from the`rotary shear 3 tothe spray B, namely, a temperature drop of about 50 degrees. In passing through the cooling liquid or water spray,the cooling of the length's of strip steel It will be understood that 45 the present instances, as shown in the graph, the strip steel is-cooled in the atmosphere to a temperature of 1175 degrees Fahrenheit. Thestrip is then held on the conveyor table for a suillcient time to cool the sameto a temperature :of about 1050 degrees Fahrenheit beforey it is .stacked or piled.

It will be seen from the graph that, for'the particular grade of steel selected as an ex'ample,

Aing rolling mill stand 2 of a train oi.' mill stands 2o -it was found that it was necessary to hold the strip on the table for 25 seconds before piling to .provide steel having a deiinite yield stre point and a prescribed ductility and this time of holding has been found to Abe a critical time factor. For example,` if the time of holding bewould be too weak and excessively ductile and it would then be necessary to adjust the water.

4spray for more stringent cooling ofthe strip above the conveyor rolls 4 at a predetermined 30 therethrough until ,the cooling time has been reduced to 25 seconds. Similarly, if the time ofandthe time of holding a particular grade of rolled steel strip before piling at a predetermined denite temperature produces a steelv which is consistent and uniform within a narr0w range of limitsin yield point and ductility. For=example,a particular grade of steel, cooled as above described, will consistently test with a -yieldlpoint between 41,000 and 44,000 pounds per squareI inch as compared with 41,000 to 50,000 pounds per square inch for steelA produced in the l conventional manner or any other method here tofore kn'ownc While we have shown and described one embodiznent o'fy our invention, it will be understood that thisembodiment is merely for the purpose of illustration and description and that,y various olter forms may be devised within the scope of t invention,'as defined in the appended claims.

We claim:

l. In"- the manufacture of hot rolled strip steel. I 60 the method which comprises cutting the strip into lengths immediately after it leaves the rolling mill finishing stand at a temperature above the critidalgtemperature of the steel, conveying the cut lengths successively through a cooling liquid spray so asto rapidly cool the same down through their upper critical temperature to a temperature slightly therebelow, then further cooling said lengths in air which is at atmospheric temperatureto a temperature of approximately 1050 degrees Fahrenheit in a predetermined time and ilnally piling said lengths one on'the other andpermitting them to cool freely in air which is substantially at atmospheric tein- .perat ure.. is, of course, quite rapid and the, lengths are 2. In the manufacture of hot'rolled strip steel,

atmospheric temperature 'to a. temperature of 10 approximately 1050 degrees Fahrenheit in a predetermined time and nally piling the lengths one on the other and permitting them to cool freely in air which is substantially at atmos- 5 pheric temperature.

FRANCIS J. HERMAN. WmLIAM F. MQGARRI'I'Y. LAURIN D. WooDWoR'rH.

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