US3011928A

US3011928A - Method for heat treating hot rolled steel rods

Info

Publication number: US3011928A
Application number: US3185A
Authority: US
Inventors: Kopec J Benedict; William A Miller
Original assignee: Morgan Construction Co
Current assignee: Siemens Industry Inc
Priority date: 1960-01-18
Filing date: 1960-01-18
Publication date: 1961-12-05
Anticipated expiration: 1978-12-05

Description

Dec. 5, 1961 METHOD FOR HEAT TREATING HOT ROLLED STEEL RODS Filed Jan. 18, 1960 WATER DRA'N SUPPLY ATOMIZER '3 Sheets-Sheet 1 FlG.l

Dec. 5, 1961 J B. KOPEC ETAL 3,011,928

METHOD FOR HEAT TREATING HOT ROLLED STEEL RODS Filed Jan. 18, 1960 '3 Sheets-Sheet 2 Dec. 5, 1961 J B. KOPEC ETAL 3,011,928

METHOD FOR HEAT TREATING HOT ROLLED STEEL RODS Filed Jan. 18, 1960 v 3 Sheets-Sheet 3 United States Patent 3,011,928 METHOD FOR HEAT TREATING HOT ROLLED STEEL RODS 3 Benedict Kopec, Hamilton Square, and William A. Miller, Roebling, N.J., assignors, by mesne msignments, to Morgan Construction Company, Worcester, Mass a corporation of Massachuse.

Filed Jan. 18, 1960, Ser. No. 3,185 12 Claims. (Cl. 148-156) The present invention relates to heat treating carbon steel rods and more particularly to a method for heat treating hot rolled carbon steel rods to render them suitable for being drawn into wire.

In producing high tensile steel wire it has been for many years common practice to process high carbon hot rolled steel rod by cold drawing through a series of successively smaller dies. With each successive cold drawing the wire becomes harder and more brittle. Consequently, there is a limit to the total percentage in cross-sectional area reduction which can be achieved before the wire becomes so hard and brittle that further drawing will cause splitting, breaking or other damage to the wire. When this point is reached the wire may be subjected to a heat treating process, commonly termed patenting after which further wire drawing can be accomplished, followed in many cases by an additional patenting step and further cold drawing.

The amount of area reduction which can be achieved before it is necessary to subject the wire to a patenting operation and the number of patenting operations required are of substantial economic importance because of the cost involved in performing a patenting operation. The percentage area reduction of a hot rolled rod which can be achieved before a patenting operation is needed depends upon two principal factors, namely, the carbon content of the steel and the distribution of the carbon in the steel. An important aspect of the invention is concerned with high carbon steel (that containing 0.4% or more of carbon) and a principal object of the invention is to provide a novel and improved method for altering the distribution of the carbon in high carbon hot rolled rod to facilitate subsequent wire drawin operations.

As steel rod leaves the finishing stand of a continuous hot rolling mill, its temperature will generally be in the range of about 1650-1800 F. With temperatures of this order, the carbon will be in solid solution in the iron. When hot rolled rod cools to a temperature below a critical temperature of about 1340 F, the carbon comes out of solution in the form of colonies of parallel plates of iron carbide (cemeutite) in a matrix of iron. This structure is commonly called pearlite. The actual temperature at which the carbon comes out of solution has important metallurgical significance. Thus, at temperatures in the area of the critical temperature the carbides separate as thick plates, commonly termed coarse pearlite. These thick plates of iron carbide are brittle and tend to fracture during wire drawing. At a temperature of about 1225 F. the plates of iron carbide formed as the carbon comes out of solution are much thinner, and the rod is much more suitable for drawing purposes. At a temperature of about l025 F. the plates of iron carbide are Xtremely fine, being visible only under the resolving power of an electron microscope. The amount of cold wire drawing which can be accomplished without damage to the wire depends primarily on the fineness of the pearlite structure, and this in turn depends upon the temperature at which the carbon comes out or" solution.

At temperatures between about 925-425f F. the carbides come out of solution in a different form. They have an acicular structure commonly termed bainite. At temperatures below about 425 F. the steel transforms to 2 martensite. Bainite has inferior ductility, while marteusite is very hard and brittle.

The rate at which the carbon comes out of solution also varies widely with temperature, being relatively low at the critical temperature and being a maximum at about 1025 F. Below 1025 F. the rate decreases. in the tem *erature range of about 900l300 F. the carbides will come out of solution to form pearlite plates of sufiicient fineness for satisfactory drawing. Of course, it is important that both the center and the outside of the rod be maintained within the suitable temperature range while the carbon comes out of solution to prevent the formation of substantial coarse pearlite structure at the center or bainitic or martensite structure at the 811118.86, a problem complicated by the high hot rolling finishing speed usually used, i.e., about 3000-5000 feet per minute. By suitable temperature range is meant that range in which the separated carbide is in the form of fine pearlite suitable for wire drawing without further heat treatment, namely, about 900-1300" F, and preferably about 1000-1225 F.

The metallurgical principles discussed above have been understood by those skilled in the art and various efforts have been made to provide proper heat treatment of the rod as it leaves the hot rolling mill. A particularly satisfactory method of effecting such heat treating to secure a fine pearlitic structure suitable for wire drawing is described in United States Patent 2,75 6,169 to Cots-on, Goetz and Lewis.

Other examples of efiorts to cool high carbon hot rolled rod as it emerges from the rod mill are described in United States Patents 2,621,914 to Morgan, 2,810,569 to Morgan and Wilson, 2,810,570 to Wilson, and 2,819,058 to Morgan, and British Patent 342,189.

The foregoing description has dealt with the advantages of a method for heat treating high carbon steel rod. The method is also advantageous for heat treating low carbon steel rod, i.e., rod having a carbon content less than about 0.4%. The metallurgical processes involved are the same, but, because of the lower carbon content of the material, the miorostructure consists primarily of grains of iron, commonly called ferrite with comparatively few colonies of pearlite. The effect of the heat treatment of the invention on low carbon steel rod is to obtain uniform small grains of ferrite containing umformly distributed small colonies of pearlite.

it is not usual to paten low carbon steel since its inherent ductility is sufficient for the wire drawing process. Thus, while use of the heat treating process of the invention on low carbon steel will not generally result in saving of patenting heat treatments, a considerable advantage will nevertheless be achieved because of the greater uniformity of cold working properties in the material. This is particularly advantageous when the wire is subject to the variety of cold forming operations in commercial use for shaping low carbon steel.

The principal object of the present invention has been to provide a novel and improved method for cooling hot rolled rod to render the same conditioned for subsequent cold drawing operations.

More particularly, it has been a principal object of the invention to provide a novel and improved method for rapidly cooling high speed hot rolled high carbon steel rod so that both the interior and surface of the rod rapidly assume temperatures in the range of about 900- 1300 F., which temperatures are maintained for a sufficient time to permit the separation of the carbide in the form of fine pearlite suitable for wire drawing directly without further heat treatment.

Another principal object of the invention has been to provide a novel and improved method for rapidly cooling high speed low carbon steel rod to obtain uniform small colonies of pearlite.

.FIG. 1.

grains of ferrite containing uniformly distributed small Another object of the invention has been to provide a method of the above type which involves two cooling steps, in a first one of which the rod leaving the rolling mill is rapidly cooled to an average temperature not below the critical temperature and preferably within the range of about 1350-l450 F. and a surface temperature not below about 900 F, and in the second one of which the rod temperature, both interior and surface, is reduced so as to be within the range of about 900-1300" F. and preferably about 1000-1225" F.

A feature of the invention has been the provision of a novel and improved method of the above type in which the reel can be located a conventional relatively short distance from the finishing stand of the rolling mill.

Other and further objects, features and advantages of the invention will appear more fully from the following description.

In accordance with the invention, hot rolled carbon steel rod leaving a rolling mill is first subjected to a water cooling step in which the rod is cooled as much as possible without producing different microstmctures at the outside and center. Thus the rod is cooled to an average temperature above the critical temperature at which carbide comes out of Solution and a surface temperature not below about 900 F. By average temperature is meant the temperature to which the rod would equalize if no heat were added or taken away. The rod is then delivered to a reeling mechanism, the rod entering the reel having a surface temperature lying within the range of about 1350-1450" F. The rod is subjected to atomized water spray while being taken up on the reel so that the rod temperature (at both center and surface) is reduced during reeling so as to be within the range of about 900- 1300 F. and preferably 1000-1225 F. Preferably, the average temperature of the rod at any and all points along the length of the rod is rapidly reduced to the l000l225 F. range. By rapidly is meant about one minute or less.

The invention will now be described in greater detail with reference to the appended drawings, in which:

FIG. 1 is a diagrammatic illustration of one embodiment of the invention as'applied to a pouring reel;

FIG. 2 is a partly'diagrammatic illustration'of another embodiment of the invention as applied to a laying reel; and

FIG. 3 is a side elevational view, partly in cross section, illustrating one form of apparatus for carrying out a portion of the method of the invention.

Referring now to the drawings, and more particularly to FIG. 1, the dotted line 10 refers to a length of hot rolled rod which progresses at high speed from right to left in FIG. 1. The rod is shown as emergingfrom a continuous hot rolling mill, the last or finishing stand of which is illustrated at 11. The speed of the rod 10' as it 7 leaves the finishing stand 11 wouldtypically be of the order of 3000 to 5000 feet per minute, but higher or lower rod speeds are sometimes used.

The rod 10 leaving the finishing stand 11 is to be taken pouring reel or a laying reel. A pouring reel is shown in In such a construction the reel is rotated at a speed synchronized with the rod speed and therod is poured into the annular space between twoconcentric rows of guide pins. The guide pins are indicated at 13 and the reel drive at .14. In a laying reel (asillustrated in FIG. 2) the coil does not rotate and the rod is laid onto a stationary plate by a synchronized rotating guide. In 'accordance with the invention, the rod is cooled. in

7 two steps. The first cooling occurs between the exit end 7 of the hot rolling mill and the reel, and is arranged to cool I the rod from its temperature at the exit end of the hot rolling mill (usually about l650-l800 F.) to a surface temperature, as it enters the reel, of about 1350-1450 F;

This first cooling step, which may be effected in any convenient way, should be conducted so'that the average The rod, as it leaves finishing stand 11, passes through bell-mouthed guide pipe 15, and then through a similar bell-mouthed guide pipe 16 into a'water cooling chamber 17, which might be of the type shown in United States Patent 2,65 8,012 to Strachan. However, unlike the operation described in the Strachan patent, the leading end of the rod is cooled to the same extent as the remainder of the rod. Should it be desired not to cool the leading. end of the rod, this leading end would subsequently be cut off and discarded. The rod passes through a series of guides 18 Within the chamber 17, Water flowing onto the rod within the guides 18 frorna header :19 to which water is supplied by a pipe 20. Water is drained from the chamber 17 through a pipe 21.

At the exit end of the chamber 17 the rod 10 enters a pipe 22- which directs the rod into the pouring reel 12 in the usual manner. As the rod 10 enters the pipe 22 the rod surface may have been cooled to a relatively low temperature, approaching 900 F. The rod surface temperature can be controlled by regulating the rate of flow of cooling water.

Because of the high speed of the rod 10, the center thereof will have cooled substantially less than the surface, so that by appropriate adjustment of the cooling water flow the rod average temperature can be maintained well above the critical temperature. As the rod 10 passes. through the pipe 22, heat transfer between the interior and exterior portions of the rod tends to equalize the tent peratures at the surface and center of the rod so that as the rod leaves the exit end of pipe 22 and passes on to reel 12, the surface temperature will have risen to a value within the range of about 1350-1450" F., i.e., from a value slightly above the critical temperature to 1450" F. The center of the rod may be at about the same temperature or slightly higher, depending on the length of the pipe 22. The longer the pipe 22 the more nearly uniform will be the temperatures across the rod cross section.v

Another desirable form of apparatus to efiect the firstv cooling step of the invention is that shown in the afore-- mentioned British Patent 342,189 of 1931. Simpler forms of water cooling baths could be used provided the specified temperature ranges-are achieved.

In accordance with the invention, a second cooling step occurs while the rod is being taken up on the reel. This second cooling step is effected by directing an atomized water spray on the coil of rod as it is being formed. Thus the atomized water is directed so as to strike primarily the uppermost layer of rod on the reel. The waterand air flow rates are adjusted so that all portions of therod (from the surface to the center) are cooled below the critical temperature and within the range of about, 900-1300" F. and preferably about l000-1225 F. However, the temperature of the surface of the rod is not allowed to fall below about 900 F. while the rod is.

P upon a reel 12, which may beof any desired type, e.g., a

The reeling usually requires a time of about one minute for the lengths ofrod normally used so that adequate cooling time at a suitable cooling temperature is afforded for the carbon to come out of solution and form a finepearlitic structure suitable for wire drawing.

. As shown in FIG. 1, water from a pipe 23 and air from a pipe 24 are mixed in an atomizer 25 and the resultant atomized water is sprayed onto the rod entering the annular coil-forming space of the reel 12 by means of a delivery pipe 25. Valves 26' and .27 are provided in the

pipes

23 and 24, respectively, to permit control of the flow rates of water and air, respectively. The delivery pipe 25' may be disposed so as to direct the atomized spray onto a limited area of the coil as the coil revolves beneath the end of the delivery pipe" The actual cooling action is a combination of the cooling effects of heating and evaporating the water in the spray, contact with the air contained in the spray and cont-act with air due to the rotation of the coil. Most of the cooling action with respect to any short length of rod occurs while that short length is near the top of the coil so that substantially un form cooling of all parts of the rod takes place. While a coil is being poured it can be observed that the rod at the top of the coil is red hot and that the brightness of the color gradually diminishes to a dark red or black toward the bottom of the coil.

It is somewhat more diificult properly to cool the rod when using a laying reel instead of a pouring reel since an atomized spray from a single stationary nozzle will generally not adequately cool the entire coil in a laying reel.

In FIG. 2 there is illustrated a laying reel 28 to which is delivered rod which has been subjected to a first cooling step as described in connection with FIG. 1. The rod leaves pipe 22 and passes through a spout 29 which is rotated by gears 39 and 31 (suitably powered) so as to lay the rod on a plate 32 in the space between annular rows of

pins

33 and 34. When a complete coil has been laid, the rows of

pins

33 and 34 may be retracted, as shown in dotted lines at 33 and 34', so that the coil can be removed by an intermittently operated conveyor 35.

As the coil is laid by the rotating spout 29, the coil is cooled by atomized Water directed primarily onto the uppermost layer of the coil by a series of circumferentially spaced atomizing nozzles, each of which may be of the same type as is shown in FIG. 1. A suflicient number of such spray nozzles should be provided so that the sprays overlap, thereby cooling all portions of the coil. The spray should be adjusted to provide temperature distributions as described in connection with PEG. 1. In general, more total water will be required to cool a coil on a laying reel than on a pouring reel because of the more compact nature of the coil on a laying reel. However, with multiple nozzles, as described, less water per nozzle will be required.

Instead of using multiple nozzles, a laying reel may be cooled by a nozzle carried on the laying spout 29. In this case the rotation of the nozzle with the spout will serve to cool all portions of the coil. Moreover, the centrifugal force due to the rotation will assist in atomizing the water, the atomizing action occurring from centrifugal force being dependent on the speed of rotation. if sumcient atomizing action occurs, a separate air supply may be dispensed with.

FIG. 3 illustrates a particularly desirable form of apparatus for spraying atom zed water on the coil and may be used with any dmired type of coiling device, e.g., a pouring reel, as in FIG. 1 or a laying reel, as in FIG. 2. The apparatus comprises an air supply pipe 36, a main air control valve 37, an air flow indicator 38, a quick shut oil vmve 39, a water supply pipe 40, a main water control valve 41, a water flow indicator 42, a quick shut ofi valve 43, a Y fitting 44 and a delivery pipe 45.

The

valves

37 and 41 serve to permit adjustment of the air and water flows, respectively, and the flow indicators, which may be of any convenient type, facilitate such adjustment by enabling the flows of air and water to be set readily to values previously found desirable. The quick shut off valves enable the flows of air and water to be shut ofi without disturbing their previous settings. Thus after a complete rod has been wound on a reel and after adequate cooling of the last delivered portion of the rod has occurred, the air and water may be shut ofif by closing the

valves

39 and 43. When a new rod is to be reeled, the air and water may be turned on again at their former flow rates simply by fully opening the

Valves

39 and 43. Prompt resumption of proper air and Water flows without delay is of course important, especially in view of the high speed at which the rod is delivered to the reel.

The water entering the Y fitting 44 is atomized by the entering this fitting, the resultant atomized water he ing sprayed on the coil through the delivery pipe 45, the delivery end of the pipe 45 being disposed so that the spray will contact the desired coil area.

The spray of atomized Water onto the reel is continued after a rod is completely wound for a time sufficient adequately to cool the last portions of the rod, i.e., the portions forming the uppermost layers on the completed reel. This time may be made equal to the reel braking and removal times.

An atomizing nozzle of the type shown in FIG. 3 was used on a pouring reel for a rod finishing 0.218 diameter high carbon steel rod. The rod leaving the finishing stand of the rod mill traveled at about 3500 feet per minute. The rod was subjected to a first cooling step, as described previously, and was then delivered to the pouring reel. It was found that satisfactory cooling, i.e., cooling within the temperature range described pr viously, was achieved with air at between 15 and 30 pounds gauge pressure and an air flow between and 250 cubic feet per minute (measured at atmospheric pressure) and a water flow between 0.25 and 2 gallons per minute. It was found preferable to provide air flow between 75 and cubic feet per minute and water flow between 0.5 and 1.5 gallons per minute. The supply pipes 36 and 4-0 were and /4" I.D., respectively, the delivery pipe 45 was /2 1.1). by 24" long, and the legs of the Y fitting 44 were 1" 1.1).

Other atomizing arrangements can, of course, be used in practicing the invention. For example, atomizing arrangements of the type where air flow inspirates the water by creating a suction or where water is aerated to form air bubbles. Water may be atomized Without using a separate source of air by supplying water under suitable pressure to an atomizing nozzle of appropriate design. In each of these cases the object is to supply atomized water to the coil to cool the rod as it is being coiled to within the temperature range of about 900 to 1300 F. and preferably about 1000-1225 F., the surface of the rod not being allowed to drop below about 900 F. during at least most of the coiling operation. 7

In one example of the invention, some 0.187" diameter steel rod containing 0.65% carbon left the rolling mill at a temperature between 1700 and 1800 F.,-was subjected to the first cooling step of the invention and was then delivered to a pouring reel. The surface temperature of the red as it entered the pouring reel was 1400 F. The rod was sprayed with atomized water as it was reeled, the flow of atomized water being adjusted so that the rod temperature during reeling was reduced to between 1000 and 1225 F. and so that the surface temperature did not fall below 1000 F. The rod had a fine pearlitic structure with small grain size and drew satisfactory tour drafts to 0.095" diameter for a total reduction of area of 75%. The grain size of the rod subjected to the two step controlled cooling in accordance with the invention was actually smaller than is frequently obtained in a conventional patenting operation, although the total permissible reduction in area was somewhat less than can be achieved with such a patenting operation.

In another example of the invention some 0.218" diameter steel rod containing 0.65% carbon was subjected to the first cooling step of the invention and was delivered to a pouring reel with a rod surface temperature of 1400 F. The rod was sprayed with atomized water to effect the second cooling step of the invention while the rod was being reeled. The cooled rod had a fine pearlitic structure and drew satisfactorily four drafts to 0.115" diameter for a total reduction of area of 72%. V

In contrast to these examples, a 0.218" diameter rod containing 0.65% carbon as hot rolled without special cooling (only the usual water quenching) had a coarse pearlitic structure and broke on drawing three drafts to 0.135" diameter, for a total reduction in area of 62%.

An important advantage obtained by the rapid controlled cooling of rod in accordance with the invention is a reduction in the formation of scale. With large compact rod coils finished at a high temperature, scale is commonly as much as 1.5% of'the weight of the coil. By rapidly cooling the rod in accordance with the method of the invention, scale can be reduced to within the range of 0.25 to 0.5% of the weight of the coil. Lower scale not'only represents a saving in steel but also a saving in acid used subsequently to remove the'scale.

While the invention has been described in connection with specific steps and in specific uses, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as set .forth in the appended claims.

What is claimed is:

l. A method of heat treating hot rolled high carbon steel rod, comprising subjecting the rod to a water quenching as the rod travels from the rolls to a coiling device, said water quenching cooling the rod to an average temperature above the critical temperature at which carbide comes out of solution and a surface temperature not below about 900 F, said rod having a surface temperature lying Within the range of about 1350 to 1450 F. when entering the coiling device, and spraying said rod with atomized water while being coiled on said device to reduce the temperature throughout the cross section of the rod to within the range of about l000-l225 E, the surface temperature of said rod during at least the major portion of said coiling not being below about 1000 F.

2. A method of heat treating hot rolled high carbon steel rod, comprising subjecting the rod to a Water quenching intermediate the rolls and a coiling device rapidly to cool the rod but without producing substantially different microstructures at the outside and center of the rod and whereby the surface temperature of the rod on tering said coiling device lies in the range of about 1350- 1450" F., and spraying atomized water on the rod While said rod is being coiled on said device to reduce the temperature throughout the cross section of the rod to values lying within the range of about 900-1300" F.

3. A method of heat treating hot rolled high carbon steel rod, comprising subjecting the rod to a water quenching intermediate the rolls and a coiling device rapidly to cool the rod but Without producing substantially different mircostructures at the outside and center of the rod, allowing at least partial equalization of the center and outside temperatures of the quenched rod whereby the surface temperature of the rod entering the coiling device lies within the range of about 1350-1450 F., and spraying atomized water on the rod while the rod is being coiled on said device to reduce the temperature throughout the cross section of the rod to values lying within the range of about 900-1300 F.

4. A method of heat treating hot rolled high carbon steel rod which leaves the rolls at a speed'of the order of 3000-5000 feet per minute and a temperature of the order of 165 -1800" F comprising subjecting the rod to a water quenching as the rod travels from the rolls to a coiling device, said water quenching cooling the rod to an average temperature above the critical temperature at which carbide comes out of solution'and a surface temperature not below about. 900 F., allowing at least partial equalization of the center and outside temperatures of the quenched rod ,wherebythe surface temperature of i the rod entering the coiling device lies within the range 1 I of about 135 0-145 0 F., and further cooling the rod while the rod is being coiled by spraying atomized water thereon, said further cooling reducing the temperature throughout the cross section of the rod to values lying within the range of about 900-1300" F;

5. A method of heat. treating hot rolled high carbon steel rod Which leaves the rolls at ai speed of the order of 3000-5000 feet per minute and a temperature of the order of p 1650-1800 -F., comprising subjecting the rod to a 'water quenching as the rod travels from theirolls to a. coiling device, said water-quenching coolingthe rod to an average temperature lying above about 1340" F. and a surface temperature not below about 900 F., allowing at least partial equalization of the center and outside temperatures of the quenched rod whereby the surface temperature of the rod entering the coiling device lies within the range of about l350-l450 F., and further cooling the rod while the rod is being coiled by spraying atomized water thereon, said further cooling reducing the temperature throughout the cross section of the rod to values lying within the range of about 900-1300" E, the surface temperature of the rod throughout the coiling operation not falling below about 900 F.

6. A method of heat treating hot rolled high' carbon steel rod which leaves the rolls at a speed of the order of 3000-5000 feet per minute and a temperature of the order of 1650-1800 F., comprising subjecting the rod to a water quenching as the rod travels from the rolls to a coiling device, said Water quenching cooling the rod to an average temperature above the critical temperature at which carbide comes out of solution and a surface temperature not below about 900 F., allowing at least partial equalization of the center and outside temperatures of the quenched rod whereby the surface temperature of the rod entering the coiling device lies within the range of about 1350-1450 PI, and further cooling the rod while the rod is being coiled by spraying atomized water thereon, said atomized water being sprayed primarily on the uppermost layer of coiled rod, the volume of water flow and the degree of atomization thereof being adjusted so that said further cooling reduces the temperature throughout the cross section of the rod to values lying within the range of about 900-1300 F.

7. A method as set forth in claim 6 in which said coiling device comprises a pouring reel and said spray is directed. primarily at a limited area of the uppermost layer of rod being coiled.

8. A method as set forth in claim 6 in which said coiling device comprises a laying reel and said spray is formed by a plurality of individual spaced sprays, adjacent sprays having overlapping areas of contact with the uppermost layer of said coil whereby all portions of the coil are subjected to said further cooling step.

9. A method of heat treating hot rolled high carbon steel rod, comprising subjecting the rod to a water quenchintermediate the rolls and a coiling device rapidly to cool the rod but without producing substantially diiierent microstructures at the outside and center of the rod and whereby the surface temperature of the rod entering the rod is being coiled on said device, said atomized water being directed primarily on at least a portion of the uppermost layer of the coil being poured on said device and the flow and extent of atomization of said water being adjusted so as to reduce rapidly the temperatures of all portions of the cross section of the rod to values below the critical value at which carbide comes out of 'solution, the temperature at the surface of the rod being maintained at a value not below about l000 F. during formation of the coil. i 7

10. in a method of preparing. carbon steelrods for wire drawing by heat treating a rod as'it leaves a hot rolling mill at a temperature of the order of 1650- 1800 F., the rod being fed to a coiling device with a crostructures at the outside and center of the rod and whereby the surface temperature of the rod entering said coiling device lies in the range of about l3501450 F., and spraying atomized water on the rod While said rod is being coiled on said device to reduce the temperature throughout the cross section of the rod to values lying within the range of about 90()l300 F.

12. A method of eat treating hot rolled low carbon steel rod, comprising subjecting the rod to a Water quenching intermediate the rolls and a coiling device rapidly to cool the rod but without producing substantially different microstructures at the outside and center of the rod, allowing at least partial equalization of the center and outside temperatures of the quenched rod whereby 10 the surface temperature of the rod entering the coiling device lies Within the range of about 1350-1450 F., and spraying atomized water on the rod While the rod is being coiled on said device to reduce the temperature throughout the cross section of the rod to values lying within the range of about 900-1300 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,658,012 Strachan Nov. 3, 1953 2,75 6,169 Corson et al July 24, 1956 2,810,570 Wilson Oct. 22, 1957

Claims

2. A METHOD OF HEAT TREATING HOT ROLLED HIGH CARBON STEEL ROD, COMPRISING SUBJECTING THE ROD TO A WATER QUENCHING INTERMEDIATE THE ROLLS AND A COILING DEVICE RAPIDLY TO COOL THE ROD BUT WITHOUT PRODUCING SUBSTANTIALLY DIFFERENT MICROSTRUCTURES AT THE OUTSIDE AND CENTER OF THE ROD AND WHEREBY THE SURFACE TEMPERATURE OF THE ROD ENTERING SAID COILING DEVICE LIES IN THE RANGE OF ABOUT 13501450*F., AND SPRAYING ATOMIZED WATER ON THE ROD WHILE SAID ROD IS BEING COILED ON SAID DEVICE TO REDUCE THE TEMPERATURE THROUGHOUT THE CROSS SECTION OF THE ROD TO VALUES LYING WITHIN THE RANGE OF ABOUT 900-1300*F.