US3231432A

US3231432A - Process for the quenching of hot rolled rods in direct sequence with rod mill

Info

Publication number: US3231432A
Application number: US402495A
Authority: US
Inventors: David W Mclean; Charles G Easter
Original assignee: Morgan Construction Co
Current assignee: Siemens Industry Inc
Priority date: 1964-10-08
Filing date: 1964-10-08
Publication date: 1966-01-25
Anticipated expiration: 1983-01-25

Description

Jan. 25, 1966 MCLEAN ETAL 3,231,432

PROCESS FOR THE QUENGHING OF HOT ROLLED RODS IN DIRECT SEQUENCE WITH ROD MILL Filed Oct. 8, 1964 2 Sheets-Sheet l FIG. I

1N VENTOR.

DAVID W. MCLEAN CHARLES G. EASTER Jan. 25, 1966 w, MCLEAN ETAL 3,231,432

PROCESS FOR THE QUENCHING OF HOT ROLLED RODS IN DIRECT SEQUENCE WITH ROD MILL Filed Oct. 8, 1964 2 Sheets-Sheet 2 INVENTOR. DAVID W. MCLEAN BY CHARLES G. EASTER United States Patent PROCESS FOR THE QUENCHING OF HOT ROLLED RODS IN DIRECT SEQUENCE WITH ROD NHLL David W. McLean, Hamilton, Ontario, and Charles G. Easter, Burlington, Ontario, Canada, assignors, by mesne assignments, to Morgan Construction Company,

Worcester, Mass.

Filed Oct. 8, 1964, Ser. No. 402,495 14 Claims. (Cl. 14812) This application is a continuation-in-part of patent application Serial No. 219,220, Process for the Controlled Cooling of Steel Rods, filed August 24, 1962, now abandoned, and of Serial No. 282,939, Improved Hot Rolled Steel Rod, filed May 24, 1963, both in the name of the present inventors.

This invention relates to rolling steel rod and preparing the same for cold working. More particularly, this invention relates to a process for quenching steel rod in a controlled manner in direct sequence with a rod rolling mill in such a way that a substantially uniform metallurgical structure is imparted to the rod along its entire length. The quenching of the rod is done at mill speeds up to 6000 feet per minute or faster with a substantial saving in scale loss and without the formation of detrimental constituents such as martensite, and, after cooling, the rod is disposed in such a way that collection and formation into an appropriately shaped circular bundle is convenient and can be accomplished without substantial mechanical descaling.

In the conventional process for making steel rod, billets of steel are rolled into red and collected into circular bundles after issuing from the final finishing stand of the rod rolling mill. In normal practice, the rod is passed through delivery pipes to laying reels which deposit the rod onto a flat plate in the form of horizontal rings, and the rings then pile up on each other to form bundles of rod each representing the product of a single billet. The temperature at which the rod leaves the rod rolling mill is usually about 1800" F., but the rod may be waterquenched in the delivery pipes to about 1450 F. depending upon the ability of the laying reel and delivery pipes to handle rod at that temperature. After collection in the laying reel, the bundles are then pushed onto a flat horizontal coil conveyor which supports the bundles on a flat surface so as to avoid sagging and allows them to cool slowly in still air. After cooling on the conveyor to about 1100 F., at which temperature sagging is no longer a danger, the bundles are transferred to a hook carrier and allowed to cool further. On the hook carrier the bundles are transported in succession to points of inspection, trimming, tying, and shipping. Thereafter, what is done with the rod depends upon what type of rod has been rolled. Some of the rod is immediately ready for use as, for instance, certain types of concrete reinforcing rod. Other types are subsequently cold-worked in operations such as wire drawing, or bolt, nail or screw forming or the like. However, prior to cold working, the rod is generally subjected to a descaling, cleaning and coating operation to prepare the surface of the rod for uniform deformation by the cold Working mechanism, and, in the higher carbon grades, the rod is often sub jected to heat-treating operations such as air or lead patenting prior to the surface preparation stages.

The conventional sequence outlined above has numerous drawbacks as follows:

In the first place, the slow rate of cooling causes an over-all increase in grain size and a higher precentage of coarse lamellar pearlite which is, in general, undesirable but especially harmful when the rod is to be coldworked. Secondly, the extended exposure to air at high temperature, in excess of 900 F. causes excessive scale loss. Normally, the total scale loss for steel rod is between 1 /2 and 2%, and although the presence of some scale on the rod is often regarded as beneficial as a rust preventor, particularly when the rod is to be stored out of doors, the normal scale percentage is substantially higher than necessary. Extended exposure to air at high temperatures also causes a degradation of the acid soluble wiistite (FeO) component of the scale into the relatively acid insoluble magnetite (Fe O form and the scale is therefore more diificult to remove by acid descaling. Excess scale growth, however, not only causes unnecessary loss of metal, but also causes pits in the rod surface which subsequently interfere with cold working operations.

Totally apart, however, from the slowness of cooling rate in the conventional process, the nonuniformity of cooling rate is also harmful. Thus, due to the fact that the core portions of the bundle remain hot substantially longer than the surface portions, the above-mentioned metallurgical structure and scale disadvantages are accentuated in the core portions and leave the rod nonuniform both as to scale and metal structure from end-toend of the bundle. This is a decided disadvantage regardless of the grade of steel being manufactured, but is more harmful when the rod is to be cold-worked, and particularly harmful in steels of higher carbon content.

Another disadvantage in the conventional process relates to inspection. Normally, an inspector periodically checks the rod at various places along its length by pulling selected rings out of the bundle. The difiiculty arises from the fact that the rings do not readily return to their proper place in the bundle and kinks or dog ears are formed in such a way that, prior to cold working, the kinks must either be straightened out at substantial expense, or the rod must be diverted to a use in which kinks are no problem.

The foregoing disadvantages of the conventional process arise out of the normal collecting and cooling procedures. Other disadvantages, however, are present in the subsequent processing steps such as air or lead patenting, and the descaling, cleaning and coating steps. Air and lead patenting are undesirable mainly because they are expensive, costing in the USA. about $14 and $17 per ton respectively. In addition, however, lead and air patenting increases both the total scale loss and the proportion of magnetite in the scale.

Acid descaling also is undesirable because it is expensive. This is due not only to acid consumption and spent acid disposal costs, but also to the labor costs resulting from the requirement that the rod be spread out on a cleaning arm for immersion in the acid and then rebundled for subsequent operations. A further disadvantage resulting from acid descaling conventional rod is that, due to the nonuniformity of the scale and the requirement that all of the rod remain in the acid until all scale is removed, there is no Way to prevent the acid from corroding and pitting the raw metal in areas where the descaling took place first.

Numerous attempts have been made in the past to overcome various of the foregoing disadvantages of the conventional process. One primary target has been the production of a uniform air or lead patented structure in direct sequence with a rod mill so as to avoid the substantial extra expense of those steps. The desirability of doing this has long been recognized (see German abandoned-but publishedpatent application Serial No. V1 453 VIa/18c), but a way to do it effectively was not suggested. The nearest thing to a practical process was developed at the I. R. Roebling Sons Corporation (see US. Patents Nos. 2,756,169 and 2,994,328) by which the rod was passed through pipes and water quenched in short, quick intervals to give it an average cooling rate comparable to air patenting. One ditficulty with this latter process, however, was that the quick quenching steps skirted dangerously close to creating undesirable quench hardened spots unless a careful control was maintained. Also, since it was an in-line operation, difiiculties were encountered due to resistance to the forward motion of the rod in the quenching pipes at mill delivery speeds. Also, extra plant space was required. Another problem resulted from winding the cold rod at mill delivery speeds, and, the process, losing the scale from the rod due tobe'nding during the winding operation. In any event, it was not a practical process for modern mills operating at speeds of 6000 f.p.m. or faster. Other efforts to force air through coils for the purpose of accelerated cooling have been made. Some improvement was achieved, but although these processes succeeded somewhat in reducing scale they fail to produce the desired metallur'glcal structure from end-to-end of the rod (see Patents Nos. 2,516,248 and 2,673,820).

One suggestion relating specifically to the removal of scale in direct sequence with a rod mill is shown in the Edwards US. Patent No. 1,232,014 (1917) in which the rod was described as being deposited in overlapping rings onto a belt conveyor and letting it cool in a narrow enclosed chamber filled with a reducing gas. The elimination of scale by the use of a reducing atmosphere is possible but the steel industry does not consider it practical or economic for modern rod making.

Accordingly, the objects of this invention are generally to provide a solution for the above-discussed problems in steel rod manufacture, and more specifically to provide a process for producing rod having uniform physical properties from end-to-end of a bundle without requiring subsequent heat treatment, a reduction in scale loss, a reduction in magnetite percentage in the scale, and a rod which can be descaled, cleaned, coated and drawn more rapidly and with fewer breaks.

The present invention achieves the foregoing objects, and solves the above-mentioned hitherto unsolved probler'ns by depositing the hot rolled rod in nonconcentric, slightly offset rings on a moving conveyor as the rod issues from the rolling mill. Water is used in the delivery pipes of the mill to quench the rod down from about 1800 F. to about 1450 F. before it reaches the conveyor. Thereafter it is drawn out of the delivery pipes by a chain guide (see U.S.- Patent No. 3,100,070) and directed through a 90 bend downwardly through a rotating laying head and onto the conveyor. The conveyor is a relatively open framework, made so to facilitate the quenching steps which follow, but its support points are spaced closely enough to avoid sagging or bending the rod at the temperatures involved, and the initial quenching in the delivery pipes is helpful for this purpose. As the rod is carried along by the conveyor, it is quenched as may be required for the given grade of steel and metallurgical structure desired. Controlled conditions are achieved by regulating the rate of flow of coolant through the conveyor or by employing other quenching methods on the rod while it is moving forward on the conveyor. One of the primary keys to the success of the present invention is the fact that, even though the rod is strewn out along the conveyor in overlapping rings with the sides of the rings closely bunched and aligned at the crossover points, a substantially uniform scale and metallurgical structure is produced throughout a full billet length of rod. In practice, the quenching rate does vary at the cross-over points of the rod, but this only causes a slight change in properties at those points which is undetectable at normal magnifications and of no consequence in cold working. More important is the fact that no harmful quench-hardened spots appear even though the quenching is carried out at mill delivery speeds in excess of 6000 f.p.m.

More specifically in the process of the present invention, the quenching may be done using forced or natural convection, depending upon the cooling rates and conditions desired. However, improved results and a more precise control can be achieved if forced convection is employed. In fact, by controlling the forced convection,- and by applying a fog nozzle water spray to the rod until it is cooled to a temperature of 1250 F., a lead patented structure is produced. It is also advantageous to apply the cooling medium over the width of the conveyor such! that greater amounts of the cooling medium are applied at the edges of the overlapping rings where the mass or concentration of the overlapping rings is greater. This: can be done by providing a greater supply of forced con-- vection at the edges, but even with natural convection, a greater flow of air is induced at the edges due to the concentration of heat there.

The invention is not limited to the type of cooling mediunt employed. Besides air, steam, water or oil quenches,. fluidized beds, means for increasing or decreasing radiant. heat loss, equalizing baths such as are used in lead pat-- enting and the like can be used. The important criterion is that the temperature of a sufiiciently large part of the entire length of the rod is brought down in conformancewith the applicable isothermal transformation diagram to produce the requisite metallurgical properties in the en-- tire rod.

The scale formed while quenching in this manner (firstl with water down to 1450 F. and then to below 900 F.. with air) is thin and friable, and contains a remarkably low percentage of magnetite. It is also extremely easy' to remove by acid, taking about one-half the time required for conventional rod with consequent savings in labor,. acid consumption and spent acid disposal. Also the re-- duction of time in the acid results in improved rod quality due to a reduction of acid-caused pits on the surface of' the rod. In addition, since the overlapping rings on the conveyor are only slightly off-set, the amount of unbend-- ing required during bundling does not excessively remove the scale.

Accordingly, the process of this invention solves, at one and the same time, a number of major problems A rod bundle having uniform scale and metallurgical properties along its entire length is provided in direct sequence with a rod mill and with virtually no more handling or processing costs than was involved in conven-- tional rod rolling and bundling. Substantial savings in! scale loss are made possible and handling steps are elim-- inated. Controlling metallurgical properties to compensate for differences in composition of successive heats is made possible, and a finished rod having structures equal to air and/ or lead patented" rod can be produced% while completely eliminating the conventional patenting: operation. Inspection of the rod can be carried out: while it is on the conveyor Without disturbing the position of the rings. Savings in acid consumption and improvements in rod surface condition are provided. And, finally, cold Working the rod produced by this process can be done at higher speeds and with less breakage.

The nature of this invention will become clear from the following examples made with reference to the drawings attached to and forming a part of this specification.

In the drawings:

FIG. 1 is a schematic illustration of one form of apparatus that can be used to carry out a preferred embodiment of the process of this invention wherein the hot rolled rod in the form of non-concentric overlapping rings is subject to quenching by means of a forcibly applied cooling medium; and

FIG. 2 is a schematic illustration of a portion of an apparatus similar to that illustrated in FIG. 1 whereby the non-concentric overlapping rings are cooled in a manner to achieve the desired results by natural convection.

At the temperature at which the rod issues from the rolling mill, the iron of which the steel is principally composed is in the form of gamma iron and has the prop erty of containing up to 2% carbon in solid solution. This solid solution is known as austenite. Upon cooling through a critical temperature the austenite undergoes transformation to ferrite which has much less capacity for holding carbon in solid solution. The carbon rejected from the solid solution during transformation as Well as the carbon retained in the solid solution may take one or more different forms depending upon the temperature at which transformation begins and the rate of cooling during transformation. Isothermal Transformation Diagrams (or Temperature, 'Iime, Transformation, or TTT, Diagrams) are often referred to to determine the microstructures that will result for a given cooling or quenching procedure. (See Atlas of Isothermal Transformation Diagrams, second edition, 1951, pages 6-11, United States Steel Company.) Because the transformation is an exothermic reaction, because there is at most times some temperature gradient within the cross-section of the rods, and because in most cases the transformation does not occur at a constant temperature, these diagrams are not numerically exact. Those skilled in the art will appreciate that these diagrams are only illustrative and qualitatively valid, and also that when a transformation occurs during cooling rather than isothermally as in the present process the beginning and completion of the transformation are delayed in time and occur at a lower temperature. Because the rate of cooling has an effect on the time and lowers the temperature for the beginning and completion of the transformation, exact values of time and temperature are, of course, difficult to determine.

To produce the desired microstructure for drawing in to wire, the transformation should be completed fully appoximately at or near the knee of the inner curve, or crescent-shaped curve of the applicable TTT Diagram. Thus can be accomplishedin various Ways. One way is by lead patenting which gives almost true isothermal transformation. In lead patenting the rod is cooled rapidly by submerging it in a liquid bath held at a constant preselected temperature, and holding it in this liquid bath at the temperature of the bath until transformation is complete. Another way is air patenting where the rod is heated to about 1800 F. and cooled in still air such that transformation will begin at a temperature sufficiently above the inner curve to have been completed before the temperature has dropped to the knee of the inner curve.

When hot rolled rod is cooled in the form of bundles, the outer strands of the bundle usually cool the fastest and the inner strands the slowest. The cooling rate obtained when the rod is in the form of bundles is overall so slow as to result in the production of objectionable amounts of coarse pearlite besides being so non-uniform as to cause an intolerable variation in properties. These must be removed or cancelled by air or lead patenting to make the rod acceptable for wire drawing.

During quenching of hot rolled rods in the form of flat overlapping non-concentric rings, as in the present invention, the more rapidly cooling portions of the rod cool at a rate sufiiciently slow to avoid the (formation of objectionable quench hardened areas such as areas that contain martensite. The slower cooling portions of the rod, usually at the points of the overlap of the rings, nevertheless cool at rates sufficiently high that the growth of undue amounts of coarse pearlite is avoided. Also, the spread between the cooling rates is insufficient to produce objectionable variations in the mechanical properties of the cooled rod. Generally speaking, while the scale formed at the points of overlap may be slightly thicker, there is no detectable difference in the microstructures of the portions of the rod at these points as compared to the balance of the rod when inspected by conventional methods, although theoretically there should be.

The microstructure of the quenched rod of this invention consists of uniformly dispersed fine grains.

Grains of fine pearlite with only minute traces of grain boundary ferrite predominate in steels having a carbon content greater than about 0.40 weight percent, and at lower carbon levels grains of ferrite and carbide occur, the relative amounts of each, depending on the chemical constituents of the steel. The microstructure is usually substantially free from bainite although in some cases the presence of bainite may be desired. The ferritic grain structure is always finer than the grain structure of a properly air patented rod or of a conventionally cooled rod from the same heat of steel.

It will be appreciated that since the quenching process of this invention operates in direct sequence with a rod mill, the rod is delivered to the quenching process in an essentially scale-free condition and is thus particularly receptive to uniform cooling without the loss of heat from the rod being inhibited in various portions by nonuniform thicknesses in the scale layer. This in part per mits the quenching rocess of this invention to produce a rod having both a uniformity of physical properties and a uniform coating of scale. In contrast, air patented rods usually have non-uniform coatings of scale which increases the difficulty of acid descaling because over etching of some portions of the rod usually occurs in attempting to remove the patches of scale that are more adherent, thicker or contain a larger amount of acid insoluble magnetite.

Because of the quenching of the rods in the manner of this invention, the scale loss is only /2 to /2 of that of air patented rods and the scale is fine and friable. The cooling rate is such that the degradation of wiistite to acid insoluble magnetite and iron is at a minimum. The magnitite layer that forms is characteristically crazed because of the different thermal coefficients of expansion of the constituent layers of the scale and the base metal. This brazing and the thinness of the scale greatly facilitate acid cleaning. Cleaning of the rods can usually be accomplished in half the time required for normally coiled and cooled rods. This advantage becomes more marked as the carbon content of the steel falls below 0.40 weight percent. Acid cleaning times using accepted procedures are Well under 30 minutes. The amount of scale is less than 1.0 Weight percent at carbon levels under 0.40 weight percent, and generally less than 0.6 Weight percent for higher carbon contents (average values for several coils from the same heat). This reduced amount of scale greatly reduces acid consumption during cleaning. Considering the total scale loss that occurs in preparing air patented rods, i.e., the scale on the as-rolled rods and the scale formed during air patenting, the light uniform scale is a significant advantage of this process. For example, on a trial of 260 tons of rod of various grades the average scale loss was 0.44 weight percent as compared to a scale loss of 0.88 weight percent for normally cooled as-rolled rods. An additional scale loss would occur, of course, when the normally cooled rods were air patented.

The nature of the scale given by the present process results in another advantage. Since it is uniform, relatively loose, and easily removed, pitting of the surface of the rod during acid cleaning does not occur, i.e., deep etching to remove exceptionally tenacious pieces of scale is not required. The surface of the cleaned rod is therefore smoother and more uniform and free from pits that lead to breaking or surfacing imperfections during drawing. While acid cleaning has been particularly referred to, the quenched rods of this invention are particularly amenable to mechanical descaling by being flexed. The ease by which the scale can be removed by simple bending is surprising.

Preliminary data indicate that with respect to scale loss rods quenched according to this invention give an additional benefit when the product is given a secondary heat treatment during wire drawing. It has been observed that when wire drawn from the quenched rods is lead patented, considerably less scale forms than in the case of wire drawn from lead patented rods. This could be the result of the inherently finer and smoother surface structure of the quenched rods.

One preferred embodiment of the present process for the quenching of rolled steel rods as they issue from the rod mill according to this invention is shown in FIG- URE 1. In this embodiment the overlapping non-concentric rings are forced cooled by the positive application of a cooling fluid, usually air, and the cooling fluid is preferably, but not necessarily applied in a greater amount or volume to the outer edges of the rings to achieve a greater uniformity of cooling.

Each length of rod is produced in a rod mill from a single billet. Each billet usually weighs at least 400 pounds and may weight as much as 1500 pounds or more. The length of the rod is dependent upon the size of the billet and is usually at least 400 feet long and may be as long as 9000 feet or more. Delivery speeds can be as high as 6000-8000 feet per minute or more.

The rolled rod issuing from the rod mill at a temperature of about 1750 to 1950 F. is directed through a cooling and guide pipe 21 to a laying reel or cone 22. Water .is introduced into the cooling pipe guide 21 to quench the rod to about 1350 F. for descaling quality low carbon grades and 1450 F. for higher carbon grades. The exact temperature depends on the end product requirements but is usually greater than 1200 F. Laying cone 22 is positioned to deposit the rod on a conveyor indicated generally by the number 23. The conveyor consists of a conveyor bed 24 upon which guide bars 26 rest. The conveyor bed is slotted as at 25 to permit passage of cooling gas blasts supplied by blowers 27. Dampers 32 are used to adjust the flow of the coolant through these slots. A conveyor chain 28 driven by drive 29 is used to drag the rod over guide bars 26. A hood 30 covers the conveyor and helps to direct the flow of the cooling gas. The hood 30 is in part broken away to expose the interior thereof, and the coils 20 of the rod and the conveyor are in part broken away as indicated to expose slots 25 in the conveyor 24, whereas in practice the coils 20 are continuous over the length of the bed from one end of the rod to the other.

The rod is deposited on the conveyor bed in Spencerian form (after Rogers Spencers style of handwriting), i.e., in the form of a succession of non-concentric, overlapping circular convolutions 20, the spacing of which is illustrated in an exaggerated manner for purposes of clarity. The deposited rod cools by radiant cooling in an equalizing zone and then enters the hood area where it is rapidly and uniformly cooled by the cooling gas. The spacing of the circular rings allows the gas to uniformly contact all portions of the rod. The mass flow rate of the rods along the conveyor is greater at the outside edges than in the middle. A larger proportion of the coolant is preferably, therefore, supplied to the outer edges of the conveyor, as illustrated by arrows 31, so that heat extraction from the rod is approximately uniform across the coils, i.e., the mass flow rate of coolant across the width of the conveyor is about proportional to the mass flow rate of the deposited rods across the width in this preferred embodiment. This can be accomplished by increasing the width or number of the slots 25 at the outer edges and/or by having hood 30 redirect the coolant passing through the center portions of the conveyor downwardly over the outer edges of the rings and out the exit slots 34 at the bottom edges of the hood. The amount of coolant supplied along the length of the conveyor is sufiicient to cool the rod rapidly enough to achieve substantially complete transformation of the austenite before the temperature has dropped to below that of the knee of the inner curve of the isothermal transformation diagram for that particular grade of steel.

The rod is discharged at a temperature below that temperature where any further material changes in metallurgical properties would occur, usually 1100 F. or less, and is collected by coiling means 33. After descaling, it can be directly drawn into wire without further heat treatment.

It is desirable to form the series of overlapping nonconcentric rings on the conveyor in such a manner that the outside edges of the rings do not exactly align or coincide. This permits the cooling medium to have greater access to the portions of the rod at the outside edges and minimizes the mutual maintenance of the temperature of these portions by radiation and/or conduction. This avoidance of a too precise overlapping of the rings at their edges can be accomplished by varying the positions of the rings with respect to the center line of the conveyor and/ or by varying the diameters of the rings as they are deposited on the conveyor. Satisfactory results have been achieved by using a laying reel 22 having a large enough diameter to permit the rings to fall onto the conveyor 23 with some random variations in their diameters and in their positions on the conveyor bed. This random positioning of the overlapping rings is aided somewhat during the cooling because the rod first contracts, then expands and again contracts during the phase changes which causes the relative positions of the rings to vary and the points of contact between successive rings to change.

It might be noted that this imparting of a random pattern to the rings as they are deposited on the conveyor results in somewhat non-uniform bundles being produced at 33. The bundles are loose and open enough after banding to accept (considering also the nature of the scale produced by the present process) acid-descaling without having to be opened up or unbundled, which feature of this process is the subject matter of a separate patent application.

It has been observed that the portions of the rod at the points of overlap of the non-concentric rings cool at a slower rate as the rings pass down the conveyor than those portions of the rod in the center of the conveyor. These hot spots or spots of slower cooling cause no particular harm contrary to what might have been expected.

FIGURE 2 illustrates a portion of a conveyor construction that can be used to accomplish the controlled cooling of this invention by means of natural draft or convection cooling of the overlapping non-concentric rings. The results given by natural draft cooling, while producing a drawable grade of rod, particularly with the lower carbon content grades of steel, are not quite as good as those given by the embodiment shown in FIG- URE l, which produces a cooled rodhaving properties superior to those of a properly air patented rod. As illustrated, the conveyor simply consists of thin rails 41 along which the non-concentric rings 42 slide. The full succession of rings is not shown in order to expose the conveyor bed. The rails are suitably supported on crossmembers 43. The floor or bed of the conveyor is open so that air can circulate upwardly past the rings. Side walls 44 are used to contain the rings 42 and to promote the natural flow of air up through the bed of the conveyor. The chain member that pulls the rings over rails 41 is not shown in this figure. The rings are deposited on and removed from the conveyor in the manner previously described.

Rails 41 are spaced closely enough together to prevent appreciable distortion or sagging of the hot rod rings during the initial period of cooling, the same being true of the embodiment shown in FIGURE 1. Also, it is preferred that the width of rails 41 contacting the rings 42 be as narrow as possible to minimize spot or local chilling of the portions of the rings contacting the rails. Rails with rounded top portions have been used, but flat-topped rails of up to one-half inch or so are satisfac- 'to'ry. Heat exchange means such as water cooled coils can be placed beneath the conveyor to control the temperature of the upwardly rising air.

EXAMPLE I With reference to Table I, all of the specimens were prepared from the same heat or Ordinary Spring Steel (0.63 weight percent carbon, 1.00 weight percent man ganese and 0.17 weight percent silicon). The billets weighed approximately 400 pounds and were rolled to 0.263 (nominal) inches diameter on the same mill. The controlled cooled rods of this invention were coiled on the conveyor shown in FIGURE 1 at about 14401470 F., in the form of 48 inch diameter overlapping non-concentric coils, with the spacing between the leading edges of the coils being about 1.5 inches. The total number of coils was 129 and the conveyor speed was 60 feet per minute. Controlled cooling by air blasts commenced within 15 seconds from the time the rod temperature reached approximately 1440" F. and the rod cooled uniformly thereafter from about 1375 F. at a rate of 800 F. per minute and was discharged from the conveyor and coiled at 480 F.

The regularly cooled rods were coiled at about 1450 F. in a conventional manner as it issued from the mill, with the coil being allowed to cool in still air.

The air patented rods were prepared from the regularly cooled rods by reheating to above 1800 F., cooling while extended in still air followed by coiling.

Table I gives the inspections that were obtained.

Table I REGULARLY COOLED finer structure is readily observable when compared to a specimen from the same rod mill billet 'or from the same heat of steel that has been conventionally coiled and cooled and subsequently properly air patented.

The scale on the rods cooled according to this invention was less in total amount, and crazed. In the samples identified in Table I, the controlled cooled rod had single phase (wiistite) bonding of the scale to the base metal whereas in the air patented rod there was a partial conversion of the Wiistite to iron and undesirable magnetite at the scale-base metal interface. The wiistite layer of the air patented rod was keyed to the steel base by the iron and magnetite. The acid insoluble magnetite area of the air patented rod was almost twice as thick as that of the controlled cooled rod.

EXAMPLE II Approximately 20 tons of steel from the same heat were processed in the manner of this inveniton as described in Example I into 101 coils of number 5 rod. The averaged coil weight was 408 pounds. The coils were then processed into 4 types of wires, as follows:

0.095 breakdown for patenting to make 0.036

drawn galvanized spring wire 8,000 0.052 breakdown for patenting to make 0.0207

M.S. spring Wire 2,000

Average Microstrue Scale thickness, inches Bundle No. Average red. of area, ture, percent .iltimate p.s.i. percent lamellar pearlite FeO Fe O F0203 Total QUENCHED ACCORDING TO THIS INVENTION AIR PATEN'IED As compared to the air patented rod, the rod of this invention had a finer grain structure of ferrite and fine pearlite and was substantially free of bainite. One reason, of course, for this finer grain size is the rapid cooling of the rod in addition to the fact that the rod has been heated only once at the rod mill billet state and not thereafter. Conventional air patenting involves reheating of the rolled rods and this encourages crystal growth. Alloy constituents do, of course, aflect the grain size as does the history of billet, but for any given grade of carbon steel the microstructure of the controlled cooled rods produced by this invention is always finer and more uniform. This The ladle analysis of the heat was (weight percent): 5

The number 5 rods were produced from rod mill billets 2 ,4 inches square using a continuous 3 strand mill with 6 primary roughing stages, 4 intermediate roughing stages, 4 stranding stages and 6 finishing stands. The rods is- 1 1 sued from the mill at a temperature of about 1875 F. and were immediately cooled to 14601490 F. by the application of water. The rods at this temperature were deposited in the form of non-concentric approximately 48 inch O.D. rings on a conveyor using a laying head. The conveyor had an overall length of 75 feet and moved at a rate of about 60 feet per minute. The spacing between the forward edges of the non-concentric coils was about 1.5 inches. The conveyor had suitable slots in it over a length of about 38 feet to permit application of blasts of cooling air to the coils. No cooling air was applied in the first feet, then the air was applied to cool the rods within the time given by the isothermal transformation diagram for that grade of steel. The rods were coiled at about 400 F.

The microstructures of these as-rolled controlled cooled rods were equivalent in quality to a good air patented structure; approximately 80 percent fine pearlite, percent medium coarse pearlite and only a minute trace of grain ferrite (at 750 magnification).

The tensile strengths of samples taken from the coils were as follows:

Front ends Back ends Number of Pounds N umberot' Samples Samples 1 0, 200 5, 249 1 0,150 0,199 2 5,100 0,149 2 12 5, 050 6, 099 12 13 5, 000 5, 049 17 3 5,950 5,999 9 22 5,900 5, 949 22 14 5, 350 5,899 10 12 5,800 5,849 14 10 5, 750 5,799 8 2 5, 700 5, 749 7 4 5, 050 5, 699 3 2 5, 000 5, 640 1 1 5,550 5, 599 Avg. breaking load 5,912 lbs. Avg. breaking load 5.923 lbs. Avg. U.T.S. 150,800 p.s.i. Avg. U.T.S. 151,000 p.s.i. Range 142,1.00 to 158,700 p.s.i. Range 143,400 to 158,500 p.s.i.

The above values are based on a nominal rod diameter of .2235". The distribution and uniformity of the tensile values are considered good. The average tensile strengths of this particular lot is approximately 10,000 p.s.i. higher than a conventional air patented .218" rod of this analysis.

Rod measurements were as follows (as determined from 12 random coils) Front ends Middle Back ends Low side .214 to .221" .210 to .221" .212 to .224". High side .227 to .239"--- .225 to 234"- .223 to .234". Average .216 x .231 .216 x .231 .217 x .231". Nominal round .2235 .2235 .224".

The following tests were also taken on the as-rolled rod:

Average Minimum Maximum Percent elongation in 10 (Bench marks):

Front ends 6. 3 4. 37 8. 75

Back ends 6. 7 4. 37 8. 75 Percent reduction in area (Tensile neckdown):

Front ends 53. 4 46. 8 59. 2

Back ends 54. 4 45.0 62.0

Chemical analysis (20 random samples):

C .62/ .64 MN .99/ 1.05

Si 171/ .188 Cu l l/ .12

til

Percent Scale on rod surface (lab. check) (20 random samples):

Average .50 Minimum .27

Maximum .72

Seams (20 random samples):

Coil #10, 1 seam .004" Coil #11, 1 seam .002"

All others examined were seam-free.

Laps (20 random samples):

Coil #9, 1 lap .003" All others examined showed no laps. Grain size (20 random samples):

As-rolled rod 6 to 8 McQuaid Ehn 6 Surface, partial decarb (20 random samples) (X001):

10 samples None 3 samples 0 to 1 6 samples 0 to 2 1 sample 0 to 3 The coils were cleaned by a batch dip in diluted sulphuric acid. Seven coils were used per yoke. The temperature of the batch. was about Fri-15 F. and the cleaning time was about 10-15 minutes per yoke. Seventy-seven coils were limed and 24 were coated with borax. Four random loads of the borax coated rods were weighed before and after cleaning and coating. With two loads no change in weight was observed, with one load the weight loss was 0.32 percent and with the remaining one it was 0.36 percent. Those skilled in the art will appreciate that this small loss of weight during the removal of the scale is startling.

The M.B. spring wire was drawn from the limed rod using 6 holes at 700 feet per minute and a dry lubricant. The total reduction was 76%. The die line-up was:

In this case, as in all the following, the wire drawing operation was accomplished without difliculty. No breaks were encountered and die life was good, The finished wires showed no brittle tendency. The .1055 MB. spring wire passed the 1X Wrap Test and had the following tensile strength (50 coils approximately 360 pounds each).

Average Minimum Maximum Front ends, p.s i 234, 700 226, 000 247, 000 Back ends, p.s .1 229, 300 219,000 248, 000 Required, p.s.i 216, 000 248, 000

The 0.076" high tensile H.S. spring wire was drawn from the limed rods using 8 holes at 700 feet per minute and a dry lubricant. The total reduction was 88.4%. The die line-up was:

The following inspections were obtained:

MECHANICAL TESTS ON 7 CARRIERS, APPROXIMATELY *Torsion and bend tests are not a requirement on this grade of spring Wire. The tests were conducted in line with improved plow rope wire testing procedure merely as a matter of general interest. All samples tested passed the torsion and bend specifications for improved plow rope wire.

Average I Minimum Maximum Front ends, p.s.i 233, 800 220, 000 243,000 Back ends, p.s.i 232, 000 227,000 241, 000 Torsions in 8":

Front ends 37 31 44 Back ends 38. 4 32 44 90 bends* over .57" radius:

106. 6 97 All samples passed a 1X wrap test *Torsion and bend tests are not usually made on this type of wire. The tests were conducted in line with improved plow rope wire testing procedure as a. matter of general interest. All samples tested passed the torsion and bend specifications for improved plow rope wire.

The 0.052" breakdown stock was drawn through 10 holes at 1000 feet per minute using a dry lubricant. The total reduction was 94.6%. The die line-up was:

The following inspections were obtained: MECHANICAL TESTS ON 7 COILS, APPROXIMATELY 300 LBS. EACH Average Minimum Maximum Front ends, p.s.i 324,000 319, 000 334, 000 Back ends, p.s,i 331, 000 326, 000 336, 000 90 bends* over .27 rad 5:

Front ends 59. 3 51 69 Back ends 60. 52 69 Ductility All sampes passed a 1X wrap test *Drawing this type of steel to .052 from a Number gauge rod is con 14 The following table shows the uniformity of the rod throughout its length.

Test Number Side of conveyor, Center of conveyor,

ultimate p.s.i. ultimate p.s.i.

EXAMPLE IV A C-1008 grade steel and a steel having a carbon content of .71/ .75 were rolled into number 5 rod and cooled under comparative conditions. A C-1020 grade rolled to a nominal diameter of 0.391 inch was also evaluated. Some coils were forced cooled on the conveyor as described in Example I, and comparative 'coils were allowed to cool on the conveyor without the blowers 7 operating, i.e. by natural radiation and convection. The tests were carried out at three different conveyor speeds. A sum- Sldeled a rather severe WllB drawing practice. mary of the results btained are given in Table IL Table II Tensile Strength Elongation (percent) Reduction of Area (in 1,000 p.s.i.) (percent) Condition F.p.m.

Range Average Range Average Range Average #5 C 1(108 Blowers 011 20 47-54 50. 6 410-47 43. 8 70. 1-80. 4 75. 1 60 49-55 52. 9 35-44 39. 5 69. 5-79. 3 73. 4 90 51-57 54. 5 36-40 37. 7 74. 0-78. 7 77. 1 Blowers off 20 -56 52.8 37-44 40.8 74. 2-78. 1 75. 8 50-54 52. 0 38-44 40. 9 70. 3-78. 5 75. 4 90 40-51 49. 7 38-47 41. 9 76. 6-81. 7 79. 0 #5 71/ 75C Blowers on 20 13-16 13.2 38. 1-43. 2 40. 2 60 11-15 13. 1 39. 4-52. 1 45. 9 90 11-15 15. 4 43. 4-46. 6 45. 5 Blowers ofi 20 13-18 14. 3 25. 4-42. 2 35.4 60 13-16 13. 5 33. 2-41. 3 37. 4 90 12-16 14. 2 36. 1-42. 7 38. 6 0.391 C-1020 Blowers on 0 38-44 40.6 66. 0-68. 3 66. 6 60 34-43 38. 3 65. 2-67. 4 66. 5 38-15 40. 9 66. 7-69. 3 68. 2 Blowers ofi 20 39-46 43. l 67. 7-71. 0 69. 6 60 36-46 40. 3 61. 5-66. 6 64. 9 38-45 42. 1 66. 9-70. 3 69. 5

1 Conveyor speed in feet per minute.

EXAMPLE III A number 5 rod was rolled from a spring steel as described in Example II. The coil weight was approximately 490 pounds. The steel contained 0.66 weight per-cent carbon, 0.83 weight percent manganese and 0.17 weight percent silicon. Test specimens were taken approximately every 10 rings alternately between the side and center locations on the controlled cooling conveyor.

It can be seen that the results obtained by natural cooling were not equivalent to those with forced cooling, but nevertheless that a drawable grade of rod was produced. The quality of the scale produced was acceptable in all cases, with there being a somewhat heavier but still uniform scale produced in the blower-off runs with, however, the magnetite contents of each scale condition being roughly the same.

The floor of the conveyor was enclosed except for the ducting that lead to the blowers 7. This arrangement of the equipment was not, therefore, very conducive to natural draft cooling, and substantially improved results will be obtained by using the open conveyor arrangement illustrated in FIGURE 2. These tests without the forced application of the cooling air do establish, however, that the openness of the overlapping nonconcentric rings permit an adequate rate of cooling to be achieved in all portions of the rod even under natural draft conditions by proper adjustment of the time of the rod on the conveyor.

In other experiments, hot rolled rod, after being quenched in the delivery pipes, has been deposited on the conveyor at 1450-1500 F. and then immediately quenched to 1250 F. by means of a water fog supplied by a fire-fighting type of nozzle, followed by cooling with the blasts of air to below 900 F. This produced a structure equivalent to a good lead quenched structure.

Until now, the industry has believed that it was impossible to secure the uniformity of properties required for wire-drawing if a hot rolled rod was cooled on a conveyor because a rate of cooling that was uniform enough could not be obtained throughout all portions of the rod. Cooling in still air with the rod free of engagement with a conveyor and with no overlapping of the rod was thought to be the ideal method. It was also generally felt that forced cooling, for example, at a rate in excess of 700 F. a minute through the critical region, would cause unacceptable non-uniform metallurgical properties. The above four examples well demonstrate that these assumptions were not true.

In summary, in the present invention the results desired in quenching hot rolled rod to permit direct cold working, i.e., uniformity of mechanical properties and controlled microstructure in the rod, are achieved by quenching the hot rolled rod in the form of overlapping non-concentric rings on a conveyor, which form permits in a reasonable area of plant space the quenching to be carried out with all portions of the rod being so exposed that the cooling medium has sufificient access thereto so that the moving rings are both cooled uniformly over the length of the rod and at such a rate as to achieve the desired microstructure and mechanical properties.

This invention permits quenching of hot rolled rod in direct sequence with a modern high speed rod mill to produce a rod having a sufficient uniformity of properties throughout its entire length to permit the rod to be directly drawn into wire without further heat treatment. One of the'major inventive features of this invention is the depositing of the hot rolled rod as it issues from the rod mill on a conveyor in Spencerian form, which form permits substantially all the surface of the rod to have contact with a cooling medium, and quenching the rings to cool the rod at a rate sufiicient to impart a predetermined microstructure and mechanical properties uniformly throughout all portions thereof with there being no objectionable quench hardened areas produced in the rod during the quenching.

It will be apparent that the present quenching process will by proper selection of conveyor speed, conveyor length and quenching conditions continuously accept a strand of rod delivered to it at practically any linear delivery rate. This is not true of air patenting furnaces which usually must operate at rates less than 100 feet per minute. A multiplicity of air patenting furnaces have to be used for each strand of a multi-strand mill and the capital investments for such furnaces can become quite high. Operations with continuous welded billets are entirely feasible with the present invention, and no other process for producing wire-drawing grade rod is known to have this ability.

A major cause of kinks and bends that occur during wire drawing as the rod is withdrawn from the bundle is that with conventional bundles individual coils are pulled out to inspect them as for caliper and then cannot be pushed properly back into place. The inspected ring may be so far out of place as to result in the formation of a dog-ear during subsequent handling. An additional advantage of the present process is that the rod while in Spencerian form on the conveyor can have any part thereof easily inspected without inducing kinkproducing distortions in the final bundle.

Having described this invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims.

What is claimed is:

1. A process for producing a hot rolled steel rod having a microstructure and mechanical properties which enable the rod without further heat treatment to be drawn into wire, comprising: depositing a rolled steel rod on a moving conveyor in the form of fiat overlapping nonconcentric rings, said rod being at an elevated temperature above the temperature at which allotropic transformation of the austenite of said rod starts to occur; applying a cooling gas to said non-concentric rings over a length and the width of said conveyor, the amount of said cooling gas applied over increments of the width of said conveyor being in proportion to the mass flow rate of said steel rod over said increments, and controlling the amount of said cooling gas applied over said length responsive to the cooling rate given by the isothermal transformation diagram for the particular grade of steel in said steel rod for securing substantially complete allotropic transformation of the austenite rapidly enough to avoid the development of coarse lamellar pearlite in quantities sufficient to interfere materially with cold working and before the temperature of said non-concentric rings drops to that of the knee of the inner curve of said isothermal transformation diagram; and collecting said non-concentric rings at the end of said conveyor.

2. The process of claim 1 when operated in direct sequence with a rod mill and wherein the rod is delivered directly from said rod mill substantially at said elevated temperature.

3. The process of claim 1 whrein the amount of said cooling gas applied across the width of said conveyor is controlled by passing blasts of said cooling gas from transversely extending slots through said non-concentric rings and then redirecting the portion of said cooling gas passing through the center portion of said non-concentric rings outwardly in both directions to contact the outer edges of said non-concentric rings.

4. The process of claim 1 wherein said cooling gas is air.

5. A process for producing a hot rolled steel rod having a microstructure and mechanical properties which enable the rod without further heat treatment to be drawn into wire, comprising: depositing a rolled steel rod on a moving conveyor in the form of fiat overlapping non-concentric rings, said rod being at an elevated temperature above the temperature at which allotropic transformation of the austenite of said rod starts to occur; applying cooling air to said non-concentric rings over a length and the width of said conveyor, the amount of said cooling air applied over increments of the width of said conveyor being substantially in proportion to the mass flow rate of said steel rod over said increments, and controlling the amount of said cooling air applied over said length responsive to the cooling rate given by the isothermal transformation diagram for the particular grade of steel in said steel rod for securing substantially complete allotropic transformation of the austenite substantially uniformly over the length of said rolled steel rod rapidly enough to avoid the development of coarse lamellar pearlite in quantities sufiicient to interfere materially with cold working and before the temperature of each of said non-concentric rings drops to that of the knee of the inner curve of said isothermal transformation diagram; and collecting and coiling said rod at the end of said conveyor.

6. The process of claim wherein said non-concentric rings are allowed to cool radiantly for a period of time without the forced application of a cooling medium prior to the application of said cooling air.

7. A method of forming steel into a length of rod and quenching the same in direct sequence with the forming step, comprising:

(a) forming at least a billet length of steel While at an elevated temperature into a length of rod;

(b) depositing said rod in the form of ofiset rings on a support while the rod is still at a temperature which is at least as high as the temperature at which transformation of the austenite of said steel occurs, the offset of said rings being sufficient to expose substantially the entire surface of said rod, with, however, the form of said rings, although offset, being close enough to the final shape of a bundle to permit ready collection of said rod into a bundle, and said rings being suported on said support at spaced points which are spaced closely enough to avoid any substantial sagging of said rod between said spaced points at the temperture at which the rod is deposited;

(c) passing said rod rings through a quenching zone while supporting the rings at said spaced points of support;

(d) quenching said rod in said zone by the application of a quenching medium to all exposed portions of said rod While controlling the amount of said quenching medium applied responsive to the cooling rate given by the transformation diagram for the particular grade of steel in process to secure substantially complete allotropic transformation of the austenite rapidly enough to avoid the development of coarse lamellar pearlite in quantities sufficient to interfere materially with cold working and before the temperature of said rod drops to that of the knee of the inner curve of said transformation diagram and maintaining the area of access of said quenching medium to the surface of said rod throughout the length of said zone sufilciently large in relation to the area of contact between said rod and said spaced points that variations in cooling rates in said rod due to unequal application of said quenching medium are sufiiciently equalized to avoid any substantial non-uniformity of metallurgical structure along the entire length of said rod; and

(e) collecting said rod rings.

8. The method of claim 7 wherein said rings are contacted with an oxidizing cooling medium during at least a portion of the quenching step with there being a substantially uniform thin friable and crazed scale of low 5 magnetite content produced on the surface of said rod over the length thereof.

9. The method of claim 7 wherein said rod is water quenched prior to being deposited on said support.

10. The medium is 11. The medium is rings.

method of claim 7 wherein said quenching positively and forcibly applied to said rings. method of claim 7 wherein said quenching air and said air is forcibly blown onto said 12. The method of claim 7 wherein said length of rod is formed in a rod mill from a billet weighing at least 400 pounds and wherein said rings are in the form of a series of overlapping, non-concentric rings on said support.

the hottest portions thereof complete transformation.

References Cited by the Examiner UNITED STATES PATENTS 11/1963 Crum 242174 7/1917 Edwards 29-81 2/ 1919 Edwards 2427 9 3/1933 Herman et a1 -63 8/1933 Bain et al. 148153 2/1934 Hood 24280 12/ 1934 Hood 24279 8/1936 Bayless 148-12 OTHER REFERENCES Continuous Conveyorized Loop ProcessingA New Concept in Rod and Wire Handling, by John Zouck, Wire and Wire Products, October 1961 (5 pages).

DAVID L.

RECK, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 231 ,432 January 25 1966 David W. McLean et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 36, for "Thus" read This columns 9 and 10, Table I, under the category "QUENCHED ACCORDING TO THIS INVENTION", seventh column, line 4 thereof, for ".00015" read .OOOOS columns 13 and 14, Table II, first column, line 2 thereof, for "#5.71/.75C" read #5 71/.75C same table, ninth column, line 14 thereof, for "66.5" read Signed and sealed this 10th day of January 1967 Attest:

EDWARD J. BRENNER Commissioner of Patents ERNEST W. SWIDER Attesting Officer

Claims

1. A PROCESS FOR PRODUCING A HOT ROLLED STEEL ROD HAVING A MICROSTRUCTURE AND MECHANICAL PROPERTIES WHICH ENABLE THE ROD WITHOUT FURTHER HEAT TREATMENT TO BE DRAWN INTO WIRE, COMPRISING: DEPOSITING A ROLLED STEEL ROD ON A MOVING CONVEYOR IN THE FORM OF FLAT OVERLAPPING NONCONCENTRIC RINGS, SAID ROD BEING AT AN ELEVATED TEMPERATURE ABOVE THE TEMPERATURE AT WHICH ALLOTROPIC TRANSFORMATION OF THE AUSTENITE OF SAID ROD STARTS TO OCCUR; APPLYING A COOLING GAS TO SAID NON-CONCENTRIC RINGS OVER A LENGTH AND THE WIDTH OF SAID CONVEYOR, THE AMOUNT OF SAID COOLING GAS APPLIED OVER INCREMENTS OF THE WIDTH OF SAID CONVEYOR BEING IN PROPORTION TO THE MASS FLOW RATE OF SAID STEEL ROD OVER SAID INCREMENTS, AND CONTROLLING THE AMOUNT OF SAID COOLING GAS APPLIED OVER SAID LENGTH RESPONSIVE TO THE COOLING RATE GIVEN BY THE ISOTHERMAL TRANSFORMATION DIAGRAM FOR THE PARTICULAR GRADE OF STEEL IN SAID STEEL ROD FOR SECURING SUBSTANTIALLY COMPLETE ALLOTROPIC TRANSFORMATION OF THE AUSTENITE RAPIDLY ENOUGH TO AVOID THE DEVELOPMENT OF COARSE LAMELLAR PEARLITE IN QUANTITIES SUFFICIENT TO INTERFERE MATERIALLY WITH COLD WORKING AND BEFORE THE TEMPERATURE OF SAID NON-CONCENTRIC RINGS DROP TO THAT OF THE KNEE OF THE INNER CURVE OF SAID ISOTHERMAL TRANSFORMATION DIAGRAM; AND COLLECTING SAID NON-CONCENTRIC RINGS AT THE END OF SAID CONVEYOR.