Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
  • B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
  • B21B45/0203—Cooling
  • B21B45/0209—Cooling devices, e.g. using gaseous coolants
  • B21B45/0215—Cooling devices, e.g. using gaseous coolants using liquid coolants, e.g. for sections, for tubes
  • B21B45/0224—Cooling devices, e.g. using gaseous coolants using liquid coolants, e.g. for sections, for tubes for wire, rods, rounds, bars
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
  • C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S72/00—Metal deforming
  • Y10S72/70—Deforming specified alloys or uncommon metal or bimetallic work

Definitions

• Our present invention relates to a method oftreating steel wire to improve its tensile, flexural and torsional properties.
• the conventional practice is to wind the hot wire from the last rolling station into a coil, allowing the coil to cool and thereafter heat-treating the wire in a fused bath, such as molten lead.
• This type of heat treatment is generally referred to as putcnting.
• putcnting a term which may also be used more broadly for the colling of wire in any medium at a controlled rate from a level above the critical point Ac" (transformation of austenite to ferrite) to a range in which austenite istransformed into pearlite.
• the wire so treated should have a predominantly sorbitic crystal structure.
• Sorbite is a fine-grained variant of pearlite and comes into existence upon transformation of austenitic steel at a temperature of approximately 550 C. If the transformation occurs at a lower level, generally below 500 C., the pearlite crystals are still smaller and form a structure known as bainite. This structure is considerably harder than the sorbite and unsuitable for drawing.
• a method of patenting such a wire in a cooling medium of the fluidized-base type i.e. a stream of carrier gas with entrained solid particles such as ceramic granules of elevated heat-transfer coefficient (preferably between about 500 and 1000 cal./m. hr. C.).
• the particles may consist, for example, of magnesia and may range between 0.03 and 0.15 mm. in diameter, with a bulk weight of 1.5 to 5 g./cm. Hydrogen, carbon monoxide or other relatively transformation before its temperature falls below the may serve as the carrier fluid.
• the temperature of the cooling medium may be well below the bainite-formation level of about 500 transformation is completed above that level because the wire is led out of the fluidized bed in a state of incipient transformation before its temperature falls below the 500 C. mark.
• This method can be applied directly to wire coming hot from a rolling mill and thus represents more economical process for obtaining the desired sorbitic structure with substantial exclusion of bainite.
• the general object of ottr present invention is to provide a steel wire of high flexural and torsional endurance, eg for use in coil springs.
• uusteuitic steel wire with a carbon content between about 0.1 and 0. thy weight is treated in a manner resulting. independently ofthe type ol'eooling medium employed. in a structure having the desired ductility and strength for the purposes specified above. This is accomplished by immediately cooling the hot-rolled wire at a rapid rate of at least C. per second to a temperature within the austenite/pearlite transformation range. i.e. a temperature lying generally between 500 and 550 C. although its lower and upper boundaries may be around 480 and 580 (1, respectively. The forced-cooling process.
• the 605 line should be penetrated during the first half of that phase, preferably within the first two seconds after discharge ofthe wire from the rolling mill.
• the final transformation phase may proceed sttbstantially isothermallly over a period of about 10 seconds.
• the initial cooling phase (past the: G08 line) may be carried out by quenching in water while the subsequent cooling is performed in a fluidized bed as described above.
• a wire so treated has surprisingly high stress resistance along with the necessary ductility allowing it to be drawn to the desired final diameter.
• transformation proceeds to completion under substantially isothermic conditions, i.e. without the use of a cooling medium other than the surrounding atmosphere.
• a cooling medium other than the surrounding atmosphere.
• the final cooling, subsequent to transformation, may also take place in air.
• the temperature of the emerging wire In order to stabilize the temperature of the emerging wire within the desired range of approximately 500 to 550 C., we prefer to measure that temperature and to compare it with a predetermined value to compensate for deviations therefrom by a corrective adjustment of the bed temperature and/or of the residence time of the wire in the fluidized bed.
• To control the temperature of the cooling medium we prefer to remove particles continuously from the bed and to let them pass through a cooling chamber before returning them to the bed; this recirculation of the particles is best accomplished with the air ofa flow of carrier gas which may itself be recirculated.
• wire so treated when observed under the electron microscope, exhibits a structure of distinct lamellate zones, not encountered in conventionally lead'cooled material, which account for a significant part of the cross-sectional area, the lamellae of the several zones extending in different directions while lying substantially parallel to one another within each zone.
• This lamellate structure may account for the surprising fact that the treated wire according to out invention has both a torsional and a flexural endurance appreciably greater than those of lead-patented wire of like composition and dimensions.
• Particularly good results are obtained with steels having a carbon content between about 0.5 and 0.7%. by weight, which pass the (E08 line near the 7 0 level so that a workpiece with an initial temperature of 800" to R50" t. can be brought to that level in I to 1 seconds by forced cooling at a rate of 30" to 50" (1 PCI' second.
• the rolling of the wire is carried out at temperatures well above the 800 level during one or more stages and is brought to approximately that level, by forced cooling leg. with the aid of a water spray), just before the final rolling stage.
• This improved technique preserves and even enhances the torsional and flexural endurance of the wire treated in the above-described manner (as disclosed and claimed in our application Ser. No. 805,941) while simplifying the preliminary shaping operation on account of the higher temperatures (up to about 1000" C.) which can be used in the earlier rolling stages.
• the preliminary rolling should take place in a range whose lower limit lies substantially 80 above the transformation point AC3, which with a carbon content of 0.5% is approximately at 760 C. whereas the rolling in the last stage (or stages) is carried out at a reduced temperature near that transformation point, i.e. within about 50 thereof.
• the wire so treated is cold-drawn, in a manner known per se, so as to undergo a deformation of approximately 80 to 90% in terms of reduction of cross-sectional area, corresponding to a decrease in diameter by a factor of roughly 1.5 to 3.5.
• the drawn wire exhibits a torsional capacity exceeding that of conventionally lead-patented drawn wire of like dimensions and composition by about 20%, its bending capacity lying by about above that of the conventional wire.
• a plant suitable for carrying out the aforedescribed method comprises a conveyor, preferably in the form of an apertured belt, passing through a channel together with the stream of carrier gas and entrained solid particles; the discharge end of the channel is provided with a gate through which the cooled wire may emerge while the particles are retained and form a nearly stationary accumulation around the exiting wire.
• the hot incoming wire may be deposited on the conveyor in a succession of loops. advantageously with the aid of a transversely oscillating dispenser as disclosed and claimed in our commonly owned application Ser. No. 675,405 filed October 16, 1967, now abandoned.
• FIG. 1 is a transformation diagram showing the conversion of austenitic steel to sorbite by conventional means and by our present process
• FIG. 2 is a somewhat diagrammatic side-elevational view of a plant for carrying out the process
• FIG. 3 is a fragmentary view similar to FIG. 2, showing a modification
• FIG. 4 represents part of the iron-carbon-equilibn'um diagram, including the G08 line;
• FIGS. 5 and 6 are two electron micrographs taken, respectively, of wire treated by the present process and of conventionally lead-patented wire.
• FIG. 7 diagrammatically illustrates the two last stages of a rolling mill supplying the wire to the plant of FIG. 2 or FIG. 3.
• FIG. 1 we have shown at A and B the boundaries of the austenite/pearlite transformation range for a typical steel wire of 5.5 mm. diameter, made from unalloyed steel with a carbon content of 0.5%.
• Graph e represents an idealized process whereby the wire is rapidly cooled, from a starting temperature of 860 C. attained at the output stage of the rolling mill, to a level of 550 C. which it reaches after 1.5 seconds and where the graph intersects the boundary curve A of the transformation range. After a further interval of about 18.5 seconds. with gradual cooling to a point at or above 500 C., the transformation to sorbite would be completed without the formation of appreciable quantities of bainite.
• Such as idealized cooling process e.g. with quenching in water, would be difficult to realize because of the problems of temperature control and appears to be impractical for any but the thinnest wires.
• Graphs applies to ceramic particles with a 850.
• the particle temperature is maintained well below 500 C., yet contact between the particle stream and the wire is terminated at a point p or q, thus after 9 or 6 seconds, respectively, when the wire temperature drops to a level of 520 C.
• Curve i represents the limiting case of cooling at a rate of 20 C. per second from a starting temperature of 800 C., reached at the exit of the last rolling stage, down to a level of 5 C., within about 10 seconds,followed by substantially isothermal completion of transformation at that level during an interval of slightly less than 15 seconds.
• the other boundary of the operative region has been partlyshown by a horizontal line j marking the 480 level.
• FIG. 4 i t From the diagram FIG. 4 i t will be noted that'th boundary between austenite and the ferrite/austenite mixture, represented by the line GOS, lies at a level of approximately 750 C. for steel having a carbon content of about 0.6%.
• the G05 line has been indicated at that level and is shown to intersect the curves b, c and h within the first two seconds and at points where the rate of cooling, as represented by the slopes of these curves, is well over 20 C. per second. If the initial cooling is carried out by an air stream or by water, e.g. with the aid of spray nozzles, the transition to a fluidized bed may take place immediately below the GOS line, thus at a temperature of about 700 C.
• the plant comprises a fluidized bed I confined within a tunnel 24, forming an elongated flow channel, to the vicinity of the upper run of an endless conveyor belt 2 which 18 continuously driven by a motor 15 so that a hot wire 3, deposited thereon after leaving the last stage of a hot-rolling mill and preferably after preliminary quenching as incidated in FIG. 1, is transported on a downwardly sloping path from right to left.
• Wire 3 passes through a guide tube 4 and a continuously rotating dispenser arm 25, driven by a motor 26, whose rotation forms the wire into a succession of loops deposited on the conveyor 2; the dispenser arm 25 may be subject to continuous transverse oscillations at a frequency related to the loop-deposifiori' rate, as described in our copending application Ser. No.
• a perforatedbase 27within tunnel 24 forms thelower boundary of bed 1 and is connected to outlets of a manifold through which a carrier gas, as indicated by the arrows, is passed at longitudinally spaced locations by way of the intersticed of belt 2 into the space thereabove.
• the branch conduits of manifold 10 contain respective valves 9 for controlling the amount of gas thus introduced.
• a further valve 28 controls the input from a COIHPI'QSSQTQILQthCJ' highpressure source, not shown, whereas two other valves 29, 30 determine the proportion in which a portion of the gas is branched off into a conduit 5 into which opens an outlet of a cooling chamber 6, the latter containing a coil 22 traversed by a coolant.
• Conduit 5 opens into the tunnel 24 in the vicinity of the housing 23 of the dispenser arm 25.
• Solid particles entrained by the gas stream accumulate in a pile just ahead of the shutter 8 where the tunnel 24 is formed with a discharge port 7 for these particles.
• a similar accumulation is formed at the entrance end of the tunnel by means of a stationary plate 31 underlying the upper run of conveyor belt 2 beneath an inlet branch 32 of conduit 5.
• Port 7 communicates with a further conduit 33 which leads to the top of cooling chamber 6 and which may include means, such as a pump 34, to promote the return of solid particles from the discharge end of tunnel 24 to the cooler.
• a bypass 20. controlled by a valve 38, enables the recirculation of some or all or the gas to manifold 10.
• a temperature feeler 11 just beyond shutter 8 senses the temperature of the emerging wire loops and feeds this information to a comparator 13 receiving a reference signal fro'rT storage device 12 adjusted to the desired exit temperature (s -e5 9 mpazatq ts qom wbieba necessary, adjusts the speed of motor to vary the residence time of the wire in the fluidized bed 1 in a manner compensating for any deviations of its exit temperature from the preset reference value.
• Dispensing arm 25 is, of course, representative of any conventional type of loop depositor including, for example,
• FIG. 3 where elements corresponding to those of FIG. 2 have been designated by the same reference numerals with addition of a prime mark, we have shown the temperature sensor 11 disposed ahead of shutter 8. Sensor 11 ascertains the exit temperature of the wire in terms of the temperature of the fluidized bed I at the discharge end of tunnel 24' and, as before, communicates this information to'a controller 14'; the output of this controller, in contradistinction to the previous embodiment, sets a servomotor 4 0 which adjusts a valve 41 to regulate the amount of cooling fluid passing through coil 22 of chamber 6.
• the system operates otherwise in the same manner as the arrangement of FIG. 2.
• the control systems ll, 11 shown in FIGS. 2 and 3 could also be combined in a single plant.
• EXAMPLE I Steel wire containing 0.58% C, 0.38% Mn, 0.24% Si, 0.01% P and 0.02% S (all percentages by weight), balance Fe and usual impurities, is rolled to a diameter of 5.5 mm. at a temperature of 800 C.
• forced cooling of the wire is started, proceeding at an average rate of 40 C. per second to a level of 520 C., this temperature being maintained for l2 seconds while the transformation from gamma. to alpha iron proceeds to completion.
• pickling and rustproofing (bonderizing) the wire is drawn without further heat treatment to a diameter of 1.8 mm., this corresponding to a deformation of about 90%.
• Wire so drawn exhibited a tensile strength of I kg./mm. and withstood 22 consecutive cycles of flexing and strightening.
• a cable formed from six strands of seven such wires each was found to have a service life two to four times as long as identical cables made from conventional lead-patented wire.
• EXAMPLE I The procedure of Example I is followed, using a wire with a content of 0.65% C, 0.55% Mn, 0.24% Si, 0.012% P ar d 0.2% S rolle d to the same diameter of 5.5 mm After P n and. bo d s t eat sd awn.wjth utiunl erheat treatment to a diameter of 2.2 mm., this corresponding to a deformation of about EXAMPLE Ill
• the composition of the steel is 0.66% C, 0.76% Mn, 0.23% Si, 0.019% P and 0.029% S, balance again iron and usual impurities.
• the rate of cooling between the 800 starting temperature and the traverse of the G05 line, within two seconds after the discharge of the wire from the rolling mill, is 43 C. per second, this rate being substantially maintained to well below the 550 level.
• the further treatment is the same as in Example ll.
• Example 111 The structure of the drawn wire obtained by Example 111 and deformed in accordance with Table 2. as observed under the electron microscope with a magnification of 4.000zl. has been illustrated in H0. which shows distinct lamellate zones distributed throughout the cross-sectional area of the steel sample; FIG. 6, representing a similar electron micrograph for lead-patented wire subjected to the same drawing process, exhibits only the rudiments of such lamellae at isolated locations.
• FIG. 7 illustrates the intermediate cooling of the wire 3 during rolling in a mill whose two last stages have been designated 10] and 102.
• Sprayers 103 direct cooling water upon the hot wire which passes between rollers 101 at a temperature of about 850 C. and arrives at rollers 102 with a reduced temperature of about 800 C.. continuing then toward the guide tube 4 or 4' of F1G.2 or 3.
• Strands of such wire may also be twisted into a cable of great flexibility.
• a method of producing wire of high torsional and flexural capacity comprising the steps of:
• said carbon content lies between substantially 0.5% and 0.7%.
• a method as defined in claim 1 wherein the rate of forced cooling is between substantially 30 and 50 C. per second.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• Physics & Mathematics (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)
• Metal Rolling (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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Cited By (8)

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• 1968
  • 1968-05-21 DE DE19681758380 patent/DE1758380B1/de active Pending
• 1969
  • 1969-02-25 BE BE728878D patent/BE728878A/xx unknown
  • 1969-02-27 AT AT199469A patent/AT294881B/de not_active IP Right Cessation
  • 1969-03-04 FR FR6905803A patent/FR2008958A1/fr not_active Withdrawn
  • 1969-03-06 LU LU58151D patent/LU58151A1/xx unknown
  • 1969-03-21 SE SE04010/69A patent/SE357981B/xx unknown
  • 1969-03-25 JP JP44022148A patent/JPS5124448B1/ja active Pending
  • 1969-05-07 GB GB23326/69A patent/GB1224306A/en not_active Expired
  • 1969-05-19 NL NL696907642A patent/NL150695B/xx unknown
  • 1969-05-20 US US826229A patent/US3584494A/en not_active Expired - Lifetime

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