US3181977A - Heat treatment of elongate metal material - Google Patents

Description

y 1965 s. MOHARDY STURGEON 3,181,977

HEAT TREATMENT OF ELONGATE METAL MATERIAL FiledMarch 4. 1963 2 Sheets-Sheet 1 15 I Q C a "4' n T I 12 f l I a- L i" Q I I E U INVENTOR GM- STURGEON BY mwk mmm masa ATTORNEYS May 4, 1965 G. M HARDY STURGEON 3,181,977

HEAT TREATMENT OF ELONGATE METAL MATERIAL Filed March 4, 1963 2 Sheets-Sheet 2 INVENTOR G- M. STURGEQN w a n f m L r QM. NH \M n. -w\ on U Ill '1. a l 5n MMWWMF L I1 a 1 M, a III R. w ma N on BY MMJMMM Mk.

ATTORNEYS United States Patent 3,131,977 HEAT TREATMENT OF ELQNGATE lldlETAL MATERIAL George McHardy Sturgeon, Dore, Shefield, England,

assignor to The British Iron and Steel Research Association Filed Mar. 4, 1963, Ser. No. 262,564 9 Claims. (Cl. 14813.1)

This invention relates to the heat treatment of elongate metal material and more particularly to the patenting of ferrous rod or wire.

Present patenting arrangements have undesirable characteristics in that they are of large size and occupy a large floor area, have a relatively low output per strand, and are thermally inefiicient.

One object of the present invention is to reduce such characteristics by use of heat exchangers employing liquid heat transfer medium.

A further disadvantage of existing patenting arrangements is that comparatively heavy gauge rod, of the order of 0.5 inch diameter or more, having optional drawability and strength cannot be readily and economically produced, and this is particularly serious in the case of high carbon steel material.

It has been found that this failure derives from the relatively slow quench rates from the austenitising temperatures in conventional plant, and another object of the present invention is to reduce the latter difificulty by use of a liquid medium heat exchanger for such quenching, in which the liquid medium is circulated in counter flow to the rod whereby a readily controllable, rapid quench may be obtained.

According to the present invention in one aspect there is provided apparatus for patenting elongate metal material comprising means for heating the material to a temperature at which the material is substantially austenitic, and a liquid bath for thereafter rapidly quenching the austenitic material, said bath being arranged for circulation of liquid medium in counterfiow relative to the flow of said material therethrough.

In the case of multi-strand operation it is preferred that the quench bath provides a substantially individual counterilow liquid medium path for each strand.

Also, while any suitable form of heating to the austenitising temperature may be employed in accordance with this invention, a fluidised bed furnace affords particular advantages for this purpose, and recirculatory forms of such furnaces are preferred.

Furthermore, it is possible to employ preheating means preceding the austenitising furnace, which preheat means can conveniently take the form of a further liquid bath connected in a loop with the quench bath for counterfiow operation relative to the material whereby thermal efliciency is increased.

In order that the present invention may be clearly understood in its various aspects and forms, the same will now be more fully described, by Way of example, with reference to the accompanying drawings, in which:

FIGURE 1 illustrates in schematic form one embodiment of rod patenting apparatus according to the invention;

FIGURE 2 illustrates a modification in the apparatus of FIGURE 1;

FIGURE 3 illustrates part of the apparatus of FIGURE 1 in more detail, and

FIGURE 4 illustrates one form of quench bath suitable for multi-strand patenting apparatus in accordance with the invention.

The apparatus of FIGURE 1 comprises a succession, in the sense of rod travel, of a first liquid metal preheat bath 11, a second liquid metal preheat bath 12, a high temperature fluidised bed 13, a first liquid metal quench bath 14, and a second liquid metal quench bath 15. High carbon steel rod is first heated to a temperature of 200 C., during passage through bath 11, then further heated to a temperature in the range of 500 C. to 700 C. or thereabouts by bath 12, and heated so that the rod material is substantially austenitic in the temperature range of 800 C. to 1100" C. by passage through the fluidised bed 13. The rod is thereafter rapidly quenched by bath 14 to a temperature below the lower critical temperature and above the martensitic start temperature such temperature being within the range 400 C. to 600 C., and is held at such temperature, by passage through this bath, for a period of about 8 seconds, the rod being finally quenched from the latter temperature by bath 15.

A suitable liquid metal for use in baths 12 and 14 is lead, and the lead is circulated between these two baths by use of connecting pipes 16 between their ends, and an electromagnetic or mechanical pump 17, as shown. Furthermore, the lead circulation is such that the lead flow through the baths is counter to that of the rod, as indicated by arrows. By this arrangement rod at high temperature entering the bath 14 is quenched by transfer of heat to the lead, so that the lead is heated. The heated lead then passes to bath 12 to preheat the incoming rod prior to entering the fluidised bed 13, so that the lead is cooled and returned to the rod outlet end of bath 14 to quench the rod leaving the fluidised bed 13.

Such a cycle as just described is of high thermal efiiciency and apart from the initial liquifying of the lead, the cycle is thermally self-sustaining by virtue of the heat input from the rod leaving the fluidsed bed 13. The temperature gradients in the baths 12 and 14 are dependent on the pumping rate and this may be readily adjusted for desirable gradients and so for a required initial quenching temperature in bath 14.

It has been found that the power consumption of the fluidised bed decreases with decrease of the pumping rate, since as a result of this the temperature of lead passing from bath 14 to 12 is increased. That is to say, more heat is transferred from the rod to lead in bath 14 with a slower pumping rate and in consequence the rod is preheated to a higher temperature in bath 12. However, this must be balanced against the desire for a rapid initial quench of rod from the austenitising temperature in bath 14, the quench rate and amplitude increasing with the speed of lead circulation. In practice, an optimum steady state can be found at which power consumption is considerably improved over conventional apparatus, and at the same time the quenching rate is sufliciently rapid to produce the desirable metallurgical properties, at least to the same degree as with conventional apparatus. In the case of large gauge material the desirable properties may be produced to a considerably greater degree with far less power requirements than heretobefore.

In the case of inital preheat and final quench baths 11 and 15, a suitable liquid metal is lead/bismuth alloy, and it is preferred to employ substantially lead/bismuth eutectic. Lead is not suitable for these baths by virtue of its higher melting point relative to the temperatures required for these baths.

Again baths 11 and 15 are connected by pipes 18 associated with an electromagnetic or mechanical pump 19 in similar manner to baths 12 and 14 to provide a counter flow system giving rise to a heat cycle of high efi'iciency and requiring little or no heat input in steady state operation in addition to that provided by the rod leaving bath 14. Other forms of initial preheating and final quenching may equally well be employed, although the above form of liquid metal heat exchanger arrangement is preferred.

It has also been found that heat transfer to and from rod or wire in patenting is considerably impaired by scale and in accordance with a preferred feature of the invention the rod is de-scaled immediately prior to entering the plant.

Also, as a measure to maintain the rod clean and the liquid metal substantially free from dross, a protective atmosphere is maintained within the hood Z0, and for this reason the rod is arranged to enter and leave the apparatus of FIGURE 1 via liquid metal gas seals 21.

In a modified form of the apparatus of FIGURE 1 a separate holding zone 22 may be employed intermedi ate baths 14 and 15 as shown by FIGURE 2. The holding zone may be of any suitable form for holding the rod at appropriate temperature and time to obtain a desired formation of fine pearlite, such as a looped or other path through a controlled temperature zone, or use may be made of a liquid metal bath individually controlled in respect of temperature. Such a separate holding zone will be preferable in any case where an otherwise advantageous temperature gradient can only be obtained in bath 14 at the loss of suitable temperature holding in such bath for fine pearlite formation.

FIGURE 3 illustrates in more detail a preferred form of fluidised bed for the arrangement of FIGURE 1. This fluidised bed is of recirculation type having a fan 23 for recirculating fiuidising inert atmosphere beneath a perforated, ceramic distribution plate 24. The walls of this fluidised bed arrangement will be constructed from refractory bricks for high temperature operation at the order of 1100 C. to heat the rod to an austenitising temperature of 1000 (3., say.

The enlarged section of the structure above the bed level is employed to reduce the exit velocity of the fiuidising gas and so reduce the number of gasborne particles which may be carried through to the fan and the distribution plate.

In the operation of the above examples the rod will leave the apparatus at a temperature of the order of 250 C. to 300 C. and it may be preferred, in accordance with another feature of the invention, to employ this heat to borax-coat and self-dry the rod before final coil- As noted above, in the case of multi-strand operation it is preferred that the quench bath provide a substantially individual counterflow liquid medium path for each strand, and this may be effected by the use of appropriately disposed batfie members in the quench bath to obtain streamlined liquid medium flow along individual strand paths. FIGURE 4 illustrates one example of such an arrangement and includes a longitudinal section (a) and a plan view (b).

The section of FIGURE 4(a) shows metal rod or wire 30 emerging from a furnace 31, passing round rollers 32, through a quench bath 33 containing liquid lead 34, above which a protective atmosphere will normally be maintained by means not shown, though this may not be essential. An electromagnetic or mechanical pump 35, in association with a pipe 36 and nozzles 37, circulates the liquid lead in counterflow to the movement or" the rod as indicated by arrows. T he pump 35 and pipe 36 may be inside the bath as shown, or external to the bath.

For multi-strand operation, bafire plates 38 are inserted separating the paths of individual strands, as more clearly illustrated in the plan view (b), with a nozzle 37 projecting into each individual path so formed.

Additional cooling means, shown as a tube 39, through which any suitable cooling fluid may be circulated, may be employed and allows a desired temperature to be maintained at that point in the bath. Alternatively, or in addition, a cooling tube may be employed with the fluid passing therethrough also passing through preheating means where such means are employed as in the case of FIGURE 1 for example.

The advantages of the present invention, which are particularly the case with high carbon rod or wire are that:

A considerable economy in power and space is obtained in comparison with existing patenting plant: for example, an 8-strand plant according to the invention for treating 5 SWG rod at the rate of 1 ton/hour may have an overall length of 70-100 feet and a power consumption of -130 kwh. compared to -220 feet and 180-220 kwh. for an equivalent plant.

At the same time treated material will have at least equivalent properties as produced by existing plant. The use of a fluidised bed for austenitising permits sufiicient grain growth to produce a desirable grain size and the use of liquid metal heat exchange for rapid quenching affords the formation of fine unresolvable pearlite by subsequent holding at the transformation temperature. Thus, the treatment according to the invention gives rise to a very fine pearlite matrix with a controlled grain size and a substantially minimum amount of free ferrite.

Although fluidised bed heating to the austenitising temperature is not as rapid as some other methods of heating it produces very uniform heating so that multi-strand treatment may readily be employed, and it is in fact preferred to off-set the somewhat slower heating rate.

Finally, considerably improved metallurgical properties can be obtained by use of the present invention for the case of larger gauge materials compared to the presently obtainable properties at the same time as economy of power and space requirements.

I claim:

1. A method of patenting elongate metal material which comprises fiuidising and heating a bed of particles to a temperature of the order of 1100 C. in associatlon with an inert fiuidising atmosphere, and recirculating said atmosphere through said particles; and treating the material by the successive steps of heating the material to an austenitising temperature by passage through said particles, and thereafter rapidly quenching the material to a temperature between the lower critical temperature and the martensitic start temperature by passage through liquid metal moving in counterfiow with the material.

2. A method of patenting elongate metal material which comprises fiuidising and heating a bed of particles; and treating the material, in sequence, by preheating the material, heating the material to an austenitising temperature by passage through the fluidised particles, rapidly quenching the material to a first temperature between the lower critical temperature and the martensitic start temperature by passage through liquid heat transfer medium moving in counterfiow with the material, holding the material at said first temperature, and then further quenching the material to a second temperature lower than said first temperature.

3. A method of patenting elongate metal material which comprises, in sequence, preheating the material by passage through a first bath of a first liquid metal, further preheating the material by passage through a second bath of a second liquid metal of higher meltingpoint than said first liquid metal, finally heating the material to an austenitising temperature, rapidly quenching the material to a temperature between the lower critical temperature and the martensitic start temperature by passage through a third bath of said second liquid metal, holding the material substantially at its exit temperature from said third bath, and then further quenching the material by passage through a fourth bath of said first liquid metal; and during operation of the method, moving said first and second liquid metals in counterflow with passage of the material therethrough, circulating said first liquid metal between said first and fourth baths, and circulating said second liquid metal between said second and third baths.

4. A method of patenting elongate metal material which comprises fiuidising and heating a bed of particles to a temperature of the order of 1100 C. in association with an inert fluidising atmosphere, and recirculating said atmosphere through said particles; treating the material by the successive steps of preheating the material by passage through a first bath of a first liquid metal, further preheating the material by passage through a second bath of a second liquid metal of higher meltingpoint than said first liquid metal, finally heating the mate rial to an austenitising temperature by passage through said particles, rapidly quenching the material to a temperature between the lower critical temperature and the martensitic start temperature by passage through a third bath of said second liquid metal, holding the material substantially at its exit temperature from said third bath, and then further quenching the material by passage through a fourth bath of said first liquid metal; and during treatment of the material, moving said first and second liquid metals in counterflow With passage of the material therethrough, circulating said first liquid metal between said first and fourth baths, and circulating said second liquid metal between said second and third baths.

5. A method according to claim 4 wherein the material is first preheated to a temperature of about 200 C., secondly preheated to a temperature in the range 500 C. to 700 C., finally heated to a temperature in the range 800 C. to 1100 C., first quenched to and held at a temperature in the range 400 C. to 600 (3., and secondly quenched to a temperature in the range 250 C. to 300 C.

6. A method according to claim 5 which comprises employing substantially the eutectic lead/bismuth alloy as said first liquid metal, and lead as said second liquid e metal.

7. Apparatus for patenting elongate metal material comprising a succession of a first preheat chamber for a first liquid heat transfer medium, a second preheat chamber for a second liquid heat transfer medium, a

fluidised bed austenitising furnace, a first quench chamber for said second medium, a temperature holding chamber, and a second quench chamber for said first medium; means for passing the material through said succession in the recited order; a first circulation system for said first medium including a first pipe connecting said first preheat chamber adjacent the entry point of the material thereinto to said second quench chamber adjacent the exit point of the material therefrom, a second pipe connecting said second quench chamber adjacent the entry point of the material thereinto to said first preheat chamber adjacent the exit point of the material therefrom, and a first pump operably connected with one of said first and second pipes to circulate said first medium from said first preheat chamber to said second quench chamber through said first pipe and vice versa through said second pipe; a second circulation system for said second medium independent of said first circulation system and including a third pipe connecting said second preheat chamber adjacent the entry point of the material thereinto to said first quench chamber adjacent the exit point of the material therefrom, a fourth pipe connecting said first quench chamber adjacent the entry point of the material thereinto to said second preheat chamber adjacent the exit point of the material therefrom, and a second pump operably connected with one of said third and fourth pipes to circulate said second medium from said second preheat chamber to said first quench chamtil 0 her through said third pipe and vice versa through said fourth pipe.

8. Apparatus for multi-strand patenting of elongate metal material comprising a fluidised bed austenitising furnace, a quench chamber for liquid heat transfer medium, means for passing the multi-strand material in parallel through said furnace and thereafter through said chamher, a plurality of bafile members disposed longitudinally within said chamber relative to the path of material therethrough and one each intermediate the paths of individual strands of the material, a manifold disposed transverse the path of material through said chamber, a plurality of nozzles each connected at one end to said manifold and individually located at their other ends adjacent the exit points of strand paths between said bafile members, and a pipe and pump operably connected with said manifold for supply of liquid heat transfer medium thereto to flow from said nozzles through said chamber in countertlow with the passage of strands therethrough.

9. Apparatus for multi-strand patenting of elongate metal material comprising a succession of a preheat chamber for liquid heat transfer medium, a fluidised bed austeriitising furnace and a quench chamber for said liquid medium; means for passing the multi-strand material in parallel through said succession in the recited order; a fiuidising gas conduit connected in closed circuit with said furnace and a fan operably connected in said conduit to impel and recirculate fiuidising gas through said furnace; baffle members disposed longitudinally within said quench chamber relative to the path of the material therethrough and one each intermediate the paths of individual strands of the material; and a circulation system for said liquid medium including a first pipe connecting said preheat chamber adjacent the entry point of the material thereinto to said quench chamber adjacent the exit point of material therefrom, a second pipe connecting said quench chamber adjacent the entry point of the material thereinto to said preheat chamber adjacent the exit point of material therefrom, and a pump operably connected With one of said first and second pipes to circulate said medium from said quench chamber to said preheat chamber through said first pipe and vice versa through said second pipe.

References Cited by the Examiner UNITED STATES PATENTS 2,300,329 10/42 Wood et a1 148-18 X 2,506,317 5/50 Rex l06 X 2,717,845 9/55 Carter.

2,892,744 6/59 Myers 266-3 X 3,053,704 9/ 62 Munday 263-40 X FOREIGN PATENTS 1,126,433 3/62 Germany.

OTHER REFERENCES Brittain et al.: Heat-Treatment in Fuidized Beds, in Metal Industry, 103(4), July 25, 1963, pages 126-129. Published by Ilitfe Production Publications Ltd, London, England.

MORRIS O. WOLK, Primary Examiner. JAMES H. TAYMAN, IR., Examiner.

Claims (1)

1. A METHOD OF PATENTING ELONGATE METAL MATERIAL WHICH COMPRISES FLUIDISING AND HEATING A BED OF PARTICLES TO A TEMPERATURE OF THE ORDER OF 1100*C. IN ASSOCIATION WITH AN INERT FLUIDISING ATMOSPHERE, AND RECIRCULATING SAID ATMOSPHERE THROUGH SAID PARTICLES; AND TREATING THE MATERIAL BY THE SUCCESSIVE STEPS OF HEATING THE MATERIAL TO AN AUSTENITISING TEMPERATURE BY PASSAGE THROUGH SAID PARTICLES, AND THEREAFTER RAPIDLY QUENCHING THE MATERIAL TO A TEMPERATURE BETWEEN THE LOWER CRITICAL TEMPERATURE

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