CZ149186A3 - Process of steel wires heat treatment and apparatus for making the same - Google Patents

Abstract

In the heat treatment of steel wires (W) in a patenting operation, the wires from an austenitizing furnace (1) are first quenched in a fluidized bed (Q). This bed (Q) is fluidized by hot gases from the furnace (1) and is also provided with a cooling system (28). The wires are then passed into a second fluidized bed (TR-S) where transformation takes place. This bed is fluidized by an independent source of hot gas (21) and is divided into regions (13) along its length which have independently controllable auxiliary heaters (14). The temperatures in the zone (Q) and the region (13) along zone (TR-S) are controlled to give a fine pearlite microstructure in the wire.

Description

SUMMARY OF THE INVENTION The present invention provides a method of heat treating steel wires by a patented process wherein austenitized steel wires are cooled in a first fluidized bed zone and transferred to a second fluidized bed zone in which a transformation is carried out and heated by a fluidizing gas. wherein the first fluidized bed zone is heated by its fluidizing gas and the temperatures of the two fluidized bed zones are controlled independently. The invention further provides an apparatus for carrying out the method as defined above, comprising a first fluidized bed zone for cooling steel wires, a second heated fluidized bed zone, and means for fluidizing and heating the second zone, comprising: for supplying heated fluidizing gas to the first fluidized bed zone and means for independently controlling the temperatures of both the first and second fluidized bed zones.

The effect of the invention is that there is no need to find a compromise between cooling and transformation processes. The temperature of the second fluidized bed zone may be selected and the heat supply controlled to provide the desired microstructure without disturbing the cooling temperature in the first zone and vice versa.

Ensuring the presence of heated fluidizing gas in the first zone ensures that the total heat input, including the heat of the processed wires, is such that the temperature of the wires does not fall below the critical level at which bainite formation is promoted. This is particularly advantageous in the processing of thin wires where the heat contained in the wires is not as great as that of thick wires. Generally, lamellar microstructures are desired, but it may be necessary to ensure that the temperature

it has not ascended to a level that would produce coarse - pearly structures at the expense of fine structures. This can be achieved by providing separately controllable heating means in the first fluidized bed zone. The equilibrium state obtained between the feeder at

This cooling means ⁷ comprises submerged cooling tubes with a fixed or preferably controlled flow rate. water or a controllable water spray or more preferably air cooling the surface of the fluidized bed.

In many cases, the temperatures of the two zones will be slightly different, although the amounts of heat supplied will be controlled independently to include the effects of different conditions and requirements. The improved control of the second band, which is thus enabled, allows the wetting temperature to be kept much more stable, further improving the microstructures obtained. Thus, another problem of known fluidized bed systems is reduced. Significant improvements are obtained in conjunction with the possibilities of controlling wire cooling and the initial transformation conditions.

The two fluidized bed zones may be provided with two separate fluidized beds with independently controlled fluidization. Alternatively, one fluidized bed may be divided into two zones.

In case both zones are to be fluidized by a single hot gas source, at least one zone should be provided with independently controlled auxiliary heating and / or cooling means. So would it? the cooling zone should be provided with the cooling means mentioned above and / or the wetting zone should be provided with the heating means ⁷ depending on the base temperature of the hot gas.

It has been found by the present inventors that in the wetting

Of the band, and in the improved behavior obtained by the measures of the invention, changes in the ideal temperature due to the exothermic nature of the transformation. This may, for example, be corrected by auxiliary heating and / or cooling means by pouring the wetting zone in several separate waists with, according to the present invention, corrected.

According to a further embodiment of the invention, the temperatures separated by the zones, the fluidized bed, are controlled by independently controlled auxiliary heating and / or cooling means.

The apparatus for carrying out such a method may also be of wider applicability and thus, according to another embodiment of the invention, the hot gas heated fluidized bed is provided with independently controlled auxiliary heating and / or cooling means for controlling the temperatures separated by the fluidized bed zones.

In connection with a dual-zone fluidized bed used, for example, in the patenting process described above, it is generally not necessary to have cooling aids for the wetting zone, while it may be advantageous to have auxiliary heating means. In a preferred embodiment, electrical resistive heaters are immersed in successive sections of the wetting zone. These can be replaced by submerged radiant tube heaters. In such an arrangement, the basic heat supply from the fluidizing gas, i.e. its inlet temperature, is set low and the auxiliary heaters are designed to bring the fluidized bed to the desired temperature.

In all fluidization gas inlet temperature control configurations for any zone, it may use lean or very lean mixtures, mix cooling air with combustion gas, or arrange a regulated heat exchanger between the fluidizing gas chamber and the combustion device.

In a preferred embodiment of the present invention, the wetted bed zone 10 includes a plurality of separate heat transfer and control compartments in the longitudinal direction to locally adjust the equilibrium state of energy resulting from the work heat load, from the input heat by directing the heat. ďacf''a ^_ '"p'omO'cnými - O'h-RI-in-AEI -a- from tert-hl-Azen d -N-CH-hermalhazards .........

This allows immediate increased accuracy of the local bed temperature, which can be kept constant over the entire length of the bed wetting area or can be programmed to adjust and maintain according to a predetermined course from the inlet to the outlet of the wetting zone.

Although the method and apparatus according to the various embodiments of the present invention are intended in particular for use in a patenting process using conventional cooling and wetting temperatures, other possibilities are contemplated. Thus, step patenting can be performed. In this procedure, the cooling temperature is lower, for example 400 ° C, but above Ms, followed by rapid heating to the selected transformation temperature. Also, gradient patenting can be performed by cooling and subsequent transformation with a selected temperature gradient using separate temperature control in different fluidized bed zones. The apparatus can further be used in other methods such as generating and subsequently tempering martensite to form hard structures. In such processes, the cooling temperature is below Ks. Other possible processes are precipitation hardening, cooling hardening and the like.

In gradient patenting, the perlitic reaction begins at a low temperature range of about 540-560 ° C and continues to a given degree. This begins the formation of fine sorbitol. Then, for example, after 10 to 20% transformation of the remaining austenite, it is decomposed at a higher temperature, for example 600 to 650 ° C or higher. The growth rate of cementite is considerably slower here. It is thus possible to create

Fine structures with low interlamellar spacing without growth defects grouped with fine perlite that isothermally reacted at higher speeds, i.e. at constant lower temperatures.

The brakes produced in this way have improved ductility and strength properties. Indeed, the fluidized bed method and apparatus according to the preferred embodiments of the invention allow for the selection of a preferred cooling / transformation curve in the T.T.I. or performing a patenting process according to a particular curve, for example to obtain particular effects or properties of wires. This is not known using generally known fluidized bed or molten lead baths.

One possibility is to take full advantage of the exothermic nature of the reaction as well as to create uniform pearlitic structures with greater interlamellar distances than normal. Thus, the reaction should start at a temperature of 580 to 600 ° C and the temperature of the wires should be allowed to grow by the effects of transformation heat by 60 to 80 ° C. Although the strength of the wire is lower, the wire has good deformation properties.

Another problem associated with the cooling of steel wires in a fluidized bed, such as the known cold air bed, is the oxidation of the wire surface, creating undesirable slag. According to the invention, it is therefore proposed to use a substantially non-oxidizing hot gas for fluidizing the cooling zone. According to this embodiment, the invention provides an improvement in the method of heat treating a steel using a fluidized bed by fluidizing the bed with substantially non-oxidizing off-gases from the austenizing furnace. The apparatus comprises an austenitization furnace and a fluidized-bed cooling and is provided with means for introducing the furnace exhaust gases into the bed to fluidize it.

The method ε of the device can be used in many areas, particularly in the patenting procedures described above.

If two fluidized bed bands are used, they may be outlet. The olines are passed through both bands, either to fluidize one bed of the divided ns band or two separate beds. In the latter case, the outlet gases may be passed through both beds sequentially.

The off-gas preferably has an oxygen fraction of 5% by volume or less, preferably at most 2% by volume, and at most 1% by volume of tar. Its proportion is preferably less than 0.5%, more preferably from 0.1 to 0.2% by volume, with a residual carbon monoxide content above 0.1%, preferably from 0.5 to 2.0% by volume.

Other types of non-oxidizing gas may be used, although they do not come from an austenitizing furnace.

According to one preferred embodiment, the hot exhaust gas is pre-cooled in a recuperator, for example a waste heat boiler, to a temperature of at most 150 ° C and then heated to the desired inlet temperature.

This can be accomplished by a battery of electric power heaters of controllable power. The inlet temperatures can vary from 100 to 150 ° C to 450 to 500 ° C depending on the working stage, that is, the highest temperature is required at the beginning, and further according to the wire diameter.

In the device according to the invention, the separate fluidising gas treatment device is preferably arranged outside the housing containing the fluidized bed. Instead of using conventional furnace structures, i.e., rigid structures with rigid connections of refractory parts to metal, to build a fluidized bed, it is preferable to use the modular modular structures described in British Patent Application No. 84.26455, although this choice is not essential for carrying out various embodiments of the invention.

-11The preferred design consists of a steel-clad refractory box forming a tunnel-shaped cavity covered by a removable or liftable

strcoem, in which at least two separate fluidized bed modules, without built-in burners, one cooling module and one or more mixing modules are housed. Preferably, the single module is formed as a metal chamber of two chambers comprising an open particle vessel and a gas chamber disposed therebetween separated from the open vessel by a gas distribution plate bottom and with fluidizing gas openings and / or nozzles, the modules being joined in one unit. Such a modular arrangement in which there are no combustion burners is advantageous for use and maintenance. The bandwidth modules can be easily mounted in the housing and, if necessary, can be detached from the assembly, for example for repair, and replaced with other modules.

The wetting zone may comprise one fluidized bed module of appropriate length or a number of smaller modules connected together if a wetting zone of considerable length is required. The supply of fluidizing gas to the wetting zone with one or more modules may be effected by a central supply from the wetting gas source to a common conduit disposed beneath the connected gas chambers.

The unsuitable prior design of such a device provided with internal burners, heat-sensitive parts exposed to the direct heat of the flames, and connecting pieces between metal and refractory parts caused frequent plant downtime, high repair costs and production losses. These persistent problems of a very diverse nature can be at least partially solved by the preferred embodiment described below.

In a preferred embodiment of the device according to the invention, each band is

-12only its own fluxdacnrm circuit and integrated system in

heat management. Accordingly, the separate cooling zone and the wetting zone are separately fluidized with suitable gas mixtures prepared at. controllable .device.the..t.eplo.t.e_mi.mQ -device.- in- z & * .......

gas conditioning controls of each zone and beyond. here systems for independent control of heat input and bed temperature. The tilt integrated band system is in practice effective with respect to starting and operating the fluidized bed line. It allows the use of a suitable gas mixture in each zone and preferably a non-oxidizing gas in the wetting zone for slag-free cooling of the hot wires. It also allows for a gradual adaptation from start to steady state of the inlet gas temperature to a specified base temperature selected depending on the type of wire and the conditions of the way as required in each band, from which base level the temperature inside the fluidized bed is further adjusted by special secondary controllers in both the cooling zone and the wetting zone. Further, since there are no burners, - for heating and fluidization in the band modules, direct thermal damage is reduced and access, repair and relocation of the modules are facilitated.

The invention is illustrated in the accompanying drawing, in which Figures 1a, 1b and 2a, 2b show a longitudinal section through a device for patenting and cooling-transformation curves for a wire, both for a molten lead bath and a conventional fluidized bed apparatus. Fig. 3 is a diagrammatic representation of the relationships between the temperature-time-transformation diagram of T.ToT. and a cooling-transformation curve of carbon steel wire treated by a molten lead bath apparatus and a conventional fluidized bed apparatus, FIGS. 4a and 4b illustrate first and second examples of a fluidized bed apparatus according to the present invention.

Figures 5a and 5b show a schematic view of a third embodiment of the device according to the invention and of the patentable

Fig. 6 shows further details of the device according to the invention; Fig. 7 shows the wire cooling curves and transformation curves obtainable by the patented fluidized bed process of the invention; Fig. S shows further details of the device of the invention. patented wire in bath in

10 shows a series of specially selected fluidized bed patenting curves.

1a and 2a schematically illustrate the prior art fluidized bed (Pb) and fluidized bed (FB) otentation lines where the wire W, after heating in an austenitizing furnace 1, is fed to the molten lead bath (2) or device (2). conventional single-band fluidized bed structures maintained at a constant temperature by suitable means (not shown).

Figures 1b and 2b show the temperature changes of the wire W ^{as a} function of time from the austenitization temperature (Ta) to the patent temperature (Tp) in

1a and 2a respectively; This shows schematically the course of the wire temperature during cooling. It can be seen from the comparison of Figs. 1b and 2b that in a conventional FB-device the start of the transformation and the real temperature of the wire transformation shown by the curve and the shielding greatly depend on said temperature (Tp). These tend to increase during the course of the reaction due to the combined effect of wire recalescence, i.e. heat release by transformation, and the low rate of heat transfer and specific heat of the fluidized bed.

In Fig. 3, the cooling-trans wire formation curves (FB) are shown

14 obtained by a conventional fluidized bed patenting process in T.T.T.

in the diagram compared to patenting in the bath (Pb). The dashed lines (TR) and (TP) ^qq indicate the start and end of the austenite transformation, and the shaded area (OTB) shows the optimal transformation band to obtain a fine pearlitic structure. It should be noted that in the case of conventional FB-patenting, the temperature is region dependent (OTB). The prior art has attempted to improve this situation, for example, by using a pre-smoothing unit such as an FB-zone of cold air or by greatly lowering the wetting temperature of the fluidized bed to create a temperature curve such as FIGS. 2b. subcooling to T_ less than T.

Fig. 4a shows schematically a general embodiment of the device according to the invention. The apparatus consists of an austenitization oven 1 and a fluidized bed apparatus 2 in two zones comprising an independent cooling zone Q and a transformation-wetting zone TR-S. Each _of these zones includes a modular assembly 3 comprising a container £ on částiceplynové chamber 2 distribution plate £ gas, for example a perforated plate, preferably with gas pipes or nozzles which is between the bottom of container £ particles and an upper region of the gas chamber 5 through the inlet 5 * of gas connected to the bottom of the gas chamber The connecting line 8, preferably detachable, connects each module to the gas distribution of the gas treatment apparatus X, which is not shown in detail, in which the desired gas is prepared in volume and composition and adjustable base temperature. This base temperature is determined for each zone according to wire type and selected process and is adjusted during processing according to the existing conditions of the bed, for example when starting or running, change of wire diameter, etc.. Possible components of the external conditioning devices χ gas as gas generators, 2R ^hο4η θ neat burners for preferential lean combustion composite air heaters and combinations thereof

-15 air heaters and combinations thereof. The O and TR-S bands are separated by a thermal insulation wall provided with suitable openings for the passage of the wire. The device is designed to process a number of wires that are legged in straight and parallel tracks. From the austenitization furnace 1 to the zone Q, the wires may pass through the protective cover.

Fig. 4b shows another embodiment of a fluidized bed apparatus according to the invention having two zones in which the outlet gas from the austenitizing furnace 1 is used as the fluidizing gas first for the wetting zone TR-S and then for the cooling zone Q or vice versa with pre-cooled exhaust gas. In this case, the outlet gas from the austenitization furnace 7 is fed via a connecting line 8 to a fluidized bed apparatus 2 by a blower 7. The basic gas temperature is set before being fed to the wetting zone modules TR-S and cooling zone Q by separate heat exchangers 10, 10 * located at the inlet of each zone.

Fig. 5a shows a particularly preferred embodiment of the device according to the invention. Herein, a gas-heated austenitization furnace 7 and a fluidized bed apparatus 2 in two zones are shown with separate modules for the cooling zone Q and the wetting zone TR-S. wherein the cooling zone Q is fluidized with the outlet, preferably non-residual gas from the austenitization furnace 1 through the supplied line 0, while the wetting zone TR-S is supplied from an independent gas generator 7, for example a suitable treatment burner. In this particular case, the temperature of the fluidized bed at the inlet of the cooling zone 6 is controlled as follows: First, the outlet gas from the austenitization furnace 1 is precooled, preferably to a temperature below 150 ° C in the recuperator 11, and then heated by a heat exchanger 1.2. to set the actual gas temperature

the desired inlet temperature is instantaneous, which can vary according to the current thermal conditions in the fluidized bed, depending on the operating mode, the inlet heat from the hot wire wires, the rate of wire passage through the device, etc. a control system for precisely controlling the temperature inside the cooling fluidized bed to maintain any setpoint. In practice, the secondary control system only operates after the operating condition has been completely established, i.e. when the additional heat input from the fluidizing gas is no longer required and the cooling gas preheating battery can be turned off. This will be described in more detail below.

The wetting zone TR-S is fluidized and heated with hot gas

They are supplied from a treatment device 7, for example a treatment burner, which delivers a gaseous combustion mixture at a given base temperature to the wetting zone module. The inlet gas temperature level required to heat and maintain the wetting bed at a constant mean temperature is automatically adjusted as a function of the actual thermal equilibrium of the wetting bed.

The heating bed and the wetting bed are fluidized separately, heated separately, and controlled to a temperature to maintain a constant bed temperature that is characteristic of each zone and is adapted to the wire and desired properties for the process. For example, in patenting wires, the internal temperature of the quench bed may be varied from 250 to 600 ° C to obtain a wire temperature between Ms and a given perlitic reaction temperature, while the set temperature in the wetting zone may be selected from 450 to 7 ° C to obtain a perlitic structures of variable fineness.

Fig. 5b shows a set of cooling-transformation curves obtained by wire-marking the method and apparatus of the invention designated FB-IN compared to the curves designated FB-FA obtained in patenting in a known single-band fluidized bed apparatus. It can be seen from the diagram that the FB-křiv curves correspond to a much more precisely controlled patenting procedure than is possible with the known method and a much better non-wire cooling setting with initial transformation conditions combined with a much more precise perlitic reaction temperature control.

The local bed temperature may tend to rise at certain locations above the optimum level at. a given degree of transformation: under the influence of the aforementioned phenomenon of recalescence, that is to say the release of transformation heat. The present inventors have found experiments that the degree of recalescence and the location of its temperature peak in the wetting zone can vary with the wire diameter depending on the wire speed and the selected transformation curve.

Accordingly, in a preferred embodiment of the invention, auxiliary heating elements and temperature sensors are provided in the fluidized bed of particles in the wetting zone module, which elements are grouped and controlled in a series of compartments forming the total length of the wetting-transformation zone.

The groups are controlled independently for each compartment to correct the local wetting zone temperature in combination with the primary fluidization heat control. To solve the problem of unequal heat losses in the presence of varying heat generation, the intermediate heat input is divided into primary and secondary fractions, the primary fraction being arbitrarily selected lower than the heating heat consumption of the continuous run. In this way, the auxiliary heaters not only provide the necessary power to compensate for the local shortage

-ιεtepla, but also part of the primary heat. As a result, possible local overheating of the bed due to wire recalescence, which may exceed the mean heat loss of the bed, may be avoided without affecting adjacent transformation regions. An additional advantage of this measure is that a programmed perlitic reaction is available, for example in steps with different temperature levels and reaction rates. This has many advantages in practice, such as increased flexibility in performing the right-to-patent patenting process, better than using a molten lead bath, the ability to control the patenting reaction beyond conventional cooling-transformation curves, and higher productivity in equipment parameters due to shorter starts and operating mode.

6 shows how the optimum reaction temperature can be set precisely during the transformation process in accordance with the principles described above in wire W. For this purpose, the TR-S wetting bed has been divided into a series of compartments 13, each containing a set of individual heating elements 14 inside the fluidized bed, a suitable temperature sensor 16 and a heating power regulator 17 connected to the control panel 15. The heating elements 14 are operated on a given power base to maintain the wetting bed at a set temperature in combination with heat input from the hot fluidizing gas supplied from the treatment device. gas for wetting bed. They are further controlled to increase or decrease the power input when the local temperature drops below or rises above the prescribed wetting temperature. Finishing equipment for heating in>

and for the fluidizing gas, it is outside the main housing of the device. The conditioning device is essentially a combustion apparatus configured to prepare a mixture of combustion gas at a desired amount, temperature and pressure and comprises a combustion chamber 20 and a gas burner 21 with a feed preferably with a compressed gas feed 22 is passed through a "19" gas fuel 23, for example Blower air temperature 2 · Inlet temperature to control panel 15. Wetting zone gas Q., e.g., pre-cooled furnace gas, flows through heater 1.2.

Fig. 7 shows the effect of the additional temperature correction in the wetting zone on the position of the stenting curves in the diagram Τ.Τ.Ϊ. As can be seen, the wire transformation temperature or perlitic reaction can be fully compressed into the desired optimum OTB region according to curve A by immediately correcting the local wetting bed temperature, while otherwise, according to curves B, it is devoid of individually regulated bed compartments. transformation, which would result in a partially annealed, coarser pearlitic structure

Figure 8 shows in more detail a preferred embodiment of the device according to the invention using the principles of Figure 6. The wire W austenitized in the austenitization furnace 1 heated by gas combustion, passes successively through the cooling zone Q and the separate wetting zone TR-S of the fluidized bed apparatus 2. The wetting zone comprises a plurality of compartments 13 with submerged auxiliary heaters and control devices as shown in FIG. 6, but not in FIG. 8. The combustion air for the burner 21 is preferably preheated and is therefore driven by the blower 2 into the recuperator 24 located. in the wet bed stack 25.

The conditioned fluidization gas from the combustion chamber 20 is routed through a conduit to the wetting zone module TR-S, which is a substantially metal assembly housed in the inner U-cavity of the FB furnace, in which the particle vessel, gas chamber and gas supply duct are united. The bed of particles 4 contained in the container 2 s ^e fluidized. Further, a gas chamber 2 with an inlet channel 5 'is shown

-20a a gas distributor 6 between the bottom of the container and the adjacent gas chamber 5. » Preferably, the apertured plate is provided with a plurality of fluidizing nozzles 6 * located at regular small spacings, for example in the range of 3 to -20 cm. Fluidizing nozzles 6 are supplied with fluidizing gas from the gas chamber whose inlet duct 5 * is connected to the supply line of the conditioning device 20 £ soaking bed and allows to obtain and maintain an optimum rate fluids.ee, usually around 10 to 12 cms ^- ^ and stable bed conditions. The wetting bed control means comprises a control apparatus (not shown) for controlling the treatment burner 21 to set and maintain the desired wetting gas inlet temperature, primary wetting bed heating and maintaining at the basic temperature, and secondary control devices explained above in connection with FIG. auxiliary heaters of each wetting zone section to correct the local temperature of the wetting bed and to increase the basic input heat of the hot fluidizing gas into the wetting zone, which is particularly advantageous when starting a fluidized bed apparatus,

The cooling zone 8 comprises one fluidized bed module of the same type as described above for the wetting zone, but of smaller lengths, preferably from 50 to 250 cm. In principle, the fluidized bed can be like the wetting band, i.e. by means of a separate external gas-fired treatment device connected to the cooling module. In this embodiment, however, the cooling gas is obtained from the outlet of the previous austenitization furnace 1 heated by gas combustion. The composition of the off-gas is capable of reducing and also prevents oxidation of hot wires during cooling. Thus, the exhaust gas mixture fed to the cooling module has an oxygen fraction of at most 2% by volume and preferably no more than 0.5% by volume to suppress or prevent unwanted oxidation of the wire surface. More precisely it is

For oxidation-free cooling, the oxygen content is limited to a maximum of 0.1% by volume, in combination with a small proportion of carbon monoxide from 0.5 to 2% by volume to ensure oxidation-free conditions. In the latter case, the energy consumption is slightly increased due to non-stoichiometric combustion in the heating furnace.

The vacuum pump 8 pumps out the off-gas that flows through a preconditioner or thermal recuperator (not shown) to lower the gas temperature and a controllable electric gas heater 12 to allow the fluidizing gas to be supplied to the cooling zone at any inlet temperature level. The primary control comprises a control apparatus 34 which controls the power supply 36 for the preheater 12 depending on the cooling bed temperature and the inlet temperature supplied by the lines 33 and 35.

The apparatus is further provided with additional cooling control means and a bed for adjusting and maintaining the desired temperature within the cooling bed during a continuous run operation, i.e. when the heat input of the heat from the hot wires significantly exceeds the heat removal capacity of the cooling fluidized bed. These additional cooling means comprise firstly cooling means, for example a submerged water pipe (not shown) and further controllable cooling means. These include a blower 28 which delivers a variable amount of cooling air from source 26 through line 26 to or onto the surface of the cooling bed. The controlled valve 21 adjusts the amount of cooling air by a suitable control system to which it is connected via a line 20. The control system 34 measures the actual bed temperature by the sensor 33. compares it with the bed temperature and accordingly controls the controlled valve 21 to supply the cooling bed.

-22Air. Alternatively, controllable water cooling by heat exchange tubes to pressurized water or boiling water located within the fluidized bed may be used, wherein the variable water flow is obtained by a controlled control valve.

In patenting carbon steel wires, the cooling zone is not set and maintained at a temperature of from 250 ° C to 650 ° C, preferably from 350 to 550 ° C for a cooling length of from 0.5 to 2.5 m and the wetting zone temperature is adjustable in range from 450 to 700 ° C, preferably from 500 to 650 ° C.

The control of the various heating and cooling means described above is preferably automatic.

The invention will now be explained in more detail by way of examples.

Example 1

Steel wires with a diameter of 1.50 mm with a carbon content of 0.71% by weight were processed in different FB patent lines and compared with the wires patented in a lead bath. The austenitization temperature and wire speed were the same in each case, namely 920 ° C and 24 m.min ^-1 .

Two fluidized bed methods were used:

FBI: Conventional β-fluidized bed device with one immersion zone; bed temperature set to T __ = 560 ° C.

FB2: Fluidized bed according to the present invention with a separate cooling zone and a wetting zone and separate fluidizing means and zone control. The bed temperatures were set as follows:

Tq = 500 ° C in the cooling zone Tpg = 560 ° C in the wash zone

-23 Cooling zone length: 2.5 a Wetting zone length: 4.5 π

The properties of the patented wires are given in Table 1:

Table 1

Way patenting Tensile strength øT.mm ^- * Scattering ^x ) voltage in N.Ban jets “* · fi & kro structure In lead 1240-1255 15 Dec Fine Perlite (100%} PEL (prior art) 1140-1204 64 mixed, g up to 20% thicker perlite PB2 (according to the invention) 1186-1222 36 Fine perlite + thicker lamellar areas (5-10%)

^x ) measured on the same r rete and between different wires according to their position in the furnace.

The results show the beneficial effect of the invention (FB-2) on the properties of the patented wire as compared to β patented fluidized bed prior art (FB-1).

Example 2

The 36-wire patent line PB was equipped with two fluidized bed zones according to the present invention wherein the cooling zone had a length of 1.5 m, a wetting zone of 5.5 m, and both zones had separate temperature settings. The cooling zone was fluidized with various gas mixtures.

Process conditions:

- wire diameter 1.3 mm, carbon content 0.69% by weight

- cooling zone temperature: 455 ° C • λ.

4-wetting temperature: 530 ° C

austenitization temperature: 900 ° C; wire speed 30 m.min “^

- cooling methods according to gas treatment and gas composition in the cooling zone: ............................. ........ ..

. FB-3: 0.15% carbon monoxide and 2% oxygen furnace outlet. FB-4: combustion gas from external burner 4% carbon dioxide, 5% oxygen, carbon monoxide-free. FB-5: hot air

The results of patenting FB wires were compared with the results of patenting wires in a lead bath by isothermal transformation at 560 ° C. 1 The properties of the wires are given in the table

2:

Table 2

Method of patenting%

Strength- Mikrostruktors in tension $

ÍT.mm “^

Surface Oxidation: Teat Thickness / Um

FB-3 56,5-53,5 12071221 fine sorbitol + traces of lamellar perlite 0.6 - 0.9 FB-4 52-57 12051222 fine sorbitol + traces of lamellar perlite 1,2 - 1,5 FB-5 41-54 11911281 fine sorbitol + coarse perlite + ferrite 1.5 Lead bath 560 ° 0 48-55 12241238 fine sorbitol 1.0 - 1.2 Yippee obvious properties i microstructure patented

The wire obtained by the process of the present invention is very close to that obtained by patenting in a lead bath, with the exception of

-25 if hot air was used to cool down with less accurate process control. The effect of using a non-oxidizing gas for cooling on the oxidation of the wire surface is readily apparent.

Example 3

The same FB-patenting line as in Example 2 was used except that the special temperature control of the wetting-transformation zone, which was divided into five compartments, with separate heating elements for auxiliary heating and temperature correction of the local mixing zone. The wire had a diameter of 1.25 mm and 0.72% by weight of carbon.

Set temperature: cooling zone 550 ° C * wetting zone 520 ° C

The line start was compared in the following circumstances:

A: The heating elements of the wetting zone compartments were switched on

AI: inlet gas temperature set to 400 ° C; the section heaters had a total power input of 12 kJff

A2: gas inlet temperature of 355 ° Cj the section heating elements had an increased power input of 25 kW to allow the local temperature λ support of the basic heating to be increased.

B: wetting zone as usual without auxiliary heaters; the fluidizing gas is supplied at a temperature of about 500 ° C.

In the case of A1, efficient operation was achieved after less than 40 minutes and in the case of A2 after less than 20 minutes.

Additionally, the temperature distribution and fluctuations during normal operation were compared in different bed sections. The results of the taplot measurements are summarized in Table 3.

* 26Table 3 · - Temperature distribution along the fluidized bed

Cooling- Wetting zone Rewind zone Section 1 Section 2 Section 3 Section 4 Section 5 xj

..... A1 ...........- 440-450 ----------- 495-510 515-525 510-520 510-515 485-500 - .. ...........

A2 440-450 515-525 520 520 520 515-520

B 440-460 490-530 520-550 525-580 540-570 450-490 ^x ) Temperature drop in compartment 5 caused by the output gas from the FB-furnace.

The beneficial effect of the separate control of the individual sections of the wetting zone on temperature equalization is evident in methods A1 and A2. In method B, the increase in local bed temperatures continues to exceed the optimum values, the actual wire temperature or transformation temperature is also slightly higher. These unexpected temperature deviations could become significant, for example, in changing wire diameters and in intermittent operation, such as line failures, and could lead to reduced wire quality and a greater proportion of discards than conventional fluidized bed patenting in the prior art. It is also evident in process A2 that careful selection of the auxiliary heating source, which must be sufficiently robust to accommodate a wide range of compensations, and a lower primary gas temperature than usual, provides excellent adaptability and allows the local temperature to be kept very close to the prescribed level.

The properties of the wires obtained by methods A1, 12 and B compared to patenting in a lead bath were as follows:

Method Stress Tensile Strength x Diffusion ₂

N.mm between N.mm wires ” ²

Al 1217 12.7

A2 1234 10.2

B 1192 19.5

Lead bath 560 ^G c 1247 12,4

Figs. 9a and 9b show a comparison of the tensile strength distributions of the treated wires by Al and B processes in relation to their furnace and lead bath wires. An improvement in the properties of the wires processed by the Al process is evident.

Fig. 10 schematically illustrates several patenting methods that can be selected and performed correctly using a dual-band fluidized bed according to the invention comprising separate wetting zone control sections. In the TTT diagram, curves 1 and 2 show FB patenting at two different temperature levels; curve 5 shows the FB patenting with the start of the transformation at the first temperature and the progress and termination of the transformation at the selected higher temperature, which in the interval (ΤΕ) _χ can follow one of the curves (3aj3b, 3c). Curve 4 is an example of step patenting with austenite subcooling prior to rapid heating to a suitable temperature for isothermal transformation to perlite.

A particular adaptation relates to the continuous martensitic quenching of the steel wire with a dual-band fluidized bed, provided for this purpose with an adapted cooling zone for deep cooling allowing soft cooling below the martensitic initial temperature Ms without intersecting the periitic extension of the T * TT curve. long, or; if necessary, an additional cooling bed module is used to ensure complete transformation of austenite to mertensite before reaching the treatment zone where the martensite is to be tempered to a preset holding temperature.

One arrangement for patenting steel wires may use a single particle bed device that is fluidized with a gas mixture supplied from the furnace outlet or treatment burner at an arbitrarily selected base temperature. The length of the module 28 is then divided into a series of separate regulated compartments, wherein the first compartment used for cooling is further provided with fixed and adjustable cooling means for dissipating excess cooling heat. The second and further compartments of the module forming the actual transformation zone are provided with adjustable internal heaters of sufficient power to set and maintain the prescribed transformation temperature. In this case, the fluidized bed housing is connected to a single modular structure, while the temperature control and compensation devices form two independent systems for cooling and transformation or wetting.

It should be noted that, at least for some of the ideas of the present invention, it is immaterial whether the particular installation is considered as a series of separate fluidized beds or as a single bed divided into separate zones. Gradient patenting can be performed using a number of adjacent, separately fluido. weighted beds. It is possible to vary the principles and apparatus described above without departing from the spirit of the invention.

Claims (4)

PATENT CLAIMS 'b \ V> A method of heat treating steel urates by a plating process, wherein austenitized steel wires are cooled in a first fluidized bed zone (Q) and transferred to a second fluidized bed zone (TR-S) in which a transformation is performed, wherein the first fluidized bed zone The second zone of the fluidized bed is fluidized with another fluidizing gas, wherein the temperatures of the two zones (Q, TR-S) are controlled independently and the two zones (Q, TR-S) are fluidized independently by regulated gas sources, characterized by: in that the temperature of the second zone (TR-S) is regulated in several individual sections (13) independently of each other by separate heating elements (14) for each section (13). Method according to claim 1, characterized in that the temperatures of the individual sections (13) are controlled to form a temperature gradient along the second zone (TR-S). 3. The method of claim 2, wherein the temperature gradient is formed such that the transformation begins at a first temperature and then continues at a second, higher temperature. 4. The method of claim 3, wherein the transformation at the second temperature is initiated when it reaches 10-20% at the first temperature. 5. A method according to any one of Claims 1 to 3, characterized in that a rapid undercooling of the austenitized wire and subsequent rapid heating of the wire to a temperature suitable for transformation is performed. Method according to any one of the preceding claims, characterized in that the temperature of the first zone (Q) is controlled at least in part by the auxiliary cooling means (28). Method according to claim 6, characterized in that the first zone (Q) is continuously cooled by the first cooling means (27) and is variablely cooled by the second cooling means (28). -308. The method according to any one of the preceding claims, characterized in that the first zone (Q) is fluidized substantially with non-oxide by its output gases from the austenitization furnace (1). Method according to Claim 8, characterized in that the outlet gases are cooled and / or heated by auxiliary means (11, 12) before entering the first zone (Q). ). Method according to claim 8 or 9, characterized in that the exhaust gases have an oxygen content of not more than 2% by volume. 11. The process of claim 10 wherein the outlet gases comprise a residual carbon monoxide to further promote non-oxidizing conditions. , 12. The process of claim 11 wherein the proportion of carbon monoxide in the off-gas is from 0.5 to 2% by volume. Method according to any one of the preceding claims, characterized in that the process conditions are controlled such that a substantially completely lamellar, pearlitic microstructure is formed. 14. The method of claim 13, wherein the conditions are controlled to form a microstructure consisting essentially of fine perlite or sorbitol. 15. Apparatus for carrying out the method according to claims 1 to 14, comprising a first fluidized bed zone (Q) for cooling the wires, a second (TR-S) -fluidized bed zone and means for independently fluidizing the first zone and the second zone and independently controlling them. The second zone (TR-S) is divided into separate sections (13) which are provided with separately controlled heating elements (14). -3116. Apparatus according to claim 15, characterized in that the first fluidized bed zone (Q) is provided with a solid cooling means (27) and an additional variable cooling means (28). Apparatus according to claim 15 or 16, characterized in that the first fluidized bed zone (Q) is supplied with off-gases from the austenitization furnace (1). Apparatus according to claim 17, characterized in that a precooler (11) and an auxiliary heater (12) are provided for the exhaust gas upstream of the first fluidized bed zone (Q). Apparatus according to claim 17 or 18, characterized in that it is provided with means for successively conducting the outlet gas through the first zone (Q) and the second zone (TR-S) as well as by means (10, 10? into the corresponding bands. Represented by: ? AND ί o FIG.5a 10 1 Q TR-S AND About C7 · 29 FIG.6 22 ^ 2 ^ 23 CD CO CD CO FIG.7 1150-1; , 1,! ^ i «[,,,« I »{|« - | -> 4 5 8 ΰ 12 14 16 18 20 22 24 26 28 30 32 34 N / mm ⁴ · • Τ '· —fJ- -i -—; -'- - --γ-t -} - _r —i — y -; - r- | -------- U, ., - I — f.— <. t 3 10 V2 14 16 18 20 22 24 26 28 30 V 34 36 ί Α i ό! 'υ ί Ξ | ! X 'X Ω! ί C 'Cί m> · _α i i 0> ΙΟ FIG.1Q