DE2009839A1 - Method and device for the heat treatment of a steel wire - Google Patents

Description

20P9839

WENDEL-SIDELOR HAYANGE / France

Method and device for the heat treatment of a steel wire rod s

The invention relates to a simple and effective method for heat treatment of a steel wire rod with less than 0.15% Carbon, which has previously been cooled in the usual, controlled manner after leaving the rolling mill, as well as devices for carrying out this process, a steel wire rod being obtained which has very good drawing properties.

The invention is particularly applicable to a soft steel wire rod with less than 0.15% carbon, such as is obtained on a wire or bar iron mill and has been cooled in the usual controlled manner. It is an addition to the usual methods and devices for controlled wire cooling.

The wire rod, as it has been manufactured in the last few years, leaves the rolling mill at a temperature in the range of 900 - 1000 C, and after initial cooling with water at a temperature between 60 ° C and 800 C, it becomes compact rings weighing several hundred kilograms to be wound up. The cooling of the wire during this winding into rings is only relatively small because of the rather considerable mass of the rings formed.

mo. rocker. 12D. i / ia / Kw / gm / y37 0Ö9839 / 1401

After winding up in the reels, these rings were by means of a transport device at a temperature of the order of magnitude from 500 - 600 C to cool slowly in the open air. The thickness or thickness of the scale layer, which forms in the course of this cooling is very considerable and represents a not insignificant loss of metal and significant cost of descaling prior to drawing Wire.

Processes for controlled cooling have already been developed, air being blown into the reels during winding. As a result, the amount of the scale layer formed was on average less, but it adhered more strongly to the surface and was unevenly distributed over the length of the wire of the ring. From this However, there was also considerable effort to remove this ignition layer.

In addition, the wire rods obtained in this way have very large irregularities and scattering of properties.

Attempts have also been made, in order to avoid some of these disadvantages, to carry out the cooling not on the ring, but on each individual turn of the ring when it is pulled apart. Here, the wire rod is immediately cooled in the form of turns, which are deposited on a moving conveyor belt in the same plane, but not concentrically, or are initially conveyed further in separate turns with a horizontal axis and then placed in this arrangement on a transport device or in separate turns be cooled with a common vertical axis. With this controlled cooling, the wire rod is exposed to various influences during the transport of the windings and before they are combined to form the ring. For example, cooling is carried out by means of an air

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current, with the windings in the same plane horizontally, but not are arranged concentrically or with a common vertical axis. Furthermore, cooling by radiation in calm air, whereby this cooling can accelerate or slow down, depending on whether the separated from each other Windings with a common horizontal axis or in the same plane horizontally »but not concentrically, arranged are.

This moderate process for a controlled cooling of the wire rod cause its even and controlled cooling. In this way, the wire rod receives only a slight, non-adhering one Scale layer, good uniformity in its strength properties, however, particularly with regard to its drawability, which can be satisfactory for a hard wire rod for a soft wire rod. This must be started one or more times in order to be able to be drawn very finely · This naturally increase in the course of pulling the processing costs of the wire.

The purpose of the invention is the production of a steel wire rod less than 0.15% carbon, which has improved drawing properties has to thereby pull this wire to thinner dimensions without further heat treatments to körinen.

For this purpose, this process is for the heat treatment of a steel wire rod with less than 0.15% carbon, which is cooled down in the usual, controlled manner after ■ leaving the rolling mill has been, according to the invention, characterized in that this wire rod for a time at a temperature »between 200 and 400 C, is preferably kept isothermally between 280 and 350 ° C.

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The duration of the isothermal stay is at least 30 seconds, preferably at least one minute.

The invention is further characterized by a chamber for isothermal stay, which is either at the end of a conventional controlled cooling device or separately behind an ordinary controlled cooling device can, with this chamber in both cases not the winding head the ordinary cooling device, as well as through a chamber for isothermal stay for performing the process according to the invention, which means for their immediate conversion for the treatment of a hard wire rod after the ordinary controlled cooling process, at which it is arranged after a soft wire rod of less than 0.15% carbon was treated according to the invention, and vice versa. For this purpose, the chamber consists of an isothermal stay at least two side walls and a removable and subdivided top wall, the latter being several movable, either individually or can be at the same time.

In addition, the. Invention the wire rod obtained by the method and apparatus of this invention, which Wire rod has been exposed to an isothermal temperature between and 400 C, preferably between 280 and 350 C, for a period of time, and this for at least 30 seconds and preferably at least one minute.

The inventive heat treatment of the wire rod gives it such a microstructure that this wire is drawn very finely without the need for intermediate heat treatments. A wire with a slight amount of non-adherence is obtained

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Amount of scale whose tensile strength and elasticity limit are lower and therefore those with the usual controlled cooling processes Outperform the properties achieved, although they have a low scatter. On the other hand, the elongation gives mean values, which are above those that are achieved with the known controlled cooling processes. Enable all of these advantages the direct production, without intermediate heat treatment, of a soft wire with an end cross-section which is three to is four times less than that obtained by the usual controlled cooling method.

In the accompanying drawings, there are, for example, embodiments of devices for practicing the invention shown, where show:

Fig.l: Schernatic representation of a first embodiment,

Fig. 2-6: various modifications thereof,

Fig. 7: a schematic side view of a conventional controlled Cooling device with subsequent device according to the invention for the heat treatment of a steel wire rod with less than 0.15% carbon,

FIG. 8: a side view of the same device according to FIG. 7 after it was instantly transformed for the cooling treatment of a hard steel wire rod,

Fig. 9ί a schematic side view of the device for simultaneous Actuation of the flaps in the device according to FIG. 7,

FIG. 10: an enlarged detail in side view from FIG. 7,

Fig.lli a section along the line A-A of Fig. 10,

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Fig. 12: an enlarged side view of the flap actuation

contraption,
13: a possible implementation of a control device for

the flap actuation device,

14: a plan view of a lever attachment,

Fig. 15: a section through Fig. 12 with a lever attachment

on the flap axis,
16: again a section through a lever attachment,

Fig. 17: the attachment of a heat insulating layer to the

Flaps by means of rivets,

18: three recordings of X-ray spectra of three selected layers of scale with one from top to bottom increasing degree of decomposition,

19, 20 and 21: Micrographs of structures with a magnification of 500 of the three layers of scale according to FIG. 18,

Fig. 19: accordingly the undecomposed layer, corresponding to the

upper spectrum of Fig. 18,

Fig. 20: the partially decomposed layer, corresponding to the middle one

Spectrum of Fig. 18,

Fig. 21: the layer with a greater degree of decomposition, ent

speaking of the lower spectrum of Fig. 18,

Fig. 22: at an enlargement of 12,650 structural defects,

Fig. 23: The fine deposit at an enlargement of 12,650

of carbides,
Fig. 24i, enlarged by 9,350, shows a more massive state

Deposition of carbides, which fine drawing cannot

affect, and
25: the schematic representation of two areas, of which

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the area no. l 'of non-harmful deposition of Carbides and area 2 correspond to the decomposition of the wüstite.

According to the method and the device according to the invention The resulting wire rod is covered only with a weak, non-adherent layer of scale and has excellent properties for a fine pull on.

This adhesion of the scale layer only takes place with a layer thickness which is below a certain limit. She is dependent from the decomposition of the so-called wustite or iron oxide layer directly on the surface of the wire. The ease the decomposition of this wustite layer i & t depends on the composition this phase under the conditions of the formation of the scale layer and the thermal action that this scale layer causes is exposed, i.e. if there is a FeO composition of the wüstite, the rate of decomposition depends on the one hand on the deviation χ from the element measurement and, on the other hand, from the thermal Influence on the wüstite when it cools down. For a certain x-value, the maximum decomposition speed is approximately

ο ο

at 400 C and quickly drops to a very weak value at 280 C.

In Fig. 18 the spectra of three layers of scale are shown, the are selected according to the increasing degree of decomposition of this layer. The undecomposed scale layer, which is in the upper spectrum in FIG. 18 corresponds, is shown in FIG. 19 with an enlargement of 500. At the same magnification, FIG. 20 shows the partially decomposed layer, which corresponds to the middle spectrum of FIG. 18, during Fig. 21 shows a scale layer showing a greater degree of decomposition having. This layer corresponds to the lower spectrum of FIG. 18.

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The inventor found that the deterioration in fine drawing properties of the wire partially with the anchoring of the dislocations (Fig. 2Z) and / or a very fine carbon nitride or carbide precipitation of the basic form iron carbide within the Ferrite crystals (Fig. 23) is connected. However, this occurrence of anchoring or excretion can be avoided by means of a heat treatment of the wire between 200 C and

ο ο

400 C, preferably between 280 and 350 C, for a period of time of at least 30 seconds, preferably at least one minute.

During rapid cooling, the supersaturated, interposed atoms collect on the dislocations (Fig. 22) or as very fine precipitations inside the ferrite crystals (Fig. 23). In contrast, these atoms form in the heat treatment according to the invention massive carbides, which have little effect on fine drawing (Fig. 24). This phenomenon permits one extraordinarily high degree of cold deformation of the steel and allows it to be drawn directly to a very small dimension.

The invention can thus be explained on the basis of the schematic representation in FIG. There are two areas for a particular wire, which are designated by 1 and 2 in FIG. The non-harmful deposition of carbide occurs in the first area and the decomposition occurs des Wüstit in the second area. There is therefore a more or less broad range depending on the chemical nature of the Steel and the scale layer as well as depending on the cooling conditions, among which the corresponding deposition of carbide occurs without the decomposition of the wustite in any remarkable Way done.

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In the following, the practical implementation and application of the invention in connection with the accompanying drawings described in more detail.

After this, the wire rod 1 is folded into a ring 2 after he the output 3 of the wire rod winding or laying device has left. Between this exit 3 and the folding, the wire rod becomes in the form of flat, fanned-out turns 5 in approximately the same plane on a transport device 6, for example transported by a chain transporter. Before leaving this transport device, the wire 1 passes through an isothermal chamber Stay 7, which is heated by means of a burner 8 and has a discharge line 9 for the fuel gases.

The speed of the transport device 6 is set so that the wire 1 traverses the chamber 7 in at least 30 seconds, preferably at least one minute. The burner 8 is regulated so

that the temperature inside the chamber 7 is between 200 and 400 C,

ο
is preferably between 280 and 350 ° C.

In the embodiment according to FIG. 2, the wire rod is wound to a ring 2 on a plate 10, which forms the cover of a chamber for isothermal stay 11.

Fig. 3 shows the next stage in which the Ring2 immediately is introduced into the chamber 11 for isothermal stay. The heating takes place through the supply line 12 from the middle of the ring, while the fuel gases are discharged at 13. Here you can use a Provide a removal device for the ring 2, for example a conveyor belt 16.

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The embodiment according to FIG. 4 differs from that according to FIG. 1 in that the fuel gases do not enter the chamber directly be introduced, but a hot air or gas stream, for example a non-oxidizing gas. A heat exchanger is used for this 17 is provided, which is heated at 18 and has a fuel gas vent. The heat exchange pipe coil is located within this heat exchanger. This coil 20 is part of a closed circuit, which consists of a feed line 21, a pumping device 22 for the hot gas flow, a return line 23 and a tap 24, through which the closed if necessary Circuit gas can be supplied.

The heat exchanger 17 is designed in such a way that the heating gases entering the heating chamber 7 are exactly the intended ones Have temperatures.

Fig. 5 shows a modification of the embodiment of FIG. 4, wherein the heat exchanger 17 is equipped with a supply 25 for cooling air to keep the temperature of the air flowing through the pipe 20 To be able to adjust the gas more precisely to the desired temperature.

Fig. 6 shows a further modification of the device according to Fig.l. Here the thermal treatment of the wire takes place through thermal radiation of a double-walled jacket 26 through which water or another heating medium is conducted. This upheaval will applied so that the temperature in zone 27 is in the selected range, i.e. between 200 and 400 C.

7 shows a side view of a conventional, controlled cooling device for wire rod, which is arranged behind a rolling mill is. This usual device is equipped with a device for

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implementation of the inventive method for treating a Steel wire rod with less than 0.15% carbon. Here the cover flaps of the heat treatment chamber are in a lowered position, creating a closed chamber is obtained.

It is of course possible to use the device according to the invention also behind any other controlled cooling device for To arrange wire rod.

In the illustration in FIG. 7, the steel wire rod 101 leaves the first Zone, not shown, in which it has been cooled by water. With the help of the device 102, this wire is in successive and partially superimposed, but not concentric Windings 103 deposited on a transport device 104. The wire windings cool down by radiation and thermal convection in 'the air along the path 105. This cooling is regulated in such a way that the temperature of the wire rod at the end of this Distance is a maximum of 400 ° C.

The wire windings then pass into a heating chamber for isothermal Stay 106 above the transport device, the cover of which consists of several movable flaps 107. These flaps are shown in the illustration in FIG. 7 in the lowered position. This heating chamber 106 also consists of the side walls 108, as is can also be seen in Fig. 11, NEN. The lower part 109 of this chamber is made of side-by-side plates UO and a chain transport device 111 of the known cooling section formed.

The wire rod windings are in this chamber of the invention

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subjected to mass heat treatment, on a stretch, as indicated by 112 in FIG. 7. In the adjoining area 113, water is sprayed, which is not disadvantageous affects the structure of the soft steel wire rod with less than 0.15% carbon. The wire windings are then rolled over 114 promoted. The water sprayed from the spray nozzles 115 collects in a basin 116 (FIG. 8) in order to enter from here Storage vessel 117 to be derived. From this storage vessel 115, the water is then transferred to an intermediate vessel by means of a pump 118 119 after being cooled if necessary.

A collecting device of known type 120 then places the Wire windings together to form a ring, which is conveyed away by a transport device of a known type, which is not shown here will.

FIG. 8 shows a schematic side view of the device as in FIG Fig. 7, but here converted for a conventional treatment of hard steel wire rod. The cover flaps of the heating chamber 105 are located in this case in a raised position so that there is no isothermal effect the stay of heat is exerted on this wire rod. The wire rod cools down in this way as on the usual devices.

The wire rod is fed in vertical turns 121, which are kept separate from one another, so that a fast Cooling takes place through radiation.

The transport of these wire windings takes over at certain intervals a known transport device 122. The wire windings then tip over and become flat and partially superimposed transported further., where they cool less quickly in the known manner. You then pass through the according to the invention

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trained device, but this is now no closed Chamber forms because the flaps 107 are raised and a free flow of air can go through the wire rod windings.

Fig. 9 shows in side view the device for a simultaneous Operation of the cover flaps. The opening or closing of these flaps is initiated by an actuating device 123, which can be a hydraulic piston, an electric motor or some other device of this type. The resulting movement opening or closing the flaps is facilitated by a counterweight, the effect of which is adjustable.

This actuating device 123 actuates a linkage 124 in the direction of the horizontal arrow as shown in FIG. Through this a simultaneous opening of the flaps 107 takes place with the aid of a adjustable counterweight 125 or, in the reverse direction of the arrow, a simultaneous closing of the flaps.

As already mentioned, FIG. 10 shows a schematic representation a section of the inventive device, with dotted in Lines show the open position of the flaps and a lever arm that sits firmly on the flaps and the opening movement transmits.

Fig. 11 is a section along line A-A of Fig. 10 with the flaps are shown in their lowered position. With the side walls 108 they form a closed hole perforated on their underside Chamber 105.

The actuating device of each flap 107 consists of a cranked one Lever arm 126 (Fig. 15), which with its lower end to

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the linkage 124 is rotatably attached, as shown in Fig. 14 in plan view is shown. This cranked lever arm 126 sits with its upper end with play on the axis 127 of the flap as Fig.l6 shows.

A further lever arm 128, on the other hand, is seated in a rotationally fixed manner on the axis 127 of the flap 107 and has an adjustable one at its lower end Stop 129, as shown in detail in FIG. This stop 129 allows the play 130 to be set and changed (FIG. 12) between the cranked lever arm 126 and the lever arm 128 on every flap. In this way a perfect closure takes place each flap by its own weight.

To open the flaps 107, the actuating device 123 actuates the Linkage 124 in the direction of the horizontal arrow in FIG. 9. As a result, the cranked lever arms 126 push against the stops 129 of the Lever arms 128 which are seated in a rotationally fixed manner on the axes 127 of the flaps 107, the latter beginning to open. The counterweight 125 sits down while in motion to facilitate the work of the actuator 123. At the same time, this counterweight holds the flaps 127 in open position without the need for the actuator 123.

To close the flaps, the actuating device 123 actuates the Linkage 124 counter to the direction of the arrow in Fig. 9, the cranked Lift the lever arms 126 from the stops 129 and the flaps 107 close under their own weight. One not shown The stop limits the pivoting of the counterweight 125.

If necessary, the duration of the inventive Shorten the heat treatment at a certain temperature by keeping one or more flaps in the open position.

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It is of course possible to use the treatment method according to the invention not only to be used with separate wire windings, but also with compact wire rings or also during their formation.

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Claims (10)

PATENT CLAIMS 1. Process for the heat treatment of a steel wire rod with less than 0.15% carbon, which before, after leaving of the rolling mill, has been cooled in the usual controlled manner, characterized in that this wire rod for a time is kept isothermally at a temperature between 200 and 400 C. 2. The method according to claim 1, characterized in that the wire rod is kept isothermal for at least 30 seconds will. 3. The method according to claim 1, characterized in that this Isothermal stay is carried out without any thermal, mechanical, electrical or other energy supply. 4. The method according to claim 1, characterized in that this isothermal stay with calorie intake in the usual way and Manner is carried out. 5. Device for performing the method according to claim 1 to 4, which is arranged in the wire running direction behind the wire winding device of a conventional controlled cooling device for wire rod is characterized by a chamber (7; 11; 106) for isothermal stay through which the wire rod is passed, and which is located at the end of this controlled cooling device, but does not include the wire winding device. 6. Apparatus according to claim 5, characterized by an immediate 009839/1 401 Convertibility to the usual treatment of a hard wire rod according to the known controlled cooling device at the end or behind which it is attached after a soft wire rod of less than 0.15% carbon had been treated according to the method according to the invention, and vice versa. 7. The device according to claim 6, characterized by a chamber of at least three united "walls, consisting of at least two side walls (108) and a top wall, the latter being removable and / or is subdivided and consists of a plurality of movable parts or flaps (107) that can be actuated simultaneously or individually. 8. Apparatus according to claim 7, characterized by at least one thermally insulated chamber wall. 9. Device for performing the method according to claim 1 to 4, which is arranged in the wire running direction behind the wire winding device for wire rod, characterized by a chamber (11) for isothermal stay, which is separated behind this usual Cooling device is located, but does not include the wire winding device. 10. Steel wire rod with less than 0.15% carbon, which according to Leaving the rolling mill cooled in the usual, controlled manner characterized in that it has been kept isothermally at a temperature between 200 and 400 C for a period of time to enable this wire rod to be drawn directly to a very small final diameter without further heat treatment. 009839/1401