LU84832A1 - METHOD OF MANUFACTURING WIRE PARTICULARLY FOR CONCRETE REINFORCEMENTS - Google Patents

Description

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/ BL-3479 / EM / EG

Claiming priority for a dfipoaCe patent application in Belgium on June 1, 1982 "or" No 893.382_

PATENT OF IHVENTIOH

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C 2195/8206.

METALLURGICAL RESEARCH CENTER -CENTRUM VOOR RESEARCH IN. METALLURGY,

Non-profit association -Vereniging zonder winstoogmerk in BRUXELLES, (Belgium).

Method for manufacturing wire, particularly for concrete reinforcement.

The present invention relates to a method of manufacturing wire rod; advantageously, the wire rod thus produced is used as a reinforcement for concrete and for this purpose it can advantageously be provided with ribs.

It is known that the wire generally used for making reinforcements for concrete consists of a steel which must have the desired chemical composition and a microstructure allowing the assembly and the shaping of the reinforcements while ensuring satisfactory mechanical properties; in general a trai- ---------------...

- 2 - machine currently available cannot at the same time have the strength and ductility properties required to obtain the products in question.

The subject of the present invention is a method of manufacturing wire rod having both these strength and ductility properties without it being necessary to subject this wire to such mechanical treatment; in addition, the method is applicable to low carbon steels, which is advantageous from the point of view of the weldability of the reinforcements.

The process which is the subject of the present invention is essentially characterized in that it comprises the following stages: a) the wire leaving the last stand of the rolling mill at a temperature between 950 ° C. and 1050 ° C. and which is in the state austenitic is subjected to cooling which lowers its temperature to 700 to 900 ° C, for example by treatment with water; b) this wire is then placed in the form of non-concentric turns, on a conveyor whose speed is adjustable between 0.1 and 1.2 m / s., and it is subjected to a slower cooling, so as to bring the temperature between 620 ° C and 720 ° C.

c) the wire is then subjected to a third cooling phase by means of either water jets, laminar or not, or of water screens having a width at least equal to the diameter of the turns, or of water jets finely sprayed (mist), either by immersion in an aqueous bath.

According to a first embodiment of the invention, the cooling conditions are regulated during the process, so that at the moment when the third phase of treatment begins, the steel is partially transformed in the ferritic field, the quantity by volume of ferrite being between 95% and 70%, and preferably between 90% and 80%.

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The optimal value of the parameters chosen to apply the cooling in its different phases depends on the composition of the steel and the desired final properties.

According to a second embodiment of the invention, the third phase of the cooling treatment is applied, so that the remaining austenite (5% to 30%, preferably 10% to 20% by volume) is transformed into martensite or bainite .

The duration of the third phase of treatment of the wire and the intensity of the cooling are advantageously adjusted in such a way that the wire leaves this operation at an unreliable temperature. below 350 ° C; preferably, the operation is carried out by passing the wire, spread out in non-concentric turns on a conveyor, in an aqueous bath the temperature of which is lower than 65 ° C.

According to another embodiment of the invention, the length between the non-concentric winding device on the conveyor and the quenching device is adjusted, as well as the speed of the conveyor as a function of the rolling speed and the desired travel time. , in order to guarantee during the quenching, the homogeneity of the cooling over the entire width of the belt of turns.

The wire must present at the point where quenching begins, as uniform a temperature as possible. With this in mind, we know that a more or less prolonged stay on a conveyor with calm air can lead to a difference in cooling rate and therefore in microstructure and mechanical properties, between the parts of turns which are on the edges of the conveyor and the parts of turns lying away from the edges of the conveyor, ie in the central zone! conveyor line.

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It is indeed well known that when the wire rod is spread in non-concentric turns on a conveyor, most of the metal of the turns is accumulated in a relatively small volume, at the two lateral edges of the sheet of turns, while at the central zone of this sheet, the accumulation of metal is less than on the edges. This results in a difference in the rate of cooling of the turns, the lateral edges of the sheet cooling less quickly than the central zone, which does not promote the homogeneity of the structure of the wire over the whole of the same turns and leads, for the wire located in the central zone, to different mechanical properties from those obtained for the wire located in the lateral zones.

To overcome this drawback, it is advantageous according to the invention, that during all or part of the cooling phase b) of the wire deposited on the conveyor, the part of the ply of the turns situated in the central zone of the conveyor is subjected to less intense cooling than that of the edges of the sheet and that the difference in cooling is adjusted, so as to obtain a homogeneous structure of the wire over its entire length.

Several methods can be used to achieve this differential cooling. It is possible, for example, by means of a heat generator, to bring to a suitable temperature a gaseous fluid which is projected onto the part of the turns located in said central zone, the temperature of the gas thus projected progressively decreasing, and appropriately, in the central area, in the direction of movement of the. conveyor. Any other means of heating the sheet of turns J located in said central zone can be used, without departing from the scope of the present invention.

Preference is given, however, to any means which, without a precise contribution of calories, contributes to slowing down in due proportion, the cooling of the said central zone in particular, all other equal factors, by reducing it, relative to the flow rate of coolant. used for the edges of the sheet, the flow rate of these same agents used for said central area.

Another particularly advantageous means for implementing this modality of the process of the present invention consists in placing above the central zone of the conveyor, and preferably just above it, at a certain distance from the sheet. of turns and over all or part of its length, a screen whose effect is on the one hand, to slow down the circulation of any gaseous fluid on the said central zone and on the other hand, to reflect towards the upper part of the central zone of the sheet of turns the calories which emanate from it, in particular by radiation. It is also interesting to provide thermal insulation of the central part of the conveyor plates.

To complete this treatment for homogenizing the structure of the wire, it is also possible to apply a certain cooling to the points of the sheet of turns corresponding to the maximum density of the wire, for example by means of a fine spray of water (mist). , or by blowing.

In a particularly advantageous implementation of the process of the invention, the first phase of the heat treatment is carried out by applying intense, but short-term, cooling to the wire which has the effect that a superficial crown of austenite is transformed into martensite or bainite; this J hardened crown is possibly subjected to an income under φ · (- 6 - the effect of residual heat in the interior of the wire. Under these conditions, phases b) - possibly very reduced - and c) of the invention are then only applicable to the central part of the wire (so-called core) not hardened.

Figures 1 and 2 are given as an indication, but not limitative to clearly understand the present invention.

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FIG. 1 schematically represents an installation for implementing the method according to the invention.

FIG. 2 is a micrograph, at 500 magnification, of a wire treated according to the cycle of the invention.

According to Figure 1, the processing line located at the outlet of the last rolling stand (1) comprises a water cooling ramp (2) of a type usually used, a wire removal head (3) in the form of non-concentric turns on a conveyor (4), a treatment installation (5) and, at the outlet of the conveyor (4), a reformation station of the coil (6).

This line may further comprise a homogenization device (not shown) between the installations (3) and (5) to ensure the wire as uniform as possible when * when it reaches the installation (5).

In the case of the treatment of a 6 mm wire, rolled at 75 m / s., Of the following composition: C = 0.08%, Mn = 0.8%, Si = 0.15%, where the temperature at the output of the rolling mill (1) is 950 ° C, the first phase of re- | 0.2 second cooling decreases the temperature to 850 ° C.

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-ΊΑ this moment / the wire is deposited in (3), on the conveyor (4) moving at a speed of 0.3 m / s. , The density of the non-concentric turns on this conveyor being 78 per meter.

During the course of the turns of the wire between the depositing head (3) on the conveyor (4) and the entry into the treatment installation (5), the temperature of the wire is lowered from 850 ° C to 700 ° C and the percentage of ferrite formed before quenching is 88%.

The wire processing installation (5) consists of a device for covering the wire with a layer of cold water, such as for example the device described in Belgian patent application no. 6 / 47.644 of 16 April 1982 of applicant.

At the end of this phase, the wire is put into the form of a compact coil in (6) and is cooled in air to room temperature.

The properties obtained are as follows: - breaking load (R ^): 682 MPa - elastic limit (R): 458 MPa e - elongation (A): 14%.

According to FIG. 2, the microstructure consists of 88% il of ferrite (white areas) and 12% of bainite in the form of small islands distributed in a homogeneous manner. uniform (black areas).

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Claims (6)

1- A method of manufacturing wire, characterized in that it comprises the following steps: a) the wire leaving the last stand of the rolling mill at a temperature between 950 ° C and 1050 ° C and being in the austenitic state, is subjected to cooling which lowers * 1 its temperature to 700 to 900 ° C, for example by water treatment. b) this wire is then placed in the form of non-concentric turns on a conveyor whose speed is adjustable between 0.1 and 1.2 m / s., and it is subjected to a slower cooling, so as to reduce its temperature between 620 ° C and 720 ° C; c) the wire is subjected to a third cooling phase, using either water jets, laminar or not, or water screens having a width at least equal to the diameter of the turns, or water jets finely sprayed (mist), either by immersion in an aqueous bath. 2. Method according to claim 1, characterized in that the cooling conditions are adjusted during the process, so that at the moment when the third phase of the cooling treatment begins, the steel is partially transformed in the ferritic field, the quantity by volume of ferrite being between 95% and 70%, and preferably between 90% and 80%. 3. Method according to either of Claims 1 and 2, characterized in that the third phase of the cooling treatment is applied in such a way that the remaining austenite (5% to 30%, and preferably 10% to 20% by volume) is transformed into martensite or bainite. r - 9 - "* · * 4. Method according to either of claims 1 to 3, characterized in that the duration of the third phase of treatment of the wire and the intensity of cooling are adjusted 1 so that the wire leaves of this operation at a time! j temperature below 350ÖC. 5. Method according to one or other of Claims 1 to 4, I characterized in that the third phase of the processing is carried out. - cooling much by passing the wire, spread out in non-concentric turns on a conveyor, in an aqueous bath whose temperature is not higher than 65 ° C. 6. Method according to either of claims 1 to 5, characterized in that the first step (a) of the heat treatment is carried out by applying intense, but short-term cooling to the wire which has the effect transforming a surface crown of austenite into martensite and / or bainite, this crown possibly being subjected to a subsequent tempering under the effect of residual heat in ____ I inside the wire. Dd jr i i!