FR2684691A1 - Process for the continuous manufacture of a travelling steel wire, especially of a wire for reinforcing concrete - Google Patents

Abstract

To manufacture the wire, which may be crenellated, a steel containing the following, by weight, is chosen, in which the equivalent carbon Ceq is lower than 0.45%. A billet (4) is heated in a furnace (6) and is rolled on a wire train comprising a plurality (1) of rolling cages. On leaving the last cage the wire (7) passes through a water box (2) and is then reeled on a reeling device (3). A wire is thus obtained which may have an elastic limit higher than 500 MPa and a diameter greater than 6 mm.

Description

PROCESS FOR THE CONTINUOUS PRODUCTION OF A STEEL WIRE IN
WINDING IN PARTICULAR OF A WIRE FOR REINFORCING CONCRETE
The invention relates to the manufacture of steel wire, including wire for reinforcing concrete.

 To make wire for reinforcing concrete, it is known to take a carbon-manganese steel, to roll it on a wire train, to soak it in the "hot" lamination by passing it through a water box and wind it up. The exact chemical composition and the quenching intensity are determined by those skilled in the art so as to obtain the desired mechanical characteristics and good weldability.

 This technique, which is very economical, has the disadvantage of not making it possible to produce very large diameter wires with high characteristics. Thus, for the Fe E 500 quality (according to the AFNOR NFA 35016 standard) it is not possible to produce wires of diameter greater than 12 mm, because they can not be wound.

 This technique also has the disadvantage of not making it possible to produce son with very high characteristics (that is to say greater than the quality Fe E 500 having good ductility, even for small diameters). However, the evolution of concrete requires reinforcing son with very high characteristics.

 To produce large diameter son Fe E 500 quality, it is known to use a microalloyed steel vanadium, hot rolled and wound directly without quenching. Quenching is avoided to allow winding and to make possible the precipitation of vanadium. This technique has the disadvantage of being expensive because of the addition of vanadium and moreover, even for small diameters, it does not allow to obtain very high mechanical characteristics.

 The object of the invention is to propose a method for manufacturing steel wire, in particular wire for reinforcing concrete, which makes it possible to obtain wires with high or very high mechanical characteristics that can have large diameters and that is economical.

To this end, the subject of the invention is a process for the continuous production of a running steel wire, in particular a wire for reinforcing concrete, characterized in that
a steel containing by weight is selected
C <0.22%, Si <0.5%, Mn <1.5%, and 0.01% <V <0.15%, or 0.01% <Nb <0.15%, or 0, 01% <V + Nb <0,15% and whose equivalent carbon is less than 0,45%
- This steel is hot rolled on a wire train to obtain a wire
- On the wire obtained is carried out a partial quenching in the hot rolling and coil the wire.

 According to the invention, the partial tempering is carried out on a wire whose temperature at the end of rolling is greater than the point AC3 of the steel, and so that the temperature of the wire at the beginning of the winding is greater than 500 ° C.

According to an advantageous implementation, the quenching is carried out by passing the thread in a water box
The invention also relates to a steel wire, in particular a wire for reinforcing concrete, made using the method according to the invention. The chemical composition of the yarn comprises, by weight,
C <0.22%, Si <0.5%, Mn <1.5%, and 0.01% <V <0.15% or 0.01% <Nb <0.15%, or 0.01 % <V + Nb <0.15% the remainder being iron and impurities and residuals resulting from the melting of the raw materials; its equivalent carbon Ceq is less than 0.45%; its section comprises an outer annular zone having a quenched tempered structure and a central zone having a ferritic structure.

 According to one embodiment of the wire according to the invention, the area of the annular zone represents more than 10% of the area of the section of the wire.

 The invention makes it possible to obtain a yarn whose yield strength of the Re yarn is greater than 500 MPa and the Agt elongation greater than 4%.

 The diameter of the son thus obtained may be greater than 12 mm, and even reach 14 mm without posing any particular winding difficulties.

The wire can be crenelated
The invention will now be described in more detail with reference to the attached figure plate on which
- Figure 1 is a diagram of the output of a wire train with a water box and a winder
- Figure 2 is a diagram of a cross section of a wire according to the invention.

 To make a yarn according to the invention, a steel billet is obtained, the chemical composition of which will be defined later, and then this billet is hot rolled on a wire train to obtain a wire which is subjected to partial tempering in the hot state. rolling. After quenching, the wire is reeled and allowed to cool in air.

 For clarity, first describe the method of rolling, quenching and winding, then specify the choice of the chemical composition and give some examples that illustrate the invention.

 To produce a wire dipped in hot rolling, according to the invention, we take a billet 4 which is heated to 11800C in a furnace 6 and that is laminated using a wire train equipped with a cooling water box. Such a known wire train itself comprises a plurality of successive rolling stands in which the product moves in the direction of the arrow. At the outlet of the successive rolling stands is disposed a water box 2 known in itself which is an enclosure provided with nozzles supplied with water, a water outlet and two inlet-outlet ports for the passage of water. thread. The wire 7 passes through the water box through the orifices.

 Downstream of the water box and at a distance from it is placed a winding device 3 in which the wire enters to be wound.

 In rolling cages, the billet is progressively transformed into wire which at the exit of the last cage then has a temperature T1. The operator sets the rolling conditions, in particular the running speed of the wire, so that the temperature T1 is greater than the point AC3 of the steel, for example greater than 9000C, so that the wire has an austenitic structure.

 At the exit of the rolling stands, the wire enters the water box and then leaves. During the crossing of the water box, the surface of the wire is watered by the water of the jets and vigorously cooled.

 At the outlet of the water box, the surface of the wire and the wire to a certain depth are cold, but the core of the wire remained hot.

 The operator adjusts the intensity of the watering so that the surface temperature or in the vicinity of the surface at the outlet of the water box is less than the point M5 martensitic transformation start so as to perform a quenching. In this way, at the outlet of the water box, the wire, to a certain depth below the surface has a hardened structure, that is to say, martensitic or possibly bainitic, however, the core has a non-structural structure. quenched, for example austenitic.

 During the journey between the water box and the winding device, the core of the wire, which is hot, warms the outer part which has been quenched, which causes a tempering of the quenched portion. Reheating the quenched portion raises the temperature of the wire surface to a temperature T2. This temperature determines the ease of winding. For winding to be possible it is desirable that T2 be greater than 500 ° C and preferably 600 ° C, especially when the diameter of the wire is large, that is to say greater than 10 mm.

 During and after winding, the wire cools slowly with air. This cooling causes a progressive transformation of the core structure of the wire which becomes ferritic.

 A yarn 7 is thus obtained, a straight section of which comprises, as shown in FIG. 2, an outer annular zone 5 having a tempered return structure, that is to say martensitic or bainitic or mixed martensite / bainite returned, and a zone central 6 ferritic.

 To adjust the mechanical tensile characteristics of the wire, we can influence the intensity of the quenching by fixing for example the number of sprinklers in service or the intensity of the water flow, but we must also choose the chemical composition of the water. to have a suitable hardenability and mechanical characteristics of different structures sufficient. It is also necessary to choose the chemical composition so that the steel is weldable.

For this, in accordance with the invention, the equivalent carbon Ceq must be less than 0.45%, with
Ceq = C + Mn + Cu + Ni + V + Cr + Mo
6 5 15 and we choose a steel containing
- less than 0,22% of C, because beyond the steel is no longer weldable
- less than 0.5% of Si, because beyond steel is difficult to weld
- less than 1.5% of Mn, because beyond the ductility drops significantly
at least one microalloy element such as vanadium, or niobium, or a combination of these two elements; the content of these microalloy elements is such that V, or Nb, or V + Nb> 0.01% to obtain a hardening effect, and V, or Nb, or V + Nb <0.15%, because beyond these elements are no longer effective.

 With such steels soaked in the hot rolling can be made son high characteristics and coils even large diameter.

 Indeed, it has been unexpectedly found that in the particular thermal cycle conditions of the partial tempering in the hot rolling, which has just been described, vanadium forms hardening precipitates.

 According to previous practice, vanadium steels are wound at a temperature higher than 900 ° C so that they are austenitic with vanadium solution, that during the slow cooling after the winding transformation to ferrite s accompanied by precipitation of vanadium.

 In the technique according to the invention, the wire is at a much lower temperature at the time of winding due to the previous partial quenching which corresponds to very different conditions for the precipitation of vanadium.

 The hardening which is observed and which comes from the vanadium allows, for a given wire diameter, to be less soaked than with a steel without vanadium and thus to obtain higher winding inlet temperatures and compatible for example with the winding of large diameter wires.

 On small diameter wires that can be drenched energetically, the addition of vanadium can increase the mechanical characteristics and bring them to levels inaccessible by the technique according to the past practice.

 The yarns produced by this method are either plain yarns or crenellated yarns. Indeed, the son for the reinforcement of the concrete are generally crenellated and the method of quenching in the hot water box rolling is found to be adapted to the crenelated son.

By way of example, a 14 mm diameter wire was produced whose composition was
C = 0.18%
If = 0.24%
Mn = 0.98%
V = 0.042% with further impurities and residuals
P = 0.025%
S = 0.036%
Cu = 0.31%
Cr = 0.12%
Ni = 0.12%
Mo = 0.025% the equivalent carbon Ceg% was 0.447%, the inlet temperature T1 in the water box was 950 ° C, and the inlet temperature at the winding T2> 650 ° C. The area of the quenched area represented 15% of the pile of the wire section.

This wire had the following mechanical characteristics
- yield strength Re = 564 MPa
- tensile strength R = 687 MPa
- Agt elongation> 5%
These are characteristics in accordance with FE E 500 quality.

It should be noted that in diameter 14 mm, it is not possible to manufacture the quality Fe E 500 by quenching a steel without vanadium; this is only possible for wires of diameter less than or equal to 12 mm.

For comparison, to make a 14 mm wire in
Fe E 500 without quenching a steel containing
C = 0.17%
If = 0.28%
Mn = 1%
V = 0.086% with further impurities and residuals
P = 0.025%
S = 0.033%
Cu = 0.3%
Cr = 0.12%
Ni = 0.11%
Mo = 0.023% the inlet temperature at the winding is about 900 ° C the mechanical characteristics are
Re = 545 MPa
R = 681 MPa
It should be noted that this steel contains 0.086% vanadium while the hardened steel according to the invention contains only 0.042% vanadium, or half less.

Yarns with very high characteristics were also produced by the process according to the invention. For example, a wire 8 mm in diameter was manufactured, the chemical composition of which was
C = 0.19%
If = 0.35%
Mn = 1.12%
V = 0.082% the remainder being iron, impurities and residuals resulting from the melting of the scrap.

With an inlet temperature in the water box of 950 ° C, a coil inlet temperature greater than 600 ° C, a hardened zone area representing more than 30% of the wire section area, got the following mechanical characteristics
Re = 781 MPa
R = 885 MPa
Agt> 8%, whereas with unhardened steel containing 0.15% vanadium, 0.2% C, 0.35% Si and 1.2% Mn, mechanical properties are obtained
Re <580 MPa
R <710 MPa therefore substantially lower than that obtained in the example above. This shows that the process according to the invention makes it possible to obtain steels with higher characteristics than by the methods according to the prior practice.

 It will be noted that the choice of the chemical composition and the intensity of quenching is very varied, which enables the skilled person to obtain a wide range of yarn quality.

 Finally, this technique is more particularly applicable to wires of diameter greater than 6 mm.

Claims (9)

 1) A method of continuously manufacturing a running steel wire, in particular a wire for reinforcing concrete characterized in that  a steel containing by weight is selected  C <0.22%, Si <0.5%, Mn <1.5%, and 0.01% <V <0.15% or 0.01% <Nb <0.15%, or 0.01 % <V + Nb <0,15% and whose equivalent carbon is less than 0,45%  - This steel is hot rolled on a wire train to obtain a wire  - On the wire obtained is carried out a partial quenching in the hot rolling;  - And we coil the wire.  2) Process according to claim 1 characterized in that the temperature of the wire at the end of rolling is greater than the point AC3 of the steel.  3) Process according to claims 1 or 2 characterized in that the temperature of the wire at the beginning of the winding is greater than 500 "C.  4) Steel wire, in particular a wire for reinforcing concrete, produced by means of the process according to any one of the preceding claims, characterized in that its chemical composition comprises, by weight,  C <0.22%, Si <0.5%, Mn <1.5%, and 0.01% <V <0.15% or 0.01% <Nb <0.15%, or 0.01 % <V + Nb <0.15% the remainder being iron and impurities and residuals resulting from the melting of the raw materials, its equivalent carbon Ceq being less than 0.45% and in that its section comprises an annular zone outer member (5) having a quenched tempered structure and a central zone (6) having a ferritic structure.  5) Thread according to claim 4 characterized in that the area of the annular zone (5) represents more than 10% of the area of the section of the wire.  6) Thread according to claims 4 and 5 characterized in that the diameter of the wire is greater than 6 mm.  7) Thread according to claims 4 to 6 characterized in that the elastic limit of the yarn is greater than 500 MPa and the elongation Agt is greater than 4%.  8) Thread according to claim 7 characterized in that the diameter of the wire is greater than 12 mm.  9) Thread according to any one of claims 4 to 8 characterized in that it is castellated.