LU85446A1 - METHOD FOR MANUFACTURING STEEL REINFORCING WIRE FOR REINFORCED CONCRETE - Google Patents

Description

I * "b C 2251/8307.

METALLURGICAL RESEARCH CENTER -CENTRUM V00R RESEARCH IN DE METALLURGIE,

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

Method of manufacturing steel reinforcing wire for reinforced concrete.

i 1 The present invention relates to a method of manufacturing wire | of steel reinforcement for reinforced concrete.

!

Processes are already known for manufacturing concrete bars by rolling ~ in a bar train at the outlet of which they are subjected, in continuous movement, to an appropriate heat treatment. Straight bars are thus produced having excellent mechanical properties.

Specialists also know that the profitability of rolling on a bar train is questionable, from an economic point of view, when the diameter of the product to be rolled is less than a certain value. It is often more advantageous to use a train | i lî - / - 2 - fr. "By wire, at the outlet of which the metallic wire is normally wound into coils. In the case of reinforcing bars of small diameter, hereinafter designated by the term. Reinforcing wire, it is also possible to apply the above-mentioned heat treatment and to give them the desired excellent mechanical properties. The winding of the wire thus treated gives rise, however, to difficulties which have not yet all been resolved at present. .

Because of the economic importance of reinforcing wire, there is therefore currently in the industry a strong desire to have a process for producing wire which, at the same time, has excellent mechanical properties and which can be delivered in reels.

It is known that, moreover, the steels used to manufacture the reinforcing bars or wires are subdivided into several categories, according to the value of their mechanical properties, in particular their elastic limit.

In this regard, frequent reference is made to the classification of these steels set by the German standard DIN 488; among the steel classes defined by this standard, the most used are classes III and IV. Recall that, according to this classification, steels of class III must have an elastic limit between 420 MPa and 500MPa, while for steels of class IV, the elastic limit must be greater than 500 MPa.

The present invention relates to a method for manufacturing reinforcing wire of classes III and IV steel, according to said standard DIN 488, which can be wound and delivered in coils.

ri - 3 -

It is based on the unexpected observation made by the Applicant, according to which it is possible to give the reinforcing wire> the desired mechanical properties without compromising its suitability for winding, thanks to an appropriate treatment applied to the wire in turns. spread out on a conveyor.

To this end, the process which is the subject of the present invention is essentially characterized in that before it enters the finishing cages, the wire is subjected to a first cooling to a temperature between 1000 ° C and 900 ° C, in that the finishing rolling is carried out at this temperature, in that the wire is deposited, at a temperature between 900 ° C and 750 ° C, in turns spread over a cont-v. voyeur, in that the wire is immersed in a bath at a temperature between 45 ° C and 65 ° C, for a period of less than 20 seconds, but, sufficient to bring its temperature to a value between 550 ° C and the transformation point Ms of the steel, so as to give the wire a bainitic structure, in that the wire of the said bath is extracted at this temperature between 550 ° C. and Ms, in that the wire coil is reformed and the cooling is completed in the still air.

In the case of a steel containing one or more dis-persoid elements, such as niobium, the first cooling can be combined with a lowering of the temperature of the furnace.

'It may happen in certain cases that the temperature of the wire leaving the finishing cages is too high for the subsequent deposit of the wire on the conveyor.

In this case, it would not depart from the scope of the invention to apply to the wire, immediately after leaving the finishing cages, an intermediate cooling to a temperature between 900 ° C. and 750 °. vs.

- According to a preferred implementation of the process of the invention, the wire is immersed in said bath while it is in the form of turns spread over a conveyor.

To this end, a device of the type which is described in Belgian patent No. 890,079 of the same Applicant is advantageously used.

It may be recalled that this device comprises a horizontal conveyor arranged in a tank which may contain a bath, and that the conveyor, as well as the wire which it carries, can be immersed or emerged, almost instantaneously, respectively by a rapid elevation or a rapid lowering of the bath level in the tank.

Thanks to this device, it is possible to very precisely adjust the conditions of stay of the wire in the bath.

The process of the invention makes it possible to give mild steels an elastic limit between 420 MPa and 500 MPa (class IIl)? it also makes it possible to hoist in class IV carbon steels containing small quantities of dispersoid elements.

The following examples illustrate the application of the process of the invention to these two types of steel.

Example 1.

A hot-rolled mild steel wire, containing 0.08% carbon, 0.6% manganese, and 0.2% silicon was first cooled, which reduced its temperature to 1000 ° C at the inlet finishing cages. The finish rolling gives r - 5 - t the final diameter of the wire, ie 7.5 mm. Immediately after this operation, the wire is subjected to intermediate cooling to a temperature of 880 ° C., at which it is then deposited in coils spread on a conveyor. Still carried by the conveyor, the wire is immersed for 7 seconds in a water bath at 54 ° C. On leaving the bath, the wire had a temperature of about 425 ° C. After final cooling in still air, it had an elastic limit of 464 MPa and an elongation of 18% over 10 d. It therefore belongs to class III.

By way of comparison, an identical wire, not treated according to the method, of the invention, exhibited an elastic limit of approximately 330 MPa and an elongation of 24% over 10 d.

Example 2.

A 7.5 mm diameter steel wire containing 0.15% carbon, 0.6% manganese, 0.2% silicon and 0.025% niobium was first cooled before the finishing cages. until a temperature of 920 ° C. After the finishing rolling, an intermediate cooling down to 800 ° C was applied to the wire, which was then deposited, at this temperature, in coils spread on a conveyor. The wire was immersed for 13 seconds in an aqueous bath at 56 ° C, from which it left at about 435 ° C. Cooling in the still air has been completed.

The wire thus treated had a yield strength of 555 MPa and an elongation of 12% over 10 d, while an identical untreated wire had a yield strength of 430 MPa and an elongation of 23% over 10 d .

I. 1 4 - 6 -

In the process of the invention, the first cooling makes it possible to refine the grain and improve the ductility of the steel, while the intermediate cooling has the purpose of avoiding the coalescence of the grain and of limiting the formation of calamine.

"/ 7

Claims (3)

1. A method of manufacturing steel reinforcing wire, characterized in that before it enters the finishing cages, the wire is subjected to a first cooling to a temperature between 1000 ° C and 900 ° C, that the finishing rolling is carried out at this temperature, in that the wire is deposited, at a temperature between 900 ° C and 750 ° C, in turns spread out on a conveyor, in that one immerses the wire in a bath at a temperature between 45 ° C and 65 ° C, for a period of less than 20 seconds, but sufficient to bring its temperature to a value between 550 ° C and the transformation point Ms of the steel, so as to give the wire a bainitic structure, in that the wire from said bath is extracted at this temperature between 550 ° C. and Ms, in that the wire coil is reformed and in that cooling is completed in still air. 2. Method according to claim 1, characterized in that immediately after leaving the finishing cages, an intermediate cooling is applied to the wire up to a temperature between 900 ° C and 750 ° C. AT 3. Method according to either of Claims 1 and 2, characterized in that the wire is immersed in said bath by depositing the wire on a conveyor arranged in a tank which can contain said bath and by varying, preferably rapidly, the level of said bath in the tank, so as to immerse or cause said conveyor to emerge. Drawings: plates -.¾ — pages of which ....... A_______ cover page ......... £ ..... description pages ...... Λ ...... claim pages ........... abridged description e ", w if î! 'yitrfirsn" "rn 1a _ _____