LU82031A1 - METHOD FOR MANUFACTURING MACHINE THREAD PARTICULARLY FOR COLD STRIKING - Google Patents

Description

I, 1 v BL - 2797 / EM / BM C 2005/7912.

| METALLURGICAL RESEARCH CENTER -CENTRUM V00R RESEARCH IN DE METALLURGIE,

Non-profit association - vereniging zonder winstoogmei in BRUXELLES (Belgium).

Wire rod manufacturing process particularly for cold stamping.

The present invention relates to a wire rod manufacturing process - advantageously, the wire rod thus manufactured, is used for the manufacture of parts for cold stamping and more particularly of high strength bolts.

For a certain category of high-resistance metal parts, the manufacturing process usually implemented up to now is as follows: -k / y r! - 2 - i l i [- hot rolling of wire rod, | - pickling, | - drawing or drawing, - cold stamping, - heat treatment,: - finishing.

I In this process, the wire rod is made of a steel which must have the desired chemical composition and a microstructure allowing the subsequent drawing and cold stamping.

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The heat treatment gives the cold-pressed part its final mechanical properties; this treatment generally comprises quenching followed by tempering.

This heat treatment is necessary due to the fact that the wire rod currently available cannot at the same time have the strength and ductility properties required to obtain the products in question.

The present invention relates to a wire rod manufacturing process having both of these two | resistance and ductility properties without it being necessary to subject this wire to such a heat treatment. The process which is the subject of the present invention is essentially characterized in that it comprises the following stages: M a) wire to be treated is subjected to a temperature included! between 950 ° C and 1050 ° C and in the austenitic state, when it leaves the last shell of the rolling mill, i I b) the temperature of the wire is lowered to 800-950 ° C, for example by treatment with the water, !! 4

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! t; "- 3 - 5, fic) this wire is then laid in the form of non-concentric turns, on a conveyor whose speed is adjustable between 0.1 and 1.2 m / sec., d) at a certain distance from the place where the wire was laid on the conveyor, it is subjected to quenching by means of either water jets, laminar or not, or water screens i having a width at least equal to the diameter of the turns, or even finely sprayed water jets (mist) as described in Belgian patent n ° 853.821 of the applicant, e) the turns are then collected in the form of a compact coil at a temperature between 100 ° C and 300 ° C, the path between the places of quenching and reformation of the coil being sufficient to dry the wire.

According to a first embodiment of the invention, the conditions for implementing the method are regulated (in particular the temperature of the turns at the time of their deposition on the conveyor and the time of travel in the air until quenching) of such so that at the time of quenching, the steel is partially transformed. in the ferritic field, the quantity by volume of ferrite being between 95% and 70%.

The optimum value of the aforementioned temperature and travel time parameters depends on the composition of the steel and on the desired final properties.

According to a second method of the invention, gold performs the quenching so that the remaining austenite (5 to 30% by volume) is transformed into martensite or / bainite.

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The duration of the wire quenching and the intensity of the cooling are adjusted so that the wire leaves this operation at a temperature between 150 ° C. and 350 ° C.

According to another embodiment of the invention, we: limit the density of the turns on the conveyor to 25 turns | to the maximum meter and 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 the purpose of guaranteeing during the quenching, the homogeneity of the cooling over the whole width of the belt of turns.

The wire must present at the point where quenching begins, as uniform a temperature as possible. To this end, along the path between the head for placing the turns on the conveyor and the quenching installation and opposite the points of the sheet of turns corresponding to the maximum density of the wire, selective cooling is carried out by means a fine spray of water (mist).

Figures 1, 2 and 3 are given as an indication, but not limiting in order to clearly understand the present invention.

Figure 1 schematically shows an installation according to the invention.

FIG. 2 relates to a temperature-time diagram of the thermal cycle according to the invention, applied in a well-defined use case.

FIG. 3 is a micrograph at 500 magnification of the wire treated according to the thermal cycle of FIG. 2.

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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 laying head 3 of the wire in the form of non-concentric turns on a conveyor 4, a quenching device and at the exit of the conveyor 4, a reel reformation station 6.

This line can also include a selective cooling device (not shown) between locations 3 and 5 to ensure the wire as uniform as possible when it reaches the quenching device 5.

According to FIG. 2, the ordinates of the representative diagram of the thermal cycle are constituted by the average temperatures of the section of the wire and the abscissae are constituted by time in seconds or by the length of the treatment line in meters.

This diagram relates to the processing of a 5.5 mm wire, rolled at 75 m / sec., Of the following composition: C = 0.08%, Mn = 0.8%, Si = 0.15%.

Point 7 represents the temperature at the outlet of the rolling mill, ie 1000 ° C.

Line 7-8 represents primary cooling lasting 0.2 seconds to 850 ° C.

At this time, the wire is deposited on the conveyor moving at a speed of 1 m / sec., The density of the non-concentric turns on this conveyor being 20 per meter.

Line 8-9 relates to the course of the turns of the wire between the depositing head on the conveyor and the entry into the quenching device. The length of this P, ™ ... is SO B and »0.., ΡΡ. - ”...

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r quenching is 50 seconds. During this course, the wire temperature is lowered from 850 ° C to 600 ° C and the percentage of ferrite formed before quenching is 88.5%.

Section 9-10 relates to the quenching zone, the length of which is 0.57 m and the duration for crossing it | 0.57 sec. The quenching device is composed of air-water nozzles with fine water spray (mist) arranged ‘on either side of the wire layer.

Zone 10-11 represents the drying operation, the duration of which is 2 seconds (point 11 = 52.77 sec.).

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

The properties obtained are as follows: - breaking load (R ^): 503 MPa - elastic limit (R ^): 282 MPa - elongation (A): 25%.

According to Figure 3, the microstructure consists of 88.5% ferrite (white areas) and 11.5% martensite in the form of small islands homogeneously distributed (black areas).

Claims (7)

1. A method of manufacturing wire rod for cold striking, characterized in that it comprises the following stages: a) the wire to be treated is at a temperature between 950 ° C. and 1050 ° C. and in the austenitic state, when it leaves the last stand of the rolling mill,. b) the temperature of the wire is lowered to 800-900 ° C, for example with water, c) 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 / sec., D) at a certain distance from where the wire was placed on the conveyor, it is subjected to quenching by means of water jets, laminar or not, or d '' water screens having a width at least equal to the diameter of the turns, or even finely sprayed water jets (fog), e) the turns are then collected in the form of a compact coil at a temperature between 100 ° C and 300 ° C, the path between the places of quenching and reformation of the coil being sufficient to dry the wire. 2. Method according to claim 1, characterized in that the conditions for implementing the method are regulated (in particular the temperature of the turns at the time of their deposition on the conveyor and the travel time in the air up to quenching) in such a way that at the time of quenching, the steel is partially transformed in the ferritic domain, the quantity by volume of ferrite being between 95% and 70%, 3. Method according to either of Claims 1 and 2, characterized in that the * quenching is carried out in such a way that the remaining austenite (5 to 30% by volume) is transformed into martensite or bainite . 0 - 8 - * 4. Method according to either of claims 1 to 3, characterized in that the duration of the quenching of the wire and the intensity of the cooling are adjusted so that the wire leaves this operation at a temperature between 150 ° C and 350 ° C. 5. Method according to either of claims 1 to 4, characterized in that the density of the turns on the conveyor is limited. 25 turns per meter maximum. |: 6. Method according to one or other of the resales; dications 1 to 5, characterized in that one adapts the length between the laying head of these turns on the conveyor and the quenching installation as well as the speed of the conveyor S as a function of the rolling speed and the time of per course desired. 7. Method according to either of the res. dications 1 to 6, characterized in that along the path between the head for placing the turns on the conveyor and the ins- | quenching plant and opposite the points of the spia mat corresponding to the maximum density of wire, selective cooling is carried out by means of a fine spray | of water (fog). : - ~ f * ~ ~: · | ! |