EP0859064A1 - Stainless steel for manufacturing drawn wire, especially tyre reinforcement wire, and process of manutacturing said wire - Google Patents

Abstract

A method is claimed for the production of a drawn wire, notably a pneumatic reinforcing wire with a diameter of less than 0.3 mm, by drawing from a base machine wire with a diameter greater than 5 mm or from a previously drawn wire based on a stainless steel with a balanced composition conforming to given individual limits for its various components. The steel has set limits for its content of oxide inclusions and its composition conforms to given relationships between its components. The base wire is subjected to a wire drawing operation satisfying the following conditions:- a) a cumulative rate of deformation greater than 6; b) keeping the wire, during the wire drawing operation and between wire drawing operations, at a temperature of less than 650 degrees C, and preferably at a temperature of less than 600 degrees C, without reheating between the wire drawing passes. The stainless steel used in this method is also claimed.

Description

The present invention relates to a method for producing yarn drawn, of stainless steel, in particular of tire reinforcement wire of diameter less than 0.3 mm, by drawing of a steel having a composition and inclusive inclusiveness. The thread obtained by the method can be used in the field of making parts subject to fatigue.

Reinforcing metal wires for elastomers for tires must have a small diameter, generally between 0.1 mm and 0.3 mm and high mechanical characteristics. The charge to the rupture in tension can be higher than 2300 MPa, the ductility residual, measured by tensile necking, torsion or by looping must be non-zero, the limit of endurance in fatigue by bending rotary or alternating must be greater than 1000 MPa.

These characteristics are necessary to support the efforts static or alternating to which the wire is subjected in the assemblies incorporated into tires.

In addition, the drawing of stainless steel wire to the diameter between 0.1 and 0.3 mm must be possible under conditions industrial, i.e. with such low case frequencies as possible, limiting costly operations such as heat treatments or intermediate annealing.

It is known the use, for tire reinforcements, of a wire of stainless steel in the highly strain-hardened state.

Patent application FR 93 12 528 deals with the use of a wire stainless steel with a diameter between 0.05 mm and 0.5 mm including the tensile strength Rm is greater than 2000 MPa. The steel of which is composed the thread contains in its composition at least 50% of martensite obtained by wire drawing at a reduction rate greater than 2.11 with intermediate annealing, the sum of the nickel content and chromium being between 20% and 35%.

The object of the invention is to produce a drawn wire, in particular of tire reinforcement wire with a diameter of less than 0.3 mm per drawing of a basic wire rod with a diameter greater than or equal to 5 mm or of a previously drawn basic steel wire of composition given, the simplified production process, ensuring on the one hand, inclusionary quality which reduces breakages in wire drawing, and on the other hand, improved mechanical properties.

• carbone ≤ 40. 10^-3%
• azote ≤ 40. 10^-3%,

   le carbone et azote satisfaisant la relation C + N ≤ 50 10^-3%

• 0,2% ≤ silicium ≤ 1,0%,
• 0,2% ≤ manganèse ≤ 5%,
• 9% < nickel ≤ 12%,
• 15% ≤ chrome ≤ 20%
• 1,5% ≤ cuivre ≤ 4%
• soufre ≤ 10.10^-3%,
• phosphore < 0,050%
• 40.10^-4% ≤ oxygène total ≤ 120.10^-4%,
• 0,1.10^-4% ≤ aluminium ≤ 20.10^-4%
• magnésium ≤ 5.10^-4%
• 0,1.10^-4 % ≤ calcium ≤ 5.10^-4%
• titane ≤ 50.10^-4%
• des impuretés inhérentes à la fabrication,

   acier dans lequel les inclusions d'oxydes ont, sous forme de mélange vitreux, les proportions pondérales suivantes:

• 30% ≤ SiO₂ ≤ 65%
• 5% ≤ MnO ≤ 40%
• 1% ≤ CaO ≤ 30%
• 0% ≤ MgO ≤ 10%
• 3% ≤ Al₂O₃ ≤ 25%
• 0% ≤ Cr₂O₃ ≤ 10%
  • la composition satisfaisant les relations suivantes:
  • Si Mn < 2%;
  • IM = 551 - 462*( C% + N% ) - 9,2 * Si% - 8,1 * Mn% - 13,7 * Cr% - 29*( Ni% + Cu% )- 18,5 * Mo% , avec
    • 150°C < IM < -55°C, et,
  • Si Mn ≥ 2% ;
  • JM = 551 - 462 *(C% + N%) - 9,2 * Si% - 20 * Mn% - 13,7 * Cr% - 29 *(Ni% + Cu%) - 18,5 * Mo%, avec
    • 120°C < JM < - 55°C,
     le fil de base étant soumis à un tréfilage satisfaisant les conditions de tréfilage suivantes:
  • un taux de déformation cumulé ε supérieur à 6,
  • un maintien du fil, pendant le tréfilage et entre les opérations de tréfilage, à une température inférieure à 650°C et de préférence inférieure à 600°C, sans recuit entre les passes de tréfilage.

The subject of the invention is a process for preparing a drawn wire from the drawing of a stainless steel base wire of the following weight composition:

• carbon ≤ 40. 10 ^-3 %
• nitrogen ≤ 40. 10 ^-3 %,

carbon and nitrogen satisfying the relationship C + N ≤ 50 10 ^-3 %

• 0.2% ≤ silicon ≤ 1.0%,
• 0.2% ≤ manganese ≤ 5%,
• 9% <nickel ≤ 12%,
• 15% ≤ chromium ≤ 20%
• 1.5% ≤ copper ≤ 4%
• sulfur ≤ 10.10 ^-3 %,
• phosphorus <0.050%
• 40.10 ^-4 % ≤ total oxygen ≤ 120.10 ^-4 %,
• 0.1.10 ^-4 % ≤ aluminum ≤ 20.10 ^-4 %
• magnesium ≤ 5.10 ^-4 %
• 0.1.10 ^-4 % ≤ calcium ≤ 5.10 ^-4 %
• titanium ≤ 50.10 ^-4 %
• impurities inherent in manufacturing,

steel in which the oxide inclusions have, in the form of a vitreous mixture, the following weight proportions:

• 30% ≤ SiO ₂ ≤ 65%
• 5% ≤ MnO ≤ 40%
• 1% ≤ CaO ≤ 30%
• 0% ≤ MgO ≤ 10%
• 3% ≤ Al ₂ O ₃ ≤ 25%
• 0% ≤ Cr ₂ O ₃ ≤ 10%
  • the composition satisfying the following relationships:
  • If Mn <2%;
  • IM = 551 - 462 * (C% + N%) - 9.2 * Si% - 8.1 * Mn% - 13.7 * Cr% - 29 * (Ni% + Cu%) - 18.5 * Mo %, with
    • 150 ° C <IM <-55 ° C, and,
  • If Mn ≥ 2%;
  • JM = 551 - 462 * (C% + N%) - 9.2 * Si% - 20 * Mn% - 13.7 * Cr% - 29 * (Ni% + Cu%) - 18.5 * Mo%, with
    • 120 ° C <JM <- 55 ° C,
  the base wire being subjected to a wire drawing satisfying the following wire drawing conditions:
  • a cumulative strain rate ε greater than 6,
  • maintaining the wire, during drawing and between drawing operations, at a temperature below 650 ° C and preferably below 600 ° C, without annealing between the drawing passes.

• la composition comprend moins de 5.10^-3% de soufre.
• la composition comprend de 3% à 4% de cuivre.
• la composition comprend en outre moins de 3% de molybdène.
• on tréfile un fil de diamètre inférieur à 0,2 mm.
• on tréfile avec un taux de déformation ε supérieur à 6,6.
• avant ou entre les opérations de tréfilage, le fil subit, en outre, une opération de laitonnage.
• le fil-machine de base d'un diamètre supérieur à 5 mm, contient moins de 5 inclusions d'oxyde de plus de 10 µm d'épaisseur pour une surface de 1000 mm².
• le fil-machine de base d'un diamètre supérieur à 5 mm, contient moins de 10 inclusions de sulfure de plus de 5 µm d'épaisseur pour une surface de 1000 mm².

The other characteristics of the invention are:
before the drawing operation, the initial base wire is subjected to a so-called hyperhardening annealing at a temperature above 650 ° C.

• the composition comprises less than 5.10 ^-3 % of sulfur.
• the composition comprises from 3% to 4% of copper.
• the composition also comprises less than 3% molybdenum.
• a wire with a diameter of less than 0.2 mm is drawn.
• one draws with a rate of deformation ε greater than 6.6.
• before or between the drawing operations, the wire is further subjected to a brass plating operation.
• the basic wire rod with a diameter greater than 5 mm, contains less than 5 oxide inclusions of more than 10 μm thick for an area of 1000 mm ² .
• the basic wire rod with a diameter greater than 5 mm, contains less than 10 sulphide inclusions of more than 5 µm thickness for a surface of 1000 mm ² .

The invention also relates to the stainless steel used in the process.

The invention also relates to the application of the wire obtained by the process in the field of tire reinforcement.

The following description and the attached figures, all given to by way of nonlimiting example will make the invention well understood.

Figure 1 shows the cumulative strain rate ε that it is possible to reach by industrial drawing without annealing between the wire drawing operations, according to the IM index defined by the relation satisfying the composition, for alloys containing less than 2% of manganese.

Figure 2 shows the martensite content after wire drawing of the diameter 5.5 mm to diameters 0.18 mm, without intermediate annealing, from annealed wires of different compositions, according to the JM index.

Figure 3 shows the breaking load after drawing of 5.5 mm to 0.18 mm without intermediate annealing, depending on the JM index.

The invention relates to a process for producing a drawn wire, in particular tire reinforcement wire with a diameter of less than 0.3 mm by drawing a basic wire rod with a diameter greater than 5 mm or a previously drawn basic wire.

The drawing of a stainless steel reinforcement wire whose diameter varies between 0.1 and 0.3 mm, must satisfy a service holding point of view of fatigue in bending or in traction or in torsion as well as a humid environment or a combined environment wet and tired.

The fine wire is produced by drawing from a machine wire or a previously drawn steel wire. Due to the composition of the steel, after live drawing without intermediate annealing, the final drawn wire has improved tensile strength properties and sufficient residual ductility for assembly, for example, in the form of tablecloths, cables.

• carbone ≤ 40. 10^-3%
• azote ≤ 40. 10^-3%,

   le carbone et azote satisfaisant la relation C + N ≤ 50 10^-3%

• 0,2% ≤ silicium ≤ 1,0%,
• 0,2% ≤ manganèse ≤ 5%,
• 9% < nickel ≤ 12%,
• 15% ≤ chrome ≤ 20%
• 1,5% ≤ cuivre ≤ 4%
• soufre ≤ 10.10^-3%,
• phosphore < 0,050%
• 40.10^-4% ≤ oxygène total ≤ 120.10^-4%,
• 0,1.10^-4% ≤ aluminium ≤ 20.10^-4%
• magnésium ≤ 5.10^-4%
• 0,1.10^-4 % ≤ calcium ≤ 5.10^-4%
• titane ≤ 50.10^-4%
• des impuretés inhérentes à la fabrication,

   acier dans lequel les inclusions d'oxydes ont, sous forme de mélange vitreux, les proportions pondérales suivantes:

• 30% ≤ SiO₂ ≤ 65%
• 5% ≤ MnO ≤ 40%
• 1% ≤ CaO ≤ 30%
• 0% ≤ MgO ≤ 10%
• 3% ≤ Al₂O₃ ≤ 25%
• 0% ≤ Cr₂O₃ ≤ 10%.

According to the invention, the drawing is carried out with a stainless steel of the following weight composition:

• carbon ≤ 40. 10 ^-3 %
• nitrogen ≤ 40. 10 ^-3 %,

carbon and nitrogen satisfying the relationship C + N ≤ 50 10 ^-3 %

• 0.2% ≤ silicon ≤ 1.0%,
• 0.2% ≤ manganese ≤ 5%,
• 9% <nickel ≤ 12%,
• 15% ≤ chromium ≤ 20%
• 1.5% ≤ copper ≤ 4%
• sulfur ≤ 10.10 ^-3 %,
• phosphorus <0.050%
• 40.10 ^-4 % ≤ total oxygen ≤ 120.10 ^-4 %,
• 0.1.10 ^-4 % ≤ aluminum ≤ 20.10 ^-4 %
• magnesium ≤ 5.10 ^-4 %
• 0.1.10 ^-4 % ≤ calcium ≤ 5.10 ^-4 %
• titanium ≤ 50.10 ^-4 %
• impurities inherent in manufacturing,

steel in which the oxide inclusions have, in the form of a vitreous mixture, the following weight proportions:

• 30% ≤ SiO ₂ ≤ 65%
• 5% ≤ MnO ≤ 40%
• 1% ≤ CaO ≤ 30%
• 0% ≤ MgO ≤ 10%
• 3% ≤ Al ₂ O ₃ ≤ 25%
• 0% ≤ Cr ₂ O ₃ ≤ 10%.

This steel whose austenite partially transforms into deformation martensite near room temperature and with controlled inclusions, makes it possible to obtain, by drawing, a cumulative deformation capacity ε without intermediate annealing greater than 6.84. The term “cumulative deformation by drawing ε” is understood to mean, the value of the natural logarithm of the ratio of the initial sections and final. (ε = Log [So / Sf])

Si Mn < 2%;

IM = 551 - 462*( C% + N% ) - 9,2 * Si% - 8,1 * Mn% - 13,7 * Cr% 29*( Ni% + Cu% )- 18,5 * Mo% , avec

• 150°C < IM < -55°C, et,

Si Mn ≥ 2% ;

JM = 551 - 462 *(C% + N%) - 9,2 * Si% - 20 * Mn% - 13,7 * Cr% - 29 *(Ni% + Cu%) - 18,5 * Mo%, avec

• 120°C < JM < - 55°C.

According to the invention, the composition satisfies the following relationships:

If Mn <2%;

MI = 551 - 462 * (C% + N%) - 9.2 * Si% - 8.1 * Mn% - 13.7 * Cr% 29 * (Ni% + Cu%) - 18.5 * Mo% , with

• 150 ° C <IM <-55 ° C, and,

If Mn ≥ 2%;

JM = 551 - 462 * (C% + N%) - 9.2 * Si% - 20 * Mn% - 13.7 * Cr% - 29 * (Ni% + Cu%) - 18.5 * Mo%, with

• 120 ° C <JM <- 55 ° C.

This composition condition is intended to ensure the capacity strong reductions by wire drawing and hardening by work hardening adequate.

• un taux de déformation cumulé s supérieur à 6,
• un maintien du fil, pendant le tréfilage et entre les opérations de tréfilage, à une température inférieure à 650°C et de préférence inférieure à 600°C, sans recuit entre les passes de tréfilage.

the base wire is subjected to a wire drawing satisfying the following wire drawing conditions:

• a cumulative strain rate s greater than 6,
• maintaining the wire, during drawing and between drawing operations, at a temperature below 650 ° C and preferably below 600 ° C, without annealing between the drawing passes.

Without annealing means that no reheating of the wire to more than 650 ° C is applied between the beginning and the end of the drawing operations. A annealing at more than 650 ° C would have the effect of converting martensite into austenite and to eliminate the hardening by recrystallization.

The wire drawing is preferably carried out on a machine multipass, the wire being on the one hand lubricated with soap or lubricant liquid, and on the other hand, temperature controlled between 20 ° C and 180 ° C.

The wire can also be brass plated before or during wire drawing operations. The brass layer improves the ability to wire drawing and adhesion of the wire with the elastomers of the tires.

From a metallurgical point of view, it is known that certain elements alloy used in the composition of steels favor the appearance of the ferrite phase of metallographic structure of cubic type center. These elements are called alpha-genes. Among these are the chromium, molybdenum, silicon.

Other elements known as gamma-genes favor the appearance of austenite phase of metallographic structure of cubic type with faces centered. Among these elements are carbon, nitrogen, manganese, copper, nickel.

It has been noted that the compositions forming a quantity excessive wire drawing martensite becomes brittle and brittle wire drawing. This limit quantity of martensite is a function of the content total carbon and nitrogen of the steel and is of the order of 90% for a total carbon and nitrogen content of less than 0.030%, of 70% for a total carbon and nitrogen content less than or equal to 0.050%, and 30% for a total carbon and nitrogen content between 0.050% and 0.1%.

Si Mn < 2%;

IM = 551 - 462*( C% + N% ) - 9,2 * Si% - 8,1 * Mn% - 13,7 * Cr% - 29*( Ni% + Cu% )- 18,5 * Mo% , avec

• 150°C < IM < -55°C, et,

Si Mn ≥ 2% ;

JM = 551 - 462 *(C% + N%) - 9,2 * Si% - 20 * Mn% - 13,7 * Cr% - 29 *(Ni% + Cu%) - 18,5 * Mo%, avec

• 120°C < JM < - 55°C.

According to the invention, the steel has a carbon and nitrogen content of less than or equal to 0.050%, the drawing conditions satisfying the following relationship:

If Mn <2%;

IM = 551 - 462 * (C% + N%) - 9.2 * Si% - 8.1 * Mn% - 13.7 * Cr% - 29 * (Ni% + Cu%) - 18.5 * Mo %, with

• 150 ° C <IM <-55 ° C, and,

If Mn ≥ 2%;

JM = 551 - 462 * (C% + N%) - 9.2 * Si% - 20 * Mn% - 13.7 * Cr% - 29 * (Ni% + Cu%) - 18.5 * Mo%, with

• 120 ° C <JM <- 55 ° C.

It has also been noted that the compositions having an index MI greater than the value determined above and a total content of carbon and nitrogen of the order of 0.040% become brittle before reach the wire drawing to the final diameter.

Likewise, the presence of an excessive amount of silicon, i.e. in an amount greater than 1%, has the effect of weaken the wire in the work-hardened state by drawing in the presence of a quantity significant martensite.

The composition of the stainless steel according to the invention, containing more than 9% nickel, more than 1.5% copper, more than 15% chromium, a total carbon and nitrogen content of less than 0.050%, a content in Mn less than 2% with an IM index less than -55 ° C or a Mn content greater than or equal to 2% with a JM index less than - 55 ° C, can be drawn to the final diameter with a breakage rate reduced, the wire retaining mechanical characteristics which allow its use in the field of tire reinforcement.

When the Mn content is less than 2%, the IM index must be in the range -150 ° C and -55 ° C. Indeed, if lM is lower at -150 ° C, the amount of martensite formed remains small, for example less than 10%, and the breaking load cannot reach values higher than 2200 MPa, even after drawing with a cumulative deformation ε close to 8. In the same way, when the Mn content is greater than or equal to 2%, the JM index must be between - 120 ° C and - 55 ° C. When JM is below -120 ° C, the amount of martensite is less than 25% and the breaking load does not can exceed 2200 MPa even after a cumulative reduction of around of 8.

This remark justifies the limit of chromium content unless 20% and that of total copper and nickel less than 16%.

A copper content greater than 4% generates segregation at solidification and ruptures or defects during hot rolling.

The process applied to the drawing of stainless steel according to the invention makes it possible to obtain a wire comprising an excellent fatigue strength measured by rotary bending with an endurance stress of 2.10 ⁶ cycles greater than 1000 MPa.

The yarn obtained contains less than 75% of austenite or more than 25% martensite. The steel used has a slightly unstable austenite with a total carbon and nitrogen content of less than 0.050%.

To obtain a breaking strength of approximately 2400 MPa it it is necessary to have a high quality basic inclusion wire.

Indeed, in the field of wire drawing, it is known that for obtain a wire with a diameter of less than 0.3 mm, said to be fine, from the drawing of a wire rod or of a previously drawn basic wire, the stainless steel used must not include an inclusion whose size generates the breakage of wire during the drawing.

In the production of austenitic stainless steels, as for all other steels produced with conventional means and economically suitable for mass production, the presence of inclusions of the sulphide or oxide type is systematic and irremediable. In fact, stainless steels may, in the liquid state, contain in solution, due to the production processes, oxygen and sulfur contents of less than 1000 × 10 ^-4 %. During the cooling of the steel in liquid or solid state, the solubility of the oxygen and sulfur elements decreases and the energy of formation of the oxides or sulphides is reached. We then witness the appearance of inclusions formed on the one hand, of oxide type compounds containing oxygen atoms and alloying elements eager to react with oxygen such as calcium, magnesium, aluminum, silicon, manganese, chromium, and on the other hand, sulfide-like compounds containing sulfur atoms and alloying elements eager to react with sulfur such as manganese, chromium, calcium, magnesium. There may also appear inclusions which are mixed compounds of the oxysulfide type.

It is possible to reduce the quantity of oxygen contained in stainless steel by using powerful reducers such as magnesium, aluminum, calcium, titanium or a combination of several of them, but these reducers all lead to the creation of inclusions. rich in MgO, Al ₂ O ₃ , CaO or TiO ₂ which are in the form of crystallized refractories, hard and undeformable under the rolling conditions of stainless steel. The presence of these inclusions generates incidents of wire drawing and fatigue breaks on products made with stainless steel.

According to the invention the production of a stainless steel having a selected inclusiveness, allows the production of wire rod or basic pre-drawn wire, wire used according to the invention for drawing tire reinforcement wire with a diameter of less than 0.3 mm or the production of parts subject to fatigue.

• 30% ≤ SiO₂ ≤ 65%
• 5% ≤ MnO ≤ 40%
• 1% ≤ CaO ≤30%
• 0% ≤ MgO ≤ 10%
• 3% ≤ Al₂O₃ ≤ 25%
• 0% ≤ Cr₂O₃ ≤10%

The invention relates to a stainless steel which includes inclusions of oxides in the form of a vitreous mixture, and whose weight proportions are as follows:

• 30% ≤ SiO ₂ ≤ 65%
• 5% ≤ MnO ≤ 40%
• 1% ≤ CaO ≤30%
• 0% ≤ MgO ≤ 10%
• 3% ≤ Al ₂ O ₃ ≤ 25%
• 0% ≤ Cr ₂ O ₃ ≤10%

In an example of application of the invention, a steel A according to the invention contains in its composition by weight 19.10 ^-3 % of carbon, 23.10 ^-3 % of nitrogen, 0.53% of silicon, 0.72% of manganese, 17.3% chromium, 9.3% nickel, 3.1% copper, 0.055% molybdenum, 4.10 ^-3 % sulfur, 22.10 ^-3 % phosphorus, 72.10 ^-4 % total oxygen , 5.10 ^-4 % total aluminum, 2.10 ^-4 % magnesium, 2.10 ^-4 % calcium, 11.10 ^-4 % titanium. Its IM stability index is -77 ° C. The steel is produced in an electric oven and then in the AOD converter, and continuously cast in section of 205 mm by 205 mm then hot rolled in wire of 5.5 mm in diameter.

At this stage of the process, the steel A was subjected to a metallographic examination by cutting in the longitudinal direction, which revealed the presence, on a surface of 1000 mm ² , of 8 inclusions of thickness between 5 and 10 µm and an inclusion of 12 µm.

After recrystallization annealing at 1050 ° C in a crown and water cooling, the wire is pickled and drawn without annealing intermediate up to the diameter of 0.18 mm successively on several multi-pass machines. The breaking load of the drawn wire is then 2650 MPa and the wire has a necking after traction.

It was found that basic wires with a diameter of 5.5 mm, of composition B and C presented in table 1 below, could not be drawn without excessive breakage and embrittlement, the embrittlement resulting in an absence of necking in traction.

For wire drawing with compositions B and C, it could not be obtained respectively that wires of diameters greater than or equal to 1.0 mm and 0.4 mm.

This observation is highlighted, in terms of cumulative deformation ε and stability index lM in Table 2, in the case of direct wire drawing from a base wire of 5.5 mm, without annealing. during wire drawing, without breaking in high numbers. Steel IM ° C Drawn diameter mm ε Breaking load MPa % martensite on drawn wire AT -77 0.18 6.84 2650 68 B -26 1.0 3.41 1980 30 VS -49 0.4 5.24 2400 72

Steel B cannot be used to draw thin wire. diameter less than 0.3 mm live from a diameter of 5.5 mm. Its IM stability index is high and moreover its overall content in carbon and nitrogen gives it a fragile character in the drawn state in below the diameter of 1 mm.

Steel C can be drawn to a diameter of 0.4 mm from a wire with a diameter of 5.5 mm. For more advanced drawing, it becomes fragile with the presence in its composition of a large amount of martensite.

Steel A according to the invention can be drawn from 5.5 mm to 0.18 mm without the process generating a brittleness of the yarn obtained. The wire thus produced has a breaking load ensuring use in the area of tire reinforcement wire.

In another example of drawing, annealed wires of 5.5 mm diameter were used, the compositions of which are given in Table 3.

The wires were drawn in 12 successive passes with soap up to a diameter of 1 mm, then in 6 soap passes with a diameter of 0.48 mm, then in 9 soap passes with a diameter of 0.18 mm, all without any annealing from the initial state. At this point, the final product has been subjected to tensile and martensite rate measurements by the saturation magnetization method.

Table 4 presents for each of the compositions the values of the indices IM and JM, as well as the breaking loads Rm and the martensite contents of the final product. Steel IM JM Rm (MPa) Martensite D -74 -81 2644 90% E -110 -156 1810 4.4% F -159 -205 1791 1.2% G -73 -119 2072 27%

Figure 2 shows the martensite content of the diameter wires 0.18 mm depending on JM.

Figure 3 shows the breaking loads of the wires 0.18 mm diameter depending on JM.

The JM index is particularly relevant for reporting on the evolution of breaking loads and martensite contents.

Wires with a JM index of less than - 120 ° C will have after extensive drawing corresponding to ε = 6.84 without annealing intermediate, low breaking loads, i.e. less than 2200 Mpa.

Wires with a JM index greater than - 55 ° C will present, for rejection rates ε greater than 6, without intermediate annealing, more 90% martensite and fragile behavior.

In a third example of application, we implemented a annealed wire with an initial diameter of 5.5 mm from steel D, the composition of which is shown in Table 3.

The wires were drawn in 12 passes, with soap, to the diameter 1mm, without intermediate annealing. We practiced on this diameter wire 1mm various treatments at temperatures between 500 ° C and 700 ° C, for total durations from 2.5 seconds to 10 seconds. Of such treatments may be necessary after deposits electrolytic thin films of copper or zinc to obtain by diffusion a homogeneous layer of brass, commonly used as bonding layer of rubber in the manufacture of tires.

The martensite contents of the sections of heat-treated wires and their breaking load were then measured. The measured values are presented in Table 5 with the values of the 1 mm reference wire not treated. Temperature - treatment ° C dry duration Rm Mpa martensite% Untreated 1780 46 500 2.5 5 10 1899 48 550 2.5 1847 46 5 1839 44 10 1650 39 600 2.5 1677 37 5 1502 27 10 1409 18 650 2.5 1378 22 5 1354 9 10 1292 3

It is observed that, for temperatures below 550 ° C., the treatment substantially retains the initial amount of martensite and may cause slight hardening for short times. AT 600 ° C, and for a shorter duration of 2.5 seconds, one part martensite minority has disappeared and the wire has softened slightly. For a period of 5 or 10 seconds at the temperature of 600 ° C, softening becomes more important. At 650 ° C, martensite tends mainly to disappear and the steel of the wire softens strongly.

From these examples, it is concluded that in the process according to the invention, the wires may be subjected, between several operations of wire drawing, heat treatments at temperatures below 650 ° C and preferably less than 600 ° C without causing a excessive disappearance of martensite or softening, which would harm obtaining very high mechanical properties as a wire wireframe having undergone total deformation by wire drawing ε greater than 6. Conversely, any treatment, even a short one, at a higher temperature at 650 ° C strongly softens the steel of the drawn wire at an intermediate stage or final, which is considered annealing.

Carbon, nitrogen, chromium, nickel, manganese, silicon are the usual elements for obtaining a steel austenitic stainless.

The manganese, chromium, sulfur contents in proportion are chosen to generate deformable sulfides of good composition determined.

The composition intervals of the silicon and manganese elements, in proportion, ensure according to the invention, the presence of inclusions of the silicate type, rich in SiO ₂ and containing a non-negligible amount of MnO, deformable by hot rolling.

The silicon has a content of between 0.2%, which corresponds to a residual due to processing and 1%, which is the content beyond which it appears excessive embrittlement of the cold drawn wire.

Mobybdenum can be added to the composition of steel stainless to improve corrosion resistance.

Copper is added to the composition of the steel according to the invention because it improves the cold deformation properties and therefore stabilizes the austenite. However the copper content is limited to 4% to avoid difficulties of hot transformation because copper significantly lowers the upper heating temperature limit steel before rolling.

The intervals in total oxygen, aluminum and calcium make it possible, according to the invention, to obtain inclusions of the manganese silicate type containing a non-zero fraction of Al ₂ O ₃ and CaO. In particular, the overall aluminum and calcium contents are each greater than 0.1 × 10 ^-4 % so that the desired inclusions contain more than 1% of CaO and more than 3% of Al ₂ O ₃ .

The values of the total oxygen contents according to the invention are between 40.10 ^-4 % and 120.10 ^-4 %.

For a total oxygen content of less than 50.10 ^-4 %, the oxygen fixes the elements magnesium, calcium, aluminum and does not form the inclusion of oxides rich in SiO ₂ and MnO.

For a total oxygen content greater than 120.10 ^-4 %, there will be in the composition of the oxides more than 10% of Cr ₂ O ₃ , which promotes crystallization, which one seeks to avoid.

The calcium content is less than 5.10 ^-4 % so that the desired inclusions do not contain more than 30% CaO.

The aluminum content is less than 20.10 ^-4 % to avoid that the desired inclusions contain more than 25% of Al ₂ O ₃ , which also promotes crystallization.

It is conceivable, after having carried out according to a process conventional and economical, a steel containing inclusions of oxide and sulfide types, to refine it to remove these inclusions using slow and unprofitable remelting processes economically such as vacuum reflow processes (Vacuum Argon Remelting) or slag remelting (Electro Slag Remelting).

These reflow processes only eliminate partially, by decantation in the puddle of liquid, the inclusions already present without modifying their nature and composition.

The invention relates to stainless steel containing inclusions of chosen composition obtained voluntarily, the composition being related to the overall composition of the steel, so that the physical properties of these inclusions favor their deformation during hot transformation of steel.

According to the invention, stainless steel contains inclusions of determined composition which have their softening point close to the rolling temperature of the steel and such that the appearance of crystals harder than steel at the rolling temperature. as in particular the defined compounds: SiO ₂ , in the form of tridymite, christobalite, quartz; 3CaO-SiO ₂ ; CaO; MgO; Cr ₂ O ₃ ; anorthite, mullite, gehlenite, corundum, spinel of the Al ₂ O ₃ -MgO or Al ₂ O ₃ -Cr ₂ O ₃ -MnO-MgO type; CaO-Al ₂ O ₃ ; CaO-6Al ₂ O ₃ ; CaO-2Al ₂ O ₃ , TiO ₂ is inhibited.

According to the invention, the steel mainly contains inclusions of oxide of composition such as this form a vitreous mixture or amorphous during all the successive operations of setting in form of steel. The viscosity of the inclusions chosen is sufficient to that the growth of crystallized oxide particles in the inclusions resulting from the invention is completely inhibited by the fact that, in an oxide inclusion, the short distance diffusion is weak and convective movements are very limited. These inclusions remained glass in the temperature range of heat treatments of steel also have a higher hardness and modulus of elasticity weak than crystallized inclusions of corresponding composition. Thus inclusions can be further distorted, overwritten and lengthened, during wire drawing operations and the concentration of stresses in the vicinity of the inclusions is greatly reduced, which significantly reduces the risk of developing, for example, fatigue cracks or breakages in wire drawing.

According to the invention, stainless steel contains inclusions of oxides of defined composition such as their viscosity in the hot rolling temperature range of steel is not too high. Therefore, the flow constraint of inclusion is significantly lower than that of steel under the conditions of hot rolling whose temperatures are generally included between 800 ° C and 1350 ° C. Thus the oxide inclusions are deformed into same time as steel during hot rolling and therefore after rolling, these inclusions are perfectly elongated, and thick very low which avoids any breakage problem during a wire drawing operation.

The inclusions described above are according to the invention, carried out with the classic and very productive means of electric steelworks for stainless steels such as electric furnace, AOD or VOD converter, pocket metallurgy and continuous casting.

• 30% ≤ SiO₂ ≤ 65%
• 5% ≤ MnO ≤ 40%
• 1% ≤ CaO ≤ 30%
• 0% ≤ MgO ≤ 10%
• 3% ≤ Al₂O₃ ≤ 25%
• 0% ≤ Cr₂O₃ ≤ 10%

The oxide inclusions below having the favorable properties described are according to the invention composed of a vitreous mixture of SiO ₂ , MnO, CaO, Al ₂ O ₃ , MgO and Cr ₂ O _{3 ,} and, optionally, trace of FeO and or of TiO ₂ , in the following weight proportions:

• 30% ≤ SiO ₂ ≤ 65%
• 5% ≤ MnO ≤ 40%
• 1% ≤ CaO ≤ 30%
• 0% ≤ MgO ≤ 10%
• 3% ≤ Al ₂ O ₃ ≤ 25%
• 0% ≤ Cr ₂ O ₃ ≤ 10%

If the SiO ₂ content is less than 30%, the viscosity of the oxide inclusions is too low and the growth mechanism of oxide crystals is not inhibited. If SiO ₂ is higher than 65%, very hard harmful particles of silica are formed in the form of trydimite or christobalite or quartz.

The MnO content, between 5% and 40% makes it possible to greatly lower the softening point of the mixture of oxides containing in particular SiO ₂ , CaO, Al ₂ O ₃ , and promotes the creation of inclusions which remain in a state vitreous under the rolling conditions of the steel according to the invention.

For a CaO content of less than 1%, crystals of MnO-Al ₂ O ₃ or of mullite are formed. When the CaO content is greater than 30%, crystals of CaO-SiO ₂ or (Ca, Mn) O-SiO _{2 are formed} . For an MgO content greater than 10%, crystals of MgO are formed; 2MgO-SiO ₂ ; MgO-SiO ₂ ; Al ₂ O ₃ -MgO, which are extremely hard phases.

If Al ₂ O ₃ is less than 3%, wollastonite crystals are formed and when Al ₂ O ₃ is greater than 25%, crystals of mullite, anorthite, corundum and spinels, especially of Al ₂ type, appear O ₃ -MgO or Al ₂ O ₃ -Cr ₂ O ₃ -MgO-MnO or alternatively aluminates of the CaO-6Al ₂ O ₃ or CaO-2Al ₂ O ₃ or CaO-Al ₂ O _{3 type} , or gehlenite .

5% < Cr < 30%

30% < Mn < 60 %

35 % <S< 45%

With more than 10% of Cr ₂ O ₃ also appearing hard crystals of Cr ₂ O ₃ or Al ₂ O ₃ -Cr ₂ O ₃ -MgO-MnO, CaO-Cr ₂ O ₃ , MgO-Cr ₂ O ₃ .
According to one form of the invention, the sulfur content must be less than 0.010% in order to obtain sulphide inclusions of thickness not exceeding 5 μm on the rolled product. In fact, inclusions of the manganese and chromium sulfide type are perfectly deformable when hot under the following conditions:

5% <Cr <30%

30% <Mn <60%

35% <S <45%

Oxides and sulfides inclusions are generally considered harmful with regard to the properties of use in the in the field of fine wire drawing and in the field of holding fatigue, in particular, in bending and / or torsion.

For an observed inclusion, we define a form factor which is the ratio of length to thickness. The form factor of inclusions in the wires can reach 10 or 20 and as a result, the thickness of the inclusion is extremely small.

These inclusions are not harmful to applications. fine wire drawing with a diameter of less than 0.3 mm or parts subject to fatigue such as springs, reinforcement pneumatic.

The inclusive characteristics are materialized by the fact, on a surface of 1000 mm ² sampled from wire rod with a diameter greater than or equal to 5 mm of less than 5 inclusions of oxides with a thickness of more than 10 μm. The sulfide inclusions are, in number, less than 10 having a thickness of more than 5 μm, for an area of 1000 mm ² .

• une faible tendance à la formation de martensite-formation en quantité suffisante pour durcir l'acier, et en quantité insuffisante pour provoquer une fragilisation du fil après tréfilage,
• une consolidation très progressive de telle sorte que la résistance à la rupture peut être comprise entre 2200 MPa et 3000 MPa pour un fil tréfilé de 0,18 mm, tréfilé depuis 5,5 mm sans recuit ou pour tout autre tréfilé obtenu avec un taux de réduction cumulé supérieur à 6 sans recuit intermédiaire,
• des inclusions contrôlées qui assurent un tréfilage avec peu de casses.

The method according to the invention from a steel of composition optimized for cold deformation and drawing in fine wire ensures

• a slight tendency to form martensite-formation in an amount sufficient to harden the steel, and in an amount insufficient to cause embrittlement of the wire after drawing,
• a very progressive consolidation so that the breaking strength can be between 2200 MPa and 3000 MPa for a drawn wire of 0.18 mm, drawn from 5.5 mm without annealing or for any other drawn wire obtained with a rate of cumulative reduction greater than 6 without intermediate annealing,
• controlled inclusions which ensure drawing with little breakage.

The wire according to the invention can be used, in its hardened state by work hardening due to wire drawing, or else after heat treatment of aging between 300 ° C and 550 ° C, which is likely to harden it again by precipitation of epsilon copper, for manufacturing, by for example, springs or reinforcements of tires.

It can also undergo, at the final diameter, a softening annealing and be used for making various objects such as woven threads or knitted, woven hoses, filters, etc.

Claims (15)

Process for the preparation of a drawn wire, in particular a tire reinforcement wire with a diameter less than 0.3 mm by drawing a basic machine wire with a diameter greater than 5 mm or a previously drawn wire base of a steel of the following weight composition: carbon ≤ 40. 10 ^-3 % nitrogen ≤ 40. 10 ^-3 %, carbon and nitrogen satisfying the relationship C + N ≤ 50 10 ^-3 % 0.2% ≤ silicon ≤ 1.0%, 0.2% ≤ manganese ≤ 5%, 9% <nickel ≤ 12%, 15% ≤ chromium ≤ 20% 1.5% <copper <4% sulfur ≤ 10.10 ^-3 %, phosphorus <0.050% 40.10 ^-4 % ≤ total oxygen ≤ 120.10 ^-4 %, 0.1.10 ^-4 % ≤ aluminum ≤ 20.10 ^-4 % magnesium ≤ 5.10 ^-4 % 0.1.10 ^-4 % ≤ calcium ≤ 5.10 ^-4 % titanium ≤ 50.10 ^-4 % impurities inherent in manufacturing, steel in which the oxide inclusions have, in the form of a vitreous mixture, the following weight proportions: 30% ≤ SiO ₂ ≤ 65% 5% ≤ MnO ≤ 40% 1% ≤ CaO ≤ 30% 0% ≤ MgO ≤ 10% 3% ≤ Al ₂ O ₃ ≤ 25% 0% ≤ Cr ₂ O ₃ ≤10% the composition satisfying the following relationships: If Mn <2%; IM = 551 - 462 * (C% + N%) - 9.2 * Si% - 8.1 * Mn% - 13.7 * Cr% - 29 * (Ni% + Cu%) - 18.5 * Mo %, with 150 ° C <IM <-55 ° C, and, If Mn ≥ 2%; JM = 551 - 462 * (C% + N%) - 9.2 * Si% - 20 * Mn% - 13.7 * Cr% - 29 * (Ni% + Cu%) - 18.5 * Mo%, with 120 ° C <JM <- 55 ° C. the base wire being subjected to a wire drawing satisfying the following wire drawing conditions: a cumulative strain rate ε greater than 6, maintaining the wire, during drawing and between drawing operations, at a temperature below 650 ° C, and preferably at a temperature below 600 ° C, without annealing between the drawing passes. Process according to claim 1, characterized in that the composition comprises less than 5.10 ^-3 % of sulfur. Method according to claim 1, characterized in that the composition includes 3% to 4% copper. Method according to claim 1, characterized in that the composition further comprises less than 3% molybdenum. Method according to one of claims 1 to 4 characterized in what a wire with a final diameter less than 0.2 mm is drawn. Method according to one of claims 1 to 5 characterized in which is drawn with a cumulative deformation rate ε greater than 6.6. Method according to one of claims 1 to 6 characterized in that before or between the drawing operations, the wire undergoes, moreover, a brass plating operation. Method according to claim 1, characterized in that the base wire with a diameter greater than or equal to 5 mm, contains less than 5 oxide inclusions more than 10 µm thick for an area of 1000 mm ² . Method according to claim 1, characterized in that the base wire with a diameter greater than or equal to 5 mm, contains less than 10 sulphide inclusions more than 5 µm thick for an area of 1000 mm ² . Stainless steel for making drawn wire, in particular tire reinforcement wire with a diameter of less than 0.3 mm obtained by drawing with a wire rod with a diameter greater than 5 mm or with a basic drawn wire characterized in the following weight composition: carbon ≤ 40. 10 ^-3 % nitrogen ≤ 40. 10 ^-3 %, carbon and nitrogen satisfying the relationship C + N ≤ 50 10 ^-3 % 0.2% ≤ silicon ≤ 1.0%, 0.2% ≤ manganese ≤ 5%, 9% <nickel <12%, 15% ≤ chromium ≤ 20% 1.5% <copper <4% sulfur ≤ 10.10 ^-3 %, phosphorus <0.050% 40.10 ^-4 % ≤ total oxygen ≤ 120.10 ^-4 %, 0.1.10 ^-4 % ≤ aluminum ≤ 20.10 ^-4 % magnesium ≤ 5.10 ^-4 % 0.1.10 ^-4 % ≤ calcium ≤5.10 ^-4 % titanium ≤ 50.10 ^-4 % impurities inherent in manufacturing, the composition satisfying the following relationships: If Mn <2%; IM = 551 - 462 * (C% + N%) - 9.2 * Si% - 8.1 * Mn% - 13.7 * Cr% - 29 * 1 Ni% + Cu%) - 18.5 * Mo %, with 150 ° C <IM <-55 ° C and, If Mn ≥ 2%; JM = 551 - 462 * (C% + N%) - 9.2 * Si% - 20 * Mn% - 13.7 * Cr% - 29 * (Ni% + Cu%) - 18.5 * Mo%, with 120 ° C <JM <- 55 ° C, steel in which the oxide inclusions have, in the form of a vitreous mixture, the following weight proportions: 30% ≤ SiO ₂ ≤ 65% 5% ≤ MnO ≤ 40% 1% ≤ CaO ≤ 30% 0% ≤ MgO ≤ 10% 3% ≤ Al ₂ O ₃ ≤ 25% 0% ≤ Cr ₂ O ₃ ≤ 10% Steel according to claim 10, characterized in that the composition comprises less than 5.10 ^-3 % of sulfur. Steel according to claim 10, characterized in that the composition includes 3% to 4% copper. Steel according to claim 10, characterized in that the composition further comprises less than 3% molybdenum. Steel wire obtained by the process according to Claims 1 to 9 in particular, tire reinforcement wire with a diameter less than 0.3 mm obtained by drawing a basic machine wire with a diameter greater than 5 mm or a wire previously drawn base, characterized by the following weight composition: carbon ≤ 40. 10 ^-3 % nitrogen ≤ 40. 10 ^-3 %, carbon and nitrogen satisfying the relationship C + N ≤ 50 10 ^-3 % 0.2% ≤ silicon ≤ 1.0%, 0.2% ≤ manganese ≤ 5%, 9% <nickel ≤ 12%, 15% <chromium <20% 1.5% ≤ copper ≤ 4% sulfur ≤ 10.10 ^-3 %, phosphorus <0.050% 40.10 ^-4 % ≤ total oxygen ≤ 120.10 ^-4 %, 0.1.10 ^-4 % ≤ aluminum ≤ 20.10 ^-4 % magnesium ≤ 5.10 ^-4 % 0.1.10 ^-4 % ≤ calcium ≤ 5.10 ^-4 % titanium ≤ 50.10 ^-4 % impurities inherent in manufacturing, the composition satisfying the following relationships: If Mn <2%; IM = 551 - 462 * (C% + N%) - 9.2 * Si% - 8.1 * Mn% - 13.7 * Cr% - 29 * (Ni% + Cu%) - 18.5 * Mo %, with 150 ° C <IM <-55 ° C, and, If Mn ≥ 2%; JM = 551 - 462 * (C% + N%) - 9.2 * Si% - 20 * Mn% - 13.7 * Cr% - 29 * (Ni% + Cu%) - 18.5 * Mo%, with 120 ° C <JM <- 55 ° C, steel in which the oxide inclusions have, in the form of a vitreous mixture, the following weight proportions: 30% ≤ SiO ₂ ≤ 65% 5% ≤ MnO ≤ 40% 1% ≤ CaO ≤ 30% 0% ≤ MgO ≤ 10% 3% ≤ Al ₂ O ₃ ≤ 25% 0% ≤ Cr ₂ O ₃ ≤10% the wire having a diameter less than 0.3 mm. Steel wire according to claim 14 characterized in that its breaking load is greater than or equal to 2200MPa.

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