EP2419543A1 - Powder for a wire cored with sulfur, cored wire and method for manufacturing a cored wire using same - Google Patents

Abstract

The invention relates to a powder for a cored wire for alloying a liquid metal bath, made of particles consisting of at least 95% of sulfur, characterized in that the granulometric population is defined by: 1 µm = d10 = 340 µm; 200 µm = d50 = 2000 µm; and 500 µm = d90 = 2900 µm. The invention also relates to a cored wire, characterized in that it contains the above-mentioned powder and in that the compaction rate of said powder inside the wire is greater than or equal to 85%. The invention further relates to a method for manufacturing a wire cored with sulfur for alloying liquid metal baths.

Description

 Powder for sulfur-cored wire, flux-cored wire and method of manufacturing flux-cored wire using it

The invention relates to the field of metallurgy, and more specifically to cored wires by means of which sulfur additions are made in baths of liquid metal, especially steel and metal alloys.

The wire filled with sulfur powder is injected into the liquid steel to improve the machinability of the final steel by promoting the formation of brittle chips that evacuate more quickly during machining parts. Sulfur also reduces the wear of cutting tools due to the lubrication effect provided by the non-metallic inclusions that contain it, and improves the surface condition of these tools. The addition by cored wire provides a satisfactory accuracy on the amount of sulfur added, especially if it must be relatively small compared to the total mass of liquid metal concerned.

Such a cored wire is composed of a metal envelope containing a compacted sulfur-based powder. The manufacture of this wire, as for flux-cored son containing other types of additives such as silico-calcium, can typically start with a gravity flow of powdered sulfur on a moving metal strip. The band must have a composition compatible with that of the metal to be additivé. It is made of steel when the sulfur has to be added to a bath of liquid steel. The strip is then welded or folded back on itself by mechanical profiling by means of a roller device, to obtain a cored wire which is then calibrated to the desired diameter. Other processes for preparing cored wire are known, some of which involve extrusion and cold rolling techniques. The invention applies primarily to son manufactured by mechanical profiling, but it is not a priori excluded to use the powder according to the invention will be described to manufacture filled son by other methods.

The production of the cored wire involves several types of mechanical stresses, including shear stresses. The sulfur powder undergoes various deformations during the manufacture of the wire, and this according to its intrinsic mechanical characteristics. By applying these constraints, the powder is densified cold at various gradients. The origin and processes of sulfur extraction are very diverse (extraction in the native state, from minerals, petroleum products, etc.). Sulfur exists under different crystallized allotropic varieties, including orthorhombic α and monoclinic β sulfur. The sulfur that makes up the cored wire used in metallurgy, in particular for steel and ferrous alloys, conventionally has a purity greater than 95%, generally greater than 98%, or even 99.5%. A wire filled with sulfur powder conventionally has an outer diameter of 5 to 25 mm and an envelope thickness of 0.1 to 2 mm.

The sulfur powder contained in the cored wire is the result of several grinding operations. This results in a particle size distribution specific to the industrial process for obtaining powders.

For the user, it is interesting that the linear density of the sulfur contained in the cored wire is as high as possible. Indeed, increasing the linear density of the cored wire brings to the user several technical and economic advantages:

a substantial saving on the costs of manufacturing the cored wire, therefore on its purchase price;

- saving on logistics costs when transporting the cored wire;

a saving on the storage space of the cored wire coils; a better diffusion of the material contained in the flux-cored wire within the liquid metal by virtue of the presence of fine particles;

a limitation of the addition of gas injected inside the baths of the liquid metals in order to carry out agitation of the bath favoring the dilution of the additives;

- absence of binding agent and / or lubrication of the original material.

To date, to the knowledge of the applicant, the optimization of the filling of the cored wire has not been the subject of specific work. Each commercial cored wire therefore has a linear density which is a function of the manufacturing process and the initial physical characteristics of the powders. The object of the invention is to provide a sulfur-cored wire manufacturing method for optimizing the linear density of the cored wire.

For this purpose, the subject of the invention is a powder for cored wire intended for the alloying of a liquid metal bath, formed of particles composed of at least 95% sulfur, characterized in that its particle size population is defined by:

1 μm <d10 <340 μm;

200 μm <d50 <2000 μm; 500 μm <d90 <2900 μm.

A preferred variant of this powder is characterized in that: - 20 μm <d10 <300 μm;

800 μm <d50 <1900 μm;

- 2000 μm <d90 <2700 μm. The powder may result from the homogeneous mixture of two particle size populations 1 and 2, the particle size population 1 representing between 50 and 90% by weight of the mixture and the population 2 representing between 10 and 50% by weight of the mixture, said populations being defined by: Population 1: - 350 μm <d10 <1400 μm

- 650 μm <d50 <2200 μm

- 1000 μm <d90 <3000 μm Population 2:

- 1 μm <d10 <250 μm - 50 μm <d50 <500 μm

- 100 μm <d90 <800 μm d10, d50 and d90 being the equivalent diameters of the particles for which the cumulative distribution values are respectively 10, 50 and 90% by mass. The population 1 optimally represents 65 to 75% by weight of the mixture and the population 2 optimally represents 25 to 35% by weight of the mixture.

The subject of the invention is also a sulfur-filled wire intended for alloying a metal bath, characterized in that it contains a powder of the above type, and in that the compaction ratio of this powder is inside the yarn is greater than or equal to 85%.

The invention also relates to a process for manufacturing a sulfur-filled wire for the alloying of liquid metal baths, characterized in that it comprises the following steps: - Preparation of a powder of the above type;

gravitational flow of said powder on a metal strip;

- Welding or mechanical folding of said strip on itself to form the wire and profiling of this wire to the selected diameter, so as to obtain a wire whose compactness of the powder is greater than or equal to 85%.

As will be understood, the invention is based on a particular constitution of the powder, in that it has a precise particle size distribution, resulting or that can result from a mixture in determined proportions of two defined and differentiated particle size populations , although it is not strictly excluded that they may sometimes have some recovery.

The advantage of the invention is to introduce a maximum of powder mass within this flux-cored wire, with constant section. This makes it possible to reduce the intergranular porosity of the final compact mixture. A granular assembly may be characterized by its ability to rearrange due to flow or vibration. This set rearranges more or less well, depending on the physical characteristics of the particles and the particle bed: the particle size, the true density of the powder material, the morphology of the particles, the compressibility of the granular set, the particle size distribution.

The quality of the granular stack after flow and / or vibration influences the filling level of the cored wire. The granular rearrangement is more or less random. It depends mainly on the morphology, size and surface appearance of the particles. The innovation provided by the invention consists of optimizing and improving this stack in order to obtain the best level of filling possible while maintaining the final mechanical characteristics of the wire. It is also necessary to take into account the intrinsic properties of the filling material, which make it that it will react in a particular way to the stresses to which it will be subjected during the manufacture of the wire, in particular during the stages of closing and welding or profiling of the envelope. For this reason in particular, the problem of optimizing the linear density of the final cored wire can not have a solution unique, valid regardless of the filling material. This optimization must be fine-tuned according to the exact nature of the material.

By a succession of experiments and different analyzes of the results obtained, the inventors have determined what they think is the best particle size distribution for optimal filling of the flux-cored wire with sulfur particles. This particle size distribution develops a dense stack, while providing an easy flow of the powder bed during the deposition of the powder on the metal strip during the manufacture of the wire. The flowability of this granular set is characterized by the Hausner index and the compressibility index. The compressibility of a granular medium is related to the flow properties, because it is representative of the intergranular forces and therefore, indirectly of the cohesion of the medium. The higher the inter-particle forces, the more the medium will be able to compress if the shocks applied are sufficiently energetic. The compressibility index is determined by the ratio of the densities aerated and packed:

Compressibility = (Ptassée - Paéré) / Ptassé where:

Ptassée is the bulk density packed, Paere is the bulk density not packed,

The Hausner I _H index, always greater than 1, increases when the flow velocity decreases, so when inter-particle friction increases. It is sensitive to the morphology, appearance, size, density of the powder and residual moisture. It is defined by: IH = Ptassée / Paereθ

During a random granular rearrangement, a reduction in intergranular porosity results after gravity flow.

The particle size populations constituting the mixture resulting from the invention are defined as indicated below: - 1 μm <d10 <340 μm;

200 μm <d50 <2000 μm;

500 μm <d90 <2900 μm.

A preferred variant of this mixture is defined by: - 20 μm <d10 <300 μm;

800 μm <d50 <1900 μm;

- 2000 μm <d90 <2700 μm.

The density in the packed state resulting from this granular assembly is in the range of 1.0 to 1.70 g / cm ³ . The morphology of the sulfur particles can be spherical as well as rounded, of the needle, fiber or polyhedron type. The compaction rate within this cored wire is usually of the order of 75 to 80%, whereas in the invention a compaction rate of at least 85% is achieved.

Preferably, this powder is obtained by an optimized combination of several distinct particle size populations of sulfur particles of purity of at least 95%, preferably greater than 98%, whose sizes are in the range [0 - 5000 μm] applied to the cored wire. This combination is a homogeneous mixture of various precise mass proportions of each population, obtained conventionally using a rotating bowl granular stirring device. The particle size distributions of the populations of the invention are defined by the indices d10, d50, d90.

the index d10 defines the equivalent diameter for which the value of the cumulative distribution is 10% by mass;

the index d50 defines the equivalent diameter for which the value of the cumulative distribution is 50% by mass;

the index d90 defines the equivalent diameter for which the value of the cumulative distribution is 90% by mass.

From mixtures of these particle size populations, a fill level increase of 10 to 70% of the linear density is typically obtained with respect to a wire of the same diameter using the same shell and manufactured under the same conditions using of any one of these populations. The compaction rate of these son filled with sulfur after the manufacture of the wire is, according to the invention, greater than or equal to 85% to achieve an optimal linear density. The particle size populations which the inventors have determined correspond to a preferred version of the invention, in which two populations 1 and 2 are used, are described as follows: Population 1: - 350 μm <d10 <1400 μm

- 650 μm <d50 <2200 μm

- 1000 μm <d90 <3000 μm Population 2: - 1 μm <d10 <250 μm

- 50 μm <d50 <500 μm

- 100 μm <d90 <800 μm

The experimental protocol applied in the laboratory is initially to mix populations with a given particle size distribution in precise mass proportions. Then, the physical characteristics of the different mixtures, such as grain size distribution and density, are measured. These data make it possible to set up a behavioral and phenomenological modeling of the system.

The models obtained indicate associations of ideal mass and particle size proportions. A granular selection is then made upstream in order to distribute the granulometric classes artfully. The optimal particle size distribution is ultimately composed of an association of several size classes.

These mixtures tested on the industrial process for manufacturing flux cored wire confirm the modeling phase of the experiment in the laboratory. For example, the optimum mixture is composed of 65 to 75% by weight of the population 1, homogeneously mixed with 25 to 35% by weight of the population 2. A mixture is considered optimal when it has the properties of flow and the highest compacities. These mixtures are created using a standard commercial type rotating bowl mixer. The internal walls of the mixer are composed of buckets judiciously fixed to limit the granular heterogeneity. They thus allow the materials to be stirred gently without any significant change in the particle size of the powder bed. The homogeneity of the mixture is ensured for a brewing time of 1 to 10 minutes.

The compaction rate of the powders within the cored wire is determined by the physical characterization of several representative samples by the mercury intrusion porosimetry technique. This destructive analysis allows to measure the pore size distribution of intra- and intergranular open porosity. In parallel, the theoretical density of a powder material is measured by helium pycnometry. This thus makes it possible to evaluate the degree of compaction and to evaluate the degree of porosity of the granular assembly within the cored wire.

The cored wire is technically characterized in particular by its linear density, depending on its degree of filling. This degree of filling is a result of the density of the pulverulent or granular population that composes it. The traditional steel-filled sulfur-filled wire, with an outer diameter of between 13 and 14 mm, has a linear density in the range [180 g / m - 205 g / m]. The usual particle size distribution of the powder it contains is in the range [0 μm - 5000 μm].

Examples of known reference sulfur-filled son and sulfur-filled son according to the invention will now be described which will demonstrate the advantages of the invention. These yarns were manufactured by the method preferred in the invention of depositing the powder on a metal strip, welding or folding said strip on itself to form the wire and profiling the wire to bring it to its nominal diameter.

Reference Example 1: Manufacture of a Standard and Known Sulfur Powder Coated Wire with an External Diameter of 13.1 mm and a Strap of 0.39 mm Thickness

For a population A whose particle size distribution and characteristics are given below:

Table n ° 1: Granulometric distribution of the population A according to the standard ASTM E1 1 -01

Purity of the population: S = 99.95%;

Pyknometric density: 2.02 g / cm ³

Packed density: 1.18 g / cm ³ ;

Aerated density: 1.09 g / cm ³ ;

Compressibility index: 7.62%; Hausner index: 1, 08; d10 between 0.800 and 1.000 mm; d50 of between 1.600 and 2.000 mm; d90 between 2,000 and 2,360 mm.

The linear density developed within the cored wire made from this population A only, whose d10 is too high to comply with the invention, is 189 g / m with a compaction rate of 78%.

Example 2, corresponding to the invention: manufacture of a cored wire of sulfur powder with an external diameter of 13.1 mm with a 0.39 mm thick strip Another population B of powder is used, whose grain size distribution and characteristics are given below:

Table n ° 2: Granulometric distribution of the population B according to ASTM standard E1 1 -01.

Purity of the population: S = 99.95%; Pyknometric density: 2.02 g / cm ³ ; Packed density: 1.13 g / cm ³ ; Aerated density: 0.90 g / cm ³ ; Compressibility index: 20.35%; Hausner index: 1, 25; d10 between 0.045 and 0.075 mm; d50 between 0.200 and 0.250 mm; d90 between 0.300 and 0.425 mm.

As the flow indices of this powder are mediocre (high compressibility index and Hausner index), this powder alone, whose d90 is too low for it to conform to the invention, does not make it possible to obtain cored wire of regular linear density under normal manufacturing conditions.

For a mixture forming a population C consisting of 70% by mass of batch A and 30% by mass of batch B, the particle size distribution and characteristics of which are given below:

Table n ° 3: Granulometric distribution of the population C according to the norm

ASTM E1 1 -01

Pyknometric density: 2.02 g / cm ³ ; Packed density: 1.47 g / cm ³ ;

Aerated density: 1.25 g / cm ³ ; Compressibility index: 14.96%; Hausner index: 1, 17; d10 between 0.100 and 0.150 mm; d50 between 1.250 and 1.400 mm; d90 between 2,000 and 2,360 mm.

A yarn with a linear density of 237 g / m and a compaction ratio of 88% is obtained. The linear density is 25% greater than that of a similar wire of the same external diameter 13.1 mm and a strip thickness of 0.39 mm manufactured under the same conditions from the only population A, although this population A was mixed with the population B which, taken separately, would not lead to satisfactory results because of its poor flowability.

Example 3, corresponding to the invention: manufacture of a cored wire of sulfur powder with an external diameter of 13.1 mm with a 0.39 mm thick strip

A sulfur powder constitutes a population D and has the particle size distribution and the following characteristics:

Table n ° 4: Granulometric distribution of the population D according to the standard ASTM E1 1 -01

Purity of the population: S = 99.95%;

Pyknometric density: 2.02 g / cm ³ ;

Packed density: 1.14 g / cm ³ ;

Aerated density: 1.03 g / cm ³ ;

Compressibility index: 9.64%; Hausner index: 1, 10 d10 between 0.800 and 1, 000 mm; d50 of between 1.600 and 2.000 mm; d90 between 2,360 and 2,800 mm.

The use of this D population alone, whose d10 is higher than that required by the invention, makes it possible to obtain a cored wire of external diameter 13.1 mm with a strip of 0.39 mm whose linear density is 181 g / m with a compaction rate of 76%.

A mixture forming a population E consisting of 60% by weight of the population D and 40% by weight of the population B is produced, and which has the particle size distribution and the following characteristics:

Table n ° 5: Granulometric distribution of the population E according to the standard ASTM E1 1 -01

Pyknometric density: 2.02 g / cm ³ ; Packed density: 1.43 g / cm ³ ; Aerated density: 1, 16 g / cm ³ ; Compressibility index: 18.80%; Hausner index: 1, 23 d10 between 0,075 and 0,100 mm; d50 of between 1.600 and 2.000 mm; d90 between 2,360 and 2,800 mm The use of this population E makes it possible to obtain a cored wire having a linear density equal to 225 g / m, 24% higher than that obtained with the population D alone and a compaction ratio equal to 86%. Here again, the mixture of the population D with the population B in the given proportions made it possible to obtain a cored wire of 13.1 mm with a strip of 0.39 mm manufactured under the same conditions, better characteristics than this one. that the only use of the population D would have allowed.

It should be noted, however, that the compactness and the linear density of this cored wire are slightly inferior to those of the wire of Example 2. This is attributable to the fact that the d90 of the population E is higher than that of the population C, and does not necessarily fall within the preferred range of the invention.

Reference Example 4: manufacture of a cored wire of sulfur powder with an external diameter of 9.2 mm and a strip thickness of 0.20 mm

A sulfur powder constitutes a population F whose particle size distribution and characteristics are as follows:

Table n ° 6: Granulometric distribution of the population F according to the standard ASTM E1 1 -01

Purity of the population: S = 99.95%;

Pyknometric density: 2.02 g / cm ³ ; Packed density: 1.14 g / cm ³ ; Aerated density: 1.01 g / cm ³ ; Compressibility index: 1 1, 40% Hausner index: 1, 13; d10 between 0.500 and 0.630 mm; d50 between 1, 000 and 1, 250 mm; d90 between 1, 600 and 2,000 mm.

The use of this population F alone, whose d10 is higher than that required by the invention, makes it possible to obtain a cored wire 9.2 mm in diameter with a strip thickness of 0.20 mm whose mass linear is 82 g / m with a compaction rate of 75%.

Example 5 according to the invention: manufacture of a cored wire of sulfur powder with an external diameter of 9.2 mm and a strip thickness of 0.20 mm

A mixture consisting of 70% by weight of the population A and 30% by weight of the population B is made according to the population C described in Example 2.

The use of this population C to manufacture a cored wire of external diameter of 9.2 mm with a strip thickness of 0.20 mm as in Reference Example 4 and under the same conditions, makes it possible to obtain a wire having a linear density equal to 109 g / m, 29% higher than that of Reference Example 4 made from the only population F, and a compaction rate of 89%.

Claims

1. Powder for cored wire intended for the alloying of a liquid metal bath, formed of particles composed of at least 95% sulfur, characterized in that its particle size population is defined by:

1 μm <d10 <340 μm;

200 μm <d50 <2000 μm; 500 μm <d90 <2900 μm.

2. Powder according to claim 1, characterized in that its granulometric population is defined by:

- 20 μm <d10 <300 μm;

800 μm <d50 <1900 μm; - 2000 μm <d90 <2700 μm.

3. Powder according to claim 1 or 2, characterized in that it results from the homogeneous mixture of two particle size populations 1 and 2, the particle size population 1 representing between 50 and 90% by weight of the mixture and the population 2 representing between 10 and 50% by weight of the mixture, said populations being defined by: Population 1: - 350 μm <d10 <1400 μm

- 650 μm <d50 <2200 μm

- 1000 μm <d90 <3000 μm Population 2:

- 1 μm <d10 <250 μm

- 50 μm <d50 <500 μm

- 100 μm <d90 <800 μm d10, d50 and d90 being the equivalent diameters of the particles for which the cumulative distribution values are respectively 10, 50 and 90% by mass.

4. Powder according to claim 3, characterized in that the population 1 represents 65 to 75% by weight of the mixture and the population 2 represents 25 to 35% by weight of the mixture.

5. Sulfur-filled wire for alloying a metal bath, characterized in that it contains a powder according to one of claims 1 to 4, and in that the compaction rate of this powder to the inside the yarn is greater than or equal to 85%.

6. A method of manufacturing a sulfur-filled wire for the alloying of liquid metal baths, characterized in that it comprises the following steps: - preparation of a powder according to one of claims 1 to 4;

gravitational flow of said powder on a metal strip;

- Welding or mechanical folding of said strip on itself to form the wire and profiling of this wire to the selected diameter, so as to obtain a wire whose compactness of the powder is greater than or equal to 85%.