DE102017210816A1 - Pre-alloy for influencing molten iron alloys, their use and method of manufacture - Google Patents

Abstract

The present invention relates to a master alloy for incorporation in molten iron alloys and to a process for the production thereof, wherein the master alloy is formed as a mixture of powdery materials and comprises a carrier material containing iron powder and crystallization nuclei, characterized in that in addition to crystallization nuclei contain at least carbon as a reducing agent and that the master alloy, besides the support material and unavoidable impurities, comprises 1 to 50% by weight of nuclei and 0.1 to 10% by weight of carbon.

Description

Technical Field

In the field of treatment of molten metals, the microstructure is influenced to adjust the material properties.

Technical Background (Background Art)

In the prior art it is known to influence the material properties of the metal solidifying from the melt in the case of a melt by adding additives or so-called master alloys with corresponding particles.

For example, is from the CN 101135023 A a mixture of very fine TiO ₂ , less than 200 nm, and iron, which is temporarily bound by a binder such as zinc stearate or paraffin. After compression and prior to sintering, the low melting point binder must be removed in this prior art.

Out US 2013/0305880 A1 For example, a composition is known which uses sulfur or oxygen based particles. Further examples of the prior art are in RU 2024641 C1 or RU 2443794 C2 known.

These examples from the prior art have in common that they only add particles to grain refining and optionally a special alloying element. Furthermore, the particles tend to agglomerate, which worsens the effect.

Summary of Invention

The invention is thus based on the object to provide a master alloy and a process for their preparation, which can be used flexibly for iron alloys, in particular steels, and can effectively achieve an influence on the properties of the material solidifying from the melt. Other objects of the invention are to allow for low manufacturability and ease of handling.

This object is achieved by a master alloy according to the features of claim 1, in particular if this was prepared by a method according to the features of claim 8.

According to the invention, a master alloy for introduction into molten iron alloys, wherein the master alloy is formed as a mixture of powdery materials and comprises a carrier material containing iron powder and crystallization nuclei, characterized in that in addition to crystallization nuclei carbon is at least still contained as a reducing agent, and that the master alloy next to Carrier material and unavoidable impurities comprises 1 to 50% by weight of crystallization nuclei and 0.1 to 10% by weight of carbon. The carbon is here primarily in pure form, for example as graphite powder before. A carbon content of at least 0.1% by weight is required in this case to ensure that possibly removed in the pre-alloy impurities with oxygen and no additional free oxygen is introduced into the molten iron alloy. By higher carbon contents on the one hand, a removal of oxygen from the molten iron alloy favors and especially at high carbon contents to 10% by weight can also be made a fine adjustment of the carbon content in the molten iron alloy. The iron powder may be in the form of pure iron or as a powder of an iron-based alloy, such as steel powder. Pure iron has the advantage that the composition of the support material can be defined more precisely. Whereas steel powder is more favorable and, especially when using a steel powder having a similar or similar composition, a change in the composition of the molten iron alloy by the iron powder can be largely avoided.

Embodiments of the master alloy are characterized in that the carrier material in addition to iron powder still contains powder of alloying elements of the iron alloy, wherein the iron powder is present as a pure iron powder or powder of an iron-based alloy. By adding alloying elements in powder form, the composition of the carrier material can either be adapted to that of the molten iron alloy, or an adjustment or change in the proportions of the alloying elements in the molten iron alloy can be made.

mit d als Versetzungsfaktor in %, a als Gitterkonstante der zu erzeugenden Eisenlegierung und a₀ als Gitterkonstante der festen Kristallisationskeime, und bei hexagonalen Elementarzellen der Versetzungsfaktor d gemäß der Gleichung II zu ermitteln ist, $${\delta }_{{\left(hkl\right)}_s}^{{\left(hkl\right)}_m}={\displaystyle {\sum }_{i=1}^3\left|\frac{\left(d{\left[uvw\right]}_m^{i}cos\theta -\text{d}{\left[uvm\right]}_s^i\right)}{\text{d}{\left[uvm\right]}_s^i}\right|}\ast \frac{100}{3}$$

mit ${\delta }_{{\left(hkl\right)}_s}^{{\left(hkl\right)}_m}$

als Versetzungsfaktor in %, (hkl)_m als Ebene der zu erzeugenden Eisenlegierung, (hkl)_s als Ebene des Kristallisationskeims, [uvw]_m als Richtung in (hkl)_m-Ebene, [uvw]_s als Richtung in (hkl)_s-Ebene, d[uvw]_m als Atomabstand entlang [uvw]m-Richtung, d[uvw]_s als Atomabstand entlang [uvw]_s-Richtung und Θ als Winkel zwischen [uvw]_m-Richtung und [uvw]_s-Richtung ist. Durch Einhaltung dieser Gleichungen für die Kristallisationskeime kann deren beabsichtigte Wirkung als Keim für Kornbildung sichergestellt werden. Abhängig von der aus der schmelzflüssigen Eisenlegierung zu erzeugenden Eisenlegierung weist dies Elementarzellen in kubischer oder hexagonaler Form auf. Dieser geometrische Unterschied hat einen Einfluss auf den Keimbildungsprozess, welcher durch die unterschiedlichen Gleichungen berücksichtigt wird.Further embodiments of the master alloy are characterized in that the crystallization nuclei have a disregistry factor d of less than or equal to 10%, wherein the dislocation factor d is to be determined in the case of iron alloys with cubic unit cells to be produced according to equation I, $$\delta =\frac{a-a_0}{a}*100$$

with d as the displacement factor in%, a as the lattice constant of the iron alloy to be produced and a ₀ as the lattice constant of the solid nuclei, and at hexagonal unit cells, the displacement factor d is to be determined according to equation II, $${\delta }_{{\left(Hkl\right)}_s}^{{\left(Hkl\right)}_m}={\displaystyle {\Sigma }_{i=1}^3\left|\frac{\left(d{\left[uvw\right]}_m^{i}cOs\theta -\text{d}{\left[uvm\right]}_s^i\right)}{\text{d}{\left[uvm\right]}_s^i}\right|}*\frac{100}{3}$$

With ${\delta }_{{\left(Hkl\right)}_s}^{{\left(Hkl\right)}_m}$

as displacement factor in%, (hkl) _m as plane of the iron alloy to be produced, (hkl) _s as plane of the nuclei, [uvw] _m as direction in (hkl) _m -plane, [uvw] _s as direction in (hkl) _s Plane, d [uvw] _m as atomic distance along [uvw] m-direction, d [uvw] _s as atomic distance along [uvw] _s -direction and Θ as angle between [uvw] _m- direction and [uvw] _s -direction is. By observing these equations for the nuclei, their intended effect as a seed for grain formation can be ensured. Depending on the iron alloy to be produced from the molten iron alloy, this has unit cells in cubic or hexagonal form. This geometric difference has an influence on the nucleation process, which is taken into account by the different equations.

Master alloy in further embodiments are characterized in that the crystallization nuclei are selected from oxides, nitrides, borides and / or carbides, and that the crystallization nuclei have a size between 0.5 .mu.m and 5 .mu.m, in particular between 0.8 .mu.m and 5 .mu.m. In these size ranges, the particles in the melt act as nucleation nuclei, in the preferred range of 0.8 to 3 microns, the effect can be best ensured as a germ. The crystallization nuclei are selected from oxides, nitrides, borides or carbides of metals, which can be selected from Ce, La, Pr, Nd, Y, Ti, Al, Zr, Ca, Co, Ba, Sr, Mg, Si, Mn, Cr, V, W, B, Nb, Mo or Fe. Of particular interest here are titanium oxides, titanium borides, titanium nitrides, aluminum oxides, cerium oxides, tungsten carbides, vanadium carbides, cobalt carbides, zirconium nitrides and zirconium oxides based on the thermochemical stability, good availability and from a cost standpoint.

Further embodiments of the master alloy are characterized in that the master alloy additionally comprises strengthening particles which prevent grain growth or form dislocations, wherein the strengthening particles are selected from oxides, nitrides, borides and / or carbides and a size smaller than 1 μm, in particular between 10 nm and 0 , 8μm, exhibit. The strengthening particles can be selected from the same materials as the nuclei. Due to the size of the solidification particles, no nucleation occurs, but the strengthening particles hinder the grain growth by forming dislocations and defects in the structure. As a result, the strength of the solidified from the molten iron alloy material is increased.

Master alloys according to further embodiments are characterized in that the master alloy additionally comprises foreign particles which influence the mechanical properties of the iron alloy, wherein the foreign particles are selected from oxides, nitrides, borides and / or carbides and a size between 2μm and 200μm, especially between 50μm and 180μm, exhibit. The foreign particles can also be selected from the same materials as the crystallization nuclei or selected from the abovementioned combinations. Due to their size, the foreign particles are interposed between the growing grains and increase the wear resistance of the solidified from the molten iron alloy material.

Embodiments of the master alloy are characterized in that a flow control agent is added to the master alloy and that the flow control agent is added in an amount of 0.7 to 2% by weight. The flow control agent is added to the powdery substances and serves to ensure the flow properties of the powder mixture in order to avoid further processing, e.g. the filling of a filler wire to simplify or allow. An example of such a flow control agent is "AEROSIL® R 9200", although other flow control agents can be used to improve the transportability, meterability and the like of the powder mixture.

• - Mischen der pulverförmigen Stoffe in einem hochenergiemischen Mischvorgang,
• - Konsolidieren der Mischung, und
• - Temperieren und Walzen der konsolidierten Mischung zu einem Vorlegierungsband.

Inventive methods for producing a master alloy according to the invention are characterized by the method steps:

• Mixing the pulverulent substances in a high-energy mixing process,
• - Consolidate the mix, and
• - Tempering and rolling the consolidated mixture to a master alloy strip.

In a first step, the powdery substances of the support material, the crystallization nuclei and the carbon are mixed together to achieve a homogeneous distribution. The mixture is carried out in a high-energy mixing process, in which a high mechanical energy input is introduced into the powder mixture. High-energy mixers have, for example, mixing speeds of more than 4m / s, usually between 4m / s and 30m / s, which is one device-dependent speed range of 300 to 4000 revolutions per minute. By this high-energy mixing process, the seeds are finely distributed and lie evenly around the surfaces of the powdery substances of the carrier material. An agglomeration of the nuclei is thereby avoided and achieved a uniform distribution, which significantly improves the effect as nuclei in the molten iron alloy. Another advantage is a possibly shorter mixing time. The high-energy mixing process can be carried out, for example, in a mixer at a speed between 300 and 4000 revolutions per minute.

In the next step, the mixture of powdered materials is consolidated, that is, solidified, to bring the master alloy from the loose powder form into a handleable, relatively dimensionally stable form.

Thereafter, the consolidated mixture of the powdery materials is tempered and rolled to produce a master alloy ribbon. The temperature control is required to remove residues of oxygen from the mixture of powdery substances. By rolling, the compound of the master alloy is compressed and strengthened, which improves the transportation, storage and handling of the master alloy. The main advantage of rolling is that deformation results in a deformation of the individual powders, in particular of the carrier material, with the crystallization nuclei distributed over their surface. As a result, the surface of, for example, iron powder is changed from a spherical to a flat, elongated shape, resulting in an enlargement of the surface. As a result of the increase in surface area, the nuclei of crystallization distributed homogeneously over the surface of the iron powder are further distributed and separated, which leads to a further improvement in the distribution effect indicated during the mixing process.

Embodiments of inventive method are characterized in that the consolidation by at least one of the methods powder extrusion, powder forging, briquetting, Füllwrahtherstellung or pressing and sintering takes place. By these methods, the mixture of powdery substances is solidified to allow better handling and further processing.

Processes according to further embodiments are characterized in that the tempering in the range of 400 ° C to 800 ° C is made. Temperatures of at least 400 ° C are necessary to allow the reduction reaction according to the Baur-Glaessner diagram, so that excess oxygen is removed from the master alloy and thus a corresponding contamination of the molten iron alloy is avoided. At temperatures above 800 ° C there is a risk that the crystallization nuclei begin to agglomerate again and thus the distribution is deteriorated again.

Embodiments of further inventive methods are characterized in that the tempering and rolling is carried out in separate steps or as hot rolling in a common step. Hot rolling, where the master alloy is rolled in the tempered state, offers advantages in terms of process times as well as rolling forces and formability of the resulting master alloy strip. However, due to the high temperature associated with mechanical deformation, the tendency for agglomeration of the nuclei may increase. Preference is therefore given to tempering and rolling, in particular cold rolling, carried out in separate process steps. Since the tendency to agglomeration can be counteracted here by appropriate temperature control and the forming at low temperatures.

Further embodiments of the method are characterized in that the master alloy strip is formed during rolling altogether with a degree of deformation of at least 90%. The higher the degree of deformation, the more the powdery substances of the carrier material are deformed and thus their surface area is increased. Due to the homogeneous distribution of the crystallization nuclei over the surface of the pulverulent substances, this further improves the distribution in the master alloy strip, which is why an effective degree of deformation of 90% is preferred.

Embodiments of the method are characterized in that the master alloy strip is separated into strips, the strips having at least a width corresponding to the thickness of the master alloy strip, or being cut into sinkers for casting molds, or separated into free-flowing bulk material with an edge length of 10 mm to 60 mm becomes. The generated master alloy ribbon can be used as such. Depending on the purpose and the equipment and manufacturing processes used, however, another form may be advantageous.

For example, for continuous addition to the molten iron alloy, the master alloy strip may be divided into strips, the width of the strips depending on the amount of molten iron alloy and / or amount of master alloy to be added. If the strip has a width in the range of the thickness of the master alloy strip, it represents a wire and can be used accordingly. The strips should not become narrower than the thickness of the master alloy strip, since for such dimensions a thinner master alloy strip with correspondingly greater width would be preferable because of the higher degree of deformation.

Likewise, a pruning of the master alloy strip in blanks is possible, which are particularly suitable for discontinuous casting processes, for example for the batchwise addition or insertion into molds.

Alternatively, the master alloy strip can also be separated into pieces with an edge length of 10 mm to 60 mm, whereby a free-flowing bulk material can be provided. The free-flowing bulk material can be finely dosed and used without problems both in continuous and batchwise casting processes. The specified range for the edge length refers to the value per edge and not to the circumference.

Pre-alloys according to the invention are used in that the master alloy is introduced into a pouring ladle, a distributor trough, a ladle, a casting mold or a pouring stream or is inserted directly into a casting mold. Depending on the casting process used, the master alloy may be added to the batched amount of molten ferrous alloy, such as a ladle, ladle or mold, or introduced into the continuous flow of molten ferrous alloy, such as a tundish, casting mold or pouring stream.

Further use is given to a master alloy according to the invention as welding filler material, in particular for hot-crack endangered steel grades. Here, the master alloy is introduced as a welding filler in the, introduced due to the welding process energy as a molten iron alloy, component material to influence the structure formation accordingly positive and to reduce the weakening by unfavorable microstructures.

In addition to the examples mentioned, devices according to the invention can also be used in other fields in which master alloys or metallic filler metals are used.

list of figures

• 1 eine Mikroskop-Aufnahme eines Trägermaterials,
• 2a eine Mikroskop-Aufnahme eines Trägermaterials mit Kristallisationskeime gemischt nach dem Stand der Technik,
• 2b ein Schliffbild eines Vorlegierungsbandes aus einer Mischung nach dem Stand der Technik gemäß 2a,
• 3a eine Mikroskop-Aufnahme eines Trägermaterials mit Kristallisationskeime gemischt gemäß der Erfindung und
• 3b ein Schliffbild eines Vorlegierungsband aus einer erfindungsgemäßen Mischung gemäß 3a.

In the following the invention will be explained in more detail with reference to figures. In detail show:

• 1 a microscope picture of a carrier material,
• 2a a microscope image of a carrier material with crystallization nuclei mixed according to the prior art,
• 2 B a micrograph of a Vorlegierungsbandes of a mixture according to the prior art according to 2a .
• 3a a microscope image of a carrier material with crystallization nuclei mixed according to the invention and
• 3b a micrograph of a master alloy strip from a mixture according to the invention according to 3a ,

Description of the Preferred Embodiments (Best Mode for Carrying Out the Invention)

1 shows a carrier material in the initial state. Here, the individual particles, in the case illustrated iron powder, can be seen, which shows a tendency to spherical basic shape with a corresponding size distribution. The particle size of the carrier material can be selected in the range of 3 .mu.m to 100 .mu.m.

In 2a a carrier material mixed with crystallization nuclei according to the prior art is shown. Here, 90% by weight of iron powder, as in 1 shown with 10% by weight zirconia (ZrO ₂ ), light particles in 2a , mixed in a conventional mixer. Mixers from the companies Lödige and MTI were used for the tests, with speeds of up to 250 revolutions per minute. Like in the 2a Recognizable, the crystallization nuclei agglomerate into larger agglomerates and intercalate between the particles of the carrier material. The agglomerates develop differently in size and deteriorate or lose their effect as nuclei during grain formation during the solidification process of the molten iron alloy.

If a mixture according to the prior art, as in 2a , rolled into a ribbon to get a microsection as in 2 B shown. Hot rolling was carried out with a degree of deformation of 90%. Here, too, the crystallization nuclei are shown brighter in this example ZrO ₂ . It can be clearly seen that the nuclei agglomerate and form large, often cohesive areas. As already too 2a explained, agglomerated crystallization nuclei have a much worse to no effect on. Furthermore, large and cohesive agglomerates are impeded as evenly as possible when used in the molten iron alloy.

3a represents a mixture of carrier material and crystallization nuclei mixed with a method according to the invention. The example shown contains, as the example in 2a . 90 Weight% iron powder and 10% by weight ZrO ₂ . It can be clearly seen that here the crystallization nuclei shown in brighter form were finely distributed by the high-energy mixer and spread substantially uniformly over the surface of the particles of the carrier material, in this case iron powder. For the experiments, a mixer of the type Cyclomix® Hochenergiemische the company Hosokawa was used. In contrast to 2a have no agglomerates formed.

Analogous to 2 B provides 3b a micrograph of a master alloy strip, which consists of a master alloy according to 3a was produced by hot rolling with a degree of deformation of 90%. It is clearly recognizable, especially compared with 2 B in that there is a much more homogeneous distribution and agglomerates have been largely avoided. As a result, the effect is retained as nuclei and a uniform distribution in the molten iron alloy is achieved. If the step of hot rolling is replaced by tempering and subsequent cold rolling, the result can be further improved.

The various features of the invention can be combined with one another as desired and are not limited to the described or illustrated examples of embodiments.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• CN 101135023 A [0003]
• US 2013/0305880 A1 [0004]
• RU 2024641 C1 [0004]
• RU 2443794 C2 [0004]

Claims (15)

Pre-alloy for incorporation in molten iron alloys, wherein the master alloy is formed as a mixture of powdery materials and comprises a carrier material containing iron powder and crystallization nuclei, characterized in that in addition to crystallization nuclei at least carbon is still contained as a reducing agent, and that the master alloy next to the carrier material and unavoidable Contains 1 to 50% by weight of crystallization nuclei and 0.1 to 10% by weight of carbon. Master alloy after Claim 1 characterized in that the carrier material in addition to iron powder still contains powder of alloying elements of the iron alloy, wherein the iron powder is present as pure iron powder or powder of an iron-based alloy. Master alloy according to one of Claims 1 or 2 characterized in that the nuclei have a disregistration factor d of less than or equal to 10%, where the dislocation factor d for iron alloys to be formed is determined using cubic unit cells according to Equation I, $$\delta =\frac{a-a_0}{a}*100$$

with d as displacement factor in%, a as lattice constant of the iron alloy to be produced and a ₀ as lattice constant of the solid crystallization nuclei, and for hexagonal unit cells the displacement factor d is to be determined according to equation II, $${\delta }_{{\left(Hkl\right)}_s}^{{\left(Hkl\right)}_m}={\displaystyle {\Sigma }_{i=1}^3\left|\frac{\left(d{\left[uvw\right]}_m^{i}cOs\theta -\text{d}{\left[uvm\right]}_s^i\right)}{\text{d}{\left[uvm\right]}_s^i}\right|}*\frac{100}{3}$$

With ${\delta }_{{\left(Hkl\right)}_s}^{{\left(Hkl\right)}_m}$

as displacement factor in%, (hkl) _m as plane of the iron alloy to be produced, (hkl) _s as plane of the nuclei, [uvw] _m as direction in (hkl) _m -plane, [uvw] _s as direction in (hkl) _s Plane, d [uvw] _m as atomic distance along [uvw] _m direction, d [uvw] _s as atomic distance along [uvw] _s direction and Θ as angle between [uvw] _m direction and [uvw] _s direction is. Master alloy according to one of the preceding claims, characterized in that the crystallization nuclei are selected from oxides, nitrides, borides and / or carbides, and that the crystallization nuclei have a size between 0.5 .mu.m and 5 .mu.m, in particular between 0.8 .mu.m and 3 .mu.m. Master alloy according to one of the preceding claims, characterized in that the master alloy additionally comprises strengthening particles which prevent grain growth or form dislocations, wherein the strengthening particles are selected from oxides, nitrides, borides and / or carbides and a size smaller than 1μm, in particular between 10nm and 0.8μm. Master alloy according to one of the preceding claims, characterized in that the master alloy additionally comprises foreign particles which influence the mechanical properties of the iron alloy, wherein the foreign particles are selected from oxides, nitrides, borides and / or carbides and a size between 2μm and 200μm, in particular between 50μm and 180μm. A master alloy according to any one of the preceding claims, characterized in that a flow control agent is added to the master alloy, and in that the flow control agent is added in an amount of 0.7 to 2% by weight. Process for the preparation of a master alloy according to one of Claims 1 to 6 characterized by the steps of: mixing the powdered materials in a high energy mixing process, consolidating the mixture, and tempering and rolling the consolidated mixture into a master alloy strip. Method according to Claim 8 characterized in that the consolidation takes place by at least one of the methods of powder extrusion, powder forging, briquetting, Füllwrahtherstellung or pressing and sintering. Method according to one of Claims 8 or 9 characterized in that the tempering in the range of 400 ° C to 800 ° C is made. Method according to one of Claims 8 to 10 , characterized in that the tempering and rolling is carried out in separate steps or as hot rolling in a common step. Method according to one of Claims 8 to 10 , characterized in that the master alloy strip is formed during rolling altogether with a degree of deformation of at least 90%. Method according to one of Claims 8 to 12 characterized in that the pre-alloy strip is separated into strips, the strips have at least a width which corresponds to the thickness of the master alloy strip, or is cut into boards for molds, or is separated into free-flowing bulk material with an edge length of 10mm to 60mm. Use of a master alloy according to one of Claims 1 to 6 in which the master alloy is introduced into a ladle, a distributor trough, a ladle, a casting mold or a pouring stream or is inserted directly into a casting mold. Use of a master alloy according to one of Claims 1 to 6 as welding filler material, in particular for hot-crack-endangered steel grades.

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