Descaling agent for removing scale in hot working of metals

Abstract

The present invention relates to a descaling agent for removing scale during the hot working of metals, in particular during hot rolling processes for the production of seamless steel tubes, wherein the descaling agent contains the following components in wt.%, based on the solids content: (a) 10 to 45 wt.% sodium sulfate, (b) 10 to 45 wt.% calcium carbonate, lithium carbonate or a mixture thereof, (c) 10 to 45 wt.% boron silicate glass frit or ground boron silicate glass, (d) 0 to 15 wt.% fatty acid, fatty acid salt or a mixture thereof, (e) 0 to 7 wt.% anti-caking agent, (f) not more than 1 wt.% of a water-soluble boron compound selected from boric acid, boric acid salt or a mixture thereof.

Description

Subject matter of the invention

[0001] The present invention relates to a descaling agent for removing scale during the hot working of metals, hereinafter also referred to as a descaling agent. The descaling agent according to the invention is particularly suitable for removing scale during hot rolling processes for the production of seamless steel pipes. Background of the invention

[0002] When metals, especially steel, are hot-formed in a temperature range of 900-1300 °C, such as during rolling or forging, hard and brittle scale forms on the heated metal surface through reaction with atmospheric oxygen from the ambient air. This scale consists primarily of layers of FeO (wüstite), Fe 3 O 4 (magnetite) and Fe 2 O 3 (hematite).

[0003] In hot rolling processes for the production of seamless steel tubes, a solid material, usually in cylindrical form, is heated to a temperature of approximately 1100–1300 °C. Using a special skew rolling process with the aid of a mandrel, it is perforated to form a hollow ingot, which is then rolled and stretched into a tube in the subsequent rolling step, elongation. For this, the hollow ingot is mounted on a mandrel bar and elongated by external, driven rolls, reducing its wall thickness. Particularly in modern continuous mandrel rolling processes with a held mandrel bar, such as MPM, PQF, and FQM processes, the risk of scale formation on the heated metal surface of the hollow ingot is especially high during the relatively long transition time of approximately 30–60 seconds between ingot formation and the elongation process.During subsequent rolling steps, the hard, brittle, and abrasive particles of the scale layer can lead to defects on the inner walls of the finished pipes. Subsequent mechanical surface treatment inside the pipe is generally not possible or economically viable.

[0004] Scale significantly increases the frictional force between the mandrel and the rolled material, even when a lubricant is used in the process. Furthermore, scale can also damage the mandrel, shortening its service life and thus negatively impacting the economic viability of the production process, as the costs for such tools are comparatively high. In the worst-case scenario, the mandrel can become stuck in the hollow block or tube, forming a so-called "plug." The rolled material can then no longer be rolled and remains in the rolling stands. The plant usually has to be stopped and the plug cleared before the process can continue.

[0005] For this reason, descaling the inner surface of the hollow ingot, as well as preventing or at least reducing scale formation during the process, is a necessary process measure, especially in modern continuous rolling processes. Typically, in a first step immediately after punching, the newly formed scale, known as primary scale, is blown out of the resulting hollow ingot, for example, with compressed air or an inert gas such as nitrogen or argon. To prevent the formation of further scale, known as secondary scale, and to convert any remaining primary scale, various compositions of substances in powder or granule form are introduced into the hollow ingot, usually by blowing. A good descaling agent is characterized by its ability to remove already formed primary scale, for example, through chemical reaction or physical removal, and to suppress the formation of new secondary scale during the process.

[0006] Lubricants are typically used in hot rolling processes, such as mandrel rolling for the production of seamless steel tubes, as lubrication is crucial for the subsequent quality and dimensional accuracy of the manufactured tubes, particularly for the condition of the tubes' inner surface. Good lubricating properties include not only reducing the coefficient of friction between the mandrel and the workpiece, but also possessing good wetting properties and forming a continuous lubricant film of sufficient thickness between the mandrel and the workpiece. Descaling agents can also contain components or additives that, in addition to descaling the workpiece surface, also provide lubrication during the rolling process.

[0007] Common formulations used in hot rolling processes contain, for example, graphite, alkali borates, boric acid, silicates, alkali sulfates, fatty acids, and / or, in some cases, phosphates. Most of these formulations are designed to melt upon contact with the hot metal surface, particularly the hot inner surface of the hollow ingot, forming a viscous molten film on the metal surface. Descaling of the metal surface can be achieved by the molten film absorbing and / or chemically transforming existing primary scale particles. Where the molten film covers the metal surface, it also protects against secondary scaling. Therefore, good film formation of the molten material on the metal surface is advantageous for effective descaling.

[0008] A group of formulations used in hot rolling processes are based on phosphates, particularly condensed alkali phosphates. These possess both good lubricating and descaling properties. However, in practical application, they can be relatively sensitive and, when applying the solid mixture by blowing, require very precise dosing to achieve uniform distribution across the entire inner surface of the hollow billet. Local overdosing within the hollow billet, in particular, increases the risk of internal defects during the rolling of the steel tubes.

[0009] Graphite is a suitable lubricant additive for hot forming of metals because it is relatively temperature-stable and possesses particularly good lubricating properties, both on its own and in combination with mineral oils and inorganic salts. Many well-known lubricants for hot forming of metals, primarily mandrel bar lubricants, therefore contain high proportions of graphite.

[0010] Many well-known formulations used in hot rolling processes contain sodium borate, particularly borax (anhydrous disodium tetraborate or as the pentahydrate or decahydrate), or other soluble boric acid salts due to their excellent descaling properties. Borax-containing formulations form a very good molten film on the hot metal surface and effectively remove existing scale by reacting with it and incorporating it into the melt. This molten film also forms a protective layer on the metal surface, effectively preventing the formation of secondary scale. Furthermore, borax-containing formulations are relatively easy to handle, especially with regard to overdosing. Unlike phosphate-based formulations, however, borax itself has little or no lubricating properties, which is why it is primarily used for its effective descaling action.One disadvantage of borax-containing descaling agents is their tendency to clump due to water absorption, for example, in high humidity during storage. This can impair subsequent application by spraying the solid powder formulation. More problematic, however, is the teratogenic effect of borax, which, due to its water solubility, can enter the wastewater of the rolling mill, requiring costly water treatment measures and potentially causing significant disposal problems. Borax has also been classified as reprotoxic, which is why strict limits apply to products containing borax. Since 2022, the EU has therefore also applied a reduced limit of 0.3% (from 5.5%) to borax-reduced products, a limit that is even lower in the GHS (Globally Harmonized System of Classification and Labelling of Chemicals) developed by the United Nations.The advantages and disadvantages described above for borax apply essentially analogously to boric acid and other water-soluble boric acid salts used for this purpose.

[0011] EP 0 169 413 describes a pickling agent, lubricant, and antioxidant for iron and steel workpieces during hot forming processes, particularly in the production of seamless steel tubes; thus, it is a descaling agent with lubricating properties. The agent contains 20–80 wt.% active pickling agents that chemically convert the oxide scale components, selected from boric acid, water-soluble boric acid salts, and sodium silicates, with sodium metaborates being described as the only examples. Furthermore, the agent contains 1–80 wt.% substances acting as solid lubricants, as well as optionally other functional components.

[0012] EP 2 000 525 describes a powder lubricant for use in hot rolling processes for the production of seamless steel tubes, which contains 30 - 80 wt.% water-soluble sodium borate, optionally up to 15 wt.% calcium and / or lithium carbonate, 5 - 15 wt.% of a sodium or calcium fatty acid salt and 10 - 40 wt.% of a layered silicate.

[0013] EP 0 743 352 describes a lubricant composition for the hot forming of metals, in particular for use in the hot rolling of blocks and profiles or in the production of hollow blocks or seamless tubes in push bench mills, which is intended to form a uniform, well-adhering and water-insoluble lubricant film on workpieces with surface temperatures of 800 °C to 1300 °C. The composition contains up to 80 wt.% glass powder and / or up to 50 wt.% glass frit, 10–25 wt.% graphite, 5–20 wt.% one or more alkali silicates, 1–6 wt.% a water-soluble sodium polymetaphosphate, 0–3 wt.% a water-insoluble sodium polymetaphosphate, 0.5–4 wt.% a thickening agent and 0–1 wt.% borax.

[0014] JP 2019-898 describes a graphite-free, water-based pre-coating agent for the hot forming of steel, containing 1 - 50 wt.% inorganic solid, 1 - 30 wt.% binder, 0.05 - 10 wt.% surfactant and 30 - 90 wt.% water. Object of the invention

[0015] Against this background, the object of the present invention was to provide a means for removing scale during the hot working of metals that does not have the disadvantages of the compositions described above. Description of the invention

[0016] This problem is solved according to the invention by an agent for removing scale during the hot processing of metals, in particular during hot rolling processes for the production of seamless steel pipes, which is also referred to herein as a descaling agent and contains the following components in wt.%, based on the solids content: (a) 10 to 45% by weight Sodium sulfate (b) 10 to 45% by weight Calcium carbonate, lithium carbonate, or a mixture thereof (c) 10 to 45% by weight Boron silicate glass frit or ground boron silicate glass, (d) 0 to 15 wt.% Fatty acid, fatty acid salt or a mixture thereof (e) 0 to 7 wt.% Free-flowing agents, (f) not more than 1% by weight a water-soluble boron compound, selected from boric acid, boric acid salt or a mixture thereof.

[0017] The descaling agent according to the invention is characterized by the highly effective removal of already formed primary scale on the hot workpiece and excellent suppression of the formation of new secondary scale during the hot processing process. Compared to known compositions, the descaling agent according to the invention contains only a very small optional proportion of water-soluble borates or boric acid.

[0018] According to one embodiment of the present invention, the descaling agent according to the invention contains a water-soluble boron compound, in particular boric acid, borax and / or other water-soluble boric acid salts, in an amount of no more than 0.5 wt.%, preferably no more than 0.3 wt.%, and particularly preferably no more than 0.1 wt.%. Most preferably, the descaling agent contains no water-soluble boron compounds at all, apart from unavoidable impurities, selected from boric acid, boric acid salts or a mixture thereof, in particular borax, since these compounds pose a high risk to humans and the environment.

[0019] Surprisingly, the combination of sodium sulfate, calcium and / or lithium carbonate, and boron silicate glass frit or ground boron silicate glass according to the invention results in faster melting compared to known compositions, forming a particularly uniform, viscous melt film on the metal surface. This film effectively removes existing primary scale and protects the workpiece from secondary scale formation during hot working. Furthermore, the descaling agent according to the invention has proven to be very reliable and relatively easy to handle, especially with regard to overdosing. In particular, the descaling agent according to the invention can be dosed using pneumatically operated injection systems with relatively wide tolerance ranges. The risk of local overdosing is comparatively low.

[0020] In a preferred embodiment of the invention, the descaling agent according to the invention has a hemispherical melting point >700 °C, preferably even >900 °C. The hemispherical melting point is reached when a test specimen, when tested for ash melting behavior under a heating microscope, has an approximately hemispherical shape. A hemispherical melting point >700 °C or even >900 °C for the composition according to the invention has the advantage that the melting point of the composition is not reached too early and a viscosity suitable for the application is maintained. If the hemispherical melting point of the composition is below this, the viscosity of the melt in the operating range of 1000–1300 °C may be too low, so that an adequate melt film is not obtained.With knowledge of the invention, a person skilled in the art can easily achieve a hemispherical melting point >700 °C or >900 °C in just a few trials by adjusting the quantities of sodium sulfate, calcium and / or lithium carbonate, and boron silicate glass frit or ground boron silicate glass. Since sodium sulfate has a comparatively low melting point, varying the sodium sulfate content allows for advantageous control of both the melting point and the hemispherical melting point.

[0021] In one embodiment of the invention, for cost reasons only calcium carbonate is used as component (b) instead of lithium carbonate or a mixture of calcium carbonate and lithium carbonate.

[0022] In a preferred embodiment of the invention, the descaling agent is in the form of a powder or granules. In this form, the descaling agent according to the invention is advantageously suited for blowing or sprinkling into the hollow billet during hot rolling processes for the production of seamless steel pipes. The particle size of the descaling agent in the powder or granules is expediently in the range of 1 µm to 1000 µm. The particle size of the powdered descaling agent is determined using a laser granulometer (e.g., Horiba LA-950 from Horiba Ltd.). Approximately 80 mg of sample is suspended in 2-propanol, and the measurement is carried out one minute after preparation of the suspension, according to the manufacturer's instructions.

[0023] In granular embodiments, the size of the descaling agent granules is preferably in the range of 25 µm to 1000 µm. This includes embodiments with spherical granules as well as agglomerates and cylindrical pellets, and intermediate forms, provided that the maximum longitudinal dimension of the granules, agglomerates, or pellets in any one dimension does not exceed 3 mm. The maximum longitudinal dimension of the granules, agglomerates, or pellets in any one dimension can be determined by mechanical sieving.

[0024] The production of granules from powdered descaling agent can be carried out by known granulation processes, for example, in a granulator by spraying water while agitating, whereby the particle size is increased by agglomeration. Alternative methods for producing granules, agglomerates, or pellets are known to those skilled in the art. If the descaling agent is in the form of granules, the addition of flow agents can be omitted. In one embodiment of the invention, the descaling agent according to the invention therefore contains no flow agent (0 wt%) or only a small proportion of flow agent of no more than 3 wt%, preferably no more than 2 wt% or no more than 1 wt%.

[0025] If the descaling agent according to the invention is in powder form, it is advantageous to use an anti-caking agent to maintain and / or improve the flowability.

[0026] In a further embodiment of the invention, the descaling agent according to the invention has a mean particle size D50 of ≤ 250 µm, preferably ≤ 200 µm, and / or D90 of ≤ 450 µm, preferably ≤ 300 µm. Due to the small mean particle sizes of the components of the mixture according to the invention, the flowability and free-flowing properties of the composition according to the invention are significantly improved compared to known descaling agents, and spraying onto surfaces as a powder is facilitated while simultaneously ensuring a uniform layer formation or coating on the metal surface.

[0027] Suitable flow aids according to the invention are selected from various silicates, secondary or tertiary calcium phosphate compounds, graphite, alkali hexacyanoferrates, aluminium hydroxide and mixtures thereof.

[0028] Examples of suitable flow aids include silicon dioxide, layered silicates such as talc or mica, aluminum silicates, and hydroxyapatite. Preferred flow aids are hydrophobic and hydrophilic pyrogenic silicas, e.g., with a SiO₂ content of > 98 wt% based on the annealed substance.

[0029] In one embodiment of the descaling agent according to the invention, the boron silicate glass frit or the ground boron silicate glass contains Na, B, Si and Al in the following weight proportions, expressed by their respective oxides: 1 to 30 wt.% NazO, 2 to 70 wt.% B 2 O 3 , 10 to 70 wt.% SiOz and 0 to 10 wt.% Al 2 O 3 .

[0030] Boron silicate glass frit or ground boron silicate glass with a grain size with a mean particle size D50 of ≤ 300 µm has proven to be suitable according to the invention to achieve a uniform distribution and rapid formation of the melt over a wide temperature range of the descaling agent on the hot metal surface.

[0031] In one embodiment of the descaling agent according to the invention, the fatty acid used as an acid or as a corresponding salt is selected from saturated and unsaturated fatty acids with 6 to 26 carbon atoms, preferably from caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, icosenoic acid, erucic acid, nervonic acid, linoleic acid, linolenic acid, arachidonic acid, timnodonic acid, and clupanodonic acid, with the proviso that the fatty acid or fatty acid salt is present as a solid at a temperature above 30 °C. The fatty acid salt of stearic acid is particularly preferred according to the invention.

[0032] The use of a fatty acid, a fatty acid salt, or a mixture thereof within the scope of the invention significantly reduces clumping of the descaling agent and improves its storage stability. Without being bound to any specific theory, it is assumed that the fatty acid or fatty acid salt binds to the granules of one or more other components of the composition, thereby preventing or reducing clumping, keeping moisture away from the granules, and thus further improving the storage stability and the free-flowing or flowing properties of the descaling agent. It is also assumed that, due to decomposition within the operating temperature range, the fatty acid or fatty acid salt forms a gas cushion, thereby improving the distribution of the melt film and contributing to the descaling and separation effect of the composition.

[0033] In one embodiment of the present invention, the descaling agent contains, based on the solids content, 15 to 45 wt.% sodium sulfate, preferably 26 to 41 wt.% sodium sulfate.

[0034] In a further embodiment of the present invention, the descaling agent contains, based on the solids content, 15 to 45 wt.% calcium carbonate, lithium carbonate or a mixture thereof, preferably 26 to 41 wt.% calcium carbonate, lithium carbonate or a mixture thereof.

[0035] In a further embodiment of the present invention, the descaling agent contains, based on the solids content, 15 to 45 wt.% boron silicate glass frit or ground boron silicate glass, preferably 26 to 41 wt.% boron silicate glass frit or ground boron silicate glass.

[0036] In a further embodiment of the present invention, the descaling agent contains, based on the solids content, 1 to 10 wt.% fatty acid, fatty acid salt or a mixture thereof.

[0037] In a further embodiment of the present invention, the descaling agent contains, based on the solids content, 0.5 to 5 wt.% free-flowing agent.

[0038] In a further embodiment of the present invention, the descaling agent contains, based on the solids content, no more than 3 wt.% graphite, preferably no more than 1 wt.% graphite, particularly preferably no more than 0.5 wt.% graphite, most preferably no graphite, except for unavoidable impurities.

[0039] The present invention also includes compositions containing the descaling agent according to the invention in combination with further components. In one embodiment of the invention, a composition for protection against scale and as a lubricant in the hot working of metals contains a descaling agent according to the invention in an amount of 40 to 90 wt.% and furthermore 10 to 60 wt.% condensed alkali phosphates.

[0040] In a preferred embodiment of this composition, the condensed alkali phosphates are selected from condensed sodium phosphates, potassium phosphates and mixtures thereof, preferably from polyphosphates, pyrophosphates, metaphosphates and mixtures thereof, particularly preferably from disodium pyrophosphate [Na₂H₂P₂O₇], trisodium pyrophosphate [Na₃HP₂O₇], tetrasodium pyrophosphate [Na₄P₂O₇], sodium tripolyphosphate [Na₅P₃O₁₀], sodium trimetaphosphate [(NaPO₃)₃], sodium polyphosphate [(NaPO₃)ₙ], dipotassium pyrophosphate [K₂H₂P₂O₇], tripotassium pyrophosphate [K₃HP₂O₇], tetrapotassium pyrophosphate [K₄P₂O₇], potassium tripolyphosphate [K₅P₃O₁₀], Potassium trimetaphosphate [(KPO 3 ) 3 ], potassium polyphosphate [(KPO 3 ) n ] and mixtures thereof.The condensed alkali phosphates can themselves possess descaling or lubricating properties and support or complement the effect of the descaling agent according to the invention in the hot processing process.

[0041] The present invention further comprises the use of a descaling agent according to the invention or a composition which contains the descaling agent according to the invention in combination with further components such as alkali phosphates, in the hot processing of metals, preferably in hot rolling processes for the production of seamless steel tubes, including MPM processes, PQF processes and FQM processes. Examples

[0042] Descaling agents (A to I) and compositions (Z1 to Z4) according to the invention, which contain descaling agents according to the invention in combination with alkali polyphosphates, are given in Tables 1 and 2 below.

[0043] The descaling agents A - E and G - I as well as the compositions Z1 - Z4 were produced as powders, while the descaling agent F was produced as granules. Table 1 - Descaling agents according to the invention ingredient A B C D E F G H I (a) Sodium sulfate (Na 2 SO 4 ) (1)< 26,00 26,00 41,00 31,00 29,75 32,34 10,00 41,50 41,50 (b) Calcium carbonate (CaCO 3 ) (2)< 41,00 26,00 26,00 31,00 29,75 32,33 41,50 10,00 41,50 (c) Boron silicate glass frit (3)< 26,00 41,00 26,00 31,00 29,75 32,33 41,50 41,50 10,00 (d) Fatty acid salt Mg stearate (4)< 5,00 5,00 5,00 5,00 5,75 3,00 5,00 5,00 5,00 (e) Free-flowing agents (5)< 2,00 2,00 2,00 2,00 5,00 --- 2,00 2,00 2,00 (1) Sodium sulfate: CAS: 7757-82-6; (2) Calcium carbonate: CAS: 471-34-1; (3) Boron silicate glass frit: CAS: 65997-18-4; (4) Mg stearate: CAS: 91031-63-9 (557-04-0); (5) Each composition was tested with different anti-caking agents: a) hydrophilic fumed silica (SiO₂): CAS: 7631-86-9; b) graphite: CAS: 7782-42-5; c) talc: CAS: 14807-96-6; d) Ca phosphate (Ca₃(PO₄)₂): CAS: 7758-87-4. Table 2 - Compositions according to the invention ingredient Z1 Z2 Z3 Z4 Descaling agent (6)< C C C C Descaling agent (wt%) 75,00 65,00 55,00 33,00 additional flow agent (6)< 4,00 6,00 3,00 7,00 Sodium tripolyphosphate (Na 5 P 3 O 10 ) 10,00 20,00 10,00 35,00 Sodium trimetaphosphate (NaPO 3 ) 3 (7)< Potassium tripolyphosphate (K 5 P 3 O 10 ) 11,00 9,00 32,00 25,00 Potassium trimetaphosphate (KPO 3 ) 3 (8) < (6) The anti-caking agent in the descaling agent and the additional anti-caking agent was hydrophilic fumed silica (SiO₂): CAS: 7631-86-9; (7) Sodium tripolyphosphate (Na₅P₃O₁₀): CAS: 7758-29-4; Sodium trimetaphosphate (NaPO₃)₃: CAS: 7785-84-4; in a weight ratio of 1:1; (8) Potassium tripolyphosphate (K₅P₃O₁₀): CAS: 13845-36-8; Potassium trimetaphosphate (KPO₃)₃: CAS: 7790-53-6 in a weight ratio of 1:1

[0044] A standard descaling agent consisting of equal weight proportions of borax (Na 2 B 4 O 7 10H 2 O; CAS: 1303-96-4); sodium sulfate (Na 2 SO 4 ; CAS: 7757-82-6) and sodium palmitate (CH 3 (CH 2 ) 14 COONa; CAS: 408-35-5) was used as a comparison composition ("REF"). Scale removal behavior

[0045] To investigate the scale removal behavior, 4 parts by weight of descaling agent were mixed with 1 part by weight of scale, melted in a crucible at 1250 °C in a muffle furnace for 20 minutes, and then allowed to cool. The crucibles were broken open, the solidified melt isolated, ground in a planetary mill with zirconium oxide spheres (Fritsch GmbH), and the powder analyzed by powder X-ray diffraction (XRD) on a D8 Advance diffractometry system (Bruker) (Cu Kα radiation; 10⁻⁷⁰ 2-theta).

[0046] The XRD peaks were identified and indexed using reference data (ICCD database; Powder Diffraction Files; JCPDS). Good scale removal, i.e., chemical conversion of the existing scale, was demonstrated in the XRD by distinct peaks of Ca-Fe oxide (Ca₂Fe₂O₅) and the absence of peaks of Fe oxide (magnetite). Instead of the compositions according to the invention, pure sodium sulfate (Na₂SO₄; CAS: 7757-82-6) and the known effective reference composition ("REF") with a high borax content, mixed with scale in the same mixing ratio as the descaling agents according to the invention, were used as references.

[0047] The following evaluation scheme was used for the scale removal behavior: (+) = "good" Distinct Ca-Fe oxide peaks; no or only weak Fe oxide peaks visually identifiable; (-) = "bad" Strong Fe oxide peaks are visually identifiable.

[0048] Table 3 below shows the scale removal behavior and free-flowing properties of the descaling agents and compositions according to the invention, as well as of reference compositions. The free-flowing agent in the descaling agents and compositions according to the invention was hydrophilic pyrogenic silica. The descaling agents and compositions according to the invention, when combined with graphite, talc, or calcium phosphate as free-flowing agents, also exhibited good scale removal behavior and free-flowing properties. Table 3: Sample properties sample Scale removal behavior Flowability A (Experience) (+) (+) B (Experience) (+) (+) C (Experience) (+) (+) D (Experience) (+) (+) E (Experience) (+) (+) F (Experience) (+) (+) G (Experience) (+) (+) H (Experience) (+) (+) I (Experience) (+) (+) Z1 (Experience) (+) (+) Z2 (Experience) (+) (+) Z3 (Experience) (+) (+) Z4 (Experience) (+) (+) REF (See below.) (+) (+) Na₂SO₄ (See below.) (-) (-)

[0049] All descaling agents A to I according to the invention exhibited a hemispherical temperature in the range of 900 to 950 °C. The hemispherical temperature of the compositions Z1 to Z4 according to the invention was at approximately 700 to 800 °C.

Claims

1. Descaling agent for removing scale during the hot processing of metals, in particular during hot rolling processes for the production of seamless steel pipes, wherein the descaling agent contains the following components in wt.%, based on the solids content: (a) 10 to 45% by weight Sodium sulfate (b) 10 to 45% by weight Calcium carbonate, lithium carbonate, or a mixture thereof (c) 10 to 45% by weight Boron silicate glass frit or ground boron silicate glass, (d) 0 to 15 wt.% Fatty acid, fatty acid salt or a mixture thereof (e) 0 to 7 wt.% Free-flowing agents, (f) not more than 1% by weight a water-soluble boron compound, selected from boric acid, boric acid salt or a mixture thereof.

2. Descaling agent according to claim 1 in the form of a powder or granules.

3. Descaling agent according to any of the preceding claims, characterized by the fact that The boron silicate glass frit or the ground boron silicate glass contains Na, B, Si and Al in the following weight proportions, expressed by their respective oxides: 1 to 30 wt.% Na2O, 2 to 70 wt.% B2O3, 10 to 70 wt.% SiOz and 0 to 10 wt.% Al2O3.

4. Descaling agent according to any of the preceding claims, characterized by the fact that The boron silicate glass frit or the ground boron silicate glass has a grain size with a mean particle size D50 of ≤ 300 µm.

5. Descaling agent according to any one of the preceding claims, characterized by the fact that The fatty acid and the fatty acid salt are selected from saturated and unsaturated fatty acids with 6 to 26 carbon atoms and their salts, preferably from caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, icosenoic acid, erucic acid, nervonic acid, linoleic acid, linolenic acid, arachidonic acid, timnodonic acid, clupanodonic acid and their salts, with the proviso that the fatty acid or the fatty acid salt is present as a solid at a temperature > 30 °C, wherein the fatty acid salt of stearic acid is particularly preferred.

6. Descaling agent according to any one of the preceding claims, characterized by the fact thatThe anti-caking agent is selected from silicates, phyllosilicates, talc (= phyllosilicate), micas (= phyllosilicates), secondary or tertiary calcium phosphate compounds, hydroxyapatite, graphite and mixtures thereof.

7. Descaling agent according to any one of the preceding claims, characterized by the fact that water-soluble boron compound is contained in an amount of not more than 0.5 wt.%, preferably not more than 0.3 wt.%, particularly preferably in an amount of not more than unavoidable impurities.

8. Descaling agent according to any one of the preceding claims, characterized by the fact that The descaling agent contains, based on the solids content, 15 to 45 wt.% sodium sulfate, preferably 26 to 41 wt.% sodium sulfate.

9. Descaling agent according to any of the preceding claims, characterized by the fact thatThe descaling agent contains, based on the solids content, 15 to 45 wt.% calcium carbonate, lithium carbonate or a mixture thereof, preferably 26 to 41 wt.% calcium carbonate, lithium carbonate or a mixture thereof.

10. Descaling agent according to any of the preceding claims, characterized by the fact that The descaling agent contains, based on the solids content, 15 to 45 wt.% boron silicate glass frit or ground boron silicate glass, preferably 26 to 41 wt.% boron silicate glass frit or ground boron silicate glass.

11. Descaling agent according to any of the preceding claims, characterized by the fact that The descaling agent contains, based on the solids content, 1 to 10 wt% fatty acid, fatty acid salt or a mixture thereof.

12. Descaling agent according to any of the preceding claims, characterized by the fact that The descaling agent contains 0.5 to 5 wt% free-flowing agent, based on the solids content.

13. Composition for the hot working of metals, characterized by the fact that the composition contains a descaling agent according to one of the preceding claims in an amount of 40 to 90 wt.% and furthermore 10 to 60 wt.% condensed alkali phosphates.

14. Composition according to claim 13, characterized by the fact that The condensed alkali phosphates are selected from condensed sodium phosphates, potassium phosphates and mixtures thereof, preferably from polyphosphates, pyrophosphates, metaphosphates and mixtures thereof, particularly preferably from disodium pyrophosphate [Na2H2P2O7], trisodium pyrophosphate [Na3HP2O7], tetrasodium pyrophosphate [Na4P2O7], sodium tripolyphosphate [Na5P3O 10 ], sodium trimetaphosphate [(NaPO3)3], sodium polyphosphate [(NaPO3) n ], dipotassium pyrophosphate [K2H2P2O7], tripotassium pyrophosphate [K3HP2O7], tetrapotassium pyrophosphate [K4P2O7], potassium tripolyphosphate [K5P3O 10 ], potassium trimetaphosphate [(KPO3)3], potassium polyphosphate [(KPO3)n ] and mixtures thereof.

15. Use of a descaling agent according to any one of claims 1 to 12 or a composition according to any one of claims 13 or 14 in the hot processing of metals, preferably in hot rolling processes for the production of seamless steel tubes, including MPM processes, PQF processes and FQM processes.

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