Method for manufacturing hot rolling rolls by laser cladding

Abstract

The present invention relates to a method for manufacturing a hot rolling roll by laser cladding a metallic outer coating layer onto a reusable steel shaft substrate having an axis of rotational symmetry, the metallic outer coating layer having a composition of a working tool steel, the composition for the metallic outer coating layer comprising 0.5-3.5% C, 2-18% Cr, 0.5-7% Mo, 0.5-8% V, 0.2-7% W, 0-5% Nb, 0-1% Ti, 0.5-2% Mn, 0.2-3% Si, and 0-3% Ni, with the balance being Fe and unavoidable impurities; - the composition for the metallic outer coating layer further comprises nitrogen in the range of 200-2500 ppm; - the sum of the atomic contents (in %) of MC carbide-forming elements selected from the group consisting of Ti, Nb, and V plus M selected from the group consisting of Mo, W, and Cr. 23 The present invention relates to a method for producing a hot rolling roll, characterized in that the sum of the atomic contents (in mass%) of C6 and / or M2C forming elements is 3 / 8 less than the sum of the atomic contents (in mass%) of the interstitial elements C and N + 0.01.

Description

Technical Field

[0001] The present invention relates to the field of manufacturing work rolls for hot rolling mills, preferably for strip rolling mills. More specifically, the present invention relates to work rolls obtained by a laser cladding method.

[0002] This application relates to an improvement of patent EP3006124B1, which is incorporated herein by reference.

Background Art

[0003] Manufacturers of work rolls for rolling mills are being forced to explore various materials that meet the increasingly stringent specifications in order to satisfy the high productivity and surface quality requirements of their customers. Under normal hot operating conditions, the table of the work roll needs to withstand wear and high-temperature thermal fatigue caused by the periodicity of its rapid cooling and reheating with each rotation of the roll. Such rolls need to have a ductile core and at the same time a very tough and wear-resistant surface, and can be manufactured by various methods, among which are conventional methods such as spin casting or centrifugal casting, laser cladding, or powder metallurgy by hot isostatic pressing of a shell constructed on a steel core.

[0004] Laser cladding is a surface treatment technology that involves depositing materials with different properties on a metal substrate using a laser beam. The consumable for cladding is deposited in the form of a wire or powder carried by an inert gas in order to coat a part of the substrate, and is injected into the molten pool in the lateral or coaxial direction of the laser beam, melted using the laser, and integrated. Laser cladding is often used to improve mechanical properties, provide higher wear resistance, heat resistance, or higher hardness, or enhance corrosion resistance.

[0005] Work rolls for hot strip rolling mills (HSMs) are typically manufactured using centrifugal casting and then heat-treated. The rolls consist of a core made of cast or forged iron or steel and an outer shell made of high-alloy steel, and their composition includes high carbon, Mn, Si, and carbide-forming elements such as W, Mo, V, Cr, Co, etc.

[0006] Document EP0070773A1 describes a method for laser cladding mild steel rolling rolls with HSS powder, i.e., high-speed steel powder. The typical composition (in mass units) of HSS powder is 0.5-2.6% C, 0.2-1.7% Mn, 0.2-1.4% Si, ≤0.2% S, 2-14% Cr, ≤12% Mo, ≤20% W, V: ≤10%, ≤16% Co, with the sum of W, V, Mo, and Co being ≥3%. Other usable types of HSS with typical elemental ranges are disclosed in this document, such as Cr-W steel, Cr-Mo steel, Cr-W-Mo steel, etc. The typical coating thickness is, for example, about 15 mm. After cladding, tempering (matrix softening, stress relaxation) is performed to precipitate carbides.

[0007] Furthermore, the references Scandella F., "Developpement d'un acier rapide pour le revetement de cylindres de laminage a chaud", Soudage et Technique Connexes, March-April 2010, pp. 35-46, and EP0533929A1 also mention the development of high-speed steel and composite rolls for rolling used as coating materials for rolling rolls (hot rolling rolls).

[0008] Document EP3006124B1 describes a method for manufacturing a rolling roll by laser cladding a metal coating outer layer to a reusable steel shaft base material having a rotationally symmetric axis, wherein the metal coating outer layer has the composition of a workpiece steel. - A process of rotating a reusable substrate around its axis of rotational symmetry; - A process for performing laser cladding on a rotating substrate by forming a molten pool on the surface of the substrate using laser light, and then supplying powder material to the laser-induced molten pool to deposit a coating layer; - A heat treatment process comprising heating a coated substrate to a temperature in the range of 500-650°C, followed by a tempering treatment in which the substrate is held at this temperature for a period of 2-5 hours, in order to soften the martensite and precipitate carbides. Includes; The composition for the metal coating outer layer consists of 0.5-3.5% C, 2-18% Cr, 0.5-7% Mo, 0.5-8% V, 0.2-5% W, 0-5% Nb, 0-1% Ti, 0.5-1% Mn, 0.2-3% Si, and 0-3% Ni, with the remainder being Fe and unavoidable impurities; The substrate is preheated by a coating head that combines induction heating with laser cladding; The cladding speed is within the range of 2.35 kg / h to 18 kg / h; and The aforementioned outer coating layer consists of a plurality of added coating sublayers, has an overall thickness ranging from 1 to 30 mm, and the thickness of each individual sublayer of the outer coating layer ranges from 0.1 to 2.5 mm. This document discloses a method for manufacturing rolling rolls.

[0009] The coating compositions for the rolls disclosed in EP3006124B1 are similar to the general alloy compositions of Scandella F. (ibid.) that have elemental ranges of C, Si, Mn, Cr, Mo, Nb, and V, with significant overlap for the ranges of W and Ti, and to the compositions disclosed in some examples of EP0533929A1.

[0010] However, the subject of EP3006124B1 proposes induction-assisted laser cladding, i.e., the use of a coating head that combines induction heating with the laser cladding process, which allows for preheating of the substrate and thereby provides a more efficient laser cladding process with a higher deposition rate and reduced tempering. This differs from the methods known in the previous three documents.

[0011] The document Bruckner F. et al., "Innovations in laser cladding and direct metal deposition," High Power Laser Materials Processing: Lasers, Beam Delivery, Diagnostics, and Applications, SPIE, 1000 20th St. Bellingham WA, USA (2012), Vol. 8239, No. 1, pp. 1-6, describes guided-assisted laser cladding with a high deposition rate of up to 18 kg / h on large cylindrical parts. However, this document does not specifically mention rolling rolls, and merely refers to Co-based (Stellite 20) and Ni-based (Inconel 625) cladding alloys in the case of guided-assisted laser cladding. HSS steel in general, or even cladding alloys for EP3006124A1, are not disclosed in this document.

[0012] Reference US2014 / 345353A1 discloses a centrifugal cast composite roll for hot rolling, comprising an outer layer having a composition containing 0.8–3.5 mass% C, 0.1–2.5 mass% Si, 0.1–2.5 mass% Mn, 1.2–15 mass% Cr, 1–5 mass% Ni, and 1–10 mass% Mo + 0.5 × W, with the remainder being substantially Fe and unavoidable impurities, and an inner layer made of an iron-based alloy and integrally fused with the outer layer; the outer layer having a Shore hardness of 67–82 at the initial diameter of the composite roll; and the maximum Shore hardness of the outer layer in the range of 30 mm or more deep from the initial diameter being 1 or more higher than the Shore hardness of the outer layer at the initial diameter.

[0013] Reference JP2020022989A aims to provide an outer layer material for centrifugal casting composite rolls for rolling that has excellent wear resistance and surface roughness resistance, and to provide a centrifugal casting composite roll for rolling manufactured by welding and integrating an outer layer and an inner layer composed of the outer layer material. Therefore, the material consists of 1.50-2.70 mass% C, 0.3-3 mass% Si, 0.1-3 mass% Mn, 0.1-2.5 mass% Ni, 4.0-7.0 mass% Cr, 4.1-8.0 mass% Mo, 5.0-10.0 mass% V, 0-0.4 mass% W, 0.1-3.0 mass% Nb, 0.005-0.15 mass% N, 0-0.05 mass% B, and substantially Fe and unavoidable impurities. An outer layer material for centrifugal casting composite rolls for rolling is provided, comprising an Fe alloy with a remainder consisting of a material, characterized in that the ratio of V content (mass%) to Nb content (mass%) is 1 to 20.0, and the C-bal, expressed by the following relationship: C-bal = C% - 0.2 × V% - 0.06 × Cr% - 0.063 × Mo% - 0.033 × W% - 0.13 × Nb%, is 0 to 0.28. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] EP0070773A1 [Patent Document 2] EP0533929A1 [Patent Document 3] US2014 / 345353A1 [Patent Document 4] JP2020022989A [Non-Patent Document]

[0015] [Non-Patent Document 1] Scandella F., "Developpement d’un acier rapide pour le revetement de cylindres de laminage a chaud", Soudage et Technique Connexes, March - April 2010, pp. 35 - 46 [Non-Patent Document 2] Bruckner F. et al., "Innovations in laser cladding and direct metal deposition", High Power Laser Materials Processing: Lasers, Beam Delivery, Diagnostics, and Applications, SPIE, 1000 20th St. Bellingham WA, USA (2012) Vol. 8239, No. 1, pp. 1 - 6 [Summary of the Invention] [Problems to be Solved by the Invention]

[0016] An object of the present invention is to provide a work roll for a hot rolling mill having a coating composed of a clad layer having very high soundness (in terms of cracks, voids, and oxidation).

[0017] In particular, an object of the present invention is to provide a method for manufacturing a rolling roll in which the cladding speed and the coating quality (i.e., in terms of the microstructure and the size of cracks) are simultaneously improved.

[0018] In addition, the present invention also aims to provide improved mechanical properties of the laser cladding layer (e.g., resistance to thermal fatigue and resistance to surface deterioration) together with a long-time cladding method for work rolls.

Means for Solving the Problems

[0019] The present invention is a method for manufacturing a hot rolling roll by laser cladding a metal coating outer layer on a reusable steel shaft substrate having a rotational symmetry axis, wherein the metal coating outer layer has a composition of a machining tool steel, - a step of rotating a reusable substrate around its rotational symmetry axis; - a step of performing laser cladding on the rotating substrate by forming a molten pool on the surface of the rotating substrate using a laser beam and depositing a coating layer by supplying a powder material to the laser-induced molten pool; - a step of subjecting the coated substrate to a heat treatment after cladding; including, the composition for the metal coating outer layer includes 0.5 - 3.5% C, 2 - 18% Cr, 0.5 - 7% Mo, 0.5 - 8% V, 0.2 - 7% W, 0 - 5% Nb, 0 - 1% Ti, 0.5 - 2% Mn, 0.2 - 3% Si, and 0 - 3% Ni, with the balance being Fe and unavoidable impurities; preheating of the substrate is performed by a coating head that combines induction heating with a laser cladding process; the cladding speed is within the range of 2.35 kg / h to 18 kg / h; and the coating outer layer consists of a plurality of additional coating sub-layers, has an overall thickness included between 1 and 30 mm, and the thickness of each one layer of the sub-layers of the coating outer layer is included between 0.1 and 2.5 mm, and further, - To enhance wear resistance, nitrogen is further included in the range of 200-2500 ppm, and in the case of multi-layer coatings, to achieve uniform hardness, the total atomic content (mass%) of MC carbide-forming elements selected from the group consisting of Ti, Nb, and V + M selected from the group consisting of Mo, W, and Cr. 23 A step of selecting a composition for the outer layer of the metal coating such that 3 / 8 of the total atomic content (mass%) of C6 and / or M2C-forming elements is less than the total atomic content (mass%) of interstitial elements C and N + 0.01; - To suppress cracking by obtaining a final hydrogen content of less than 1 ppm in the outer layer of the metal coating, the process involves drying or heating the powder used for cladding, strictly controlling the ambient humidity, and performing the cladding process under a controlled protective atmosphere. The present invention relates to a method for manufacturing a hot-rolling roll, characterized by including [a specific element].

[0020] According to preferred embodiments of the present invention, the method is further limited by one or a suitable combination of the following features: - The composition for the metal coating outer layer contains nitrogen in the range of 200 to 400 ppm; - The ambient dew point between cladding is between -5°C and +15°C; - The controlled protective atmosphere consists of N2 or Ar; - Laser output: 10-80 W / mm 2 Set within the range; - This method includes a preliminary step of preparing a reusable substrate by cleaning and / or machining the surface of the reusable substrate; - The surface roughness of the substrate before cladding is between 1 and 8 μm; - To reduce smoke generation during high-temperature cladding and further reduce oxidation of the coating, surface degreasing is performed before cladding, at 1 mg / m². 2 Obtain less than 50% surface organic carbon; - The composition for the metal coating outer layer further contains nitrogen in the range of 200 to 1500 ppm; - Preheating of the substrate is carried out in the range of 20°C to 500°C, preferably in the range of 200°C to 300°C; - The heat treatment after cladding is a tempering process that involves controlled cooling or heating to a temperature in the range of 500-650°C to soften the martensite and precipitate carbides, followed by holding at this temperature for a period of time between 2 and 5 hours; - The composition of the steel shaft material consists of 0.2-0.5% C, 0.5-5% Cr, 0-1% Mo, 0-1% Mn, and 0-0.4% Si, with the remainder being Fe and unavoidable impurities; - The composition of the steel shaft material includes 0.4% C and 1-2% Cr. [Modes for carrying out the invention]

[0021] The present invention relates to an improved laser cladding method for coating a roll having a steel shaft (or shaft or spindle) base material with a deposit of a "layer" of hot or cold-worked tool steel, which can be obtained from a continuous sublayer. The tool steel used is similar to and / or has a higher carbide content than the steel grade of an HSS work roll.

[0022] The inventors have extensively considered various options to enable complete industrial commissioning and improvement of the laser cladding manufacturing method for rolling rolls described in EP3006124B1.

[0023] Numerous parameters influence the integrity of the laser-clad layer, characterized by reduced (or absent) cracking, voids, and oxidation. Voids should be less than those found in products obtained by centrifugal casting, as measured by the DGS (Distance-Gain-Size) method described in ISO 16811:2012(en) (Non-destructive testing - Ultrasonic testing - Sensitivity and range setting) and ISO 5577:2017(en) (Non-destructive testing - Ultrasonic testing - Vocabulary).

[0024] No defects larger than 4mm in DGS (AVG) were observed at the interface between the laser cladding layer and the substrate. No defects larger than 0.5mm in DGS (AVG) were observed in the laser cladding layer, and the maximum number of <4mm indications on a 10cm x 10cm surface was 5.

[0025] According to some embodiments of the present invention: - The hydrogen content of the laser cladding layer is less than 1 ppm; - The hydrogen content of the powder used for cladding is less than 1 ppm, achieved by pre-drying or heating the powder; - The ambient dew point between cladding is between -5 and +15°C; - Cooling or post-cooling after cladding is controlled; - The substrate is preheated; - Laser output: 10-80 W / mm 2 It is within the range.

[0026] In particular, the hydrogen content must be kept as low as possible throughout all processing. In applications of this difficult-to-weld steel, hydrogen can cause weakening at grain boundaries, which can lead to cracking, but this can be avoided in the present invention.

[0027] Hydrogen may be present in traces of water or in the humidity of the atmosphere and cladding powder. Therefore, according to the present invention, the cladding powder is dried or heated, the ambient humidity is strictly controlled, and the cladding process is carried out under a controlled protective atmosphere, preferably consisting of N2 or Ar.

[0028] Furthermore, several parameters must have values ​​that produce a favorable effect on long-term cladding. According to some embodiments of the present invention: - The surface roughness of the substrate is between 0.2 and 8 μm; - Surface degreasing is performed before cladding, at 1 mg / m². 2Obtain less than 100% surface organic carbon. Proper degreasing is crucial because smoke generated during high-temperature cladding can lead to harmful oxidation of the coating.

[0029] Finally, in more detail, many parameters influence the mechanical properties of the laser-clad layer. An essential feature of the present invention is that the composition of the clad layer of the coating must follow a special relationship that depends on the ratio of carbon (or more generally, interstitial elements) to carbide-forming elements.

[0030] According to some embodiments of the present invention: - In order to achieve uniform hardness in multi-layer coatings, a specific relationship (i.e., an inequality) must be satisfied between interstitial elements and carbide-forming elements. According to the present invention, the atomic content (mass%) of MC carbide-forming elements (e.g., Ti, Nb, V, Ta, etc.) + M 23 3 / 8 of the atomic content (mass%) of C6 and / or M2C-forming elements (e.g., Mo, W, Cr, etc.) must be less than the atomic content (%) of interstitial elements (e.g., C, N, B, etc.) + 0.01; - The Mn content is between 0 and 2%, and the W content is between 0.2 and 7%; - The enhanced wear resistance is achieved by adding nitrogen in the range of 200 to 2500 ppm, preferably in the range of 200 to 400 ppm. [Examples]

[0031] Table 1 shows the above-mentioned relationship between carbide-forming elements and interstitial elements for a series of 11 coating alloys obtained by the present invention. For each case, the uniformity of hardness was checked and compared to see whether the inequality was satisfied. Hardness was considered uniform if the deviation was less than 50 HV (EN ISO 6507-1~6507-4).

[0032] [Table 1]

[0033] The characteristics of the laser cladding method used in this invention are as follows: - Strong metallurgical bond; - The advantages of having few or no cavities, and a fast cooling rate, are that they lead to a very fine microstructure; - Uniform composition; - Coating thickness: 0.1-2 mm per (sub) layer; - A thicker coating obtained by adding multiple layers, with the total thickness of the outer layer ranging from 1 to 30 mm, preferably about 20 mm; - Cladding speed of 2.35 kg / h to 18 kg / h achieved by using a special head (combination of induction heating and laser cladding); - Preheat the substrate if necessary; - Post-treatment (e.g., tempering).

Claims

1. A method for manufacturing a hot rolling roll by laser cladding a metal coating outer layer to a reusable steel shaft base material having a rotationally symmetric axis, wherein the metal coating outer layer has the composition of a processing tool steel. A process of rotating a reusable substrate around its axis of rotational symmetry; A process for performing laser cladding on a rotating substrate by forming a molten pool on the surface of the substrate using laser light, and then supplying powder material to the laser-induced molten pool to deposit a coating layer; A process of subjecting a coated substrate to post-cladding heat treatment; Includes, The composition for the metal coating outer layer comprises 0.5–3.5% C, 2–18% Cr, 0.5–7% Mo, 0.5–8% V, 0.2–7% W, 0–5% Nb, 0–1% Ti, 0.5–2% Mn, 0.2–3% Si, and 0–3% Ni, with the remainder being Fe and unavoidable impurities; The substrate is preheated by a coating head that combines induction heating with laser cladding; The cladding speed is in the range of 2.35 kg / h to 18 kg / h; and The aforementioned outer coating layer consists of a plurality of added sub-coating layers, has an overall thickness between 1 and 30 mm, and the thickness of each individual sub-layer of the outer coating layer is between 0.1 and 2.5 mm, further comprising the following steps: To enhance wear resistance, nitrogen is further included in the range of 200 to 2500 ppm, and in the case of multi-layer coatings, to achieve uniform hardness, the total atomic content (mass%) of MC carbide-forming elements selected from the group consisting of Ti, Nb, and V + M selected from the group consisting of Mo, W, and Cr. ２３ C ６ and / or M ２ A step of selecting a composition for the outer layer of the metal coating such that 3 / 8 of the total atomic content (mass%) of C-forming elements is less than the total atomic content (mass%) of interstitial elements C and N + 0.01; The process involves drying or heating the powder used for cladding, controlling ambient humidity, and performing the cladding treatment under a protective atmosphere, in order to suppress cracking by obtaining a final hydrogen content of less than 1 ppm in the outer layer of the metal coating. A method for manufacturing a hot-rolling roll, characterized by including [a certain element].

2. The method according to claim 1, wherein the selected composition for the metal coating outer layer contains nitrogen in the range of 200 to 400 ppm.

3. The method according to claim 1, wherein the ambient dew point between the claddings is between -5°C and +15°C.

4. The protective atmosphere is N ２ The method according to claim 1, comprising Ar or

5. Laser output: 10-80 W / mm ２ The method according to claim 1, which is set within the range.

6. The method according to claim 1, comprising a preliminary step of preparing a reusable substrate by cleaning and / or machining the surface of the reusable substrate.

7. The method according to claim 6, wherein the surface roughness of the substrate before cladding is between 1 and 8 μm.

8. To reduce smoke generation during high-temperature cladding and further reduce oxidation of the coating, surface degreasing is performed before cladding, at a rate of 1 mg / m². ２ The method according to claim 6, for obtaining surface organic carbon of less than 100%.

9. The method according to claim 1, wherein the composition for the metal coating outer layer contains nitrogen in the range of 200 to 1500 ppm.

10. The method according to claim 1, wherein the preheating of the substrate is performed in the range of 20°C to 500°C.

11. The method according to claim 1, wherein the heat treatment after cladding is a tempering treatment comprising controlled cooling or heating to a temperature in the range of 500 to 650°C, followed by holding at this temperature for a period of time between 2 and 5 hours, in order to soften the martensite and precipitate carbides.

12. The method according to claim 1, wherein the composition of the steel shaft material comprises 0.2 to 0.5% C, 0.5 to 5% Cr, 0 to 1% Mo, 0 to 1% Mn, and 0 to 0.4% Si, with the remainder being Fe and unavoidable impurities.

13. The method according to claim 12, wherein the composition of the steel shaft material comprises 0.4% C and 1-2% Cr.

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