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US-12623303-B2 - Method for manufacturing a work roll by laser cladding

US12623303B2US 12623303 B2US12623303 B2US 12623303B2US-12623303-B2

Abstract

A method for manufacturing a hot rolling mill roll by laser cladding a reusable steel axe substrate having a rotational symmetry axis with a metal coating external layer, the metal coating external layer having a work tool steel composition, the method including: rotating the reusable substrate around the rotational symmetry axis; effecting a laser cladding on the rotating substrate by forming a melt pool on a surface of the rotating substrate by a laser beam as a laser-induced melt pool and affixing the coating layer by feeding a powder material into the laser-induced melt pool to form a coated substrate; and submitting the coated substrate to a post-cladding thermal treatment. The composition for the metal coating external layer is 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, a remainder being Fe and inevitable impurities.

Inventors

  • Gisèle Walmag
  • Grégory Esser
  • Mario Sinnaeve

Assignees

  • Centre De Recherches Métallurgiques ASBL

Dates

Publication Date
20260512
Application Date
20211013
Priority Date
20201013

Claims (14)

  1. 1 . A method for manufacturing a hot rolling mill roll by laser cladding a reusable steel axe substrate having a rotational symmetry axis with a metal coating external layer, the metal coating external layer having a work tool steel composition, the method comprising: rotating the reusable substrate around the rotational symmetry axis; effecting a laser cladding on the rotating substrate, by forming a melt pool on a surface of the rotating substrate by a laser beam as a laser-induced melt pool and affixing the coating layer by feeding a powder material into the laser-induced melt pool to form a coated substrate; and submitting the coated substrate to a post-cladding thermal treatment, wherein the composition for the metal coating external 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, a remainder being Fe and inevitable impurities, wherein a preheating of the substrate is performed due to a coating head combining induction heating with a laser cladding process, wherein a cladding rate is in a range from 2.35 kg/h to 18 kg/h, and wherein the external coating layer comprises multiple added coated sublayers and has a total thickness between 1 and 30 mm, a thickness of each single external coating sublayer being between 0.1 and 2.5 mm, wherein the method further comprises: selecting a composition for the metal coating external layer that comprises nitrogen in a range 200-2500 ppm, so as to increase abrasion resistance and in which a sum of atomic contents (mass %) of MC carbides forming elements, selected from a group consisting of Ti, Nb, and V, +3/8 of a sum of atomic contents (mass %) of M 23 C 6 and/or M 2 C forming elements, selected from a group consisting of Mo, W, and Cr, is lower than a sum of atomic contents (mass %) of interstitial elements C and N, +0.01, so as to achieve homogeneous hardness for a multilayer coating; and drying or heating the powder used for cladding, controlling strictly ambient humidity, and performing the cladding process under a controlled protecting atmosphere so as to obtain a final hydrogen content in the metal coating external layer lower than 1 ppm, permitting suppression of cracks.
  2. 2 . The method of claim 1 , wherein the selected composition for the metal coating external layer comprises nitrogen in a range of 200-400 ppm.
  3. 3 . The method of claim 1 , wherein an ambient dew point during cladding is between −5° C. and +15° C.
  4. 4 . The method of claim 1 , wherein the controlled protective atmosphere comprises N 2 or Ar.
  5. 5 . The method of claim 1 , wherein a laser power is set in a range from 10 to 80 W/mm 2 .
  6. 6 . The method of claim 1 , further comprising: preliminarily preparing the reusable substrate by cleaning and/or machining a surface of the reusable substrate.
  7. 7 . The method of claim 6 , wherein a surface roughness of the substrate before cladding is between 1 and 8 μm.
  8. 8 . The method of claim 6 , wherein a surface degreasing is applied before cladding to obtain less than 1 mg/m 2 of surface organic carbon to reduce production of fumes during high temperature cladding and to reduce oxidation of the coating.
  9. 9 . The method of claim 1 , wherein the composition for the metal coating external layer comprises nitrogen in a range 200-1500 ppm.
  10. 10 . The method of claim 1 , wherein the preheating of the substrate is performed in a range of 20° C.-500° C.
  11. 11 . The method of claim 10 , wherein the preheating of the substrate is performed in the range of 200° C.-300° C.
  12. 12 . The method of claim 1 , wherein the post-cladding thermal treatment comprises a controlled cooling, or a tempering treatment comprising a heating up to a temperature in a range 500-650° C. followed by a holding at such temperature for between 2 and 5 hours, in order to soften martensite and precipitate carbides.
  13. 13 . The method of claim 1 , wherein the composition of the steel axe comprises 0.2-0.5% C and 0.5-5% Cr, 0-1% Mo, 0-1% Mn and 0-0.4% Si, a remainder being Fe and the inevitable impurities.
  14. 14 . The method of claim 13 , wherein the composition of the steel axe comprises 0.4% C and 1-2% Cr.

Description

CROSS-REFERENCE TO PRIOR APPLICATIONS This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/EP2021/078329, filed on Oct. 13, 2021, and claims benefit to European Patent Application No. EP 20201483.3, filed on Oct. 13, 2020. The International Application was published in English on Apr. 21, 2022 as WO/2022/079108 A1 under PCT Article 21(2). FIELD The present invention is related to the field of manufacturing work rolls intended for hot mills, and preferably intended for strip rolling mills. The invention is more specifically related to work rolls obtained by the laser-cladding method. The present application is related to an improvement of patent EP 3 006 124 B1, which is incorporated by reference in the present patent application. BACKGROUND In order to meet high productivity and surface quality requirements of their customers, manufacturers of work rolls for rolling mills are led to explore different materials submitted to increasingly harsh specifications. Under normal hot operating conditions, the table of the work roll has to withstand wear and hot thermal fatigue induced by the periodicity of its fast cooling and reheating at each revolution of the roll. Such rolls, that are required to have a very tough and wear-resistant surface while having a ductile core, can be manufactured by various techniques, among which spin or centrifugal casting, which is the conventional method, laser cladding or powder metallurgy by hot isostatic pressing of a shell built up to a steel core. Laser cladding is a surface-processing technology involving the deposition of a material of different nature on a metal substrate using a laser beam. Cladding consumables are deposited in either wire or powder form transported by an inert gas, injected into the molten pool, either laterally or coaxially to the laser beam, melted and consolidated by use of the laser, in order to coat part of the substrate. It is often used to improve mechanical properties, to provide higher wear resistance, heat resistance or higher hardness or to increase corrosion resistance. Work rolls for hot strip mills (HSM) are usually manufactured using the spin-casting method followed by a heat treatment. The roll is constituted by a cast or forged iron or steel core with an external shell of highly alloyed steel grade, which composition comprises high carbon, Mn, Si and elements generating carbides, such as W, Mo, V, Cr, Co, etc. Document EP 0 070 773 A1 relates to a method for laser cladding a HSS powder, i.e. a high speed steel powder, on mill rolls made of mild steel. The HSS powder has a general composition (in mass) of: 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, Co≥3. Additional usable types of HSS with typical elemental ranges are disclosed in this document, e.g. Cr—W steels, Cr—Mo steels, Cr—W—Mo steels. A typical coating thickness is e.g. about 15 mm. The cladding is followed by a tempering treatment to precipitate carbides (soften matrix, stress relief). In addition, documents Scandella F.; “Développement d′un acier rapide pour le revêtement de cylindres de laminage á chaud”, Soudage et Technique Connexes, Mars-Avril 2010, pp. 35-46, and EP 0 533 929 A1 also refer to the development of high speed steels used as coating materials for mill rolls (hot working rolls) and to composite rolls for use in rolling. Document EP 3 006 124 B1 discloses a method for manufacturing a rolling mill roll by laser cladding a reusable steel axe substrate having a rotational symmetry axis with a metal coating external layer, said metal coating external layer having a work tool steel composition, comprising the steps of: rotating the reusable substrate around its axis of rotational symmetry;effecting a laser cladding on the rotating substrate, by forming a melt pool on the surface of the rotating substrate by means of a laser beam and affixing the coating layer by feeding a powder material into the laser-induced melt pool;submitting the coated substrate to a thermal treatment made of a tempering treatment comprising a heating up to a temperature in the range 500-650° C. followed by a holding at this temperature during a time comprised between 2 and 5 hours, in order to soften martensite and precipitate carbides;wherein the composition for said metal coating external layer is consisting 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, the rest being Fe and inevitable impurities;wherein a preheating of the substrate is performed, thanks to a coating head combining induction heating with laser cladding process;wherein the cladding rate is in the range from 2.35 kg/h to 18 kg/h; andwherein said external coating layer is made of multiple added coated sublayers and has a total thickness comprised between 1 and 30 mm, the thickness of each single external coating sublayer being comprised betw