Restoration surfacing of metallurgical equipment components with flux-cored wires in «TM.WELTEC Ltd.»

L.N. Orlov, A.A. Golyakevich («TM.WELTEC Ltd.», Kiev, Ukraine)

Poster Paper for International Conference WELDING AND RELATED TECHNOLOGIES. PRESENT AND FUTURE (25—26 November, 2013, Kiev, Ukraine).

The electric arc surfacing with flux-cored wire occupies the strong positions in renovation of parts of machine and mechanisms of metallurgical equipment.
     For restoration surfacing of rollers of machines for continuous casting of billets the enterprise «TM.WELTEC Ltd.» is manufacturing the flux-cored wire WELTEC-H470 of 2.0—4.0 mm diameter in combination with fluxes AN-20 and AN-26 and self-shielding wire WELTEC-H470S of 2.0—2.4 mm diameter. These flux-cored wires provide a spontaneous removal of slag crust, absence of pores and cracks in deposited metal if the technological recommendations are kept. The comparative tests of flux-cored wires WELTEC-H470 and WELTEC-H470S showed that they are at the level of wires of leading foreign companies, such as OK15.73 (ESAB), 4142MM-S LC, 414MM-S (Weldclad), WLDC-3N (Welding Alloys). The as-surfaced rollers have a service life of not less than 1.5 million tons.
     Mill rolls are the main technological tool in rolling process of metallurgical plants. The technical-economical characteristics of operation of milling shops and, first of all, the efficiency of rolling mills, quality of ready rolled metal and expenses for its production depend mainly on their reliability, wear resistance of working surface, inter-repair period of service life.
     «TM.WELTEC Ltd.» together with metallurgical plants «Krivorozhstal», Dneprovsky Metallurgical Works after name of Dzerzhinsky, «Zaporozhstal» has carried out a complex of works, directed to the improvement of surfacing materials, technologies and equipment for surfacing the mill rolls. On the base of standard flux-cored wires of grades FCW-Sw-35W9Cr3SiV and FCW-Sw-25Cr5VMoSi the alloying systems were optimized and new flux-cored wires were developed with account of conditions of service of mill rolls: WELTEC-H370-RM, WELTEC-H460, WELTEC-H500-RM, WELTEC-H500-RM, WELTEC-H505-RM, WELTEC-H550-RM Surfacing with these wires is performed under fluxes AN-20, AN-26, AN-348A. The application of offered wires increased the efficiency of mill rolls operation. The task of increasing the effectiveness in use of pipe-rolling mills is urgent, including the increase of period of inter-repair service life of rolls.
     Together with Nikopol plant of seamless pipes (CJSC «Niko Tube») the works were made on implementation of continuous mill of flux-cored wire WELTEC-H480NT with alloying system C—Si—Mn—Cr—V—Mo—W into the process of strengthening surfacing of rolls. The wire provides a stable process of surfacing under fluxes AN-20S, AN-26P at direct current of reversed polarity, easy removal of slag crust, absence of cracks and pores in the deposited metal. Hardness of deposited metal is 50—56 HRC. The improvement of quality of pipes being rolled and increase in period of servile life of mill rolls became the premises of application of the wire at the CJSC «Niko Tube».
     There is a whole series of flux-cored wires at the «TM.WELTEC Ltd.» for the repair of the metallurgical equipment components.
     The self-shielding flux-cored wire WELTEC-H250-RM of 1.6—3.0 mm diameter is used successfully at restoration of pads of rolling stands and shears, spindles and couplings of drives of mill rolls, sprockets, bushings, shafts, hubs, etc. As to their characteristics the VELTEK-N250-RM is at the level of the best foreign samples of wires, for example DUR 250-FD (Bohler).
     The surfacing of center-punches of tong-type cranes and bites of stripping crane, which during service undergo the shock and compressive loads under high-temperature conditions, was realized. Center-punches contact the metal heated up to 800—1250 °C and subjected to thermal cycling (periodic cooling in water tanks). For this purpose the self-shielding flux-cored wire of grade WELTEC-H480S of 2.0 mm diameter with alloying system (C—Cr—W—Mo—V—Ti) was used, providing the hardness HRC 50—54 of deposited metal after surfacing, hot hardness HRC 40—44 at 600 °C. The application of mechanized surfacing with wire WELTEC-H480S instead of electrodes T-590, T-620 allowed increasing the period of service life of punches by 4—5 times. The task of restoration of punches was integrally solved (equipment-material-technology).
     For surfacing the crane wheels the flux-cored wires of grades WELTEC-H300-RM, WELTEC-H350-RM of 1.6—4.0 mm diameter were offered. The surfacing is realized under fluxes AN-348, AN-60 or in CO₂. During recent years, WELTEC-H300-RM is successfully applied instead of solid wire Np-30KhGSA. For surfacing of wheels of heavy loaded cranes the technology of surfacing under flux AN-348 with fluxcored wire of WELTEC-H285 grade of 3.6 mm diameter was developed. Chrome-manganese deposited metal with a structure of metastable austenite provides the high wear resistance of wheels due to the development of the self-strengthening process under the effect of cold working.