Modern metallurgical production is unthinkable without the technology of continuous casting of steel and is due to significant savings in energy and time costs, increased productivity and product quality, reduced production losses, and the implementation of more effective investments. In this regard, the systematic introduction of continuous casters is being carried out and, as a result, an increase in the volume of their production and repair is expected. The experience of metallurgical enterprises shows that the technical and technical-economic indicators of continuous casting machines (CCMs) largely depend on the durability of the rollers of the supporting systems. The rollers of the support and extension units operate under severe thermal cycling conditions; the maximum surface temperature of the rollers can reach 650–750 °C. The rollers absorb forces from ferrostatic swelling and forces from unbending the ingot. In straight sections, the rollers are subject to abrasive wear (Fig. 1). Destruction of the working surface of the rollers manifests itself in the form of wear of the surface layer and the formation of cracks. In accordance with production requirements, the wear rate of the working surface material should not exceed 0.1-0.25 mm per 1 thousand melts, while the continuous caster must produce at least 1 million tons of workpieces without changing rollers. It is known that electric arc surfacing of the working surfaces of rollers with wear- and corrosion-resistant steel is the most effective and widespread way to increase the service life of such parts. This method of strengthening rollers is used by most companies creating continuous casters both in our country and abroad.
The TM.VELTEC company solves this problem for metallurgical plants and repair enterprises by providing a wide range of surfacing flux-cored wires and know-how on surfacing technology (table). The wires are adapted to submerged arc surfacing processes, in CO 2 and Ar+CO 2 and open arc, and their characteristics are not inferior to foreign and domestic analogues.
Fig.1. Scheme of a continuous steel casting installation.
Submerged Surfacing
Submerged arc surfacing technologies are implemented along a helical line with a single and split arc, without oscillations and with transverse oscillations starting from a diameter of 70 mm and more. The most common technology is two-layer surfacing, and a number of repair services use three-layer surfacing. For this surfacing method, we produce wires with a diameter from 2.0 to 4.0 mm. The offered flux-cored wires make it possible to fuse a layer of metal onto the working surface of the rollers that is resistant to multi-factor wear. The combination of flux-cored wire and flux makes it possible to obtain a high-chromium (Cr-Mn-Ni-Mo-N, Cr-Mn-Ni-Mo-V-Nb) weld metal with a ductile structure of low-carbon martensite, strengthened by dispersed carbides and nitrides while minimizing the δ content ferrite 5-10% (Fig. 2).
Fig.2. Microstructure of the deposited metal WELTEC-N470(×1000) (volume fraction of δ-ferrite 3.8%, hardness after surfacing 42–46 HRC).
This problem was solved by reducing the carbon content C< 0,1% и частичной замены его азотом реализацией нами разработанного способа легирования азотом, оптимизации хрома и карбидообразующих элементов, а также параметров термического цикла наплавки. Наши порошковые проволоки адаптируется к различным вариантам технологии наплавки: количество наплавляемых слоев и марка основного металла роликов, выполнение наплавки с подслоем или без него с цель обеспечения требуемого химического состава и структурного состояния наплавленного металла. К преимуществам наплавки под флюсом можно отнести: высокую производительность, малый припуск на механическую обработку при соблюдении режимов и техники наплавки, отсутствие светового излучения и минимизация выделения дыма. Для наплавки высокохромистых сплавов рекомендуется применять флюсы марок АН26Н, АН20С. Недостатком этих флюсов является ухудшение отделимости шлаковой корки при температуре поверхности наплавляемого ролика более 300°С, что связано с высоким содержанием двуокиси кремния в составе флюсов. Состав шихты порошковой проволоки частично нейтрализует окислительную способность флюсов и достигается улучшение отделимости шлаковой корки (рис. 3). Наиболее предпочтительно применение нейтральных керамических флюсов, например, WAF325 (Welding Alloys), Record SK (Soudokay), OK 10.33, ОК 1061 (ESAB), которые обеспечивают самопроизвольное отделение шлаковой корки и более низкое содержание вредных примесей (S, P) в наплавленном металле (рис.3).
Fig.3. Surfacing of a continuous caster roller with WELTEC-N470 flux-cored wire under WAF325 flux.
Surfacing in shielding gas.
The use of surfacing in a protective gas is most effective in a mixture of 82Ar+18CO 2 or Ar compared to carbon dioxide due to the higher stability of the process, reduced oxidizing ability of the protective gas, and reduced penetration of the base. The advantages include acceptable process performance, visual control of the surfacing process, the chemical composition is set by the composition of the wire and there is no influence characteristic of the flux, lower hydrogen content in the deposited metal compared to flux, and easier implementation of the process with transverse vibrations of the wire. The surfacing process is characterized by good metal formation, easy separation of the slag crust and the possibility of surfacing the subsequent layer without removing the slag. The disadvantages include: the need for protection from splashes and arc radiation, a less smooth surface of the deposited metal, the need to use smoke exhausters, and splashing of the shielding gas supply nozzle. For this surfacing method, we produce wires with a diameter of 1.6 to 2.4 mm both for applying the sublayer and working layers of the deposited metal.
Open arc surfacing.
The open arc surfacing process has the advantages inherent in the process in shielding gas and is complemented by the absence of the need to use shielding gas, a more simplified configuration of the surfacing installation, but its most significant advantage is in the metallurgical aspect. With this surfacing method, the possibility of alloying the deposited metal with nitrogen is realized. The need for such a metallurgical solution is due to the urgency of increasing the service life of continuous caster rollers by increasing the resistance of the deposited metal to heat and corrosion. This solution was most successfully implemented by the English company Welding Alloys. The working surface of the roller is subjected to cyclic exposure to high temperatures, which leads to a change in the structural state of the near-surface layer of the metal. The enlargement of grains and the formation of chromium carbides at their boundaries are observed, which leads to the development of intergranular corrosion. The loss of carbon by the martensitic matrix leads to the formation of a soft ferrite layer with low resistance to mechanical wear. Replacing part of the carbon with nitrogen suppresses the processes of grain coarsening and the formation of chromium carbides at the grain boundaries. The resulting nitrides are evenly distributed in the metal structure, and the effect of secondary strengthening appears during thermal cycling. The implementation of these mechanisms allows you to increase the service life of the rollers. For this surfacing method, we produce wires with a diameter of 2.0–2.4 mm.
Flux-cored wires from the TM.VELTEC company for surfacing caster rollers.
| Process | Wire | Diameter, mm | Protection |
| Submerged Surfacing | Weltek-N470(C-Cr-Ni-Mo-V-Nb) 2 and 3 layers, HRC 40—45 Base steel: 15Х1МФУ. 25Х1М1Ф 16CrMo4(DIN10083) 21CrMoV511, 25CrM04 St52-3 (DIN10025) | 2,0—3,6 | AN20, AN26 WAF325 Record-SK OK10.33 OK 10.61 |
| Veltek-N470.01(Cr-Ni-Mo-V-Nb-N) 2 layers, HRC40-45 Base steel: 42CrMo4 (DIN10083) | 2,4—3,6 | ||
| Weltek-N470(C-Cr-Ni-Mo-V-Nb) 1 layer HRC40-45 Base steel: 42CrMo4 (DIN10083) Sublayer Weltek-N472(Cr-Mn) | |||
| Veltek-N470.02(C-Cr-Ni-Mo-V) 2 and 3 layers, HRC47-54 Base steel: 15Х1МФУ. 25Х1М1Ф 16CrMo4(DIN10083) 21CrMoV511, 25CrM04 St52-3 (DIN10025) | |||
| Surfacing in shielding gas | Veltek-N470G(Cr-Ni-Mo-V-Nb-N) 2 layers HRC40-45 Base steel: 15Х1МФУ. 25Х1М1Ф 16CrMo4(DIN10083) 21CrMoV511, 25CrM04 St52-3 (DIN10025) | 1,6—2,4 | CO 2 Ar 82Ar+18CO 2 |
| Open arc surfacing | Weltek-N470S(Cr-Ni-Mo-V-Nb-N) 2 layers HRC44-50 Base steel: 15Х1МФУ. 25Х1М1Ф 16CrMo4(DIN10083) 21CrMoV511, 25CrM04 St52-3 (DIN10025) | 2,0—2,4 | self-protective |
| Veltek-N470S.01(Cr-Ni-Mo-N) 2 layers HRC38-42 Base steel: 15Х1МФУ. 25Х1М1Ф 16CrMo4(DIN10083) 21CrMoV511, 25CrM04 St52-3 (DIN10025) |
Orlov L. N., Golyakevich A. A., Khilko A. V., Giyuk S. P. (TM.VELTEC, Kiev)
2.4 Materials of caster rollers
The roller is made from a centrifugally cast billet from steels 25Х1М1Ф, 40ХГНМ, Х12МФЛ.
This method is used, as a rule, in the manufacture of a new continuous caster roller, since the features of centrifugal casting make it possible to use the manufactured barrel without welding the surface layer. Later, during repairs, the barrels undergo welding of a surface layer with increased hardness
2.4.1 Consider a roller made of steel 25Х1М1Ф:
Steel properties:
1) Chemical composition:
Table 1
2) Temperature of critical points:
Ac1 = 770 - 805, Ac3(Acm) = 840 - 880
3) Physical properties of the material:
table 2
T - Temperature at which these properties were obtained, [degrees]
E- Elastic modulus of the first kind, [MPa]
a - Coefficient of thermal (linear) expansion (range 20o - T),
l- Thermal conductivity coefficient (heat capacity of the material), [W/(m deg)]
r- Material density, [kg/m3]
C - Specific heat capacity of the material (range 20o - T), [J/(kg deg)]
R - Electrical resistivity, [Ohm m]
3 Special part
3.1 Equipment and materials
3.1.1 Turning before and after surfacing is carried out on lathes with a center height and center-to-center distance that allows a roller, type 1M63, to be fixed in them.
3.1.2 Surfacing is carried out using a standard surfacing installation UDGN - 401, designed for surfacing bodies of rotation.
The surfacing head is equipped with gas equipment (burner for surfacing with a consumable electrode in shielding gases, flow meter reducer, mixer, gas valve, gas cylinder) equipment.
The installation for surfacing in protective gases is expediently equipped with a pump and a tray for collecting water. Water is supplied by a pump to cool the burner and small rollers (< 200 мм) диаметров. Сварочный выпрямитель должен имеет жесткую (пологопадающую) характеристику.
3.1.3 Electric furnace N-60 for heat treatment of rollers with a heating temperature of up to 400°C and dimensions of the working space.
3.1.4 Surfacing of continuous caster rollers is planned to be done with heat-resistant stainless steels, ensuring the hardness of the deposited layer NYAS E 32...47.
Sv-06Х19Н10М3Т – for mold rollers, bender rollers.
Np-20Х16МГСФР, Нп-30Х16МГСФР - for rollers experiencing predominantly mechanical wear;
Sv-12Kh15G2 with predominant cracking of the roller barrel;
Sv-10Х14Г14Н4Т – for surfacing seats and places for seals and bender rollers.
Shielding gas “Ag+CO 2 10%”.
3.1.5 For layers preceding the working one (sublayer), the use of Sv-08G2S wire is allowed, the protective medium is “Ag + CO 2 10%”.
3.1.6 Grinding of rollers is carried out on a 3K228A cylindrical grinding machine.
3.2. Preparatory operations
3.2.1 Groove for surfacing
3.2.1.1 Grooving fits for oil seals and bearings - to a depth of 1.5 mm per side or 3.0 mm per diameter from the drawing size
3.2.1.2 Grooving the roller barrel
Table 3
| № | Side removal, mm | Conditions |
| 1 | If the roller has not been ground to repair size | |
| 2 | If the roller has been ground to a repair size or to remove heat cracks | |
| 3 | For removing particularly large fire cracks |
3.2.1.3 Mode of turning rollers for surfacing using VK8 cutters, with cooling of the cutter by emulsion:
cutting speed – 40 m/min;
feed – 0.25-0.4 mm/rev;
cutting depth, mm - 1-2 mm;
The main angle of the cutter in the plan is 60°.
3.2.1.4 The turner is obliged to write down its actual diameter with a marker on each machined surface
3.2.2 Special preparation of surfacing wire for surfacing is not required, because it is resistant to atmospheric corrosion and does not rust
3.2.3 Heat rollers with a diameter of more than 200 mm along the edge of the beginning of surfacing to 100°C
3.3 Surfacing
3.3.1 The last (working) layer must be fused onto a surface with a diameter less than the nominal diameter by 4.0 ± 0.2 mm. In this case, a turning allowance of 1.5 +1.0 mm per side (3.0 +2.0 mm per diameter) must be provided.
3.3.2 To avoid additional grooves for surfacing, surfacing of the layer preceding the last one (sublayer) must be done “to size”, that is, ensure a surface diameter corresponding to the groove according to clause 1 in Table 1
3.3.3 When surfacing in a mixture of “Ar + CO 2 10%”, it is important to do the following. Mixture flow rate -10-15 l/min
The welding wire must be fed continuously, not get caught anywhere, and not rub against sharp corners to remove chips, otherwise there may be disruptions in the stability of the arc process.
The current-carrying tip must not be allowed to wear too much, as this will cause “shooting” and sticking of the wire; worn out - replace in a timely manner.
The process of transferring molten metal at currents above 270A should have a jet nature; droplet transfer indicates insufficient current and voltage. To increase the welding current, increase the filler wire feed speed or arc voltage.
Stability of the arc process with jet transfer is possible only with optimal mixture content and optimal arc voltage.
It is important that:
The end of the electrode wire and the current-carrying tip were located in the center of the gas nozzle. Otherwise, due to poor quality protection of the weld pool with shielding gas, pores may form. With good gas protection, the surface of the directional rollers is yellow or light red, but not gray-black;
the distance from the nozzle cut to the surface of the welded part was no more than 15...20mm;
The distance from the nozzle exit to the end of the current-carrying tip was about 5 mm;
The protrusion of the electrode wire was about 20...25 mm, this is the distance from the end of the current-carrying tip to the surface of the welded part.
As a result, with a well-tuned process, the arc emits a smooth hum without “snorting” or crackling, and the voltmeter and ammeter needles have only a subtle fluctuation.
3.4 Restoring the seating of the continuous caster rollers under the oil seal and bearing
Worn and damaged roller seats are restored by surfacing. The modes for turning the landings are the same as when turning the roller barrel. Surfacing of seats for bearings and seals is carried out using Sv-10Kh14G14N4T wire, Ø1.4... 1.6 mm in the “Ar + CO 2 10%” environment. Water is supplied to the bead adjacent to the bead for cooling at a flow rate of 2-3 l/min. In order to ensure high-quality penetration of the fillet, surfacing the neck should begin with it.
3.5 Post-surfacing operations
3.5.1 After surfacing, the rollers are placed in a thermostat (electric furnace) with a temperature of 400°C, where they are kept for 4 hours, allowed to cool with the furnace to 100°C, then removed
It is allowed to cool the roller in the workshop before release, but in this case the roller barrel must be completely covered with asbestos cloth, and the temperature in the workshop should not be lower than 10...15°C without drafts.
3.5.2 Grinding the roller to the working size is carried out in 3 passes: the first is roughing, the second is semi-finishing, the third is finishing. Turning modes are given in table No. 2
Table 4. Modes of mechanical processing of continuous caster rollers
| № | m/o modes Holy material, hardness (HRC) | Cutter grade | V cut, m/min. | S mm/rev. | t, mm | Number of passes |
| 1. | Rough pass Sv-12Х15Г2, Нп-20Х16МГСФР, Sv-06Х19Н9МЗТ, Sv-10Х14Г14Н4Т | VK-8 | 33-39 | 0,4-0,5 | 1,5 | 1 |
| 2. | P/finishing and finishing passes | VK-8 | 45-72 | 0,15-0,2 | 0,15-0,3 | 2 |
| 3. | Rough pass 30X16MGSFR, (NKS 48-52) P/finishing and finishing passes | VK-8 | 25-30 | 0,2-0,3 | 1,5 | 1 |
| VK-8 | 35-55 | 0,15-0,2 | 0,1-0,2 | 2 |
3.5.3 Boil local defects (pores, lack of fusion) after rough turning with an argon arc with filler wire similar to the deposited one. Single pores with a diameter of less than 1 mm are allowed, no more than 5 pcs. per barrel
3.5.4 Defects occupying a significant area (track of pores) must be removed by grooving and subsequent surfacing according to these instructions
3.6 Safety precautions
3.6.1 Persons who have the right to work on automatic surfacing installations and have passed a knowledge test (under signature) of the provisions of this instruction are allowed to surfacing caster rollers
3.6.2 When restoring caster rollers by surfacing, it is sufficient to comply with the requirements of safety instructions for those working on automatic surfacing installations, manual argon-arc welders, turners, heat treatment technicians and slingers
3.6.3 Particularly dangerous factors and measures to protect against them when restoring caster rollers:
Damage to the eyes from pieces of slag when beating off a slag crust - work with glasses;
Damage to the eyes and skin from light radiation from an argon arc - wear glasses to protect your eyes from ultraviolet radiation, use light filters and light-protective screens.
Table 5 Surfacing modes for continuous caster rollers
| № | Roller Ø, mm, length, mm. | Ø, mm. | Surfacing modes | |||||||
| Wire brand | Protection | t pitch, mm/rev | m/hour n rpm | |||||||
| Ø pr. | Ø fill | |||||||||
| 1 | Ø100* L=630, 300, 202, 134. | Sv06Х19Н10М3Т, Ø1.4 | 230-240 | 28 | 5,5 | |||||
| 2 | Ø150 L=565, 435. | Sv10Х14Г14Н4Т Ø1.4 | ---- | 270-280 | 29 | 6,5 | ||||
The invention relates to material compositions used for hardening surfacing of rollers of open or closed arc continuous casting machines. The material contains, wt.%: carbon 0.01-0.07, manganese up to 2.0, silicon up to 1.0, chromium 11-16, nickel 3.0-5.0, molybdenum 1.0-2.5 , vanadium 0.1-1.0, tungsten 0.1-1.0, nitrogen 0.05-0.2, cobalt up to 2.0, niobium 0.1-1.0, sulfur and phosphorus 0.03 max , iron - the rest. The performance indicators in the operation of rollers of continuous casting machines are improved. 3 tables
The present invention relates to continuous casting of steel, and more precisely to the compositions of materials used for hardening surfacing of continuous caster rollers.
The technology of continuous casting of steel has a set of advantages that determine its prospects and growth in application volumes. The productivity and efficiency of continuous casting machines (CCMs) are related to the number of repairs due to the durability of the rollers. The development and application of highly efficient surfacing materials and restoration surfacing of continuous caster rollers is an urgent task.
Abroad, the actual durability of rollers has been achieved at 3,000,000 tons, and in domestic metallurgy 500,000 tons. This difference is determined by the higher quality of the surfacing material and surfacing technology. In the domestic metallurgy, solid and flux-cored wires 2Х13, 20Х17 are traditionally used for restoration surfacing of continuous caster rollers, providing chromium deposited metal with a ferritic-martensitic structure.
The difference in the structural and phase composition of the deposited metal determines the performance of continuous caster rollers, which are operated under conditions of long-term cyclic and thermomechanical loads. The rollers of the support and extension units operate in severe temperature conditions. The surface temperature of the rollers reaches 670-750°C. The rollers absorb forces from ferrostatic swelling and forces from unbending the ingot. In straight sections, the rollers are subject to abrasive wear. Destruction of the working surface of the rollers manifests itself in the form of wear of the surface layer and the formation of cracks. In connection with the above, it is most promising to apply reinforcing layers of complexly alloyed chromium metal to the working surface of the rollers.
A composition of surfacing material is known, containing in %:
C 0.1-0.3; Si<1; Mn <3; Мо <1,5; Ni <3; остальное - железо (патент Великобритании GB 2253804 В).
The closest to the claimed one is the surfacing material according to patent RU 2279339 C2. However, the increased carbon content in this surfacing material leads to the precipitation of chromium carbides along the grain boundaries, depleting the grain boundaries of chromium, which, in turn, increases intergranular corrosion and the tendency to cracking. Reducing the carbon content reduces the formation of carbides, but at the same time the hardness of the alloy decreases, which reduces wear resistance.
The objective of the invention is to create a surfacing material for parts such as continuous caster rollers, which has increased resistance to high-temperature corrosion, resistance to thermal fatigue, impact load, resistance to abrasive wear and the ability to perform surfacing with both open and closed arcs.
Achieved by surfacing the material with the following ratio of components, %:
The addition of niobium in the composition of the surfacing material in the range of 0.1-1.0% gives the material strength at high temperatures.
The given surfacing material has a martensitic microstructure with a delta-ferrite content of less than 10% with a small remainder of austenite.
An example of the use of surfacing material according to the present invention.
Two specimens were prepared and fused under an open and closed arc using an agglomerated neutral flux—designated specimen 1 and specimen 2. The cladding was performed at 400 amperes, 28 volts, at a stroke speed of 16 in/min, with a heat input of 45 kJ/in. Samples and tests were in accordance with American National Standards Institute (ANSI), American Welding Society (AWS), and American Society for Testing and Materials (ASTM) standard procedures. The results of testing for tension, yield strength, and elongation were compared with the results of a standard surfacing material according to patent RU 2279339 C2 at different temperatures (see Table 1).
Samples 1 and 2 show the best results when tested for elongation at temperatures of 426°C and 648°C. Increased ductility means reduced crack development, which increases part life.
| Table 1 | ||||
| Temperature, °C | Tensile test results | |||
| Material | Tensile strength | Yield strength | Elongation, % | |
| 25 | Pat. RU 2279339 C2 | 167 | 132 | 12 |
| Sample 1 | 166 | 134 | 15 | |
| Sample 2 | 164 | 142 | 13,5 | |
| 426 | Pat. RU 2279339 C2 | 112,7 | 130,7 | 7,0 |
| Sample 1 | 132,9 | 102,2 | 11,5 | |
| Sample 2 | 139 | 112,4 | 11,5 | |
| 648 | Pat. RU 2279339 C2 Sample 1 Sample 2 |
69,9 | 54,0 | 24,0 |
| 52,0 | 36,4 | 29,5 | ||
| 41,0 | 26,9 | 36,5 |
Table 2 compares the results of tests for hardness and the appearance of cracks from heating of a standard material according to patent RU 2279339 C2 and samples 1 and 2 (exposure to heat and water - 1000 cycles in a special device).
As can be seen from the table, even with a low carbon content in the surfacing material, the same level of hardness is maintained and a higher resistance to the appearance of cracks from heating has been revealed.
Table 3 shows the American Society for Testing and Materials (ASTM) G-65 wear test results (Accelerated Wear Test Method).
As can be seen from Table 3, under equal operating conditions, the inventive surfacing material is more resistant to wear compared to standard materials used.
Material for surfacing rollers of continuous casting machines with open or closed arc, containing carbon, manganese, silicon, chromium, nickel, molybdenum, vanadium, tungsten, nitrogen, cobalt, sulfur, phosphorus and iron, characterized in that it additionally contains niobium in the following ratio of components, wt.%:
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Electric arc surfacing with flux-cored wire occupies a strong position in the renovation of machine parts and mechanisms in various industries. The choice of flux-cored wire is made taking into account the operating conditions of the part being restored, the type of protection, the design features of the part, and the available equipment.
Caster rollers
In developed countries, about 80% of all steel produced is processed using continuous casting technology, which is energy-saving and has a set of advantages that determine its prospects and growth in application volumes. Currently, it is important to increase the efficiency of continuous casting machines, which is largely determined by the durability of the rollers. Continuous caster rollers are operated under conditions of long-term cyclic and thermomechanical loads in the presence of an aggressive environment. The rollers of the supporting and extension units operate in severe temperature conditions, the maximum surface temperature of the rollers can reach 670-750 ° C, and they absorb forces from ferrostatic swelling and from the extension of the ingot. In straight sections, the rollers are subject to predominantly abrasive wear. Destruction of the working surface of the rollers manifests itself in the form of wear of the surface layer and the formation of cracks. Manufacturing and restoration surfacing of rollers is most effective using flux-cored wires as surfacing material. The effectiveness of the developed solution is determined by the cost of flux-cored wire, process productivity, thickness of the deposited layer, energy intensity of all stages of the technology, cost of installation work, and equipment downtime. In the domestic metallurgy, for the restoration surfacing of continuous caster rollers, solid and flux-cored wires 12Х13, 20Х17 are traditionally used in combination with AN20S and AN26P fluxes, which provide chromium deposited metal with a martensitic-ferritic structure, which is characterized by the formation of large fields of δ-ferrite (more than 15%) ( Fig. 1), which causes the formation of cracks and increased wear.
Fig.1 Microstructure of metal deposited with wire Np-20Х17 (×500).
In addition, the surfacing process is characterized by difficult separation of the slag crust, which causes the appearance of defects in the form of extended slag inclusions and complicates the working conditions of the surfacing installation operator. The service life of such rollers is 300-400 thousand tons, which does not meet modern requirements. The reason for this is the unsatisfactory structural state of the deposited metal.
To eliminate these shortcomings, the company "TM. WELTEC" proposes to use flux-cored wires WELTEC-N470 and WELTEC-N470S (TUU 19369185.018-97) in combination with fluxes AN20 and AN26. In order to ensure high performance of the deposited metal, complex alloying of chromium metal with nickel, molybdenum, vanadium, niobium and rare earth metals was used. The optimal contents and ratios of alloying elements, the parameters of the technology and surfacing technique have been determined and implemented, making it possible to stably obtain a martensitic structure with an insignificant volume fraction of δ-ferrite (3.5-5%) (Fig. 2), ensuring high resistance of the deposited metal to wear and in full swing
Fig.2 Microstructure of metal deposited with flux-cored wire WELTEC-N470 (×1000)
The volume fraction of δ-ferrite is 3.8%, hardness after surfacing.
Flux-cored wires ensure spontaneous separation of the slag crust, the absence of pores and cracks in the deposited metal, subject to technological recommendations. Comparative tests of WELTEC-N470 and WELTEC-N470S flux-cored wires showed that they are at the level of wires from leading foreign companies OK15.73 (ESAB), 4142MM-S LC, 414MM-S (Weldclad). WELTEC-N470 wire was successfully used by NKMZ (Kramatorsk) when fulfilling export orders (Fig. 3). Over the past 8 years, MMK im. Ilyich (Mariupol) also uses this brand of wire to restore caster rollers. Welded rollers have a service life of at least 1.5 million tons. JSC "DMKD" (Dneprodzerzhinsk) used self-protecting flux-cored wire WELTEC-N470S to restore caster rollers with a diameter of up to 150 mm and obtained an increase in their performance by 5-6 times compared to traditional materials. Currently, the TM.VELTEC enterprise produces an improved modification of wires that provide a company of rollers in the range of 2.5-3.0 million tons.
rolling rolls- the main technological tool in the rolling process of metallurgical plants. The technical and economic performance indicators of rolling shops and, first of all, the productivity of rolling mills, the quality of finished products and the costs of their production mainly depend on their reliability, wear resistance of the working surface, and service life between repairs. The working surface of the roll is subjected to cyclic mechanical and thermal effects. As the rolls are used, metal adhesion, uneven wear and the formation of heat cracks are observed on their working surface. To maintain the required roll fleet, restoration surfacing with solid and flux-cored wires is used. For surfacing hot rolling rolls, surfacing materials Np-30KhGSA, Np-35V9Kh3SF, Np-25Kh5FMS, Np-30Kh4V2M2FS in combination with fluxes AN348, AN60, AN20, AN26 are traditionally used. Currently, metallurgical enterprises require increasing the service life of restored rolls of rolling mills.
"TM.WELTEK" and ChNPKF "REMMASH" together with the metallurgical plants KMMC "Krivorozhstal", DMK named after. Dzerzhinsky and Zaporizhstal Iron & Steel Works completed a set of works aimed at improving surfacing materials, technology and equipment for surfacing rolling rolls. Based on the profile of the rolling stage of the metallurgical plants participating in the work, the main attention was paid to surfacing materials and surfacing technology for hot rolling rolls, blank, section and partly sheet rolling mills. An analysis of the literature data on the performance of deposited rolling rolls showed that the capabilities of the C-Si-Mn-Cr-Mo-V and C-Si-Mn-Cr-W-V alloying systems have not been fully realized. Based on standard flux-cored wires of the PP-Np-35V9Kh3SF and PP-Np-25Kh5FMS grades, alloying systems for new flux-cored wires were developed taking into account the operating conditions of the rolling rolls (Table 1).
Table 1.
| Wire grade | Flux brand | Alloying system | Hardness HRC | Wear resistance | Crack resistance |
| relative to 30ХГСА | |||||
| WELTEC-N370RM | AN60, AN348A | C-Si-Mn-Cr-Mo-V-Ti | 36—42 | 2,0 | 0,9 |
| WELTEC-N460 | AN20, AN26 | 44—48 | 2,2 | 0,8 | |
| Regarding 35V9H3SF | |||||
| WELTEC-N500RM | AN60, AN348A | C-Si-Mn-Cr-W-Mo-V-Ni | 38—44 | 0,9 | 1,5 |
| WELTEC-N500RM | AN20, AN26 | 44—50 | 1,2 | 1,2 | |
| WELTEC-N505RM | AN20, AN26 | 50—54 | 1,3 | 2,0 | |
| WELTEC-N550RM | AN20, AN26 | 55—59 | 2,0 | 1,0 | |
By changing the structure of the deposited metal, an increase in the performance of the rolls was achieved. The structure of the deposited metal PP-Np35V9Kh3SF is: along the boundaries of the primary austenite grain there are open deposits of δ-ferrite, in which there are no carbides. Matensite and isolated small carbides are formed in crystallization cells. δ-ferrite is formed at the cell boundaries. The size of the primary austenite grain is 6. In the overlap zones of the rollers, changes in the structure and microhardness H µ50 50 from 650 to 450 are observed (Fig. 3). Structure of the deposited metal WELTEC-N500: The boundaries of the primary austenite grains are clearly expressed, with intermittent precipitation of δ-ferrite and small carbides. Dispe martensite and disperse carbides are formed inside the crystallization cells. Structure of the deposited metal WELTEC-N505: along the boundaries of the primary austenite grain with a size of 17-20 microns, there are very small precipitations of δ-ferrite and carbides similar to eutectic ones. Fine-needle martensite and many dispersed carbides are formed in the crystallization cells. Structure of the deposited metal WELTEC-N550: along the boundaries of the primary austenite grains, δ-ferrite precipitates and dispersed carbides are observed, and in the cells there are eutectic-like carbides and fine-needle martensite. In places where the rollers overlap, no change in structure is observed.
Rice. 3 Microstructure of deposited metal (×500)
During the operation of the roll under the influence of high temperatures, coagulation and enlargement of carbides along the grain boundaries is observed, followed by their spalling and the development of heat cracks. Reducing the development of these processes was achieved by changing the structural state of grain boundaries by optimizing the ratio of carbon and carbide-forming elements. The results obtained were implemented in alloying systems for new flux-cored wires. The structure of the metal deposited with WELTEC-N550RM wire is characterized by the formation of austenite rims along the grain boundaries and is distinguished by a larger volume fraction of the austenite component and insignificant precipitation of carbide eutectic along the grain boundaries. The structure of the deposited metal WELTEC-N500RM is acicular troostite with a small amount of martensite and the formation of individual inclusions of austenite and carbides along the grain boundaries. The structure of the deposited metal WELTEC-N505RM is a mixture of trostite and martensite with thin austenite rims along the grain boundaries. At the grain boundaries, inclusions of carbide eutectic form in small quantities.
Table 1 shows flux-cored wires that have already found application in metallurgy for surfacing rolling rolls and have shown their effectiveness. Average indicators of relative wear resistance were determined by the amount of wear, relative resistance to crack formation and their number, the size of the opening and the depth of penetration of cracks on the rolling rolls. Below are examples of the use of new cored wires.
1. Surfacing of edge stand rolls at the ZAPORIZHSTAL plant
Vertical rolls of the edger stand on the continuous thin-sheet hot rolling mill of OJSC "Zaporozhstal" (mill "1680") perform lateral compression and alignment of the side edges of the rolled sheet. During operation, the cylindrical surface of the rolls experiences intense abrasive wear and significant specific compressive pressures at the point of contact with the end of the hot sheet. As a result, an annular groove up to 100 mm high and up to 5 mm in diameter is formed on the surface of the roll barrel near the flange, which necessitates the replacement of rolls, since further operation in this state can lead to uneven compression and rolling speed, which will negatively affect the quality rolled metal. The study of the nature and dynamics of wear showed that wear occurs as a result of oxidation and tearing off particles of oxidized metal from the surface of the rolls by the ends of a hot sheet with a surface temperature of 1100-900 ° C, partially covered with a thin layer of scale. In this case, the surface of the rolls at the point of contact with the sheet being rolled is heated to a temperature of 400–500°C. The service life of rolls strengthened by surfacing with PP-Np-35V9Kh3SF or PP-Np-25Kh5FMS flux-cored wires was no more than 3-4 months, which did not meet production requirements. The use of surfacing with flux-cored wire WELTEC-N550RM made it possible to increase the wear resistance and service life of the rolls by 3 times.
2. Surfacing of hot rolling mill rolls.
2.1 At the Dneprovsky Metallurgical Plant (Dnepropetrovsk), one set of rolling rolls is restored from five to ten times. For a long period of time, the restoration of rolling rolls of the 900v TZS mill and the 500v iron rolling shop mill was carried out using surfacing with solid Np-30KhGSA wire in combination with grooving or regrinding of gauges to a smaller diameter. The use of this technology did not provide the required “hot hardness” and wear resistance of the deposited working layer of the gauges. The use of standard surfacing materials PP-Np-35V9Kh3SF, PP-Np-25Kh5FMS, PP-Np-30Kh4V2M2FS after a technical and economic analysis in this production turned out to be inappropriate, due to a significant increase in the labor intensity of restoring rolls and capital costs. For the strengthening restoration of the rolls of the stand “500” of the iron rolling shop, flux-cored wire WELTEC-N500RM was used. Tests of the hardened rolling rolls on the mill “500” of the iron rolling shop showed that the service life of the rolls after hardening increased more than 2 times.
2.2 For strengthening surfacing of the vertical walls of the rolling roll calibers of the TZS stand “900”, WELTEC-N370RM wire was used. The technology for surfacing the rolls of the “900” stand of the TZS, with the exception of the absence of preheating, is similar to the technology of surfacing the rolls of the “500” stand of the iron rolling shop. An increase in the rolled metal on one pair of rolls from repair to repair has been achieved from 18-20 to 45-50 thousand tons.
2.3 The hot rolling rolls of the NZS-730 mill of the Blooming-1 shop of the Krivo-Rozhstal KMMC, made of steel 50, were traditionally repaired using standard flux-cored wire of the PP-Np-35V9Kh3SF brand. During the operation of the restored rolls, a number of shortcomings were revealed: during the rolling process, the formation of “spikes” up to 2 mm high is observed on the surface of the roll due to the adhesion of the rolled metal. The formation of “spikes” led to the need to stop the rolling process and use labor-intensive cleaning of the calibers from the “spikes,” otherwise the rolls with “spikes” would apply a defective pattern to the surface of the rolled metal. After rolling 50-60 thousand tons of metal, a groove with a depth of 2-3 mm was formed on the surface of the grooves, which necessitated the need to replace the rolls. The penetration depth of individual cracks after 50–60 thousand tons of rolled metal reached 30–40 mm. This led to increased costs for their elimination, and often to the need for premature rejection of the rolls. To eliminate the considered shortcomings, the WELTEC-N505RM flux-cored wire surfacing technology was used. The technology for hardening NZS-730 rolls using WELTEC-N505-RM flux-cored wire is similar to the technology for surfacing with PP-Np35V9Kh3SF wire. A reduction in the formation of “spikes” and cracks by 2-3 times was achieved, which made it possible to transfer 80-90% of the rolls for repair using a shortened technology and significantly reduce all types of costs by 20% and increase the turnaround time of the mills.
Details of metallurgical equipment.
Self-shielding flux-cored wire WELTEC-N250RM with a diameter of 1.6-3.0 mm is successfully used in the restoration of rolling stand and shear pads, spindles and couplings for drives of rolling rolls, sprockets, bushings, shafts, hubs, etc. According to its characteristics, WELTEC- N250РМ is not inferior to the well-known cored wire DUR 250-FD (Bohler).
Surfacing of cores of clamp valves and jaws of stripper valves, which during operation experience shock and compressive loads at high temperatures, has been carried out. The cores are in contact with metal heated to 800-1250 °C and thermal cycling with periodic cooling of the cores in tanks of water. For this purpose, self-shielding flux-cored wire of the WELTEC-N480C brand Ø2.0 mm with an alloying system (C-Cr-W-Mo-V-Ti) was used, which ensures the hardness of the deposited metal after surfacing 50-54 HRC, hot hardness 40-44 HRC at 600 °C and resistance to cracking (100 thermal cycles before the first crack appears).
The use of mechanized surfacing with WELTEC-N480S wire instead of T-590 and T-620 electrodes made it possible to increase the service life of cores by 4-5 times and reduce repair costs. The problem of core recovery was solved in a complex (equipment-material-technology).
When surfacing parts subject to impact-abrasive wear with PP-AN170 flux-cored wire, there is an increased tendency to cracking and spalling, and the thickness of the surfacing is limited to 1-2 layers, which in some cases limits its use. To solve this problem, we used self-shielding flux-cored wires WELTEC-N600 (C-Cr-Mo-V-Nb-Ti-B), WELTEC-N620 (C-Cr-Mo-V-Ti-B), which ensure the hardness of the deposited metal. talla 55-63HRC. Compared to PP-AN170, the wear resistance of the deposited metal is increased by 30–50%. With the possibility of performing 4–5 layers. Wires are produced with diameters from 2 to 5 mm. Using mechanized and automated surfacing with WELTEC-N600 Ø3.0 mm flux-cored wire, the surface of the large cone of the blast furnace was restored, a significant increase in wear resistance was achieved compared to T590 electrodes, and the repair time was also reduced by 2 times. When automatically surfacing a small cone with WELTEC-N620 Ø4.0 mm flux-cored wire, higher wear resistance was obtained compared to surfacing with PL-AN101 tape. In addition, these wires were successfully used for hardening surfacing of excavator bucket teeth, bulldozer blades, and grab jaws. Surfacing of the grates and sprockets of the single-roll sinter crusher was carried out using self-shielding flux-cored wires. One crusher set includes 16 grate bars weighing 270 kg each and 15 stars weighing 85 kg each, made of 35L or 45L steel. Before the introduction of the new technology, the grate bars were not strengthened, but replaced with new ones. Flux-cored wire of the WELTEC N6OO brand with the C-Cr-Mo-B-V-Ti alloying system allows for multi-layer surfacing with high resistance to impact and abrasive loading at elevated temperatures. Multilayer surfacing was carried out with a wire with a diameter of 2.6 mm at a direct current of reverse polarity in the mode: Id = 280-300 A, Ud = 26-28 V. The hardness of the deposited metal was 59-62 HRSe. Compared to PP-AN170 flux-cored wire, the deposited metal is significantly less prone to cracking and chipping under strong impacts. Taking into account the unevenness of wear, surfacing in terms of the number of layers and thickness was carried out to differentiate the degree of wear of each grate and sprocket with a total layer of thickness from 3 to 12 mm.
Periodic inspection of the experimental set showed the following dynamics of wear of grates and sprockets in various zones of the crusher (Fig. 4):
Rice. 4. Diagram of comparative wear of hardened and non-hardened grates of the sinter crusher after two months of operation of the crusher.
- in 2 months — from 3% on the periphery to 6% in the center;
- in 4 months — from 5% on the periphery to 12% in the center;
- after 6 months - from 8% on the periphery to 25% in the center.
A threefold increase in the overhaul period of the crusher has been achieved, the quality of the sinter has been increased, and repair costs have been reduced.
Crane wheels
Wear of crane wheels made from steel grades 45L, 40L, 60L, 55L occurs from metal-to-metal friction under large alternating dynamic loads both on the treading surface and on the flange. At the same time, the wear on the wheel tread is on average 6-10 mm per diameter, and the flanges are 15-25 mm per side, which generally leads to the need to replace it after 1-3 months.
For surfacing crane wheels, we offer flux-cored wires of the brands WELTEC-N300, WELTEC-N350 Ǿ1.6–4.0 mm in combination with AN348, AN60 fluxes and carbon dioxide protection. In recent years, WELTEC-N300RM has been successfully used to replace solid wire Np-30KhGSA. For surfacing wheels of heavily loaded cranes, a technology variant was developed in which more intensively worn flanges were surfaced using AN348 flux cored wire of the WELTEC N285RM grade Ø3.0 mm. Chromium-manganese deposited metal with a metastable austenite structure provides high wear resistance due to the development of self-strengthening under the influence of work hardening, which is manifested in an increase in hardness from 28-32 HRCe to 42-45 HRCe, and less wearable rolling surfaces were surfaced under AN348 flux-cored wire with VELTEK N300RM flux-cored wire with the hardness of the deposited metal 300-350 HB (Fig. 5).
Fig.5 Scheme of surfacing of crane wheels
This technology made it possible to double the service life of crane wheels while increasing the cost of materials by only 70%, and the labor intensity of machining by 35%.
Machine parts for mining and crushing and grinding equipment. Currently, Krivoy Rog Mining Equipment Plant CJSC is a leading machine-building enterprise in Ukraine for the production and repair of mining equipment. A large amount of work is performed using arc welding and surfacing. The range of welding and surfacing materials is wide due to the need to weld low-carbon low-alloy, low-alloy high-strength, high-manganese and heat-resistant steels, make welded joints of dissimilar steels, weld cast steels and correct casting defects. In most cases, these are large-sized products, which impose special requirements on welding materials, technology and techniques for welding and surfacing. In connection with this, the task of improving the quality of work performed and reducing material, energy and labor costs is urgent. These requirements are fully met by the use of cored wires. Over the past 5 years, Krivoy Rog Mining Equipment Plant, together with TM.VELTEC, has been carrying out a set of joint works to increase the volume of arc welding and surfacing with flux-cored wire. As a result of these works, a range of flux-cored wires for various purposes was developed and introduced. In the total volume of materials used for welding and surfacing, the share of flux-cored wires increased from 15 to 85%. Compared to coated electrodes, the efficiency of welding and surfacing has increased due to increased productivity and quality of work. The volume of work on repeated quality control has decreased. The traditional mistrust of flux-cored wires in terms of the quality of welded joints and hardening coatings has significantly decreased. Here are some examples of the use of flux-cored wires from the TM.VELTEC company.
The bowl of the KKD-1500 cone crusher was welded. A bowl weighing 50 tons made of 35L steel was assembled from two parts, upper and lower, which were welded together. A horizontal assembly joint with a diameter of 2980 mm is made with a double-sided cup-shaped edge groove with a metal thickness of 180 mm. Welding was performed using PPs-TMV29 flux-cored wire Ø1.6 mm at direct current of reverse polarity with carbon dioxide protection (Fig. 6)
Fig.6 Welding the mill bowl
Welding of parts and assemblies of sintering and processing equipment, mining equipment, including excavator assemblies made from steels St3ps, 09G2S, as well as welding of casting parts from steels 20L, 35L is carried out with gas-protected flux-cored wires of the PPs-TMV5, PP-AN8, PPs-TMV8, PPs brands -TMV29 and PP-AN57 units made of low-alloy high-strength steels 12Х2НМСА, 12Х2НВСА. For welding defects in casting steels 20L, 35L, the most effective is the use of PPs-TMV5 metal cored wire. A small amount of slag of 4-5% does not require the cost of removing it during the welding of deep grooves, the high coefficient of wire utilization K = 1.08, high resistance to the formation of pores and cracks determine the advantage of this wire over other welding materials.
For welding parts and welding casting defects from heat-resistant Cr-Mo steels 15KhM, 12KhM, 20KhML, 35KhML, gas-protected flux-cored wire with a carbonate-fluorite type core of the PPs-TMV14 brand Ø1.6-2.0 mm is used.
Welding of casting defects in high-manganese steels 110G13L is carried out with self-shielding flux-cored wire WELTEC-N220 Ø2.0 mm.
Surfacing of reinforcing layers on bottom bolts, cutting edges and bodies of excavator buckets, scoop buckets, edges of ball mill inlet devices, slurry pump bodies, dredger pumps, grader and bulldozer knives is carried out with self-shielding flux-cored wires of the brands WELTEC-N580, WELTEC-N600, WELTEK-N605, WELTEC-N620 Ø2.0-3.0 mm instead of electrodes T590, T620 and flux-cored wires PP-AN125, PP-AN170, Linocore 60-O, Linocore 60-S, Linocore 65-O, DUR 600-FD, DUR 650, DUR 650MP, OK Tubrodur 14.70, OK Tubrodur 15.52.
For restoration surfacing of hydraulic press plungers, protective sleeves of slurry pumps for pumping pulp, flux-cored wire WELTEC-N410 Ø2.4-3.6 mm is used in combination with AN20 and AN26 fluxes, and for open-arc surfacing WELTEC-N420 Ø1.4-3 ,0. For surfacing of mine hydraulics elements, flux-cored wire WELTEC-N425 Ø2.0 mm is used in combination with AN20 and AN26 fluxes. The surfacing process is characterized by high stability, good metal formation, and spontaneous separation of the slag crust. The deposited metal has high corrosion resistance during operation in the face.
Ph.D. Orlov L.N., engineer Golyakevich A. A. (TM.VELTEC LLC, Kiev), Titarenko V. I. (ChNPKF "REMMASH", Dnepropetrovsk), Peleshko V. N. (KZGO, Krivoy Rog)