Most of the service environments of the parts of iron and steel metallurgical equipment on the production line are high temperature, high variable load, hot and cold alternation, corrosion, wear and fatigue conditions.
During use, some cast iron parts are very prone to corrosion and wear, and need to be replaced and maintained regularly. Especially in the production and processing of high-end automotive steel plates, the surface quality requirements for parts such as rollers and transmission rollers are extremely high.
For such parts with large usage and high maintenance frequency, how to further effectively improve the service life and reduce maintenance costs is crucial to the development of the industry.
At present, the surface protective layer of iron and steel metallurgical equipment parts is mostly prepared by electroplating, thermal spraying, arc surfacing and other methods.
The application of laser cladding technology can more effectively improve the service life of parts coatings and reduce maintenance links, and has greater flexibility in terms of coating thickness and coating performance regulation.
Principles and advantages of laser cladding technology
Technical principle
(1) The high-energy laser beam is transmitted through a lens or optical fiber, moves synchronously with the CNC machine tool system or robot, and cooperates with the rotation of the workpiece to achieve precise scanning of the laser beam on the workpiece surface.
(2) During the scanning process, when the high-energy laser beam irradiates the surface of the workpiece, the substrate is melted, and at the same time, the alloy powder for laser cladding provided by the powder feeding head is melted. The two parts of liquid alloy are mixed together to form a molten pool. The molten pool is in an inert protective atmosphere to prevent the molten pool from being oxidized by air.
(3) After the laser beam leaves, the mixed liquid alloy solidifies rapidly to form a laser cladding layer, that is, laser repair is achieved.
Technical advantages
(1) The temperature rise of the substrate during laser processing does not exceed 80°C, and there is basically no thermal deformation after laser processing. The substrate material is only slightly melted on the surface during laser processing, and the micro-melting layer is 0.05-0.1mm. The heat-affected zone of the substrate is extremely small, generally 0.1-0.2mm. The heat-affected zone of laser cladding is one-tenth of that of argon arc welding.
(2) Laser cladding technology has good controllability and is easy to realize automatic control.
(3) There is no coarse casting structure in the cladding layer and the substrate. The cladding layer and its interface structure are dense, the crystals are fine, and there are no defects such as holes, inclusions, and cracks.
(4) The substrate and the cladding material are metallurgically bonded, and the bonding strength is equivalent to that of the parent material;
(5) Laser cladding can achieve the purpose of surface modification, repair or remanufacturing;
(6) Laser cladding technology has the characteristics of high efficiency, fast speed, green environmental protection and no pollution in repairing worn and failed materials, and good post-processing workpiece performance;
(7) For large non-detachable parts, portable and movable laser cladding equipment can be used for on-site repair.
Comparison table of ultra-high speed laser cladding and traditional processes
| Surface Technology Type | Single coating thickness/mm | Combination method | Heat affected zone | Production costs | Surface flatness | Environmental protection level |
| Ultra-high-speed laser cladding | 0.02-1.0 | Metallurgical bonding | Small | Low | smooth | No pollution |
| Ordinary laser cladding | 1-2 | Metallurgical bonding | Smaller | high | Rough | No pollution |
| TIG Arc Additive | 2-4 | Metallurgical bonding | big | Low | Rough | No pollution |
| Ultra-high velocity flame spraying | 0.01-0.05 | Mechanical bonding | Smaller | medium | smooth | Dust + noise pollution |
| Plasma spraying | 0.02-0.05 | Mechanical bonding | big | medium | Relatively flat | Dust + noise pollution |
| Hard chrome plating | ＜0.1 | Physical bonding | none | Low | smooth | Heavy metal pollution |
Industry application case analysis
Repair process: pre-repair inspection → initial processing to remove fatigue layer → PT flaw detection → laser cladding → finishing (turning, grinding)
Laser treatment effects of common rollers
(1) Forged steel rollers – By using laser quenching and melt quenching technology, a hardened layer with a hardness of 59-63HRC and a layer depth of more than 2mm can be obtained on the surface of the forged steel roller, thereby greatly extending the service life of the roller. The roller surface and the journal of the roller can also be repaired by using laser cladding technology.
(2) Cast steel rollers – By using laser quenching and melt quenching technology, a hardened layer with a hardness of 59-63HRC and a layer depth of more than 2mm can be obtained on the surface of the cast steel roller, thereby greatly extending the service life of the roller. The roller surface and the journal of the roller can also be repaired by using laser cladding technology.
(3) Alloy semi-steel rollers – After laser quenching, melt quenching and alloying treatment, the surface hardness can be increased to 45-54HRC accordingly. For semi-steel strip roughing rollers, medium rolling rollers, etc., as well as bar and wire roughing and medium rolling rollers, the use effect is remarkable. The roller journal can also be repaired by using laser cladding technology.
(4) Cast iron rolls – Laser quenching, melt quenching and laser alloying technologies can be used to obtain a hardened layer with high hardness and good red hardness on the surface of chilled cast iron rolls and infinitely chilled cast iron rolls, thereby greatly improving the service life of the rolls. Laser cladding technology can be used to repair the journals of cast high-chromium steel rolls.
Laser processing of other vulnerable parts
The main vulnerable parts in the steel industry also include: pinch rollers, conveyor rollers, tension rollers, flying shears, large circular saws, wheels, reels, auxiliary rolls, etc. The main materials, properties and process requirements for laser processing are shown in the table.
| Artifact Name | Use Materials | Main performance requirements | Processes suitable for laser processing |
| Pinch Roller | Centrifugally cast ductile iron, infinitely chilled cast iron, semi-steel 35 steel, 45 steel | Wear-resistant and heat-resistant | Laser quenching, melt quenching and alloying, laser cladding can be used to repair the journal and the 35 steel and 45 steel roller surface. |
| Conveyor roller | Solid forged steel, hollow forged steel, hollow cast steel | Wear-resistant, heat-fatigue-resistant, impact-resistant | A full set of strengthening processes including laser quenching, melt quenching, alloying and cladding can be used to repair the roller surface and journal. |
| Tension roller | 35 steel, 35CrMo steel | Certain hardness, good comprehensive mechanical properties | Laser melting quenching, alloying and cladding can repair the roller surface and journal. |
| Flying Shears | CrMo tool steel | High hardness, wear resistance | Laser quenching |
| Large disc shears | 70CrMo steel | Red hardness is good | Laser quenching and alloying |
| Travel wheels | 45 steel, 42CrMo steel | Certain wear resistance, good comprehensive mechanical properties | Laser quenching |
| Winding roller | 50CrV,45 steel,20CrNiMo | Good wear resistance | A full set of strengthening processes including laser quenching, melt quenching, alloying and cladding can be used to repair the roller surface and journal. |
| Guide | Steel, cast iron | Good wear resistance | Laser quenching and melt quenching |
| Descaling roller | 35CrMnMo, 42CrMo steel | Good wear resistance and good comprehensive mechanical properties | Laser quenching, melt quenching and alloying can be used to repair the roll surface and journal by laser cladding technology. |
Application example of laser surface strengthening treatment of rollers
| Metal material | Hardness before and after laser treatment | Improvement of workpiece service life under constant thickness wear | Direct economic benefits created | |
| forward | back | |||
| ZG65CrNiMo Workpiece | 40-42HSD | 70-80HSDde2 | >2.6 | Reduce consumption by nearly 50% |
| 70Mn2 Workpiece | 38 HSD | 80 HSD | >2.5 | Reduce consumption by nearly 50% |
| 75CrMnMo Workpiece | 42HSD | 80HSD | >2.5 | Reduce consumption by nearly 50% |
| Low and medium chromium nickel infinitely chilled cast iron workpieces | 38HRC | 53HRC | 6.6 | Reduce consumption by 30% on average (generally processing workpieces after the 2nd stage) |
| 4.4 | ||||
| Low and medium chromium nickel infinitely chilled cast iron workpieces | 40HRC | 55HRC | 2.6 | Reduce consumption by 40% on average (new workpieces are not processed) |
| 1.4 | ||||
| Semi-steel workpiece | 22HRC | 40HRC | 2.2 | Reduce consumption by 40% on average |
| NiMo heat-resistant alloy workpiece | – | – | 2.0 | Reduced cost by 50%. |
| Shear blade workpiece | 35 HRC | 55-60HRC | 1 – 1.6 times the new blade | The consumption cost of shear blades is reduced to 1/3 of the original cost. (Note: New shear blades are not processed) |
| 6-10 times the cutting edge after sharpening | ||||
| Guide workpiece | – | – | Double | – |
Laser additive repair of piston rod
The piston rod is a connecting component that supports the piston to do work. Most of them are used in oil cylinders and cylinder motion actuators. It is a frequently moving transmission component and is generally made of 45# steel, 40Cr, and stainless steel. Taking the hydraulic cylinder as an example, most of the piston rod surfaces are damaged or scratched, causing the coating to fall off, or even leaking oil, resulting in serious rust on the piston rod surface, thus affecting the normal operation of the piston rod.
Ultra-high-speed laser cladding repair can achieve the preparation of piston rod surface coating by efficient cladding at 0.5-1.2m²/h (depending on the coating thickness), and the single-layer cladding thickness is 0.05-1mm. Because the heat input of the cladding process is small and the thermal impact on the workpiece is small, thin-walled or large aspect ratio parts that cannot be applied by conventional laser cladding can be processed without deformation. According to different customer application requirements, hard and wear-resistant coatings of different materials such as cobalt-based, nickel-based, and composite materials can be prepared on the surface of the parts. The maximum hardness of the coating reaches HRC50-60, and crack control is effectively achieved.
Laser additive repair process
Grinding to required size after repair
Laminar Roller Laser Additive Repair
Usually, the failure modes of laminar rollers include thermal cracking, peeling, fatigue wear, abrasive wear, etc. The traditional laminar roller manufacturing adopts Ni60 spraying technology, but the bonding strength between Ni60 spray layer and substrate is low and the service life is short.
The laminar roller surface material is generally 45# steel. Laser cladding technology is used. According to its material, working environment and technical requirements, the corresponding cladding alloy powder and cladding process are selected. The cladding layer and substrate achieve good metallurgical bonding, the cladding layer has a dense structure, and the surface hardness can reach 50-60HRC, which plays a good strengthening role.
In addition, the high-speed laser cladding technology has a small heat input, and will not cause repair resistance due to the excessive size and hardness of the substrate heat affected zone; the surface hardness of the cladding layer is evenly distributed, and the steel plate will not be scratched due to local hardness. The wear resistance and impact resistance of the repaired roller surface are several times higher than those of traditional repair processes.
Laser additive repair process
Additive repair of cylinder block and end cover
The failure modes of the cylinder end cover seat include fatigue wear, abrasive wear, etc. Its material is 45# steel, and laser cladding technology is used. According to its material, working environment, and technical requirements, the corresponding cladding alloy powder and cladding process are selected. The cladding layer and the substrate achieve good metallurgical bonding, the cladding layer has a dense structure, and the surface hardness can reach 50-60HRC, which plays a good strengthening role.
