How to apply laser cladding head to steel surface? Listen to what users say

The components used in steel strip manufacturing operate in extremely corrosive environments and must withstand mechanical wear and frequent and severe shock loads. Traditionally, parts with higher levels of wear or corrosion have been manufactured from chemically rich steels or hardfaced using sub-arc overlay martensitic stainless steel to extend their service life without sacrificing product quality. , to maximize production line output by extending maintenance intervals.

Martensitic stainless steel (MMC) welding alloys generally have good wear and corrosion properties, but are not suitable for severe wear between metals and also lose mechanical and corrosion properties at high temperatures. Arc-welded MSS alloys also suffer from welding sensitivity issues in the grain boundaries of the heat-affected zone (HAZ), which precipitate chromium carbides, resulting in reduced chromium content in surrounding areas, ultimately making these areas susceptible to localized corrosion.

Thermal spray coatings can be used in alloys and metal matrix composites (MMC) and are therefore widely used throughout the steel industry. However, the relatively low strength of the mechanical bond interface of thermal spray coatings (unless post-spray fusion techniques are used) limits their practical application in environments subject to very severe impacts.

In 2009, a system was established at the Port of Talbot in the UK in an attempt to develop laser cladding technology (Figure 2) for coating critical engineering components to extend their service life. In rolling mills in the steel industry, different rolls with lengths from 0.3 to 3.5 meters are used. Laser cladding coatings have been proven to extend the life of components by up to 6 times.

Since the installation of the laser cladding system at Port Talbot (Figure 3), the process has been improved and a variety of nickel-cobalt and iron-based material alloys have been tested in terms of microstructure, mechanical properties, wear resistance and corrosion resistance. Evaluation to achieve customized coating performance for each application within steel plants

Preliminary results from production line trials are very encouraging, with laser-clad components achieving unprecedented wear and corrosion properties. Therefore, the company decided to build a production facility to meet anticipated demand.

01 Significant advantages of laser cladding process

The laser cladding process is a hardfacing method that can be used to improve the wear/corrosion/impact resistance of metal parts. The process uses a precisely focused, high-power laser beam to create a weld pool in which the metallic material is melted.

The precision of the laser beam enables fully dense cladding with minimal dilution (< 5%) while achieving a perfect metallurgical bond. A variety of coatings can be used, and the composition of the coating can be designed based on the failure mechanism of each component.

One of the main advantages of laser cladding is the ability to finely control heat input. This enables the deposition of a two-phase metal matrix composite structure, namely:

Substrate - usually a nickel-based alloy. This matrix is tough, ductile and impact-resistant, while being wear-resistant at high temperatures.

Reinforcing hard phase - usually tungsten carbide, but can also be titanium carbide, chromium carbide, etc.

Fine control of the input heat allows the matrix to completely melt and adhere to the substrate surface. At the same time, the ceramic particles remain unmelted and evenly distributed on the substrate surface, making the coating extremely wear-resistant and impact-resistant. The ratio between the hard phase and the matrix can be adjusted according to the use conditions, that is, the larger the ratio of the hard phase, the stronger the wear resistance, and the smaller the ratio of the hard phase, the stronger the impact resistance.

Other benefits of this process include:

Minimal heat input, therefore cooling is fast

The microstructure is very fine and deformation is negligible

Due to minimal dilution, the desired coating chemistry is achieved in the first coat.

Able to produce hard top coatings with extremely high surface finish (rolls can be coated and installed without machining)

Although laser cladding involves many parameters, powder mass flow rate is a particularly critical parameter during the laser cladding process. Once the optimal laser spot diameter, cladding speed and laser power speed are determined, powder flow can be used to control cladding thickness, hardness and dilution. As shown in Figure 5. It can be seen that increasing the powder flow rate effectively controls dilution.

Once the optimal parameters for a single pass weld on the board are determined, large area coverage can be achieved by producing overlapping passes. The amount of overlap determines the coating thickness for a single pass weld, ranging from 0.3 mm to 3.0 mm.

To demonstrate and quantify the potential advantages of laser cladding compared to traditional hardfacing techniques, we produced some samples of laser cladding and immersion hardfacing.

Operation of Tata Steel R&D and Technology machines at the University of Sheffield, UK, is controlled by a touch-screen human-machine interface. The department produced arc-shaped cladding steel plates and designed them to operate automatically, so the robot can perform damage testing. Wear test results at low and high temperatures are automatically programmed. The system uses a laser rangefinder, as shown in Figures 6a and 6b. Determine part geometry, start and stop positions that can be clearly seen, distance from standard materials and hard surfaces, and the laser head. This ensures that only a small amount of build-up is required compared to laser cladding technology, which can significantly improve the training required to operate state-of-the-art processes. The tail monitor has high wear resistance. function ensures stable machining processes, while automatic stop and retraction functions prevent damage in the event of unexpected interruptions.

02 Laser cladding production equipment

Machine tools capable of laser cladding are available directly from suppliers in Europe and the United States, but Tata Steel engineers decided to build a custom laser cladding production machine. The system is based on a Laser Line fiber-coupled diode laser, equipped with a Precitec YC 52 cladding head and a Metallisation mass flow controlled powder feeder. The system is controlled by a Fanuc robot with an additional 7th axis that can rotate cylindrical parts weighing up to 6 tons and up to 3.5 meters in length (Fig. 7).

The operation of the machine is controlled by a touch screen human machine interface. The system is designed to operate automatically, so the robot can be programmed automatically. The system uses a laser rangefinder to determine the part geometry, start and stop positions, and the distance to the laser head. This ensures that only minimal training is required to operate state-of-the-art processes. Tail monitoring ensures stable machining processes, while automatic stop and retraction prevent damage in the event of unexpected interruptions.

With the advent of high-power diode laser systems and specialized laser cladding nozzles, the design and integration of rugged cladding processes in hardfacing applications has become easier.