In the production of strip steel, components must operate in harsh environments, endure high temperatures and corrosive atmospheric environments, and withstand mechanical wear and frequent heavy impacts. Traditionally, the raw materials for components that have to withstand high wear or corrosion usually come from the use of submerged arc cladding martensitic stainless steel (MSSs) surfacing materials to increase their service life, so that they can be down on the premise of not affecting product quality. Try to extend the maintenance interval as much as possible to maximize mass production.

MSS welding alloys usually have good wear resistance and corrosion resistance. However, they are not suitable for strong metal-to-metal wear and will lose their wear resistance and corrosion resistance in high-temperature environments. Arc welding MSS alloys will also be affected by welding sensitization in the grain boundaries of the heat-affected zone (HAZs). This is because the chromium carbide in the heat-affected zone precipitates and depletes the chromium in the surrounding area. These local areas become easy Corroded.

Thermal spray coatings have a wide range of applications throughout the steel industry because they can be used very flexibly with a wide range of alloys and metal matrix composites (MMCs). However, their mechanical joints have relatively low strength (unless the spray melting method is used), which limits their use in heavy-impact environments.

In 2009, in Port Talbot, South Wales, UK, TataSteel Strip Products UK company tried to develop key working components of laser cladding coating to increase its service life. Rolling mills in the steel industry require rolls of different lengths, ranging from 0.3 to 3.5 meters. Laser cladding coatings have been proven to extend the service life of components up to 6 times.

Since the laser cladding system was installed in Port Talbot, this process has begun to develop. Many cobalt-nickel and iron-based alloys have been evaluated in terms of microstructure, mechanical properties, wear resistance, and corrosion resistance. Corresponding process development needs to be carried out for the coating characteristics required by different applications.

The preliminary results of the production line test are very encouraging: the laser cladding components have achieved unprecedented wear and corrosion resistance. To this end, the company decided to build production equipment to meet the expected demand.

Benefits of laser cladding：

Laser cladding is a surfacing method that can be used to increase the wear resistance, corrosion resistance, and impact resistance of metal components. This method uses a precisely focused high-power laser beam to form a weld pool and add the metal powder to it. The powder is fed coaxially through a laser beam through a series of the inert protective gas. The accuracy of the laser beam makes it possible to obtain a dense cladding layer with extremely low dilution (<5%), and at the same time, there is a perfect metallurgical bond between the cladding layer and the substrate. The coating can be applied in many places, and its composition can be designed according to different situations to overcome the corresponding failure mechanism of each component. One of the main benefits related to laser cladding is the ability to well control the heat input to achieve a two-phase deposited metal matrix composite (MMC) structure: the matrix is usually a nickel-based alloy with good toughness, ductility and Impact resistance and wear resistance at high temperatures; the enhanced hard layer is usually tungsten carbide or titanium nitride/titanium carbide, chromium carbide, etc.

The fine control of the heat input enables the substrate to be completely melted and alloyed on the surface of the substrate, while the ceramic particles are not melted and are evenly distributed in the substrate so that the entire coating has strong wear resistance and impact resistance. The ratio between the hard layer and the substrate can be adjusted according to the operating environment. For example, a larger hard layer ratio has better abrasion resistance, and a smaller hard layer has better impact resistance.

Due to the minimum heat input, the cooling rate is fast, and the deformation is negligible; due to the extremely low dilution, the uppermost layer of the coating can achieve the required chemical composition; special surfaces can be produced Processed hard-face coating (maybe rolled and installed without processing); unlike all other low-heat input spraying processes (super sonic flame HVOF spraying, cold spraying, D-Gun explosive spraying, etc.), laser cladding There is a perfect metallurgical bond between the cladding layer and the substrate.

Laser cladding has many related technical parameters, and the powder mass flow rate is particularly critical. For a specific application, once the optimal laser spot diameter, cladding speed, and laser power are determined, the powder mass flow rate can be used to control the thickness, hardness, and dilution of the cladding layer.

Equipments of laser cladding：

The laser cladding system includes a fiber-coupled semiconductor laser and Precitec YC52 cladding head, as well as a metal powder mass flow control feeder. The system is controlled by a Fanuc manipulator, which has an additional seventh axis that can rotate cylindrical parts weighing 6 tons and 3.5 meters long.

Through the man-machine interface to control the operation of the machine. The system is designed to operate autonomously by a robot that can be programmed automatically. Besides, a distance measuring laser is needed to determine the shape of the component, where to start and stop, and the distance of the laser head holder. This ensures that only a small amount of training is required to achieve this top-notch craft. Detailed monitoring can ensure a stable process, and the automatic stop and retract function can prevent damage in the event of an accidental interruption.

In the iron and steel industry, laser cladding processing has demonstrated its major advantage in improving the critical service life of working components. With the advent of high-power diode laser systems and dedicated laser cladding nozzles, WILA can easily perform surfacing welding. The application has designed a robust cladding process and is well integrated with it.