Laser Cladding Project at Tata Steel

In the manufacture of steel strip work, components have to perform in exceptionally aggressive environments and withstand service at high temperatures in corrosive atmospheres under mechanical wear and frequent and heavy impact loading. Conventionally, components that are subject to high wear or corrosion have often been manufactured from rich chemistry steels or hardfaced using submerged arc clad martensitic stainless steels (MSSs) to increase their service life and therefore maximize line throughput by extending maintenance intervals without any sacrifice to product quality.

MSS-welded alloys generally have good wear and corrosion characteristics; however, they are not suitable for severe metal-on-metal abrasion, and they also lose their mechanical and corrosive properties at high temperatures. Arc-welded MSS alloys also suffer from weld sensitization in grain boundaries in the heat affected zones (HAZs) where chromium carbides are precipitated, leaving the surrounding areas depleted in chromium. These areas are therefore susceptible to localized corrosion.

Thermally sprayed coatings are also in widespread use throughout the steel industry because of their flexibility in the types of alloys and metal matrix composites (MMCs) that can be applied. However, their mechanically bonded interfaces have relatively low strength (unless post spray fusing is employed), limiting their practical use in an environment with very heavy impacts.

In 2009, a system was built in Port Talbot, South Wales, UK, in an attempt to develop laser cladding for coating critical works components to increase their service lifetime (FIGURE 1). In the rolling mills of the steel industry, different rolls of 0.3 to 3.5 meters in length are needed. Laser clad coatings have been proven to extend the lifetime of components by up to 6×.

FIGURE 2. The YC52 cladding head with a coaxial nozzle.

Since the installation of the laser cladding system in Port Talbot, the process has been developed and numerous nickel cobalt and iron-based-material alloys have been assessed in terms of microstructure, mechanical properties, and wear and corrosion resistance. Detailed process development is required to tailor the coating properties for each application within the steel works.

The initial results from line trials were extremely encouraging: components that were laser clad obtained unprecedented wear and corrosion performance. As such, it was decided to build a production machine to cope with the anticipated demand.