Development of crack-free cladding for white cast iron alloys

Laser metal deposition (LMD) process has been investigated to deposit clad overlay on a white cast iron alloy. This specific alloy contained high carbon and chromium and is hard and highly resistant to abrasive wear, and is widely used in making components such as slurry pumps, conveyor chutes, etc. which are used in slurry and mineral transport systems. In these applications component failure is common and due to severe wear, and causes unwanted and expensive plant shutdown. Despite their high wear resistance these components are regularly replaced due to wear loss. The white iron alloys are also highly susceptible to cracking when subjected to weld repair and this is due to the formation of hard microstructures in the heat affected zone (HAZ) adjacent to fusion zone. In many cases a buttering layer is added with soft metal for crack susceptible alloys. In this investigation a high power fibre delivery industrial laser system was used for cladding process, and laser cladding was carried out with nickel based powder as a buttering layer and a high chromium matching alloy powder as a top layer at various level of preheating. Metal powder was blown in to the laser beam through a coaxial powder delivery nozzle. Thermocouples were embedded in to the plate to monitor preheating temperature as well as temperature rise during laser cladding process. Results have shown that this specific alloy produced high number of cracking starting from HAZ. However at proper level of dilution with buttering layer and preheating temperature the right conditions were achieved to eliminate cracking in the clad overlay.