Hardfacing of a Modified 9Cr-1Mo Steel Component Using a Nickel-Base Alloy

A dashpot piston made of modified 9Cr-1Mo steel is hardfaced with NiCr-B alloy by the Plasma Transferred Arc (PTA) process. During initial trials, a large number of cracks were observed in the hardface deposit when hardfacing was carried out directly on the modified 9Cr-1Mo steel substrate using a preheat temperature of 723 K. Both the deposit and the martensitic structure formed in the heat affected zone of the substrate during deposition are hard and hence were unable to absorb the thermal stresses generated, leading to cracking. Subsequently, hardfacing trials carried out with an intermediate layer of 2 mm thick Inconel-625 alloy, were successful and deposits were crack-free. Use of a relatively soft Inconel-625 between the hardface deposit and the substrate reduced martensite formation in the substrate, and thus the cracking susceptibility of the deposit.