Corrosion-resistant weld overlays are used to improve the service life of components made with an otherwise corrosion-prone material, but one of the major concerns affecting their use is the impact of excessive dilution – the filler metal mixing with the parent metal.
Restrictive standards
Codes and standards for qualification of weld overlay procedures generally attempt to control dilution by restricting the heat input, but as this can be achieved by proportionally varying both the welding current and the welding speed, the resulting dilution can be different even if the heat input is controlled.
Due to these uncertainties, industry takes a conservative view when specifying the permissible dilution. For Inconel Alloy 625 weld overlay, for example, the permissible amount of iron in the overlay is restricted to five per cent: the same level as that permitted in Alloy 625 wrought product, resulting in substantial productivity losses, an increase in cost, and associated issues such as distortion of components.