Estimation of hardness in nickel-base hardafacing deposits on 316ln stainless steel by magnetic techniques

Abstract

Nickel-base Colmonoy-6 (AWS ERNiCr) alloy is the material chosen for hardfacing of austenitic stainless steel (SS) components used in India's Prototype Fast Breeder Reactor. Gas Tungsten Arc deposited Colmonoy hardfacing alloys suffer from significant loss in hardness and wear properties due to dilution from the austenitic stainless steel substrate. Although both austenitic SS and the undiluted Colmonoy-6 alloy are non-magnetic, the hardfacing deposit diluted by SS becomes ferromagnetic. In a multilayer deposit, magnetism is highest in the first hardfacing layer and decreases progressively in the subsequent layers. As in actual hardfacing deposits, dilution is difficult to control for any deposited layer, it is not easy to study variations of magnetic properties as a function of dilution. Hence, a separate set of deposits (twin-deposits) were produced by co-deposition of Colmonoy-6 alloy rods and austenitic SS filler wire on a copper block. Magnetic properties of hardfacing and twin-deposits were examined using Magnegage and Feritscope equipments. The saturated magnetic moments and Curie temperature of the twin-deposits were measured from room temperature to 873 K. Further, optical, scanning electron microscopy, energy dispersive X-ray spectroscopy and hardness measurements were performed for both hardfacing and twin-deposits. Correlation between hardness, microstructure and bulk magnetic property of deposits with different dilution levels could be established. It was also possible to correlate hardness with the magnetic property of the deposits. Thus, the present study indicates a potential use of magnetic techniques for estimating hardness and dilution of the Colmonoy hardfacing deposit in a component, which cannot be subjected to destructive examination.