Study of thermal ageing behaviour of Fe-Cr model alloys by magnetic hysteresis loop technique

Abstract

Fe-Cr alloys with different Cr content (5–20 wt. %) were prepared by arc melting technique. The alloys were solution annealed at 1050 oC/ 2h and air quenched and then tempered at 750 oC/ 1h followed by air cooling. Thermal ageing was carried at 475 oC for various lengths of time up to 1000 hours (hrs) to produce thermal embrittlement. The hardness and coercivity of Fe−20% Cr alloys were increased and the remanence was decreased, being due to the precipitation of Cr-rich a' phase and their subsequent growth. In Fe−15% Cr and Fe−10% Cr alloys, it was found that the coercivity decreased at the initial ageing period and then increased subsequently due to the competing effect of recovery of dislocations and precipitation of Cr rich phase. The change in magnetic properties in Fe−5% Cr alloy was different than other alloys since it was within the solubility limit of Cr in Fe. A linear relationship was found between the coercivity and hardness in Fe−20% Cr alloy, indicating that Magnetic Hysteresis Loop (MHL) technique would be a good tool for the Non-Destructive Evaluatiion (NDE) of embrittlement in Fe-Cr alloys.