Synthesis, thermal treatment, and characterization of sintered hard magnetic Fe–30Cr–16Co alloy

Abstract

A powder metallurgy process for manufacturing hard magnetic alloy Fe–30Cr–16Co (wt%) was optimized. An acceptable level of magnetic properties of the alloy was reached upon sintering within the temperature range 1100–1400 °C (with a maximum at 1350 °C; Br = 1.21 T, Нс = 54.6 kA/m, and (BH)max = 37.6 кJ/m3) and at an overall duration of thermal treatment of 15 h. Lowest magnetic properties (Br = 1.12 T, Нс = 48.6 kA/m, and (BH)max = 31.1 KJ/m3) were observed at 1100 °C most likely due to higher porosity of about 7%. After full thermal treatment with temperature of thermomagnetic stage, 670 °C, we observe the presence of non-magnetic σ-phase, which leads to a sharp drop in magnetic properties. Based on the magnetic measurements at intermediate stages it can be deduced that the σ-phase is formed during the 2nd stage of thermal treatment during cooling down from 670° to 580°C Significant ductility is observed upon material failure during compression tests; fracture strain (εf ∙100%), around 40%. Yield strength, compressive strength, and linear thermal expansion for obtained alloys are presented. The yield strength decreases with increasing sintering temperature within the range 1100–1400 °C due to grain growth.