Structure and magnetic properties of milled maraging steel powders

Abstract

We demonstrate that high-energy ball milling of gas-atomized maraging steel powder followed by suitable thermal-treatment produces nanocrystalline maraging steel powders having improved magnetic properties, compared to the gas-atomized powders. Milling for five to eighthours formed powders comprised of, primarily, nanocrystalline martensite. The saturation magnetization (MS) of the milled powders ranged between ~164 Am2/kg and ~169 Am2/kg, while the intrinsic coercivity (HCI) ranged between ~4.9kA/m and ~6.7kA/m. At sub-ambient temperatures, from 60K to 390K, both MS and HCI decremented with the increment in temperature. The thermomagnetic behavior of the milled powders was somewhat reversible. At supra-ambient temperatures (500K–900K), both MS and HCI monotonically decreased with the increase in temperature. The thermally treated powders constituted nanocrystalline martensite and exhibited increment (by ~6%) in MS and decrement (~nearly halved) in HCI compared to the milled powder, i.e., the powders exhibited improvement in soft-magnetic properties.