Structure and magnetic properties of milled maraging steel powders

• Published in: Powder technology Vol. 360; pp. 80 - 95
• Main Authors: Thotakura, G.V., Goswami, R., Jayaraman, T.V.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.01.2020; Elsevier BV
• Subjects: Ambient temperature; Atomizing; Ball milling; Coercivity; Grain size; Heat treatment; High-energy ball milling; Magnetic properties; Magnetic saturation; Magnetism; Maraging steel powder; Maraging steels; Martensite; Nanocrystals; Steel; Grain size; Maraging steel powder; High-energy ball milling; Magnetic properties
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2019.09.054

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. [Display omitted] •Milling of gas-atomized maraging steel powder resulted in nanocrystalline powder.•The milled and thermally-treated powders were primarily comprised of martensite.•The grain size and particle size (D90) were < ~50nm and < ~10μm, respectively.•The saturation magnetization (MS) of the milled powders was ~165 Am2/kg.•Thermal treatment of milled powders increased MS and decreased coercivity.