Ce-Bearing FeSi Alloy Inoculation of Electrically Melted, Low Sulphur Grey Cast Irons for Thin Wall Castings

Electrically melted and over-heated (>1500 °C) grey cast iron at less than 0.04%S, as commonly used, solidifies large amounts of carbides and/or undercooled graphite, especially in thin wall castings; this is necessary to achieve a stronger inoculation. The efficiency of Ce-bearing FeSi alloy is tested for lower ladle addition rates (0.15 and 0.25 wt.%), compared to the base and conventional inoculated iron (Ba,Ca-bearing FeSi alloy). The present work explores chill and associated structures in hypoeutectic grey iron (3.6–3.8%CE, 0.02%S, (%Mn) × (%S) = 0.013–0.016, Alres < 0.002%), in wedge castings W1, W2 and W3 (ASTM A 367, furan resin sand mould), at a lower cooling modulus (1.1–3.5 mm) that is typically used to control the quality of thin wall iron castings. Relatively clear and total chill well correlated with the standard thermal (cooling curve) analysis parameters and structural characteristics in wedge castings, at different wall thickness, displayed as the carbides/graphite ratio and presence of undercooled graphite morphologies. The difference in effects of the two inoculants addition is seen as the ability to decrease the amount of carbides and undercooled graphite, with Ce-bearing FeSi alloy outperforming the conventional inoculant, especially as the wall thickness decreased. It appears that Ce-bearing FeSi alloy could be a solution for low sulphur, electric melt, thin wall iron castings production.

Preparation of ε-Fe(Si)3N Powder Using a Salt Bath Nitriding Reaction and a Study on the Soft Magnetic Properties of the Powder

In this paper, a single phase ε-Fe(Si)3N powder was successfully synthesized through the salt bath nitriding reaction method. The flaky FeSi alloy powder was used as the iron source, and non-toxic CO(NH2)2 was used as the nitrogen source. The nitridation mechanism, the preparation technology, the soft magnetic properties, and the magnetization temperature dependence of the powder were studied. The research result showed that ε-Fe(Si)3N alloy powders were synthesized in a high temperature nitrification system after the surface of flaky FeSi alloy powders were activated by a high-energy ball mill. The optimum nitriding process was nitridation for 1 h at 550 °C. The ε-Fe(Si)3N powder had good thermal stability at less than 478.8 °C. It was shown that ε-Fe(Si)3N powder has good soft magnetic properties, and the saturation magnetization of the powder was up to 139 emu/g. The saturation magnetization of ε-Fe(Si)3N powder remains basically constant in the temperature range of 300–400 K. In the temperature range of 400–600 K, the saturation magnetization decreases slightly with the increase of temperature, indicating that the magnetic ε-Fe(Si)3N powder has good magnetization temperature dependence.

Formation of Non-metallic Inclusions of Si-killed Stainless Steel during GOR Refining Process

The formation mechanism of inclusions in Si-killed 304 stainless steel was studied by industrial experiments during GOR refining process and thermodynamic calculations. A lager number of CaO-SiO2-MgO-Al2O3-MnO-CrOx liquid spherical inclusions with different size (from 1 μm to 22 μm) had been found after deoxidization of FeSi alloy in 10 minutes. The calculation result of FactSage 6.3 software assisted in confirming that the inclusions in size of less than 5 μm that had less than 30 % CaO mainly came from the deoxidation of FeSi alloy with Ca and Al. The inclusions in size of more than 5 μm that had more than 30 % CaO mainly came from the modification of involved slag droplets through the oxidation of Si and Al and the collision with deoxidation-type inclusions, and the degree of change was bigger for smaller inclusions. The MgO in slag and refractory was reduced by Si and Al in steel, which leaded to the unceasingly increase of Mg content in steel. Subsequently, SiO2, MnO and CrOx in inclusion were reduced by Mg, which resulted in the increase of MgO content in inclusion and the degree of increase of MgO content was greater for the larger size of inclusions.