Abstract: A magnesia aggregate for a refractory article, which comprises: a core portion comprising magnesia; a covering layer excellent in slag penetration resistance, which comprises a refractory material excellent in slag penetration resistance and covers the surface of said core portion; and an intermediate layer excellent in slag penetration resistance, formed between said core portion and said covering layer through combination thereof. Said magnesia aggregate is manufactured by: forming, on the surface of a core portion which comprises magnesia and has a particle size of from 40 .mu.m to 10 mm, a covering layer which comprises a powdery refractory material excellent in slag penetration resistance and has a covering thickness of from 20 .mu.m to 2.0 mm, to prepare a green aggregate; and firing said green aggregate at a temperature of from 1,700.degree. to 2,200.degree. C.

Abstract: A method for blowing a gas from below into a molten steel in a refining vessel, which comprises: using a refining vessel including at least one gas blowing aperture provided in the bottom wall thereof and a frustoconical plug matching with said aperture, releasably inserted into said gas blowing aperture, which has a small-diameter bore having a diameter within the range of from 0.5 to 6.