Abstract: This invention is intended for providing a soft magnetic steel material having excellent DC magnetization properties and corrosion resistance, and capable of being manufactured at a low cost, and a method of manufacturing the same.The soft magnetic steel material of this invention contains 0.8 to 3.5% by weight of soluble aluminum, as well as limited amounts of C, total nitrogen, Si, Mn, P, S and total oxygen, and has an average ferrite crystal diameter of which the minimum has a specific relation to the thickness or diameter of the material. The material has a surface covered densely with aluminum oxide particles having a diameter of 0.01 to 5 microns. It exhibits a coercive force not exceeding 0.4 Oe in the absence of any strain and a magnetic flux density of 15,000 G or more at a magnetomotive force of 25 Oe. The aluminum oxide particles formed on the surface of the material are preferably formed with a density of 1.times.10.sup.12 to 1.times.10.sup.16 particles, or more preferably 1.times.10.sup.13 to 1.

Abstract: The austenite alloy tube has a composition of 15.about.26% of Cr, 8.about.35% of Ni, 1.0% or less of Si, 2.0% or less of Mn and less than 0.25% of N and the balance of iron and impurities. The nitrogen content on the inner surface of the tube is at least 0.25%. If desired, one or more of 0.6% or less of Ti, 0.6% or less of Al, 3.0% or less of Mo and 1.0% or less of Nb may be incorporated.