| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 103 === Low magnetism steel is commonly used for the application of transformer core, permanent magnet materials mold, concentrator and others. It is also a key material for precision machinery and automatic control .But low magnetism steel usually with low hardness，sometimes in special circumstances，low magnetism steel should provided with higher mechanical strength，and must improve by heat treatment or work hardening.
This research focuses on the development of new cast steel (iron) that is with the characteristics of high hardness and Low magnetic permeability under as-cast status. The alloy mainly contains 3 wt % of carbon, 1 wt % of silicon, 30 wt % of manganese. The hardness of the as-cast material is between HRC 45 ~ 50; while the alloy’s relatively magnetic permeability (μr) is about 1.002125. Because this research alloy got high hardness and low magnetic permeability under as-cast status，so do not need heat treatment or work hardening process，It benefit of production costs , save energy and shorten the process.
The principle of the alloy, make the base structure become austenite phase after melted steel cooling down, and growth large amount of ferromanganese carbide simultaneously. Since the austenite phase has characteristics of low magnetic, and ferromanganese carbide with high hardness, this dual-phase structure intersect distribution, as a result get a low magnetic with high hardness of both. This alloy in the as-cast, after subzero, after solution and aging, can maintain 44-50HRC of hardness, its relative permeability was still maintained at 1.002, showing not easy to change its hardness and magnetism by heat treatment .
On the characterization of wear test, since this material contain high hardness ferromanganese carbide, grinding with tungsten carbide to got the coefficient of friction (COF) was 0.516, better than the M2 tool steel (COF=0.6) and HSS rapid steel (COF=0.85). Another via density test, obtained the density of the as-cast alloy is 7.59-7.64 g / cm3 at room temperature, compared to common of the 304 non-magnetic steel density 8.03 g / cm3, its about 5% lower. If the demand for use in large engineering project, can reduce the weight and volume of material
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