The Influence of Atomizing Gas on the Formation of Metastable Phase Powders in an Fe_<56>Cr_<20>Si_6C_<18> Alloy and on the Microstructure and Mechanical Properties of the Hot-pressed Products

概要

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Metastable phase powders with chi, ferrite and M_7C_3 have been produced by atomizing an Fe-20Cr-6Si-18C alloy with N_2, Ar or He gas. The hot-pressing of the atomized powders in a temperature range of 1253 to 1343 K brings about a fully dense material with a finely and homogeneously mixed structure of ferrite and M_7C_3 phases. The particle size and interparticle distance of the carbide are as small as 1.1 to 2.7μm and 2.1 to 4.4μm, respectively. The hot-pressed alloy has high hardness, e.g., 705 to 765 DPN at R.T. and 515 to 550 DPN at 873 K, comparable to that of conventional heat resistant alloy steels. The hardness of the hot-pressed products made from N_2-gas atomized powder is higher by 25 to 70 DPN than for that made from Ar- or He-gas atomized powder over the entire temperature range. Furthermore, wear resistance is also better for the former products. The difference was presumably due to the solid solution strengthening of ferrite and M_7C_3 through the dissolution of a small amount (≃0.017 wt%) of N_2. It has thus been demonstrated that the application of the high-pressure N_2 atomization to the alloy containing Cr and Si elements with a large negative heat of mixing against N_2 results in a heat-resistant tool material with characteristics better than that prepared by Ar- or He-gas atomization.
東北大学の論文
1988-03-31