Superplastic behavior of two ultrahigh boron steels |
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Authors: | J A Jiménez G González-Doncel P Acosta O A Ruano |
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Affiliation: | (1) Max Planck Institut für Eisenforschung, Max Planck Str. 1, 4000 Düsseldorf 1, Germany;(2) C.S.I.C., Centro Nacional de Investigaciones Metalúrgicas, 28040 Madrid, Spain;(3) Krupp VDM, W-5990 Altena, Germany |
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Abstract: | The high-temperature deformation behavior of two ultrahigh boron steels containing 2.2 pct and 4.9 pct B was investigated.
Both alloys were processedvia powder metallurgy involving gas atomization and hot isostatic pressing (hipping) at various temperatures. After hipping at
700 °C, the Fe-2.2 pct B alloy showed a fine microstructure consisting of l-μm grains and small elongated borides (less than 1μm) . At 1100 °C, a coarser microstructure with rounded borides was formed. This alloy was superplastic at 850 °C with stress
exponents of about two and tensile elongations as high as 435 pct. The microstructure of the Fe-4.9 pct B alloy was similar
to that of the Fe-2.2 pct B alloy showing, in addition, coarse borides. This alloy also showed low stress exponent values
but lacked high tensile elongation (less than 65 pct), which was attributed to the presence of stress accumulation at the
interface between the matrix and the large borides. A change in the activation energy value at theα-γ transformation temperature was seen in the Fe-2.2 pct B alloy. The plastic flow data were in agreement with grain boundary
sliding and slip creep models.
J.A. JIMéNEZ, Postdoctoral Fellow, formerly with Centro Nacional de Investigaciones Metalurgicas, C.S.I.C. |
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