Crystallography and tempering behavior of iron-nitrogen martensite
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I.
INTRODUCTION
A large amount of established knowledge on the crystallography and the tempering behavior of iron-carbon martensites exists (cf. reviews presented in References 1 through 3). This contrasts with the few corresponding data available for iron-nitrogen martensites (cf. References 4 through 8). This may reflect the great technological importance of iron-carbon martensites, whereas no distinct technological application of iron-nitrogen martensites is apparent at present. However, the case-hardening process of carbonitriding implies the development of ternary ironcarbon-nitrogen martensites. Even aging at room temperature of carbonitrided workpieces leads to significant changes in microstructure and mechanical properties. The microstructure and the tempering behavior of the ternary martensite, however, are not well known. It is against this background that an investigation into the microstructure of iron-nitrogen martensite, before and after tempering, appears desirable: (i) from a fundamental point of view in order to understand correspondences and differences with iron-carbon martensite, and (ii)from a technological point of view, as a first step toward understanding ternary iron-carbon-nitrogen martensite as produced by carbonitriding. In this paper results are presented on both low- and highnitrogen martensites (lath vs plate morphology). Apart from optical microscopy and hardness measurements, transmission electron diffraction and microscopy and differential thermal analysis were employed to study the crystallography and the tempering behavior of iron-nitrogen martensite. II.
EXPERIMENTAL PROCEDURES
0.009 at. pct Cu; 0.0014 at. pct Mn;
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