Papers by Author: Hung Wei Yen

Abstract: An Fe-1.0C-17Cr (wt.%) stainless steel was subjected to subzero treatment to investigated the structure of martensite midrib. The midrib region appeared in the thin plate and lenticular martensites have been observed detailed by TEM. The TEM result reveals that the transformations of thin plate martensite and lenticular martensite are initiated at the same midrib region. The former keeps the lattice-invariant deformation mode of twinning during subsequent growth, whereas the latter combines both twinning and slip modes. Midrib region is a preferential position for carbide precipitations after tempering. M₃C and M₂₃C₆ carbide were found in this alloy, and related to the ferrite by Bagaryatsky OR and K-S OR, respectively.

Abstract: The ferrite phase strengthened by the highly dense nanometer-sized carbides is named super ferrite. The effects of Ti, Ti-Mo, and Ti-Nb micro-alloy additions on the precipitation strengthening in three experimental high-strength low-alloy steels have been investigated by using transmission electron microscopy and micro-hardness measurement. The objective of this work was to study the carbide precipitation under the conditions of isothermal transformation. It was found that interphase precipitation of nano-sized carbide in Steel Ti-Mo had very strong contribution to the hardness of the steel. The distribution of interphase precipitated carbides is associated with both the sheet spacing and the inter-particle spacing, which have been studied. The result implies that (Ti, Mo)C particles possess an excellent effect on precipitation hardening.

Abstract: The effect of the degree of supersaturation in a coarse-grained h-ferrite matrix on the consequent isothermal transformation of h-ferrite to austenite at 1150‖ in a 2205 duplex stainless steel has been investigated. The results indicate that rapid cooling (at the cooling rate 100‖/s) to the ambient temperature after 135P‖ solution treatment of h-ferrite matrix leads to a very high supersaturated solid solution state, which significantly enhances the formation of the intragranularly nucleated austenite in the subsequent isothermal transformation at 1150‖. The feature of the intragranularly nucleated austenite has been revealed; it appears that after the initial nucleation events for intragranularly nucleated austenite, subsequent small particles of austenite can form sympathetically on the ferrite/austenite interface.