Papers by Author: Jer Ren Yang

Abstract: Dual precipitates of carbide and copper particles formed within Cu-Ti microalloyed DP (Dual Phase) steel in the present study. The precipitation behaviors of tiny precipitates, especially in the ferrite matrix, were checked precisely by several methods, such as optical microscopy, high resolution transmission electron microscopy, and hardness testing. It was found that copper particles nucleated only on the interphase precipitated TiC and were not dispersed randomly within the ferrite matrix. Therefore, the formation of dual precipitates within the ferrite grains should be considered as separated phase transformation; initially, only titanium carbides form during the austenite decomposition reaction, after which copper particles heterogeneously nucleate on these carbides. Furthermore, as compared to Cu microalloyed DP steel, the tempering behavior of martensite in the Cu-Ti microalloyed DP steel showed a tempering hardening characteristic.

Abstract: In this work, the investigation of transmission electron microscopy has elucidated the morphologies of the interphase precipitated carbides in an experimental Ti-Mo-bearing steel into three types: (1) planar interphase precipitation with regular sheet spacing (designated as PIP), (2) curved interphase precipitation with regular sheet spacing (designated as Regular CIP), and (3) curved interphase precipitation with irregular sheet spacing (designated as Irregular CIP). The planar sheets of carbides have also been analyzed and found to be oriented close to ferrite planes {211}, {210} and {111}; the results of transmission electron microscopy provide strong evidence to suggest that the development of interphase-precipitated carbides can be associated with the growth of incoherent ferrite/austenite interface by the ledge mechanism. The sheet spacing and inter-carbide spacing in the sheet have been measured and estimated in this work. The sheet spacing is found to be finer than the inter-carbide spacing in the sheet for all samples investigated. The result reflects that the distribution of interphase-precipitated carbides is anisotropic and cannot be considered random distribution. The relevance of the Orowan mechanism to the non-random distribution of interphase-precipitated carbides has been considered. The contribution of the dispersion of interphase-precipitated carbides to the yield strength of the steel studied has been estimated. It is revealed that an optimum component about 400 MPa contributed by interphase-precipitated carbides can be achieved, and the finding is consistent with the hardness data. Other examples of the different alloy steels are also addressed.

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.