Temperature dependence of metal desulfuration in steelmaking units

It is theoretically and experimentally shown that with the temperature increase the degree of metal desulfuration by a slag increases for unkilled iron-carbon alloys and decreases for killed steel.     

Simple models for the omega phase transformation

In the late sixties, it was recognized that the omega phase transformation occurring in bcc Ti, Zr, and Hf alloys was a displacive transition which could be described, at least qualitatively, by simple models. Since the displacive wave responsible for the transition to perfect omega was a Brillouin zone boundary wave, displacements and volume changes were rather small, in contrast to the classical martensite case. The nonideal, or modulated omega phase requires further consideration, and calls for soliton models, for example. Recent first principles electronic structure calculations, briefly reported upon here, have also shed light on the athermal omega transformation. This paper is based on a presentation made in the symposium “Pre-transformation Behavior Related to Displacive Transformations in Alloys≓ presented at the 1986 annual AIME meeting in New Orleans, March 2-6, 1986, under the auspices of the ASM-MSD Structures Committee.     

The as-quenched form of the omega phase in Zr-Nb alloys

The as-quenched Ω phase was examined in the Zr-Nb system using high resolution dark field electron microscopy and selected area diffraction. The morphology of the Ω phase was shown to be based upon (111) tl(0001) rows of particles 10 to 15Å in diameter with an interparticle spacing of 15 to 25Å. The row morphology is in agreement with previous observations on a Zr-Ti alloy. In the Zr-8 wt pct Nb alloy, clusters made up of many rows were observed and, as the solute content increased up to 15 wt pct Nb, the clusters became smaller and the length of the individual rows decreased. Sharp ω reflections and {111} planes of intensity in reciprocal space were observed in the 8 wt pct Nb alloy. As the niobium content increased, the ω reflections broadened and became more diffuse, while the thickness of the {111} planes of intensity increased. It was suggested that the sharp ω reflections result from scattering by the clusters while the {111} planes of intensity result from scattering by isolated rows of particles. Comparison of the ω morphology with the diffraction effects showed good agreement with these suggestions. In alloys with 15 wt pct and higher Nb content, the 0001 and 0002 broadened ω reflections were observed to be displaced toward each other alongω phase. It was suggested that these displacements are related to the mechanism of the transformation, which is thought to involve instability of the bcc structure relative to atomic displacement waves. The electron diffraction patterns were in agreement with predictions concerning this mechanism.     

The Stress-induced omega phase transformation in Ti-V alloys

The deformation behavior of bcc (β) Ti-V single crystals containing the athermal ω phase was studied using tensile tests, optical and electron microscopy and X-ray and electron diffraction. The stress-strain curves were characterized by a marked yield point and an essentially zero work hardening rate. The deformation structures consisted of wavy slip and stress-induced plates. Both X-ray and electron diffraction showed that the stress-induced plates consist of one variant of the omega phase, with the orientation relation to the parent? phase close to (0001)ω ‖(001)ω; (•1120)ω ‖(110)β. The habit plane was of the type 554. A small amount of ά (hcp) phase was present within the ω plate, with orientation relation to the β phase close to the Burgers relationshipi.e. (0001)_ά, ‖(110)β; [•1120]ά ‖[•111]_β. It is suggested that the ω phase may be an intermediate structure in the stress-induced bcc → hep transformation. R. R. AHRENS, formerly Research Assistant in the Department of Materials Science and Engineering, Cornell University     

The Stress-induced omega phase transformation in Ti-V alloys

Metallurgical and Materials Transactions A - The deformation behavior of bcc (β) Ti-V single crystals containing the athermal ω phase was studied using tensile tests, optical and electron...