James L. McCall

COMPARISON OF THE SINGLE ROLLER AND DOUBLE ROLLER PROCESSES FOR CASTING LOW CARBON STEEL

Publisher Summary This chapter provides a comparison of the single-roller and double-roller processes for casting low-carbon steel. The direct casting of thin metal strip and sheet eliminates many process steps currently needed in conventional processes to produce sheet/strip. The elimination of these process steps reduces energy requirements of the process and enables manufacturers of sheet/strip to significantly lower their processing costs. There are three carbon steel sheet/strip processes, namely, ingot, continuous casting, and direct strip casting (DSC). The calculation for the direct strip casting process includes estimates for ladle holding and heating, tundish preheating, casting, and postcasting treatments such as pickling, rolling, and annealing. The chapter presents a study in which two direct strip-casting processes, namely, the double-roller (DR) process and the single-roller (SR) process, were compared. Using the results of these analyses, a generalized model was developed. Based on this model, a sensitivity analysis was made to determine the way in which each parameter affects the metal and heat-flow patterns. The sensitivity analysis shows that the process parameters can be approximately split into two categories that include those which significantly affect the strip thickness and those which only weakly affect thickness.

Scanning Electron Microscopy for Microstructural Analysis

Probably the most exciting instrument which has been added to a metallographer’s repertoire of capabilities in the past several years has been the scanning electron microscope. Photographs taken with SEM’s have appeared widely in metallurgical literature and, in fact, it is not uncommon to see them in the daily newspapers or even in popular magazines. Perhaps the main reason for their wide use is that SEM images generally are easily recognizable; i.e., an SEM image of a small crystallite looks very much like one might expect a crystallite to look. At the same time, almost contrary to the above, the images are often so striking and show features in ways that no previous methods have been able to show, that the simple esthetics of the images cause them to appear in technical literature. Unfortunately, in many instances, these advantages of the instrument may have caused it to be used simply to produce a vast quantity of pretty pictures. In looking over the published technical literature of a few years ago, and even some of our own technical reports, it is obvious that SEM photographs were used in this way, and, quite frankly, frequently added nothing to the technical content of the publication. As might be expected, SEM photographs frequently adorned the covers of technical publications; in fact, the author counted a total of 14 covers containing such photos in a period of only 3 months on the relatively few technical publications that regularly pass across his desk. Now, however, this initial flurry of excitement appears to have quieted down, and SEM’s have acquired quite justified positions in many metallographic laboratories alongside metallographs, transmission electron microscopes, and other image- forming instruments Even though the SEM has had a tremendous impact on metallographic laboratories, it really hasn’t eliminated the need for those instruments which existed in metallographic laboratories prior to its introduction, but, rather, it serves to complement them.

Increasing the microscopic contrast of phases with similar reflectivities

A number of methods have been developed to increase the optical contrast between microscopic phases in metal specimens. These methods include stain etching, heat tinting, and vapor deposition. ls2 Unfortunately, these methods are often difficult to control and are limited to only a few materials. Also, the vapor deposition method can be relatively time-consuming and requires the use of equipment not available to most metallographers. This note describes a technique which overcomes many of these limitations, since it involves only the application of a thin layer of Parlodiona to the surface of a polished and etched specimen. The technique is rapid and inexpensive, and it does not require any auxiliary equipment. Apparently, the technique causes increased contrast as a result of interference phenomena due to variations in the thickness of the Parlodion film. By proper polishing, etching, and application of the Parlodion film, it is possible to cause a different film thickness to form over each phase. As a result, different reflectivities occur. By increasing the contrast, phases can be more readily distinguished, photomicrography is eased, and automatic methods of quantitative metallographic analysis which depend on differences in reflectivity can be used (see Figs. 1 and 2).

Metallographic studies of archeological artifacts from Ecuador

Abstract Metallographic studies have been made of archeological artifacts recovered from an excavation of a civilization which existed in La Compania, Los Rios Province, Ecuador South America, in the period of 700–1519 a.d. All the artifacts are described as collar buttons, and most were copper-silver alloys. The studies primarily were conducted using optical metallographic methods. Interpretations of the microstructures and the joints between the various parts of the artifacts revealed significant information regarding the methods used to fabricate the artifacts. Some speculations are offered regarding the specific manufacturing methods employed by the ancient metalsmiths.