'Scope' Offers Different Iron Reality.

Drawing upon his 35 years of studying cast iron metallurgy, G.M. Goodrich, Professional Metallurgical Services, Buchanan, Michigan, presented this year's Cast Iron Honorary Lecture (01-121). Entitled "A Microview of Some Factors That Impact Cast Iron (Or the Little Things that Mean a Lot)," the lecture shared his perspective on the world seen through a microscope. "To an outsider, many of these factors would have no significance whatsoever, Goodrich said, "but seeing the world through a microscope can focus attention on microscopic issues that have had a macroscopic impact on the cast iron world."

Noting that the differences between success and failure can be very small for the iron metallurgist, Goodrich shared different views of "small issues" as they pertain to microstructure, inoculation, magnesium treatment, voids, inclusions and all other aspects of cast iron metallurgy.

"The advances in metallographic sample preparation techniques and microscopes alone in the last 35 years have provided the foundry industry with a fast procedure and affordable equipment for the purpose of conducting evaluations," he said. "The little things that mean a lot certainly are magnified when a microscope is used."

Throughout the presentation numerous microstructure images were shown. Following is a sampling of some of the examples cited by Goodrich on some of those "little things."

Widmanstatten Graphite--While the presence of this graphite form is barely discernible in cast iron, Goodrich said the influence of this graphite structure is profound. "It is capable of reducing the tensile strength of gray iron from 35,000 psi to 15,000 psi with its very presence. In sufficient to cause this type of structure and result in the significant loss of mechanical strength. Even more astounding is the fact that most commercial laboratories cannot tell you when you have 0.0005% lead."

Hard Spots/Machinability--Carb ides and steadite are typical examples of hard spots. In some instances, he said these carbides are microscopic in nature and occur at intercellular locations not discernible unless viewed at magnifications in excess of 400X. He shared a microstructure showing intercellular alloy carbides associated with molybdenum, chromium, vanadium, niobium, titanium and even antimony. "The presence of deleterious levels of these elements cannot be detected using macroscopic chemical analysis. They are generally identified using the microscopic tool known as energy dispersiv X-ray analysis." The source of many of these deleterious elements has been identified as high-strength, low alloy steel in the scrap train.

Inoculation-"It is fascinating that the difference between a quality casting and an unacceptable casting is related to both the quantity of the inoculant-generally in the range of 0.02-0.06%--and the time after the inoculant has been added," he said. "If the strides made during the past 35 years are any indication of the strides that will be made in the future, the cast iron industry will be successfully producing thin-wall castings without the metallurgical concern that seems to be apparent in this day and age."

"The future will continue to show how the relationship between micro conditions and macroscopic quality control events are generated," said Goodrich. "However, the question remains, 'When is it enough and why is more not better?'"