Using Modules to Analyze Grain Size in Metals and Alloys
ASTM E112 is the dominant international standard for measuring grains in metallic and alloy samples, with ASTM E112 test methods covering procedures for estimating the average grain size of metals consisting entirely, or principally, of a single phase.
Prior to today’s advanced micro-imaging software, most quality control labs would analyze these grains by performing a visual estimation of the grain size by comparing a live image under an optical microscope to a micrograph chart, usually posted on a wall near the microscope. Or, instead of using a micrograph poster, the operator would insert an eyepiece reticle containing images of predefined grain size patterns into the microscope’s optical path. This way, the comparison would be performed directly in the microscope (see Figure 2).
Since grain size is being visually estimated by the microscope user, both of these methods often lead to inaccurate and unrepeatable results — and results that are not reproducible between different operators. Furthermore, quality control technicians are required to manually enter their results into a spreadsheet or report, providing an additional opportunity for error.
Today, with modular micro-imaging software, operators can use very specific custom software modules to accurately analyze grains in compliance with ASTM E112 and other international standards. Grains intercept and grains planimetric modules provide metallurgical quality control laboratories with fully automated grain analysis, eliminating potential inaccuracies, automatically archiving all data, and generating custom analysis reports.
Grain Analysis via the Grains Intercept Module
Using a grains intercept module, a pattern (circles, crossand- circles, lines, etc.) is overlaid on a digital grains image (live or captured). Each time the overlaid pattern intercepts with a grain boundary, an intercept is drawn on the image and recorded. Taking the system calibration into consideration, the grains intercept module (see Figure 3) automatically calculates the ASTM “G Number,” or grain size, and mean intercept length (based on the intercept count and pattern length).
Grain Analysis via the Grains Planimetric Module
A grains planimetric module (see Figure 4) executes the planimetric grain analysis method, which determines the grain size on an image (live or captured) by calculating the number of grains per unit area. Since all results are calculated internally within the grains planimetric module, uncertainty previously attributed to the human element is removed.
With both the grains intercept module and the grains planimetric module, grain analysis results can be automatically archived onto a spreadsheet or integrated database. Grain analysis reports containing all relevant analysis data and associated images can also be generated.
Specific Application-Based Solutions
As illustrated in the example above, module-based image analysis software gives operators access to very specific application- based solutions, allowing them to execute complex analysis tasks quickly and in compliance with today’s most important international standards. Repetitive measurement is essential to industrial microscopy — modularity provides the ability to choose the interface function designed specifically for the task at hand. Depending on their needs, users can pick and choose from modules designed for their exact application: particle distribution, porosity, grain analysis, nodularity, etc. Each module then delivers advanced functionality built around that application, including fully guided processes that enable ease of use and reliable repeatability.
As module-based software systems continue to ensure consistently accurate results, users will likely expect even more automation from new imaging software packages. Micro-imaging software development is progressing at an extremely fast rate, with auto-measuring and auto-alignment as definite possibilities in the future. No matter what advances we see, however, the ultimate goal of personalized software systems will remain the same as they continue to evolve — allowing operators to complete their very specific tasks as efficiently and as accurately as possible.
This article was written by Jeri Reed, Associate Product Manager, Olympus Corporation (Center Valley, PA). For more information, visit http://info.hotims.com/45601-140.