iWorks FG
Microscope Software for ASTM Grain Size Analysis & Measurement in Metals & Alloys
The structures of metals or alloys and mechanical properties of various metallic materials change due to heat treatment and other factors. Most metals have a crystalline structure containing grain boundaries. During processing, the atoms in each growing grain in a metal or alloy are arranged in a specific pattern based on the material’s crystal structure. To evaluate materials properly, reliable analysis of grain sizes is required in compliance with industrial standards.
Note: All functions of iWorks FX are included in the iWorks FG. The Advanced Measurement Tool (interactive measurement) is also available.
Tutorial Video: iWorks FG plus Report Manager
Determine the Average Grain Size Using iWorks FG Software
The average grain size of an alloy is generally expressed in terms of the grain size number "G", as indicated in the standard ASTM E112. The value of G ranges from 00 to 14 where 00 corresponds to an average grain diameter of 0.508 mm and area of 0.2581 mm2 and 14 a diameter of 2.8 µm and area of 7.9 µm2.
iWorks FG software provides all of three common methods described in the standards ISO 643:2012 and ASTM E112-13, to evaluate the grain size number of an alloy: Comparison, Intercept, and Planimetric procedures .
Supported Standards of Grain Size Analysis in iWorks FG
iWorks FG software includes the international standards and methods for grain size analysis. (see below table)
Chart Comparison Method
The "Chart Comparison" is the most commonly used in metallographic laboratories for grain analysis. Different from traditional comparison method using a microscope eyepiece reticle (refer to Figure 1) or wall chart, iWorks FG provides a digital overlay Grain Chart comparing with the grain structure image (refer to Figure 2). This method is fast and convenient, but the values of grain size are much less accurate than those calculated from the intercept or planimetric approaches below.
Figure 1: Example of a microscope eyepiece reticle used to compare against a live image.
Figure 2: The Grain Chart function of iWorks FG.
Intercept Method
The "Intercept Method", is an automated digital grain analysis solution, which involves overlaying of a pattern atop the live or acquired digital image and drawing an intercept on the image whenever the overlaid pattern intercepts with a grain boundary (refer to Figure 3).
The greater the number of intercepts or intersections, the greater the precision of the G number. Generally, the intercept method is fast and delivers good accuracy.
Figure 3: Example of the intercept method used to measure the grain size of a steel alloy. A raw image [left] was acquired with a microscope. A geometric pattern with lines and circles [center] was drawn over the grains seen in the image and the image data processed [right] using the intercept approach of the iWorks FG software. The values of G number, Intecept Count, Test Length, and Mean intercept Length were determined and show in a table [below].
Planimetric Method
Planimetric method is another approach for grain size analysis, determining the grain size on the live or captured image by estimating the grain count per unit area (Figure 4).
Figure 4: Grain analysis via the Planimetric method.
With this method, the number of grains within a defined circular area are counted. The number of grains per unit area, NA, is used to determine G (grain size number). The value of NA is calculated with:
Where M is the magnification, A is the circular area, ninside is the number of grains falling completely within the circle, and nintercepted is the number of grains intercepted by the circle’s perimeter (refer to figure 10). Then G can be calculated from the equation:
The greater the number of grains counted, the greater the precision of G. In general, results from the planimetric method are very reproducible and precise. In the planimetirc method, iWorks FG software also provides a powerful classification function. Grains can be classified as per area or other indicators. Four groups filling color of classification make the working of grain analysis more vivid and intuitive (Figure 5).
Figure 5: Default colors, Rainbow colors, RGB15 colors and System colors (from left to right).
The results in the iWorks FG software have undergone intelligent internal calculations, removes the guesswork of operators, thus providing accurate, repeatable and reproducible results (Figure 6). In addition, it is possible to configure the iWorks FG software package with the plug-in module "Report Manager" for automatic generating report of the grain analysis results into a Excel sheet.
Figure 6: Grain size analysis result export to Excell sheet. Data includes Summary, Class, Class graph, Statistics etc.
