Performing a Grains Analysis in 5 Easy Steps: A Simple ...

1 1 Performing a Grains Analysis in 5 Easy Steps: A Simple Guide to Understanding Discover Essentials Grains Analysis What is astm e112 standard, and why is this of importance? astm e112 standard is commonly practiced within the United States for determining the quality of a specific alloy. This standard is routinely performed by inspecting a polished sample underneath a metallurgical microscope (generally an inverted model such as the GX41/GX51 or GX71) and determining Grains distribution within a specific area. Using this standard, a G-Number is derived, which directly relates to the quality of the alloy. Before the days of Image Analysis software, engineers or quality control technicians would inspect a polished sample underneath the microscope and estimate the G-Number by superimposing a reticle into the microscope s optical path. Alternatively, operators would estimate a G-Number by comparing the image underneath the microscope to a poster or chart for comparison.

2 With the advent of digital image Analysis , this task can now be performed with much greater accuracy and speed, also providing a media for instant communication and documentation. So why perform Grains Analysis using old fashioned and perhaps inaccurate methods, when you can use the quick and reliable Discover Essentials Grains Analysis Module? Intercept Method vs. Planimetric Method: There are two methods for Grains Analysis Intercept and Planimetric. Since the majority of our customers prefer Intercept, we will primarily focus on this method (Planimetric will be described later in this document). The intercept method derives a G Number by superimposing a pattern over the image and counting how many times this pattern intercepts with a grain boundary. Figure 1: An example of an astm - e112 microscope reticle Figure 2: A pattern of a given length digitally superimposed over a Grains image.

3 Intercepts are counted every time a grain boundary intercepts with the pattern. 2 Figure 2 shows a horizontal line pattern is superimposed over the image. An aqua colored circle (intercept) denotes when the pattern intercepts with a grain boundary. The software then calculates how many intercepts were counted per the given pattern length, and calculates this G Number . Therefore, an image with very small size Grains will have more boundaries, resulting in a higher G Number (see above reticle in figure 1). Image Analysis Prerequisites: Prior to executing a successful Grains Analysis , one must obtain a fully focused, high quality calibrated digital image of the polished sample. Accurate image calibration is of extreme importance, as this will directly influence the accuracy of your results. Grains Analysis must be performed on a grayscale image. Should you acquire your image in color, it must be converted to an 8-bit grayscale image (Oper Color Separation Intensity) prior to Analysis .

4 If desired, this operation can be written into a macro format to eliminate repetitive keystrokes (or you can use the ColorView camera or Olympus DP series in BW mode). Step 1 Setting Thresholds: When Performing a Grains Analysis using the Intercept method, you must set your thresholds to detect the grain area, or body (not the boundaries). For example, the image below contains dark grain boundaries. Therefore, the thresholds are set to detect all grayscale values without detecting the dark boundaries. Step 2 Define Info: From the Grains menu, choose Define Info . Here, a user can enter specific parameters of their sample. These parameters will be utilized during the last step, generating an astm e112 report. 3 Step 3 Define Intercept Counting: Choose Define Intercept Counting from the Grains menu. A pattern will shortly be digitally superimposed over the Grains image. Obviously, you do not want the image size to exceed that of the image window.

5 Therefore, judging by the image scale bar, enter a reasonable pattern size. Note: If the pattern size is too big, you will not see the pattern superimposed over your image. Next, click on the Display tab and ensure that Auto Update is checked (and set for 1 second). This will ensure that your changes are automatically updated within the Grains Analysis . Also, make sure that Show intercepts and lines is checked. From the Boundary tab, check Use Threshold Only . Also, ensure that the boundary color (dark or bright) is properly selected to correspond with the color of your sample s boundaries. From the Pattern tab, choose the pattern of choice (that you customer desires). If you are uncertain, the most popular pattern is Cross and Circles . Don t worry about the other parameters in this dialogue box; the defaults are fine. Click OK when finished. Step 4 Execute an Intercept Count: From the Grains menu, choose Intercept Counting.

6 Once executed, you will notice an intercept has been drawn at every position where the pattern intercepts with a grain boundary. Discover Essentials will also generate a spreadsheet displaying 2 key parameters; how many intercepts were counted and the total length of the given pattern. Don t close this spreadsheet this information is crucial for the next 4 Step 5 Generating a fully Populated astm e112 Report: From the Grains menu, choose Grain Size Report . A fully populated astm e112 report will be automatically generated. The parameters you have entered in step 2 (Define Info) are utilized within the content of this report. Note: This report template can easily be modified by choosing Grains Define Grain Size Report. Tweaking Your Results: 5 After Performing a Grains Analysis , the derived results may not meet your customer s expectations or appear different from the anticipated results.

7 There are a few ways to increase the accuracy of your Grains Analysis : A) Visually, should too many or too few intercepts appear within the superimposed image, re-adjust your threshold settings. This will alter the amount of calculated intercepts. B) Manually add or remove intercepts: Within the Define Intercept Counting window, click the + or buttons to interactively add or remove intercepts within the image C) Separator Filter: With many samples, the grain boundaries may not be pronounced enough (low contrast) to obtain accurate results. Since the boundaries may appear very faint, intercepts are not identified at the junction between the boundary and pattern. A separator filter will automatically write these boundary lines, at great intensity, directly into the Grains image. Using the Separator Filter: From the Grains menu, choose Define Separator . Check the Preview box to superimpose the separator filter on your image.

8 Click the Window button and resize the window to cover your entire image. At the top of the Define Separator window, choose the boundary shape that best corresponds with the color of the grain boundaries (ie. Dark or Light). For example, the image below has dark boundaries, so Dark is chosen. Step is only used for images with both dark and light boundaries (rare). In the Result window, choose Burn Black or Burn White depending on the color of your grain boundaries. For example, the image below contains black grain boundaries, so Burn Black is chosen to burn a black, corresponding line into the image. Although choosing Burn White / Black will burn a separator line into, and maintain, the original image, alternatively choosing Black / White will result in a binarized image. Move both the Smooth and Fine / Course sliders until you superimpose the Separator Filter to best represent the grain boundaries.

9 You may not see a perfect representation; just get as close as possible. Fine tuning can be performed by clicking the Edit button. Here, you can erase false boundaries by clicking the Erase button and interactively add missing boundaries by clicking the Polygon or Trace buttons. Once you are finished, click OK and the Separator Filter is executed. 6 Planimetric Grains Analysis : Unlike the Intercept method, which calculates G number via mean intercept length, the Planimetric method calculates grain size via the area of the grain. For automatic Planimetric Analysis , grain boundaries must be continuous ( unbroken). Therefore, a Separator Filter must be applied as a prerequisite when executing a Planimetric Grains Analysis . Further, you do not need to set grayscale thresholds when using the Planimetric method. To execute a Planimetric Grains Analysis (as opposed to Intercept), simply follow the above instructions, choosing Grains Planimetric Counting instead of using Intercept Counting or Define Intercept Counting.

10 Written By: Mario J. Gislao, Manager of Industrial Light-Microscopy Products North America, Olympus Soft Imaging Solutions Corporation Edited By: Linda H. Sikel, Product Manager, SEG Industrial Division, Olympus Corporation of the Americas Example of a Planimetric Grains Analysis . A grain size frequency distribution histogram is automatically generated, as well as a spreadsheet containing all detailed planimetric results. Which ever method you feel is best for your laboratory, you can have confidence in knowing Discover Essentials Grains Analysis Module will provide fast, accurate, and comprehensive results that is database searchable within seconds.