Structure news. In this issue. Structure news. e-education

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1 1 # 17 March In this issue e-education Struers online e-education course provides objective and independent training in the fundamentals of materialography, and is recognized internationally by materialography professionals as the leading course available in the field. Enroll and benefit from their knowledge, combined with the wealth of experience gained by Struers over many years of leadership in materialographic specimen preparation. The course consists of step-by-step modules and is available 24/7 with no restrictions by geographical distances. You can find more information about Struers e-education on our website or by contacting your local Struers representative. e-education 1 Etching Techniques for Image Analysis 2-6 Courses and Events 7 is a quarterly letter from Struers, the world leader in materialography. The letter provides you with up-to-date information on materialography, applications and new innovative products. For more information about our products, please contact your local sales representative, listed on To subscribe to, please go to our website Do you also want to have your beautiful structure published in Struers annual wall calendar? If you have prepared any samples where you are particularly proud of the result and with excellent micrographs documenting the microstructure - please do not hesitate to send them to: application_dk@struers.dk We need details about the material, the preparation method and the magnification. Image requirements are: 10 Mb / 300 dpi.

2 2 Application Struers application knowledge represents a cornerstone in our daily work whether it be inside or outside our company. We offer a wide range of tools to share our knowledge, involving the whole process, hands-on training and best practices with and to our customers. Etching Techniques for Image Analysis by George F. Vander Voort, Consultant for Struers A/S this problem today can be eliminated by using various image manipulations, but it does create potential for some errors. Automated image analyzers detect features primarily by differences in gray level between different features in the image. When I first started using such a system in 1976, I quickly realized that most of the standard reagents that I had been using, while adequate for qualitative examinations or manual measurements, were inadequate for image analysis. Iron based alloys - grain boundaries Nital, which is by far the most widely used etchant for ironbased alloys, is commonly used to etch low-carbon steels so that the ferrite grain size can be observed and measured. But, nital is orientation sensitive and dissolves ferrite at a rate that varies with crystal orientation. On average, a ferrite grain shares boundaries with about 5 neighboring grains. Due to the uneven dissolution rates between a grain and its surrounding grains, some of the grain edges are revealed well, some appear over-etched and others are invisible. To some extent, Figure 1 shows a relatively high quality delineation of the ferrite grain boundaries using nital on high-purity iron specimen. Overall, this result is adequate for measurement of grain size, although some image manipulations will be required. Much poorer grain boundary delineation of low-carbon steels with nital, unfortunately, are common. Color etching can be utilized with today s systems, although image manipulations are required. Figure 2 shows a low-carbon motor lamination steel etched with Klemm s I reagent and viewed with polarized light and a sensitive tint filter to enhance the color. Klemm s I produces the strongest coloring of ferrite of any tint etch. A random crystal orientation is required for this application and the random distribution of a wide range of colors proves that this has been achieved. Figure 1: High-purity iron etched with 2% nital (100X) gave a reasonably good presentation of the ferrite grain boundaries, although some of the grain edges are weak or invisible. Figure 2: Color etching of this low-carbon motor lamination steel with Klemm s I reagent (100X) gave a good rendering of the grain structure, but there are adjacent grains with the same color, which will present difficulties, but this problem can be overcome.

3 3 The same specimen is shown in Figure 3 after detection of the grain boundaries (those intersecting the edge will be deleted before measurement of the grain areas). Figure 4 shows the distribution of grain areas according to the ASTM grain size classes. The mean ASTM grain size was 6.6. Figure 3: Grain boundary detection by image analysis of the colored ferrite grains in the motor lamination type low-carbon steel. Figure 4: The distribution of grain areas by ASTM grain size classes on an area percent basis revealed a normal distribution with grains in 8 classes and an average grain size of 6.6.

4 4 Stainless steel twins and delta ferrite Revealing austenitic grain boundaries presents an even greater challenge for image analysis due to the presence of annealing twins within the grains. When measuring grain size, the twins must be ignored, which is difficult to do manually or by image analysis. Most standard etchants for austenitic stainless steels reveal only a portion of the grain and twin boundaries; Figure 5 shows a classic example, type 316L etched with Kalling s No. 2. Fortunately, electrolytic etching with aqueous 60% nitric acid at 1.5 V dc for s reveals the grain boundaries with a very high success rate while not revealing the twins, as shown in Figure 6. This can be measured easily. Figure 5: Partially revealed grain and twin boundaries in type 316L stainless steel solution annealed at 1750 F (954 C) using Kalling s No. 2 reagent. Similar results were obtained using acetic glyceregia, Marbles reagent and electrolytic 10% oxalic acid (magnification bar is 50 μm). Figure 6: A different area on the same 316L specimen shown in Fig. 5 after electrolytic etching with aqueous 60% HNO3 at 1.5 V dc, 120 s, using a Pt cathode. This etchant revealed nearly all of the grain boundaries and none of the twins (magnification bar is 50 μm). The darkish horizontal bands are from segregation which can be seen well in Nomarski DIC.

5 5 Detection and measurement of delta ferrite in precipitation hardened stainless steels is a common metallographic task. The amount of delta ferrite usually must be measured due to various limits placed upon these grades by different service applications. Figure 7 shows that the delta ferrite can be observed using a modified Fry s reagent, as well as many other standard etchants for martensitic stainless steels, but this image is far from ideal for image analysis work. Figure 8 shows that electrolytic etching with aqueous 20% sodium hydroxide colors the delta ferrite uniformly with sharp phase boundaries. Reducing the voltage to 3 V dc and cutting the time to 10 s colors only the delta ferrite without revealing the matrix. Electrolytic etching with 10N KOH (2.5 V dc, 10 s) produces variable coloring of the ferrite and blurred phase boundaries. These examples illustrate that etchant selection is not a trivial task in specimen preparation for image analysis; and, that it is also extremely important to do correctly in order to obtain precise measurements that are reproducible. Figure 7: Longitudinal plane in 17-4PH stainless steels etched with modified Fry s reagent revealing un-etched (white) delta ferrite stringers in a martensitic matrix. Figure 8: The same specimen as in Fig. 7 electrolytically etched with aqueous 20% NaOH at 20 V dc for 20 s. This uniformly darkens the delta ferrite.

6 6 LectroPol - Automatic Electrolytical Preparation Instead of time consuming trial and error testing of parameters it is now easy to find the correct settings after a single scan of a new sample material. Electrolytic polishing has now lost a lot of its mystery and is used in a more scientific way to prepare metallographic specimens. Struers LectroPol-5 is an apparatus for automatic, microprocessor controlled electrolytical polishing and etching of metallographic specimens. Scentis - Intuitive Image Software and Clever Workflow Imagine a working day where all your lab data is collected in one place and logically organised, and where reports are generated automatically and results are instantly shared with your colleagues. Struers offers a software for imaging analysis; Scentis, offering much more than just image archiving and image analysis. Capture, analyse, archive and share your materialographic work using Scentis. Some of Scentis features: Easy and intuitive user interface that matches your workflow Built-in Extended Depth of Field (EDF) features Tiling feature: Auto-align and stitch images together into single images of a large surface Using the Snap to edge options makes exact measuring easy Easy-to-use reporting templates and built-in report generator Read more on Scanning function for easy determination of parameters Built-in safety features Database with methods for various materials Short polishing times and maximum reproducibility Read more on

7 7 Courses and Events Struers offers a wide variety of on- and off line courses and events for your benefit all over the world. Feel free to join one of our courses or events listed below: Poland, Struers, Niederlassung Polen, User Meeting Hardness Testing 25-27/3 UK, Rotherham, The Professional Materialographer 11-13/3 France, Saint-Etienne, Rencontre Métallographie et Microscopie 18/3 Sweden, Älvsjö, Manufacturing & Automation Expo (MAX) 18-21/3 France, Annecy, Hardness Testing Workshop 20/3 Germany, Struers, Niederlassung Kernen, Anwendertag Härteprüfung 20/3 Germany, Weimar, Workshop 27/3 Germany, Ottensoos, Schulung Härteprüfung 1-2/4 China, Shandong, Demobus roadshow 7/4 United Kingdom, Birmingham, MACH 7-11/4 France, Champigny sur Marne, Stage Préparation d échantillons Métallographiques 8,9,10/4 Denmark, Ballerup, The Professional Materialographer (in English) 8-10/4 Germany, Berlin, Workshop 10/4 UK, Rotherham, The Professional Materialographer 15-17/4 Japan, Tokyo, METAL JAPAN /4 Japan, Tokyo, Japan International Welding 23-26/4 UK, Rotherham, The Professional Materialographer 13-14/5 China, Tianjin, Demobus roadshow 5/5 Germany, Stuttgart, Control /5 China, XiAn, XiAn Seminar 14/5 Germany, Willich, Anwendertreffen Materialografie 14-15/5 France, Toulon, Workshop 15/5 China, Beijing, Demobus roadshow 19/5 France, Toulouse, Workshop 20/5 Finland, Helsinki, The Professional Materialographer (in Finnish) 20-22/5 UK, Rotherham, The Professional Materialographer 10-12/6 China, Chongqing, ChongQing Seminar 11/6 France, Reims, Salon SVTM 11-12/6 Germany, Struers, Niederlassung Ottensoos, Anwendertag Härteprüfung 24/6 Germany, Willich, Anwendertreffen Materialografie 2-3/7 China, Shanghai, Webex - Hardness Testing application 17/7