Q: “For cross polarization, are the two polarizer filters upstream of the sample, or downstream, or what? The black material is now showing up as orangish-brown material and there’s a lot more of it—smaller features kind of scattered around that image—that we really wouldn’t even notice with the brightfield illumination. The etching does remove those very fine scratches. The clear coating was fortunate because we were able, then, to look through the coating down to the base steel—tin plated steel, and to see these brown regions that were causing the stain. I want to draw your attention to what’s happening within that yellow box. When you buy bar steel, the direction is normally with the bar in common carbon steels. All mill bar steel is already forged by the rolling process. It’s final polished with 1 µm diamond paste slurry, and the brightfield illumination is what most metallographers would be looking at to look at their polishing system. It’s edited by Williams, Pelton, and Bronsky, and there are various authors that have contributed to this book. Q: “Can Normarski be retrofit to a standard light microscope?”. How are the cross polarizers planned in the optical transmitted path, and does it matter which one rotates?”. Here’s an example of an electrolytic tin plated steel surface with crossed polarizers. It is simple to use and requires very little effort to obtain a shinier, better cared for piece of metal. On the left-hand side, we have the plane polarized light illumination and we have the weld zone, which is highlighted here: you can see that much different crystal structure, or grain structure, of the weld area versus the surrounding base metal to the right and left of the weld. Only in size. Least of my worries. Molecules are like building blocks with no linkage between them other than maybe electrical charges. WN: I guess it depends on the microscope—if the Nomarkski accessories are available for it. My polarizing light microscope is the Olympus BX51. In this stage, the microstructure of the metal becomes coarse and makes the workpiece lose some of its strength. Remember that you are dealing with a metal not wood; the grain is totally different in the two. As a general rule, the grain line must run perpendicular to the bend to avoid the potential for cracking or fracture. Whatever method you choose, note the direction of the grain of the stainless steel. It is atomically arranged crystals that form grains. We can manually control the grain direction of the metal in the flat pattern, and subsequently how the bounding box is oriented to address these concerns. Is it something software based, or just accessories based?”. It’s actually pretty good for fiber use, looking especially at the natural fibers, to look at the surface structure of natural fibers. Add your contact information to our list, and we’ll let you know when new webinars become available. This is an outstanding book because the author goes through some preparation techniques, metallography preparation techniques, optical microscopy stuff, different alloys, different cross sections from metal forming, deep drawing operations, welding operations, other joining type systems, and so forth. This is unetched; we don’t want to see the grain structure so much—we’re more interested now in actually seeing the corrosion cracks rather than the grain structure of the metal. Now if we cross the polarizers—and these are unetched again—now we can just highlight the interior coating if we want to by adjusting brightness and contrast, and take the metal out of the image, if we’d like. It’s dissolving the surface away and penetrating down into the grains of the metal. I certainly appreciate you taking time out from your busy schedules to join us today, so hopefully I can provide some useful information for you in examining metals by light microscopy. As far as cosmetic, you cannot see grain direction in steel with the naked eye anyway, unless you see alloy banding, or some similar flaw that might follow grain direction, or after using acid on it. Q: “What kind of configuration is needed for NDIC?”. It isn't many wacks with the huge dies before it goes to machining. Tin, again, is an anisotropic metal; the iron base steel is not. I also want to bring your attention to the detail that this can bring up. You must pay careful attention to grain or rolling direction when bending high-strength metals, especially when trying to achieve a small inside bend radius. Now we can see a couple of things that really jump out at us. In the right-hand image, we can see that there’s a little notch, a little opening, at the very base of the “V.” That’s a potential site for corrosion attack—crevice corrosion attack—from the outside if the can gets involved with some sort of liquid on the outside of the end. Acually, the grain direction is not just cosmetic, but adds only a little more strength than cross grain does, and does have a slight advantage over cross grain. Q: “Do you have a particular brand of microscope that you use?”. You can also insert a polarizing filter into the light path and that’ll help reduce some of the glare, just like it would from polarizing sunglasses that reduce glare on ripples and waves from a lake. Directional grain does impart a tad bit more load resistance in high stressed parts and tools. McCrone Microscopes & Accessories would sell that type of thing for that microscope and also for the Nikon microscopes. That’s used quite often for carbon steel to highlight the grain structure so that we can see the flow of the grains, and so forth. Or, we can go ahead and insert that first-order red compensator and just highlight the base metal itself, separate from the coating, and have the two side by side. This is a polished aluminum sheet section, cross section, that has one huge, major inclusion in it. four techniques to show you what they can really tell you, Nomarski differential interference contrast (NDIC). NDIC is really, really good for topography information on reflected opaque subjects like this. Here is an examination of some polished beryllium metal. We can also see some heavier scratches that also are kind of parallel to these little smearing things. Let’s take a look now at the base steel versus the weld zone, and the structure of that material. There is a dark kind of webbing type net in the structures that is interwoven in there amongst the flatter grains in the sample. At an angle of 45 degrees from the selvage is the bias of the fabric. Q: “Which method would you recommend to highlight transfer of metal from one source to another via contact?”. Certainly, you look at light microscopy first, that’s usually always the first thing that we would do, and then you can put it into—if you can—you can get it into an scanning electron microscope, and get a little more detailed information about it, and perhaps elemental analysis of material that has been transferred from one to the other to try to verify if that material was consistent with that metal having touched it. Look inside the red box here, you might not be able to see it too well, but there’s a grain in there that has parallel structures spaced at about at a 45° angle, and spaced only a micrometer or two apart from each other.

how to tell grain direction in metal

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