A number of etchants have been reported in the literature to selectively outline, outline and color, or attack specific types of carbides in steels. These etchants have been developed during the first half of the 20th century but have not been studied systematically since the development of modern analytical techniques. To evaluate these etchants, eight specimens (seven different compositions) with M₃C, M₂₃C₆, M₇C₃, M₆C, M₂C and MC carbides were studied, first by electron-backscattered diffraction (EBSD) to verify the carbides present.

The matrix of each specimen was darkened to measure the total carbide content. Then, the various etchants were tried and the results were compared to past publication results. Quantitative measurements were made after each etchant was used. This revealed some minor differences with the prior literature and showed that, while useful for qualitative evaluations, they are not useful for quantitative measurements. By George Vander Voort

Thermal Processing, Coatings & Laboratory Services Tajecina 114, 36-002 Jasionka near Rzeszow – Poland Tel: (48) 17 771-39-80  / Fax: (48) 17 771-39-80 Contact VAC AERO Website: vacaero.com.pl VAC AERO Rzeszow is the second facility in Poland to provides specialized metallurgical processing services. Profile & Specialization VAC AERO’s technologically advanced special processes are performed on…

Read More

Over the years I’ve helped many brazing shops resolve common brazing problems (such as leakers, non-wetting surfaces, etc.). In evaluating these situations, it is not uncommon to discover that sub-components (such as brackets, or fittings, etc.) from outside suppliers can actually be the trouble-makers!

Often the brazing shop is not aware of how some of their suppliers are making the sub-components that will be subsequently brazed. Then when there is a problem brazing some of the assemblies containing these sub-components, the brazing shop may try to solve the problem by trying to find out what is wrong with their own in-house brazing operations, getting very frustrated when an in-house cause for the problem can’t be found. Many suppliers are not aware that their own manufacturing processes can have a negative impact on brazing. Unless you have talked with them extensively about how certain processes will, or will not, hurt brazing, they will continue to do what works best for them in supplying a nice looking product for you in as cost-effective a manner for themselves as possible. By Dan Kay

Although some publications have claimed that mechanical specimen preparation is inadequate for producing damage-free specimens for EBSD, this is certainly not true. Our methods have concentrated upon producing the best possible surfaces using an automated grinder-polisher with standard consumable products in a reasonable amount of time and at low cost. Furthermore, these methods are highly reproducible as demonstrated by extensive tests on many metals and alloys from aluminum to zirconium.

Success depends first, and foremost, upon limiting cutting damage by using the proper blade and cutter. Next, commence grinding with the finest abrasive that will remove the cutting damage in a reasonable time and make all of the specimens in the holder co-planar. Polishing is done in counter rotation with a low holder rotational speed to keep the cloth as uniformly covered with abrasive and lubricant as possible. The grinding and polishing steps must keep the surface perfectly flat for best results. After the final polish, a general purpose etch can be applied, with the specimens in the holder, to evaluate the success of the preparation and determine what the structure is. Then, remove the etched surface by repeating the final step but with about half the required time. Preparation procedures are influenced by the crystal structure of the specimen. Face-centered cubic specimens will always exhibit more damage from each step than less ductile HCP and BCC metals and alloys. By George Vander Voort

The microstructure of iron-based alloys is very complicated, being influenced by composition, homogeneity, processing and section size. Microstructures in coarse-grained steels are much easier to observe than in fine-grained steels. Of course, steels are normally made with a fine grain size for best mechanical properties.

In general, it is easiest to identify heat-treated structures after transformation and before tempering. But, in most applications, hardened steels must be tempered and they are usually examined in this condition.  If a mixed microstructure of bainite and martensite is formed during quenching, these constituents will become more difficult to identify reliably as the tempering temperature given the product increases towards the lower critical temperature.  By George Vander Voort

Even with built-in “holds” when heating low-carbon steel parts up to brazing temp, some heat treaters are getting a high percentage of the tubular brazements “pulling apart” somewhere during the cycle, i.e. the smaller-diameter tubing pulls away from the larger-diameter tubing, even snapping the welded clips off one of the tubes so that they are not brazed together along their length. What’s happening, and how can they “fix” this problem? By Dan Kay

Metallography with George Vander Voort Conducting the Failure Examination Failures in metallic components may be caused by any of the following factors or combinations of factors: Design shortcomings, imperfections due to faulty processing or fabrication, overloading and other service abuses, improper maintenance and repair and environmental factors. Not all failures are catastrophic. Many failures involve…

Read More

Vacuum Technology with “The Heat Treat Doctor” Metallurgy for the Vacuum Heat Treater The role of materials science is to study, develop, design, and perform processes that transform raw materials into useful engineering products intended to improve the quality of our lives. It is said by many that material science is the foundation upon which…

Read More

Vacuum Brazing with Dan Kay Stress Concentration Don’t Blame the Braze because Joint was Poorly Designed, and NO, larger fillets won’t compensate for that! Have you ever heard someone tell you something like this: “Well, brazing may be okay, but if you really want a strong joint, you should weld it!” Such comments are often…

Read More

VAC AERO News, Education & Training Kay & Associates Brazing Seminars Since brazing plays an important part in your company’s products, plan to have your staff attend one of the high-powered, three-day seminars being held in 2016. Our Brazing Seminars cover all the essentials for successful brazing of commercial and aerospace components. The improvements to…

Read More