MEi Introduces New Faces
Our company has grown in the past year, with two people added to our technical staff. We are pleased to announce the additions of Steve Strack, Materials/Metallurgical and Corrosion Engineer, and Doug Tannenbaum, Metallographer/Metallurgical Technician.
Steve Strack (left) and Doug Tannenbaum (right).

Steve Strack comes to us from Packer Engineering in Naperville, Illinois, where he has spent the past eight years as a metallurgical/ corrosion expert. His tenure at Packer included analysis of corrosion related failures in the chemical processing and petroleum industries. Much of his experience was in processing and manufacturing plants inspecting failed equipment and diagnosing problems. Many of these corrosion related problems involved heat exchangers, boilers, pumps, piping components and process vessels, covering materials from carbon steel to stainless steels, copper alloys, nickel alloys, aluminum alloys and high temperature alloys. Failures also included non-metallics such as fiberglass, PVC, paints and coatings. Steve not only did work on corrosion problems, he also conducted laboratory failure analysis of a variety of materials and components failing due to fatigue, overload, material defects, improper manufacturing techniques or operating parameters, solving problems and recommending corrective actions.
Prior to joining Packer, Steve spent 15 years solving materials problems as Materials/Corrosion Manager with Velsicol Chemical Corporation, a supplier of pesticides, herbicides, chlorinated organic compounds, brominated compounds, organic/inorganic acids and plasticizers. He supported six operating plants, corporate engineering, R&D and other corporate groups on corrosion mitigation, failure analysis, material selection, equipment inspection and corrosion testing.
Steve also has experience as a Materials Engineer for several engineering/construction firms in the chemical processing and petroleum industries. Steve has an associate degree in Metallurgical Technology, and a BS degree in Metallurgical Engineering from Michigan Technological University.
As you can see, Steve has extensive experience which he brings to MEi, complementing our expertise in failure analysis, and expanding our expertise and capabilities in corrosion, processing equipment and non-metals.
Doug Tannenbaum joined MEi in 1998 from Bodycote Taussig in Skokie, Illinois, bringing additional expertise in metallography to us. After receiving his BS degree in Science from the College of St. Francis in Joliet, Illinois, Doug has spent his entire professional career in metallurgical laboratories. He began his career in the lab at Caterpillar, conducting hardness and mechanical testing, sample preparation, metallography, NDT and operating the spectrometer. While at Taussig, he conducted sample preparation, metallography, microhardness, macro and micro photography and testing of non-metallics. Doug's experience covers virtually every aspect of materials analysis and testing, and expands our expertise and know how in these areas.
Doug is taking care of all metallurgical technician duties, including microscopy, sample preparation, photography, microhardness and hardness. Doug will also be sharing scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) duties with the rest of our staff.
We are excited to have Steve and Doug at Materials Engineering, Inc. They will allow us to continue to offer highly professional engineering and metallurgical services, while remaining responsive to your schedule needs as our business continues to grow.


When To Use "L" Grade Stainless Steel
Low carbon or "L" grade stainless steels have been widely discussed as offering improved corrosion resistance over regular grades. But will using a L grade stainless offer improvements in your application, or will you simply be wasting your money? By understanding their metallurgy and history, you can answer this question.
Background
As early as the 1930's it was well recognized that austenitic stainless steels of the then termed"18-8" variety (referring to the 18% chromium and 8% nickel composition of the first austenitic stainless steel grades) occasionally suffered corrosion adjacent to but slightly removed from welds when exposed to certain environments. The cause was traced to the depletion of the effective chromium content within that area resulting in a localized reduction in corrosion resistance.

Preferential corrosion in the HAZ of a weld sample, indicated by arrows.

This condition is termed sensitization, and occurs in a region one-sixteenth to one-quarter inch away from the weld known as the heat affected zone, or HAZ. The corrosion is intergranular in nature, attacking along the grain boundaries between the grains of the metal. The chemical species which cause this type of corrosion are called intergranular corrodents. When regular grade stainless steels are exposed to temperatures between 900°F and 1400°F in the HAZ during welding, the chromium combines with available carbon forming chromium carbides (Cr23C6), which are useless in providing corrosion resistance. The chromium carbides migrate to the grain boundaries leaving a localized chromium depleted region in the grains adjacent to the grain boundaries, resulting in lower corrosion resistance than the rest of the material. Thus when exposed to certain environments in which intergranular corrosion does occur in the HAZ, the corrosion proceeds along the grain boundaries eventually causing individual grains to fall out. Under the microscope the corroding surface has the appearance of rock candy.

Metallographic cross section showing corrosion at the grain boundaries in the HAZ.
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Closer to and in the weld, the temperature is above the critical 900° to 1400°F range, and any chromium carbides that form are re-dissolved into the alloy. Farther away from the weld at temperatures below this range, the carbide forming reaction is too sluggish to occur in the short period of time during welding.
Metallurgical Improvements
Sensitization can occur if the carbon content of the stainless steel is above 0.03%. Prior to World War II, steel making technology could only produce stainless steels with carbon contents ranging from 0.05 to 0.08%. The first approach to alleviate sensitization was to add what are called stabilizing elements, which are more reactive with carbon than chromium. Small additions of titanium or columbium react with the excess carbon forming carbides (TiC or CbC) before the chromium does. 321 and 347 stainless steels are the resultant stabilized grades that are still available today. However, they have their own particular idiosyncrasies and are not always the best solution.
With the advent of steel making technology that permits commercial products with carbon contents lower than 0.03%, the low carbon or "L" grades were developed. These grades are virtually immune to sensitization. The most common "L" grades are 304L and 316L, which are identical to 304 and 316 except they contain less carbon. If additional corrosion resistance is required, a higher chromium/molybdenum content 317L is also available.
Beyond alloy selection, sensitization can be eliminated by solution annealing the regular grades after welding. The exact recipe varies with the grade of stainless steel, but generally involves heating to 1850 to 2050 F to dissolve all chromium carbides present. The material must then be rapidly cooled to prevent chromium carbide reformation as it passes through the critical 900 to 1400 F temperature range. This, of course, cannot be applied to large components, and some strength reduction and distortion must be taken into account.
Should You Use "L" Grade Stainless Steel?
The "L" grades have been embraced with enthusiasm throughout industry to the point that they have developed a reputation of being more corrosion resistant than the regular grades, and usually command a premium in pricing. In reality, they are only more corrosion resistant if the material is sensitized and used in certain environments. The environments that cause intergranular corrosion are not as widespread as may be imagined.

SEM photograph showing intergranular corrosion and a "rock candy" surface appearance in the HAZ.

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In general, they consist of acidic environments that are not corrosive to stainless steel containing 18% effective chromium, but are corrosive to stainless steel containing only 8-12% effective chromium. If your parts are not destined for such service, using an "L" grade may be an expensive luxury.
As a final note, since there is no lower limit on carbon, some items such as piping are being marketed as complying to both "L" grade and regular grade material. This may be detrimental since the "L" grades have 5-10% lower yield strength up to 1000 F, and are not recommended for service above 1200 F. If strength or fatigue resistance are critical for your components, it would be wise to determine the actual carbon content of your raw material.
Summary
The "L" grades are an important part of the stainless steel arsenal in the fight against corrosion, primarily for specific corrosion problems involving the production and use of chemicals. If you are unsure if your parts need to be "L" grade or not, give us a call as we would be pleased to discuss it with you.


MEi Gets Good Grades
Over the past year, you may have noticed a customer satisfaction survey in with your report. The survey allows you to grade us (from A to F) in such areas as technical competence, courtesy of staff, communications, cost, report quality and timeliness of results, as well as provides an opportunity to make general comments and complaints. We know you, our customer, the best source of information on how well we are meeting your needs.
We have recently reviewed your responses, and are happy with the high level of satisfaction you have shown. While we did not quite achieve a "4.0" grade point average, we would have made most honor rolls.
Some of the comments received were:
"Your service is Great. It is nice to have a good external engineer to consult with."
"At last, a lab I can communicate with."
"The size of your company affords you the luxury of staying focused on the things
that are important. I am very satisfied with the work done."
"As usual, MEi provides us with the right amount of information and detail for what
we need to accomplish."
"Very nice job, my customer was very happy with the professional results."
"We consider MEi our "in house" metallurgist."
Our highest marks were in timelines of results (81% A's) and courtesy of staff (91% A's) All of the respondents indicated they would use MEi again, and would recommend MEi to others.
Thank you for your input. We plan to do everything possible to continue to keep you satisfied in the future, and we look forward to hearing your comments.


Let Us Spread the Word About Your Business
The nature of our business puts us in contact with many people working on improving their products. They are often looking for sources of materials, processing, products, coatings and technologies. We are often asked "Do you know of anyone who...?" We keep extensive technical files and can often help to point someone to a good source, but not always. We are hoping you can help us.
We have a general understanding of the products and service available from many of our customers, but our knowledge in not complete. If we had more knowledge on the complete extent of the products and services that you provide, we may be able to point potential customers toward your products or services to assist them.
If you can, we are requesting you to send to us information describing the range of products that your company offers, or the services you provide. This does not apply just to materials suppliers or materials processors, but to all customers. You might be surprised at the range of products which are of interest to our other customers. So mail your marketing literature to Bill's attention at our address. Thanks.


The "What Is It?" Contest
The scanning electron microscope (SEM) is a powerful tool, capable of magnifications up to 180,000 times. It allows us to reveal information which is critical to metallurgical investigations, such as fracture modes and surface characteristics.
The SEM can also be fun to play with, because it allows one to view the surface of anything at high magnification with great depth of field. All of us have been amazed by the pictures of various insect parts, especially the eye of a fly.
In our contest, we take a look at an object on the SEM that should be familiar to all of you.In this issue, our photographs show a natural substance from our 50th state, at two different magnifications. Good Luck.

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Please fax, mail or e-mail us (don't call) with your answer. We will draw a winner from all correct entries received by June 6. The correct answer and the winner will be published in the next issue Of Materials Interest.
The prize is a $50 restaurant gift certificate, so put on your thinking caps.
Results:
Last issue, we provided the clue that 'might be found in your kitchen, but you really wouldn't want to eat it.' While our favorite answer came from Andy Johnson at Excel of Iowa, who knew just from the clue that it had to be quiche, the correct answer was mold.
Our winner, drawn at random from the correct entries, was Ed Gade of Taylor Company in Rockton, Illinois. His efforts earned he and his wife a nice dinner at Cliffbreakers Restaurant in Rockford. Taylor Company designs and manufactures food service equipment, including soft serve ice cream and frozen yogurt machines, shake machine, and cooking grills for fast food and restaurants, such as McDonalds. Look for the Taylor name on the machine next time you order an ice cream cone. You can learn more about them at www.taylor-company.com
Congratulations, Ed.