Stainless steel is defined as any steel containing a minimum of 10-3/4% chromium, or 11%, depending on what your reference is.
Stainless steel generally resists corrosive damage better than carbon steel and medium-alloyed carbon steel. Corrosion might be atmospheric (airborne particles), spray, gaseous, or liquid. How bad the corrosion is will be subject to an infinite number of variables, such as:
- Variations in temperature (service temperature)
- movement
- solution strength
- stress
- torque
- air bubbles (aeriation)
- vibration,
There is not just one type of corrosion. That would be like saying that Mankind defines just one type of human being.
In the steel community stainless steel is defined by grades that may fall within different groups, just as tool steels are broken into logical groups. With stainless steel, grain type has the most influence on the grades. If I try to talk from a molecular level here, it will not be good. I will stay on more familiar ground and use baking again. When you think of grain composition of steel, think of the differences between bagels and angel food cake; different consistency, different texture, very different personalities. You have probably tasted a bagel. But, if you haven’t had angel food cake you need to have a piece so you get the point on grain structure. Do it for research sake.
In this post, however, stainless groups will be defined by the business-type they most likely serve. In the final analysis, global usage determines price and most importantly, availability. Your definition of “availability” of the steel will be dependent on whether or not you can not only get the grade, but get it in the right shape, size, length, condition, and quantity that you need.
Stainless for general use and production -generally those grades have been engineered to be economical, serviceable, and subject to ease of manufacturing. They are also WIDELY AVAILABLE, so long as somebody continues to use them in sufficient quantity. Generally, they will be available in the form most often utilized by the biggest end user. An example would be types 303, 304L and 316L. For decades these have been accepted as “standard grades” because they continue to enjoy a robust usage. Other steel grades (not just stainless) have pretty much gone the way of the Dodo bird; to a large extent 4330, 4135, 6150, and others come to mind. They may be available to certain groups for specific needs, but, in general they are no longer considered to be standard grades.
Economical grades that have been slightly modified for specific service in specific applications. – Such as “muffler stock” (which we really are going to discuss here in a bit), stainless material for appliances, etc.
Very refined stainless materials, expensive and somewhat less available. These grades have been engineered to solve particular problems in critical service conditions. I have always referred to these grades as “Exotics”. In context of any posts written here, they will include the “high nickel” grades. You can purchase them, but they are generally cost prohibitive for resolution of all but the most serious of problems in a plant. They will be available in somewhat of a limited availability of shape, and size, etc. To repeat: these high end grades are most appropriate for the industries that can afford them. They are generally cost prohibitive for all but military, aerospace, medicine, and grant projects.
-Howard Thomas, September 5th 2017
Introduction to a Series
Over the 45 years of working with materials used for heavy industrial maintenance, I’ve seen that matching stainless grades of steel with the appropriate application can be awfully confusing to the many support folks who do not have a background in the sciences. I speculate that a lot of hard working “non-metallurgical” people would be happier and more effective if they understood a bit more of what governs the decisions and requests coming from maintenance and reliability personnel. I am one of those “job taught” individuals and it is my hope that the posts that follow will provide a very general overview, i.e. the help that I would have relished many years ago. Becoming familiar with the various “personalities” of the most common available grades of stainless will hopefully encourage a familiarity within the potential supply chain and its value or limitations. Even a casual understanding of the distinct stainless personalities relative to the particular needs of the applications would help the two better get along. Think E-Harmony for stainless materials and applications.
In the coming weeks and months we will pass along some hard learned tips and stories that might help to broaden your understanding of the stainless picture. We will answer questions like; “What is Muffler Stock”, Can non-magnetic stainless attract a magnet, are there magnetic grades of stainless, Can you harden stainless, Can you buy pre-hardened stainless, why does stainless tend to “move around when you’re trying to keep it straight”, along with a host of other nagging questions.
We hope to stimulate questions that will generate future posts. If you consider yourself “non-technical” i.e. just another soul immersed in an industry that is drawn to an increasing reliance on the material, this should be right up your alley!
My approach to these articles will be a little like the differences between cooking and baking: When cooking, you can make a darn good chili without a recipe. You can measure ingredients by handfuls and cook it until it “looks right”. Baking, on the other hand, requires keen attention to the recipe with ingredients, time and temperature. Detailed information that would be appropriate for engineering decisions is not what I’m hoping to present. So, if you are a scientist, metallurgist, or engineer who is reading this post expecting a soufflé, you will be sorely disappointed to find that it might only be even a moderately good chili.
All comments and criticisms are encouraged and welcomed however, understand that this Soufflé is going to be simmered with kidney beans and hot peppers! Hopefully, these posts will act as catalysts for readers to seek more detailed information from structured resources better equipped to deal with the on-site conundrums they may encounter.
As politicians are so fond of saying; “Let me be perfectly clear”;
What follows is not intended for the credentialed metallurgist, the engineer, or chemist. The information is not to be used for engineering purposes. This is more like an energy drink for the unsung work-a-day-support stiffs charged with keeping the supply chain flowing. They need to be incorporated into the wonders of the maintenance materials world that they have an undisputed effect on. From their caves under the catwalks, in the bowels of plants, to the mazes of cubbies in the cooler parts of the plant, they long to be a part of what it is they get blamed for anyway.
-Howard Thomas, July 31st 2017
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Howard Thomas
Experience
Sr. Acct. Mgr. (US Southwest) / Metallurgical Consultant
Associated Steel Corporation
Jan 2017 – Present
Past Vice President / General Manager
Associated Steel Corporation
Apr 1998 – Jan 2017
Past Vice President / General Manager
Baldwin International
Apr 1974 – Mar 1997
Education
Cleveland State University
Kent State University
University of Denver
