It’s Not So Obvious

“If you live in a hard-partying area of the country, you may not want to buy a new car that was assembled on a Monday. And, you may not want to shoot pool with someone whose first name is the name of a major city”. Just some considerations learned from experience.

In heavy industrial maintenance, seasoned professionals have their own hard-won cautions like the above. Those may not always be obvious. Wouldn’t it be great if those tidbits of knowledge, however, were somehow automatically transferable through the generations? However, natural powers, or gremlins, seem to insure constant attrition; constant turnover of experienced maintenance personnel, and the subsequent loss of their esoteric talents.

It’s a terrible thing to know you have solved a problem only to see things go from bad to worse because of a less-than-obvious semi-related circumstance.

Let’s say you are trouble shooting a problem where there is obvious “pitting” on the surface of a stainless shaft. For a host of reasons, pitting will eventually lead to a shaft failure. Before you begin looking into the usual suspects related to corrosion, do a little forensic investigation and see if that is really the main problem you want to solve. Pitting may not be The Big Offending Kahuna.

The shaft in question may be extra long with a small diameter (Linguini). Straightness, as in the case of a vertical mixer shaft, may be a primary concern. Let’s assume the opposite configuration of a larger diameter shaft with relatively short length (fat and stubby). In either case, straightness happens to be a key element. So, in the hierarchy of concerns; pitting is subordinate to straightness.

Most stainless-steel shaft grades, by nature of their chemistry and grain structure, retain substantial amounts of stress. Those retained stresses contribute to bow, twist, or fracture. There are grades of stainless steel, however, that respond well to thermal stress relief.  Most of the retained stress is able to be removed. (less retained stress, less movement in machining and in subsequent service). These grades resist pitting, but maybe not as well as other grades. Remember though, if the shaft never makes it into service, the potential life expectancy is irrelevant.

You know steel shafts may be straightened mechanically; so, just solve the pitting problem with a material change and then straighten the shaft. But, if the shaft configuration, or the final machined configuration, does not allow for conventional mechanical straightening, or that process would require equipment that is not readily available, or the straightener guy is just plain incompetent, experience may have opted for a steel chemistry that would be less susceptible to warp and bow; either in machining or in service. The luxury of post machining straightening was not considered an option. The best steel choice in this case may not be the one with the best Pitting Resistance Equivalency (PRE). (If the shaft never makes it into service, service life is irrelevant).

To be effective in the industrial maintenance field you must be intuitive and organized. Assuming you are, then pointing out the need to look at more than one contributor to material failure is obvious. Considering the relativity of an incompetent straightener to a pitting condition, is not so obvious.

-Howard Thomas, March 6th 2018

Does Your Stainless Remember Things?

Most likely it does, regardless of the state of your memory.

When I first heard the term “Memory”, relative to stainless steel, I was anxious to find out what it referred to. An associate with one of the stainless mills responded with this little tidbit; “Memory, regarding stainless steel, generally refers to retained stress, specifically in austenitic grades. That relates to “Movement”, or “Walking”. (Bars won’t hold straightness). Those grades of stainless (304L and 316L) have memory. They are difficult to straighten in the first place. Then, after you have manhandled them into the straightness you want, they have a tendency to return to the straightness they “remember”.

If you have a bar that looks like a tapeworm and you cold straighten it to a beautiful pump shaft, then ship it across the country, expect to find a tapeworm when you open the box.

Same with people. Take an annoying coworker. Explain why you are transferring them to your sister company. Instruct them to straighten up. Ship them across the country, and bingo!  Your sister company now has an annoying coworker.

If you want to look at this annoying tendency of memory in stainless steel a bit closer, you can start by noticing that we specifically mentioned austenitic grades of stainless. Those tend to be the most commonly used in industrial maintenance. And, of the austenitic grades two are by far the most common to the industry; type 304L and type 316L.

Coincidentally, it is just those two grades that seem to have the most profound memory issues.

They probably occupy over 70% of the grades used on a daily basis. Type 316L (we’ll talk about the “L” later) is a modified grade of 304L. It is an upgrade developed to better resist the damaging effects of corrosion. Both 304L and 316L are products that come under the general category of 18-8 stainless.

In that grouping, the first number represents carbon content, and the second represents nickel content; the two primary alloying elements in the austenitic grades mentioned.

Austenitic Stainless grades 304L and 316L;

Are non-magnetic; under most circumstances they will not attract a magnet.

Are not hardenable by thermal treatment

Can be hardened by cold work, strain hardening

Are generally of moderate strength as purchased

Are resistant to most common forms of general corrosion

Are resistant to the negative effects of service temperature to a little over 1000F.

They possess some annoying attributes, however. In addition to memory issues, they tend to gall (Get stuck to mating parts, or, “cold weld” to mating parts), are a bit gummy, and tend to be of lower strength.


Since 304L and 316L do not respond to thermal treatment, and since the most commonly employed stress relief for steel bars is thermal conditioning. It is understandable that austenitic stainless bars retain stresses from the manufacturing process.

Since they do retain stress, and stress will not stay in a material (it will come out as movement, warp, or fracture), it is expected that those grades would have Memory; the retained stress being released as bow, twist or warp.

Once you have made pump shaft from austenitic stainless bars, you may anticipate the stress induced in the straightening process to manifest somewhere down the road. The catalyst may be: vibration, heat, torque, whatever.



MEMORY                   Has trouble with authority

GALLING                    Doesn’t play well with others


FUTURE TOPICS:                    “The One Handed Metallurgist”


-Howard Thomas, January 5th 2018


Review of Earlier Posts (Pop Quiz)

At this point perhaps we should have a little review of the earlier posts, just to see how things are going.


1. 304 and 316 can be thermally hardened to

a. They can’t be thermally hardened to

b. The consistency of a ripe peach

c. A hardness that would hurt if you were struck on the head


2. Muffler Stock is material used to make

a. An article of women’s winter apparel

b. Similar to Woodstock

c. An economical type of stainless steel


3. Grades of stainless steel sometimes fall within groups based on

a. Grain Type

b. Length

c. Weight


4. Steel that contains more than 10-3/4% chromium is considered to be

a. Very shiny

b. Stainless Steel

c. Generally resistant to corrosion

d. both b and c


5. The great thing about “exotic grades of steel is that

a. They are affordable for everyone

b. They are engineered to solve difficult maintenance issues

c. They look great on the beach


Answers on the next post.

-Howard Thomas, December 6th 2017



Muffler Stock (Finally!)

For a long time, austenitic stainless grades enjoyed the lion’s share of business in the world. Austenitic refers to the grain type, Austenite.

Very simply described, these were non-magnetic (would not attract a magnet) grades of stainless, that were not hardenable by heat treatment.

They were very good for general corrosion and had some strength. These grades contained significant amounts of Chromium and Nickel. They were often referred to as Type 18-8. (Where 18 was roughly the percent of chromium contained, and 8 was nickel content). More on that later. We will also look at alternate ways to harden austenitic stainless steels.

There were needs for harder and stronger stainless materials, and usage supported the manufacturing. Modifications were made. Necessity may be the mother of invention, but don’t forget that “Pay to play” governs availability in the marketplace.

Stainless grade 410 was developed based on the need for a less expensive stainless grade that could be thermally hardened. As mentioned above, most commercially available stainless at the time was lower hardness lower strength. Differences in chemical make-up of Type 410, from the Austenitic types (410 had a different grain structure called Martensite) among other things was the lower content of Nickel and chrome. The new grade was affordable, hardenable by heat treatment, and immediately gained acceptance in many industries. Because of this, it was generally available in many shapes and sizes. Specifically, it was found to be a prime candidate for car and truck mufflers, although the cost was still a consideration.

Similarly, a common 4000 series alloy (not a stainless) was being used for the brackets that held the mufflers to the car. That grade was not holding up to the temperatures developed at the muffler and tail pipe.

The brackets would eventually weaken an fail, causing the related parts to be deposited on the street. That grade was modified by adding a small content of Vanadium, which raised its ability to resist the higher temperatures, and the grade 6150 was born.

It was discovered that Type 410 could be modified by reducing the content of some of the more expensive chemical elements, thus reducing the cost while still maintaining an effective material for the task at hand. The resultant grade was 409, or “muffler stock”.

Years later, another major modification to the grade was prompted by the needs of an ailing coal industry. Certain types of coal caused applications already subject of abrasion, to now be subject to higher degrees of corrosion. The combination caused hardened steel wear plates to wear out faster than ever. Standard grades of stainless that would resist the corrosion, would fail quickly due to corrosion. Plus they were too expensive to be practical. So, an industry that had even less disposable income to play with than the automotive industry required a material that could address this difficult climate that was also affordable. Once again, 409 was modified, and an affordable corrosion /abrasion resistant wear plate was developed and used to process high sulfur coal.

Like the story of the little girl; “When she was good, she was very very good. However, when she was bad she was horrid.”

There are always trade-offs when responding to the esoteric needs of specific industries. While this new corrosion/abrasion resistant wear plate served the needs of the coal industry, it was neither a stellar wear plate nor a stellar corrosive resistant material for many other maintenance applications.

But back to “muffler stock”. When I was young, shortly following the end of WWII, I lived on one of the small cookie cutter city blocks, in a blue collar neighborhood in Cleveland, Ohio. Notable in these post WWII neighborhoods were three things that littered the red brick streets, kids, rusted car mufflers and tail pipes. Kids were everywhere mostly playing baseball in the street. Those ubiquitous children were the “Baby Boomers”, prodigy of “The Greatest Celebration.”

Rusted Mufflers and tailpipes, on the other hand, were the result of them being made from steel that simply rusted. Soon, the milk truck, the ice truck, the coal delivery truck, and even your father’s car sounded like freight trains; God’s way of warning the kids playing in the street that something was coming.

Mufflers eventually commanded so much of the usage of 409 stainless, it was easy to find in sheet form but almost impossible to find as bar; unlike 410. Usage determines availability. That is even more true today than it was when Baby Boomers were knocking out windows and cursing “nickel smashers” (cheap baseballs had the consistency of a ripe peach).

Types 410 or 409 stainless represented only a small portion of stainless usage. Types 304 and 316 were the defacto standard for decades for commercial stainless usage. They were great for general corrosion, they were readily available, and somewhat affordable. Even those grades, however, have seen modifications over the years, as costs of raw materials fluctuate and the needs of manufacturing change.

In the coming posts we hope to present other materials topics related to the maintenance world of industry.

We may look at; why stainless walks and moves around

                             Is it possible for stainless to attract a magnet

                             Why are some grades of stainless gummy

                             What steels have memory

Along with a host of other topics that command our attention.

-Howard Thomas, November 7th 2017



Are you able to find the particular material, grade, size and shape, by conducting a simple web-search? Availability will be influenced by many factors. Let’s assume the adage; “If you got the money and the time, you can probably get it.” is still very true. But since most often general plant maintenance is the last rung on the “Exotic Metals Food Chain”, most of us will not have the money nor the time. The global state of the raw materials, usage, cost, geography, political climate, shape, size, and condition, and perhaps most importantly, the minimum required order size required. Not necessarily in that order.

During WWII, nickel (considered one of the key ingredients in stainless steel) was in short supply and was being rationed. Metallurgical engineers discovered that they could recreate stainless grades, with similar properties by substituting cheaper elements, like manganese and nitrogen for the more expensive nickel. It was a case of: “live with a little less performance from these modified grades or, have no stainless at all.”

Similarly, a screw machine shop driven by production, speed, and cost, may specify free-machining grades of stainless for which they are willing to sacrifice a bit of performance for processing speed. Those grades may have been treated by adding a mineral element that allows the tooling to pass through the steel more easily than would be possible with a non-treated grade. The addition of that mineral may not contribute to the strength or corrosion resistance or weldability of the steel. It has been added simply to promote machinability. In fact, the addition may diminish other key properties of the steel. Recent innovations have developed free-machining grades that still have high mechanical properties. Note that treated grades may only exist in the form that is used by the most screw machine shops. Such as bar only, no sheet or plate.

-Howard Thomas, October 4th 2017

So, How is Stainless Steel Different Than Mild or Carbon Steel?

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



Stainless Steel

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