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

 

Availability

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