Hardening Steel With Heat

We have touched on the topic of the effects of heat on steel in the past. These little reminders are directed at those of us who are not accomplished thermal treaters of steel. And, that is based on the assumption that you wouldn’t be reading this article if you are already proficient in hardening steel. NOT INSTRUCTIONAL! “Random thoughts on hardening steel” in his article are strictly for information purposes only.

To a large part the carbon content of steel determines its hardenability. More carbon/higher hardness. Low carbon (below .26), virtually means no hardenability. Although some people will argue that, and that’s fine, it makes for a nice bet in a bar. A very general guide for a novice is; “through-hardening” alloy or carbon steel yields a maximum hardness equal to carbon times one hundred, i.e. .30 carbon = 30RC, .40 carbon = 40RC, etc. For general reference, most pre-hardened steels offered to the public, will be roughly 30RC. At that hardness, they have good “toughness”, which is a combination of hardness and strength. Surface hardness (skin hardness, flame hardness), is somewhere around ten points over the above shown numbers, so, you can get approximately a 50RC surface hardness on a piece of 4140. It’s actually a little harder but that will give you a ballpark idea.

Through hardened steel has many advantages. One potential disadvantage might be that it could be a bit brittle. Surface hardening is generally preferred when the application may have impact or flex. In that case you would want to retain some core “flex” (ductility) in the steel you are working with. In general terms; strength goes up when hardness goes up. Too hard and brittleness (potential for abrupt fracture) becomes a factor.

The speed at which you cool the steel from the hardening temperature will affect the resultant hardness. Like baking bread or deserts; think ingredients, time and temperature. Get them worked out correctly and you have a pleasant result.

Other elements added to steel (inside the steel) or added to the furnace as a gas, will also affect the overall hardenability. There is no substitute for knowing the grade of the steel and its current hardness.

ALL IS NOT LOST! If at first you don’t succeed, try, try, again. Steel is generally very forgiving. You can repeat the thermal treatment over and over without damaging the material provided you have not exceeded the hardening temperature. If you end up with a lot of surface decarb (the powdery grey skin and scale that forms on the surface of the heated steel due to the carbon burning off), you will have to remove that so that it doesn’t act as a “heat sink” and inhibit subsequent hardening attempts. You will also have to research the thermal treatment procedure of “annealing”, as that may be required prior to your subsequent hardening attempts.

It will be necessary to remove the decarb anyway if you intend to accurately determine the hardness of the steel. The old rule used to be; “Grind to bright metal.” Decarb can still be present in bright metal. So, grind to remove all decarb. It is a safe bet, with almost any carbon or alloy steel; if you are getting a Rockwell “C” hardness reading under 22RC, you are probably still in decarb, since most carbon and alloy steels will pick up some hardness following a thermal procedure unless you just happened to accidentally perform a  perfect anneal.

-Howard Thomas, August 6th 2019

 

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Cut To Length Steel And Random Bar Lengths

Some time ago we posted an article about random bar lengths. The attention from that blog contributed to this follow-up about cut-to-length bars. More importantly, how that term differs from random (rdm) bar lengths.

Random bar lengths can be anything the distributor deems beneficial to his selling of the steel bars in  his, or her, inventory. It is most common in the general steel marketplace to see random bar lengths listed as 10/12ft rdm, stainless bars were often listed as 11 to 14ft rdm. You might say that is more less the default in the industry. However, even that category does not define exactly what might be shipped to you. You may get a 13ft bar, or even a 16ft bar; depending on what the distributor has on the floor at the time. In rare instances you may get an 8ft bar or 9ft bar, although shipping a shorter bar is not all that common. The practice of offering random bar lengths can be a very good thing. You should be able to save money on the purchase, less than the higher cost of requiring a bar to be cut to a specific length. Just make sure you and the seller are on the same page at the point of inquiry.

Cut-to-length bars are just that; bars are cut to the exact length you require. You just need to be clear in expressing your requirements; and include a length tolerance that works for both parties. For many decades “plus 1/8″, minus 0” was quite common, and the default if nothing was specified. It pays to be sure both parties understand the same requirement. Especially if it is a first time order or a new vendor or customer. Your expectations understood by one supplier may be lost on the new supplier.

There are other concerns that may affect your order regarding cut-to-length. You may want to specify “No Mill Ends”, or, “Trim Mill Ends”. Mill ends (the original ends of the bars as they were shipped to the distributor from the steel mill), may have been trimmed at the mill, and just fine. They may also be sheared, in which case there may be a slight taper to the end of the bar. The diameter at the bar end may be a bit undersize. It may not be a square cut. It may be slightly dished, it may have identification stamped into the end. If you have not allowed some trim stock to the length you ordered, this may be an issue. It is not a major issue on most orders, but it is worth mentioning if it could be.

If the type of cut required is to a very close tolerance you may want to specify “Square Cut Ends”, and then the tolerance you require. There may be additional charges depending on how specific your needs are.

Very small diameters (those under 5/8″ Dia.) may require special dialogue or instructions if your expectations are exacting. Can the vendor bundle and cut? Once again, there could be additional charges incurred. Very large diameters (over 10″Dia.) usually require a little extra stock be left on the cut. Depending on the size and the intended use, some people will leave 3/8″ or 1/2″ on the cut. Chromed bars often come with “masked areas” at the end of mill length bars. That is an area that has not been chromed. It may be several inches. If you typically purchase full mill random lengths of chrome bars from one supplier, you may want to insure both you and your new supplier understand the specific bar mults of the finished shafts you intend to make. Discuss “trimmed ends” at the point of inquiry.

Newer saws and better saw blades are able to cut phenomenally close these days. There seem to be blades for nearly every metal and hardness. But, just because the saw and the blade can cut close, does not mean that’s what you will be getting. Communication goes a long way to avoid a mishap. Remember; “When it goes bad, who’s wallet comes out?”

-Howard Thomas, June 21st 2019

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Bending Steel

There is a famous saying; “A man must know his limitations.” I am sure it is also appropriate for a woman. So it is with this topic. Some steel grades can be bent fairly easily. And, some steel grades in some conditions should never be bent. Before attempting to bend steel you must fully understand its limitations. If you are one of those who never reads instructions and just charges ahead, then there is another appropriate quote from the same person; “Do you feel lucky, kid? Well, do you…?”

The thing is, bending steel is dangerous, even steel listed as “formable”. Ideally, it should be left to experts. But, if you are going to do it anyway, you must know some things about the metal you are contemplating bending. The grade and internal cleanliness are important. But more important is the hardness and the depth and uniformity of that hardness. Soft malleable (ductile) steel in a very light gage may take a nice bend simply by “hand”. Harder (heat treated) heavier gage steel may require high capacity sophisticated equipment that has built-in protections for the machine operator. Very hard steel may not tolerate even the slightest bend, or even pressure for that matter. To put it in perspective, when you think of very hard steel, think of a pane of glass. You wouldn’t push the center of a large pane of glass to see if it bends. At least I hope not. When hard steel fails during a bending process, it literally explodes! As in, loud noise and a section of the roof leaving the building rather quickly.

Before you attempt to bend a piece of steel say this out loud three times; “This is an angry piece of steel that doesn’t want to be played with, and there is a reason why everyone behind me is stepping back.” Then step into your safety gear, study everything you can about the steel, then call a person who bends steel professionally. If that is just not possible and you are required to bend it yourself, do some serious research before you begin and remember, wear appropriate safety gear. Bending steel is not a job for amateurs. Use certified/qualified expert technicians.

Some key words that may help you discover a bit about bending steel are listed below:

Forming, Press Brake, Rolling, Open Air Die, Bottom Die, Bullnose Die, Arc, Degree of Arc, Knife Die (as in; don’t use this type of die), Degree of Bend, Radius of Bend, Hardness HB, Hardness RC, Decarb Removal, Surface Preparation Steel, Brinell, Rockwell, Plasticity, Plastic Deformation, Spring-Back, Work Hardening, Heat Treating, Surface Hardness, Through Hardness, Gushing Head Wound, Depressed Skull Fracture, Life Insurance

4T, 8T, 12T relate to how many times you multiply the thickness of the steel to determine a suggested minimum bend radius. 4T would require a radius of four times the thickness, 12T would be twelve times the thickness, etc.

And, one more famous quote; “Don’t try this at home!”

-Howard Thomas, June 4th 2019

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What is Lean Duplex Stainless Steel?

So, what is Lean Duplex Stainless Steel? When and where would you use it? A big topic for a short article. This is merely a brief introduction. Perhaps it will encourage further investigation. Also, we are referring here only to solid round bar, sheet and plate.

For many decades, Austenitic Stainless Grades dominated the industrial and commercial marketplace. They provided excellent general corrosion resistant properties. Then, hardenable martensitic grades began to see usage where increased strength was required. The successful combination of the grain types (Austenite and Ferrite) into one steel introduced Duplex Stainless Steel. Duplex grain structures allowed the broadest utilization of the properties of each. The initial concept was not terribly new; having been introduced about 80 years ago. LEAN DUPLEX stainless steels were the offspring of that product. Early improvements to the Duplex grade involved the enrichment of chemistry of the initial Duplex grade creating upgrades called; Super Duplex and Hyper Duplex; elevated property products with elevated price tags. A significant nickel shortage in the late 1960’s sent engineers scrambling to reverse the “richer is better” trajectory. They embarked upon a project that would minimize the expensive elements in the steel to lower the cost. Minimizing the content of key elements was expected to likewise minimize effectiveness. That was acceptable provided any new grade was still effective in combatting corrosion (specifically Stress Corrosion Cracking, or SCC) and increasing strength over the levels provided by the Austenitic and Martensitic grades used prior to the inception of Duplex.

The resultant steel was Lean Duplex (LDX). It was leaner and cheaper by a long shot. The great surprise was that the resultant loss in corrosion resistance and strength was not as significant as was anticipated. In fact, it was minimal for most intended service applications.

Fairly quickly, the LDX grades enjoyed overwhelming acceptance in the global manufacturing of various tanks, vessels and tubing. So much so, that it is rare these days to find any of those items that do not contain some percentage of Lean Duplex Stainless Steel. What was not readily apparent was the huge potential for daily use as upgraded replacements for the myriad of mundane, and unheralded daily maintenance wear parts and widgets that represent the lowest rung on the maintenance metals food chain; the gremlin maintenance parts that bend and pit and wear. The parts that won’t disassemble because of galling.

My opinion: Lean Duplex shafting, sheet and plate is under-used as a maintenance material. It needs a publicist, promoter or talent agent. Some gnarly champion that might say; “You can use that sh..t on anything!”

It’s that good. Why, it’s the Ginsu knife, the Veg-O-Matic of stainless shafts.

the lean duplex grades are stronger than the austenitic grades of 304 and 316. In my opinion they are generally better grades than 410 and 416. But wait, there’s more, Lean Duplex resists Stress Corrosion Cracking in Sour Service Applications. Since it will most likely be non-similar to your current stainless grades and because it will most likely have a different hardness, it is not disposed to gall. Plus, it is stronger and easier to machine.

Conclusion & Sales Pitch: Associated Steel is one of the few service centers that carries Lean Duplex (ASC2250® LDX) in long shafts they will cut to size. They also carry IN STOCK two different shaft finishes; Fine Turned Oversize “the size will make the size” resulting in less machining and less wasted material, and a Precision polished finished guaranteed bearing fit. Try it! Inquire on hi-def plasma cut parts from plate. Make maintenance life a little easier. Note: Your particular maintenance application has unique characteristics. Always refer to published material information sheets for qualification. 

-Howard Thomas, May 6th 2019

 

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What is Brake Die Steel?

Let’s begin this post with two of my favorite words; Ubiquitous; (everywhere, like raindrops during a storm), and, Esoteric; (known by a select small group of people).

What do these mean? Brake Die, Gun Barrel or Rifle Stock, Pump Shaft Straightness, Boat Shaft, Food Service Grade Stainless, Cold Roll, “Ultrasonic Inspect to 388, (and even FDA approved). While they may have a specific meaning to someone (esoteric), they do not have a defined meaning to everyone (ubiquitous in certain industries). In reality these are generic descriptions without reference to defined requirements and properties, at best they are like answering someone’s question regarding the location of your pending vacation by responding; “Up North.”

From my experience, and from a supplier’s point of view, the only real commonality they have is the suggestion of liability. You cannot hope to avoid potential mishap if you really do not have more information on the chemical and physical requirements of the steel the person is discussing.

Brake Die Steel – Generally, a high quality carbon or alloy, appropriate for dies, that may be, or is, hardened. Often an alloy from the 4000 series. Is it pre-machined? Not necessarily. Is it pre-hardened? Not necessarily. Is it oversized square and shiny? Not necessarily.

Food Service Grade Stainless – Generally means it does not contaminate food with residue from the steel and it maintains a clean finish. Most often some grade of stainless. More information is needed.

Gun Barrel and Rifle Stock – Generally a 4000 series high integrity hardened alloy. But, not a specific grade.

Boat Shaft – You really have no information from that term. Could be anything, carbon, alloy, stainless, monel, bronze, etc. Most customers will require specific properties that conform to some sort of Marine Agency such as ABS, etc.

Cold Roll – Not a steel grade but a production method. Need more information.

FDA Approved – A misnomer. FDA does not grant approvals for metals.

Pump Shaft Straightness – The specifics are different for everyone. There are ASTM specifications but many large companies have their own “esoteric” specifications. You need to know more.

Ultrasonic Test 388 – An ASTM test method to determine the internal integrity of steel. Requires more detail such as acceptability and reject-ability levels.

-Howard Thomas, April 22nd 2019

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Defective Material

So, for almost 50 years I have had the opportunity to investigate various material/component failures, and with all the variables, two things have been fairly consistent. The first statement that is most often heard, aside from; “Don’t look at me!” is, “It looks like defective material.” Eventually, and more often than not, the actual reason for failure involves something other than material defect; incorrect material, design and engineering misunderstandings relative to material availability and the creativeness of people when it comes to overcoming those obstacles, changes in the application or environment, or a mishap in the installation, assembly, disassembly or earlier repair, etc.

The instances of material defect are very often the least contributory to failure. Perhaps the cleanliness or toughness of the steel was not up to the task. But that is not really a defect. It is a specification problem.

There are of course defects in material. That is true with any product. The point here is, don’t make that the first assumption. Besides, you are more apt to be able to quickly fix the problems that are most often contributory, right there on location, if you can identify them early.

Not to be MOTO (Master of the Obvious) here, if you are in maintenance you already have developed a mental checklist to identify the most frequent culprits; steel grade, toughness, change in temperature, alignment, moisture, chemical environment, load, vibration, lubrication, wear, surrounding forces, surface scratches, gouges, or cuts, new employees (Don’t look at me!!), sabotage, Keyser Söze, Russian interference, inc.

When the usual suspects have been ruled out, begin planning for some failure analysis testing. You will eventually need to provide a specimen of the failed piece (preferably at least 4″ to either side of the break). Contact your supplier and request their assistance. They may contact their local independent testing facilities, may have their own lab, and/or, they may contact the producing mill. I have been reminded; “In maintenance, as in life, most of our wounds are self-inflicted”.

Routine industrial applications can destroy some of the toughest materials known. And that is just during the daily conduct of business. Be mindful of the effects of those forces and respect the potential for catastrophic failure (whether it results from material defect or not). Make use of appropriate safety gear, stay alert, and if you don’t know, ask!

-Howard Thomas, April 9th 2019

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Conclusion – Ten Things to Know About “Finish Size”

REMAINING FIVE POINTS – elaborated

  1. If the finish shaft involves substantial step downs, or, if only a small portion of the bar needs to finish… share that information.
  2. Remember, your supplier cannot be responsible for a third parties work, and/or mistakes.
  3. If liability on the shaft is considerable, consider parking it in another parties driveway.
  4. Try to “Talk the Talk” Phrases like, “a stick of steel”, or, “cold roll”, or, “a length of steel”, will get you in trouble.
  5. Share important ancillary facts with your suppliers; have you received steel in the past that has not been straight enough, hasn’t cleaned up, or was inappropriate in another way?

Why share info on details of a finished part with the supplier?

Well, you don’t need to go over everything, but statements like; “It’s going to be a long small diameter shaft with a big lollipop head on one end” will tip off an astute vendor to the potential of post machining stress related problems. On the other hand, a statement such as: “There is only a very small high spot near the middle of a short shaft that needs to finish to 8″ Dia. The rest of the shaft is 7” Dia. That might make a difference on how much stock is needed for allowance on the raw material.

The caution stated in number 2, above, is just a gentle nudge to limit how much responsibility you find yourself mentally assigning to the supplier. In the final phase, except for mill defect, unless the vendor is handling the job from cradle to grave, the responsibility for success or failure is really out of their hands.

Jobbing the actual machining to an outside source is not just about saving money, mostly because it will generally cost more. But, there are times when “potential problems are probable”. Who knows the product better than the supplier? You may want to see if they felt confident making a difficult piece. If so, why not let them. That eliminates lots of “finger pointing” if the job goes south. If the job goes wobbly, who’s wallet comes out? Their product, their method, their machining, their liability. If they screw it up the burden is on them to do it over at their expense.

TALK THE TALK

Like it or not, many terms are esoteric to specific industries. With hydraulic components, a bar of steel is a rod. When dealing with freight haulers and steel coils, they use terms like; “Eye to the sky”, or, “Suicide”. If you find yourself working within the maintenance steel industry, try to use the same terms you hear the suppliers using. It will go a long way to eliminating surprises. Surprises in maintenance are generally not good.

In closing, if you know some relevant history about a specific shaft or application, by all means share it. If the bar diameter did not clean up the last time, share that. If the shaft broke or bent, share that. If you encountered hard spots or glazing, share that.

Now, if your supplier is decidedly not interested in your ancillary comments, or, if they cut you short and enjoin you to just tell them the dimensions of the steel you want, perhaps you should try a second source. No harm no foul. You can always go with the first source. It is always nice to test the waters.

-Howard Thomas, April 1st 2019

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Finish Sizes & Bar Clean-Up Part 2

The following is a continuation from our last blog on ROUND bar clean up.

It is important to share both your finish diameter AND length. They would like to know if you have a short stubby shaft, where straightness is not often an issue. Or, if it is a small diameter shaft that is 18ft. long. Big difference in how you approach the raw material for the job.

We are not suggesting that you ask the supplier what size they recommend, since a savvy supplier will avoid answering that. Yes, they are there to help you, but they can’t possibly know how talented you are in making a difficult shaft. It always comes down to; When things go South, who’s wallet comes out? Sufficient stock allowance for one, might be trouble for another.

You might also share information on what grinding, or machining method you intend to use; are you grinding or turning on centers, or will it be a centerless operation; which is by far the most common. Clean-up stock and straightness requirements will be different.

What surface finished are they able to supply? Do they have pre-machined, or, rough turned stock, is it fine-turned, cold drawn, hot rolled, or as-forged? Each may have a different allowance for removal that has been left on the bar. There are of course standards that govern each type of finish, BUT, there are variances from one mill to another.

Share “end-use” information with the supplier. What is the application it is being used in. If you are making Hydraulic Rods for instance, that would be an important bit of information you might want to share.

Subsequent Operations that will be incorporated, is also important. Will you be changing the hardness, adding surface hardness or surface-coating? If they don’t seem to be interested, no harm done. They just assume you’re verbose. A good supplier, however, will recognize that your contributions are important to a successful transaction.

In the next post, we will finish up elaborating on the last of the 10 points relative to “Stock Allowance on Round Steel Bar”.

 

-Howard Thomas, March 6th 2019

 

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Ten Points to Eliminate Mistakes on Finish Size – Bar Clean Up, For Steel Bars

We have talked about round bar grinding in the past. The following posts will look deeper into the communicating skills that will help you minimize disappointments in this area. Unfortunately, more people than not have purchased a bar of steel and found that it won’t make their part because there was not sufficient stock allowance to “clean-up”. That need not be the case. Most often, communication is again the culprit. We are speaking of ROUND STEEL BARS.

  1. Diameter size relative to length will be important.
  2. Subsequent machining or grinding method will be important.
  3. Mill finish and mill tolerance will be important. This often varies by mill.
  4. You should share “end use” with your supplier.
  5. Also, share any subsequent operations you will be doing on the bar.
  6. If the finished shaft involves substantial step downs, or, if only a small portion of the bar needs to finish…share that information.
  7. Remember, your supplier cannot be made responsible for a third party’s work, and/or, mistakes.
  8. If liability on the shaft is considerable, consider parking it in another party’s driveway.
  9. Try to “Talk the Talk” phrases like, “a stick of steel”, or, “cold roll”, or, “a length of steel”, will get you in trouble.
  10. Share important ancillary facts with your supplier; have you received steel in the past that has not been straight enough, hasn’t cleaned up, or was inappropriate in another way?

Each one of the above should solicit further discussion. That is going to come under the header of; TO BE DISCUSSED (TBD). I will try to do just that over the next several weeks. So, stay tuned.

-Howard Thomas, February 26th 2019

 

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