Modified Steel Grades (Part 1)

Part One of Two

Steel grades in the U.S. are generally referred to by the materials standards and grading systems presented by various entities. The most common being: SAE (Society of Automotive Engineers), ASTM (American Society of Testing Materials), AISI (American Institute of Iron and Steel), and ASME (American Society of Mechanical Engineers). Those are certainly not all of them. Add to those an entire host of international agencies and it becomes a very large index. Grading systems are often common within a particular industry. Automotive may primarily use one numbering system, while pressure vessel operations would typically use another. As your time in a particular job builds up, it will serve you well to become familiar with the “esoteric” agencies and specifications typically used in that job. Be cautious, however, that your familiarity does not lead to assuming that grading systems used by your suppliers are the same because you recognize similar numbering. Be certain that the agency matches the specification referenced. Then pay special attention to any prefix, suffix, or reference to nomenclature, such as, “Modified”. The presence of that word does not have any specific connotation or purpose, other than to alert you to the fact that something relative to the specification is noteworthy. Nor does it mean that the original specification is no longer valid. While it may well mean an improved grade for one application, it may not affect your application at all.

The scope of potential modifications is broad. For instance, the content brackets for a certain element that the grade allows may have been tightened (restricted) for a particular heat-lot (melt) of steel, the bulk of which may have been destined for a particular industry. Let’s say the standard grade allows a carbon content of .38 to .42. If the melt content simply happens to fall within that grade, no modifier will be shown. However, if the ladle metallurgist has intentionally restricted the low-end content to be no less than .40, or a new restricted range of .40 to .42, the words “modified analysis” should be shown. For your needs, there may be no concern, since the content still falls within the range for the original grade. But, for the customer whose parts must hit a minimum hardness, it is very important that the carbon content is higher. For that privilege, that end-user will have paid an up-charge. Modifications may be made to element content to facilitate temperature resistance in service, strength, cleanliness, etc.

Prefix and suffix indications are more specific. An “E” prefix may mean Electric Furnace, which is a specific type of furnace treatment. An “H” suffix (H-band) relates to a chemistry adjusted to insure specific hardening results. An “H” modifier does not change the grade of the steel, it does change the hardenability potential. There may be “S” for sulfur additions, “L” for lead additions in steel, or low-carbon for stainless.

If you are not charged with the actual engineering and safety of the job, but are in an affiliated support position, you are not required to understand all of the specifics that relate to the metallurgy involved and the certification of the grade of steel. The thing to understand is that steel grades commonly bantered about in the industrial marketplace are a means of dialog. But, by the time the pen hits the paper on a requisition or purchase order, it is important that all parties are on the same page. Your general familiarity with numbering and grading systems will help you to effectively accomplish your tasks from a non-engineering position. The action you take will differ with each situation. It may be as simple as pointing out that a modifier appears. Expect a response like; “Thanks for the heads-up dimwit,” whether they were aware of it or not. Be forensically functional in whatever you do. Pay attention wherever you see the word “modified”, whether on your lunch order or marriage license.

 

-Howard Thomas, February 7th, 2022

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What About Steel Properties?

MECHANICAL PROPERTIES: Generally, density, thermal and electrical conductivity are considered to be PHYSICAL PROPERTIES. The following represent MECHANICAL PROPERTIES.

If you expect a piece of steel to make a certain part, or provide certain benefits, you should know something about the nature of the steel you are purchasing. Understanding the mechanical properties of the steel will give you a better understanding as to how hard it will be to fabricate (cut, form, drill, tap), as well as an idea about how the steel might perform in your intended application (wear resistance, twist or bow, gouging, etc.).

HARDNESS How hard is it? This relates directly to strength, and/or brittleness.
Note: Hardness could well be an entire study i.e., variables affecting results, and interpretation.

YIELD At what point will it bend? (Plastic Deformation)

TENSILE At what point will it break? (Ultimate Tensile)

% REDUCTION IN AREA Pull it from both ends to the point of fracture. This measures the ratio of the reduced diameter at the break, to the original diameter. FUN WITH MECHANICAL PROPERTIES; roll a piece of Playdough to a pencil shape. Then pull it from each end until it breaks. The longer you can pull it and the smaller the diameter at the break, the more desirable.

% ELONGATION When pulled from both ends to the point of fracture, this measures the ratio of the length, at fracture, to the original length once it has been pulled apart from both ends. FOR MORE FUN SEE ABOVE. Once again, the longer you can pull it, the more desirable it is. There are always exceptions to your particular needs, but greater Reduction and Elongation are most often desired.

LCVN (Longitudinal Charpy “V” Notch) How much impact will it withstand?
Stick a short test specimen vertically protruding from a vice.
Notch it, then strike it above the notch with a weighted pendulum. Measure how far the pendulum travels after the specimen breaks
This is the closest indicator of “Toughness.” (Generally accepted as the standard for measuring impact strength.). “Toughness” is the main deterrent to Fatigue Failure, one of the greatest causes of shaft failure in heavy industrial applications.
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RULES OF THUMB – NOT FOR ENGINEERING PURPOSES!
Two of the most common hardness testing methods are The Rockwell Test and The Brinell Test.
30 RC Hardness, in Rockwell “C” scale equals roughly 300BHN in The Brinell Test, 40RC = 400bhn, and so on…
Tensile (Breaking Point) equals about one half of The Brinell (BHN) reading.
EXAMPLE: Where BHN is 300, the Tensile will be approximately 150,000psi.
Yield (Bend Point, or point of plastic deformation) = is approximately 70% of Tensile
Generally, you want the yield strength to be somewhat lower (by 20 to 30%) than
the tensile. “Gives you a chance to get out of the room before the shaft breaks.”

THOUGHTS TO REFLECT ON: The test reports (TRs) for steel mill heat lots (batches of steel), are simply random checks. For 5000pcs of ½” Diameter steel bars, only a sampling will be tested. Even within those tests, results will vary. Recorded readings will usually show some variation which may be due to interpretation of results, test preparation, instrumentation, location in furnace, bar ends, etc. The surface of a wear plate may display several different hardness readings when tested in different places on the plate, by different facilities or by different people. This is not to suggest that readings recorded on Test Reports (TRs) are invalid. It is to encourage perspective within the realm of any mechanical testing. In fact, in situations where criteria are highly critical, the best method is to statistically check the actual finished part. Endurance limit testing is an excellent example of this. Many times, customers will request endurance limits on raw steel. Unless the actual finished part is tested, endurance limits posted on any raw steel product are useful only for the broadest suggestion of potential performance.

There is an excellent movie that illustrates this perspective; I believe it is “No Highway in the Sky”, starring Jimmy Stewart. It is an old movie (1950). Very popular among metallurgists and engineers. Enjoy.

 

-Howard Thomas, January 7th, 2022

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Welding 11 to 14% Manganese Work Hardening Hadfield Steel

From January 2020 post: NOTE: These are tips and guidelines/suggestions, acquired over the years. Not instructions.

There are steel grades (Mild Steel) that pretty much won’t harden by heat treatment. There are steel grades that are hardenable by thermal treatment. And there are steel grades that won’t harden during heat treatment but will harden if you whack em’ around; known as Work Hardening, Strain Hardening, or Cold Working steels. The most common of the work hardening grades (Austenitic) are the stainless grades 304L or 316L. They belong to a group of steel, categorized by grain type, as the austenitic stainless grades (typically 300 series, and the less common 200 series).

However, there is a non-stainless alloy steel that also work hardens; Hadfield Manganese Steel (or 11 to 14% Manganese, Austenitic Manganese Steel, or simply Manganese). It is a somewhat unique product that has found a home in heavy industrial applications where a combination of impact and abrasion tear up perfectly good steel. The railroad industry and the shot-blast industry are two of the prime venues for this product. As good as Manganese is in brutal service, it can also be somewhat “user adverse”; difficult to fabricate pretty much in every operation you might consider. It wants to work harden. During machining, it will harden ahead of your tooling, it will harden in the forming process, and it will be unforgiving of any misadventures in the welding process. Lack of attention to some simple details during welding, and you will be rewarded with embrittlement and fracture.

WELDING MANGANESE STEEL is not exotic or complex. The steel is just big and ugly, has a hard time making friends, and you need to respect some simple precautions. Think of everything you know about welding hard alloys, and pretty much reverse most of it. Don’t preheat Manganese Steel. Keep it cool, keep the interpass temp cool. Assist the welded unit to cool quickly; even if you have to spray some water to cool it. Employ techniques that tend to minimize welding temperature i.e short arc, minimize puddling, skip and backstep.

Don’t use carbon or low-alloy rods. Use Manganese Electrodes

If welding Manganese to Manganese:
Use Covered Electrodes (AWS A5.13, EFeMn-A) E-FeMnA
If welding Manganese to carbon or alloy
Use Covered Stainless Electrodes (AWS A5.4, E309) E-FeMn B
Use High Speed GMAW and FCAW not SMAW

If the Manganese has work-hardened in service (such as may likely be encountered in repair jobs),
cut away the hardened surface. Then apply a “butter-coat” of 307 stainless. The hardened surface, if not removed, will contribute to embrittlement and eventual fracture at the welded area.

Peen the welds while hot
Arc Welding is Good Don’t use OxyAcetylene (contributes to embrittlement)
Lean rod into direction of travel – flow the bead, don’t push it
Minimize energy input (65,000 joules max).

So, when welding hardened alloy steel, you are trying to get sound welds and maintain the hardness.
When welding Manganese, you’re trying to get sound welds period. Not protect any pre- hardened condition. Hardness will occur (or reoccur) when placed or placed back into service.

-Howard Thomas, December 7th 2021

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Heavy Maintenance Royal Pains – Galling Stainless

Over the years we have looked at the nuisance of galling in several separate blogs.

That is because, every year galling makes it to the leader’s group of “Heavy Maintenance Royal Pains”, alongside, magnetism, barber pole-ing, and cupping or oil-canning.

So, let’s begin with this for anyone absent those days; Galling is the seizing of mating parts. A sort of Cold-Welding as it were.

When it is time to disassemble for inspection or repair, often the parts (hubs, casings, flanges), won’t come apart. That leads to hours of lost time and materials, often to find internal parts were savable, had you not destroyed the case. One industry I occasioned to visit finally gave up and inspections switched to mandatory replacements. Ouch!

Galling is a special thrill with the stainless assemblies often found in industries that prohibit the use of lubricants (food service and production).

Parts tend to gall as a response to friction and low-yield strength deformation. Eliminate the friction, eliminate the deformation, minimize galling. Not so fast. Can’t use most lubes in food service due to contamination.

If you’re using stainless shafts, you are most likely accustomed to a certain amount of gumminess in machining; a product of reduced strength that also contributes to deformation.

When mating parts encounter friction (resistance) they bind. Subsequently, they may deform and “cold-weld” together (gall). You can try minimizing binding during installation by slowing the installation speed; perhaps use a hand feed to detect potential galling areas; then back off pressure and speed. You can make sure the parts fit nicely (snug) to eliminate pulling the part together using the threads like a turnbuckle.

SMOOTHER & STRONGER THREADS would help as they would minimize friction and resist deformation. Using dissimilar steel parts with dissimilar hardness would also help deter galling. Try using “Rolled Threads”. Rolled Threads are smoother than cut threads so they have less surface defects which means less propensity for fatigue failure. But let’s keep the focus on galling. Rolled Threads are stronger because they are compressed or displaced into shape. That work-hardens (strain-hardens, cold-works) the thread; especially if it is a stainless steel.

“Roll-Threaded Rod Minimizes Galling”, may not be headline-making news. But it is a byproduct of that thread production method. Life is short. Be easy on yourself. Take advantage of available benefits before reengineering the whole job.

-Howard Thomas, November 8th 2021

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Wear Resistant Structurals: Is it Possible?

Let me know if this reads a better, changed the order and made it (in my opinion ) a little easier of a flow without altering the message

Are there hardened (400bhn) wear plate angles and channels? November 2021 Blog

NO SUCH THING AS WEAR RESISTANT STRUCTURALS? (Other than low-hardness A588)

It is possible to make your own!

We stock a true 400bhn wear plate (sheet), 1/8” x 60” x 120”. It is clean, flat, and easy (relative to wear plates) to fabricate. We can Hi-def-plasma-cut pieces to order; simple rectangles and strips, or configurations per sketch. The cuts look almost like laser-quality with very little heat effected zone along the edge.

If you are involved with heavy plate maintenance and fabrication; more specifically, if you occasionally handle hardened wear plate, you will have a need for this unique product.

It forms well, is readily weldable (not too rich of a chemistry to cause problems), and it provides weight reduction where installation and handling might be a problem; not to mention you can make wear resistant containers, hoppers, tanks, that are lighter and therefore increase payload.

Where can it be used?

Strip it and tack weld it into the high wear areas of structural (A36) shapes. Tack it into the throat of a “U”, or, on the inside of one or both legs of an angle. You now have wear resistant structural steel.

Is a cart riding on top of a rail wearing down the top surface? Tack on a strip of this to add a 400bhn wear surface.

The material is perfect for emergency temporary patching of blow-outs on job sites until heavier fabricated pieces can be delivered. An installer can get the pieces into hard-to-reach places where a repairman could handle the plate by hand. This is an alternative to 3/8” and ½” thick A36 liners. That’s a big reduction in weight! You may even find you benefit from the competitiveness of your bids.

Cutting: oxy, plasma, band saw (use blades for hardened alloys), abrasive wheel, laser, and water-jet.

Welding: Standard Low Hydrogen Method (7018, 8018)

Form: using standard precautions for working with wear plate. Form against the grain. Leave a large radius at the bend (when wear-lining angles and channels utilize a cut-and-weld operation)

I know this reeks of a sales pitch, but, we have customers who keep this on hand around the plant for; “As Needed by Anyone Needing It” purposes. It is a life-saver for keeping things moving while you are otherwise attempting to resolve the issue.

CAUTIONARY NOTE; Working with hardened steel, anyone’s hardened steel, involves risks. Be sure to use appropriate safety gear (hot-mill gloves, hard hat, safety glasses, etc.), Utilize persons experienced in handling hardened steels, including certified welders, etc. Try to form against the grain, incorporate the largest bend radius the application will handle. And, COMMUNICATE, COMMUNICATE, COMMUNICATE.

If there is something you are not sure of; ask your vendor!

-Howard Thomas, October 27th, 2021

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Keystock Revisted

Or, “Keystock, we hardly knew ye. . .”

So, back in April of last year I was eulogizing Keystock; at least the longer length, higher strength, plus-tolerance kind, that for years had been a “go-to” product for a lot of people. It seemed Keystock would be going the way of the Dodo bird. But, I was apparently wrong. More correctly, it was going the way of Coke, or New Coke, or Original Coke, whatever. The point is . . . “It’s baaaack.” And, that’s a good thing.

As I mentioned then, in the steel business in most general terms, anytime you see the word “stock” attached to another word; think, “stock used to make”. Bar-stock, Bushing-stock, Brake-Die-Stock, Rifle-Barrel-Stock, Pump-Shaft-Stock, etc., would be stock that might typically be used to make those items. While it may seem to infer that there are other attributes specifically suited for the particular application specified, it may simply mean this is a material some people have chosen to make this type of part. Details should be clarified; is it closer tolerance, harder, squarer, whatever? Facetiously, a tree might be “Tooth-Pic Stock”. Works the same with the term Quality, as in; Rifle barrel quality, or Military Quality, or Drawing Quality. The explanation and caution remain the same; It may mean the steel possesses a special grade certification, but it may as likely mean that “Someone, at some time, used it for that.” So, “Trust but verify”.

Keystock is generally a low to mid-strength mild or carbon steel square or flat bar, used to make keys. Those keys are inserted into shafts. A drive motor chuck will engage with the protruding key, and rotate the shaft. The idea is that the key is of less cost and strength than the expensive shaft. If something interrupts the motion of the shaft and causes failure, it should be the cheap little key that fails not the big expensive shaft. Clear the obstruction, put a new key in, and you’re good to go, hopefully with an undamaged shaft.

The perfect piece of keystock would have less mechanical strength than the shaft, but tuned to the actual application, close enough that the shaft doesn’t fail prematurely, contributing to expensive downtime. There is the conundrum; too soft of a key and you have frequent expensive delays. Too hard of a key and you risk damaging an expensive shaft.

Ideally, commercial Keystock would be a precision cold drawn bar possessing slightly elevated strength properties, with good cross-sectional accuracy and a close oversize tolerance. The ideal oversize tolerance for many years was considered to be +.002”/ .000”. That tolerance would allow you to cut a standard keyway that would fit nice and snug. Undersize tolerance resulted in sloppy, loose keys. Too much oversize required unwelcomed machining.

Unfortunately, over the past decade or so, tolerances on commercially available Keystock gradually opened up to +/- .004 to .007” (plus or minus); even with sources that promoted “Keystock”. For several years now, it has been common to only be able to source low property mild steel, undersize Keystock, in short lengths (12” and 36”).
Longer lengths, no matter how beneficial to the end user, require expensive additional processing to eliminate camber and bow.

Running multiple draughts (passing the bars repeatedly through drawing dies) is a good practice to increase strength (strain harden) and refine tolerance. However, that process adds cost, as does additional straightening. Those expensive practices were eliminated as the marketplace shrank.

Hardness (through multi-pass cold drawing/strain hardening), tolerance, cross-sectional accuracy and straightness, are all doable. Expensive, but doable. It requires a bit of fiddling in production for an item that does not represent significant tonnage. This current economic burst has allowed “The Return of Keystock”. Check with your vendor and take advantage of a simple perk that will make your life easier.

-Howard Thomas, September 15th 2021

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Lean Duplex – Part Two: Who Can Use This Product?

The easier question to answer would be; who can’t use it?

A continuation of last month’s post:
Service temperatures should not exceed 750F. Any customer currently using stainless of the following types: 304L, 316L, 410, 416, 17-4ph should consider LDX, (ASSOCIATED STEEL’S ASC2250 LDX).

LDX is now made by several steel mills, to their own specific variances. In general, it is a great stainless grade for heavy maintenance applications where the grades listed immediately above are being used. It is more corrosion resistant, stronger, less apt to gall, better at resisting SCC, easier to machine and weld, than many of the commercial grades shown.

Lean Duplex work hardens. As shipped, it is generally about 28RC. The Austenitic portion of the grain structure contributes to strain hardening; it cold works as the size is drawn. As mentioned in part one; It is harder (hence stronger) than commercially available 304 and/or 316, but is still easier to machine. Duplex grades of stainless steel contain grain structures of equal parts Austenite and Ferrite. They are considered to be magnetic in their most common form.

It resists bending, (minimizes twisting), abrasive wear, resists failure due to SCC, resists galling, adds strength. It’s like the Ginsu knife of stainless steels. (Probably have to be my age to know what that means). Lean Duplex is not intended for use in applications currently requiring advanced alloy grades, such as; 2507, AL-6XN, Hastelloy C, 20cb, Ni625, etc.

ADVANTAGES OF ASC2250 LDX
The PRE (pitting resistance) is the accepted standard for determining a stainless grade’s comparable resistance to pitting and crevice corrosion. The lower the number, the less resistance.
304 is 18 316 is 24 Duplex grades are nearer to 40.
Associated Steel carries Lean Duplex (ASC2250 LDX) in two surface finishes; Fine-turned oversize (The size will make the nominal size), and Precision Polished Guaranteed Bearing Fit (Minus/minus tolerance). It is inventoried in long mill bars and may also be sold to specific required lengths.

ASC 2250 LDX offers advantage in:
Resistance to Stress Corrosion Cracking (SCC)
Resistance to Chloride pitting
Resistance to Crevice Corrosion Cracking
Elevated Strength Levels
Ease of machining
Ease of welding
Greater fatigue resistance
General corrosion resistance superior to 316L
Excellent resistance to “Thermal Shock” (low-cycle fatigue)
Excellent service to -30C

-Howard Thomas August 6th, 2021

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Lean Duplex Stainless: What Is It?

If memory serves, I did a post on Lean Duplex some time ago. It is an important grade of stainless and worth a revisit.

Basically, Lean Duplex is a leaner chemistry derivative of Duplex Stainless Steel. Duplex Stainless Steel is recognized as having a unique shared grain structure; Austenite and Ferrite. Each of those grain types contributes to the characteristics and performance of the steel grade. The grade was developed to provide resistance to Stress Corrosion Cracking (SCC), a type of corrosive failure prevalent in SOUR SERVICE applications in operations such as Refineries and Pulp & Paper plants. Sour Service applications involve acidic or base (alkaline) exposure. 2205 Duplex is probably the most common grade of Duplex that the industry is familiar with; although there are several others. I refer to 2205 as the “Original Grade”.

The short and sweet history of steel usage to combat SCC in sour service maintenance applications is this: 304 and 316 (Austenitic grain) worked tolerably well, but lacked strength. 410 and 416 (Martensitic Grain) provided the needed strength, but offered less general corrosion resistance. Turns out the catalyst was nickel content, but that’s another topic. The thought was, develop a grade that was half Austenite and half Martensite (Duplex), and enjoy the best of both worlds. The development of the original chemistry 2205 Duplex did just that. It fit the bill, but it was expensive and somewhat user unfriendly.

Years later, when the cost of elements used in the chemistry of the Duplex grades became prohibitive, those grades were pruned to the bone (reduced the expensive elements) to develop a new “More Economical” grade, Lean Duplex. Engineers were content to live with a much less effective product, in order to come up with a more affordable product. Nickel prices alone, had seen a ghastly increase at that time. The new LEAN DUPLEX, however, displayed an unexpected phenomenon; resistance to general corrosion and SCC was very near that of the original grade. Strength was also maintained; and, machinability was increased dramatically.

Today, LDX is most commonly used globally in tube and sheet form in construction of container vessels and conveyance items.

Lean Duplex (LDX)
Resists pitting and crevice corrosion similar to 316L
Resists Intergranular attack better than 304L or 316L
Resists Stress Corrosion Cracking better than 304L, 316L, 410, 416
Resists General Corrosion better than 304L, and 316L
Weldability – less restrictive than 2205

-Howard Thomas, July 6th 2021

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About Chromed Rods Part Three of Three

This is the last of our three-part post on chromed shafts.

In order to extend service life, by resisting surface wear on the rod, the rod surface needs to be hard. It also needs to be relatively smooth, so as not to tear up the seals.
And the rod needs to be straight. In most cases, chrome is an ideal surface coat for Hydraulic Rods. Hard Chrome may be better. IHCP is better still.

The finish however, cannot be so bright that it will not attract and hold the lubricant. Inadequate lubrication is just one of many potential contributors to shaft failure, chromed or not. You might to consider the following information, for a broader scope on this topic:

Fatigue Failure and The Importance of Design;
I have always felt that approximately 80% of shaft failures in heavy industrial maintenance applications are related somehow to fatigue. The following article found in Machinery Lubrication magazine compliments that supposition.

In his article on cylinder rods, Brendan Casey states that it is recorded that approximately 25% of hydraulic rod failures are design related. In hydraulic cylinder applications, one in four shafts fails to provide adequate service life. Bent rods make up a considerable portion of failures. It is important to clarify the straightness tolerance your vendor is proposing to supply.

Rods that are of insufficient diameter and insufficient strength will often bend in service. Once the rod bends, excessive load is placed on the seal. That results in premature seal failure. If a rod is bent, and use of a larger diameter rod is not practical, then the tensile of the rod must be increased. Induction hardened material (IHCP) offers a significant boost in strength.

A NOTE ON BAR ENDS
When full bars are chromed, most mills hold the bars by the bar ends and vertically coat them. In those instances, the bars are not fully chromed the length of the mill random bar. Several inches on each end will be bare. This is generally not trimmed off when random bars are sold. It is recommended that you specify “trimmed ends” when you order random length chromed bars. Probably a good idea to specify this on even cut-to-length material, even though most vendors provide that service as a default.

This completes our post on chromed rods. If you want to pursue information gathering on this type of material, you may want to do some additional research on; Black Nitrided Rods. That process is showing improved service life in similar applications.

 

-Howard Thomas, June 11th 2021

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About Chromed Rods – Part Two of Three

Continuing from our last post, we are discussing chromed rods. When they are applied correctly, chromed Rods typically extend service life compared to standard carbon and alloy bars. Variables relative to those materials would be the steel type, actual hardness, and the type of hardness (surface or throughout). The benefits of chromed rods address sliding surface abrasion and corrosion.

In actual service, however, even sliding abrasion applications are not just limited to sliding abrasion. Small bits of debris (tramp elements) find their way onto the exposed rod and then get pulled through the seal (intended to keep tramp elements out), between the rod and the cylinder. The motion of the rod is often interrupted by impact causing shock and twisting or bending of the rod.

Deciding between IHCP and Hard Chrome HP & Too great of a surface finish has a downside.

Since chrome plating is most often applied to a rod surface very thin (thousandths), the importance of a surface hardened sub-straight should not escape consideration. Where severe impact and gouging may be experienced, a hardened sub-straight will resist damage. You would think that, to be on the safe side, everyone should always order the IHCP material. The problem is, surface hardened sub-straights may be furnished at a hardness of 60 to 62RC (approximately 600bhn). Not everyone has machinery sufficient to handle that hardness. Drilling, cutting, machining may be a problem.

The thin chrome “skin” covering the rod is easier to penetrate when the sub-straight is soft. Various fabrication processes are readily accomplished. Smaller shops will find fabrication processes easier.

It is also important to always remember that high hardness in steel (carbon or alloy surface or throughout) also affects ductility. Application consideration must be given to the propensity for fracture.

CHROME SURFACE FAILURE
Abrasive related chrome surface failures often damage seals. When chrome gets very thin due to wear, it cracks and peels, exhibiting a razorblade sharp projection that often curls up, like the bark on a Birch tree. This type of failure is often experienced where there the surface of the shaft is subjected to severe temperature change (furnace). That projection tears up seals. In applications were liquid may escape, such as sludge from a barge pump, the contamination could be catastrophic. Read as “expensive”. In those applications, some alternative (such as utilizing hardened stainless shafts) should be considered.

Our last post of this three-part series will cover, lubrication, bar cut-ends, and dent bars.

 

-Howard Thomas, May 6th 2021

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