Manufacturing highlight: Mechanical property enhancement through the use of grain refinement

Grain refinement

There are many applications that can benefit from grain refinement. Grain refinement is a result of specific manufacturing techniques which allow for a finer grain. In almost every case, a finer grain material will outperform a coarser grain item of the same material. The basis of finer grains being stronger is that while there are more dislocations in the material, it is more difficult to make all these dislocations line up. Finer grains also typically have less precipitates in the boundaries. Precipitates are oxides, carbon, and interstitial elements that are not in solution of the grain. Precipitates are normally not as strong as the material itself - tending to make a precipitated material more brittle.
Microphotograph above shows ASTM Grain size No. 5.5, ALA ASTM No. 1
Some grain refinement comes from the material itself, through additions of elements such as Columbium (Cb), Zirconium (Zr) and Boron (B). In small amounts, known as trace or residual amount, these elements tend to be grain creators or form grains in localized sites around them. While this type of grain refinement is good because it enhances the properties of the materials, it doesn't have to be the end of the grain refinement process.
Materials can receive further grain structure enhancement through specific manufacturing techniques of the material while it is being forged, rolled, or drawn. The steps immediately preceding the final processing and anneal can be essential to having the best product possible. This means during the last major heating cycle, the temperatures attained during the processing, as well as the final anneal it is given. Proper manufacturing techniques and methods of processing are essential, and rarely will it make up for abuses the material could have been subjected to in prior processing during a more raw stage.

Quality requirements

You want to ensure that the billet a product is going to be made from is of good quality. Heating metals to temperatures outside its normal limits can cause issues like burning out Carbon, incipient melting, or cause oxides or precipitates to collect at grain boundaries. A simple billet test can reveal many of these by performing a macro view of the ends of the material. ASTM A604 is a common specification for preparation and macroetching of samples. You may see spots, pins, rings or nodules in this very simple test. It is pretty commonly used for higher melt materials, such as VIM VAR and ESR melt methods, as it ensures the quality of the billet at a fairly early stage. It could even be used by lower quality melted materials such as EF and AOD.
 Macrophotograph above shows ASTM A604

Processing methods

Now that we have covered the basis of good melting, processing and checks along the way we can now cover the final steps that can really have an impact on your material and its resultant properties. Mechanical strengthening of materials can be achieved by several methods. The most commonly used is through heat treatment, sometime known as aging or precipitation hardening. We briefly touched on these earlier, but we failed to mention the impact of such an easy method of raising the strength. Not only do precipitation hardening treatments lower ductility (more brittle), it can also cause the material to be subject to corrosion issues that the annealed material was not.
How can this be, it is the same material - and the composition didn't change? The mechanics of precipitation are basically the elements contained in the material change. During the temperature cycle(s), various phases in the material will be developed. The most common is gamma, or gamma prime - used in Inconel 718. This is the effect of Titanium & Vanadium additions. In Titanium Grade 5, the strengtheners are Aluminum and Vanadium to make Alpha-Beta phase alloy. Many elements can have phases associated with them, some are good and some are bad. The good ones are typically not as brittle as the bad ones, and when I say good typically it is enhancing the strength of the material rather than detrimental.
I know what question you are asking: If precipitation hardening is sometimes too brittle or it affects the corrosion resistance too much, what options are left? There are still a few ways to strengthen the material without having to use precipitation hardening. One way is through the use of hot rolling. Hot rolling material does elevate the mechanical properties, but the effects are normally reversed when it is annealed after processing. It is hot rolled and left it in the unannealed condition. I say hot roll, but it could also be hot forged, warm forged, warm worked or warm rolled. Do these methods attain the same strength as precipitation hardened material? Well, no they don't. Normally not enough strength is imparted during warm or hot processing to reach near 180 KSI UTS. It might get between 115 to 155 KSI UTS though, which helps in many instances.
I might add at this point that hot or warm processing can leave precipitates in the grain boundary, so refer back to the quality issues already identified, and you may need to look at the microstructure as well to tell if the issues could be detrimental. Typically if the outside of the grains are completely enclosed with precipitation or carbides, you have found what is called sensitized. Sensitized is a condition where precipitates are left at the grain boundary, rather than being in solution or homogeneous of the grain. The etchant would eat away the precipitates around the grain and leave a trench, known as a ditch structure. The etchant solution is your friend, because it will tell you what could happen in the field. If a corrosive media can dissolve these areas with a short treatment, how well will they hold up in real life? Pick an etchant solution and technique that is commonly used for the alloy, has good coloring or dye properties and is aggressive enough to show the detail you need without lots of prep.
The problem of attaining 200 KSI UTS isn't over yet. We still have a few processing methods to review that can attain the strengths of a precipitation hardened material. We have cold processing, which at the basic level, means that there is no heat added to the material before forming. It's basically processed at room temperatures, and it might be called cold rolling, cold drawing, cold forging, or cold swaging. Cold processing is, what I feel, the best way to mechanically strengthen a material. Let me clarify with - it's the best way if it has good quality going into production (a minor caveat). I'm sure you have heard the term garbage in equals garbage out. It definitely applies, and it applies on every type of metal processing. With that said, can you mess up good material? As long as you stay within known strain rate limits of the material, it is difficult to process material cold and end up with something bad. Bad is kind of relative, so let's look at it compared to precipitation hardened material and make some comparisons. Depending on the level of strength needed the elongation is going to be at least twice that of precipitation material. Elongation (Elon. %) is typically showing the ductility a material has. When a material only has 3 or 5% Elongation, we think of it as not very ductile. Most applications want 10-15% as a minimum Elongation. It should also be noted that the reduction of area is normally much higher in sold processed then precipitated material. A materials reduction of area property (R/A %) of a material shows its tendency to be brittle, or have low impact resistance. Lower numbers means it is more brittle, or that the material has been sensitized at some point.

Superalloy and Super-stainless Alloy Summary

So what alloys and strengths are available with this mechanical strengthening? High Performance Alloys supplies several alloys with properties capable of 180 to 200 KSI UTS. Many superalloys are austenitic, which means it has low magnetic permeability. Superalloys are either a Nickel-base or Cobalt-base material and will normally have a UNS that starts with N or R. So if you wanted a high strength C-276, the UNS would be N10276 and you simply state the properties that you need. High Performance Alloys also works with C-22 or Alloy 622, which is UNS N06022. 686 is UNS N06686.
There is also a group of material called super-stainless, which means that they normally outperform a stainless counterpart. High Performance Alloys can attain these properties with super-stainless NITRONIC grades; such as NITRONIC 60 UNS S21800 and NITRONIC 50 UNS S20910.
If you look at the alloys mentioned that can be work strengthened so far, you will notice that these are all corrosion materials, alloys that are used to solve corrosion issues. There is not much point in cold processing alloys that will be used for high heat. For medium temperatures to 1600F, work strengthening a cobalt base high temperature material that can be aged can enhance its properties at temperature as well. Examples of these alloys are L605 (Haynes 25), as well as MP35N. These two grades actually also have medical applications for their corrosion resistance.
While many Superalloys and super-stainless material can be strain hardened, there are only a few that will reach these ultra high strengths. A few were mentioned, the common ones, but there are more. There are many more that can be strengthened through grain refinement that will only take 10 to 30 percent reduction, and will benefit from an enhanced grain structure as well as enhanced properties.
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Visit us at NACE CORROSION 2017

Corrosion 2017 Conference & Expo

Come meet with us at NACE CORROSION 2017, March 28-30 in New Orleans.

David and Glenda will be at booth # 828.  Please stop by and say hello. Existing and past customers have promotional items waiting for them!

If you need a complimentary pass to attend the expo booth, please ask David, Glenda or your salesperson.

Understanding Nitronic alloys

As seen on Modern Metals November 2016

Nitrogen-strengthened stainless steels can provide many benefits, says Jeff Kirchner, COO of High Performance Alloys

MM 1016 face lead - MM: How did Nitronic alloys get their name? Are there any common misconceptions about these grades?
Jeff Kirchner: Armco, the inventor of these grades, had several alloys. They were calling them 21-2N, 21-4N/22-4-9, and those became 21-6-9, 18-2Mn, 18-3Mn and 22-13-5. The commonality among these alloys was chromium, manganese and nickel with saturation additions of nitrogen. For marketing purposes in the 1970s, these alloys were branded as the Nitronic series and given alloy designation numbers. A common misconception is that the number relates to strength, when in actuality all the Nitronic grades have yield strengths in the 50-60 ksi range when annealed. The numbering system has more to do with the order in which the alloys were developed than with strength, so it just makes it more literal and associative to the manufacturer.

MM: What are some of the benefits of adding nitrogen to stainless steel?
Kirchner: Adding nitrogen to alloys has several effects on the properties. The most common benefit is an immediate boost in the yield strength, or the point at which a material will deform. The nitrogen also improves the impact resistance of alloys. For an example of the enhanced impact resistance, many of these grades will need to be Charpy tested at sub zero temperatures to conduct a valid V-notch test, which is where it breaks.

MM: Can you briefly touch on the different grades of Nitronic alloys, their characteristics and applications?
Kirchner: Nitronic 30 is a corrosion resistant, or basic, stainless-manganese steel, meaning it is good for abrasion resistance. It is commonly used for liners, chutes, and because of its extra strength and lightweight properties, it is now also being used for body panels in transportation. Nitronic 30 is available primarily in heavy sheet and light plate.
Nitronic 40 is a high-temperature stainless with low magnetic permeability. Common applications include instrument or hydraulic tubing, but it is also found in bar and sheet. 22-13-5 Nitronic 50 is a corrosion-resistant stainless, commonly used for saltwater and marine applications. It has a very low magnetic permeability. 18-8Mn (+Si +N) Nitronic 60 is an oxidation resistant (elevated temperature) as well as a corrosion- and wear-resistant stainless. It is well known for its resistance to wear and galling, but the composition performs well in many environments.

MM: What should material specifiers consider when questioning the applicability of Nitronic alloys?
Kirchner: The obvious advantage to the Nitronic series is an immediate increase in strength. Many times we have recommended Nitronic 60 to replace grade 304L or Nitronic 50 for grade 316L. They are basically quick upgrades with little change in their machining or processing capabilities. Another consideration is that these two alloys excel at the low magnetic permeability, but the biggest difference is the permeability doesn’t change when forming and fabricating. During forming and welding, grades 304L and 316L are known to transform some austenite to ferrite, raising the magnetic permeability. There are definitely some applications where this magnetism potential is not an issue at all, but it can be a concern if you have magnetic fields or sensitive electronics near a rotating assembly.
Nitronic 60 solves a common problem where a stainless or corrosion-resistant grade is needed that must also resist wear and galling. It is unique in that it has these characteristics and can still be formed and fabricated with a moderate price point. There are some great cobalt alloys that can be used for wear and galling and will resist staining from the atmosphere or cleaning, but these cost more as cobalt is normally above $12 per pound.

High Performance Alloys, based in Tipton, Indiana, with locations in Oregon and Texas, is a global distributor of wear-, corrosion- and heat-resistant alloys. Kirchner has been with the company for more than 25 years. Call or browse at 800/472-5569 or

Source: Modern Metals, November 2016

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Select the Alloy that you are interested in either through an Alloy page specific to that grade in the store, [see links below in Available Alloys] or from a central page where any Alloy we carry can be selected.

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Available Alloys

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Customer Reviews Summary

Customer service is important. We know, we have to buy products too. We have all experienced bad customer service and we know it is to be avoided. At High Performance Alloys, the service comes before the sale, with the sale and after the sale. We are extremely proud of our customer service. Here are some of the reviews we have received from customers:

"HPA has always been a trusted supplier for our Nitronic stainless steel needs. Quotations are always prompt and clear as to what is being offered if a substitution is being made. That said, HPAlloys is a pleasure to work with."
"I appreciate the ability to easily order small quantities of hard-to-find materials. I also appreciate being able to specify my desires regarding composition and mechanical properties and mostly get exactly what I need."

"Many times the order goes to the company that responds quickest. HP Alloys quotes are always quick. You don't have to nag them to get your quotes. "
"I do like that I go to the same sales rep. for each order not just another operator in the system."
"One area of concern in general with metal suppliers is the quality of packaging / protection during delivery. Your pieces arrive to our shop without marring, packaging intact and ready to machine. We are able to order closer to final dimensions when this is done which saves us time and money."
"High Performance always help us find the materials we need with the quickest turn around possible. We normally don't have a lot of time to too work with and they always seem to help us get the job done."

Still not convinced? Read more

Give us a call at +1 (765) 945-8230 or toll free in the US @ (800) 472-5569

NITRONIC: Material Tradename

NITRONIC: A material Tradename 
   Material definition - Nitrogen strengthened stainless steel series

The NITRONIC family of alloys was developed by Armco in the 1960s. The name NITRONIC comes from the addition of Nitrogen that is added to the composition of the alloys in this series. Typically this Nitrogen addition is made to the full solubility of the alloy. There are other ways that Nitrogen is used to enhance various materials, such as Nitriding or using liquid Nitrogen as a tempering medium. Unique to these alloys is that prior to these grades being developed, adding Nitrogen to the alloy was as a by-product. 

  A common misconception about NITRONIC alloys pertains to the grade designation, or numbering system within the material series. Some people think the grade numbers designate the strength of the alloy. People were saying they could use 40, 50 or 60. While all three of these grades are corrosion resistant to some extent, with low magnetic permeability - they are not normally used in similar applications. They are all Nitrogen strengthened grades, which helps the impact properties and lowers the ferrite number (pushing further to full Austenitic). Read the embedded article below for more information about how each grade came along. Nitronic 60 being the last one in the series, developed primarily for heat resistance.
  The primary engineer working on this project was Bill Schumacher (now retired).  I reached out to Bill for a clarification of the naming and he had a great write up about it.  Bill's story of "Naming the NITRONICS" follows, in its entirety.

NAMING the NITRONICSBill Schumacher, May 18, 2016
   Over the years, some end users have questioned the origination of the Trade name “Nitronic”.  They even speculated that it might be a reflection of the alloy's strength level.  However, this is not the case. The term relates to the fact that these stainless steel alloys are nitrogen-strengthened, and thus, "nitronic".
   The addition of nitrogen (N) to stainless steels has a long history dating back to the early '50's during the Korean War.  To conserve on the expensive nickel (Ni) content in austenitic stainless alloys like 301 and 304, N and Mn (manganese) were added and later identified as the 200 Series grades: 201, 202 and 205.   N has the most benefit to replace Ni, but the Mn was usually added to increase the N solubility so higher levels could be introduced.  These changes had little detrimental effect on corrosion resistance but made the alloys functional and available at a fair price.  The N was low enough to not greatly increase the strength and impair fabricability.
   In some cases N was added to very high levels for high temperature strength for automotive engine valves.  These were called 21-2N and 21-4N and a plate version 22-4-9.  These alloys also increased the carbon level such that the C+N total = 1%.  A further refinement of  22-4-9 led to 21-6-9 for sheet and strip products with intermediate N and low C levels respectively.  
   As markets were developed and stainless steel melting became more economical, other N + Mn alloys were developed for specific applications and not necessarily for low cost.  Armco, (the original trademark owner of Nitronic), added 18-2Mn, 18-3Mn and 22-13-5 austenitic stainlesses.  In the early '70's these alloys were becoming more accepted in the market, so Armco decided to streamline the names using the Nitronic trademark and help “brand” these modern alloys.  Armco 18-2Mn became Nitronic 32.  Armco 18-3Mn became Nitronic 33.  Armco 21-6-9 became Nitronic 40 and Armco 22-13-5 became Nitronic 50.  During all this name changing, a new alloy was being developed that also contained N and Mn but also a high silicon content.  This alloy was released under the Nitronic name as Nitronic 60, an anti-galling grade.
   All the above Nitronics have similar yield strengths of about 50-60 ksi.  Later developments included Nitronic 30, a leaner version of Nitronic 33 and Nitronic 19D, a duplex stainless steel with a 50% mixture of austenite and ferrite.  This last alloy also has much higher yield strength due to its mixed microstructure. The original intent of the name was to follow the level of alloy content-the lower numbers tended to be leaner in expensive elements like Ni.  However, later alloys diverged from this.  Nitronic 60 is not richer in alloy content than Nitronic 50 and Nitronic 19D even less so, but they both had high Mn and added N levels.

Hopefully this helps to straighten out some of the questions about the NITRONIC grades and how they were named.

NITRONIC is now a registered tradename of AK Steel.