Finding the right stainless steel grade for your next project can be a struggle. This is because each grade has both desirable and non-desirable attributes. As such, you should aim to grasp the ins and outs of the grade you are considering. Alloy 254 is widely regarded as the common austenitic stainless steel grade. In this article, we will provide a thorough overview of this type of steel for you to understand it better.
What is Alloy 254
Alloy 254 is a highly austenitic stainless steel with superior resistance to corrosion. Austenitic here refers to its crystal structure. Also, the crystal structure is attributed to the corrosion resistance, toughness, and ductility of the stainless steel.
Alloy 254 is commonly known as 6% moly stainless steel or 254 SMO. The acronym “SMO” is not an industry standard, and therefore it might refer to different things. Often, alloy 254 will be called UNS S31254. This naming is a universal code and it denotes technical information like the chemical composition and properties of this stainless steel grade.
Austenitic stainless steel grades
People like you who are looking for stainless steel have various specifications and expectations grounded in the projects’ requirements. Subsequently, stainless steel must be graded and classified into various categories to ease the decision-making process. Austenitic is one of these types of stainless steel.
Austenitic steel remains the most prevalent type of steel. Being a highly cost-effective, versatile, and durable material, it makes the perfect stainless steel for any project. A new sub-type of steel is derived when austenitic steel is further subdivided. Alloy 254 is one example of this subcategory of this steel type.
Why Alloy 254 is called super austenitic?
A number called Pitting Resistance Equivalent Number (PREN) is utilized to designate the degree of relative pitting resistance of stainless steel. This resistance shows how much the material has a high probability to resist pitting corrosion in high chlorine environments.
The PREN of 254 SMO is known to be greater than 40. Therefore, it earns the title of super austenitic stainless steel. To put it in simpler terms, 254 SMO exhibits greater resistance to pitting corrosion than most austenitic stainless steels.
The takeaway for you here is that; if you are hunting for the perfect stainless steel to use in marine environments, chemical processing, the food industry, or the energy industry, 254 SMO is the ultimate material.
Chemical Composition of Alloy 254
The following table shows the chemical composition of the different elements found in alloy 254 in wrought and casting forms. These two terms imply different ways of forming shapes with 254 SMO. Wrought is when mechanical processes such as rolling or forging are used while casting refers to molding molten metal into various shapes.
| Element | Wrought | Castings |
| Copper | 0.50-1.00 | 0.50-1.00 |
| Chromium | 19.5-20.5 | 19.5-20.5 |
| Nickel | 17.5-18.5 | 17.5-19.5 |
| Carbon | ≤0.020 | ≤0.025 |
| Nitrogen | 0.18-0.22 | 0.180-0.240 |
| Molybdenum | 6.0-6.5 | 6.0-7.0 |
| Iron | Balance | Balance |
| Sulfur | ≤0.010 | ≤0.010 |
| Phosphorus | ≤0.030 | ≤0.045 |
| Silicon | ≤0.80 | ≤1.00 |
| Manganese | ≤1.00 | ≤1.20 |
Role of alloying elements in the material’s properties
As one might expect, the elements found in alloy 254 contribute to its properties, to a certain extent. Since alloy 254 is primarily known for its high corrosion resistance, most of these elements enhance this property of the material.
Specifically, corrosion resistance is attributed to chromium, whereas pitting and crevice resistance is caused by Molybdenum. Nitrogen also enhances the pitting and crevicing properties.
Nickel is responsible for making sure alloy 254 is ductile. Silicon and manganese ensure the weldability of the material. Ductility and weldability are major properties to factor in when you are looking for good stainless steel. Those are the roles of the main elements in 254 SMO.
Properties of Alloy 254
Physical Properties of Alloy 254
There are several physical properties of alloy 254. For purposes of decision-making, there are those properties that matter to you most. These are the properties that will help you decide if this material is suitable for your projects.
Here are some of these properties;
| Property | Value |
| Specific Electrical Resistance | 85.0 µΩ•cm |
| Thermal conductivity | 13.5 W/mK |
| Thermal expansion | 13.6 µm/m°C (20-100°C) |
| Melting point | 1320-1390°C |
| Density | 8.0 g/cm³ |
| Specific heat capacity | 500 J/kg•K |
| Magnetic Permeability (20°C) | <1.05 |
The above properties make this material ideal for a wide range of applications. In another section of this article, we will discuss some of these applications.
Mechanical Properties of Alloy 254
When you hear of the mechanical properties of a material, think of the characteristics of a material that are exhibited when force is exerted on it. To put it differently, how well does the material handle force?
Alloy 254 tends to have rather excellent mechanical properties. Here is a list of them with their corresponding values;
| Property | Value |
| Poisson’s constant | 0.3 |
| Yield strength annealed | 300 MPa |
| Tensile strength, annealed | 650 MPa |
| Elongation at break | 50 % |
| Modulus of rigidity | 73 to 82 GPa |
| Modulus of elasticity | 195 GPa |
| Hardness, Rockwell | 96 |
| Hardness, Brinell | 210 |
Whereas the technical details might not count all along, it helps to learn about them. It comes at a time when your project demands very specific properties. Under such circumstances, you will have the ability to cross-check what you need from this table.
How is Alloy 254 Made?
Manufacture of Austenitic Grades of Stainless Steel
Alloy 254 is manufactured using specific methods to achieve its industry standards composition and properties. Still, a number of the methods used in its manufacture are also used for other stainless steel grades.
These processing methods include:
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Electric Arc Furnace (EAF):
Manufacturers select high-grade steel scrap and melt it in the electric arc together with alloying elements to produce alloy 254. This approach is effective and also a common steelmaking method.
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Vacuum Induction Melting (VIM)
VIM is predominantly a secondary purifying process for stainless steel. Alloy 254 is melted in a vacuum where several purification techniques are used to remove the impurities and regulate the contents of the alloys.
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Vacuum Arc Remelting (VAR)
VAR is closely related to VIM only that in VAR, an electric arc is utilized for melting the feedstock in the VAR vacuum. It is like EAF but in a vacuum. VAR produces high-purity alloy 254 which provides excellent corrosion resistance.
Other uncommon methods of manufacturing this material include cold drawing, hot rolling, and welding. Manufacturers choose methods that are cost-effective, practical, and also effective for many reasons.
Working with Alloy 254
By now, you must be wondering what it’s like to work with this material. Is it easy to weld, machine, and shape? All these are valid concerns when selecting an alloy. Now, let’s explore these attributes in more detail.
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Weldability
Like most stainless steels, alloy 254 is quite responsive to welding. TIG, MIG, and stick welding methods are part of the common welding techniques that can be used to weld this material. This makes it suitable for applications where welding is inevitable.
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Machinability
Nickel and molybdenum in alloy 254 make it difficult to machine this material. As discussed earlier, these elements increase the strength and hardness of steel. Although this is a challenge, you can bypass it by using special tools. The drawback is that these tools might be relatively costly.
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Hot Working
It is somewhat effortless to work alloy 254 using heat. However, caution needs to be excised to ensure you are operating below its melting point. Applicable hot working techniques suitable for alloy 254 include forging, forming, and upsetting.
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Cold working
This working procedure is also applicable to alloy 254, although it might be challenging due to the strength of the material. Some cold working methods such as bending and rolling would require more effort and care to ensure positive results.
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Annealing
In case you need to perform annealing to increase the ductility or hardness of alloy 254, you will find it relatively doable. This heat treatment technique is particularly crucial if you intend to use the alloy in high-stress conditions.
Advantages of Alloy 254
Apart from being a super austenitic stainless steel, alloy 254 has other several benefits over its counterparts. These include;
- High-corrosion resistance: Alloy 254 can sustain high halide (halogen element environments) exposure for extended periods of time with minimal corrosion. This resistance also includes crevices and pitting.
- High strength: The ability to withstand massive force is a huge advantage. Such remarkable yield and tensile strengths add to the versatility of alloy 254.
- High-temperature resistance: The ability to maintain form and structure at high temperatures is an advantage. It gives you the freedom to use the alloy in multiple situations since thermal stability is guaranteed.
Disadvantages of Alloy 254
Amid all the glory of being the ideal stainless steel, this material has its limitations, albeit a few. They include;
- Cost: Expectedly, a product that is as versatile as alloy 254 would be costly. Again, costly is relative. The point here is the initial price to acquire the material can be considered high, with regard to grades in the same category. Regardless, the huge cost is justifiable given the value you are getting.
- Limited stock: The main components of alloy 254 (nickel and molybdenum) are hard to find, expensive, and high in demand in other industries. A combination of these factors might lower the production quantity of alloy 254, thereby limiting its availability.
Evidently, the advantages supersede the disadvantages. That means you should go ahead and proceed with the decision to use alloy 254 for your next project. If you are still unsure whether it is applicable, the following are some of the common areas where this material is largely used.
Common Applications of Alloy 254
Stainless steel can be utilized in practically every industry. However, specific grades of stainless steel, such as 254 SMO, must be utilized in particular industries to fully utilize their unique properties. Specifically, alloy 254 is best suited for use in environments with high halogen groups of elements like chlorine, fluorine, iodine, and other halides.
These environments are in industries such as：
Marine
Marine environments have high concentrations of chlorides which can corrode metals. This is where the corrosion resistance of alloy 254 comes in handy. In particular, molybdenum enhances its resistance to cracking due to stress corrosion. Some of the common uses of 254 SMO in marine environments include the making of ships, docks, and offshore platforms.
Chemical processing
Alloy 254 has a huge tolerance for various chemicals. Vessels, pipes, and reactors made using this material are able to resist pitting and corrosion caused by substances such as sulphuric, nitric, hydrochloric, and phosphoric acids. Therefore, if you produce these chemicals, consider using reactors and vessels made from alloy 254.
Pulp and paper
Corrosion resistance properties of 254 SMO also come into play in the pulp and paper industry. The manufacture of paper involves highly corrosive acids which damage equipment made of low-quality material. The excellent resistance of this super-austenitic makes it an ideal material for the pulp and paper industry.
Oil and gas
Equipment used in the oil and gas industry needs to be strong, durable, and robust. These are some of the mechanical properties of alloy 254. Such properties ensure pumps, pipelines, and storage facilities made of alloy 254 are safe and last long in these harsh environments.
Food processing
Perhaps, this is the most common application of alloy 254. As you know food processing requires non-toxic materials to guarantee consumer safety. The elements found in this alloy are non-toxic. This aspect makes 254 SMO suitable for the manufacture of food processing equipment such as mixing tanks, conveyors, and piping systems.
Other applications of alloy 254 include medical, aerospace, and construction. These are industries that would benefit from the properties of alloy 254 such as strength, non-toxicity, and durability.
Conclusion
This article has provided you with an in-depth overview of alloy 254. We covered its composition, properties, manufacture, and use to help paint a clear picture of this super austenitic stainless steel.
Undoubtedly, this grade of stainless steel ticks several boxes if you are looking for a material to use in specific projects. On top of that, it doubles as a multifaceted material for application in diverse fields. No matter the industry you are in, the properties of alloy 254 will be demanded by one piece of equipment or another.
