Stainless steel, known primarily for its corrosion resistance, is used in a wide variety of applications. The diverse range of grades allows it to accommodate various applications across many different industries. However, having so many grades requires the know-how to select the appropriate one for the job.
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If the application requires good formability, avoid the martensitic group of stainless steels. Try an austenitic grade such as 304 or a ferritic grade such as 430. Martensitic stainless steels like 410 tend to be brittle and are not readily formable. Austenitic stainless steels are usually the best choice when it comes to formable stainless steels.
Welding stainless steel is very different than welding carbon steel, and can lead to problems such as intergranular corrosion, hot cracking and stress corrosion cracking. The most weldable stainless steels are typically in the austenitic group. When welding austenitic stainless steels, grades such as 304L or 347 should be used. Grade 304L has lower carbon while 347 has niobium stabilizers added to it which help to deter intergranular corrosion. Ferritic stainless steels such as grade 430 or grade 439 are also readily weldable, as are Duplex stainless steels. Martensitic stainless are generally not suitable for welding, however, some martensitic stainless steel grades with lower amounts of carbon can be welded. With precipitation hardened stainless steels, care should be taken to ensure that the original mechanical properties are not compromised during the welding process.
If machining is required, special considerations must be accounted for when working with stainless steel. Most grades of stainless steel can be machined, however, stainless steel is very susceptible to work hardening. The machining process must be optimized to work at a rate that helps alleviate this issue, and the tools used for machining must also be kept in good working condition. Similar to carbon steels, sulfur can be added to increase machinability; grade 303 is an example of this. It is very similar to grade 304 except that sulfur has been added to it for machining purposes. Grade 416 is example of a ferritic stainless steel with added sulfur.
Stainless steel is usually chosen for its corrosion resistant properties, but it is important to know that different grades provide different amounts of corrosion resistance. Austenitic stainless steels generally provide the most corrosion resistance because of their high amounts of chromium. This makes grade 304 an excellent choice when corrosion resistance is important. Grade 316 is similar to grade 304, but it has molybdenum as part of its chemical makeup, further increasing its corrosion resistance. Ferritic stainless steels and martensitic are generally more affordable than austenitic stainless steel because they have less nickel and sometimes less chromium than austenitic stainless steels, which can result in a loss of corrosion resistance. Duplex stainless steels can be used to avoid the stress corrosion cracking associated with austenitic stainless steels.
If the stainless steel is going to be subjected to heat treatment, it is important to know how the various grades of stainless steel can be affected. For the most part, austenitic stainless steels and ferritic stainless steels are non-hardenable when heat treated. The heat treatable stainless steels are typically martensitic or precipitation hardened. Examples of these are grade 440C and 17-4 PH, respectively.
Very high strengths can be achieved with martensitic stainless steels, like grade 440C; and precipitation hardened stainless steels, like grades 17-4 PH and 15-5 PH. Austenitic stainless steels, such as grade 316, can provide high strengths as well, though not as high as the martensitic grades. Austenitic stainless steels also have more nickel than other stainless steels, so a grade like 316 will have greater toughness and ductility than ferritic and martensitic stainless steels. Duplex stainless steels can provide ferritic stainless steel properties while still maintaining a ductility and a toughness close to austenitic stainless steels.
Sometimes the best way to find out what grade of stainless steel should be used is to see what has been used in the past. Here are some examples of where certain grades of stainless steel are used.
Ferritic Stainless Steels:
Austenitic Stainless Steels:
Martensitic Stainless Steels:
Precipitation Hardened Stainless Steels:
Duplex stainless steels:
Disclaimer: Please note this information is not to be used for design purposes, and in no event shall MSFFC be liable for any damages arising from the misuse of this information.
From composition to form, a range of factors impact the characteristics of stainless steel products. One of the most important considerations is which grade of steel to use.
This will determine a range of characteristics and, ultimately, both the cost and lifespan of your stainless steel products.
So how do you know where to start?
While every application is unique, these 7 questions highlight critical considerations to help you narrow down your options and find the grades best suited to your needs or application.
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When you think of stainless steel, the first things that come to mind are probably resistance to acids and chlorides--such as those found in industrial applications or marine environments. However, temperature resistance is an important consideration as well.
If you need corrosion resistance, you’ll want to avoid ferritic and martensitic steels. Ideal stainless steel grades for corrosive environments include austenitic or duplex alloys such as grades 304, 304L, 316, 316L, , and 904L.
For high-temperature environments, austenitic grades are often best. Finding a grade with high chromium, silicon, nitrogen, and rare earth elements will further alter the steel’s ability to withstand high temperatures. Common grades for high-temperature environments include 310, S, and 446.
Austenitic steel grades are also ideal for low-temperature or cryogenic environments. For added resistance, you can look at low carbon or high nitrogen grades. Common grades for low-temperature environments include 304, 304LN, 310, 316, and 904L.
A steel with poor formability will become brittle if overworked and offer lower performance. In most cases, martensitic steels are not recommended. Furthermore, steel with low formability might not hold its shape when complex or intricate forming is required.
When choosing a steel grade, you’ll want to consider the form in which you’d like it delivered. Whether you want rods, slabs, bars or sheets will limit your options. For example, ferritic steels are often sold in sheets, martensitic steels are often sold in bars or slabs, and austenitic steels are available in the widest range of forms. Other steel grades available in a variety of forms include 304, 316, 430, , and 3CR12.
Machining isn’t typically a problem. However, work hardening can produce unintended results. The addition of sulfur can improve machinability but reduces formability, weldability and corrosion resistance.
This makes finding a balance between machinability and corrosion resistance a critical consideration for most multistage stainless steel fabrication processes. Depending on your needs, grades 303, 416, 430, and 3CR12 offer a good balance from which to narrow options further.
Welding stainless steel can lead to trouble—including hot cracking, stress corrosion cracking, and intergranular corrosion—depending on the grade of steel used. If you plan to weld your stainless steel, austenitic alloys are ideal.
Low carbon grades can further help with weldability while additives, such as niobium, can stabilize alloys to avoid corrosion concerns. Popular grades of stainless steel for welding include 304L, 316, 347, 430, 439 and 3CR12.
If your application requires heat treatment, you must consider how the various grades of steel respond. The final characteristics of certain steels are drastically different before and after heat treatment.
In most cases, martensitic and precipitation hardening steels, such as 440C or 17-4 PH, offer the best performance when heat treated. Many austenitic and ferritic stainless steels are non-hardenable once heat treated and therefore are not ideal options.
Steel strength is an essential factor to consider to maximize safety. Yet, overcompensating can lead to unneeded cost, weight, and other wasteful factors. Strength characteristics are loosely set by the family of steel with further variations available in different grades.
For example:
All of the previous considerations feed into the most important question in choosing a stainless steel grade—lifetime cost. Matching the stainless steel grades to your intended environment, usage and requirements, you can ensure long-lasting performance and exceptional value.
Take care to analyze how the steel will perform over the intended period of use and what costs might be involved in maintenance or replacement before deciding. Limiting costs upfront might result in far more spending over the life of your project, product, structure, or other application.
Of course, if the initial price is too great, you might need to make compromises. Finding a balance is essential to both short-term and long-term success. But by considering these seven points, you’re eliminating potential hazards and setting the foundation for choosing the optimal solution for your needs.
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