Stainless steel, which is best known for its corrosion resistance, is used in a wide range of applications. Because of the wide range of grades available, it can be used for a wide variety of applications across a wide range of industries. Having too many grades, however, necessitates the need to pick the best one for the job.
Here is a guide to consider when choosing a stainless steel grade:
- Does it need to have good formability?
- Does it need to be welded?
- It does need to be machined?
- What level and form of corrosion resistance is desired?
- Does it need to be heat treated?
- What are the physical requirements?
Does the stainless steel need to have good formability?
Avoid the martensitic category of stainless steel if the application demands strong formability. Try an austenitic grade like 304 or a ferritic grade like 430. Martensitic stainless steels, such as 410, are brittle and difficult to mold. When it comes to formable stainless steels, austenitic stainless steels are typically the better option.
Does the stainless steel need to be welded?
Welding stainless steel differs greatly from welding carbon steel which can result in problems such as intergranular corrosion, hot cracking, and stress corrosion cracking. Austenitic stainless steels are usually the most weldable. Grades such as 304L or 347 can be used for welding austenitic stainless steel. Grade 304L contains less carbon, whereas 347 contains niobium stabilizers, which help to prevent intergranular corrosion. Welding is also possible for ferritic stainless steels such as grade 430 or Stainless Steel 409m Plates, as well as Duplex stainless steels. Martensitic stainless steels are normally unsuitable for welding; however, some martensitic stainless steel grades with lower carbon content can be welded. When welding precipitation-hardened stainless steel, care should be taken to ensure that the original mechanical properties are not affected.
Does the stainless steel need to be machined?
When dealing with stainless steel, special precautions must be made if machining is needed. Most stainless steel grades can be machined; nevertheless, stainless steel is highly vulnerable to work hardening. The machining process must be optimized to work at a pace that alleviates this problem, and the machining tools must also be maintained in good working conditions. Similar to carbon steel, sulfur can be added to improve machinability; grade 303 is an example of this. It is somewhat similar to grade 304 except for the addition of sulfur for machining purposes. Grade 416 is ferritic stainless steel with sulfur added.
What level and form of corrosion resistance is desired?
Stainless steel is commonly selected for its corrosion-resistant properties, although it is important to understand that different grades have varying degrees of corrosion resistance. Because of their high chromium content, austenitic stainless steels have the best corrosion resistance. When corrosion resistance is essential, grade 304 is an excellent option. Grade 316 is similar to grade 304, but it contains molybdenum as part of its chemical composition, which increases corrosion resistance. Ferritic and martensitic stainless steels are usually less expensive than austenitic stainless steels since they have less nickel and, in some cases, less chromium, which can result in a lack of corrosion resistance. Duplex stainless steels should be used to prevent stress corrosion cracking, as is common in austenitic stainless steels.
Does the stainless steel need to be heat treated?
If the stainless steel is to be heat-treated, it is critical to understand how the different grades of stainless steel will be affected. When heat-treated, austenitic and ferritic stainless steels are generally non-hardenable. Heat-treatable stainless steels are usually martensitic or precipitation hardened. Grade 440C and 17-4 PH are two examples.
What are the physical requirements?
Martensitic stainless steels, such as grade 440C, and precipitation-hardened stainless steels, such as grades 17-4 PH and 15-5 PH, can reach exceptionally high strengths. Austenitic stainless steels, such as grade 316, can also have high strengths, but not to the same extent as martensitic grades. Austenitic stainless steels also have more nickel than other stainless steels, so 316 has better hardness and ductility than ferritic and martensitic stainless steels. Duplex stainless steels can have ferritic stainless steel properties while also having ductility and hardness similar to austenitic stainless steels.
