Each type of stainless steel has distinct properties that best suit specific applications. For example, the 400 series stainless steels corrode and rust under certain conditions. With a higher carbon content, their martensitic crystalline structure gives end products higher strength and makes them more resistant to wear. For those who need to work with it or otherwise utilize this alloy, understanding what 400 series stainless steel is and what it can do will help find the best stainless steel for the application.
What Is 400 Series Stainless Steel?
While, like all steels, it’s made mainly from iron, the remaining elemental makeup of the 400 series stainless steels is from 11 to 27 percent chromium, around 1 percent carbon, and a maximum of 2.5 percent nickel. With predominantly martensitic structures, these steels vary widely in their hardness and strength. These stainless steels resist corrosion less well than the 300 series, but they’re stronger and often offer a more effective solution, depending on the conditions the alloy must withstand. When choosing the best 400 series stainless steel for the application, it’s essential to consider each type’s general properties, resistances, and working methods.
Now, let’s look at the more common stainless steels in the 400 series, their applications, and the best treatment methods.
409 Stainless Steel
409 stainless steel is a general-purpose alloy containing 11 percent chromium, with titanium used as a stabilizer. As ferritic stainless steel, it’s primarily used for vehicle exhaust systems, though it also has other industrial uses. The alloy’s chromium content is the minimum required to form the passive corrosion-resistant layer for which stainless steel is known. Combining corrosion resistance at elevated temperatures, 409 steel is a cost-effective alloy with good formability and medium strength.
As with all other stainless steels, it resists corrosion much better than carbon steel, for which it often serves as a replacement in specific challenging environments. Used for its ability to oxidize in high temperatures and resist corrosion, 409 stainless steel offers an advantage in many situations. Unlike other stainless steel, it’s used due to its mechanical and other properties rather than appearance.
Applications include:
- Catalytic converters
- Farm equipment
- Furnace parts
- Hangers
- Mufflers
- Structural supports
- Tailpipes
- Transformer casings
- Tubing for heat exchangers
- Vehicle exhaust systems
The alloy’s resistance to corrosion from exhausts and other situations that produce gas-related corrosion makes it ideal for use within vehicles, especially at points where the steel interacts with gasses. However, the light surface rust it develops that then prevents further corrosion makes this steel unappealing visually. Considering heat treatments, the alloy generally resists scaling when exposed for short periods to temperatures up to 1499°F (815°C), while it can operate continuously without trouble up to 1247°F (675°C).
410 Stainless Steel
Another general-purpose alloy, 410 stainless steel is martensitic and used for components that experience high stress. Resisting corrosion well, 410 stainless steel is also known for its hardness and strength. It contains chromium at a percentage of at least 11.5 percent, just enough to make it useful as a corrosion-resistant alloy in certain environments, including those containing mild chemicals or steam. Often provided in machinable but hardened condition for applications requiring moderate resistance to corrosion and heat, along with high strength, this steel grade resists corrosion best when hardened, tempered and polished.
Applications include:
- Blades for gas and steam turbines
- Bolts, nuts and screws
- Components for pumps, including shafts and valves
- Cutlery
- Dental and surgical instruments
- Hardened steel balls and seats for
- Kitchen utensils
- Mine ladder rugs
- Nozzles
- Oil well pump components like hardened steel balls and seats
410 steel resists corrosion well in mildly corrosive environments, though proper cleaning must be done after use to ensure good performance; this includes resistance against milder mineral and organic acids. When it comes to welding, this alloy can be readily welded via conventional techniques. However, to keep the risk of cracking down, it’s best to preheat workpieces to between 350-400°F (177-204°C), with annealing also recommended to preserve maximum ductility. For heat treatments, temperature range should be between 2000-2200°F (1093-1204°C), though the alloy shouldn’t be worked below 1650°F (899°C).
410S Stainless Steel
As a low-carbon iteration of 410 stainless steel, 410S has a 12 percent chromium content with properties that minimize austenite formations at higher temperatures, which keep the alloy from hardening. As a martensitic 400 series stainless steel, when cooled rapidly under specific conditions, it stays ductile and soft. This feature keeps the steel from hardening and prevents cracking when welded or exposed to high temperatures. When annealed, 410S is ferritic, exhibiting similar corrosion resistance to the regular 410 grade, though it resists oxidation better.
Applications include:
- Annealing boxes
- Distillation trays
- Equipment used in petroleum refining
- Gate valves
- Heat exchangers
- Mining and ore processing machinery
- Partitions
- Petrochemical processing equipment
- Press plates
- Quenching racks
- Stainless steel columns
- Thermal processing equipment
The 410S grade resists oxidation well and can continually operate at temperatures as high as 1300°F (705°C). However, above 1500°F (811°C), scaling becomes excessive. The alloy also resists corrosion from alkalis, atmospheric conditions, certain chemicals, and fresh water, and milder mineral and organic acids. When properly cleaned, the alloy performs well when exposed to chlorides during activities like food preparation.
Due to its unique properties, 410S stainless steel can’t be hardened with heat treatments. To anneal the alloy, temperatures need to reach a narrow temperature range of 1600-1650°F (871-899°C), after which it should be air-cooled to relieve any stress from cold working. To keep the alloy from becoming overly brittle, it shouldn’t be exposed to temperatures over 2000°F (1093°C). Should large grains be found in the steel after cold-working, annealing temperatures should instead fall between 1200-1350°F (649-732°C).
When it comes to welding, joint fusion and resistance methods can be used. To avoid weld fractures due to brittleness, special attention during the process should occur to maintain low weld heat input, minimize discontinuities and intermittently warm the workpiece sufficiently before forming. 410S stainless steel won’t weld as well as the 409 grade, as additions to the alloy require higher heat when welded.
410HT Stainless Steel
This alloy is also martensitic as the general-purpose, heat-treated version of 410 stainless steel. Used in situations where corrosion isn’t a significant concern, it too contains just enough chromium (11.5 percent) to resist corrosion under milder conditions.
Applications include:
- Blades for gas and steam turbines
- Bolts, nuts and screws
- Cutlery
- Dental and surgical instruments
- Hardened steel balls
- Kitchen utensils
- Mine ladder rugs
- Nozzles
- Oil well pump seats
- Parts and shafts for pumps and valves
Characteristics of this 400 series stainless steel alloy concerning corrosion, welding and heat treatments are essentially the same as conventional 410 stainless steel.
416 Stainless Steel
Considered the first free-machining stainless steel, this alloy has the highest machinability of any other type of stainless steel. However, 416 stainless steel is most machinable at a subcritical phase in an annealed condition. As a martensitic alloy with 13 percent chromium, it gets harder and more corrosion-resistant when heat treated. Though not as resistant as ferritic or austenitic stainless steel, 416 resists rust and other corrosion, while it has considerable strength when hardened and tempered. Its heat-treated version, 416HT, has high machinability and magnetic properties and low surface friction.
Applications include:
- Components for automatic screw machines
- Electric motors
- Gears
- Nuts and bolts
- Pumps
- Studs
- Valves
- Washing machine parts
This 400 series stainless steel resists corrosion from basic and neutral salts, most atmospheric conditions, natural food acids, and waste products. With a high sulfur content, 416 isn’t suitable for marine or other environments high in chlorides. It’s also less resistant than austenitic stainless steel grades and ferritic alloys composed of 17 percent chromium. The alloy must be hardened with smooth surface finishing to achieve the best corrosion resistance.
This stainless steel resists scaling at intermittent temperatures up to 1400°F (760°C), and is capable of continuous operation in temperatures reaching 1247°F (675°C). However, it doesn’t weld well, so if welding is needed, it should be done with a 410 steel alloy low in hydrogen electrodes and preheated to a range of 392-572°F (200-300°C). After welding, this steel should be annealed or hardened immediately or heated to relieve stress at a temperature range of 1202-1247°F (650-675°C).
416HT Stainless Steel
This is the heat-treated version of 416 stainless steel, with high strength and hardness but lower corrosion resistance. It, too, has better machinability than austenitic steel types, with magnetic and low friction qualities to reduce seizing and galling.
Applications include:
- Electric motors
- Gears
- Nuts and bolts
- Parts for automatic screw machines
- Pumps
- Studs
- Valves
- Washing machine parts
Corrosion and heat resistance properties are identical to regular 416 stainless steel, while its weldability is similarly poor.
430 & 430F Stainless Steels
This grade combines beneficial mechanical characteristics with decent formability and corrosion resistance properties for a ferritic alloy in the 400 series. 430 stainless steel is used in specific chemical applications. However, it’s primarily used for appliance components and automotive trim.
The free-machining stainless steel type is 430F, which comes in a bar form used for 434 stainless steel. 434 has all the beneficial properties of the 430 grade, with molybdenum added to improve corrosion resistance, including for pitting corrosion. The 430 series has specific qualities that make it the go-to stainless steel for coil, plate, or sheet.
Applications for 430 stainless steel include:
- Automotive trim
- Cabinet panels in refrigerators
- Chimney liners
- Dishwasher linings
- Element supports
- Fasteners
- Lashing wire
- Stove trim rings
Specific applications for 430F stainless steel include:
- Repetitively machined parts
The 430 grade can resist an array of corrosive conditions, such as nitric and certain organic acids, though it’s the most corrosion-resistant when buffed or highly polished. Regarding pitting and crevice corrosion, the 430 stainless steel resists similarly to the 304 grade, though 430F has much reduced resistance due to its higher sulfur content. The 430 alloy also has very high resistance to cracking, as per ferritic stainless steel grades.
430 stainless steel can resist oxidation intermittently at temperatures approaching 1598°F (870°C), and continuously at temperatures reaching 1499°F (815°C). The alloy can become brittle after sustained heating between 752-1112°F (400-600°C) once it cools to room temperature. However, annealing can eliminate this effect.
Still looking to answer the question, “What is 400 series stainless steel?” To learn more about our products and services, we invite you to contact the experts at Atlantic Stainless today.
