Knowledge

In some cases, the corrosion resistance of stainless steel depends on the material series it belongs to. But generally speaking, the key lies in the content of the alloying element molybdenum. A rule of thumb is that the higher the molybdenum content, the stronger the corrosion resistance of the material. Molybdenum can also enhance the material's strength at high temperatures. Let's explore many commonly used stainless steel grades and determine their corrosion resistance levels based on the presence of molybdenum.

 

Stainless steel materials with high molybdenum content

Many of these steels belong to the austenitic stainless steel series.

303

The free-cutting version of 304 is suitable for automatic processing. It is resistant to atmospheric exposure, sterilizing solutions, most organic and inorganic chemicals, most dyes, nitric acid and food.

317

Higher chromium and molybdenum contents provide better corrosion resistance and pitting resistance than 316/316L. The low carbon content offers the best welding characteristics.

316

It has better corrosion resistance than 304 and higher strength at high temperatures. The ultra-low carbon content can prevent carbide precipitation during welding. It is used in pumps, valves, textile and chemical equipment, as well as in pulp and paper and marine applications.

316L is an ultra-low carbon variant that can prevent carbide precipitation during welding. It is used in pumps, valves, textile and chemical equipment, as well as in pulp and paper and marine applications.

 

Stainless steel materials with medium molybdenum content 304

The maximum carbon content is 0.08%, reducing intergranular corrosion typically associated with carbide precipitation during welding. It has excellent resistance to various corrosive and atmospheric exposures.

304L is an ultra-low carbon variant of 304, which can prevent harmful carbide precipitation during extensive welding. It has the same corrosion resistance as 304, but with slightly limited mechanical properties.

347

Stabilized by Cb & Ta, it can be used in the carbide precipitation range of 800 - 1500°F without compromising corrosion resistance. Its properties are similar to those of 321.

440

440A: High carbon chromium steel, designed to provide the stainless steel characteristics with maximum hardness. The carbon content of 440A is lower than that of 440C (up to a maximum of 0.75%), thus, it has lower hardness in the hardened state but higher toughness. It can achieve a minimum of 55 HRC.

 

440C: High carbon chromium steel, achieving the highest hardness among all standard stainless steel grades (Rockwell C60). When hardened and stress relieved, 440C offers maximum hardness, high strength and corrosion resistance. The required hardness is 58 HRC.

410

As one of the most commonly used martensitic stainless steel grades, 410 can be heat-treated and is widely used in environments with less severe corrosion conditions - air, fresh water, certain chemicals and food acids. Typical applications include valve and pump components, fasteners, cutlery, turbine parts and bushings.

410 Double Tempered: A variant of 410 that has been quenched and double tempered, conforming to NACE MR-01-75 and API 6A PSL 3. It is used for components in hydrogen sulfide service.

410S: An alternative chemical variant of 410 with a lower carbon content (max 0.08%). It offers improved weldability and lower hardenability. It cannot be heat-treated.

17-4

This precipitation hardening grade combines high strength and hardness with corrosion resistance similar to 304. A simple low-temperature heat treatment (900-1150°F) can remove scale and prevent excessive warping.

The H1150 version is solution annealed and aged at 1150°F to improve mechanical properties and resistance to stress corrosion cracking.

Double-aged H1150 is solution annealed and double-aged according to the procedure specified in NACE MR-01-75. It is used for pressure control applications in the energy industry.

Vacuum arc remelting grade, with high strength and hardness. Excellent corrosion resistance combined with superior transverse toughness.

 

Low-molybdenum content stainless steel grades 301

It has high strength and good ductility when cold worked. It has excellent corrosion resistance similar to 304. It can be welded by all methods suitable for stainless steel.

321

Weld seams stabilized with titanium can withstand severe corrosion. There is no carbide precipitation. It has excellent resistance to various corrosive media. It is immune to most organic chemicals, dyes and many inorganic chemicals.

309

Suitable for high-temperature applications. High resistance to pitting. Superior corrosion resistance compared to 304. Performs exceptionally well in resisting sulfite solutions, nitric acid, nitric-sulfuric acid mixtures, acetic acid, citric acid, and lactic acid.

439

It has excellent resistance to stress corrosion cracking, good weldability, high thermal conductivity and low thermal expansion. It is suitable for many high-temperature applications.

201

It has excellent toughness at low temperatures. It is non-magnetic in the annealed state and may be slightly magnetic after cold working.

201N is a low-carbon, nitrogen-treated material for cryogenic applications down to -320°F. It offers strength, toughness and good formability.

 

Nitronic 30

Nitrogen-enriched, suitable for applications requiring good resistance to water corrosion. It features excellent wear resistance and toughness. The yield strength is nearly 75% higher than that of 304.

310

Alloy content is higher than 309, with improved properties. Corrosion resistance is superior to 304. It has excellent oxidation resistance. 310S (with a maximum carbon content of 0.08%) provides enhanced corrosion resistance in welded components.

409

Originally designed for muffler inventory and used for non-critical corrosion applications on external components. Economical and easy to process.

430

As one of the most commonly used non-hardening chromium types, 430 stainless steel combines good heat resistance and mechanical properties. It has high resistance to corrosive substances such as nitric acid, sulfur gas, and many organic and food acids.

 

Vigor has more than 20 years of experience in producing stainless steel castings and forgings. If anything we can help and any parts you need to develop, please feel free to contact us at info@castings-forging.com