Is Stainless Steel Corrosion Resistant?

In some instances, it depends on the family of stainless steel grades. But for the most part it comes down to the  level of the alloying element molybdenum. A general rule of thumb says that the higher the presence of molybdenum, the more corrosion resistant the grade. Molybdenum also increases the temperature strength of the grade.

Let’s explore many of the commonly used grades of stainless steel and determine their level of corrosion resistance based on the presence of molybdenum.

Use this tool to determine the corrosion resistance of the various grades of stainless, as determined by the scale to the right of each group (magnetic and non-magnetic grades). Consider it a useful resource when evaluating alternative grades.

Stainless Steel Grades with Higher Levels of Molybdenum

Many of these grades fall in the austenitic family of grades. 

317
Higher level of chrome and moly provide better corrosion resistance and pitting resistance than 316/316L. Low carbon provides optimum welding characteristics.

316
Better corrosion resistance than 304, plus higher strength at elevated temperatures. Extra low carbon to avoid carbide precipitation from welding. Used for pumps, valves, textile and chemical equipment, and pulp/paper and marine applications.

316L is an extra low carbon variation to avoid carbide precipitation from welding. Used for pumps, valves, textile and chemical equipment, and pulp/paper and marine applications.

303
Free-machining version of 304 for automatic machining. Corrosion-resistant to atmospheric exposures, sterilizing solutions, most organic and inorganic chemicals, most dyes, nitric acid, and foods.

Stainless Steel Grades with Moderate Levels of Molybdenum

304
The 0.08 max carbon content reduces intergranular corrosion usually associated with carbide precipitation that can occur during welding. It offers excellent resistance to a wide range of corrosive and atmospheric exposures.

304L is an extra low carbon variation of 304 avoids harmful carbide precipitation under extensive welding. Same corrosion-resistance as 304, with slightly more limited mechanical properties.

347
Stabilized with Cb & Ta for use in the carbide precipitation range of 800-1500°F without impairment of corrosion-resistance. Characteristics similar to 321.

440
440A: High-carbon chromium steel designed to provide stainless properties with maximum hardness. 440A with lower carbon (0.75 max) than 440C results in lower hardness but greater toughness in the hardened condition. Capable of 55 min HRC.

440C: High-carbon chromium steel attains highest hardness (Rockwell C60) of any standard stainless grade. When hardened and stress-relieved, 440C has maximum hardness plus high strength and corrosion-resistance. Capability requirements of 58 HRC.

410
As one of the most commonly used martensitic grades of stainless steel, 410 is heat-treatable and widely used where corrosive conditions are not severe—air, fresh water, some chemicals and food acids. Typical uses include valve and pump parts, fasteners, cutlery, turbine parts and bushings.

410 Double Tempered: Quenched and double-tempered variation of 410 conforming to NACE MR-01-75 and API 6A PSL 3. For parts used in hydrogen-sulfide service.

410S: Alternative chemistry variation of 410 with lower carbon (0.08 max). Offers improved weld ability and lower harden ability. Not heat treatable.

17-4
This precipitation hardening grade combines high strength and hardness with corrosion-resistance similar to 304. Simple low-temperature heat treatment at 900-1150°F eliminates scaling and prevents excessive warpage.

H1150 version is solution-annealed and age-hardened at 1150°F to improve mechanical properties and resistance to stress-corrosion cracking.

Double-aged H1150 is solution-annealed and double-age hardened to procedures required by NACE MR-01-75. Used in pressure-control applications in the energy industry.

15-5
A vacuum arc remelt grade with high strength and hardness. Excellent corrosion-resistance plus superior transverse toughness.

Stainless Steel Grades with Low Levels of Molybdenum

301
High strength and good ductility when cold-worked. Excellent corrosion resistance, comparable to 304. Readily weldable by all methods suitable for stainless.

321
Stabilized with titanium for weldments subject to severe corrosion. No carbide precipitation. Excellent resistance to a variety of corrosive media. Immune to most organic chemicals, dyestuffs and many inorganic chemicals.

309
Used in high-temperature application. High-scale resistance. Superior corrosion-resistance to 304. Excellent in resisting sulfite liquors, nitric acid, nitric-sulfuric mixtures, acetic, citric and lactic acids.

439
Excellent resistance to stress corrosion-cracking, good weldability, high thermal conductivity, and low thermal expansion. Ideal for many high-temperature applications.

201

Excellent toughness at low temperatures. Non-magnetic in the annealed condition, it may become slightly magnetic after cold-working.

201N is a low carbon, nitrogen-treated for sub-zero application down to -320°F. Strength, toughness, and good fabrication.

Nitronic 30

Nitrogen-strengthened for applications requiring a good level of aqueous corrosion resistance. Has good wear characteristics and good toughness. Almost 75% higher yield strength than 304.

310
Higher alloy content with improved characteristics than 309. Corrosion-resistance better than 304. Excellent oxidation resistance. 310S (0.08 max carbon) offers improved corrosion resistance in welded parts.

409
Originally designed for muffler stock and used for exterior parts in non-critical corrosive applications. Economical and easily fabricated.

430
One of the most widely used of the non-hardenable chromium types, 430 stainless steel combines good heat-resistance and mechanical properties. High resistance to corrosives like nitric acid, sulfur gases and many organic and food acids.