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In some cases, the corrosion resistance of a stainless steel depends on the material family it belongs to. But in general, the key lies in the content of the alloying element molybdenum. A rule of thumb is: the higher the molybdenum content, the more corrosion resistant the material is. Molybdenum also increases 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 Contents Many of these steels belong to the austenitic stainless steel family.
Higher chromium and molybdenum content provides better corrosion and pitting resistance than 316/316L. Low carbon content provides optimal welding characteristics.
Better corrosion resistance than 304, as well as higher strength at high temperatures. Ultra-low carbon avoids carbide precipitation when welding. Used in pumps, valves, textile and chemical equipment, and pulp, paper and marine applications.
316L is an ultra-low carbon variant that avoids carbide precipitation when welding. Used in pumps, valves, textile and chemical equipment, and pulp, paper and marine applications.
303 Free-cutting version of 304, suitable for automated machining. Corrosion resistant to atmospheric exposure, sterilizing solutions, most organic and inorganic chemicals, most dyes, nitric acid and foods.
Medium Molybdenum Content Stainless Steels
The maximum carbon content is 0.08%, which reduces intergranular corrosion normally associated with carbide precipitation when welding. It has excellent resistance to a wide range of corrosive and atmospheric exposures. 304L is an extra low carbon variant of 304 that avoids harmful carbide precipitation under extensive welding. Same corrosion resistance as 304, but slightly more limited mechanical properties.
Stabilized with Cb & Ta, it can be used in the 800-1500°F range for carbide precipitation without compromising corrosion resistance. Similar properties to 321.
440A: High carbon chromium steel designed to provide stainless steel characteristics with maximum hardness. 440A has less carbon than 440C (0.75% maximum), so in the hardened condition it is less hard, but more ductile. Capable of achieving a minimum of 55 HRC. 440C: A high carbon chromium steel that achieves the highest hardness of all standard stainless grades (Rockwell C60). When hardened and stress relieved, 440C has maximum hardness, high strength, and corrosion resistance. Capability requirement is 58 HRC.
One of the most commonly used martensitic stainless grades, 410 can be heat treated and is widely used where corrosive conditions are not severe - air, fresh water, certain chemicals, and food acids. Typical uses include valve and pump components, fasteners, cutlery, turbine components, and bushings.
410 Dual Temper: A quenched and dual tempered variant of 410 that complies with NACE MR-01-75 and API 6A PSL 3. For components in hydrogen and sulfur service.
410S: Alternative chemical variation of 410 with lower carbon content (0.08% max). Offers improved weldability and lower hardenability. Not heat treatable.
This precipitation hardening grade combines high strength and hardness with corrosion resistance similar to 304. A simple low temperature heat treatment (900-1150°F) removes scale and prevents excessive warping.
The H1150 version is solution annealed and age hardened at 1150°F for improved mechanical properties and stress corrosion cracking resistance. Double Aged H1150 is solution annealed and double aged per the procedure required by NACE MR-01-75. Used in pressure control applications in the energy industry.
A vacuum arc remelted grade with high strength and hardness. Excellent corrosion resistance coupled with superior transverse toughness. A low molybdenum grade of stainless steel 301 with high strength and good ductility when cold worked. Excellent corrosion resistance similar to 304. Can be welded by all methods suitable for stainless steel.
Welds stabilized with titanium to withstand severe corrosion. No carbide precipitation. Excellent resistance to a wide range of corrosive media. Immune to most organic chemicals, dyes and many inorganic chemicals.
For high temperature applications. High scale resistance. Superior corrosion resistance to 304. Excellent in resistance to sulfite liquids, nitric acid, nitric-sulfuric acid mixtures, acetic acid, citric acid and lactic acid.
Excellent resistance to stress corrosion cracking, good weldability, high thermal conductivity and low thermal expansion. Suitable for many high temperature applications.
Excellent toughness at low temperatures. Nonmagnetic in the annealed condition, may be slightly magnetized after cold working.
A low carbon, nitrogen treated material for sub-zero applications down to -320°F. Strength, toughness and good machinability.
Nitrogen enhanced for applications requiring good aqueous corrosion resistance. Has good wear characteristics and toughness. Yield strength is nearly 75% higher than 304.
Higher alloy content than 309 with improved properties. Better corrosion resistance than 304. Has excellent oxidation resistance. 310S (0.08% carbon max) offers improved corrosion resistance in welded components.
Originally designed for muffler stock and used for external parts in non-critical corrosion applications. Economical and easy to machine.
One of the most commonly used non-hardenable chromium types, 430 stainless steel combines good heat resistance and mechanical properties. High resistance to corrosive agents such as nitric acid, sulfur gases and many organic and food acids.
