There is no simple, universally applicable ranking for the corrosion resistance of metallic materials, as their resistance is highly dependent on the specific corrosive environment (e.g., medium type, concentration, temperature, pH value, presence of chloride ions, flow rate, etc.). The same material may be extremely corrosion-resistant in one environment but corrode rapidly in another.
However, based on the overall corrosion resistance potential exhibited by materials in a wide range of environments (especially in harsh oxidizing and reducing acids and chloride-containing environments), they can be broadly categorized into several tiers:
Tier 1: Extreme Corrosion Resistance (typically used in the most demanding environments)
Noble Metals and Their Alloys:
Platinum (Pt), Gold (Au): Extremely stable in most environments, with very high chemical inertness. Primarily used in specialized chemical equipment, electrodes, jewelry, and the electronics industry.
Tantalum (Ta): Exhibits exceptional corrosion resistance to inorganic acids (including boiling concentrated sulfuric acid, hydrochloric acid, nitric acid, and aqua regia), second only to platinum. It also has good corrosion resistance to liquid metals. Commonly used in strong acid heat exchangers, reactor linings, chemical equipment components, and medical implants (due to its biocompatibility).
Niobium (Nb): Corrosion resistance is close to tantalum but slightly inferior (especially in hot concentrated acids), with lower cost. Also used in the chemical and aerospace industries.
High Corrosion Resistance Nickel-Based Alloys:
Hastelloy C-series (e.g., C-276, C-22, C-2000): Specifically designed to resist reducing acids (such as sulfuric acid, hydrochloric acid, phosphoric acid), oxidizing acids (such as nitric acid, acids containing Fe³⁺/Cu²⁺), and pitting, crevice corrosion, and stress corrosion cracking in chloride-containing environments. Widely used in chemical, environmental (FGD), marine engineering, and pharmaceutical industries; it is one of the most versatile engineering alloys.
Inconel alloy 625/825: 625 exhibits good corrosion resistance to oxidizing acids, seawater, and high-temperature environments, with high strength; 825 is better suited for reducing acid environments. Both are resistant to localized corrosion caused by chloride ions.
Nickel-Molybdenum Alloys (e.g., Hastelloy B-series - B-2, B-3): Particularly good at resisting reducing acids (especially hydrochloric acid and sulfuric acid), but sensitive to oxidizing media (e.g., environments containing Fe³⁺, Cu²⁺, or dissolved oxygen).
Tier 2: Very High Corrosion Resistance (widely used in various industrial environments)
Titanium and Titanium Alloys:
Pure titanium (Gr 1, 2) and Ti-0.2Pd: Exhibit excellent corrosion resistance to oxidizing media (such as nitric acid, wet chlorine gas, seawater, hypochlorites), particularly known for their excellent resistance to chloride ion pitting and crevice corrosion. Widely used in seawater desalination, chemical processing, offshore platforms, swimming pool equipment, and medical implants. Their corrosion resistance to reducing acids (such as hydrochloric acid and sulfuric acid) is poor, but Ti-Pd alloys show some improvement.
Advanced Stainless Steels (Pitting Resistance Equivalent PREN > 40):
Super Duplex Stainless Steel (e.g., 2507, Zeron 100): Combines high strength with extremely high resistance to chloride ion pitting, crevice corrosion, and stress corrosion cracking. Commonly used in seawater treatment, oil and gas extraction (H₂S/CO₂ environments), chemical processing, and papermaking.
Super Austenitic Stainless Steel (e.g., 254 SMO, AL-6XN, 904L): Contains high molybdenum, high nitrogen, and high chromium, with extremely high PREN values. Their resistance to general and localized corrosion (especially pitting and crevice corrosion) far surpasses that of standard austenitic stainless steels. Used in seawater cooling systems, chemical containers, and flue gas desulfurization units.
6% Molybdenum Austenitic Stainless Steel (e.g., 254 SMO, AL-6XN): Belongs to the super austenitic category, with excellent corrosion resistance and lower cost than higher alloyed grades.
Advanced Copper-Nickel Alloys:
Copper-Nickel Alloys (e.g., 90-10 CuNi, 70-30 CuNi): Exhibit excellent corrosion resistance to seawater, brackish water, and marine atmospheres, especially resistant to erosion corrosion and biofouling. One of the standard materials for seawater pipelines, condensers, and heat exchanger tubes. Acid resistance is poor.
Tier 3: Good Corrosion Resistance (used in moderately corrosive environments)
Standard High-Alloy Stainless Steels:
Austenitic Stainless Steel (e.g., 316/316L): Contains molybdenum (2-3%), performing well in mild corrosive environments (atmospheric, freshwater, weak organic acids) and limited chloride-containing environments. One of the most widely used stainless steels. However, it corrodes in high-concentration chlorides and strong reducing acids.
Duplex Stainless Steel (e.g., 2205): Has higher strength and better resistance to chloride ion stress corrosion cracking and pitting than 316L. Used in chemical, petrochemical, and seawater treatment equipment.
Monel Alloys (400, K-500): Exhibit good corrosion resistance to seawater, neutral salt solutions, non-oxidizing acids (especially hydrofluoric acid and hot concentrated alkaline solutions), and organic media. Used in marine engineering, chemical processing, and the petroleum industry. Corrosion resistance decreases in oxygenated acids or oxidizing salt solutions.
Nickel 200/201: Exhibits excellent corrosion resistance to reducing environments and high-temperature, high-concentration caustic alkalis (NaOH/KOH). Also resistant to dry halogen gases and neutral/alkaline salt solutions. Very important in the alkali industry.
Forms a dense oxide film in atmospheric environments, exhibiting very good atmospheric corrosion resistance. However, its corrosion resistance is poor in chloride-containing environments (such as seawater), strong acids, and strong alkalis.
Tier 4: General Corrosion Resistance (used in mild environments or requiring protective measures)
Standard Stainless Steel:
Austenitic Stainless Steel (such as 304/304L): Good corrosion resistance in oxidizing environments (such as nitric acid) and clean air, fresh water. Sensitive to chloride-containing environments (prone to pitting, crevice corrosion, stress corrosion cracking). Extremely wide range of applications.
Ferritic Stainless Steel (such as 430): Superior to 304 in atmospheric corrosion resistance and stress corrosion cracking resistance, but with poorer overall corrosion resistance and weldability, sensitive to pitting. Often used for decoration and automotive exhausts.
Martensitic Stainless Steel (such as 410, 420): High strength, but relatively poor corrosion resistance (inferior to 304), mainly used where strength, hardness and a certain degree of corrosion resistance are required (such as cutting tools, shafts, pump parts).
Has a certain degree of corrosion resistance in the atmosphere, soil, and neutral water (especially gray cast iron), but is generally far lower than stainless steel. Easily corroded in acids and alkalis. Commonly used for infrastructure components and water pipes (requires lining).
Carbon Steel/Low Alloy Steel:
Significant corrosion (rusting) occurs in the atmosphere, soil, and fresh water, with poor corrosion resistance. It is the most widely used engineering material, but it must rely on coatings (paint, galvanizing), cathodic protection or corrosion inhibitors to prevent corrosion. Rapid corrosion in acids, alkalis, and salt water.
Environment Determines Everything: There is no absolute champion of "most corrosion-resistant." Material selection must be based on the specific service environment. Tantalum is invincible in strong acids, but inferior to nickel in strong alkalis; titanium is excellent in seawater, but inferior to Hastelloy B in hot concentrated sulfuric acid.
Localized Corrosion is Key: For materials such as stainless steel, aluminum, and titanium that rely on passive films, the ability to resist pitting, crevice corrosion, and stress corrosion cracking is often more important than resisting uniform corrosion, especially in chloride-containing environments.
Cost-Performance Trade-off: First and second-tier materials (precious metals, advanced nickel-based alloys, titanium, super stainless steel) have excellent performance, but are expensive. Engineering applications need to find a balance between performance requirements and cost.
Other Factors: Mechanical properties (strength, toughness), processability, weldability, wear resistance, thermal expansion coefficient, magnetism, biocompatibility, etc., should also be considered.
For the most demanding chemical environments (strong reducing acids, mixed acids, high-temperature high-concentration chloride media), Hastelloy C series, tantalum, and advanced nickel-based alloys are preferred.
For seawater, chloride-containing oxidizing environments, titanium and titanium alloys, super duplex/austenitic stainless steel, and copper-nickel alloys are the preferred choices.
For general industrial atmospheres, fresh water, and weakly corrosive chemical environments, 316L, 2205 duplex steel, 304L, etc., stainless steels are commonly used.
For atmospheric exposure structures, carbon steel + coating, galvanized steel, aluminum alloy, and standard stainless steel (304/316) are mainstream.
Carbon steel/cast iron has the lowest cost, but corrosion protection measures must be applied.
In practical engineering applications, it is strongly recommended:
Consult authoritative corrosion databases (such as NACE Corrosion Data Survey, DECHEMA Corrosion Handbook).
Conduct laboratory simulation tests or on-site coupon tests.
Consult material suppliers or corrosion engineers. Do not make decisions based solely on theoretical rankings, as actual corrosive environments are often far more complex than imagined.
It is hoped that this ranking, based on extensive industrial experience, will provide you with valuable reference! Selecting the appropriate corrosion-resistant material is a key step in engineering design and requires a comprehensive consideration of various factors.
