Views: 72 Author: Shirley Publish Time: 2025-06-30 Origin: Site
What is stainless steel 304 or 316? What is the difference between them and what does each have to offer? The ASTM 304 and 316 each have advantages and disadvantages. Before choosing a company for a metal project, it is important to understand your options.
This article introduces the difference of physical properties, chemical properties, mechanical properties and application fields of 304 and 316 stainless steel, helping you understand the basic knowledge of Typical Stainless Steel.
Type 304 stainless steel—also known as 18-8 stainless (18% chromium, 8% nickel) or by its UNS designation S30400—is the most widely produced and consumed stainless steel grade in the world. It belongs to the austenitic family, meaning its crystal structure is face-centered cubic (FCC) at room temperature, which gives it excellent ductility, formability, and weldability.
304 achieves corrosion resistance through its chromium content (18-20%), which forms a self-healing passive chromium oxide (Cr2O3) film on the surface. The nickel content (8-11%) stabilizes the austenitic structure, preventing the formation of brittle martensite during cold working and providing toughness at cryogenic temperatures. Carbon is kept at 0.08% maximum to limit sensitization during welding.
The "L" variant, 304L, reduces carbon to 0.030% maximum, virtually eliminating sensitization and making it the preferred choice for welded components. The "H" variant, 304H, raises carbon to 0.04-0.10% for improved high-temperature creep strength.
304 is the default stainless steel for a vast range of applications: kitchen sinks, cookware, architectural trim, elevator interiors, food and dairy equipment, chemical storage tanks, automotive trim, brewery mash tuns, and household appliances. Its combination of good corrosion resistance, excellent formability, moderate strength, and low cost makes it the first grade to consider for any non-aggressive environment. It is specified in ASTM A240 (plate/sheet/strip), A276 (bar), A312 (pipe), A269/A270 (tubing), and A313 (wire).
Type 316 stainless steel (UNS S31600, EN 1.4401) is the second most common austenitic grade and the premium upgrade from 304. It shares the same austenitic crystal structure and similar chromium-nickel base but adds 2-3% molybdenum—the single alloy addition that defines its superior performance in corrosive environments.
Molybdenum serves three functions: (1) it increases the pitting resistance equivalent number (PREN) from ~18 to ~24, raising the chloride threshold for pit initiation by approximately 44%; (2) it enhances resistance to crevice corrosion in stagnant chloride environments; and (3) it improves resistance to sulfuric acid, phosphoric acid, and other non-oxidizing acids. The chromium is slightly lower (16-18% vs. 18-20%) and nickel is slightly higher (10-14% vs. 8-11%) to maintain phase stability with the molybdenum addition.
As with 304, the "L" variant (316L, UNS S31603, EN 1.4404) is the standard for welded applications due to its 0.030% max carbon. The "Ti" variant (316Ti) uses titanium stabilization instead of low carbon for applications requiring both weldability and high-temperature strength. The "H" variant (316H) has higher carbon for creep resistance.
316 is specified wherever chlorides, salt spray, or aggressive chemicals are present: marine fasteners and fittings, coastal architectural cladding, pharmaceutical process equipment, food processing with salt exposure (brine, sauces, seafood), chemical plant heat exchangers, medical implants and surgical instruments, brewery fermenters, and nuclear reactor components. It is governed by the same ASTM specifications as 304 (A240, A276, A312, A269/A270, A313).
The chemical composition difference between 304 and 316 is small in percentage terms but enormous in performance impact. The table below presents the full composition per ASTM A240.
Element | Type 304 (%) | Type 316 (%) | Function in Alloy |
Carbon (C) | 0.08 max | 0.08 max | Strength; causes sensitization if too high |
Manganese (Mn) | 2.00 max | 2.00 max | Deoxidizer; hot-work strength |
Silicon (Si) | 0.75 max | 0.75 max | Deoxidizer; oxidation resistance |
Phosphorus (P) | 0.045 max | 0.045 max | Impurity; embrittlement if excessive |
Sulfur (S) | 0.030 max | 0.030 max | Impurity; improves machinability if added |
Chromium (Cr) | 18.0 - 20.0 | 16.0 - 18.0 | Forms passive Cr2O3 film; primary corrosion resistance |
Nickel (Ni) | 8.0 - 11.0 | 10.0 - 14.0 | Stabilizes austenite; ductility; toughness |
Molybdenum (Mo) | 0 (not specified) | 2.0 - 3.0 | Pitting resistance; crevice corrosion; acid resistance |
Nitrogen (N) | 0.10 max | 0.10 max | Strength; austenite stabilizer; pitting resistance |
Iron (Fe) | Balance | Balance | Base matrix |
The 2-3% molybdenum in 316 is the only composition difference that matters in practice. Molybdenum acts at the passive film interface, where it enriches the film with MoO4^2- ions that actively repassivate pits before they can propagate. This is why 316 can resist pitting in chloride concentrations that would destroy 304 within weeks.
The slight chromium reduction in 316 (16-18% vs. 18-20%) does not reduce overall corrosion resistance because molybdenum more than compensates. The PREN formula captures this synergy: PREN = %Cr + 3.3 x %Mo + 16 x %N. For 304: 18 + 0 + 1.6 = ~19.6. For 316: 17 + 3.3 x 2.5 + 1.6 = ~26.8. In practice, nominal PREN values are cited as ~18 for 304 and ~24 for 316, using mid-range compositions.
For the low-carbon "L" grades, the only difference is C max: 0.030% for 304L/316L vs. 0.08% for 304/316. All other elements are identical. The EN designations are: 304 = 1.4301, 304L = 1.4307, 316 = 1.4401, 316L = 1.4404. The JIS designations are SUS304 and SUS316 respectively.
Each alloy has different physical properties. 304 is a soft, low-carbon steel that is easy to machine. It has a balanced combination of strength, toughness, and weldability.
316 is a hard, high-carbon steel that is at risk of cracking if machined thoroughly. It is also very difficult to weld and can only be used to join parts that are very small or do not require heavy loads. It has high toughness and excellent wear and tear resistance, making it suitable for blade and automotive parts applications.
Each alloy has its advantages depending on your needs, and you must know their physical properties before buying or choosing a company.
Grade | Alloy 304 | Alloy 316 |
Density | 7.93 g/cm3 | 8.00 g/cm3 |
Melting Point | 1400-1450℃ | 1370-1400℃ |
Thermal Expansion | 17.3×10^-6/℃ | 16.5×10^-6/℃ |
Thermal Conductivity | 16.2-24.9W/(m·K) | 16.2-21.5W/(m·K) |
Electrical Conductivity | 1.45×10^6 – 1.6×10^6 S/m | 1.29×10^6 – 1.4×10^6 S/m |
Magnetic Properties | Yes | No |
304 and 316 share virtually identical mechanical properties in the annealed condition. The molybdenum addition in 316 does not significantly alter strength, hardness, or ductility. Both grades are relatively low-strength, high-ductility austenitic alloys that can be significantly strengthened by cold working.
Mechanical Property | Type 304 | Type 316 | Difference |
Yield Strength, 0.2% offset (MPa) | 205 min | 205 min | Identical |
Tensile Strength, ultimate (MPa) | 515 min | 515 min | Identical |
Elongation in 50 mm (%) | 40 min | 40 min | Identical |
Hardness, Brinell (HB) | 201 max | 217 max | 316 slightly harder |
Hardness, Rockwell B (HRB) | 92 max | 95 max | 316 slightly harder |
Modulus of Elasticity (GPa) | 193 | 193 | Identical |
Poisson's Ratio | 0.29 | 0.29 | Identical |
Density (g/cm3) | 8.00 | 8.00 | Identical |
Melting Range (degrees C) | 1400 - 1450 | 1370 - 1400 | 316 slightly lower |
Thermal Conductivity (W/m-K at 100 degrees C) | 16.2 | 16.2 | Identical |
Coefficient of Thermal Expansion (micrometers/m-degrees C, 0-100) | 17.3 | 15.9 | 304 slightly higher |
Electrical Resistivity (micro-ohm-m at 20 degrees C) | 0.72 | 0.74 | 316 slightly higher |
The mechanical similarity means that grade selection is almost never driven by strength requirements. If a component must resist a specific load, both 304 and 316 will perform equally—the designer does not gain or lose structural margin by switching grades. What changes is the corrosion margin, not the mechanical margin.
Both grades can be strengthened by cold working. A 50% cold reduction raises the yield strength of 304 from ~205 MPa to ~800-1000 MPa, and 316 responds similarly. However, cold-worked austenitic stainless steel becomes magnetic and loses ductility. For structural applications requiring higher strength without cold work, consider duplex grades (e.g., 2205 at ~450 MPa yield) or precipitation-hardening grades (e.g., 17-4PH at ~1000 MPa yield).
At cryogenic temperatures, both grades retain excellent toughness. 304 and 316 do not exhibit a ductile-to-brittle transition and are suitable for liquid nitrogen (-196 degrees C) and even liquid helium (-269 degrees C) service. This makes them standard materials for cryogenic vessels, LNG storage, and superconducting magnet housings.
304 is more heat resistant than 316 due to its higher chromium content and is easy to weld. Its application range is wide and it can even be used in places with extreme temperatures, although it can be used at lower temperatures than 316.
In contrast to the easy welding of 304, the hardening process of 316 stainless steel makes it very difficult to weld. Even incorrectly shaped parts can cause difficulties before they break. Therefore, parts made of 316 can only be welded by professionals, as they usually break when welded by amateurs or hobbyists.
Due to the high chromium content, 304 has a better surface flatness than 316. However, 316 tends to be harder and requires more force. In addition, in stamped or forged parts, 316 is prone to defects, especially when the forging temperature is high.
Welding alloys with a higher carbon content than pure steel can cause cracks where there is too much tension, and this is also the case with 304. This means that if you are welding workpieces made of 304, you should use TIG welding to ensure that cracks do not appear. No cracking when welding. If you are welding workpieces made of 316, direct MIG welding is recommended because the weld is more likely to withstand higher loads.
Therefore, if you are welding parts made of 304 or 316, use TIG welding instead of MIG. If you want to use an AWS welder, choose the right TIG or MIG welding wire. When using TIG welding, make sure that the anodizing work is not covered too much so that the weld is hidden behind the anodized surface. Otherwise, the weld will not be able to withstand higher loads.
Corrosion resistance is the single most important differentiator between 304 and 316. While both grades rely on the same chromium oxide passive film, the molybdenum in 316 makes that film significantly more resistant to localized breakdown in chloride and acidic environments.
Pitting Corrosion Resistance
Pitting is the most common failure mode for stainless steel in chloride environments. The PREN value predicts relative pitting resistance: 304 (PREN ~18) begins to pit in chloride concentrations as low as 100-200 ppm at ambient temperature, while 316 (PREN ~24) resists pitting up to 500-1000 ppm under the same conditions. In seawater (~19,000 ppm chlorides), 304 will pit within days to weeks; 316 will resist for months to years but is not suitable for permanent seawater immersion (use 904L, 2205, or super duplex for that).
Crevice Corrosion
Crevice corrosion occurs in shielded areas—under gaskets, bolt heads, deposits, and lap joints—where chlorides concentrate and oxygen is depleted. 316 resists crevice corrosion at temperatures roughly 10-15 degrees C higher than 304 in the same chloride environment. For example, in 3% NaCl solution, 304 begins crevice attack at ~15 degrees C, while 316 resists up to ~30 degrees C. This is why 316 is mandatory for flanged and gasketed piping systems in coastal and chemical plant environments.
Stress Corrosion Cracking (SCC)
Both grades are susceptible to chloride stress corrosion cracking (Cl-SCC) above 60 degrees C in chloride-bearing environments. 316 is only marginally better than 304 in this regard—the Mo addition helps but does not provide immunity. For SCC resistance above 60 degrees C, duplex grades (2205) or high-nickel alloys (Inconel 625) are required. This is a critical limitation that buyers often overlook: 316 is not a cure-all for chloride service at elevated temperatures.
Acid Resistance
Acid Environment | Type 304 | Type 316 |
Sulfuric acid (<10%, ambient) | Marginal | Good |
Sulfuric acid (10-50%, ambient) | Fails | Marginal |
Sulfuric acid (>50%) | Fails | Fails (use 904L) |
Hydrochloric acid (any concentration) | Fails | Fails |
Nitric acid (all concentrations) | Excellent | Good (304 is better here) |
Phosphoric acid (<25%, ambient) | Good | Excellent |
Acetic acid (all concentrations) | Excellent | Excellent |
Formic acid (<50%) | Good | Excellent |
Citric acid (food concentrations) | Excellent | Excellent |
A surprising reversal: 304 actually outperforms 316 in nitric acid service. Molybdenum does not improve resistance to oxidizing acids and can slightly reduce it. For concentrated nitric acid tanks and piping, 304L (or the specialized 304L low-carbon variant) is the correct choice, not 316.
304 is more resistant to oxidation than 316. Therefore, 304 is better suited for exterior applications, although corrosion is a concern in seawater. This means that 316 should be used when corrosion is a concern in a marine environment.
Due to its higher carbon content, 316 is easily oxidized by the atmosphere. Therefore, if it is not grounded during the forming or welding process, 316 may corrode. 316 can also rust if the atmosphere is moist and salty, which makes it unsuitable for exterior uses.
The high carbon content of 316 stainless steel makes it less suitable for welding interiors than 304 stainless steel. However, due to its hardening treatment and heat resistance, it can be safely used by professional welders. The hardening treatment also makes it less susceptible to creep, which in other words means it is more durable.
Type 316 costs approximately 40-60% more than Type 304 per unit weight. This premium reflects the additional cost of molybdenum (a strategic metal with volatile pricing), higher nickel content (10-14% vs. 8-11%), and lower production volumes. The exact premium fluctuates with commodity markets but has historically remained in the 35-65% range.
Cost Factor | Type 304 | Type 316 | Notes |
Raw material cost per kg (relative) | 1.00 | 1.40 - 1.60 | Fluctuates with Mo and Ni prices |
Sheet/plate cost premium | Baseline | +40-60% | 2B finish, 2mm thickness |
Bar cost premium | Baseline | +35-50% | Hot-rolled, annealed |
Pipe/tube cost premium | Baseline | +45-70% | Seamless sanitary tubing |
Welding filler wire premium | Baseline | +50-80% | ER316L vs ER308L |
Lifecycle cost (mild environment) | Lower | Higher | 304 adequate; 316 unnecessary |
Lifecycle cost (chloride environment) | Higher | Lower | 304 fails early; 316 lasts longer |
Scrap value (% of new) | ~60-70% | ~60-70% | Both highly recyclable |
The cost decision should always be made on total lifecycle cost, not initial material cost. In a mild, indoor environment, 304 is the economically correct choice—specifying 316 wastes 40-60% of the material budget with no service benefit. In a chloride or acid environment, 316 is the economically correct choice—specifying 304 saves 40-60% upfront but guarantees premature failure, replacement costs, and potential downtime that far exceed the initial savings. The break-even point is typically reached within 2-3 years of service in moderately corrosive environments.
304 stainless steel is one of the most common stainless steels. It has excellent corrosion resistance, high temperature resistance and good processing performance, so it is widely used in the following fields:
Architectural decoration: 304 stainless steel has a smooth surface and corrosion resistance, and is widely used in indoor and outdoor decoration, stair handrails, wall decoration, elevator internal installation, etc.
Food processing industry: 304 stainless steel has excellent corrosion resistance and hygiene, so it is widely used in food processing equipment, kitchen utensils, tableware, etc.
Medical instruments: 304 stainless steel is clean, so it is widely used in the manufacture of medical equipment, surgical instruments, surgical implants, etc. Machinery manufacturing: 304 stainless steel has excellent strength and corrosion resistance, and is widely used in the manufacture of various mechanical parts, bearings, valves, etc.
Petrochemical, chemical and marine engineering: 304 stainless steel can withstand high temperature, high pressure and corrosive media, so it is widely used in petrochemical, marine engineering, chemical equipment and other fields.
Transportation fields such as automobiles and trains: The corrosion resistance and strength of 304 stainless steel make it an important part of automobiles and trains, such as exhaust pipes, doors, roofs, etc.
316 stainless steel is a kind of steel with good corrosion resistance and high temperature resistance, which is widely used in the following fields:
Chemical industry: 316 stainless steel can resist corrosion from a variety of chemicals, so it is used in the chemical industry to manufacture storage tanks, pipes, valves and other equipment.
Food processing industry: 316 stainless steel is one of the commonly used materials in the food processing industry, used to manufacture containers, equipment, pipes, etc.
Medical instruments: 316 stainless steel is used to manufacture medical devices, surgical tools, surgical implants, etc. due to its corrosion resistance, high strength and high temperature resistance.
Shipbuilding: 316 stainless steel has good corrosion resistance in seawater, so it is widely used in shipbuilding and marine engineering.
Construction industry: 316 stainless steel has the characteristics of high strength, beauty and corrosion resistance, and is widely used in architectural decoration, building components, indoor furniture and other fields.
Cosmetic packaging: Cosmetic bottles, powder boxes, lipstick tubes and other cosmetics made of 316 stainless steel have exquisite appearance and are durable, which can meet consumers' requirements for beauty and quality.
JN is a 304 and 316 stainless steel plate, pipes, bars, fittings, flanges, forgings, and pipe spools supplier, with 20+ years experience. If you have stainless steel, duplex steel and nickel alloy needs, please contact me immediately.
Use this step-by-step decision framework to select the correct grade for any application.
Step 1: Assess the Chloride Environment
The single most important question: Will the component be exposed to chlorides? Sources include: seawater, coastal atmosphere, road salt, de-icing chemicals, swimming pool environments, bleach/chlorine sanitizers, hydrochloric acid, and chloride-bearing process fluids (brine, salt solutions). If yes, 316 is required. If no, 304 is likely sufficient.
Chloride Exposure Level | Recommended Grade | Rationale |
None (indoor, dry, non-chemical) | 304 | No corrosion driver; 316 wastes money |
Trace (indoor, occasional moisture) | 304 | Passive film self-heals; adequate |
Low (urban, non-coastal, mild chemicals) | 304 or 316 | 316 adds margin for long service life |
Moderate (coastal, food salt, CIP chemicals) | 316 | Mo content essential for pitting resistance |
High (seawater, brine, chemical plant) | 316 minimum | Consider 904L or 2205 for immersion |
Severe (permanent seawater, hot chloride) | 904L / 2205 / S32750 | 316 insufficient; use higher alloy |
Step 2: Check the Acids and Chemicals
If the service environment involves acids, check the corrosion resistance table above. For nitric acid, choose 304 (molybdenum does not help). For sulfuric, phosphoric, formic, or acetic acids, choose 316. For hydrochloric acid or concentrated sulfuric acid, neither grade is adequate—specify a higher alloy.
Step 3: Evaluate Temperature
For service above 60 degrees C in chloride-bearing environments, neither 304 nor 316 will resist stress corrosion cracking. Use a duplex grade (2205) or nickel alloy. For high-temperature service (550-750 degrees C continuous), 316 has ~30% better creep strength. For intermittent service up to 870 degrees C, either grade works. Above 870 degrees C, use 309S, 310S, or 253MA.
Step 4: Consider Welding
If the component will be welded, always specify the "L" variant (304L or 316L). The 0.030% max carbon prevents sensitization and intergranular corrosion in the heat-affected zone. For heavy-section welding (>6 mm), consider 316Ti (titanium-stabilized) as an alternative to 316L.
Step 5: Evaluate Total Lifecycle Cost
Compare the 40-60% material cost premium of 316 against the cost of premature failure: replacement, downtime, lost product, and potential safety incidents. In mildly corrosive environments, 304's lower initial cost wins. In moderately corrosive environments, 316's longer service life wins. The break-even point is typically 2-3 years in environments where 304 will pit but 316 will not.
Step 6: Check Regulatory Requirements
Pharmaceutical (ASME BPE, FDA 21 CFR): 316L mandatory for product contact. Food processing (3-A Sanitary Standards): 316L for salt-exposed surfaces, 304 acceptable for non-salt. Medical implants (ASTM F138): 316L. Marine (coastal codes): 316 minimum. When a regulation specifies the grade, there is no room for cost-driven substitution.
Q1: Is 316 stainless steel magnetic?
No. Both 304 and 316 are austenitic stainless steels and are essentially non-magnetic in the annealed condition. However, cold working (bending, forming, drawing) can transform some austenite to martensite, causing slight magnetism. This is more pronounced in 304 than 316. If a component shows strong magnetism, it is likely a ferritic or martensitic grade (e.g., 430 or 410), not 304 or 316.
Q2: Can 304 and 316 be welded together?
Yes, but it is not recommended for corrosion-critical applications. When welding 304 to 316, use ER309L filler wire (a transition alloy that accommodates the dilution from both base metals). The weld deposit will have intermediate corrosion resistance. If the joint is in a corrosive environment, the 304 side will be the weak link and may pit at the weld. For sanitary and corrosion-critical applications, use the same grade throughout the system.
Q3: What is the difference between 316 and 316L?
Only the carbon content: 316 has 0.08% max C, while 316L has 0.030% max C. The "L" stands for "low carbon." The lower carbon in 316L prevents sensitization (chromium carbide precipitation) during welding, making 316L the standard choice for all welded components. Mechanical properties are nearly identical—316L has marginally lower tensile strength (~485 vs. ~515 MPa). In practice, 316L is specified far more frequently than 316 in modern fabrication.
Q4: Will 304 stainless steel rust outdoors?
In most inland, non-industrial environments, 304 will not rust because the passive film self-heals in the presence of oxygen. However, in coastal areas (salt spray), industrial areas (SO2 acid rain), or areas with high humidity and pollution, 304 can develop surface rust staining and eventually pit. For any exterior application within 5-10 km of the ocean or in polluted industrial zones, 316L is recommended.
Q5: Is 316 stainless steel food safe?
Yes. Both 304 and 316 are FDA-approved (21 CFR) for food contact surfaces. 316 is actually preferred over 304 for food processing involving salt, brine, acidic foods, or aggressive cleaning chemicals. The 3-A Sanitary Standards that govern food and dairy equipment specify 316L for all product-contact surfaces in salt-exposed applications. 304 remains acceptable for non-salt food contact.
Q6: How much more expensive is 316 than 304?
Typically 40-60% more expensive per unit weight, depending on product form (sheet, plate, bar, pipe, fitting) and market conditions. The premium is driven by molybdenum pricing (a volatile strategic metal) and higher nickel content. The premium is highest for seamless tubing and precision fittings (50-70%) and lowest for hot-rolled bar (35-45%).
Q7: Can 316 stainless steel be used in seawater?
Only for intermittent or splash-zone exposure, not for permanent immersion. 316 will resist seawater splashing for months to years, but permanent immersion will cause pitting and crevice corrosion, especially in stagnant areas. For permanent seawater service, use 2205 duplex, 904L, super duplex S32750, or copper-nickel alloys (90/10 or 70/30 CuNi).
Q8: What is the difference between 18-8 and 304 stainless steel?
"18-8" is a generic term referring to any austenitic stainless steel with approximately 18% chromium and 8% nickel. Type 304 is the specific grade that falls within this composition range (18-20% Cr, 8-11% Ni). Other 18-8 grades include 302, 303, and 305. In practice, "18-8" and "304" are often used interchangeably, but "304" is the precise ASTM/UNS designation and should be used for engineering specifications.
Q9: Which is better for high temperature, 304 or 316?
Both have similar maximum oxidation temperatures (870 degrees C intermittent, 925 degrees C continuous). However, 316 has approximately 30% better creep rupture strength at 650 degrees C due to molybdenum's solid solution strengthening effect. For continuous service at 550-750 degrees C under load (pressure vessels, heat exchangers), 316 is the better choice. For intermittent or no-load high-temperature service, either grade works equally well.
Q10: Can I use bleach to clean 304 or 316 stainless steel?
No. Sodium hypochlorite (bleach) contains chloride ions that will destroy the passive film on both 304 and 316, causing rapid pitting. Even dilute bleach solutions (100 ppm) can pit 304 within hours. Use non-chlorinated sanitizers instead: peracetic acid (PAA), hydrogen peroxide, iodophor, or quaternary ammonium compounds. For cleaning, use neutral or mildly alkaline detergents followed by thorough rinsing.
Q11: Does 316 stainless steel contain nickel?
Yes—10-14% nickel. Both 304 and 316 are austenitic grades whose crystal structure is stabilized by nickel. People with severe nickel allergy (contact dermatitis) may react to prolonged skin contact with either grade. For hypoallergenic applications, consider 316L (which has slightly lower nickel leaching due to its more stable passive film) or nickel-free alternatives such as 444 ferritic stainless or titanium.
Q12: What is the PREN value and why does it matter?
PREN (Pitting Resistance Equivalent Number) is a formula that predicts the relative pitting corrosion resistance of stainless steel based on its composition: PREN = %Cr + 3.3 x %Mo + 16 x %N. Higher PREN means better pitting resistance. 304 has PREN ~18 (no Mo); 316 has PREN ~24 (2-3% Mo). As a rule of thumb: PREN < 22 is unsuitable for coastal environments; PREN > 32 is needed for seawater splash zones; PREN > 40 is needed for permanent seawater immersion.
Q13: Which grade is better for machining, 304 or 316?
Neither is ideal—both are austenitic grades that work-harden rapidly during machining, causing tool wear and chip-breaking difficulties. 303 (a free-machining variant of 304 with added sulfur) is the best austenitic grade for machining. Between 304 and 316, 304 is slightly easier to machine due to its lower work-hardening rate. For machined components requiring corrosion resistance, consider 416 (martensitic, free-machining) or 430F (ferritic, free-machining) for non-critical applications.
Q14: Can I substitute 304 for 316 to save cost?
Only in non-corrosive environments. Substituting 304 for 316 in chloride or acid service is the most common cause of premature stainless steel failure. The 40-60% material cost savings will be wiped out by replacement costs, downtime, and potential liability. If budget is the primary concern, consider reducing wall thickness (if structurally feasible) or optimizing the design rather than downgrading the alloy grade.
Q15: What are the equivalents of 304 and 316 in other standards?
Type 304: UNS S30400, EN 1.4301 (WNr), JIS SUS304, GB 06Cr19Ni10. Type 304L: UNS S30403, EN 1.4307, JIS SUS304L, GB 022Cr19Ni10. Type 316: UNS S31600, EN 1.4401, JIS SUS316, GB 06Cr17Ni12Mo2. Type 316L: UNS S31603, EN 1.4404, JIS SUS316L, GB 022Cr17Ni12Mo2. Always verify the full chemistry certificate (mill test report, EN 10204 3.1) when purchasing; grade designations alone do not guarantee compliance.
