Chemical Resistance Table for Screws in A2 and A4
A 100-plus-agent corrosion-resistance table for A2 (304-type) and A4 (316-type) stainless fasteners, rated 0-3 with a pitting flag L per agent, concentration and temperature — from acetone to sulphuric acid fuming, including the rows where the two grades genuinely differ (chlorides, reducing acids, brines) and the many where they do not.
Last updated: 2026-11
Specifications
A2 versus A4 is the most common stainless decision on a fastener RFQ, and it is decided agent by agent, not by a blanket "marine grade" label. This table — two 58-row blocks covering one alphabetical agent list from effluent water and acetone through potassium salts, mixed nitrating acids and wine — rates each agent for A2 and A4 separately on the collected source's five-point scheme: 0 resistant (but see L), 1 slight attack usable in certain areas, 2 hardly any resistance, 3 practically unusable, and L flagged where pitting threatens even in a resistant class. The rows that repay careful reading are the divergent ones: acetyl chloride (A2 rates 1 at boiling, A4 rates 0), aluminium chloride 5% at 50° (A2 rates 2, A4 rates 1), sodium chloride saturated (A2 pits at hot saturation — rated 1 — while A4 holds 0 cold but still rates 1 at 100°), oleic acid with sulphuric traces (2 vs 1), sauerkraut brine (2 vs 1), fuming sulphuric acid ladders and sulphurous acid under pressure (A4 holds 0 where A2 rates 1-2), spinning bath liquor (2 vs 1) and water vapour with SO2. Just as instructive are the many 0/0 rows: for most organics, alkalis and food products the grades are interchangeable. Multi-value cells print compounds on one line on the collected page (e.g. "0 1 2 0 2" across paired concentrations), carried verbatim — read them against the concentration column's own line breaks rather than assuming alignment.
| Rating scheme (source) | 0 = resistant (but see L); 1 = slight attack, usable in certain areas; 2 = hardly any resistance at all, practically unusable; 3 = no resistance; L = danger of pitting even in resistant class |
|---|---|
| Coverage | Two 58-row blocks, one continuous alphabetical agent list: water types, organics (acetone, alcohols, acids), salts (chlorides, cyanides, sulphates), mineral acids (nitric, sulphuric incl. fuming, hydrochloric), alkalis, food products, process liquors (spinning bath, dyer's bath, sauerkraut brine) and atmospheres (water vapour ± SO2/CO2) |
| Where A4 earns its premium | Chloride-bearing and reducing agents: acetyl chloride, aluminium chloride, ammonium chloride ladders, bleaching solution, sodium chloride at heat, oleic acid + H2SO4 traces, fuming sulphuric ladders, sulphurous acid under pressure, spinning bath, sauerkraut brine — A4 rates one or more steps better on each |
| Where the grades tie | Most organics and alkalis rate 0/0 (acetone, caustic potash up to 50%, milk of lime, sugar solution, wine) — grade selection there can follow availability or thread-form needs rather than corrosion |
| Verbatim quirks (flagged) | Compound cells print multi-ratings on one line ("0 1 2 0 2"); "boiling20°" and "00" concatenations carry as printed; "–" prints no concentration; the "NaCl O2 / NaOH" compound row label and its "2 3 02 / 2 2 02" ratings are the source's own characters |
| Not a substitute for | Joint-specific corrosion engineering: concentration, temperature, aeration, crevice geometry and stress state all shift real service behaviour — treat ratings as screening, and confirm critical duty per RFQ |
| Corrosive Agent | Concentration | Temp °C | Material | |
|---|---|---|---|---|
| A2 | A4 | |||
| Effluent water (with traces of sulphuric acid) | – | up to 40° | 0 | 0 |
| Acetone CH3COCH3 | all concentrations | 20° | 0 | 0 |
| Acetyl chloride Ch3CoCl | – | boiling | 1 | 0 |
| Aluminium Al | molten 750° | 3 | 3 | |
| Aluminium Chloride L Al Cl3,6H2O | 5% | 50° | 2 | 1 |
| Formic Acid H•COOH | 10% 15% 100% | 20° 20° 20° | 0 0 0 | 0 0 0 |
| Ammonia NH3 | – | – | 0 | 0 |
| Ammonium chloride (sal ammoniac) L NH4OH | 10% 25% 50% cold and hot saturated | boiling boiling boiling 20° boiling | 0 1 2 0 2 | 0 1 1 0 1 |
| Ammonium hydroxide NH4OH | all | 20° boiling | 0 | 0 |
| Ammonium perchlorate L NH4CIO4 | 10% | 20° boiling | 0 0 | 0 0 |
| Aniline C6H7NH2 | 20° | 0 | 0 | |
| Malic acid (COOH)2CH2CH OH | up to 50% | 20° | 0 | 0 |
| Cider | – | 20° | 0 | 0 |
| Ethyl alcohol (ethanol) C2H5OH | all concentrations | 20° | 0 | 0 |
| Ethyl ether (C2H5)2•O | – | boiling | 0 | 0 |
| Atmosphere | – | – | 0 | 0 |
| Petrol | all concentrations | 20° | 0 | 0 |
| Benzoic acid C6H5CO O OH | all concentrations | 20° | 0 | 0 |
| Beer | – | 20° | 0 | 0 |
| Blood | – | – | 0 | 0 |
| Spirits | – | 20° | 0 | 0 |
| Bromine Br L | – | 20° boiling | 3 3 | 3 3 |
| Buttermilk | – | 20° | 0 | 0 |
| Butyric acid C3H7COOh | 100% | 20° | 0 | 0 |
| Chlorine Cl Gas in dry state Gas in moist state L | – – | 20° 20° 100° | 0 3 3 | 0 3 3 |
| Chloride of lime L Ca (IO)2, CaO, 2 H2O Bleaching solution | dry moist 2.5g Cl/l | 20° 20° 20° | 0 1 1 | 0 1 0 |
| Chloroform CH CL3 | water free | 20° | 0 | 0 |
| Chlorine water L =cold water saturated with water | – | 20° | 1 | 1 |
| Hydrogen chloride gas L HCI | – – – – | 20° 50° 100° 400° | 1 1 2 3 | 1 1 1 3 |
| Chromic oxide CrO3 | 10% pure 50% pure | 20° 20° | 0 1 | 0 1 |
| Ferrogallic ink L | – | 20° | 0 | 0 |
| Iron phosphate solution, bonder process | – | 98° | 0 | 0 |
| Mineral oil | – | 20° | 0 | 0 |
| Vinegar = spirit vinegar | – | 20° | 0 | 0 |
| Acetic acid CH3COOH | 10% 50% | 20° 20° | 0 0 | 0 0 |
| Glacial acetic acide boiling | 100% | 20° boiling | 0 1 | 0 1 |
| Acetic acid + hydrogen peroxide CH3COOH + H2O2 | 10 u. 50% | 20° 50° 90° | 0 0 0 | 0 0 0 |
| Dyer's bath alkaline or neutral organically acid slightly sulphuric acid or organically acid + sulphuric acid (H2SO4 below 1%) | – – – | 20° boiling boiling20° boiling | 0 0 00 1 | 0 0 00 |
| Oleic acid C17H33COOH | 30 bar technical | 150° | 0 | 0 |
| Oleic acid + traces H2SO4 | – | hot | 2 | 1 |
| Meat | – | – | 0 | 0 |
| Hydrofluoric acid = hydrogen fluoride H2 F2 | 40% | 20° | 3 | 3 |
| Fruit juices and fruit acids | – | 20° | 0 | 0 |
| Vegetables | – | boiling | 0 | 0 |
| Tannic acid = tannin | 5% | 20° | 0 | 0 |
| Glycerin C3 H5 (OH)3 | conc. | 20° boiling | 0 0 | 0 0 |
| Pit water | acid | 20° | 0 | 0 |
| Urine L | – | 20° | 0 | 0 |
| Iodine I L | dry moist | 20° 20° | 0 1 | 0 0 |
| Coffee | – | 20° boiling | 0 0 | 0 0 |
| Potassium aluminium sulphate = alum KAL(SO4)2, 12H2O) | 10% | 20° | 0 | 0 |
| Potassium chloride L K Cl | hot saturated | 20° boiling | 0 0 | 0 0 |
| Potassium ferricyanide = red prussiate of potash K3(Fe[CN]6) | – | 0 | 0 | 0 |
| Potassium ferrocyanide = yellow prussiate or potash K4[Fe(CN)6], 3 H2O) | – | 20° boiling | 0 0 | 0 0 |
| Potassium hydroxide = caustic potash solution | 20% | 20° | 0 | 0 |
| Caustic potash KOH | 50% | 20° | 0 | 0 |
| Corrosive Agent | Concentration | Temp °C | Material | |
|---|---|---|---|---|
| A2 | A4 | |||
| Potassium permanganate K Mn O4 | all concentrations | 20° boiling | 0 0 | 0 0 |
| Calcium chloride L CaCL2, 6H2O | cold saturated | 20° | 0 | 0 |
| Calcium hydroxide Ca(OH)2 = milk of lime | – | 20° | 0 | 0 |
| Cheese | – | 20% | 0 | 0 |
| Carbon dioxide = carbonic acid CO2 | dry moist | hot hot | 0 0 | 0 0 |
| Carbon tetrachloride C CL4 | water free | 20° | 0 | 0 |
| Aqua regia L H CL + HNO3 | – | 20° | 3 | 3 |
| Cupric sulphate CuSO4, 5H20 = copper vitriol +3% H2SO4 | all concs. | 20° boiling 20° boiling | 0 0 0 0 | 0 0 0 0 |
| Glue (including acid) | – | boiling | 0 | 0 |
| Linseed oil +3% H2SO4 | – | 20° 200° | 0 0 | 0 0 |
| Magnesium sulphate MgSO4, 7H2O = Epsom salts | concentrated | 20° | 0 | 0 |
| Methyl alcohol CH3OH | all concentrations | 20° | 0 | 0 |
| Milk | fresh sour | up to 70° c up to 70° C | 0 0 | 0 0 |
| Lactic acid CH3 CHOH COOH | 1.5% 80% | 20° 20° | 0 0 | 0 0 |
| Mixed acids (nitrating acids) | 50% H2SO4 +50% HNO3 75% H2SO4 +25% HNO3 20% H2SO4 +15% HNO3 70% H2SO4 + 10% HNO3 30% H2SO4 +5% HNO3 | 50 ° 50 ° 50 ° 50° 50 ° | 0 1 0 0 0 | 0 0 0 0 0 |
| Monochloracetic acid L CH2 Cl COO H | 50% | 20° | 1 | 1 |
| Sodium chloride L NaCl = cooking salt | cold saturated hot saturated | 20° 100° 100° | 0 1 1 | 0 0 1 |
| Sodium chloride L Na Cl O2 Sodium hydroxide =caustic soda solution =caustic soda NaOH | 5% 25% 50% | 20° boiling 20°boiling | 2 3 02 | 2 2 02 |
| Sodium hypochlorite L NaClO =bleaching solution | 5% | 20° boiling | 1 1 | 1 1 |
| Sodium carbonate Na2 CO3, 10 H2O | 10% cold saturated | boiling | 0 | 0 |
| Sodium sulphate Na2 SO4, 10 H2O | cold saturated | 20° | 0 | 0 |
| Novacaine | – | 20° | 0 | 0 |
| Fruit pulp containing SO2 | – | – | 0 | 0 |
| Oil (lubricating oil) | – | 20° | 0 | 0 |
| Oil (vegetable) | – | 20° | 0 | 0 |
| P3 washing agent | – | 95° | 0 | 0 |
| Persil | – | 20° and boiling | 0 | 0 |
| Petroleum | – | 20° | 0 | 0 |
| Phosphoric acid H3PO4 chemically pure | 1% 10% 45% 60% | 20 ° 20 ° 20 ° 20 ° | 0 0 0 0 | 0 0 0 0 |
| Photographic developer (Agfa-glyzin developer) | – | 20 ° | 0 | 0 |
| Photographic fixing bath L | – | 20 ° | 0 | 0 |
| Pickling brine L | – | 20 ° | 0 | 0 |
| Nitric acid HNO3 | 7% 10% 25% 37% 50% | 20 ° 20 ° 20 ° 20 ° 20 ° | 0 0 0 0 0 | 0 0 0 0 0 |
| Hydrochloric acid L HCl | 0.5% | 20 ° boiling | 1 3 | 1 3 |
| Sauerkraut brine L | – | – | 2 | 1 |
| Lard | – | 20 ° | 0 | 0 |
| Soft Soap | – | 20 ° | 0 | 0 |
| Sulphur, dry | fused | 130° | 0 | 0 |
| Carbon disulphide C S2 | – | 20° | 0 | 0 |
| Sulphuric acid H2SO4 fuming (11% free SO3) fuming (60% free SO3) | 1% 2.5% 5% 7.5% 10% 20% 80% 98% =concentrated – – | 20° boiling 20° boiling 20° boiling 20 ° boiling 20 ° 20 ° 20 ° 70° 20° 70°20° 100° 20° 80° | 1 1 1 2 1 3 1 2 2 1 1 3 0 20 1 0 0 | 0 1 0 2 0 2 0 2 1 1 1 2 0 20 0 0 0 |
| Hydrogen sulphide dry H2S | <4 | 20° | 0 | 0 |
| Sulphurous acid H2 S O2 | saturated 4 bar 5-8 bar 10-20 bar | 20° 135° 160° 180-200° | 0 1 2 2 | 0 0 1 1 |
| Schweinfurt green 3 Cu (As O2)3, Cu (CH3 COO)2 | – | 20° | 0 | 0 |
| Sea Water L | – | 20° | 0 | 0 |
| Soap | – | 20° | 0 | 0 |
| Mustard L | – | 20° | 0 | 0 |
| Spinning bath | up to 10% H2SO4 | 70° | 2 | 1 |
| Tar (pure) | – | 20° and hot | 0 | 0 |
| Turpentine | – | 20° and hot | 0 | 0 |
| Vaseline | – | 20° and hot | 0 | 0 |
| Water Tap water Pit water = acidic water | – | 20° 20° | 0 0 | 0 0 |
| Water vapour Water vapour with SO2 Water vapour with CO2 | – – – | 400° – – | 0 1 0 | 0 0 0 |
| Wine (white and red) | – | 20° and hot | 0 0 | 0 0 |
| Tartaric acid COOH (CHOH)2 COOH | 10% 50% | 20° 20° | 0 0 | 0 0 |
| Lemon juice Citric acid HO C(CH2 COOH)2, COOH, H2) | – 1% 10% 25% 50% | 20° 20° 20° 20° 20° | 0 0 0 0 0 | 0 0 0 0 0 |
| Sugar solution | – | 20° boiling | 0 0 | 0 0 |
Materials
- A2 is the general-purpose austenitic (304 family); A4 adds molybdenum (316 family) for chloride and reducing-acid duty. We supply both grades across the screw range with material certificates; where an agent here rates 2 or 3, moving grade is cheaper than moving maintenance schedule — but crevices, gasket joints and chlorinated wash-downs can defeat even a good table rating, so name the actual medium and temperature on the RFQ
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (Chemical Resistance Table for Screws in A2 and A4) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 10,000 pieces. Stock items run 3–7 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
The table rates sodium chloride 0 for A4 cold-saturated but 1 at 100°. What does that mean for outdoor or wash-down hardware?
It captures the real failure mode: chloride pitting is temperature- and concentration-driven, so an A4 (316-type) screw that shrugs off cold brine can still pit in a hot, evaporating corner — a heated tank rim, a crevice under a gasket where salt concentrates, or a wash-down line that dries slowly. The L flag on the chloride rows is the table's own warning that even a resistant rating carries pitting risk in crevice geometry, because crevices locally concentrate chloride beyond the bulk concentration the rating was measured at. Practical reading for hardware selection: cold, rinsed, aerated salt exposure → A2 may serve, though A4 is the standard specifier's choice wherever spray or splash zones exist; hot or evaporating salt duty, or creviced joints in brine → treat the A4 rating as conditional and consider the task beyond the table — crevice-free detailing, periodic rinsing, or a higher-alloy grade quoted per RFQ. Ratings screen materials; they do not certify a joint.
Most rows are 0 for both grades. When can I legitimately skip the A4 premium?
When your medium sits in the 0/0 rows and no L flag applies — the organics, alkalis and food products that dominate many plants: caustic solutions up to 50%, milk of lime, acetone and the alcohol families, sugar solutions, wine and food acids at room temperature. In those duties the corrosion performance of A2 and A4 is equivalent by the table's own ratings, and the choice can follow what actually differentiates the grades on your order: availability, price, certification scope (some food and pharma specs name A4 by default regardless), or thread durability. Two cautions before skipping the premium: first, check the temperature column — several 0/0 ratings carry "20°" only, and the same agent at heat can diverge (sodium chloride is the canonical case); second, check the system, not just the agent — a "benign" product line still sees chloride-containing cleaning chemicals, and the fastener sees the cleaning cycle too. If your service sits inside one row of this table, use the row; if it spans several, quote per RFQ with the full medium list.
Related knowledge
- Thread-Forming vs Thread-Cutting vs Thread-Rolling Self-Tapping Screws: What the Evidence Settles on Base Material
- Screw Family Selection by Base Material: Wood, Machine and Self-Tapping Threads, Engagement and Coating
- Hex Bolts vs Socket Head Cap Screws: What the Evidence Settles on Strength, Clearance and Cost
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support